Radiation Therapy Techniques for Gynecological Cancers
A Comprehensive Practical Guide
Editors
Kevin Albuquerque
Department of Radiation Oncology
UT Southwestern Medical Center
Dallas, TX USA
Akila N. Viswanathan
Department of Radiation Oncology
Johns Hopkins University Baltimore, MD USA
Sushil Beriwal
Department of Radiation Oncology
UPMC Hillman Cancer Center Pittsburgh, PA USA
Beth Erickson
Department of Radiation Oncology
Medical College of Wisconsin Milwaukee, WI USA
ISSN 2522-5715
ISSN 2522-5723 (electronic)
Practical Guides in Radiation Oncology
ISBN 978-3-030-01442-1
ISBN 978-3-030-01443-8 (eBook) https://doi.org/10.1007/978-3-030-01443-8
Library of Congress Control Number: 2018967708
© Springer Nature Switzerland AG 2019
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Preface
Radiation is an integral component of the definitive and adjuvant treatment of gynecologic cancers. This can be external beam irradiation to the pelvis or abdomen or interstitial or intracavitary brachytherapy or a combination of the two. The possibility of both acute and late toxicities due to this modality needs to be balanced against the very effective treatment that radiation provides. The ability to cure gynecologic cancers with an acceptable risk of significant complications requires an in-depth understanding of pelvic and abdominal anatomy as well as the appropriate volumes and radiation doses required to afford this cure. It also requires brachytherapy skills which can adapt to the many complex disease presentations inherent to gynecologic cancers. Image guidance, for both external beam radiation and brachytherapy, is the key in achieving this balance. Over many decades, there has been a transformation from 2D film-based dosimetry into 3D image-based dosimetry utilizing CT, MRI, PET, and ultrasound for both external beam and brachytherapy planning. This book will focus on the importance and the practical details of these image-guided techniques in creating effective and safe radiation treatment plans. From simulation, to contouring, to plan generation, to brachytherapy techniques, each of the gynecological disease sites and modalities will be explored. Additionally, the book will close with a look at evolving techniques that may provide helpful solutions for challenging disease presentations. This book will be a very practical guide for the clinician and will instruct and affirm important guiding principles in the management of these variable and complex disease presentations.
Dallas, TX, USA Kevin Albuquerque Pittsburgh, PA, USA Sushil Beriwal Baltimore, MD, USA Akila N. Viswanathan Milwaukee, WI, USA Beth Erickson
Diandra N. Ayala-Peacock, Shruti Jolly, Sudha Amarnath, and Kevin Albuquerque
Karen S. H. Lim and Meena Bedi 3
Matthew Harkenrider, Courtney Hentz, and William Small Jr.
Colette J. Shen and Akila N. Viswanathan 5
Shari Damast, Eric Leung, and Junzo Chino
O. Lee Burnett III, Xun Jia, Elizabeth A. Kidd, and Ann H. Klopp
Teresa Meier, Tracy Sherertz, Eric Paulson, Sook Kien Ng, and Jordan Kharofa 8 Intracavitary Brachytherapy:
Yasmin Hasan, William Y. Song, and Christine Fisher
9 Interstitial Brachytherapy - Definitive and Adjuvant 197
Brandon A. Dyer, Jyoti S. Mayadev, Mitch Kamrava, Scott Glaser, Sushil Beriwal, and Antonio Damato
10 Stereotactic Ablative Radiotherapy and Other Newer Treatment Delivery Techniques for Gynecologic Cancers 237
Jonathan Feddock, Charles Kunos, Arnold Pompos, Kevin Albuquerque, and Lilie L. Lin
CT and MRI Simulation for Radiation Planning
Diandra N. Ayala-Peacock, Shruti Jolly, Sudha Amarnath, and Kevin Albuquerque Contents
1.1
1.4
1.5
D. N. Ayala-Peacock (*)
Department of Radiation Oncology, Vanderbilt University Medical Center, Nashville, TN, USA
e-mail: diandra.n.ayala.peacock@vanderbilt.edu
S. Jolly
Department of Radiation Oncology, University of Michigan Hospitals and Health Centers, Ann Arbor, MI, USA
S. Amarnath
Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH, USA
K. Albuquerque
Department of Radiation Oncology, UT Southwestern, Dallas, TX, USA
© Springer Nature Switzerland AG 2019
K. Albuquerque et al. (eds.), Radiation Therapy Techniques for Gynecological Cancers, Practical Guides in Radiation Oncology, https://doi.org/10.1007/978-3-030-01443-8_1
1.8.4
D. N. Ayala-Peacock et al.
1.1 Introduction: General Principles of Radiation Therapy for Gynecologic Cancers
Gynecologic cancers arise from female reproductive and sexual organs with varying biology and tumor types that can occur at different points over a patient’s lifetime. Radiation therapy is a critical component in the multidisciplinary management of the majority of adult female cancers. In certain sites with advanced presentation, including cervix, vulvar, and vaginal cancers, it is the primary therapeutic modality to control tumors while preserving form and, in some cases, function of the affected area.
In general, carcinomas are the most common histologic type of gynecological tumors, with squamous carcinomas arising from organs that are lined by squamous epithelium, such as the vulva, vagina, and cervix. The uterus, ovaries, and fallopian tubes arise from Müllerian glandular epithelium with adenocarcinoma as the predominant tumor type. For adenocarcinomas originating from these sites, in particular uterine cancers, radiation is often indicated as adjuvant therapy, post-resection. Gynecological squamous cancers, like those of the head and neck, can be related to HPV infection and tend to develop and spread in a stepwise fashion. This involves local primary invasion followed by regional nodal metastases before distant spread. This characteristic natural history enables the utilization of curative-intent radiotherapy for these radiation-responsive tumors. Regional radiation therapy generally encompasses the pelvic nodes and primary organs, and sometimes the para-aortic and inguinal nodal chains, when clinically indicated. In addition, the communication of the organ lumen to the exterior, as seen in cervix, uterine, and vaginal malignancies, also makes these sites amenable to brachytherapy when appropriate.
Three- and four-dimensional imaging with modern stereotactic and intensitymodulated radiation delivery technologies have enabled the use of radiation in previously exempt situations. Modern radiation requires accurate and thoughtful tumor evaluation and planning which begins with the treatment simulation process as described in the next section.
1.2 Practical Guidance on Simulator Equipment and Workflow Design
1.2.1
Computerized Tomography Simulation
Computed tomography (CT) scanners are a ubiquitous and essential component of any modern radiation therapy center. Three-dimensional (3D) volumetric conformal radiotherapy techniques are now used routinely in the management of a myriad of different malignancies and allow for better target accuracy as well as
avoidance of nearby organs at risk. In modern practice, CT-based treatment planning is the most commonly used technique for gynecologic malignancies, including treatment planning for both external beam radiotherapy (EBRT) and brachytherapy applications [1].
Prior to simulation, it is imperative that the staging workup is complete to ensure optimal treatment setup for coverage of appropriate targets (pelvis ± retroperitoneal lymph nodes ± inguinal lymph nodes) as well as to minimize dose to normal tissues. The proximal limit of nodal coverage can greatly influence patient arm positioning, and, similarly, the distal limit of the target can impact leg positioning. Additionally, the type of technique used (3D conformal radiotherapy vs. intensity-modulated radiotherapy) should be determined prior to simulation to ensure that the correct markers and scans (full and/or empty bladder) are acquired for treatment planning. Most modern CT simulators allow for a variety of options to be utilized in order to obtain the best image acquisition based on each individual patient.
1. Slice thickness: For most gynecologic patients, after immobilization and marker placement on the CT table, the scan borders are determined based on the targets and organs at risk. CT slices of 2–3 mm thickness are acquired. This slice thickness is typically of high enough resolution for target delineation, but for very small tumors or in more complex situations, the slice thickness may be adjusted as needed [2].
2. IV and oral contrast: Oral contrast can be utilized to highlight the small bowel and stomach. This can be most helpful in settings where para-aortics are to be treated or in postoperative cases where bowel can sink into the pelvis. A Canadian study investigated the dosimetric effect of small bowel oral contrast on conventional radiation therapy, linear accelerator-based intensity-modulated radiation therapy [IMRT], and helical tomotherapy plans for rectal cancer treatment planning. There was no clinically significant effect on dose calculations with 0.1% variance in the dose ratio for conventional plans, a 1% decrease in the mean dose ratio for IMRT, and <0.2% mean dose ratio for helical plans [3]. Intravenous contrast has traditionally been most useful for evaluating nodal disease. A 2010 series evaluating the effect of intravenous contrast agent on dose distribution in postoperative whole pelvic radiotherapy (WPRT) plans for gynecologic cancers identified mean dose differences of <1–2 Gy, representing tolerably small errors clinically for postoperative 3DCRT [4]. Either IV or oral contrast may be helpful at the time of radiation planning. However, given the additional staff support needed for these agents coupled with patient tolerance, these agents may not always have to be used at the time of simulation. As an alternative, some practitioners will use image fusion of higher-quality diagnostic imaging with the simulation scan.
3. Image fusion: Modern treatment planning software allows for the fusion of diagnostic imaging (MRI, PET-CT) with the CT simulation scan images for improved target and normal tissue delineation. These scans should be utilized as often as possible to ensure the optimal treatment planning (Fig. 1.1a). In some instances, fusion of diagnostic images may assist in resolving discrepant findings between imaging modalities [5].
Fig. 1.1 63-year-old female with locally advanced cervix cancer. (a) PET scan showing cervix squamous cell carcinoma. (b) MRI/CT fusion delineating the cervix lesion in red
1.2.2 MR Simulation
Magnetic resonance imaging has been increasingly incorporated into radiation planning due to its superior soft tissue contrast as compared to CT. This can be achieved with acquisition of an MRI in the treatment position or fusion with the diagnostic MRI (Fig. 1.1b). Recently, MR simulators have made their appearance in the market as tools to obtain better images for target delineation and also afford dynamic imaging techniques for motion assessment without the added radiation exposure to the patient. These devices present their own unique challenges including MR-compatible immobilization devices at the time of simulation and concerns regarding geometric distortion at the time of treatment planning. As MRI does not intrinsically provide electron density information as input for dose calculations, most clinical treatment planning workflows include registration of an MRI dataset to a primary CT dataset or generation of synthetic CT images. A more robust discussion regarding the use of MRI for simulation/radiation planning is included later in this chapter.
1.2.3 PET-CT Simulation
Some centers have access to PET-CT scanners for simulation purposes. Although this varies among centers, a CT simulation can be performed in the radiotherapy department to create an immobilization device and ensure proper patient setup before obtaining the PET-CT in the treatment position. 18-Fluorodeoxyglucose (18FDG) is still the most commonly used tracer, but F-MISO (fluoromisonidazole, a hypoxia tracer) and other radiotracers can also be used in the simulation setting for treatment planning purposes. This resource is most commonly used in the management of head and neck cancers [6] and lymphomas [7] but can also be employed for gynecologic malignancies such as locally advanced cervix cancers, where PET is often utilized.
1.2.4 CT on Rails
CT on rails is another option that may be available at some centers. CT on rails produces diagnostic quality images to be generated while the patient is in the
treatment position on the linear accelerator. CT on rails can be especially helpful for adaptive replanning when there is tumor regression or a change in weight to help decrease dose to normal tissues and deliver the intended dose to the target (Fig. 1.2).
1.3 Patient Positioning for External Beam Planning
Proper simulation of the patient for treatment planning is arguably the most important part of the treatment planning process for external beam radiation therapy. Simulation allows providers the opportunity to ensure patient comfort and reproducibility of the treatment plan on a daily basis. Ideally, the patient is also simulated in a position that will help to minimize the radiotherapy dose delivered to normal tissues/organs at risk, to reduce the risk of both acute and late toxicities of treatment. When treating patients with gynecologic malignancies, there are two potential options for patient position: prone versus supine. Each option for positioning and the selection of setup should be determined by taking into account patient factors (comfort, body habitus), as well as the expected mode of treatment delivery and fields and anticipated acute toxicities that may compromise patient setup during the course of treatment.
1.3.1 Prone
The prone setup is frequently used in the simulation and treatment of patients undergoing radiotherapy for pelvic malignancies—most notably, in the treatment of rectal
Fig. 1.2 Computed tomography (CT) scanner mounted on rails to facilitate stereotactic localization
cancer. In order to achieve prone positioning for treatment, the patient is typically immobilized using a system that includes a belly board. There are a variety of different types of boards available, each with a cutout at the level of the abdomen, so that when the patient lies on the board, some small bowel “falls through” and can be excluded from the pelvic area [8] (Fig. 1.3a). The use of a belly board can help to minimize the dose delivered to small bowel during pelvic radiotherapy. A recent 2016 publication looked at small bowel dose with either 3D conformal or intensity-modulated radiotherapy for both prone and supine positions from 11 rectal cancer patients. It was concluded that although there was no statistical difference in mean gross tumor dose found between planning types, there was a significant difference in small bowel sparing when using the prone position on a belly board when comparing 3DCRT and IMRT plans, favoring IMRT with a 29.6% reduction in dose (p = 0.007). There was also a statistically significant difference in small bowel sparing when comparing supine position IMRT to prone belly board IMRT favoring prone belly board IMRT with a reduction of 30.3% (p = 0.002) [9]. In the modern era, this potential exclusion of small bowel from the treatment field is the most beneficial aspect of a prone setup. However, there are several potential limitations with a prone setup that may be particularly less beneficial when treating patients with gynecologic malignancies.
1. Patient (dis)comfort: Many patients find that lying in the prone position is uncomfortable and cannot tolerate lying prone for the time required for simulation and, most importantly, for the amount of time required for delivery of treatment daily (with or without image guidance such as standard ports and/or CBCT). This discomfort may be even more pronounced in the postoperative setting when patients are being simulated at a time when their surgical scars may still be healing.
2. Daily reproducibility: The prone setup can be more challenging to reproduce for daily treatment due to patient discomfort issues as described in (1), as well as due to the patient’s body habitus. In patients that are obese, the patient’s position based on skin marks may vary widely from day to day in any position. Even with daily image guidance, it can be even more difficult to correct and shift the patient
Fig. 1.3 Prone (a) and supine (b) positioning of patient
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on a daily basis in the prone position to ensure reproducibility and appropriate delivery of radiation [10, 11].
3. Inguinal coverage: One of the major goals at the time of simulation is to position the patient in a way that will minimize normal tissue toxicity. Frequently when treating lower gynecologic malignancies such as vulvar tumors and tumors with distal 1/3 vaginal involvement, the inguinal lymphatic regions must be covered. To decrease uncomfortable radiation dermatitis reactions in the groin and upper thighs, the legs are often placed in a frog-like position to minimize skin folds and self-bolusing of the skin. This type of positioning is not possible with the prone setup. Electron boosts, if required, are also difficult to deliver with a prone setup. Additionally, the patient undergoing inguinal irradiation may develop desquamation during treatment that causes discomfort when lying in the prone position, thus affecting both patient tolerance and successful reproducibility. Furthermore, a prone setup can pose a challenge for those clinical scenarios requiring inguinal bolus placement. Lastly, the retroperitoneal nodes are frequently treated in patients with advanced gynecologic malignancies, especially those patients with cervical cancer and stage IIIC2 endometrial cancer. In these patients, displacement of the small bowel out of the pelvis and into the abdomen with a belly board does not significantly help to minimize radiation dose to the small bowel, particularly if a 3D conformal setup is used.
4. Patients who have a very low BMI may not benefit from prone positioning as there is little soft tissue to displace. Additionally, elderly and frail patients may not be able to get into the prone position.
1.3.2 Supine
The supine setup (Fig. 1.3b) is more frequently used in the management of patients with gynecologic malignancies but also has its own advantages and disadvantages.
1. Patient comfort: Most patients find lying on their back to be a more comfortable position for simulation and daily treatment compared to lying on their abdomen. This is especially true for patients with central adiposity, who often have significant discomfort with prone setups. Similarly, those patients undergoing inguinal irradiation may also find supine positioning with frog-legging more tolerable in settings where radiation dermatitis has developed. Postoperative patients may also find supine positioning more tolerable. Lastly, patients who are treated with a full bladder to help minimize bladder and small bowel toxicity may also tolerate a supine position that minimizes additional external pressure on the bladder, particularly later in treatment when bladder irritation symptoms (urgency, frequency) tend to manifest.
2. Reproducibility: In general, the supine setup tends to be more reproducible due to patient comfort and the ability to more easily make adjustments in patient positioning as needed with image-guided techniques. This is of particular importance in obese patients where skin markings can lead to significant translational
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shifts. Also, the supine setup typically allows for a wider array of immobilization devices to be utilized which may be better tailored to each individual patient.
3. Inguinal coverage: As contrasted with the prone setup disadvantages, the supine setup allows for frogging of the patient’s legs to minimize skin folds/auto-bolus effect in the groin region. This can decrease radiation dermatitis and improve patient comfort and tolerance of treatment when inguinal irradiation is necessary. The supine setup also allows for direct visualization of the groins during treatment if an electron boost is needed, so that the light fields can be directly verified. Better visualization and reproducible bolus placement is also easily achieved with patients in the supine position. However, this open-leg position can introduce a small degree of uncertainty in leg positioning each day.
4. When the para-aortic nodes are included in the treatment fields, the supine position is essential.
Though there are several advantages with a supine setup, there are also a few potential disadvantages.
1. Patient comfort. In some patients with acute or chronic back pain, the supine setup may prove to be more uncomfortable for the patient to tolerate and lead to poorer reproducibility during treatment. The patient should be asked at the time of consultation or prior to simulation if they have any significant discomfort or medical conditions that would preclude lying in either the prone or supine position before proceeding with simulation.
2. Normal tissue sparing. As noted, the prone setup with a belly board may allow for increased sparing of the small bowel from radiation dose and thus may lead to fewer acute and late toxicities. In a supine setup, a full bladder tends to be useful in pushing small bowel superiorly and out of the pelvis, but the patient’s ability to have a consistently full bladder during treatment is difficult. This can be a particular challenge with the acute bladder toxicities that most patients experience during treatment. Thus, there is a potential disadvantage of higher small bowel dosing during external beam radiotherapy with a supine setup [10, 12].
1.4 Immobilization and Motion Compensation
1.4.1
Immobilization Devices
During initial simulation for external beam radiotherapy, immobilization techniques vary widely and are in part a reflection of the radiation delivery technique being utilized and the availability of onboard imaging to confirm appropriate alignment of the patient. A vac-lock bag can improve upon extremity positioning to facilitate reproducibility of setup. Aquaplast or similar materials are also available to be utilized as partial body casts in order to help minimize pelvic rotation. In each of these cases, the patient is placed in the supine position with their arms on their chests. For extended fields, such as in the setting of para-aortic adenopathy, patients can also be
positioned with their arms above their heads with a variety of different devices ranging from a wingboard, a customized cradle, or a simple support sponge. More intensive immobilization of the upper body is often recommended as changes in arm positioning could result in misalignment or malpositioning of the spine that can impact targeting of paraspinal targets and contribute to organ motion. This can be reduced with upper body marks and leveling tattoos at the time of simulation in order to ensure reproducible positioning.
Belly boards can be utilized when treating the patient in the prone position. Prone positioning on a belly board has been shown to decrease the small bowel dose, particularly in the setting of gynecologic pelvic IMRT [3]. As previously discussed, setup reproducibility and patient comfort are often limiting factors with this device. With either prone or supine positioning, oral contrast can be used to help delineate the bowel and help distinguish small from large bowel. This can be critical during planning, particularly in settings of node-positive disease (such as in locally advanced cervical cancers) where additional dose to involved lymph nodes is a treatment goal [13] and can be limited or compromised by the approximation of the target to nearby bowel. IV contrast can also be useful when simulating patients with nodal disease as well as to better visualize the primary lesion.
1.4.2 Motion Compensation
The pelvic anatomy is not fixed, and there are many potential sources of uncertainties in organs at risk [OARs] and the tumor target itself. Internal organ motion and deformation, as well as tumor motion and tumor volume regression, must all be accounted for during radiation planning.
1. Fiducial markers: Fiducial markers, particularly in the setting of lower gynecologic organ involvement, can be critical in defining treatment borders and subsequent daily image guidance. These can be placed during an exam under anesthesia prior to radiation planning. It is imperative that these be placed prior to the start of treatments as tumors can often regress after initial external beam. In the absence of a need to define vaginal tumor involvement, it is often still helpful to apply a radiopaque vaginal swab at the time of simulation in order to radiographically identify the top of the vagina. This can easily be achieved by coating a swab in contrast and covering the contrast-soaked swab with a lubricated condom (Fig. 1.4a). Care must be taken not to distort the vagina and adjacent organs with placement of too large or rigid a marker. The vagina is a collapsible, mobile organ, and in some clinical instances, daily vaginal positioning has been utilized [14]. However, vaginal markers or fiducials are often preferred for patient comfort and when taking into account the variability of the nearby organs at risk. Surface landmarks for the anus, the introitus, and the urethra can also be of assistance in delineating external anatomy on CT (Fig. 1.4a). Similarly, any scars or skin lesions should be marked with a radiopaque wire for appropriate targeting (Fig. 1.4b).
Fig. 1.4 (a) CT simulation for a vulvar cancer with vaginal involvement. Note the vaginal swab (red asterisk) to demark the vaginal apex as well as the use of introitus and anal markers (yellow arrow). (b) Radiopaque wires are typically utilized to outline the visible borders of the tumor in these cases
2. Bladder filling: In the management of cervical cancer treatment planning, the uterus and cervix have been shown to move substantially on a daily basis in conjunction with changes in bowel and bladder filling [15, 16]. Efforts to account for this motion have resulted in the common practice of acquiring bladder-full and bladder-empty scans at the time of simulation (Fig. 1.5). There is data to suggest that an ideal planning bladder volume of 150–300 cc can be achieved with shorter waiting time on post-chemotherapy days and adequate hydration throughout treatment [17, 18]. Methods to achieve reproducible bladder filling can vary from utilizing a Foley catheter to first empty the bladder and then fill it with 200–250 cc of saline and clamp to less rigorous methods of instructing patients to drink 12–16 ounces of water prior to simulation and treatment. However, some providers have argued that the most reproducible bladder full has been to simply allow the patient to maintain their daily habits of intake around the time of simulation and treatment. In these instances, it is imperative to utilize onboard imaging to confirm stable bladder volumes throughout the course of therapy. The other option is to treat with an empty bladder, but this will also mean that there is the potential for increased small bowel irradiation.
3. Rectal distention: Rectal wall motion can equally vary substantially over the course of therapy, but this has proven more difficult to estimate. Laxatives at planning and throughout treatment may be beneficial [15, 16]. Recent publications have also recommended more generous PTV expansions to account for the range of observed rectal filling [19]. A catheter to decompress a gas-filled rectum can be utilized when needed to naturally position the rectal mucosal wall away from the target area. Even with these measures, regular imaging at the time of treatment delivery remains vital when implementing advanced radiotherapy techniques for gynecological cancers. The patient’s intake and ability to maintain a full bladder and/or empty rectum can change over the course of treatment due to inadequate hydration secondary to nausea, diarrhea from chemotherapy or radiation proctitis, and radiation cystitis.
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Common setups for GYN CT simulations
Scenario Position
Definitive pelvis
Postoperative pelvis
Extended field (pelvis + PA LNs)
Pelvis + inguinals + external genitalia
Supine, arms across chest
Supine, arms across chest
Supine, arms above head
Supine, arms across chest, frog leg
Fig. 1.5 Full-bladder (shown in green) and empty-bladder (shown in yellow) contours in a postoperative cervix cancer patient meeting Sedlis criteria for adjuvant radiation treatments
Immobilization device
Vac-lock bag or similar
Vac-lock bag or similar
Vac-lock bag with wingboard or similar
Vac-lock bag or similar
Isocenter
Midpelvis
Midpelvis
L4/L5
Markers/special aids
IV/oral contrast, introital/ anal BBs, BB to mark distal end of tumor
IV/oral contrast, vaginal swab, introital/anal BBs, full/empty bladder scans
Follow definitive or post-op pelvis guidelines depending on situation
Midpelvis
IV/oral contrast, wire vulva/post-op bed, introital/anal BBs
1.5 Considerations for CT-Based Brachytherapy Simulation
CT simulation is most commonly used for brachytherapy treatment planning in the United States. The specifications for acquiring CT images are similar to those used with external beam radiotherapy as outlined above, with a few notable additional considerations:
1. Anesthesia and sedation. For patients undergoing simulation for intrauterine brachytherapy where sedation is being utilized, additional caution and safe practices must be exercised when placing the patient on the CT simulator table. A Velcro band
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should be placed around the upper body of the patient to prevent the patient from falling off the CT table during image acquisition. Additionally, the patient should be closely monitored to ensure that they are comfortably sedated and that there is no movement that will lead to motion artifact while they are being simulated. Patient positioning during brachytherapy procedures is important to ensure patient comfort during treatment and ensure reproducibility of the treatment plan. This is especially true when performing high-dose rate (HDR) brachytherapy procedures that require multiple insertions of the same applicator system over several days.
2. Patient positioning. Patients undergoing brachytherapy procedures are setup in a supine position in the dorsal lithotomy position using stirrups. For longer procedures, it is recommended that soft padded stirrups be used to ensure patient comfort during the procedure. Prior to placing the patient into stirrups, it is important to discuss any hip or leg/knee issues that a patient may have to avoid discomfort and/or exacerbation of an already existing problem. The stirrups should also be mobile to allow for proper exposure and visualization of the vulvar/vaginal region to ensure the best applicator placement. Arm boards, if available, can also help with patient comfort during a procedure. At a minimum, the patient should be placed on top of a sheet to allow for adjustments to the patient’s position such as translational shifts to allow for proper speculum use and applicator placement and to facilitate rotational shifts that ensure that the hips are straight and even. A slide sheet placed underneath the patient can be especially helpful in heavier patients to facilitate transfers to carts/beds for CT or MRI scans. If the patient is transferred in the leg-down position, plastic slider boards can also be used with careful rolling and transfer of the patient.
3. Medical support devices. Patients under sedation are typically attached to several lines and monitors, including blood pressure cuffs, EKG leads, pulse oximeters, oxygen (via nasal cannula or mask), IV fluids, and IV lines for medications. Care must be taken to keep all of these lines off of the pelvic area where CT images will be obtained, as well as ensure that the lines are long enough to allow for the patient to be moved through the CT scanner for image acquisition. For the safety of the patient under sedation, timely review of the CT images to ensure proper applicator placement for planning is very important, and the treating physician should be present during the entirety of the simulation process.
4. Brachytherapy-specific immobilization. Details of brachytherapy application will be addressed in a subsequent chapter. With regard to immobilization for simulation (and subsequent treatment), a perineal bar, external tandem clamp/ immobilizer, or a combination of the two can be very helpful to immobilize the applicator and ensure reproducibility between fractions. Some institutions will utilize these devices along with a vacloc in order to maintain relative spatial locations between stabilizing devices and the applicator/patient (Fig. 1.6). More modern alternatives include devices such as a Slessinger Board, a padded sliding board that is CT and MR compatible and will maintain patient positioning during transfer for treatment, and the Zephyr HDR system, which combines stirrups and hover technology so as to maintain patient positioning and minimize applicator movement during transfers (Fig. 1.7). Depending on the type of simulation the patient is undergoing, it may be necessary to place radiopaque markers to visualize
Fig. 1.6 Use of vac-loc bag with indexing of stabilizer bar for brachytherapy immobilization
Fig. 1.7 Female subject using the Zephyr HDR system at time of CT (Courtesy of DIACOR, Inc.)
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the applicator in a CT scan or use C-arm X-rays. MRI-compatible applicators can be visualized in an MRI simulation. If available, ultrasound is invaluable to ensure adequate applicator placement. Other options for immobilization and quality assurance also exist and will be addressed in greater detail within the brachytherapy chapter.
1.6 General Workflow Limitations
In most departments, there are well-established workflows for simulating external beam radiation therapy patients. For gynecologic patients, there are a few additional considerations that must be incorporated into the workflow. Any pre-treatment imaging and/or fiducial placement needed to define target volumes should be performed prior to simulation in order to inform setup and image acquisition. Intravenous and/or oral contrast agents are frequently used in the CT simulation process for patients with gynecologic malignancies. The patient should be scheduled to arrive at least 30–45 min prior to their scheduled CT simulation time to have adequate time to have an IV placed, drink oral small bowel contrast, and drink water for a full bladder scan at the time of CT simulation.
As previously discussed, many gynecologic patients in the modern era are being treating using advanced techniques such as IMRT or VMAT. These treatment modalities typically necessitate acquiring two CT scans at the time of simulation—a full bladder scan and an empty bladder scan. Additional simulator time is necessary in order to acquire the full bladder scan, place an isocenter, and then remove all markers and allow the patient to empty their bladder before returning, repositioning, and acquiring a second bladder-empty image. Adequate time must be reserved on the CT simulator to acquire both scans to avoid disruption of overall clinic workflow.
The workflow for brachytherapy procedures can be quite complex, and it is recommended that, if feasible, a specialized team (physicians, therapists, dosimetrists, physicists, nurses) be involved in brachytherapy treatments to facilitate timely treatment planning, treatment delivery, recovery from sedation, and department workflow [20]. With regard to the CT simulation process/workflow, maintaining proper immobilization and reproducibility following patient transfers not only can be timeintensive but also requires thoughtful planning. Patient safety and comfort are of the utmost importance in the simulation process. The treating physician, simulation therapist, and/or dosimetrist/physicist involved in the brachytherapy procedure should be on hand at the CT simulation to ensure timely acquisition of imaging and appropriate applicator placement.
1.7 Magnetic Resonance Imaging, Simulation, and Technique
Magnetic resonance imaging (MRI)-based treatment planning for gynecologic cancers has been gaining popularity in the United States, especially for image-guided adaptive brachytherapy (IGABT) in the management of cervical cancer [21–25].
Development and implementation of a robust MRI-based IGABT program requires close collaboration between radiologists and radiation oncologists. Compared to CT, MR provides superior soft tissue resolution, clear distinction of tumor from adjacent organs at risk, clear distinction of the lower gynecologic tract organs, and better volumetric planning due to the ability to adapt and conform dose to individual patient anatomy. T2-weighted MR images can improve target and OAR delineation (Fig. 1.8). Pelvic MRI imaging can assist in identifying tumor location and depth for uterine, vulvar, and vaginal malignancies. Pre-treatment MRI has been shown to be prognostic in cervix cancer. The mean apparent diffusion coefficient (ADC) value of the primary tumor on pre-treatment MRI has been found to be an independent predictor of disease-free survival in cervical cancer patients treated with chemoradiation [26, 27]. Recent evidence also shows possible benefit in better delineating the postoperative vaginal cuff target for brachytherapy [28, 29].
MRI simulation for pelvic tumors allows for better visualization due to the variety of tissue contrasts that can be achieved by simply varying scan parameters. However, some specifics relevant to radiation therapy need to be considered; some sequences required for treatment planning are not commonly used in diagnostic radiology evaluation. Furthermore, patient positioning and immobilization during treatment needs to be defined, and it is preferred that images be acquired in this position when possible. Geometric accuracy of images in radiation therapy is much more important than in radiology, and MRI is a modality where distortion can be of concern. MRI safe vaginal markers and vaginal gel can be utilized to help view the anatomy.
Limitations to MRI-based planning include concerns with image distortion and lack of electron density for dose calculation [30]. MRI can still be used if the planning system integrates tools for CT/MR image registration. Work is being done to generate synthetic CT scans from MRI data for planning purposes [31]. However, applicator reconstruction is challenging because scanning sequences need to be optimized, commercial MR-compatible markers are limited, in-house markers are
Fig. 1.8 T2W 3T MRI obtained during HDR brachytherapy planning. Pneumo-occluder balloon filled with saline in the vagina to increase bladder and rectum separation
N. Ayala-Peacock et al.
prone to errors, and certain applicators introduce artifacts [32, 33]. Brachytherapy treatment planning systems now often supply applicator libraries which can bring a wide variety of applicators into the plan and allow accurate reconstruction.
Patient comfort needs must also be considered at the time of simulation, especially with regard to brachytherapy simulation. General anesthesia, conscious sedation, and/or anxiolytics may be needed if an applicator will be placed and stay in place for several hours to days. For each brachytherapy fraction, patients can be anesthetized with general, monitored, or spinal techniques for the duration of instrumentation, imaging, treatment planning, and treatment phases [34, 35].
General Workflow Considerations
The physical layout of each local institution will determine what transportation factors must be considered. In some institutions, the MR scanner is located within the radiation oncology department itself, in which case, the transportation needs of the patient will be minimal. In other institutions, the MR scanner is distant from the radiation oncology department requiring substantial transportation to and from the scanner. The greater the transportation distance, the more time the care team will have to monitor the patient in transport. Regardless of the geographical separation between the radiation oncology department and MR scanner, great care is needed to ensure that the applicators are not dislodged during patient transfer to and from the MR gantry and during transportation to the treatment area. There are several commercially available patient transfer systems. At some institutions, the MR tabletop can be detached and serve as its own cart to transport the patient from the brachytherapy suite to the MR scanner, minimizing motion. Additional imaging may be needed to confirm that the applicator has not shifted during transfer.
Patients may undergo brachytherapy using spinal anesthesia with an epidural catheter. Therefore, it is imperative that all members of the care team are aware of MR safety considerations. In the setting of spinal anesthesia, care must be taken to implant an MR-compatible spinal catheter. In the setting of general anesthesia or monitored sedation, the team must be prepared to transport and care for the patient within the room in which the MR scanner is located [36].
With regard to additional MR safety concerns, understanding the brachytherapy applicator compatibility with regard to whether it is MR safe, MR unsafe, or MR conditional is paramount. It is also important to have supervised and controlled access to an MRI unit. Proper screening guidelines need to be followed for patients and proper training for all staff. All patients must be screened preferably with a written screening form and verbal interview. Common contraindications to MRI scanning include pacemaker, pacer wires, unsafe aneurysm coils/clips and stents/filters, cochlear implants, and metal in the eyes. All patients must remove clothing items with metallic fasteners, hearing aids, metallic makeup, jewelry, body piercings, analog watches, and wallet/ credit cards. Special considerations for inpatients include cardiac monitors, pulse oximeters, medication patches or bandages containing silver, metal snaps on gowns, IV poles, and medication pumps, in addition to stretchers, wheelchair, and oxygen tanks. Patient’s ability to undergo MRI scanning with regard to claustrophobia should also be considered in cases where they will not be anesthetized.
D.
1.8 Special Circumstances
1.8.1 Extended Field of View (EFOV)
In larger patients with more central adiposity, it may be necessary to use an extended field of view (even with a large bore CT scanner) to obtain all of the skin edges and external contours needed for dosimetric computation of fields (Fig. 1.9). If extended field of view options still do not allow the entire patient to be imaged or EFOV is not available on the CT scanner, dosimetry and physics consultation should be obtained at the time of simulation to determine best treatment planning options. If a patient’s external contours are cut off in a particular location, care should be taken to avoid a treatment field going directly through that area due to dosimetric uncertainty.
1.8.2 Metal Artifact
Most modern CT scanners/simulators have an option to reduce metal artifact in patients with hip replacements, since this artifact can obscure important anatomical features needed for treatment planning. This setting should be used, if available, to ensure the best treatment planning (Fig. 1.10).
1.8.3 Adaptive Replanning
In patients in whom an adaptive replanning is expected to occur in order to reduce normal tissue dose after tumor regression, or when there is substantial weight loss or weight gain, it is recommended that CT simulation be repeated and performed
Fig. 1.9 Extended field of view (EFOV) makes it possible to encompass the entire body contour of this obese patient. The red circle shows the soft tissues that would be missed without EFOV
to
patients, in order to encompass the entire body
side
patient
which results in defect as shown. This is completed by fusing the missing body tissue to original scan after shifting patient to other side and rescanning (right panel)
exactly the same way as the initial CT simulation scan. This will allow for fusion of planning CT images and composite treatment plans for more accurate determination of dose to targets and organs at risk.
1.8.4 Super Obese Patients
Super obese patients can be of particular challenge due to physical limitations in setup, unreliable surface marks, as well as ability to acquire a complete image of the patient’s external contour at the time of CT acquisition. Any portion of the external anatomy that is clipped off on a CT scan will reduce the beam angles available for treatment planning. Single institution publications have attempted to offer techniques for these challenging cases including a 3-CT fusion with the patient centered on the table and then shifted left and right in order to acquire the entire body contour (Fig. 1.11) needed for planning [37]. Other publications discuss treatment on a stretcher for those patients that
Fig. 1.10 Bilateral hip replacements before (a) and after (b) metal artifact reduction
Fig. 1.11 In severely obese
contour,
is scanned while shifted
one
(left panel)
D. N. Ayala-Peacock et al.
exceed table limits, with multi-field designs in an attempt to improve upon the dose distribution and heterogeneity that can be seen with larger patients [38]. When available, these patients can be scanned on a CT-on-rails linear accelerator which has a larger bore and greater weight limits than many simulators.
1.8.5 Stereotactic Body Radiotherapy
Encouraging early SBRT outcomes have stimulated further investigation into the use of SBRT for treatment of persistent or recurrent gynecological cancers [39–41]. KROG 14-11, a multi-institutional cooperative study of the Korean Radiation Oncology Group, evaluated the local control and patient survival for recurrent or oligometastatic uterine cervical cancer treated with SBRT using CyberKnife with 2-year and 5-year local progression-free survival rates of 82.5% and 78.8%, respectively. Biologically equivalent dose >90 Gy (p = 0.072) and >69 Gy (p = 0.059) and longer disease-free interval (p = 0.065) predicted marginally superior local control. Chronic toxicities of grade 3 or more occurred in five cases, suggesting that SBRT for recurrent or oligometastatic cervical cancer could be considered a therapeutic option [42]. As in all cases of SBRT, more rigid patient immobilization, methods to account for respiratory motion, complex treatment planning, and use of onboard imaging are all required to minimize the increased risk of normal tissue injury or geographic miss with this modality. Caution should be utilized when pursuing this option, with the understanding that the emerging literature is most robust in the recurrent/reirradiation setting or in oligometastatic patients.
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psili´um (ψιλά, land without trees), a prairie formation; psilad, a prairie plant.
psychrometer (ψυχρός, chill), an instrument that measures humidity by means of a fall in temperature; psychrograph, a psychrometer that records automatically.
ptenophyti´um (πτηνός, passing), an intermediate formation.
pterospore (πτερόν, wing), a plant with winged disseminules.
purpureus, purple.
pycnophyti´um (πυκνός, thick), a closed formation.
pyri´um (πῦρ, fire), a burn succession.
quadrat (quadratum, a square), a square meter of vegetation marked off for counting, mapping, etc.; major, a quadrat of 2–14 square meters.
reaction, the effect of the formation upon the habitat.
relict (relictus, left), a species belonging properly to an earlier type of succession than the one in which it is found.
repi´um (ῥέπω, sink), a succession due to subsidence.
rhoi´um (ῥόος, stream), a creek formation; rhoad, a creek plant.
rhoptometer (ῥοπτόν, something absorbed), an instrument to measure absorption of water by the soil.
rhyaci´um (ῥύαξ, ακος, mountain torrent), a torrent formation; rhyacad, a torrent plant.
rhysi´um (ῥυσίς, a flowing of fire), a succession due to volcanic action.
ruber, red.
saccospore (σάκκος, sack), a plant with sack-like disseminules.
sarcospore (σάρξ, σαρκός, flesh), a plant with fleshy disseminules.
sciad (σκιά, shade), a sciophyte; sciophyll, the leaf of a shade plant; sciophyte, a shade plant; sciophyti´um, a shade plant
formation; sciophilous, shade-loving.
selagraph (σέλας, light), an instrument for recording light values automatically.
serotinal, late, pertaining to autumn.
social, used of plants in which the individuals are compactly grouped; exclusive, excluding individuals of other species; inclusive, permitting the entrance of individuals of other species.
society, a subdivision of the formation, characterized by a principal species.
sparse, scattered singly.
spermatostrote (σπέρμα, ατος, seed), a plant migrating by means of seeds.
sphyri´um (σφύρον, ankle, talus), a succession in a talus soil.
spongophyll (σπόγγος, a sponge), a leaf consisting of sponge tissue.
sporadophyti´um (σποράς, άδος, scattered), an open formation.
-spore (σπορά, seed, fruit), combining term for migration contrivance; sporostrote, a plant migrating by means of spores.
stability, the condition in which the plant makes little or no response.
stabilization, the tendency typical of succession, in which the successive stages become more stable.
stasi´um (στάσις, a standing), a stagnant pool formation; stasad, a plant of stagnant water.
staurophyll (σταυρός, a pale), a leaf consisting of palisade tissue.
sterrhi´um (στερρός, barren), a moor formation; sterrhad, a moor plant.
-strote (στρώτος, strewn), combining term for means of migration.
subcopious, scattered somewhat loosely.
subgregarious, arranged in loose groups.
subquadrat, a quadrat of 1–8 decimeters.
succession, complete and continuous or repeated invasion, in consequence of which formations succeed each other.
symmetry, used of topography when it shows uniform changes; radial, a condition in which the different areas are concentric; bilateral, where the areas occur in two similar rows.
syrtidi´um (σύρτις, ιδος, sandbar), a dry sandbar formation; syrtidad, a plant of a dry sandbar.
taphri´um (τάφρος, ditch), a ditch formation; taphrad, a ditch plant.
telmati´um (τέλμα, ατος, water meads), a wet meadow formation; telmatad, a wet meadow plant.
testaceus, pale brick colored.
thalassi´um (θάλασσα, sea), a sea formation; thalassad, a sea plant.
thallostrote (θαλλός, shoot), a species migrating by means of offshoots.
theri´um (θήρ, wild animal), a succession due to animals.
thermi´um (θέρμη, hot spring), a hot spring formation; thermad, a hot spring plant.
thini´um (θίς, θινός, a dune), a dune formation; thinad, a dune plant.
tiphi´um (τῖφος, pool), a pool formation; tiphad, a pond plant.
tiri´um (τείρω, rub away), a bad land formation; tirad, a bad land plant.
tonobole (τόνος, tension), a plant whose seeds are scattered by projection from calyx or involucre.
transect (transectus, cut through), a cross section of vegetation.
trechometer (τρέχω, to run off), an instrument for measuring run-off.
tribi´um (τρίβω, wear or rub away), a succession in an eroded soil.
umbrinus, umber.
variable, able to produce variants; variant, a form arising from origin by variation; variation, the origin of new forms by the action of selection upon minute differences.
vegetation form, a characteristic plant form, e. g., tree, rosette, etc.
vernal, pertaining to spring.
vicine (vicinus, neighboring), invading from adjacent formations.
viridis, green.
vixgregarious, arranged in small or indistinct groups.
water-content, the water of the soil or habitat; physiological, the available soil water; physical, the total amount of soil water.
xenodoche (ξένος, strange), an anomalous succession.
xerad (ξηρός, dry), a xerophyte; xerasi´um (ξηρασία, drought), a succession due to drainage or drought; xeriobole (ξηρία, dryness), a plant whose seeds are scattered by dehiscence due to dryness; xerohyli´um (ὕλη, forest), a dry forest formation; xerohylad, a dry forest plant; xerophyll, the leaf of a xerophyte; xerophyte, a dry soil plant; xerophyti´um, a xerophytic formation; xerophilous, dwelling in a dry habitat; xeropoi´um, a heath formation; xeropoad, a heath plant; xerosta´tic (στατικός, standing), used of successions which are completed under xerophytic conditions; xerotro´pic (τροπικός, turning), applied to successions which become xerophytic.
zonation, that condition in which plant groups or formations appear in belts or zones.
zone, a belt of more or less uniform vegetation.
zoochore (ζῶον, animal), a plant distributed by animals.
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