Innovations & Trends
VMAT: advances in radiation therapy
By Dr Raphael Chee, Radiation Oncologist
External beam X-rays became part of cancer management in the 1920s but use has widened in the past 30 years thanks to advances in computing and hardware technology. The aim is to improve therapeutic efďŹ ciency by maximising cancer control (better tumour targeting, dose escalation) and minimising toxicity for the patient. VMAT (Volumetric Modulated Arc radiation Therapy) is part of that technological evolution, minimising damage to normal critical structures while delivering nearly all dosimetric endpoints that form part of 3D-Conformal Radiation Therapy (CRT) plans. Beam modulation allows clinicians to shape the radiation dose to tumours whilst reducing dose to healthy tissue and sensitive organs. The beneďŹ ts are obvious. VMAT is fast when using highly modulated beams: most treatments use ONEĂĽORĂĽTWOĂĽROTATIONALĂĽARCS ĂĽTWOĂĽMINUTESĂĽEACH ĂĽWHICHĂĽCUTSĂĽ ĂĽOFFĂĽ treatment times compared to 3D Conformal and Intensity Modulated Radio Therapy (IMRT); shorter treatment usually translates into patient comfort and targeting accuracy. Figure 1 shows how VMAT can shape the high dose region (the thick red line) to match the shape of the target (the teal shaded area) whilst reducing the dose to the normal, healthy tissue, especially the parotids (charcoal grey organ). Standard conformal RT can still shape dose to a target but not to the same degree as VMAT, as seen in Figure 2.
Fig 1. VMAT plan. Note the ability for the dose to “curve� around normal tissue structures.
Fig 2. 3D-CRT plan. Note extra dose to parotid and oral cavity. In addition, the dose coverage is less homogenous, with greater “hot and cold� spots.
It is the improved targeting of cancers that makes Modulated Radiation Therapy (RT) the standard of care in the treatment of head and neck, PROSTATEĂĽ ESPECIALLYĂĽPOST PROSTATECTOMY ĂĽANDĂĽANAL VAGINAL VULVAĂĽCANCERS ĂĽ Head and neck RT allows clinicians to conserve parotid gland (salivary) function, which drastically improves quality of life for patients. As experience grows with VMAT, different tumours in situations previously prevented by toxicity are being targeted. Figure 3 shows advanced distal oesophageal adenocarcinoma with bulky celiac and para-aortic nodes: “radical intentâ€? type treatment induced minimal grade 1 toxicities of fatigue and nausea; the postTREATMENTĂĽ&$' 0%4ĂĽSCANĂĽSHOWEDĂĽNEARĂĽCOMPLETEĂĽ response; in the 3D-CRT era, his treatment plan would have been “medium-doseâ€? palliation.
Fig 3. Advanced distal oesophageal adenocarcinoma with bulky celiac and para-aortic nodes
Trends in Urology Penile Cancer. The incidence of squamous cell carcinoma (SCC) of the PENISĂĽAPPEARSĂĽTOĂĽBEĂĽINCREASINGĂĽINĂĽ7!ĂĽ FROMĂĽ ĂĽCASESĂĽPERĂĽYEAR ĂĽOVERĂĽ the last 25 years), probably due to an increase in HPV-related cancers SUBTYPESĂĽ ĂĽANDĂĽ ĂĽANDĂĽAĂĽREDUCTIONĂĽINĂĽNEONATALĂĽCIRCUMCISION ĂĽ)NCIDENCEĂĽ MAYĂĽWELLĂĽREDUCEĂĽAGAIN ĂĽWITHĂĽTHEĂĽUPTAKEĂĽOFĂĽ(06ĂĽVACCINATION ĂĽ!ĂĽNEWĂĽ7!ĂĽ service aims to provide state-of-the-art management that seeks to cure cancer with maximum functional and cosmetic preservation of the penis: early referral and plastic surgical techniques are key. The introduction in 2014 of dynamic sentinel node biopsy of the groin completes the picture, minimising morbidity whilst enabling accurate staging and treatment of metastatic disease. Urethral strictures. These affect males from birth to death. Causes include the delayed consequences of infant hypospadias surgery, trauma (including fall astride injuries, pelvic fracture, catheterisation and endoscopic procedures) and less commonly infection (gonnorrhoea, TB, and schistosomiasis). The concept that “dilatation is palliationâ€? remains as true today as when coined 150 years ago. Modern reconstruction for
38
By Dr David SoďŹ eld, Urologist, Palmyra
ďŹ t men usually involves free grafts (most commonly oral mucosa), with high success rates that bring a dramatic quality of life beneďŹ t. Radiationrelated strictures are increasingly common and can be very difďŹ cult to manage; new temporary removable stents have an emerging role in these patients or the elderly. Surgery for male urinary incontinence. As surgical treatment of prostate cancer has climbed, so too has the incidence of stress urinary incontinence (SUI) in men, a rare condition otherwise. Between 5% and 15% of men will remain incontinent 12 months after radical prostatectomy and most of these can be improved surgically. For those with mild to moderate SUI (1-3 pads or up to 400ml loss per day) a variety of minimally invasive suburethral sling procedures are available and have high success rates (85-90%). For those with more severe SUI, artiďŹ cial urinary sphincters are very successful, although more complicated to insert and they require patient operation of the device. The quality of life beneďŹ t is great in men who have already suffered considerable trauma through their cancer diagnosis and treatment.
MEDICAL FORUM