Page 35

AAPM Newsletter

September/October 2011

Letter to the Editor Dear Editor: As practicing clinical medical physicists, located both within hospitals and working as consultants, we wish to express our concerns over the proposed CT phantom, which consists of three sections, each weighing approximately 30 pounds. While the concept of this proposed phantom is commendable, and we understand that there is a need in some situations to make dose measurements in such a phantom, it appears that practical realities have been overlooked. It must be realized that the vast majority of CT scanners in this country are supported by consulting medical physicists. Even those who are located within hospitals are typically spread across several campuses. This reality necessitates frequent moving of phantom. At present, consultant physicists are already obligated to carry both imaging and dose assessment phantoms. Even though the proposed phantom breaks down into three pieces and nominally includes dose and image quality modules, it is not trivial to transport 100 pounds of phantom. Loading, unloading, and transporting these phantoms into facilities will become a major challenge. If other survey work is needed, such as R/F testing, the amount of equipment required may well not even t into a standard sedan. Weight limits are important. Many medical physics consultant companies may be negatively impacted by requiring the employees to lift and maneuver 100 pounds. Many medical physicists of smaller stature including some female physicists or those with medical conditions may not be able to accomplish this at all. Such a heavy lifting requirement can seriously impact the insurance status of employers, as the risk of injury is greatly increased. We do not see that there is a need to perform these types of dosimetry measurements in phantom in the eld at all. This is purely an historic holdover that does not add to our ability to quantify the output of a CT scanner. If the manufacturers use this phantom, characterizing and quantifying their system, and provide physicists with those values and the associated air values, the physicists in the eld can easily and condently verify performance of the scanner, using these air measurements for dosimetry estimates. As was stated by Dr. Boone at the ACMP meeting in Chattanooga, it is possible to adequately characterize the beam in air, as we do with all other diagnostic systems. CT beams are very well understood, and well modeled in Monte Carlo calculations. Such calculations, which are in many ways more dependable than phantom measurements, require air kerma input, not phantom values. We strongly wish to encourage the careful consideration of the full consequences and practical realities of promoting this phantom design for regular clinical use. Measurements of air kerma and, if necessary, doses in the existing phantoms can be used to qualify that the unit is operating within the manufacture’’s designed outputs. Let the more detailed measurements be made where they belong, with the manufacturers and research institutions. Allow the rest of us to make reasonable measurements in a reasonable manner, using the more appropriate evaluations tools. Signed, Steven Amzler, Benjamin Archer, James Astarita, Libby Brateman, Dean Broga, Kenneth Coleman, Richard DiPietro, Tyler Fisher, Steven Jones, Melissa Martin, Katie Mavinkurve, Nikolaos Perdikaris, Douglas Pfeiffer, Stephen Steuterman, Kevin Strining

35 35

35 35

Profile for aapmdocs

AAPM Newsletter September/October 2011 Vol. 36 No. 5  

AAPM Newsletter September/October 2011 Vol. 36 No. 5  

Profile for aapmdocs