Intensity Modulated Radiation Therapy (IMRT) is in widespread use within the Radiation Oncology community. Because of the cost associated with this modality, institutions must have this procedure commissioned in a timely and accurate manner. P&CP was among the first physics groups to implement IMRT in a private clinical setting. To date, we have commissioned over a dozen programs.
IMRT is a complex process whereby the profile of the x-ray beam is shaped to match a pattern predetermined by the treatment planning computer. This technique offers dramatic improvements in normal tissue sparing as well as dose conformity to the tumor. The shaping process described above may be performed by compensatory filters or with Multi-leaf Collimator devices (MLC).
The data required for an IMRT calculation is specialized, as the algorithms rely on precise information for extremely small field sizes. Small beam sizes are more difficult to characterize accurately because small changes in size, depth, etc. can result in large changes in the x-ray beam intensity. Correctly measuring this data is critical to the effective and accurate application of IMRT. In addition, this data must be characterized or modeled in the treatment planning system. This modeling must match the actual beam measurements as closely as possible. Again, because the planning system calculates small field sizes in the optimization process, it is important that the time and energy be spent “up front” to assure that this computerized model is the best it can reasonably be. The P&CP staff has years of experience in both the measurement and modeling of these special beams; we can correctly assist you in these crucial processes.
An excellent example demonstrating the quality of our work in developing IMRT programs would be to examine our clients’ performance in the RTOG IMRT Head & Neck phantom program.
Operated by the M.D. Anderson Radiological Physics Center (RPC), this national QA evaluation program is used to qualify the RTOG protocol of the same name. The phantom contains a variety of targets and an organ-at-risk, simulating the spinal cord. The participating clinic receives the phantom from the RPC whereupon a CT study set of the phantom is acquired, specified contours are drawn, and the treatment isocenter is located. The phantom is then marked, and an IMRT plan is run to specified criteria followed by irradiation according to the treatment plan. The data is then returned to the RPC for analysis.
A presentation at the 2005 ASTRO meeting indicated that even with the "relaxed criteria" of +7 and 5 mm distance-to-agreement (DTA), only 68 of the submitting institutions, nationwide, passed on their initial submissions.
Two of our largest clinical sites have completed this procedure, each with a different IMRT planning system. Both easily passed on their initial submissions. Results from institution A were +2 to the targets with DTA = 2mm and results from institution B were .better still,, with +1 to the targets and 1mm DTA.
IMRT also changes the paradigm as it relates to patient planning and patient specific quality assurance.
We can provide a complete program or training in those areas where your staff requires assistance.
P&CP offers our experience and expertise, reducing the IMRT complexity to an IMRT reality.
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An independent, confidential radiation therapy physics auditing program
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Why should your clinic have an independent medical physics audit?
P&CP offers you a safe and efficient auditing system to ensure a sustainable safeguard of your QA program.
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“P&CP has performed exceptionally well in commissioning our new equipment and technology efficiently through experienced physicists with varied backgrounds and resources.”
Karen Johnson
Radiation Oncology Manager Presbyterian Cancer Services/Charlotte, NC |
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