AbstractID: 8156 Title: Quality Assurance of Intensity Modulated Radiation Therapy
(IMRT)
It has been shown that the dose distribution can often be significantly improved by
Intensity Modulation Radiation Therapy (IMRT). However, the dosimetry verification
for IMRT remains difficult for physicists. The purpose of this study is to demonstrate a
reliable quality assurance (QA) method to verify a “step and shoot” IMRT dosimetry. In
total 20 patients’ IMRT dosimetry are analyzed in this study. For each patient's IMRT
plan, we use three independent methods to verify the IMRT plan dosimetry, namely the
film dosimetry, the ionization chamber measurement and the computerized dose cal to
the central axis. Based on the overlaid film result, we found that on all the axial cuts, the
agreement between the isodose curves obtained from the film and generated from the
computer is within +- 4mm down to 70%. On the coronal plane and sagital plane, we see
the greater disagreement near the superior and inferior border of the field, where the
discrepancy can be as much as +- 6mm down to 70%. For the ion chamber measurement,
we see the discrepancy between the measurement result and the prescribed dose at
isocenter average +- 2.0% for those 20 patients. We also wrote a computer program to
calculate each segment contribution to the isocenter point and the result is within +- 5%.