SU‐GG‐T‐255: Experimental Verification of Lung Tumor Dose with Radiochromic Film
Purpose: To assess the absorbed doses in and around lung tumor by performing radiochromic film measurements. Method and Materials: A phantom was made to have a water equivalent central core, a low‐density middle layer and a water equivalent outer layer to simulate tumor in the lung, lung and chest wall, respectively. GafChromic™ EBT films were placed in the anterior and posterior surfaces and middle plane of the tumor. Three plans with a single anterior beam, opposed anterior‐posterior beams and five‐field‐IMRT were delivered separately. A calibration curve was generated to convert the optical density to absorbed dose. The measured doses in the three planes were compared with the calculated doses from Eclipse™ system which uses a Pencil Beam convolution‐superposition Algorithm with modified Batho inhomogeneity correction. The single‐beam, opposed beams were delivered for both low (6 MV) and high (15MV) energy photon. The IMRT plan was delivered with 6 MV. Results: For both single‐ and opposed‐beam plans, the measured dose was very close to the calculated dose in the middle plane (<2 %). In the anterior and posterior surfaces of the tumor, the measured dose was substantially lower than the calculated one. For the single‐beam plan, the difference was 10.0% (6MV) and 13.6% (15MV) for the anterior surface and was 9.8% (6MV) and 6.8% (15MV) for the posterior surface. For opposed beams, the difference was about 8% (6MV) and 11% (15MV) for both surfaces. Similar dose differences were observed for the IMRT plan (∼ 10 %). Conclusion: EBT film measurements demonstrated that the dose calculation algorithm used by a typical treatment planning system is precise (<2%) for the deep locations inside the tumor, but may overestimate the surface dose about 10%. © 2008, American Association of Physicists in Medicine. All rights reserved.
Zhang, J; Yoo, S; Kim, S; Yin, F
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