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In-Vivo Dosimetry and Range Verification for Proton Therapy

Y Zheng

Y Zheng1*, (1) ProCure Treatment Centers, OKLAHOMA CITY, OK

SU-E-T-449 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Accurate calculation of proton dose and penetration range is critical in proton therapy. However, in-vivo studies on dose and range verification are very limited, and there is no consensus on the appropriate amount of range uncertainty. The purpose of this study is to verify the proton dose and range and evaluate the range uncertainty using in-vivo measurement of patients under proton therapy.

Methods: Gafchromic EBT2 films were used in the study. The film was calibrated using proton beams, and its energy dependence was measured for various proton energy beams. Water phantom and animal tissues were first used to test the application of EBT2 on dose and range verification before the in-vivo dosimetry study. Several patients, such as lung and brain cases, were carefully selected for in-vivo film measurement. For example, we measured a lung case with tumor located posterior, and the EBT2 film was placed immediately under the patient to measure the dose in the distal falloff region from an anterior-posterior beam. The measured plane dose was compared to the calculated dose from the treatment plan, which was created using the XiO treatment planning system (TPS). The dose difference at the distal falloff region was used to evaluate the range difference between measurement and planning.

Results: The EBT2 film showed a minimal energy dependence and was able to measure proton range accurately, within 1 mm in a phantom setting. Preliminary data for a lung treatment indicate a less than 3 mm range difference between EBT2-measured range and the TPS-calculated one. More studies for various disease sites are in progress.

Conclusions: Our animal tissue and in-vivo study shows that the measured and calculated proton ranges are within 2% plus 2 mm for most cases. Further in-vivo studies are needed to confirm our findings and evaluate range uncertainties at different facilities.

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