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Integral Dose for Photon and Proton Hodgkin Lymphoma Radiotherapy

S Flampouri

S Flampouri*, B Hoppe , University of Florida, Jacksonville, FL


SU-I-GPD-T-125 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This work aims to evaluate irradiated volumes (IV) and integral doses (ID) to normal tissues of Hodgkin lymphoma patients receiving radiotherapy and compare IV and ID values for passively scattered proton (PSPT) vs. IMRT dose distributions.

Methods: Twenty patients with mediastinal involvement were analyzed. Each patient had PSPT and IMRT plans designed to provide similar coverage to the target (CTV) while incorporating patient specific, relevant per modality, calculation and delivery uncertainties. Planning CTs included whole lungs, breasts (15 females) and target with at least 3cm superior/inferior margin. IV for dose>0.5GyRBE and ID (volume x density x mean dose), were calculated for non-target-body, lungs and breasts. Non-target-body IV was also defined in four dose bins with limits 0.5GyRBE, 25, 50, 75, 100%.

Results: On average (range) proton ID / photon ID was 58% (39-84%) for non-target-body, 69% (24-96%) for breasts and 72% (42-112%) for lungs. Two patients had higher proton lung ID than photon. On average (range) proton IV / photon IV was 23% (8-48%) for non-target-body, 33% (15-56%) for breasts and 46% (21-69%) for lungs. No patient or organ had a larger irradiated volume with protons compared to photons. The effect is attributed mainly to the reduction of the low dose volume. For the non-target-body, protons reduced the IV on average (range) by 9.0L(2.2-17.2L) in the dose range 0.5Gy-25% of prescribed dose, 1.7L(0.4-5.6L) in the dose range 25-50%, 1.2L(0.2-5.0L) in the dose range 50-75%, and only by 0.6L(0.1-1.2L) in the high dose range (75-100%).

Conclusion: This study comparing ID and IV produced by IMRT and PSPT plans ignored neutron contributions and advanced proton techniques. However, it is important to report the large reductions on both quantities with protons for these young, highly curable patients for which model assessments and clinical studies show correlation of dose with secondary cancer risks.

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