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Radiogenic Second Cancer Risk Differences in Female Hodgkin Lymphoma Patients Treated with Proton Versus Photon Radiotherapies

K Homann

K Homann1*, R Howell2, A Giebeler3, J Eley4, K Randeniya5, W Newhauser6, (1) UT MD Anderson Cancer Center, HOUSTON, TX, (2) UT MD Anderson Cancer Center, Houston, TX, (3) UT MD Anderson Cancer Center, HOUSTON, TX, (4) UT MD Anderson Cancer Center, HOUSTON, TX, (5) UT MD Anderson Cancer Center, Houston, TX, (6) Louisiana State University, BATON ROUGE, LA

SU-C-BRB-1 Sunday 1:30:00 PM - 2:15:00 PM Room: Ballroom B

Purpose: To determine the significance of neutron and scatter dose in comparing the predicted risk of developing a radiogenic second cancer (RSC) to the breast and lungs of a female Hodgkin Lymphoma (HL) patient irradiated at 30 years old when treated with photon Intensity Modulated Radiotherapy (IMXT) versus Passive Scatter Proton Therapy (PSPT).

Methods: Clinically approved IMXT and PSPT treatment plans were designed and prescribed 36 Gy to the treatment volume. For both plans, the therapeutic dose was calculated using a commercial treatment planning system (TPS). To account for inaccuracies in the TPS, the stray and neutron dose was calculated using an in-house Monte Carlo code for IMXT and with an analytical model fit to Monte Carlo data for PSPT. The mean equivalent dose was calculated for the breasts and lungs for both techniques, input into the BEIR VII Excess Relative Risk (ERR) models, and RSC risk compared at subsequent 10 year intervals.

Results: Mean dose to the patient's breast, including neutron and scatter dose, was 6.5 Sv for both the PSPT and IMXT plans which led to nearly equivalent ERR values. Sparing of the lungs was seen from PSPT (4.5 Sv) compared to the IMXT plan (8.4 Sv), however, which led to a reduction in ERR of nearly 50% for PSPT compared to IMXT. For the PSPT plan, the mean neutron equivalent dose contribution for the breast was 0.38 Sv (5% of the ERR contribution) and 0.28 Sv (6% of the ERR contribution) for the lungs. The IMXT plan had no neutron dose since it was planned with a 6 MV beam.

Conclusions: Mean breast dose was nearly equivalent for both plans leading to equal ERR to the patient. The mean lung dose, however, was reduced by a factor of two for PSPT, even taking into account the dose from neutrons.

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