In 2010, all young patients treated for intrathoracic Hodgkin lymphoma (HL) at one of 10 radiotherapy centers in the province of Quebec received 3D conformal photon therapy. These patients may now be at risk for late effects of their treatment, notably secondary malignancies and cardiac toxicity. We hypothesized that more complex radiotherapy, including intensity‐modulated proton therapy (IMPT) and possibly IMRT (in the form of helical tomotherapy (HT)), could benefit these patients. With institutional review board approval at 10 institutions, all treatment plans for patients under the age of 30 treated for HL during a six‐month consecutive period of 2010 were retrieved. Twenty‐six patients were identified, and after excluding patients with extrathoracic radiation or treatment of recurrence, 20 patients were replanned for HT and IMPT. Neutron dose for IMPT plans was estimated from published measurements. The relative seriality model was used to predict excess risk of cardiac mortality. A modified linear quadratic model was used to predict the excess absolute risk for induction of lung cancer and, in female patients, breast cancer. Model parameters were derived from published data. Predicted risk for cardiac mortality was similar among the three treatment techniques (absolute excess risk of cardiac mortality was not reduced for HT or IMPT (p>0.05,p>0.05) as compared to 3D CRT). Predicted risks were increased for HT and reduced for IMPT for secondary lung cancer (p<0.001,p<0.001) and breast cancers (p<0.001,p<0.001) as compared to 3D CRT.PACS numbers: 87.55.dh, 87.55.dk

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Purpose: To evaluate the potential reduction of risk of late radiation‐ induced effects for young patients with Hodgkin's lymphoma treated with intensity modulated proton therapy (IMPT) as compared to 3D conformal involved‐field photon radiotherapy. The late effects considered were cardiac mortality and secondary cancer in the lungs and breasts (for female patients). Methods: Patient data was acquired for eleven patients who were under thirty years of age and were treated with radiotherapy for Hodgkin's lymphoma in Quebec in 2010. The original CT simulation images were used to re‐plan the patients with IMPT using commercially‐available treatment planning software. The contours of the critical organs of interest were reviewed for each patient by a physician and modified when necessary for consistency. The dose‐volume matrices of the original photon plans and the new proton plans were analyzed using radiobiological models to assess the risk of late effects. The relative seriality model was utilized to predict excess risk of fatal cardiotoxicity. The organ equivalent dose concept was utilized in conjunction with a modified linear quadratic model to predict the excess absolute risk for induction of lung cancer and breast cancer. Parameters for each model were derived from retrospective studies in the literature. Results: Mean excess risk of fatal cardiotoxicity was 0.9% for photon plans and 0.6% for proton plans. Mean excess absolute risk of developing lung cancer thirty years post‐treatment was 11.9/10,000 patients per year (PY) for photons and 6.9/10,000 PY for protons. Mean excess absolute risk of developing breast cancer thirty years post‐treatment was 6.0/10,000 PY for photons and 2.1/10,000 PY for protons. Conclusions: IMPT has the potential to reduce the risk of fatal, radiation‐induced late cardiotoxicity as well as the risk of radiation‐induced secondary cancers in the lungs and breasts of young patients receiving radiotherapy for Hodgkin's lymphoma. This work has been funded in part by a grant from the Fonds de recherche Santé Quebec (FRSQ).

IMPT may significantly reduce the risks of radiation-induced cardiac mortality and secondary cancer in the lungs and breasts of young patients receiving radiotherapy for HL, NHL, or breast cancer.

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