The need for individualized studies to compare radiogenic second cancer (RSC) risk in proton versus photon Hodgkin Lymphoma patient treatments

Abstract

For Hodgkin Lymphoma (HL), proton therapy has been shown to potentially reduce therapeutic dose to healthy tissue and therefore the risk of developing a radiogenic second cancer (RSC) relative to photon therapy. Currently, commercial treatment planning systems (TPS) do not account for stray radiation doses for these treatments and their risks of late effects. Treatment plans were created and therapeutic doses were calculated with commercial TPSs for the breast, lung, and thyroid of nine HL patients. Stray dose contributions were added by thermoluminescent dosimeter (TLD) measurements in an anthropomorphic phantom for the intensity modulated radiation therapy (IMRT) treatments and personalized Monte Carlo simulations for the proton treatments. The mean relative risk (RR) of developing a RSC following HL treatment with proton therapies was then calculated and compared to photon IMRT, and reported with the metric ratio of relative risk (RRR). Results showed generally lower RSC risks after proton therapy than photon IMRT when averaged over all patients in the cohort for the breast (RRR = 0.84±0.03), lung (RRR = 0.77±0.03), and thyroid (RRR = 0.83±0.05), but were not universal across all patients examined. Our findings revealed that it is important to include stray dose contributions when comparing the RSC risks for different HL treatment techniques and demonstrated the importance of personalized dose and risk calculations for modern HL radiotherapy.