Selection of patients for proton therapy to reduce risk of second primary lung and breast cancer

Aim: We previously published selection criteria for proton therapy (PT) in the Netherlands for breast cancer (BC) and thoracic lymphoma patients, based upon the Absolute Excess Risk (AER) for acute coronary events. The aim of the current paper was to define additional criteria to select BC and thoracic lymphoma patients for PT, to reduce the risk of second primary BC and lung cancer (LC). Methods: Based on a literature review, we identified Excess Relative Risks (ERR)/Gy mean organ dose of second primary BC and LC, for selected patient groups. We combined the ERR with the absolute incidence of second primary BC and LC in the Dutch population to approximate the AER/Gy mean organ dose. This was used to define selection criteria for PT. Results: The AER for second primary BC was estimated to be 2.5 %/Gy mean breast dose in female patients ≤40 years. The AER of second primary LC was calculated based on an ERR of 11 %/Gy, separately for female and male smokers ≤50 years, with an ERR of 0 % for non-smokers. Consensus was reached for the following selection criteria for PT: ≥5% absolute risk reduction of second primary BC in the contralateral breast, or a ≥2.0 % absolute risk reduction of second primary LC. Thoracic lymphoma patients were also eligible for PT if the sum of AERs of second primary BC in both breasts exceeded 7.5 %. Conclusions: Selection criteria were added to the Dutch indication protocol for proton therapy to identify BC and thoracic lymphoma patients who would benefit most from PT, based on an estimated reduced risk of second primary BC and LC.