What is the risk of hypothyroidism after regional nodal irradiation for breast cancer? The RadComp trial compared proton and photon regional nodal irradiation, and this substudy investigated whether proton therapy reduced the risk of developing hypothyroidism. The study included 71 patients randomized to proton or photon therapy. The cumulative incidence of clinical hypothyroidism at 3 years was 9% for photons and 16% with protons (p=0.14). Though not statistically significant, the rate of hypothyroidism was 0% with 3D conformal photon therapy compared with 16% for both IMRT and proton therapy. Dose constraints to reduce the risk of hypothyroidism were mean thyroid dose <21 Gy and >2.2 cc spared from receiving 20 Gy. | Neibart, Int J Radiat Oncol Biol Phys 2026
