With dosimetric data from 90 treatment plans of six anatomical sites, five patients per site and radiation delivered by IMPT, proton arc therapy (PAT) and VMAT,  this study published in the Green Journal reported the calculated risks of developing radiation-induced secondary cancer (SC) among the three different modalities. The six anatomical sites were head and neck, skull base, mediastinum, breast, prostate and thoracic spine. Risk estimates were based on the organ-equivalent dose (OED) concept using dose-response models. For protons, the factor OED_IMPT/OED_PAT ranged from 0.7 to 1.8 with both the mechanistic and linear model, while for photons OED_VMAT/OED_PAT ranged from 1.5 to 10 using the mechanistic model and 1.3 to using the linear model. The authors concluded that the transition from IMPT to PAT should not substantially affect SC risk in patients treated with proton therapy.