Photons or protons for re-irradiation in (non-)small cell lung cancer? Results of the multicentric ROCOCO in silico study.

OBJECTIVE Locally recurrent disease is of increasing concern in (non-)small cell lung cancer patients [(N)SCLC]. Local re-irradiation with photons or particles may be of benefit to these patients. In this multicentre in silico trial performed within the Radiation Oncology Collaborative Comparison (ROCOCO) consortium, the doses to the target volumes and organs at risk (OARs) were compared when using several photon and proton techniques in patients with recurrent localized lung cancer scheduled to undergo re-irradiation. METHODS Twenty-four consecutive patients with a second primary (N)SCLC or recurrent disease after curative-intent, standard fractionated radio(chemo)therapy were included in this study. The target volumes and OARs were centrally contoured and distributed to the participating ROCOCO sites. Remaining doses to the OARs were calculated on an individual patient's basis. Treatment planning was performed by the participating site using the clinical treatment planning system and associated beam characteristics. RESULTS Treatment plans for all modalities (5 photon and two proton plans per patient) were available for 22 patients (N = 154 plans). 3D-conformal photon therapy and double-scattered proton therapy delivered significantly lower doses to the target volumes. The highly conformal techniques, i.e., IMRT, VMAT, CyberKnife, TomoTherapy and IMPT, reached the highest doses in the target volumes. Of these, IMPT was able to statistically significantly decrease the radiation doses to the OARs. CONCLUSION Highly conformal photon and proton beam techniques enable high-dose re-irradiation of the target volume. They, however, significantly differ in the dose deposited in the OARs. The therapeutic options, i.e., re-irradiation or systemic therapy, need to be carefully weighed and discussed with the patients. ADVANCES IN KNOWLEDGE Highly conformal photon and proton beam techniques enable high-dose re-irradiation of the target volume. In light of the abilities of the various highly conformal techniques to spare specific organs at risk, the therapeutic options need to be carefully weighed and patients included in the decision making process.