Dosimetry of particle radiotherapy for liver cancer adjacent to gastrointestinal tract

Objective To investigate the dosimetric advantages of proton and heavy ion radiotherapy (particle radiotherapy) for liver cancer adjacent to gastrointestinal tract. Methods Ten patients with liver cancer adjacent to gastrointestinal tract receiving radiotherapy were recruited in this study. The prescription was first given with 50 Gy (RBE)/25 fractions to planning target volume 1(PTV-1) using proton irradiation, and then administered with 15 Gy (RBE)/5 fractions to PTV-2 using carbon-ion irradiation. A simultaneous integrated boost regime was established using the same variables and prescription. The organ at risk (OAR) constraints were referred to RTOG 1201.All plans were performed for dose evaluation after qualifying the OAR constraints. Results The dose coverage of 95% of the prescribed dose(V95) for PTV-1 from the photon plan (97.15%±4.27%), slightly better than (96.25±6.69%) from the particle plan (P=0.049). The V95 of PTV-2 from the particle plan was (94.6%±6.22%), comparable to (95.12%±3.49%) from the photon plan (P=0.277). The integral dose of Body-PTV-1 delivered by the particle plan was merely 39.9% of that delivered by the photon plan. The mean liver-GTV dose from the particle plan was only 81.8% of that from the photon plan. The low-dose irradiation to the stomach and duodenum from the particle plan was significantly lower than that from the photon plan. Conclusions The dose to the liver-gross tumor volume (GTV) is the main factor limiting the increase of total dose to the tumors. When the absolute GTV in the liver is relatively large, particle radiotherapy can maintain comparable dose coverage to the tumors as the photon radiotherapy whereas significantly reduce the dose to the liver-GTV. Key words: Particle radiotherapy; Photon radiotherapy; Liver neoplasm; Dosimetriy Dosimetry