Relative risk of cardiac mortality and dosimetric comparison among three-dimensional radiotherapy, volume-modulated arc therapy and proton beam in vertebral-body reduced-dose craniospinal irradiation.

Abstract

We aimed to compare dose to organs at risk (OARs) and the excess relative risk (ERR) of cardiac mortality among three-dimensional conformal radiotherapy (3D-CRT), volume modulated arc therapy (VMAT) and proton beam therapy (PBT) in craniospinal irradiation (CSI). CSI plans of 3D-CRT, VMAT and PBT were generated. Vertebral body reduced dose (VBR)-CSI according to the International Society of Paediatric Oncology recommendation was used for VMAT and PBT. We delineated two sets of target volumes, i.e. target volume (TV) 1 for brain and thecal sac and TV2 for the vertebral body. Two sets of CSI dose, 23.4 and 36 Gy, were prescribed for TV1, and VBR doses, 18.4 and 20 Gy, were prescribed for TV2. For 3D-CRT, we prescribed a dose only to cover TV1. For VMAT and PBT, 23.4/18.4Gy and 36/20 Gy in 13 and 20 fractions were optimized. To evaluate the ERR of cardiac mortality compared with the normal population, we incorporate the mean heart dose with the linear model. In a total of eight patients, 48 treatment plans were generated (24 plans for each dose set). PBT showed the lowest mean dose to all OARs, i.e. heart, lung, liver, kidney, esophagus, oral cavity, thyroid and vertebral body. PBT showed significantly less ERR of cardiac mortality compared with 3D-CRT and VMAT for both 23.4 and 36 Gy prescriptions. With VBR-CSI, PBT reduced the mean dose to all OARs and significantly reduced the ERR of cardiac mortality compared with 3D-CRT and VMAT. The advantage of PBT was manifest, especially with high-dose CSI.