Dosimetric Comparison of 3DCRT, IMRT and VMAT for Spine Radiotherapy based on Secondary Cancer Risk

This study evaluated the secondary cancer risk after 3D-conformal radiotherapy (3DCRT), intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for spine. Computed tomography image set of a RPC spine anthropomorphic phantom was exported to the Pinnacle3 treatment planning system. Radiation treatment plans for spine were created using the four-field 3DCRT, seven-field IMRT and dual-arc VMAT techniques. The mean and maximum doses, dose-volume histograms and volumes receiving more than 2 Gy and 4 Gy of organs-at-risk (OARs) were calculated and compared. The lifetime risk for secondary cancers was estimated according to NCRP Report 116. Quality Assurances of IMRT and VMAT were performed using the ArcCHECK method with gamma index criteria set to 3%/3mm. For our dosimetric comparisons, planning target volume coverages were found to be 90.5 %, 91.4 % and 95.9 %, for 3DCRT, IMRT and VMAT, respectively. VMAT was found to deliver the lowest maximum dose to esophagus (3.22 Gy), bone (6.48 Gy), heart (1.69 Gy), spinal cord (5.15 Gy) and the whole lung (4.52 Gy). Volumes of esophagus receiving more than 4 Gy were 0% for VMAT, 37.56% for IMRT and up to 43.76% for 3DCRT. The estimated risk for secondary cancer in the respective OAR is considerably lower in VMAT compared to other techniques. Results of maximum doses and volumes of OARs suggest that the risk of secondary cancer induction for spine in VMAT is lower than IMRT and 3DCRT, whereas VMAT has the best target coverage.