Planning target volume-Is it still suitable for intensity modulated proton therapy for lung cancer? / 中华放射肿瘤学杂志

ABSTRACT

Objective:To demonstrate the concept of planning target volume (PTV) is not suitable for intensity proton therapy (IMPT) in lung cancer, plan differences were compared based on the concept of PTV and Internal target volume (ITV), aiming to provide clinical reference.Methods:Six patients were retrospectively selected and approved by the local ethics committee. Each of the six patients received two IMPT plans based on a synchronous accelerator model, developed by SINAP team (Shanghai Institute of Applied Physics, China Academy Science University) and commercial treatment system one with the PTV-based robust IMPT (PTV-IMPT) plan and the other with ITV-based robust IMPT (ITV-IMPT) plan. Three beams were set in all plans, and the final dose was calculated using Monte Carlo dose algorithm. The plan quality and robustness of PTV-IMPT and ITV-IMPT plans were evaluated quantitatively.Results:Compared to the PTV-IMPT plan, ITV-IMPT plan showed better target conformity index (conformability index 0.58 vs.0.43), better homogeneity index (homogeneity index 0.96 vs.0.92), lower V 5Gy in normal lung tissue (13.1% vs.13.5%) and maximum dose in spinal cord (8.9 Gy vs. 9.5 Gy) as well as plan monitor unit (MU 338 vs. 401) . In addition, ITV-IMPT plan showed more robust in target coverage (0.003-0.032 vs. 0.02-0.28), and normal lung tissue was also found a bit robust in the ITV-IMPT plan ( 0.06-0.11, 0.07-0.13). Conclusions:Compared with the PTV-IMPT plan, ITV-IMPT plan has the advantages of high planning quality, well robustness and better tumor motion mitigation. Therefore, ITV concept is recommended to be applied in the IMPT plan for lung cancer.