Influence of collimator angle optimization on intensity-modulated radiotherapy planning for gastric cancer

Abstract

Objective To investigate the impact of four different collimator angle optimization techniques on the planning target volume (PTV) and organ at risk (OAR) during intensity-modulated radiotherapy (IMRT) for gastric cancer. Methods Ten patients with gastric cancer undergoing IMRT in Zhongnan Hospital of Wuhan University from 2015 to 2016 years were recruited in this study. All IMRT plans were designed by conventional five fields (330°, 10°, 45°, 90°and 180°). In the Eclipse treatment planning system, four different collimator angle optimization techniques with consistent planning optimization parameters were employed to design the IMRT plan. Collimator angle optimization techniques included the following aspects. The collimator angle was set at 0 degree (CL0), collimator angle was set at 90 degree (CL90), Eclipse automatic collimator angle optimization (CLA) was adopted and collimator angle was set as the angle when the distance between X-Jaws and PTV (CLX) was the shortest. The dosimetric parameters mainly included the conformal index (CI) of PTV, the homogeneity index (HI), the mean dose (Mean), and the dosage of OAR.The treatment time (Time), monitor unit (MU), control point (CP), split field (SF) and conformal distance (Fx) were also considered. Results Regarding CL0 as the control, the CI, HI and Mean did not significantly differ among four collimator angle optimization techniques (all P>0.05), whereas CLX could significantly increase the average dose of PTV in the target area (P<0.05); CLX optimization reduced the liver(V30 reduction by 1.54%), left kidney(V12 decrease by 1.46%), right kidney and other OARs, whereas it slightly increased the maximum dose of the small intestine and spinal cord (<1%). CL90 and CLA optimization elevated the dose of OAR in gastric cancer. Among four different collimator angle optimization techniques, CLX optimization reduced the MU (25.02%), CP (26.03%), Fx (20.27%) and SF (by 1.3 separate fields on average) and treatment time (10.03%). CL90 and CLA optimization could decrease the MU, CP, Fx and SF.CL90 optimization had certain advantages in shortening the treatment time, whereas CLA optimization could prolong the treatment time by 5.04%. Conclusions During IMRT for gastric cancer, CL90, CLA and CLX collimator angle optimization techniques can obtain comparable dosimetry distribution to CL0 optimization technique, which can reduce the MU, decrease the radiation leakage, shorten the treatment time and improve treatment efficiency. Key words: Collimator angle optimization; Gastric neoplasms/intensity-modulated radiotherapy