瓦里安加速器高分辨多叶准直器位置偏移对前列腺癌调强放射治疗剂量分布的影响

Objective To evaluate the influence of position deviation of high definition multi leaf collimator (HDMLC) on the dose distribution under different dose rates in the intensity modulated radiotherapy (IMRT) of prostate cancer. Methods 32 pa-tients with prostate cancer from February 2014 to April 2015 were selected and performed the radiotherapy by using the IMRT plan-ning with 9 irradiation fields, the irradiation interval of 40°,Varian Truebeam accelerator HDMLC, Eclipse treatment planning sys-tem, the MLC position deviation of introduced fixed numerical values (0.3,0.5,1.0,2.0 mm) for each planning was under the follow-ing conditions:(1)simultaneous enlargement of MLC X1 and X2 directions;(2)simultaneous shrink of MLC X1 and X2 directions. The two indexes were used for the comparison of each planning results:(1)the 95%isodose line conformal index(95%CI);(2) the rectum maximum dose(rectum Dmax). Results (1) If MLC amplified deviation at the MLC X1X2 collimator directions≥0.3 mm, 95%CI was decreased, while rectum Dmax was increased, moreover this influence was directly proportional to the enlargement of dose rate and deviation amount;(2)if the MLC shrunk deviation at the MLC X1X2 collimator directions≥0.3 mm, 95%CI was firstly increased to the peak value;if MLC shrunk deviation≥1.0 mm, 95%CI was rapidly dropped, moreover the higher the dose, the more obvious the drop;however, rectum Dmax showed a obviously decreasing trend and this reduce was directly proportional to the dose rate and deviation amount. Conclusion If the leaf deviation of HDMLC is more than 0.3 mm, a large number of dose deviation could occur in the IMRT planning of prostate cancer, moreover this deviation could be more obvious with the increase of dose rate, therefore the MLC daily quality assurance should control the average MLC position deviation within 0.3 mm. [ABSTRACT FROM AUTHOR]