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Tolerance and dosimetric study of multi-leaf collimator leaf position accuracy for dynamic intensity-modulated radiotherapy
Yang Jiming1, Ma Min2, Wu Yong3, Ren Jiangping1
1Radiotherapy and Chemotherapy Center, Ningbo First Hospital, Ningbo 315000, China; 2Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Scicences and Peking Union Medical College, Beijing 100021, China; 3Department of Radiotherapy, Xingyi People's Hospital, Xingyi 562400, China
AbstractObjective To evaluate the dosimetric effect of multi-leaf collimator (MLC) position error on dynamic intensity-modulated radiotherapy (dMLC-IMRT), aiming to provide guidance for the establishment of MLC quality control accuracy and operation tolerance. Methods In the phantom study, the virtual water phantom established in the treatment planning system (TPS), and three dynamic sliding window test fields with gap width of 5mm, 10mm and 20mm were designed. Clinical treatment plans of 7 common tumor types were extracted, including nasopharyngeal carcinoma, glioma, lung cancer, esophageal cancer, cervical cancer, prostate cancer, and breast cancer, with 6 cases in each. MLC errors were introduced into the copy from original plan to generate the simulation plans. MLC errors included systematic open/close error, systematic deviation error and random error. The dosimetric differences between the original and simulation plans were compared. Results The phantom study showed that the symbol of dose deviation was the same as that of systematic open/close error, and the value was increased with the increase of MLC error and decreased with the increase of gap width. The results of patient study showed that the systematic open/close error had a significant effect on dosimetry, the target volume dose sensitivities of different plans were 7.258-13.743%/mm, and were negatively correlated with the average field width. The dosimetric deviation caused by the systematic shift error below 2mm was less than 2%. The dosimetric change caused by the random error below 2mm could be neglected in clinical treatment. Conclusions The minimal gap width should be limited in TPS, whereas the quality control of MLC should be strengthened. In addition, for the dynamic intensity-modulated treatment technology, 2mm random error was suggested to be the operation tolerance during treatment delivery, and 0.2mm alignment accuracy on each side (or 0.4mm unilateral) is recommended to be the MLC quality control accuracy to ensure the dose accuracy of radiotherapy for different tumors.
Yang Jiming,Ma Min,Wu Yong et al. Tolerance and dosimetric study of multi-leaf collimator leaf position accuracy for dynamic intensity-modulated radiotherapy[J]. Chinese Journal of Radiation Oncology, 2021, 30(11): 1167-1172.
Yang Jiming,Ma Min,Wu Yong et al. Tolerance and dosimetric study of multi-leaf collimator leaf position accuracy for dynamic intensity-modulated radiotherapy[J]. Chinese Journal of Radiation Oncology, 2021, 30(11): 1167-1172.
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2021, Vol. 30 
