Study on the sensitivity of different 3D detectors to MLC positioning errors in volumetric modulated arc therapy (VMAT) plan for nasopharyngeal carcinoma / 中华放射肿瘤学杂志

ABSTRACT

Objective To compare the sensitivity of Deha4 and ArcCHECK 3D detectors to detect the multi-leaf collimator (MLC) positioning errors in the dose verification of volumetric modulated arc therapy (VMAT) plans for nasopharyngeal carcinoma (NPC).Methods Ten NPC patients receiving VMAT plans were selected.The positioning error of 0.5-4.0 mm was introduced into the leaves of each MLC segment in the original file to expand,contract or shift the whole segments.The possible positioning errors of MLC in the treatment of VMAT were simulated.The Delta4 and ArcCHECK were utilized to verify the measurements.The absolute gamma passing rate was compared between the calculated dose and the measured dose of the VMAT plan by using the paired t-test.Results When the evaluation criterion was taken as 3 mm/3％,the absolute passing rate verified by the original plans of two detectors was greater than 95％.The positioning errors of MLC expansion,contraction and shifting detected by Delta4 and ArcCHECK were 1.5 mm,1.0 mm,2.0 mm and 3.0 mm,1.0 mm,and 3.0 mm,respectively.When taking 2 mm/2％ as the evaluation criterion,the absolute passing rate verified by the original plan was decreased significantly.Delta4 and ArcCHECK detected that the positioning errors of MLC expansion,contraction and shifting were 1.0 mm,1.0 mm,2.0 mm and 1.5 mm,0.5 mm,and 2.0 mm,respectively.Conclusions The dose verification of the VMAT plan for NPC by Delta4 and ArcCHECK can detect different types and sizes of MLC positioning errors,whereas the detection sensitivity slightly differs between Delta4 and ArcCHECK.Both of them are not sensitive to detect the MLC positioning errors less than 1.0 mm.It is fairly necessary to strengthen the quality assurance of MLC in the daily work.