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Impact of Plan Complexity On the Delivery Accuracy and Dosimetric Accuracy of Volumetric-Modulated Arc Therapy

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G Li

G Li1*, Y Li2 , Q Wang3 , J Xiao4 , S Bai5 , (1) West China Hospital, Chengdu, Sichuan, (2) the Second Xiangya Hospital, Changsha, Hunan, (3) West China Hospital, Chengdu, Sichuan, (4) West China Hospital, Chengdu, Sichuan, (5) West China Hospital, Chengdu, Sichuan


SU-I-GPD-T-279 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: This work evaluated the impact of the new metric of plan complexity on the delivery accuracy and dosimetric accuracy of volumetric-modulated arc therapy.

Methods: The performance of the new modulation complexity score for VMAT (NMCSv) was evaluated through correlation analyses with the patient-specific quality assurance results using two three-dimensional diode arrays and with the delivery accuracy of the linac machine parameters. For comparison, the following parameters were also evaluated using the same correlation analyses: average field width, average leaf travel (ALT), modulation complexity score (MCSv), and leaf travel modulation complexity score (LTMCSv). Pearson's r correlation analysis was performed to examine any relationships among the metrics, delivery accuracy of linac machine parameters, and patient-specific QA results.

Results: In both diode arrays, the gamma passing rates (3%/3 mm) for patient-specific QA were significantly correlated to all complexity metrics, and the highest correlation was observed between NMCSv and the gamma results (R = 0.652 Delta4, R = 0.504 ArcCheck).The absolute Pearson’s r values were below 0.3 for all of the plan complexity metrics and the errors of machine parameters, except for the values between the multi-leaf collimator (MLC) leaf position error and both ALT and LTMCSv. The Pearson’s r values for the gantry angle and MLC leaf position errors to the gamma passing rates were about -0.2 and -0.3, respectively. No statistically significant correlation was observed between the passing rates and either MU or jaw position errors.

Conclusion: The NMCSv metric showed good performance for assessing the plan complexity of VMAT. The effect of the delivery accuracy of linac machine parameters on the patient-specific VMAT QA results was minimal. The proposed complexity metric was an effective tool for evaluating the plan complexity, and each cancer center should clarify the primary dose deviation factor and select the proper complexity metric for their center.

Funding Support, Disclosures, and Conflict of Interest: This research work was supported by National Natural Science Foundation of China (Grant No. 81472807).

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