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A Study On Beam Reduction of Circular Aperture Based Robotic Radiotherapy Treatment Planning

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B Liang

B Liang1*, B Liu1 , Y Li1 , B Guo1 , X Xu1 , R Wei1 , F Zhou1 , Q Wu2 , S Xu3 , J Piao4 , H Xu4 , (1) Image Processing Center, Beihang University, Beijing, Beijing, (2) Duke University Medical Center, Durham, NC, (3) Chinese PLA General Hospital, Beijing, Beijing,(4) 302 Military Hospital, Beijing, Beijing 100039


SU-I-GPD-T-560 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Reducing the number of beams (NB) in circular aperture based plan optimization is essential to improve the efficiency of robotic radiotherapy. In this study, we propose a linear programming (LP) based optimization algorithm, of which the beam reduction mechanism is validated by comparing with a mixed integer programming (MIP) model.

Methods: The standard LP model optimizes beam weight by minimizing the deviation of relax constraints (RCs) subjected to hard constraints (HCs), without limiting NB. NB is reduced by removing the resulting beams with lower weight, and optimizing the weight of remaining beams again with the same RCs and HCs. In MIP model, a set of binary variables (BVs) are added, which is either 0 or 1 corresponding to 0 or positive beam weight. NB is limited by constraining the sum of BVs. Both models were demonstrated and compared on a lung case with a PTV of 15.5cm³

Results: Both models used the same set of 2207 input beams, which were initialized with 94 available nodes and circular collimators of 15mm & 20mm diameters. The same set of AAPM TG101 report based RCs and HCs were used. NB was reduced and constrained to 150 by LP and MIP models, respectively. The beam coincidence of the two resulting plans is 98.7% (148/150). DVH comparison indicates the dose distributions of two plans are equivalent. Optimization time of LP and MIP models is 160s and 6814s, respectively.

Conclusion: The beam selection capability of LP model is demonstrated and validated by the MIP model. The treatment plan generated by LP model and beam reduction mechanism is similar to the global optimum plan of the MIP model. However, the LP model is one to two orders of magnitude faster than the MIP model, therefore it is more suitable for robotic radiotherapy treatment planning.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Natural Science Foundation of China (61601012).

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