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Assessment of Beam and Delivery Quality for Interchanging Intensity-Modulated Treatment Plans with Two 6MV Beam-Matched Linear Accelerators

C Fang1,2, Y Song2, W Xu1, L Cao2, Y Tao1, Z Wang2, L Zhu2, B Qu1, S Xu1,2,3*, (1) Department of Radiation Oncology, the First Medicine Center of PLA General Hospital, Beijing, 100853, China(2)Department of Radiation Oncology, Hebei Yizhou Cancer Hospital, Zhuozhou, 072750, China(3) Beijing Advanced Innovation Center for Big Data-Based Precision Medicine, Beihang University, Beijing 100083, China

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
The purpose of this study is to compare the beam characteristics and explore the feasibility of interchanging intensity-modulated treatment plans without replanning with two beam-matched linear accelerators (Linacs).
Methods:
The beam data of 6MV X-ray with two beam-matched Linacs (Elekta VersaHD and Synergy with Agility head) were measured and analyzed using IBA Blue Phantom. 12 nasopharyngeal carcinoma, lung and prostate plans, respectively, were generated using fixed-beam IMRT and VMAT with the same beam model. Doses were measured using A1SL ion chamber and ArcCheck. The measurements were compared with the calculated doses by absolute dose gamma comparison using 3%/2mm and 3%/3mm criteria. Correlation between the differences in passing rates between beam-matched Linacs was evaluated using the Pearson coefficient.
Results:
For the beam characteristics, the difference in PDDs, beam profiles and output factors of two beam-matched Linacs were all within ±1%. The deviations of point doses in two Linacs were within ±2% with a Pearson's correlation coefficient of 0.725 (p<0.0001) and the differences had no statistical significance. For all 36 cases for three diseases, the passing rates of measured doses on two Linacs were well higher than 95% when using 2mm/3% and 3mm/3% gamma criterias with 10% threshold. A strong correlation was observed between the passing rates of two Linacs with Pearson's correlation coefficients of 0.674 (p<0.0001)and 0.745 (p<0.0001).
Conclusion:
The beam parameters between two Linacs showed a good matching. And the minimal differences and strong correlations in point doses and passing rates proved the feasibility of swapping IMRT and VMAT plans between the beam-matched Linacs.

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Funding Support, Disclosures, and Conflict of Interest: National Key R&D Program of China, 2017YFC0112100

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