Study on the dosimetric effect of respiratory motion on boron neutron capture therapy for lung cancer

[Background]: Boron Neutron Capture Therapy (BNCT) is an emerging radiotherapy technique. However, respiratory motion has a critical impact on the dose accuracy in BNCT treatment of lung cancer. [Purpose]: This study aims to quantify the dosimetric impact caused by respiratory motion during BNCT treatment of lung cancer. [Methods]: This study employs the Monte Carlo simulation method to develop a dynamic model capturing the spatiotemporal variations of tumors and organs due to respiratory motion in lung cancer treatment, and performs Monte Carlo dose calculations for BNCT. Firstly, using the Multi-function And Generalized Intelligent Code-bench based on Monte Carlo method (MagicMC), this study modeled the adult male phantom provided by Oak Ridge National Laboratory (ORNL). Then, by incorporating high-order cosine functions that describe respiratory motion, this study established a dynamic dose calculation model. Finally, this study employed MagicMC to calculate the dose errors in tumors and organs resulting from respiratory motion in different directions within three-dimensional space. [Results]: The results indicate that during a respiratory cycle, the tumor in all three motion directions exhibits the largest percentage dose difference at the 50% phase. In the left-right direction(LR), it is 0.310%; in the anterior-posterior direction(AP), it is 5.830%; and in the superior-inferior direction(SI), it is -2.852%. The closer healthy tissues are to the irradiation field, the higher the dose rate they receive. The maximum percentage dose difference for the heart in the LR direction is 2.070%, and the maximum percentage dose differences for the right lung in the AP and SI directions are 4.128% and -11.962%, respectively. During BNCT treatment irradiation, organ motion in the AP direction has the greatest impact on tumor dose, resulting in a dose error of 1.644%. For healthy tissues, the dose errors induced by motion in all three directions remain within ±4%. [Conclusions]: The study demonstrates that organ respiratory motion during BNCT treatment for lung cancer affects the doses received by tumors and healthy tissues, the calculation results can provide a reference for precise dose calculation and clinical irradiation dose correction in BNCT treatment of lung cancer.