SU‐E‐T‐432: Dosimetric Computation of Cyberknife SBRT Plans for Treatment of Kidney and Adrenal Gland

Purpose: It is well‐accepted that Monte Carlo algorithm (MCA) methods are superior to Ray‐Tracing algorithm (RTA), i.e., effective path length (EPL), methods for computing radiation dose, especially for structures with heterogeneous tissue compositions. In this study, the differences of dose distribution in target volumes (kidneys and adrenal glands) and adjacent organs at risk (OARs) were evaluated while the treatment plans were computed using MCA and RTA for Cyberknife™ stereotactic body radiotherapy (SBRT). Methods: A total of 14 renal tumor (10 kidney and 4 adrenal gland) patients who had prescriptions in the range of 24Gy–48Gy (mean=42Gy) were selected. Treatment plans were computed using RTA and MCA in Cyberknife MultiPlan™ (version‐3.5.2). First, dose was calculated using RTA and then was recomputed using MCA, keeping total MU the same. Liver, heart, stomach, spleen, bowel, and contralateral kidney were considered as OARs. Dosimetric parameters considered for the target and OARs were minimum dose, mean dose, and maximum point dose. Additionally, dose delivered to 95% and 5% of the target volumes were evaluated. Dose computed with two algorithms were compared and statistically analyzed using two‐tailed t‐tests. Results: This study revealed that differences (average) in mean dose (0.79Gy), maximum dose (2.02Gy), 95% (0.76Gy) and 5% (0.83Gy) of target coverage dose were not statistically significant (p‐value>0.05). Differences in minimum dose (average=0.04–3.75Gy) to OARs exhibited significance (p‐value 0.05). Conclusion: Although Monte‐Carlo is more accurate compared to Ray‐Tracing for dosimetric computation, especially tumors in heterogeneous tissue composition, dose computation and delivery using MCA are quite involved due to additional computational time and associated patient‐specific quality assurance. This study indicated that both RTA and MCA are almost equally effective as dosimetric computation methods for renal tumors, and RTA can be used without compromising dosimetric accuracy.