A dosimetric study on flattening filter free beam impact of multi-criterial optimization in hepatocellular carcinoma stereotactic body radiotherapy using Monte Carlo algorithm

Background: Studying the influence of multi-criterial optimization (MCO) on dosimetry in stereotactic body radiotherapy (SBRT) for hepatocellular carcinoma patients, utilizing Flattening Filter Free (FFF) photon energies through Monte Carlo (MC) algorithm. Materials and Methods: Hepatocellular carcinoma SBRT plans were generated at a prescribed dose of 35 Gy in 5 fractions, with Standard Direct Machine Optimization (SDMO) and multi-criteria optimization for two energies of 6 and 10 MV FFF using MC algorithm in Monaco Planning Station. These plans were compared within and across the groups based on various plan quality metrics such as target coverage, Conformity Index (CI), Homogeneity Index (HI), Monitor Unit (MU) and Organ at Risk (OAR) dose. Results: Using MCO technique, plans with comparable target outcome measures and slightly improved OAR sparing are produced, with the consequence of increased MU for both energies (p=0.030 & p=0.002 respectively). In the case of 6 MV FFF plans using MCO, the degree of CI within the target showed a statistical significance (p=0.013) and provided plans with better OAR sparing and for 10 MV FFF energy showed no observable statistical significance for any target outcome measures such as CI, HI or V95%. Conclusion: With efficient treatment planning time, MCO is a valuable tool for providing optimal SBRT plans, however it results in longer treatment times due to increase in MU. Out of the SBRT plans generated the MCO plan using 6 MV FFF energy shows little superiority than others, with a better balance in target coverage and OAR sparing.