Dosimetric verification of stereotactic body radiation therapy for lung cancer treatment plans using flattening filter-free beams

Aims: This study aimed to analyze the dose distribution using different dosimetric tools in conducting pretreatment quality assurance for lung cancer stereotactic body radiation therapy (SBRT) plans with flattening filter free (FFF) beams. Methods: Nine patients with lung cancer treated via SBRT were randomly selected, and their treatment plans were generated using the Eclipse treatment planning system (TPS) with FFF beams. For each patient, the same plan was applied to the Delta4 phantom and MatriXX by the TPS, which calculated the dose distribution. The Delta4 and MatriXX phantoms were then used to measure the actual dose distribution at the linear accelerator, and these measured doses were compared to with the calculated doses. Gamma analysis was employed in verifying the correspondence between the dose distributions. The absolute point doses were measured by a 0.016 mL Microchamber with the RW3 phantom and Thorax phantom. Results: The absolute point doses measured by the 0.016 mL Microchamber were within ±3% of the calculated results for the central point of the RW3 and Thorax phantoms. The Delta4 and MatriXX dose distributions agreed well with the measured and calculated doses, over 98%, based on the 3% maximum dose and 3 mm gamma criteria. Conclusions: Both measured and calculated doses for the Delta4 and MatriXX phantoms agreed well for each patient with lung cancer. The absolute point dose measurements using the 0.016 mL Microchamber exhibited excellent agreement with the TPS calculated between the RW3 and Thorax phantoms.