Purpose: High-risk brain lesions are large, located in eloquent brain region, and/or with aggressive histology. Online CBCT imaging guidance has primarily focused on daily patient setup without detailed analysis of dose accumulation effects along the full course of treatment. In this study, we aimed to develop a time series analysis approach by integrating temporal analysis with imaging guidance prior to the beam delivery for each treatment fraction in hypofractionated Gamma Knife radiosurgery of high-risk brain lesions.
Methods: As a proof-of-concept, eight lesions (mean volume=17.4±15.8 mL) from five patients treated to 30Gy in five fractions with online CBCT-guided hypofractionated SRS were retrospectively analyzed. CBCT scans were acquired at each fraction prior to delivery. 3D dose distributions were projected onto daily CBCT and compared to the planned treatment. The accumulated and biological equivalent dose over previously delivered treatment fractions were also computed to form a time series across all fractions. Comparison of 3D dose distribution against the original dose distributions for each treatment fraction was analyzed.
Results: Examining the full treatment, a mean target dose deviation of -0.21Gy (-0.10Gy, -0.35Gy) was obtained averaging all cases/time points and represented an almost negligible deviation of <1.5% in target dosing. Further, a mean target EQD2 deviation of -0.42Gy (-0.2Gy, -0.7Gy) was also obtained, representing <3% deviation from the initial prescription. The largest dose deviation occurred with two lesions within 3cm. No systematic trend in the accumulated dose patterns was detected.
Conclusion: Integrating temporal dose accumulation time series analysis has been demonstrated for the first time to be best of our knowledge. Initial analysis on a small number of cases pointed to precision and robustness of CBCT image-guided hypofractionated SRS of high-risk intracranial targets. On-going analysis over a large number of cases treated across different modalities will lend more support to encouraging results already seen.