Room: Exhibit Hall
Purpose: Stereotactic radiosurgery with Gamma Knife has been a standard treatment for brain metastases for decades. Some treatments for multiple metastases, however, can be prohibitively long. New linac-based techniques have provided clinicians with more options to effectively treat multiple brain metastases while sparing intracranial organs at risk. The purpose of this work was develop an algorithm to predict Gamma Knife treatment time as a function of target volume and number of shots.
Methods: A Gamma Knife treatment parameters of single or multiple brain metastases from August 2014 to June 2017 were retrospectively reviewed. Parameters included number of lesions, number of shots, target volumes, treatment time, and prescription/dosimetry data. After normalizing for source decay and prescription dose, treatment time was plotted against target volume for each treated lesion and against number of shots per lesion.
Results: Data was collected for 1604 metastases. Treatment time was loosely correlated with target volume (RÂ²=0.51). Spread in the data suggests that other factors influenced this correlation. Treatment time was more closely related to the number of shots per lesion (RÂ²=0.77), which suggests lesion morphology may play a role. Substantial variability in the data was noted at smaller volumes, which may be due to varying effective output factors for the same number of shots.
Conclusion: A predictive algorithm for Gamma Knife treatment time has been developed. Further refinement of the algorithm will include lesion morphology, effective output factors, and analysis of brain metastasis velocity to extend the predictive algorithm to the diagnostic MRI used at consultation. Ultimately, treatment time prediction could be a facet of a multi-factorial decision support algorithm for radiation therapy of multiple brain metastases.