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In Gamma Knife (GK) radiosurgery, dose rate decreases during the life cycle of its radiation source, extending treatment times. Prolonged treatments influence the amount of sublethal radiation injury that is repaired during exposure, and is associated with decreased biologically-equivalent dose (BED). We assessed the impact of treatment times on clinical outcomes following GK of the trigeminal nerve - a rare clinical model to isolate the effects of treatment times. This is a retrospective analysis of 192 patients with facial pain treated across three source exchanges. All patients were treated to 80 Gy with a single isocenter. Treatment time was analyzed in terms of patient anatomy-specific dose rate, as well as BED calculated from individual patient beam-on times. An outcome tool measuring pain in three distinct domains (pain intensity, interference with general and oro-facial activities of daily living), was administered before and after intervention. Multivariate linear regression was performed with dose rate/BED, brainstem dose, sex, age, diagnosis, and prior intervention as predictors. BED was an independent predictor of the degree of improvement in all three dimensions of pain severity. A decrease in dose rate by 1.5 Gy/min corresponded to 31.8% less improvement in the overall severity of pain. Post-radiosurgery incidence of facial numbness was increased for BEDs in the highest quartile. Treatment time is an independent predictor of pain outcomes, suggesting that prescription dose should be customized to ensure iso-effective treatments, while accounting for the possible increase in adverse effects at the highest BEDs. [ABSTRACT FROM AUTHOR]

Introduction: Patients with small cell lung cancer (SCLC) brain metastasis (BM) typically receive whole brain radiotherapy (WBRT) as data regarding upfront radiosurgery (SRS) in this setting are sparse. Methods: Patients receiving SRS for SCLC BM without prior brain radiation were identified at three U.S. institutions. Overall survival (OS), freedom from intracranial progression (FFIP), freedom from WBRT (FFWBRT), and freedom from neurologic death (FFND) were determined from time of SRS. Results: Thirty-three patients were included with a median of 2 BM (IQR 1-6). Median OS and FFIP were 6.7 and 5.8 months, respectively. Median FFIP for patients with =2 versus >2 BM was 7.1 versus 3.6 months, p=0.0303. Eight patients received salvage WBRT and the 6-month FFWBRT and FFND were 87.8%. and 90.1%, respectively. Conclusions: Most SCLC patients with BM who received upfront SRS avoided WBRT and neurologic death, suggesting that SRS may be an option in select patients. [ABSTRACT FROM AUTHOR]