Session Item

The standard of care after resection of a single brain metastasis is to treat the cavity with stereotactic radiation therapy (SRT) to minimize the risk of recurrence. The 2022 ASTRO/ASCO/SNO guidelines recommend stereotactic radiation in one to five fractions.  SRT is associated with reduced neurocognitive toxicities as compared to whole brain radiation therapy.  However, prospective randomized trials of SRT show higher than expected rates of local recurrence, possibly due to geographic miss.  Adding larger target volumes to reduce misses may increase the risk of radiation necrosis.  Conformal partial brain irradiation (CPBI) over approximately two weeks is an alternate technique that allows a larger margin of healthy tissue to be safely irradiated, potentially decreasing the risk of tumor recurrence.  

Patients receiving post-operative cranial radiotherapy after resection of a brain metastasis from 2015-2022 were eligible for this retrospective single-institution analysis.  All SRT patients were treated using a robotic linear accelerator with a median dose of 24 Gy in 3 fractions.  The median dose for the CPBI group was 33 Gy in 11 fractions.  Information on local control, complications, complete or incomplete resection, radiation treatment modality, cavity location, and years of follow-up was extracted from the charts and a statistical analysis was conducted.

57 patients met the eligibility criteria (SRT, n=32; CPBI, n=25).  Median follow up was 11 months (SRT, 11 months; CPBI, 10 months).  Of the surviving patients, median follow up was 14 months (SRT, 14 months; CPBI, 27.5 months).  The crude rate of local recurrence rate was 21.9% (SRT) vs 0% (CPBI) (P<0.037).  The crude rate of radiation necrosis was 18.8% (SRT) vs 0% (CPBI) (p = 0.064, NS).  The mean cavity volume was 10cc (SRT) vs 37cc (CPBI), (p <0.001).  Distal rates of brain recurrence were 37.5% (SRT) vs 80% (CPBI) (p = 0.003), but this was no longer significant on multivariate analysis.  

In this single institution cohort, stereotactic radiation therapy was statistically associated with a higher risk of both local failure and radiation necrosis as compared to conformal partial brain irradiation.  Despite the cavity being much larger, none of the CPBI patients suffered either local failure or radiation necrosis. Post-operative CPBI may represent a safer and more effective treatment than the current standard of care and should be compared to RS in a prospective randomized trial.