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RAPid simPLE (RAPPLE) Targeted Radiation Treatment Versus Whole Brain Radiation Therapy: A Retrospective Cohort Study
Gurjit S Parmar1,2, Tim Kong1,2, Richard Musoke2
1Faculty of Medicine, Department of Surgery, Division of Radiation Oncology, University of British Columbia, Vancouver, British Columbia, Canada.
Purpose:
Patients with brain metastases whose poor prognosis does not warrant stereotactic radiosurgery (SRS) often receive whole brain radiation therapy (WBRT). We compared the outcomes of patients treated with a novel brain-sparing radiation therapy technique with those of matched patients treated with WBRT.
Methods And Materials:
RAPid simPLE (RAPPLE) uses single-isocenter, coplanar volumetric modulated arc therapy to target brain metastases with 20 Gy in 5 fractions. Patients treated with a first course of RAPPLE between January 1, 2017, and November 5, 2021, were identified in an institutional database. Using age, cancer diagnosis, number of brain metastases, and treatment date, we 1:1-matched patients who received RAPPLE and WBRT. Endpoints were overall survival, calculated using the Kaplan-Meier method, and cumulative incidence of intracranial progression with a competing risk of death. Log-rank, Gray's test, Cox regression, and Fine-Gray analyses were used for comparisons. Ten cases were randomly selected from an institutional database, each representing a unique lesion count from 1 to 10 brain metastases, and treated with 35Gy in 5 fractions using linear accelerator SRS. These were replanned using RAPPLE to compare the mean dose to the brain minus gross tumor volume.
Results:
The study cohort comprised 248 patients. Median survival was 4.5 months for RAPPLE and 4.0 months for WBRT (log-rank P = .4), and 18-month survival was 11% (95% CI, 7-19) for RAPPLE and 12% (95% CI, 8-19) for WBRT. In multivariable analysis, using RAPPLE versus WBRT was not predictive of overall survival (hazard ratio, 0.82; 95% CI, 0.62-1.09; P = .2). The 18-month cumulative incidence of intracranial progression was 50% (95% CI, 41-59) for RAPPLE and 31% (95% CI, 23-40) for WBRT (Gray's test P = .002). After RAPPLE, 12% received more focal RT, and 3% required salvage WBRT. The mean dose to brain minus gross tumor volume was 5.04 Gy for SRS and 4.31 Gy for RAPPLE.
Conclusions:
There was no difference in survival between the matched groups. RAPPLE spares normal brain volume to a degree analogous to that seen with SRS. Among patients treated with RAPPLE, 97% avoided WBRT.
