RAPid simPLE (RAPPLE) targeted radiation treatment versus whole brain radiotherapy: a retrospective cohort study of matched patients with brain metastases and poor prognosis

Purpose: Patients with brain metastases whose poor prognosis does not warrant stereotactic radiosurgery often receive whole-brain radiotherapy (WBRT).We compared the outcomes of patients treated with a novel brain-sparing radiotherapy technique with those of matched patients treated with WBRT.Materials/Methods: 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 that received RAPPLE and WBRT.Endpoints were overall survival (OS), 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 treated with 35 Gy in 5 fractions linear accelerator stereotactic radiosurgery (SRS), selected to have one through 10 brain metastases, were replanned using RAPPLE to compare the mean dose to Brain minus gross tumor volume (GTV). Results:The study cohort comprised 248 patients.Median survival was 4.5 months for RAPPLE and 4.0 months for WBRT (Log-rank p = 0.4), and 18-month survival was 11% (95% CI: 7-19) for RAPPLE and 12% (95% CI: 8-19) for WBRT.On multivariable analysis, using RAPPLE versus WBRT was not predictive of OS (HR = 0.82, 95%CI: 0.62-1.09,p = 0.2).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 = 0.002).After RAPPLE, 12% received more focal RT, and 3% required salvage WBRT.The mean dose to Brain-GTV 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 brain as well as linear accelerator SRS for patients with 1-10 brain metastases.Among patients treated with RAPPLE, 97% avoided WBRT.