Pulsed-Reduced Dose Rate (PRDR) Radiotherapy for Recurrent Primary Central Nervous System Malignancies: Dosimetric and Clinical Results.

ABSTRACT

PURPOSE: The objective was to describe PRDR outcomes and report EQD2 OAR toxicity thresholds. METHODS: Eighteen patients with recurrent primary CNS tumors treated with PRDR at a single institution between April 2017 and September 2021 were evaluated. The radiotherapy details, cumulative OAR doses, progression-free survival (PFS), overall survival (OS), and toxicities were collected. RESULTS: The median PRDR dose was 45 Gy (range 36-59.4 Gy); the median cumulative EQD2 prescription dose was 102.7 Gy (range 93.8-120.4 Gy). The median cumulative EQD2 D0.03cc for the brain was 111.4 Gy (range 82.4-175.2 Gy). Symptomatic radiation necrosis occurred in three patients, for which the median EQD2 brain D0.03cc was 115.9 Gy (110.4-156.7 Gy). The median PFS and OS after PRDR were 6.3 months (95%CI 0.9-11.6 months) and 8.6 months (95%CI 4.9-12.3 months), respectively. The systematic review identified five peer-reviewed studies with a median cumulative EQD2 prescription dose of 110.3 Gy. At a median follow-up of 8.7 months, the median PFS and OS were 5.7 months (95%CI 2.1-15.4 months) and 6.7 months (95%CI 3.2-14.2 months), respectively. CONCLUSION: PRDR re-irradiation is a relatively safe and feasible treatment for recurrent primary CNS tumors. Despite high cumulative dose to OARs, the risk of high-grade, treatment-related toxicity within the first year of follow-up remains acceptable.