# Fractionated Stereotactic Radiotherapy to Resection Cavities Following Brain Metastasis Surgery: Clinical Outcomes and Challenges

## TL;DR

This study examines the effectiveness and risks of radiation therapy after brain tumor surgery, finding it controls tumor regrowth but causes brain injury in a third of cases.

## Contribution

The study provides new clinical insights into the outcomes and challenges of postoperative fractionated stereotactic radiotherapy for brain metastases.

## Key findings

- Radiation therapy controlled tumor regrowth in most patients, with 82.3% local control at one year.
- Radiation-related brain injury occurred in 33.3% of treated areas, often mimicking tumor recurrence.
- Re-irradiation was used in 22.2% of cases, with varying success in managing recurrent disease.

## Abstract

Brain metastases are common, and surgery is often used to remove them when they cause symptoms. After surgery, focused radiation in the operated area can help prevent the tumour from coming back, but it may also damage healthy brain tissue. This study looked at how effective and safe this type of radiation was in 47 patients treated at one centre. The aim was to see how often tumours returned, how long patients lived, and how often patients developed radiation-related brain injury, which can mimic tumour regrowth on scans and cause symptoms. The results showed that radiation controlled tumour regrowth in most patients. Patients lived a median of about 20 months after treatment. However, one-third of treated areas showed signs of radiation-related brain injury, and in many cases, it was difficult to tell this apart from true tumour return, even with advanced scans. These findings highlight the need for better ways to select patients, plan treatment, and interpret follow-up scans. Improving these areas could reduce harm, avoid unnecessary treatments, and improve quality of life for people living longer with cancer.

Purpose: The purpose of this study was to evaluate local control, survival outcomes, radiation necrosis (RN), patterns of failure, and the role of re-irradiation in patients receiving postoperative fractionated stereotactic radiotherapy (SRT) of brain metastasis (BM) resection cavities. Methods: A retrospective, single-centre analysis was conducted on adult patients treated with postoperative RT of BM resection cavities from 2018 to 2024. Each cavity was evaluated individually, including those receiving re-irradiation. MRI-based treatment planning followed institutional SRT standards. Primary endpoints were local control and RN; secondary endpoints included overall survival (OS), failure patterns, and salvage interventions. Kaplan–Meier methods were used for time-to-event analyses. Results: Forty-seven patients underwent postoperative RT of 54 cavities, with 10 patients receiving salvage re-irradiation, yielding 67 treatment plans. The median age was 64 years, and non-small cell lung cancer was the most common primary tumour. Fractionation regimens predominantly consisted of 30 Gy in five to six fractions. Median radiologic follow-up was 17 months. Local recurrence, i.e., new or progressive contrast-enhancing tissue within or directly adjacent to the planning target volume, occurred in 12 cavities (22.2%). One- and two-year local control rates were 82.3% and 70.0%. Re-irradiation was used in eight first local failures—most commonly with 30 Gy in six fractions. Two patients required multiple subsequent re-irradiations, and repeat resection was performed in two additional lesions, emphasizing the complexity of managing recurrent disease. Salvage outcomes varied, with some patients achieving durable control after repeated local therapy. RN developed in 18 cavities (33.3%), including 9 cases (16.7%) of grade ≥ 2 RN. RN occurred a median of 15 months after treatment, with high-grade RN presenting earlier (median of 7 months). Four RN events followed re-irradiation, and over half occurred in patients receiving temporally adjacent systemic therapy. Differentiating RN from recurrence remained difficult: in nearly half of cases evaluated with advanced imaging, diagnosis remained uncertain. Conclusions: Postoperative fractionated SRT provides moderate long-term local control but is associated with a substantial RN burden, particularly in re-irradiated cavities. Improved imaging, standardized contouring, and optimized treatment strategies are needed to reduce toxicity and enhance outcomes.