ESTRO 2024 - Abstract Book

S908

Clinical - CNS

ESTRO 2024

Radionecrosis in stereotactic radiotherapy for resected brain metastases: role of dosimetric indeces

Nicola Dinapoli 1 , Elisabetta Lepre 1 , Francesco Beghella Bartoli 1 , Lucrezia Bernabucci 1 , Ciro Mazzarella 1 , Rosellina Russo 2 , Chiara Schiarelli 2 , Antonella Martino 1 , Alessandro Perna 2 , Serena Bracci 1 , Silvia Mariani 1 , Stefania Manfrida 1 , Mariangela Massaccesi 1 , Roberta Bertolini 1 , Fabio Marazzi 1 , Alessandro Olivi 3 , Vincenzo Valentini 1 , Luca Tagliaferri 1 , Maria Antonietta Gambacorta 1 , Simona Gaudino 2 , Silvia Chiesa 1 1 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Radioterapia, Roma, Italy. 2 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Neuroradiologia Diagnostica, Roma, Italy. 3 Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Neurochirurgia, Roma, Italy

Purpose/Objective:

Brain metastases (BMs) are the most common intracranial tumours in adults, occurring in 20-40% of cancer patients. Among the existing therapeutic modalities, the primary two are surgery and radiotherapy. Historically, post-surgery, whole brain radiotherapy (WBRT) was employed as an adjuvant local treatment. However, due to its association with neurocognitive impairment, its use has progressively declined, giving way to postoperative stereotactic radiotherapy (pSRT). One of the most significant and concerning side effects of brain SRT is undoubtedly radionecrosis (RN). While a lower incidence of RN has been reported with hypofractionated SRT, it remains a concern. This is primarily because, with the rising survival rates in cancer patients, the requirement for retreatments has become more frequent. The objective of this retrospective study is to identify relevant dosimetric parameters associated with RN risk that can guide the radiation oncologist's clinical practice.

Material/Methods:

Adult patients treated with pSRT between January 2015 and December 2022 were included in the study. Responses were assessed according to the Response Assessment in Neuro-Oncology Brain Metastases (RANO-BM) [1]. RN was studied by analyzing MRIs performed by a team of neuroradiologists with at least 10 years of experience. The clinical target volume (CTV) was set on the surgical cavity with a margin of 1 mm. The planning target volume (PTV) was defined as the CTV plus an additional margin of 2 mm. Treatments were fractionated into 3, 5 (pSRT) or 10 fractions (WBRT in case of retreatments). Patients underwent fractionated treatments with variable dose normalization (median dose or 80% isodose). Cumulative dose-volume histograms were collected for each patient. In case of multiple treatments or retreatments, the sum of DVHs was considered. All histograms were converted to an equivalent dose using an α/β ratio of 2 Gy (EQD2). The impacts of Vdose and Dvolume on RN risk were analyzed. DVHs of the "brain minus PTV" (brain-PTV) structure were analyzed by dividing the entire dose range into bins of 1 Gy and dividing the absolute volume of brain-PTV into bins of 1 cc. Vdoses and Dvolumes were calculated for each patient, and their sets of values were tested repeatedly for each bin with the Mann-Whitney test according to the presence or absence of RN.

Results:

A total of 59 patients with 67 cavities were included in the analysis. The median age was 59 years (ranging from 33 88). Forty of the cavities were treated with 3 fractions of pSRT, and the remaining with 5 fractions. When a whole brain retreatment was performed, it was administered in 10 fractions. Radionecrosis was observed in ten surgical cavities, accounting for 14.9% of the total. Thirty-four patients underwent brain retreatment: of these, 3 developed