ESTRO 2023 - Abstract Book

S343

Sunday 14 May 2023

ESTRO 2023

For brain metastases (BM) requiring surgery, pre-operative stereotactic radiosurgery (SRS) may have advantages compared to post-operative cavity SRS. The aim of this study was to prospectively assess outcomes for a cohort of patients receiving pre-operative SRS for BM treated at a single centre. Materials and Methods Participants required a confirmed diagnosis of metastatic cancer prior to enrolment and had at least one BM for resection. Pre-operative SRS treatment was agreed to in a multidisciplinary forum and intended to be given no more than 2 days prior to surgery. SRS was delivered in a single fraction on the Leksell Gamma Knife ICON platform, with dose adjusted according to BM volume ( ≤ 8.2cc received 18-20Gy, 8.2-14.1cc received 16-18Gy, ≥ 14.1-22.5cc received 14-16Gy and ≥ 22.5cc received 14Gy). Post-operative T1-weighted gadolinium-enhanced MRI was performed within 48 hours of surgery to assess extent of resection, followed by standard clinical and radiological MRI surveillance imaging every 2-3 months. Results 21 participants (a total of 22 BM treated on protocol) were recruited between January 2020 and August 2022. The most common primary histologies were non-small cell lung cancer (36%), melanoma (36%) and breast cancer (9%). The median BM volume prior to surgery was 6.8 cc (range 3-40); 10 BM were ≥ 10 cc volume and 5 BM were >20 cc. All participants received protocol treatment as planned. The median interval between pre-operative SRS and surgery was 1 day (range 0- 15). Post-operative MRI confirmed gross total resection in all cases. The median duration of inpatient stay after surgery was 3 days (range 1-40). 15 patients restarted and/or commenced systemic therapy, with a median interval of 22 days from SRS (range 6-99). One local recurrence occurred, and was within 3 months of initial surgery. No cases of leptomeningeal recurrence, wound complications or radionecrosis were observed. The most common acute toxicities experienced within 3 months of SRS were headaches (9%) and fatigue (14%). Overall survival from date of pre-operative SRS was 67% at 1 year (95% CI: 48–93%) and median follow up was 14.7 months (range 2-29). Conclusion SRS delivered before surgery for BM confers a high rate of local control and no apparent increase in the risk of acute wound complications. Compared to post-operative cavity SRS, pre-operative SRS may also help reduce the risk of leptomeningeal disease and radionecrosis, whilst facilitating prompt initiation of systemic therapy after surgery. OC-0442 Low incidence of RT-induced MRI changes and stable QoL following proton irradiation C. Luetgendorf-Caucig 1 , M. Pelak 1 , B. Flechl 1 , P. Fossati 1 , M. Stock 2 , C. Reschl 1 , P. Georg 3 , E. Hug 1 1 MedAustron, Radiation Oncology, Wiener Neustadt, Austria; 2 MedAustron, Medical Physics, Wiener Neustadt, Austria; 3 MedAuston , Radiation Oncology, Wiener Neustadt, Austria Purpose or Objective Irradiation of intracranial tumors may induce endothelial damage in the surrounding normal brain tissues, resulting in an increase of capillary permeability. These changes can be depicted on MRI as a new contrast non-tumoral contrast enhancement. Radiation-induced contrast enhancement (RICE) occur after photon as well as proton therapy (PT). This study evaluated the incidence of RICE after PT and their impact on Quality of Life (QoL). Materials and Methods 421 patients treated between 01/2017 and 06/2021 were included. All patients participated in a prospective registry study. Follow-up evaluations including MRIs were at 3,6,12 months after treatment completion and annually thereafter. QoL parameters were assessed by EORTC-C30 questionnaires. All follow-up MRIs underwent an independent second look evaluation by a radiation oncologist and diagnostic radiologist. Images were reviewed with focus on response and on onset of new intra-parenchymal contrast enhancement outside GTV but inside the irradiated volume. Results 49% (n=206) patients received therapy for intracranial non-CNS tumors (meningioma, pituitary adenoma, and other), 27% (n=113) for head and neck cancer with skull base involvement, 15% (n=61) for primary CNS tumors and 10% (n=41) for skull base tumor. Median follow-up was 24 months (range 6-54), 352 (86%) patients had proton therapy as primary treatment, 59 (14%) had salvage treatment with proton re-irradiation (ReRT). Median prescribed dose was 58.5 GyRBE (range 40-78 GyRBE), median D1% of brain tissue was 54.3 GyRBE (range 30-76 GyRBE). Local control and overall survival were 91% and 95% at 2 years. The cumulative RIBL incidence was 15% (n=63), with significantly lower occurrence in the primary RT group vs. the ReRT group (13% vs. 27%; p<0.001). According to Grade, the distribution was 10.5% (n=44) Grade I (asymptomatic, MRT finding only), Grade II RIBL, 13 (3%) (moderate symptoms) (grade 2) and 1% (n=6) developed Grade 3 toxicity. Actuarial 2-year RIBL incidence was 18% for the all Grades and the entire, 16% following primary radiation and 34% after ReRT. All RICE developed outside the residual tumor, but inside the Planning Target Volume (PTV), median D1% was 60GyRBE (range 46- 122GyRBE), median time to development was 11.8 months (range 2.7-37 months) in the total cohort, for primary RT 14.2mo (4mo -37mo) and 6mo (3mo -19mo) following ReRT. At the time of analysis 26 of the 63 RICE had resolved (41.3%). Following proton radiation, general QoL was not compromised. In a matched-pair analysis of 54/50 patients with/without RICE, functioning scales and symptoms’ scales remained stable. Only at the 12-month patients with RICE had stable global health score, whereas patients without RICE improved (p<0.05). At 24 months the score for RIBL patients improved without difference between the groups. Conclusion Overall incidence of RICE after proton radiotherapy is very low - even for skull base tumors requiring high total doses and it had no significant negative impact on long term QoL.

Proffered Papers: CT reconstruction and synthetic CTs