ESTRO 2023 - Abstract Book

S1797

Digital Posters

ESTRO 2023

Results Average largest linear dimension and volumes of CTVs were 4.9+1.2 cm and 27.4+7.7 cc, respectively. MRL plans were developed with 39 to 41 beams arranged in a pseudo-arc geometry with a total of 120-180 segments. All MRL plans met clinical goals with a median PCI [Interquartile range] of 0.95 [0.94-0.95], median GI of 3.0 [2.9-3.2] and average mean brain dose of 4.0±1.3 Gy. PCIs of MRL plans were better compared to GK (2.6%; 0.95 [0.94-0.95] vs. 0.93 [0.91-0.93]; p<0.05), and not significantly different as compared to CK (2.1%; 0.93 [0.91-0.94]; p>0.05) and VMAT plans (-1.1%; 0.96 [0.94-0.97]; p>0.05). GI values of MRL plans (3.0 [2.9-3.2]) were inferior(p<0.05) to GK(2.5 [2.4-2.6]), CK(2.7 [2.5-2.8]) and VMAT (2.4 [2.3-2.4]) plans. Average volume of normal brain receiving 24Gy with MRL was significantly higher compared to GK and VMAT plans (39.9±12.6 cc vs. 33.4±10.0 cc, 37.5+10.4cc, p<0.05). Median MRL BOT was lower than GK and CK (3.2 [2.9-3.7] min vs. 31.0 [28.2-34.7] min @2.5Gy/min, 26.5 [25.0-29.0] min, p<0.05) and was higher than VMAT (2.6 [2.5-2.7] min, p<0.05). Maximum dose (D0.03cc) received by CNS OARs in MRL plans was not statistically significantly different to GK, CK, and VMAT plans.

Conclusion Cranial SRT plans using MRL IMRT is comparable to established stereotactic delivery modalities while providing daily, high contrast and real-time imaging. Due to the fixed coplanar beam arrangements of MRL plans as compared to non-coplanar beams of other modalities, the GI is statistically significantly inferior, but within acceptable clinical goals.

PO-2024 Effectiveness of Non-coplanar Monoisocenter Multifraction Radiosurgery for Multiple Brain Metastases

F. Colombo 1 , F. Salaroli 2 , I. Renna 2 , G. Ceccon 2 , E. Lattanzi 2 , S. Gianni 2 , C. Grondelli 2 , M. Bergamini 2 , C. Dell'Anna 2 , M. Galaverni 2 , F. Bozzetti 3 , P. Tortoli 4 , M. Maddalo 4 , A. Mazzilli 4 , G. Benecchi 4 , C. Ghetti 4 , N. D'Abbiero 2 , N. Simoni 2 1 Azienda Ospedaliero Universitaria di Parma - Scuola di Specializzazione UNIMORE, Radiation Oncology Unit, Parma, Italy; 2 Azienda Ospedaliero Universitaria di Parma, Radiation Oncology Unit, Parma, Italy; 3 Azienda Ospedaliero Universitaria di Parma, Neuroradiology Unit, Parma, Italy; 4 Azienda Ospedaliero Universitaria di Parma, Medical Physics Unit, Parma, Italy Purpose or Objective Synchronous irradiation of multiple brain metastases (mBMs) by means of Multifraction Stereotactic Radiosurgery (mfSRS) represents a challenge due to complex dose delivery process. Aim of the present study was to evaluate long-term outcomes of mfSRS for mBMs, using an innovative mono-isocenter non-coplanar technique. Materials and Methods Patients with mBMs, good performance status (ECOG ≤ 2), and life expectancy > 3 months, treated with mfSRS from 2019 to 2021 at our Institution, were retrospectively evaluated. For radiotherapy planning, a mfSRS VMAT plan was generated with 5 non-coplanar arcs using HyperArc (Varian Medical System, Palo Alto, US). Primary endpoints were local progression- free survival (LPFS) and intracranial progression-free survival (iPFS). Results A total of 67 patients accounting for 399 brain metastases were analyzed. Non-small cell lung cancer (NSCLC) (55.2%), breast cancer (25.4%) and melanoma (14.9%) were the most frequent histologic types. The median number of treated metastases for mfSRS course was 3 (range 1-16), and the median lesion (GTV) and intracranial cumulative target volume (iPTV) were 0.2 cc (range 0.1-19.8) and 5.1 cc (range 0.3-108.7), respectively. With a median follow-up (FU) time of 10.5 months (range 0.8-36.4), the overall local control (LC) rate was 75.5%, with a 1- and 2-year LPFS of 72.2% and 65.6%, respectively. Median iPFS after first mfSRS course was 6.9 months (95% CI 4.5-11.9), and 30 (44.8%) patients received repeated mfSRS courses (range 2-4) for intracranial progression (IPD). Salvage whole-brain radiotherapy (WBRT) was used in 5 (7.4%) patients. At multivariate analysis, number of treated lesions ( ≥ 5) and histology (melanoma) correlated with LC and iPFS (HR 4.59 [95% CI 1.48-14.24]; p = 0.008 and HR 3.05 [95% CI 1.13-8.23]; p = 0.009) respectively. Radiological signs of radionecrosis or hemorrhage occurred in 1.6% of treated lesions; no other acute or late grade ≥ 3 toxicities were reported. The median overall survival (OS) of the entire cohort was not reached (95% CI 19.6 months-NE), with a 1- and 2-year OS of 76.7% and 60.7%, respectively.