ESTRO 2024 - Abstract Book

S2005

Clinical - Mixed sites, palliation

ESTRO 2024

This investigator-initiated multi-center phase II trial included patients across six centers in Denmark and Norway. Referral to study treatment was decided by the treating oncologist at outpatient clinics.

Eligible patients had genuine or induced OMD from any solid cancer with up to five metastases all accessible for ablation and at least one spine or non-spine bony metastasis < 5 cm. Exclusion criteria were mechanical instability or epidural invasion. Doses of 30 or 37.5 Gy in three fractions, were inhomogeneously prescribed to the gross tumor volume (D99% > 95%), with 80% and 67% isodose coverage of the clinical- and planning target volumes (CTV/PTV) respectively. Risk adaptation meant that dose constraints to certain predefined organs at risk were prioritized over target dose coverage. Conebeam-guided intensity-modulated radiotherapy or volumetric modulated arc therapy techniques were applied. GTV on axial CT images, guided by MRI for the spinal targets. A 5 mm isotropic margin was added to generate the CTV (shaped to the bone outline). For spine targets, it was recommended to follow the Cox et al. 2012 delineation guideline to define the CTV. The isotropic PTV margin was 2 mm for spine targets and followed institutional practice for non-spine targets. The primary endpoint was 1-year local control rate. Secondary endpoints include toxicity, change in pain score, quality of life, and survival measures. Adverse events were categorized as treatment-related if assessed as related or possibly related to SABR. Pain intensity and response were assessed as the International Consensus Pain Response Endpoints based on a numeric pain rating scale (NPRS) from 0 to 10 and analgetic intake. Pain flare was defined as pain progression at the 2-week follow-up which was resolved at the 12-week follow-up. Assessment of lesion-by-lesion response and fractures was centrally performed by a consultant radiologist on axial CT images. Local progression was recorded if tumor growth was reported within or bordering the PTV (MD Anderson criteria) [1]. Fractures were recorded if within or bordering the PTV. Fracture-, LC-, and survival rates were estimated by the Kaplan-Meier method and reported with 95% confidence intervals. Follow-up was estimated by the reverse Kaplan-Meier method censoring patients at death from any cause. Subgroup analyses were assessed by the Log-Rank test. Statistical analyses were performed in R Statistics version 4.01 (R-CRAN project). Patients were followed with CT scans, toxicity (Common Terminology Criteria for Adverse Events v. 5.0) registration, pain response, and analgetic consumption at 2-, 12-, 24-, 36-, and 52 weeks after SABR

Results:

From December 2019 until January 2022, 68 patients with 79 bone metastases (31 spine, 48 non-spine lesions) were included from six centers in Denmark and Norway. Baseline characteristics are presented in Table 1. The preferred prescribed dose was 37.5 Gy (78% of targets).