Top Line: In 2021 MDTB stands for mets-directed therapy board since that seems to be the universal answer to oligometastatic disease, but there is surprisingly little granular data on how to do that.
The Study: For instance, should treatments to different sites be delivered step-wise or all together? What if there is bridging between two adjacent mets? As the number of treated mets increases, so does the cumulative radiation dose to organs at risk. Enter the phase 1 NRG-BR001 study to prospectively address some of these issues. This initial report includes 35 evaluable enrollees with breast, prostate, or non–small cell lung cancer metastatic to 3-4 sites or 2 adjacent sites (≤5 cm apart) amenable to stereotactic body radiation (SBRT)—with that last part meaning all targets could receive standard prescription doses while nearby organs could meet all constraints. Prescriptions were hefty at 50Gy/5 for central lung or cervical / mediastinal nodal mets, 45Gy/3 for peripheral lung or liver or other abdominal / pelvic mets, and 30Gy/3 to spine / paraspinal or other bone mets. All targets, other than spine, had a 5-7 mm planning margin. All targets near diaphragm underwent 4D CT-planning with some form of motion management (e.g., fiducial tracking, breathhold or gating) for >1 cm movement. Physicians could choose to treat sites concurrently or sequentially, and the median time to complete SBRT was 8 days (range: 3-27). No dose-limiting toxicities occurred within the pre-specified 6-month window, but eight grade 3 toxicities occurred as far as 18 months out. A couple of final notes here: half of these were lung toxicities. One was pneumonitis in a woman with three thoracic targets, highlighting the need to evaluate total lung dose on a sum plan, and two others were bronchial stenosis and bronchial fistula after the hilum received full prescription dose for hilar nodal targets.
TBL: When strict protocols are followed, ablative radiation for up to 4 mets concurrently is safe, but as always maximum caution is advised for central lung structures. | Chmura, JAMA Oncol 2021