Reduction of oesophageal toxicity with VMAT dose-sparing radiotherapy in thoracic metastatic spinal cord compression: A feasibility study

Background: Palliative radiotherapy for metastatic spinal cord compression (MSCC) is given to halt disease progression and sustain quality of life for patients with advanced cancer. Radiotherapy can however induce toxicity, contradicting treatment intention. Advanced radiotherapy offers possibility of sparing organs at risk (OARs). The purpose of this dosimetric study is to establish the feasibility and potential benefits of dose sparing of the oesophagus.

Materials and methods: 30 patients receiving radiotherapy of 30 Gy/10# for MSCC were retrospectively included and the oesophagus delineated. Two new dose plans were created for each patient (eso-crop and PTV-crop) with the intention of optimising the oesophageal dose. In the eso-crop plan maintaining full target volume coverage was prioritised, for the PTV-crop plan oesophageal dose was further reduced through cropping the planning target volume (PTV) overlapping oesophageal/PTV-area. Time added for delineation was measured. Plans were compared using Wilcoxon signed rank test with p < 0.05 considered statistically significant. Bivariate associations between dose metrics and patient characteristics were quantified using linear regression models.

Results: Oesophageal delineation took a mean of 8.6 min. There was significant dose reduction for both V7.7 Gy, D2% and mean oesophageal dose, without significant change in CTV coverage. The mean achievable oesophageal dose reduction was 29.1% and 50.4% for the eso-crop and PTV crop plans, respectively. Minor changes in dose distribution to the lungs was observed, with increased mean and V20Gy for the eso-crop plan and decreased V5Gy to the PTV-crop plan.

Conclusion: This study demonstrated the possibility of significant dose sparing of the oesophageal dose using single arc VMAT without impacting on CTV coverage