Development of Planning Template for Online Adaptive Radiotherapy for Ultra-Central Lung Hypo-Fractionated Treatment
Abstract
Purpose
We aim to develop and evaluate a template for Ethos v1.1 online adaptive planning using the intelligent optimization engine (IOE) for hypo-fractionated ultra-central lung IMRT (60Gy in 8 fractions). The template includes a dose-boosting planning volume to help deliver a higher dose to the Internal Target Volume (ITV) and to control the location of hot spots. Here, we compare dosimetric results for planning with and without this auxiliary volume.
Methods
The ITV_120 planning structure, i.e., the part of the ITV receiving 120% of the prescription dose, was created by cropping out adjacent OARs, including the proximal bronchial tree, trachea, esophagus, great vessels, spinal cord, and brachial plexus, with a 2-mm margin. Template-generated plans, with and without the ITV_120 structure included in the optimization process, were compared using standard dose metrics.
Results
With the ITV_120 optimization structure in place, the adaptive plan delivered ITV D98% of 7.78±0.38Gy (7 fractions), which is 3.7% higher than the prescription dose of 7.5Gy/fx, whereas without it, it was 7.23Gy (1 fraction). In addition, D99% of the PTV_eval (PTV excluding OARs) for the adaptive plan without the ITV_120 in the template was 6.57Gy, and with the ITV_120 present it was 6.53±0.15Gy on average. The dose to the adjacent OARs: proximal bronchial tree and great vessels of the heart was 7.32Gy and 6.77Gy, respectively, for the template without the ITV_120, and 7.16±0.13Gy and 6.70±0.10Gy, respectively, for the template with the ITV_120.
Conclusion
Our preliminary results show that incorporating the optimization structure ITV_120 into the 8fx Lung hypo-fractionated adaptive treatment template achieved intentional dose escalation to the ITV, focused hotspots in areas free of the adjacent OAR, and facilitated meeting the OAR tolerances.