Purpose: To analyze the dosimetric variation of treatment plans utilizing interfraction dose tracking from daily CBCT images. Considering organ shifting, tumor shrinkage, and weight-loss, the feasibility of effectively tracking dose to normal tissues and tumor volumes can be determined.
Methods: Daily CBCT images were performed on twenty-one patients undergoing head and neck radiation therapy with 6 MV or 10 MV energies. All images were imported into Raysearch planning software and registered to the original treatment planning CT using first, a rigid registration, then a deformable registration algorithm. Once a patient’s treatment had been completed, the deformed dose for each fraction was computed according to the corresponding deformed CBCT. Finally, the accumulated deformed dose was determined in reference to the target volumes and the organs at risk.
Results: The percent difference between the planned and accumulated delivered organ doses exhibited irregular results. The analysis, thus far, was based on six patients and the deviations in terms of their organs at risk (OARs) and target volumes (GTVs and PTVs). Most of the accumulated delivered dose fell within +/- 5% of the planned dose. However, broken down into each fraction, the tissue volume change, trended daily, proved results that varied more significantly with increasing time. These dosimetric differences have been associated with changes in volume due to loss of weight but more data are needed to establish trends and thresholds.
Conclusion: Effectively tracking the dose to OARs and PTVs throughout a treatment will allow development of adaptive re-planning of patient plans. With the current data, it is recommended to track plans of patients who could potentially exhibit the greatest biological differences throughout their treatment course. The feasibility of this study would imply that adaptive conformation, based on an automated daily or weekly CBCT analysis, would benefit the overall dosimetric outcome of radiation therapy.
Cone-beam CT, Dose, Adaptive Sampling
IM/TH- Image Analysis (Single Modality or Multi-Modality): Computer-aided decision support systems (detection, diagnosis, risk prediction, staging, treatment response assessment/monitoring, prognosis prediction)