Accuracy of dose calculation based on artefact corrected Cone Beam CT images of lung cancer patients

Abstract

Background and purpose: Accurate Cone Beam CT (CBCT) based dose calculations are hindered by limited CBCT image quality. Using retrospective artefact corrections, this paper investigated the accuracy of dose calculations performed directly on CBCT images of lung cancer patients. Materials and methods: Dose calculations were made directly on clinical and artefact corrected CBCT images of 21 lung cancer patients with a re-simulation CT (rCT) image acquired during radiotherapy. The original treatment plan was copied to the rCT and CBCT images and dose was recalculated. Dose comparisons were made using gamma analysis and dose statistics. Gamma comparisons were made using 2%/2 mm and 1%/1 mm criteria, and pass rates of the clinical and improved CBCT images were calculated using the rCT based dose as reference. Results: Dose distributions calculated on the artefact corrected CBCT images had a median 2%/2 mm gamma pass rate of 99.4% when compared to the reference rCT. Doses calculated on the clinical CBCT images had a median 2%/2 mm gamma pass rate of 93.1%. Wilcoxon signed rank test showed the pass rates in the entire CBCT field of view different at p<0.001. Clinical CBCT image based dose calculations overestimated the dose, while the improved CBCT doses were in closer agreement with the rCT doses. Conclusions: Comprehensive artefact correction of CBCT images allowed highly accurate dose calculations to be performed directly on CBCT images of lung cancer patients, following the standard CT-based workflow in a treatment planning system. Keywords: Image guided radiotherapy, Adaptive radiotherapy, Dose of the day, Cone Beam CT