Evaluation of deformed image-based dose calculations for adaptive radiotherapy of nasopharyngeal carcinoma
- Department of Radiotherapy, Hong Kong Sanatorium & Hospital (Hong Kong)
- Sheffield Hallam University, Sheffield (United Kingdom)
The ultimate goal of adaptive radiotherapy (ART) is to deliver truly customized radiation treatments. Currently, the quality of cone-beam computed tomography (CBCT) images is still inferior to that of conventional CT images in contour delineations and dose calculations for replanning purposes. This retrospective study aims to evaluate the dosimetric accuracy of using deformed conventional CT images for dose calculations, in the hope of inferring the feasibility of ART using planning CT (PCT) images that deformed to up-to-date CBCT images for patients with nasopharyngeal carcinoma (NPC). Thirty consecutive patients with NPC who had undergone 1 replan in their radiotherapy treatments were selected. The pretreatment PCT images were deformed to match the mid-treatment PCT images by deformable image registration. The same volumetric modulated arc therapy plan was then calculated on the deformed PCT images. The resulting dose distributions and dose volume histograms of the tumors and organs at risk (OARs) were compared with the original plan. Five dose levels, D{sub 98%}, D{sub 95%}, D{sub 50%}, D{sub 5%}, and D{sub 2%}, were recorded for 9 NPC targets. Four dose levels, D{sub max}, D{sub 10%}, D{sub 50%}, and D{sub mean}, were recorded for 15 OARs. The greatest percentage difference in observed dose for D{sub 98%}, D{sub 95%}, D{sub 50%}, D{sub 5%}, and D{sub 2%} of the targets were 1.71%, 1.55%, 0.64%, 0.97%, and 1.13%, respectively. The greatest percentage difference in observed dose for D{sub max}, D{sub 10%}, D{sub 50%}, and D{sub mean} of the OARs were -26.51% (left optic nerve), -17.06% (left optic nerve), 56.70% (spinal cord), and 18.97% (spinal cord), respectively. In addition, 29 of 45 (64%) dosimetric end points of the targets showed statistically significant dose differences (p p < 0.05). Dose calculations using deformed PCT images could result in significant dose uncertainties in target volumes and OARs. Larger dose deviations were found in OARs in comparison with target volumes. The spinal cord and optic nerve showed the greatest percentage dose differences and the clinical significance has yet to be determined. Deformable registration error was believed to be the problem causing the dose deviations. Owing to unknown clinical significanceof dose deviation results obtained from this study, a conventional CT scan is still required for replanning in patients with NPC who are experiencing significant anatomical changes during the course of radiation treatment.
- OSTI ID:
- 22824165
- Journal Information:
- Medical Dosimetry, Vol. 42, Issue 4; Other Information: Copyright (c) 2017 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0958-3947
- Country of Publication:
- United States
- Language:
- English
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