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Adaptive radiotherapy for NSCLC patients: utilizing the principle of energy conservation to evaluate dose mapping operations
- Source :
- Physics in Medicine and Biology. 62:4333-4345
- Publication Year :
- 2017
- Publisher :
- IOP Publishing, 2017.
-
Abstract
- Tumor regression during the course of fractionated radiotherapy confounds the ability to accurately estimate the total dose delivered to tumor targets. Here we present a new criterion to improve the accuracy of image intensity-based dose mapping operations for adaptive radiotherapy for patients with non-small cell lung cancer (NSCLC). Six NSCLC patients were retrospectively investigated in this study. An image intensity-based B-spline registration algorithm was used for deformable image registration (DIR) of weekly CBCT images to a reference image. The resultant displacement vector fields were employed to map the doses calculated on weekly images to the reference image. The concept of energy conservation was introduced as a criterion to evaluate the accuracy of the dose mapping operations. A finite element method (FEM)-based mechanical model was implemented to improve the performance of the B-Spline-based registration algorithm in regions involving tumor regression. For the six patients, deformed tumor volumes changed by 21.2 ± 15.0% and 4.1 ± 3.7% on average for the B-Spline and the FEM-based registrations performed from fraction 1 to fraction 21, respectively. The energy deposited in the gross tumor volume (GTV) was 0.66 Joules (J) per fraction on average. The energy derived from the fractional dose reconstructed by the B-spline and FEM-based DIR algorithms in the deformed GTV's was 0.51 J and 0.64 J, respectively. Based on landmark comparisons for the 6 patients, mean error for the FEM-based DIR algorithm was 2.5 ± 1.9 mm. The cross-correlation coefficient between the landmark-measured displacement error and the loss of radiation energy was -0.16 for the FEM-based algorithm. To avoid uncertainties in measuring distorted landmarks, the B-Spline-based registrations were compared to the FEM registrations, and their displacement differences equal 4.2 ± 4.7 mm on average. The displacement differences were correlated to their relative loss of radiation energy with a cross-correlation coefficient equal to 0.68. Based on the principle of energy conservation, the FEM-based mechanical model has a better performance than the B-Spline-based DIR algorithm. It is recommended that the principle of energy conservation be incorporated into a comprehensive QA protocol for adaptive radiotherapy.
- Subjects :
- Cone beam computed tomography
Lung Neoplasms
Mean squared error
Finite Element Analysis
Image registration
Image processing
Radiation Dosage
Article
Displacement (vector)
030218 nuclear medicine & medical imaging
03 medical and health sciences
0302 clinical medicine
Carcinoma, Non-Small-Cell Lung
Image Processing, Computer-Assisted
Humans
Radiology, Nuclear Medicine and imaging
Retrospective Studies
Mathematics
Radiological and Ultrasound Technology
business.industry
Radiotherapy Planning, Computer-Assisted
Uncertainty
Radiotherapy Dosage
Cone-Beam Computed Tomography
Finite element method
Tumor Burden
Intensity (physics)
030220 oncology & carcinogenesis
Nuclear medicine
business
Algorithm
Algorithms
Energy (signal processing)
Subjects
Details
- ISSN :
- 13616560 and 00319155
- Volume :
- 62
- Database :
- OpenAIRE
- Journal :
- Physics in Medicine and Biology
- Accession number :
- edsair.doi.dedup.....693c753574e6316096f7499ac319b5a0