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Technical Note: Efficient and accurate MRI-only based treatment planning of the prostate using bulk density assignment through atlas-based segmentation

Lookup NU author(s): Dr Hazel McCallum, JJ Wyatt, Neil Richmond, Chris Walker


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© 2020 American Association of Physicists in Medicine. Purpose: This study investigates the dosimetric accuracy as well as the robustness of a bulk density assignment approach to magnetic resonance imaging (MRI)-only based treatment planning of the prostate, with bulk density regions automatically identified using atlas-based segmentation (ABS). Methods: Twenty prostate radiotherapy patients received planning computed tomography (CT) and MRI scans and were treated with volumetric modulated arc therapy (VMAT). Two bulk densities were set, one for bone and one for soft tissue. The bone contours were created by using ABS followed by manual modification if considered necessary. A range of soft tissue and bone density pairs, between 0.95 and 1.03 g/cm3 with increments of 0.01 for soft tissue, and between 1.15 and 1.65 g/cm3 with increments of 0.05 for bone, were evaluated. Using the density pair giving the lowest dose difference compared to the CT-based dose, dose differences were calculated using both the manually modified bone contours and the bone contours from ABS. Contour overlap measurements between the ABS contours and the manually modified contours were calculated. Results: The dose comparison shows a very good agreement with the CT when using 0.98 g/cm3 for soft tissue and 1.20 g/cm3 for bone, with a dose difference less than 1 % in average dose in all regions of interest. The mean Dice similarity coefficient for bone was 0.94 and the Mean Distance to Agreement was <1 mm in most cases. Conclusions: Using bulk density assignment on MR images with suitable densities for bone and soft tissue results in clinically acceptable dose differences compared to dose calculated on the CT, for both atlas-based and manual bone contours. This demonstrates that an integrated MRI-only pathway utilizing a bulk density assignment for two tissue types is a feasible and robust approach for patients with prostate cancer treated with VMAT.

Publication metadata

Author(s): McCallum HM, Andersson S, Wyatt JJ, Richmond N, Walker CP, Svensson S

Publication type: Article

Publication status: Published

Journal: Medical Physics

Year: 2020

Volume: 47

Issue: 10

Pages: 4758-4762

Print publication date: 01/10/2020

Online publication date: 18/07/2020

Acceptance date: 02/07/2020

ISSN (print): 0094-2405

ISSN (electronic): 2473-4209

Publisher: John Wiley and Sons Ltd


DOI: 10.1002/mp.14406

PubMed id: 32682337


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