The Feasibility of Synthetic Computed Tomography (sCT) Generated from Magnetic Resonance for Calculating ATenuation (MRCAT) in Prostate Cancer for External Beam Radiotherapy Dose Calculation
Keywords:
MRCAT, MR-only planning, Prostate cancer, Synthetic CTAbstract
Background: Magnetic resonance (MR) image has recently become a trendy use for external beam radiotherapy (EBRT) dose calculation according to the dominance of high soft tissue contrast. However, the main challenge of applying an MR image for dose calculation is the lack of a correlation between the material's density and the computed tomography (CT) number in the MR image, which is mandatory for dose calculation in a commercial treatment planning system. Thus, synthetic CT (sCT) is introduced for EBRT dose calculation.
Objectives: This study aims to examine the feasibility of using MR image for Calculating ATtenuation (MRCAT)-sCT imaging in prostate cancer patients to calculate the external beam dose.
Materials and methods: Ten prospective prostate cancer patients were enrolled in this study. The pCT and MR images were acquired using the pre-imaging protocol. Tumors and organs at risk (OARs) were delineated on planning CT (pCT) and sCT. The Hounsfield unit (HU) of each organ was compared between pCT and sCT. The volumetric modulated arc therapy (VMAT) plan was generated on pCT and calculated based on the Acuros XB (AXB) algorithm using Eclipse, then recalculated on sCT. The similarity between pCT- and sCT-based dose was evaluated using dosimetric data extracted from the dose-volume histogram and 3D gamma analysis.
Results: This study demonstrated a minor difference in HU between sCT and pCT in soft tissue (13.02 15.58 HU) while the discrimination of HU was larger in femur bone (51.59 49.08 HU). The mean HU of soft tissue in sCT was greater than in pCT; contrastingly, the mean HU of bone from sCT was lower than in pCT. The dose distributions calculated from sCT and pCT were similar (>95% gamma passing rate at all criteria (varies from 3%3mm to 1%1mm). Each dosimetric determination showed insignificant differences across all relevant contours.
Conclusion: MRCAT-generated sCT can calculate prostate cancer EBRT doses with a negligible dose difference from pCT. This study promotes prostate EBRT using MR-only workflow.
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