MO-FG-CAMPUS-JeP2-03: Clinical Commissioning of MR-Only Prostate Treatment Planning Workflow

Authors


Abstract

Purpose:

To quantify the effect of MR-only treatment planning on dose distributions for prostate cancer for the clinical validation of MR-only workflow.

Methods:

For pre-clinical validation of the MR workflow where five-value stratified synthetic CT (Magnetic Resonance for Calculating Attenuation (MRCAT) algorithm Philips Ingenia 3.0T) are used for dose calculation instead of CT we (1) converted conventional 12-bit CT scans to five-value stratified CT and (2) applied the measured geometric distortions (deformation vector field measured with a dedicated phantom) from the MR scanner to the CT scans of 10 patients to quantify the effect on dose to target and organs-at-risk (OAR) for IMAT prostate plans. For the clinical validation we calculated the gamma index of the 3D dose distribution for MR-only and conventional CT dose calculations for the same patient.

Results:

Five-value perturbed CT and conventional CT dose distributions were equivalent. No difference was observed for DVH-parameters for standard CT compared to five-value CT with MR distortion vector field applied. DVH-parameters were generally higher for five-density CT/CT dose calculations; PTV mean dose was 100.5% compared to 100% for CT-based plans. For rectum the effect of CT HU histogram reduction on the mean dose and D2cc was not significant (rectum Dmean_CT=31.2 Gy, rectum Dmean_5valCT=31.6 Gy). MR-only compared to CT 3D dose distribution 3D gamma analysis (1mm/2%) pass rates were >95% except for one patient (92%) in the 50% and 90% isodose volumes.

Conclusion:

Synthetic CT dose distributions are equivalent to CT for OARs and slightly overestimate the dose to the target. The differences due to the simplified CT composition and deformation are small. 3D gamma analysis (1mm/2%) pass rates for MR-only dose distributions compared to CT are >95% for comparable organ filling at both scans.

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