Room: Exhibit Hall | Forum 2
Purpose: Magnetic resonance imaging (MRI) only radiotherapy is performed without computed tomography (CT) and instead, a synthetic CT (sCT) is used for treatment planning. With the introduction of new procedures for treatment planning, development of quality assurance (QA) tools must be considered. The aim of this study was to develop and validate a clinically feasible QA-procedure for sCT using the cone-beam CT (CBCT), in an MRI-only workflow for prostate cancer patients.
Methods: Three criteria were addressed; 1. Stability in Hounsfield Units (HUs), 2. Deviations in HUs between the CT and CBCT and 3. Validation of the sCT QA procedure. For the initial two criteria, phantom measurements were performed. For the third criterion, sCT, CT and CBCT for ten patients were used. Treatment plans were created based on the sCT (MriPlannerTM). Based on a rigid image registration, the sCT-treatment plan was copied and recalculated on the CT and CBCT. Dose-volume histogram metrics were used to evaluate dosimetric differences between the sCT-plan and the recalculated CT and CBCT-plans. Well defined errors were artificially introduced in the sCT for one patient (Figure 1) to evaluate efficacy of the QA procedure.
Results: The kV-CBCT system was stable in HU over time (SD <40 HU). Difference in HUs between CT and CBCT was very small (<60 HU). The differences between sCT-CT and sCT-CBCT dose distributions were below or equal to 1.0%. The highest mean dose difference for the CT and CBCT dose distribution was 0.6%. No statistically significant difference was found between total mean dose deviations from recalculated CT and CBCT-plans, except for right femoral head. The proposed QA method was found very helpful in identifying the artificially introduced errors.
Conclusion: The results in this study indicate that CBCT can be used as a clinically feasible QA-tool for MRI-only radiotherapy of prostate cancer patients.
Funding Support, Disclosures, and Conflict of Interest: Funded by VINNOVA, The Swedish Innovation Agency