Evaluation of Abdomen IMPT Treatments Using Deformed Treatment Planning CT Based On Pre-Treatment Cone-Beam CT
Presentations
MO-H345-IePD-F4-2 (Monday, 7/11/2022) 3:45 PM - 4:15 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 4
Purpose: To evaluate intensity-modulated proton therapy (IMPT) treatments of abdomen patients using treatment planning CT (TPCT) deformed onto pre-treatment cone-beam CT (CBCT).
Methods: We retrospectively evaluated plans for 10 patients previously treated with IMPT-based to abdominal targets. To cover the larger span of the treatment course, we evaluated a total of five CBCTs of every other fraction. TPCT and contours for each patient were deformed onto the CBCT images of the day because they represent the patient’s anatomy and position for that day (fraction). Deformations were performed using Varian’s Velocity AI and manual adjustments were made to ensure accurate registration. The dose was recalculated on the deformed TPCT using the same dose grid and the dose calculation engine. We evaluated differences in the following metrics: CTV D95, hotspot, and a number of compromised organs-at-risk (OAR) constraints to quantify our evaluation. Since the field-of-view (FOV) of the CBCT is smaller than that of the TPCT, only OARs that were in the CBCT FOV are considered in the evaluation.
Results: Across all 50 fractions delivered, the mean differences in D95, hotspot and the number of compromised OARs were determined as -0.15%, 0.98%, and 0.49. The maximum deviations in D95, hotspot and number of OARs were 5.6%, 9.96%, and 4. Detailed analysis of metrics showed the maximum hotspot and loss in coverage occurred in a single fraction of the same patient.
Conclusion: Overall, our evaluations showed a good agreement between the original plan and the plan calculated on the deformed TPCT indicating the robustness of the abdomen IMPT treatments and accurate setup. The proposed workflow can easily be performed daily in a relatively short time to provide a decision if a re-plan is necessary, increasing the frequency of evaluation of plan integrity while reducing the need for additional quality assurance CTs.
Keywords
Protons, Cone-beam CT, Quality Control
Taxonomy
IM- Particle (e.g., Proton) CT: Radiation dosimetry & risk
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