Program Information
Dosimetric Accuracy for MRI Based Intensity Modulated Proton Therapy for Prostate Cancer
J Zhang*, S Chen , X Ding , D Krauss , D Yan , William Beaumont Hospital, Royal Oak, MI
Presentations
WE-RAM2-GePD-J(B)-4 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: Magnetic Resonance Imaging (MRI) based radiotherapy treatment planning workflow for prostate and brain cancer has gained increasing popularity and rapid clinical adaptation. This study aims to investigate the dosimetric accuracy of intensity modulated proton therapy (IMPT) plans based on synthetic computed tomography (sCT) for prostate cancer.
Methods: The sCT data of two patients were reconstructed using a previously published algorithm, which consists of atlas-based auto-segmentation and deformable image registration of MR-CT image pairs. T2-weighted turbo spin-echo (TE/TR=110/5000ms, 90 flip angle, 0.45x0.45x3 mm3 pixel resolution) images were acquired right after CT simulation on a 3T Philips Ingenia system. Laterally opposed two-field IMPT plans with robustness optimization (3.5% and 5 mm) were created for both standard simulation CT and sCT in a commercial treatment planning system. Dose agreement was evaluated using 3D gamma criteria (1%, 1 mm) for CTV coverage and normal tissue structures. Both pencil beam (PB) and Monte Carlo (MC) dose calculations were performed independently for comparison.
Results: The maximum absolute dose difference between sCT and standard CT in CTV, femoral heads, rectum, and bladder were 4.2%, 0.33%, 0.37%, and 2.2% respectively for the PB dose engine; 3.67%, 2.99%, 1.96%, and 3.14% of dose difference was observed for the MC dose calculation. There was no significant change in gamma passing rate between the two dose calculation methods. The overall global gamma passing rate for the sCT IMPT plans were 97.9% (PB) and 95.8% (MC). The maximum dose difference of 31.5% occurs near the external surface.
Conclusion: The current study found that IMPT with both pencil beam and MC dose calculations on sCT showed favorable dose agreement with the simulation CT. Future studies will include more patient data and investigate sCT generation algorithms that can further improve the HU value accuracy near patient surface.
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