Mitigation of Dosimetric Uncertainty in MRI-Based Proton Planning Using Spot-Scanning Proton Arc (SPArc) Technique

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Conference Proceeding

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Publication Title

International Journal of Radiation Oncology, Biology, Physics


Purpose/Objective(s): MRI-based synthetic CT (SCT) images created using generative adversarial network (GAN) have been demonstrated to be feasible for intensity-modulated proton therapy (IMPT) planning. However, dose calculation accuracy can be uncertain in some regions within/ near the target of head and neck patients due to the local CT number estimation error or sharp dose fall-off. This study investigated the feasibility of using the SPArc technique to mitigate such dosimetric uncertainty. Materials/Methods: A GAN using a 3D U-net as the generator and a 6- layer 3D convolutional neural network as the discriminator was trained with T1-weighted MR-CT image pairs from 162 nasopharyngeal carcinoma patients (14 for validation). The generator was used to generate SCT images from MR images for 7 test patients. For each test patient, the CT image was used to create a SPArc plan and an IMPT plan with the same clinical objectives. The SPArc plans (control point frequency sampling, arc trajectory, etc.) were optimized using a previously developed iterative approach. The dose distributions of both SPArc plans and IMPT plans were re-calculated on the SCT images and compared to the one calculated on the CT images. The dosimetric uncertainty was quantified using the gamma index. Results: The 2%/2mm and 3%/3mm passing rates for SPArc plans were (96.9¡A2.7) % and (98.6¡ A1.5) %, while the passing rates for IMPT plans were (94.0¡A3.9) % and (96.4+2.9) %. A signi ficant reduction in dosimetric uncertainty was identified for SPArc plans (p ¡U0.021). Table 1 shows the € passing rates for the 7 test individuals. Conclusion: SPArc can mitigate the uncertainty of dose calculation in MRI-based proton planning. Further research needs to validate these findings on a larger patient cohort. The study paves the road map for using MRI for SPArc planning.




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American Society for Radiation Oncology 65th Annual Meeting ASTRO 2023, October 1-4, 2023, San Diego, CA