Feasibility study: Polymer Gel Dosimetry On 0.35T MR-Linac System
L Marage*, J Boudet, L Aubignac, I Bessieres, A Petitfils, Centre Georges-Francois Leclerc, Dijon, 21, FR
Presentations
PO-GePV-M-263 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: In radiotherapy, the polymer gel has shown several advantages for End-to-End (E2E) treatment verifications. The gel access is now facilitated by external solutions that proposed to help physicists in their dosimetry verifications with a dedicated gel shipment and the possibility to send back the irradiated gel for an external analysis service. Nevertheless, the increase of MRI systems in radiotherapy departments for simulations and/or treatments allows a direct analysis by the costumers. While the analysis is generally running on high field MRI (1.5 T), the purpose of this work is to investigate the feasibility of polymer gel dosimetry analysis based on a low field (0.35 T) MR-Linac system imaging and measurement.
Methods: Each irradiation and MR acquisitions have been carried out on a 0.35 T MR linac MRIdian from ViewRay. A dose of 0, 2, 5, 8 and 11 Gy has been delivered respectively to 5 gel vials in order to evaluate the linear relation between the transverse relaxivity and the calculated dose. This calibration has then been verified by measuring the dose distribution of simple fields on depth and transversal dose profiles for two level of maximum of dose: 3 and 10 Gy. MR acquisitions have been performed after irradiation using a 2D multi-echoes HASTE sequence.
Results: After SNR management proper to 0.35 T acquisitions, the linearity from ROI analysis has been showed (R²=0.997). Encouraging gamma index score have been observed on the depth and transversal dose profiles between the calculated dose and the measured one.
Conclusion: This feasibility study shows the potential of the gel dosimetry analysis with a 0.35 T MR measurements. Nevertheless, the analysis sequences have to be improved for the whole available dose range. This work needs to be done before investigate 3D high resolution acquisitions necessary for an E2E treatment verification.
Funding Support, Disclosures, and Conflict of Interest: All polymer gels used in this study have been granted without charge from the RT-Safe company through a collaboration.
Keywords
Gel Dosimeter, Low-field MRI, Quality Assurance
Taxonomy
IM/TH- MRI in Radiation Therapy: MRI/Linear accelerator combined Quality Assurance
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