Author: Esteban Arzaga-Barajas, Paola Jazmin Guadarrama Huerta, Jose Alejandro Jimenez, Guerda Massillon-JL, Maria Adela Poitevin-Chacón, Alejandro Rodriguez-Laguna 👨🔬
Affiliation: UNAM, Medica Sur 🌍
Purpose: To perform patient-specific quality assurance (PSQA) tests for four SBRT treatments of patients diagnosed with vertebral, ilium, pelvic lymph node and lung tumors.
Methods: MAGIC gel consisting of methacrylic and ascorbic acid in gelatin initiated by copper, was manufactured and poured in five 2 mm thickness glass sphere flask phantoms. One phantom was used for calibration and the others to verify the SBRT treatments. Optical computed tomography (OCT) scans were performed before and after irradiation to measure changes in the optical density (OD) per centimeter. For the treatment verification, computed tomography (CT) scans of the phantoms were acquired and the patient's treatment plan was exported to the CT phantom images. The gel phantoms were irradiated under similar conditions of the patients using a 6 MV FFF X-ray beam generated by a Varian TrueBeam linac with at a dose rate of 1200 MU/min for prescribed doses ranging from 20 Gy to 30 Gy. The delivered dose distribution was calculated through the treatment planning system (TPS) and the measured dose distribution was obtained using the OCT.
Results: Both dose distributions were compared using the 3D-gamma index to assess clinical agreement. The gel coupled with the OCT exhibited sufficient sensitivity to accurately register the dose distributions from all treatments. Similarity was observed between the morphology of each pair of dose distributions. Additionally, when comparing profiles in the horizontal and vertical directions, similar trends were obtained for the same evaluated slices. Furthermore, it was found that the overall 3D gamma passing rate exceeded 90% at acceptance criteria of 2% dose difference and 2 mm distance-to-agreement for a dose threshold of 20%.
Conclusion: The results suggest that the polymer MAGIC-gel in conjunction with the optical CT is a suitable PSQA system for SBRT treatments
Project supported by PAPIIT-UNAM IN106825 and MSCA-SE Project MAMBA 101131245