Patient-Specific Quality Assurance (PSQA) Using 3D Polymer Gel Dosimetry In Spatially Fractionated Radiotherapy (SFRT)
Abstract
Purpose
Spatially fractionated radiotherapy (SFRT) focused on the heterogeneous application of the dose to the tumour and effectively used in bulky solid or radioresistant tumours. This work presents the dose distribution received by patients treated with SFRT using 3D gel dosimetry
Methods
Twelve and half litres of MAGIC-type gel were manufactured and poured into twelve spherical flasks: three of 16 cm diameter to verify the SFRT treatments of patients diagnosed with pelvic and abdominal cancer and nine of 8 cm diameter for calibration purpose. The calibration was performed using a 6 MV X-ray beam from a Varian TrueBeam linac at doses between 0.5 Gy and 40 Gy. Prior and post irradiation, all the flasks were imaged using an X-ray CT scanner. For the SFRT plan we used four-arc VMAT 6MV FFF mode. The lattice spheres were placed in a hexagonal pattern with alternating regions: vertex tumour volume high (VTVH) of 18 Gy and vertex tumour volume low (VTVL) of 6 Gy
Results
Despites the relatively high noise level on the CT images, the 3D dose distribution measured with the gel reproduced quite well that provided by the treatment planning system (TPS). In the VTVH region, differences of 0.5% to 9.5% on the absorbed dose are observed while in the VTVL, the discrepancies are between 0.1% and 14%. This notable difference could be associated with the quality of the X-ray CT image.
Conclusion
The results of this study suggest that the use of the X-ray CT is not the best readout method for MAGIC polymer gel. Within a Patient-specific quality assurance (PSQA) program for SFRT treatments using MAGIC gel, an optical CT scanner as readout method should be considered. We acknowledge CG Ruiz-Trejo, E López-Pineda and F Márquez for technical support. Project supported by PAPIIT-UNAM grant-IN106825 and MSCA-SE MAMBA Project grant-101131245