부산대학교 도서관

With contemporary SRS, the interlinked dosimetry- and geometry-related treatment parameters, require a highdegree of accuracy and precision. This translates into the need for reduced uncertainties at each step of this complex procedure. This work presents an innovative phantom-based audit methodology that, combining results from different dosimetry methods, evaluates all stages of the radiotherapy chain, serving as an ideal tool to promote best practice and assure high-quality treatments. The phantom used was a 3D-printed head phantom, accommodating inserts for film, OSL, and gel dosimeters, calibrated at an SSDL. The user received an explicit, for the practice to be audited, RTstructure set, and was challenged to achieve a specific level of accuracy. Following the patient SRS treatment local protocol, the phantom treatment was simulated, planned, and exported to the delivery platform by the staff members who are normally involved at each step of the treatment chain. To assess whether QA results met the pre-defined standards, the latest recommendations of AAPM-RSS Medical Physics Practice Guideline 9.a. for SRS-SBRT were adopted for film dosimetry. A linacbased single-isocenter multi-focal SRS treatment was evaluated. 3 similar VMAT plans were generated, one for each detector type, taking into account the calibration dose range of each detector. Localization was performed with a kV CBCT. 6D corrections were applied prior to delivery. The OSL and film dosimeters were unloaded for analysis, and the phantom incorporating the irradiated gel-filled cylinder was MR scanned for the dose readout 24 hours post-irradiation at a fully characterized MR scanner. Results from one selected center audited has not indicated any concerns regarding the local practices for the specific aspects of dosimetry for intracranial SRS. Measured and calculated dose distributions were spatially co-registered and compared. Calculations were experimentally validated within uncertainties. The maximum deviation between measurements and TPS calculations for OSL dosimetry was 4.08%. The 3D GI of the film plane was 99.17% and the total spatial offsets of the planned and the corresponding gel-measured distributions for the targets involved were 0.77mm, 0.45mm and 0.81mm, respectively. Further work is required for the full characterization of OSLDs response to reduce the experimental uncertainties. Novel dosimetry audit techniques allow the multi-step evaluation of the radiotherapy treatment chain. To keep up with the clinical need and novel equipment future developments will be focused on aspects such as treatment planning based on MR images and online intrafraction replanning strategies, as these are being increasingly applied into routine clinical services. [ABSTRACT FROM AUTHOR]