ESTRO 2023 - Abstract Book


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ESTRO 2023

compare the experimental results with the simulation. Different dosimetric parameters were evaluated to verify the characteristics of the detector at low and high doses. Finally, MSD was used to test under high and low dose rates BT to realize the accuracy of the dose delivery.

Results Measurements under LINAC show that the detector can measure a very low dose to a high amount dose avoiding any Cerenkov corrections for both photon and electron beam treatment. Good repeatability (0.20 % variation) and reproducibility (0.30% variation) were obtained. A high lateral beam profile was successfully performed with a spatial resolution of 50 µ m for the beam field of 0.5 x 0.5 cm ² and 1 x 1 cm ² both in inline and crossline. The FWHM was achieved around 0.60 ± 0.15 cm and 1.05 ± 0.17 cm for both beam fields, and a good agreement was obtained while comparing with the simulated beam profiles (1.5-2% variation). An acceptable range of depth dose distribution was achieved (<0.75% average variation) with respect to the simulation results. Field output factor was measured for reference (10x10 cm2) until the smallest beam fields and a comparison is shown with the PTW microdiamond reference dosimeter. Finally, in BT, a comparison with the TG-43 reference dataset shows that measurement can be in good agreement within 0.75% up to 0.20 cm source-to-detector distances from a distal distance of 8 cm. Conclusion The proposed micro-dosimetry system in this study requires no Cerenkov or volumetric corrections thanks to its compact and provide efficient performance. Therefore, it is anticipated that the system can be promoted to validate with direct clinical investigations, such as in small-field dose verification, in-vivo dosimetry, intra-beam measurement, etc. for treatment quality assurance. Purpose or Objective ClearRT helical kVCT imaging for the Radixact helical tomotherapy system was recently installed at our department; the system is intended to enhance image fidelity in radiation therapy treatment planning and delivery compared to the prior MV-based onboard imaging approach. The purpose of this work was to measure the dose contribution to the patients from a radiation protection perspective. Materials and Methods The ClearRT system consists of a kV X-ray source and a flat-panel detector mounted orthogonal to the MV beam on the Radixact machine and the image is acquired by a fan Beam. This system can be utilized for both IGRT and ART image acquisitions. The user cannot directly adjust the tube technique (kVp and mAs) but the selection of specific protocols (named according to their expected use) specifies scan acquisition parameters. Selecting a specific anatomy determines the kV energy and reconstructed slice interval, whereas the choice of body (small, medium or large) configures the beam fluence to obtain an appropriate image quality. The field of view determines filtratiotn type. Accuray provided data for CTDIvol free in air measured with A1SL chamber, calibrated in terms of absorbed dose at kV energy, measured in air and with helical acquisition for each protocol. The CTDIvol and CTDIw in cylindrical phantom (head and body) were also measured. CTDIw acquisitions were only possible in a service condition with static couch during the beam rotation. All the protocols with various combination of the parameters were considered for large patient: a rescale of the results should be performed for small and medium patient (lower tube current).The software ImPACT CTDosimetry ver 1.0.4 was used to simulate organ doses for all the considered protocols. Results The values of CTDIvol free in air where in very good agreement with Accuray table (< 5% of difference). Table 1 shows data regarding CTDIw and CTDIvol in phantom for all the parameters and protocols (with highest value of mA). The difference PO-1770 Clear RT for Radixact: evaluation of different dose indicators and organ doses for patients. F. Giglioli 1 , G. Lo Moro 1 , V. Richetto 1 , E. Gallio 1 , O. Rampado 1 1 A.O.U. Città della Salute e della Scienza di Torino, Medical Physics Unit, Torino, Italy

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