C Jeon¹*, S Ahn², Y Han^2,3, (1) Sungkyunkwan University, Seoul, 11, KR, (2) Samsung Medical Center, Seoul, ,KR, (3) Sungkyunkwan University School of Medicine, Seoul, ,KR

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  C Jeon

PO-GePV-T-155 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Dose rate calculation is an important part of verifying a treatment machine’s dose delivery in FLASH radiation therapy. Several dose rate calculation methods were introduced recently, but it is difficult to decide an absolute standard for calculating dose rate. In this study, we developed a fine dose rate calculation method using a machine log file and Monte-Carlo simulation. The feasibility of confirming the dose rate in FLASH radiation therapy was tested.

Methods: A log file has irradiation time, spot, MU related information which were used for Monte⁻Carlo simulation beam parameters. Log files of box plans for scanning beams were acquired from Samsung Medical Center proton therapy center. For the Monte-Carlo simulation, TOPAS 3.5 based on Geant4 10.7 was used. A log file’s irradiation time was applied to the TOPAS time feature, and time was divided by 3 groups (0⁻700, 700⁻1400, 1400⁻2300 milliseconds). Each group’s dose was scored to a 2mm slice of solid water phantom at 2cm depth and the obtained result was scaled by a scaling factor to convert absolute dose in the phantom. The dose rate was calculated using log file time and the calculated dose rate was compared with RT plan dose rate information. Output was exported as DICOM RT dose file format.

Results: In each time group, the planned dose rate was 0.1540 Gy/s, and the calculated dose rate was 0.1538, 0.1541, and 0.1539 Gy/s in each time group, which showed high consistency with the planned dose rate.

Conclusion: In this study, we confirmed the feasibility of the dose rate calculation method based on machine log files and Monte-Carlo simulation. We will evaluate this method for FLASH radiation therapy patient plans in future works.

Keywords

Monte Carlo, Protons

Taxonomy

TH- External Beam- Particle/high LET therapy: Proton therapy – experimental dosimetry

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