Presenter of 1 Presentation
OPTICAL CALORIMETRY, A PROMISING DOSIMETRY TECHNIQUE FOR FLASH RADIOTHERAPY
Abstract
Background and Aims
Optical calorimetry (OC) is a technique based on laser interferometry that spatially reconstructs energy absorbed in a transparent medium. The proposed approach measures absorbed dose to water without requiring correction factors, making it a promising technique for ultra-high-dose-rate beams. To investigate OC as a FLASH dosimeter, a standard linear accelerator was converted to deliver dose rates > 40 Gy/s.
Methods
The electron gun parameters of an Elekta Synergy linac were optimised to increase dose output of a 6 MV photon beam. Further modifications included removing the target, flattening filter, and scattering foils. An in-house built optical calorimeter built around a water phantom was placed at central axis. The image-based dosimeter was operated at a fixed frame rate. An in-house constructed pulse counting device measured the number of radiation pulses delivered per frame. The dose per frame was determined and used to calculate the dose rate achieved at the point of measurement.
Results
In the converted linac beam the OC system measured a dose/frame of 4.2 ± 0.4 Gy/frame. The dose rate was determined to be 210 ± 20 Gy/s at the point of measurement, which is within the expected range reported in the literature. A 10% measurement variation was observed between trials.
Conclusions
A recently decommissioned linac was successfully converted to deliver ultra-high FLASH dose rates. The optical calorimeter determined absolute dose in a FLASH beam without the need for correction factors. Further improvements to reduce the measurement variability would enhance the usefulness of OC as a dosimetry system for FLASH radiotherapy.
Author Of 1 Presentation
OPTICAL CALORIMETRY, A PROMISING DOSIMETRY TECHNIQUE FOR FLASH RADIOTHERAPY
Abstract
Background and Aims
Optical calorimetry (OC) is a technique based on laser interferometry that spatially reconstructs energy absorbed in a transparent medium. The proposed approach measures absorbed dose to water without requiring correction factors, making it a promising technique for ultra-high-dose-rate beams. To investigate OC as a FLASH dosimeter, a standard linear accelerator was converted to deliver dose rates > 40 Gy/s.
Methods
The electron gun parameters of an Elekta Synergy linac were optimised to increase dose output of a 6 MV photon beam. Further modifications included removing the target, flattening filter, and scattering foils. An in-house built optical calorimeter built around a water phantom was placed at central axis. The image-based dosimeter was operated at a fixed frame rate. An in-house constructed pulse counting device measured the number of radiation pulses delivered per frame. The dose per frame was determined and used to calculate the dose rate achieved at the point of measurement.
Results
In the converted linac beam the OC system measured a dose/frame of 4.2 ± 0.4 Gy/frame. The dose rate was determined to be 210 ± 20 Gy/s at the point of measurement, which is within the expected range reported in the literature. A 10% measurement variation was observed between trials.
Conclusions
A recently decommissioned linac was successfully converted to deliver ultra-high FLASH dose rates. The optical calorimeter determined absolute dose in a FLASH beam without the need for correction factors. Further improvements to reduce the measurement variability would enhance the usefulness of OC as a dosimetry system for FLASH radiotherapy.