Room: AAPM ePoster Library
In recent years, several studies have reported the effectiveness of ultra-high dose rate (FLASH) irradiation. In this study, we investigated the usefulness of low-sensitivity radiochromic film measurement in synchrotron-based FLASH proton irradiation.
For an experimental measurement, we used a new type of low-sensitivity radiochromic film (EBT-XD, Ashland) and plane-parallel ionization chamber (Advanced Markus, PTW).
The calibration curves of the EBT-XD were obtained by irradiation at a normal dose rate. The response characteristic of the EBT-XD due to the difference in linear energy transfer (LET) was also verified by obtaining the calibration curve at the plateau region and near the peak. A synchrotron-based scanning system (PROBEAT?, Hitachi) used in clinical treatment at Nagoya Proton Therapy Center was used for FLASH irradiation. To form a small spread-out of Bragg peak, a small ridge filter made by a 3D printer was inserted into the beamline. The absolute dose and the dose distribution were measured using EBT-XD.
There was no difference between the calibration curve obtained by the two depths. The differences between absolute doses measured using the film and ionization chamber were 1.7% near the peak and 1.9% at the plateau. The doses were 24.0 Gy and 10.8 Gy, respectively, with dose rates of 480 Gy/s and 216 Gy/s. In the measurement of the depth dose distribution, the range agreed in two dose rates, however, there was a difference in the dose distribution upstream of the peak. The lateral dose distribution was successfully obtained by EBT-XD film.
Synchrotron-based FLASH proton beam irradiation was successfully performed. It was shown that the absolute dose could be measured with high accuracy by EBT-XD film. EBT-XD film is useful as a dose distribution measurement system for FLASH irradiation.