Christina Ankjærgaard (Denmark)
DTU Health techAuthor Of 2 Presentations
GRAPHITE CALORIMETRY AND ALANINE FOR TRACEABLE DOSIMETRY IN PROTON FLASH BEAMS
Abstract
Background and Aims
A graphite calorimeter with a small core (5 mm diameter, 7 mm height) has been designed with the objective to characterize solid-state detectors in new radiotherapy modalities with respect to response changes resulting from changes in LET, dose rate and other parameters. Using a replica of the calorimeter, one can, for example, substitute the graphite core with the detector under investigation to obtain paired measurements with the graphite core and the detector under investigation under near-identical scatter conditions. In this study, we used the calorimeter to test alanine dosimetry for dose-rate effects in proton FLASH beams.
Methods
Measurements were performed at the Varian ProBeam system at the Danish Center of Particle beam using 250 MeV PBS beams with nozzle currents ranging from 4 nA to 215 nA (FLASH). For the main tests, we compared alanine pellets placed in the beam entrance with the temperature increase in the graphite core placed about 8 cm downstream.
Results
14 proton irradiations delivered doses of 10-11 Gy at different nozzle currents using a fixed 7 x 7 spot pattern (30 mm x 30.6 mm field size with a 50 Gy/s field dose rate for 215 nA nozzle current). The alanine doses correlated strongly with the temperature increases in the graphite core. Within experimental uncertainty, the ratio between alanine dose and temperature increase was found to be independent of the nozzle current in the tested dose rate range.
Conclusions
This study supports that alanine can be used for proton FLASH dosimetry without correction for dose-rate effects.
THE EFFECT OF PBS PROTON FLASH ON ACUTE SKIN TOXICITY AND TUMOR CONTROL IN A MOUSE MODEL
Abstract
Background and Aims
The aim of this study was to test the effect of proton FLASH delivered with a pencil beam scanning (PBS).
Methods
The right hind limb of CDF1 mice were irradiated in a single fraction in the entrance plateau of a scanning proton pencil beam using either conventional dose rate (0.4 Gy/s field dose rate, 244 MeV) or FLASH (69.7-88.7 Gy/s field dose rate, 250 MeV). The study included 292 non-tumor bearing mice and 80 mice with a C3H mouse mammary carcinoma implanted in the foot. The mice were irradiated with doses of 26-40Gy (non-tumor, conventional), 40-60Gy (non-tumor, FLASH) or 45-67Gy (tumor). The endpoints were the level of acute moist desquamation to the skin of the foot within 25 days post irradiation, and tumor control.
Results
Full dose response curves for acute damage to skin for both conventional and FLASH dose rate demonstrated a distinct normal tissue sparing effect in the FLASH arm of the study, with a mean value for the tissue sparing factor of 1.46. For tumor control, the pre-liminary dose response curves shows no difference between conventional and FLASH dose rates (follow up on tumor control is ongoing).
Conclusions
This study demonstrates a normal tissue sparing effect of proton FLASH delivered with pencil beam scanning, while no differences was found in tumor control rates. Compared to conventional dose rate, 41-55% higher dose were required to give the same biological toxicity in the normal tissue when using FLASH dose rates.