Presenter of 1 Presentation
ULTRAFAST TRACKING OF OXYGEN DYNAMICS DURING PROTON FLASH
Abstract
Background and Aims
Radiotherapy at ultrahigh dose rates (FLASH, >40Gy/sec) compared to conventional radiotherapy (CR; <1 Gy/sec) has been shown to provide an advantage by selective protection of normal versus tumor tissue. Depletion of molecular oxygen causing radioprotection has been proposed to underpin the FLASH effect, however no experimental data have been presented to test this hypothesis. Our goal was to assess the oxygen dynamics during and following proton FLASH versus CR.
Methods
Measurements of oxygen were performed in vitro (solutions in sealed vials) and in vivo in mice (healthy leg muscle and tumors) using the phosphorescence quenching method with probe Oxyphor PtG4 at rates reaching 3 measurements/millisecond during proton irradiation delivered with CR or FLASH dose rates.
Results
In closed systems in vitro the rate of oxygen depletion is oxygen-independent for both FLASH and CR when [O2]>~70 μM. The g-values are lower for FLASH than for CR by ~15%. In vivo oxygen is depleted upon FLASH with rates that correlate with baseline pO2 (partial pressure of oxygen) values throughout the entire pO2 range: at 30-40 mmHg (normal tissue) a 30 Gy FLASH (100 Gy/s) results in ΔpO2 of -8 mmHg, while at 5-7 mmHg (tumor) ΔpO2 is only -1 mmHg.
Conclusions
This study features the first demonstration of the phosphorescence quenching oximetry at ultrafast rates and in the presence of proton radiation. Oxygen depletion by FLASH in vitro was found to be smaller than by CR, and appears to correlate with baseline pO2 values, being greater for normal tissue than for tumors.
Author Of 1 Presentation
ULTRAFAST TRACKING OF OXYGEN DYNAMICS DURING PROTON FLASH
Abstract
Background and Aims
Radiotherapy at ultrahigh dose rates (FLASH, >40Gy/sec) compared to conventional radiotherapy (CR; <1 Gy/sec) has been shown to provide an advantage by selective protection of normal versus tumor tissue. Depletion of molecular oxygen causing radioprotection has been proposed to underpin the FLASH effect, however no experimental data have been presented to test this hypothesis. Our goal was to assess the oxygen dynamics during and following proton FLASH versus CR.
Methods
Measurements of oxygen were performed in vitro (solutions in sealed vials) and in vivo in mice (healthy leg muscle and tumors) using the phosphorescence quenching method with probe Oxyphor PtG4 at rates reaching 3 measurements/millisecond during proton irradiation delivered with CR or FLASH dose rates.
Results
In closed systems in vitro the rate of oxygen depletion is oxygen-independent for both FLASH and CR when [O2]>~70 μM. The g-values are lower for FLASH than for CR by ~15%. In vivo oxygen is depleted upon FLASH with rates that correlate with baseline pO2 (partial pressure of oxygen) values throughout the entire pO2 range: at 30-40 mmHg (normal tissue) a 30 Gy FLASH (100 Gy/s) results in ΔpO2 of -8 mmHg, while at 5-7 mmHg (tumor) ΔpO2 is only -1 mmHg.
Conclusions
This study features the first demonstration of the phosphorescence quenching oximetry at ultrafast rates and in the presence of proton radiation. Oxygen depletion by FLASH in vitro was found to be smaller than by CR, and appears to correlate with baseline pO2 values, being greater for normal tissue than for tumors.