CHUV
Institute of Radiation Physics

Presenter of 1 Presentation

PLASMID DNA DAMAGES AFTER FLASH VS CONVENTIONAL DOSE RATE IRRADIATIONS IN VARIOUS OXYGEN CONDITIONS

Session Type
FLASH Mechanisms Track (Oral Presentations)
Date
Wed, 01.12.2021
Session Time
18:00 - 19:00
Room
Room 2.15
Lecture Time
18:50 - 19:00

Abstract

Background and Aims

In our work we thought to compare the effects of conventional (CONV) vs ultra-high dose rate (UHDR) by quantifying DNA strand breaks (SB) after irradiation of plasmid-DNA (pBR322) under various oxygen concentrations.

Methods

Supercoiled pBR322 was irradiated dry or in water using a 6 MeV FLASH-validated electrons beam, with increasing doses (1-100 Gy) and dose per pulse (0.01 Gy/s (CONV), 5.0*102 to 5.6*106 Gy/s (UHDR)) and at atmospheric (21%), physoxic (4%) and hypoxic (0.5%) oxygen level. The increase of relaxed (R) and linear (L) plasmid forms after irradiation was quantified by agarose gel electrophoresis and used to compute single and double SB yields.

Results

Dry, atmospheric conditions cause similar yields of SB in CONV and UHDR. Aqueous conditions shows higher SB yields as expected. Physoxia induces radioprotection compare to atmospheric condition: 50% of R at 10 Gy (4% O2) vs 2 Gy (21% O2), but no difference relative to dose rate. Hypoxia revealed higher SB yields than physoxia in CONV (50% of R at 6 Gy) but 2x less SB in UHDR for doses >30 Gy (see figure for L).

layout 3_redim.jpg

Conclusions

First results in dry condition suggest that direct effects are not involved in FLASH. In aqueous condition, 4% oxygen mimicking healthy tissues shows no difference between UHDR and CONV, while 0.5% oxygen mimicking tumors shows less damages in UHDR. These results are opposite to the preclinical results showing the FLASH effect. Thus, plasmid irradiation might be useful to understand DNA damage at UHDR but seems barely relevant to investigate the FLASH effect at the biological level.

Hide

Author Of 2 Presentations

A PURSUIT FOR A HIGH-THROUGHPUT INDICATOR OF THE FLASH EFFECT

Session Type
FLASH Modalities Track (Oral Presentations)
Date
Wed, 01.12.2021
Session Time
10:20 - 11:30
Room
Room 2.31
Lecture Time
11:00 - 11:10

Abstract

Background and Aims

Despite an immense research interest in FLASH-RT, the precise beam requirements for obtaining the FLASH effect have still not been elucidated. Yet, there is an increasing number of reports assigning the name FLASH to beams and irradiators without any supportive biological data.

Methods

Currently, the FLASH effect can be confirmed only in vivo, which requires time-consuming animal studies and corresponding ethical approvals. The FLASH community would therefore greatly benefit from a high-throughput FLASH beam indicator that can validate an UHDR beam for FLASH-RT. Such indicator has to generate an observable that follows the same dependency on temporal beam characteristics as the FLASH effect.

Results

We used our published data on sparing of the normal mouse brain and killing of GBM to monitor the impact of gradually changing electron beam parameters (dose rate, dose per pulse) on the occurrence of the FLASH effect. These data were considered as a template to investigate responses of various high-throughput assays over the same range of beam parameters. In particular, we studied assays that previously showed differential response to our FLASH and Conv beams: H2O2 yield, O2 depletion, plasmid DSB, lipid peroxidation and zebrafish embryo. Only the length of zebrafishes grown from irradiated embryos showed the dependency on beam parameters mimicking the cognitive protection in vivo with low energy electron beam (Oriatron).

Conclusions

Since mechanistic differences between different types of beams (protons, X-ray) are possible, further investigations are mandatory to confirm universal validity of this model as a general FLASH indicator.
Hide

PLASMID DNA DAMAGES AFTER FLASH VS CONVENTIONAL DOSE RATE IRRADIATIONS IN VARIOUS OXYGEN CONDITIONS

Session Type
FLASH Mechanisms Track (Oral Presentations)
Date
Wed, 01.12.2021
Session Time
18:00 - 19:00
Room
Room 2.15
Lecture Time
18:50 - 19:00

Abstract

Background and Aims

In our work we thought to compare the effects of conventional (CONV) vs ultra-high dose rate (UHDR) by quantifying DNA strand breaks (SB) after irradiation of plasmid-DNA (pBR322) under various oxygen concentrations.

Methods

Supercoiled pBR322 was irradiated dry or in water using a 6 MeV FLASH-validated electrons beam, with increasing doses (1-100 Gy) and dose per pulse (0.01 Gy/s (CONV), 5.0*102 to 5.6*106 Gy/s (UHDR)) and at atmospheric (21%), physoxic (4%) and hypoxic (0.5%) oxygen level. The increase of relaxed (R) and linear (L) plasmid forms after irradiation was quantified by agarose gel electrophoresis and used to compute single and double SB yields.

Results

Dry, atmospheric conditions cause similar yields of SB in CONV and UHDR. Aqueous conditions shows higher SB yields as expected. Physoxia induces radioprotection compare to atmospheric condition: 50% of R at 10 Gy (4% O2) vs 2 Gy (21% O2), but no difference relative to dose rate. Hypoxia revealed higher SB yields than physoxia in CONV (50% of R at 6 Gy) but 2x less SB in UHDR for doses >30 Gy (see figure for L).

layout 3_redim.jpg

Conclusions

First results in dry condition suggest that direct effects are not involved in FLASH. In aqueous condition, 4% oxygen mimicking healthy tissues shows no difference between UHDR and CONV, while 0.5% oxygen mimicking tumors shows less damages in UHDR. These results are opposite to the preclinical results showing the FLASH effect. Thus, plasmid irradiation might be useful to understand DNA damage at UHDR but seems barely relevant to investigate the FLASH effect at the biological level.

Hide