Purpose: To investigate the capability of low energy x-rays to elicit the FLASH effect, Drosophila melanogaster larvae were irradiated with ultrahigh dose-rate (UHDR) and conventional radiotherapy (CONV-RT) dose rates using an inexpensive x-ray tube system.
Methods: Drosophila melanogaster third instar larvae were irradiated with 120 kVp x-rays produced by a conventional x-ray tube outfitted with a tungsten rotating shutter system. UHDR dose rates of >100 Gy/s were achieved with tube currents of 25 mA during single shutter exposures of 25-100 ms, which delivered doses of 4.9-19.5 Gy. CONV-RT dose rates were obtained by reducing the tube current to 5mA and delivering 5 fractions separated by 25 seconds (100 second total irradiation time). Larvae were irradiated one at a time while immobilized with double-sided tape on a PMMA cylinder within the shutter system. Ten larvae were irradiated per dose group (a total of 100 larvae). After irradiation, the larvae were tracked for emergence from pupae and the survival of adult flies 6 days post irradiation. Dosimetry was performed with scintillators and radiochromic film.
Results: Film dosimetry measurements showed that the 50 ms exposure delivered doses of 11.0 and 9.8 Gy, and average dose rates of 110.0 and 0.1 Gy/s, for the UHDR and CONV-RT groups, respectively. A difference in both emergence from pupae and survival of adult Drosophila was observed between the UHDR and CONV-RT groups. For the 50 ms exposure setting, the UHDR group had 30% higher emergence from pupae, and 40% greater survival compared to the CONV-RT group.
Conclusion: A preliminary FLASH radiobiological study of Drosophila melanogaster was performed using a conventional x-ray tube capable of both UHDR and CONV-RT dose rates. The differential survival observed in this work suggests that continuous 120 kVp x-rays can induce a FLASH effect.
Funding Support, Disclosures, and Conflict of Interest: This work is funded by an NFRF and NSERC Discovery grant as well as the Canada Research Chairs program.
Not Applicable / None Entered.