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Radiobiological Advantage of Very Rapid Irradiation

M Bazalova

M Rafat1, M Bazalova1* , B Palma1 , M Kozak1 , D Jiang1 , M Dunning2 , D McCormick2 , J Nelson2 , E Hemsing2 , F Lartey1 , E Graves1 , A Koong1 , P Maxim1 , B Loo1 , (1) Stanford University, Stanford, CA, (2) SLAC National Accelerator Laboratory, Menlo Park, CA


SU-C-BRE-6 Sunday 1:00PM - 1:55PM Room: Ballroom E

Purpose: To characterize the effect of very rapid dose delivery as compared to conventional therapeutic irradiation times on clonogenic cell survival.

Methods: We used a Varian Trilogy linear accelerator to deliver doses up to 10 Gy using a 6 MV SRS photon beam. We irradiated four cancer cell lines in times ranging from 30 sec to 30 min. We also used a Varian TrueBeam linear accelerator to deliver 9 MeV electrons at 10 Gy in 10 s to 30 min to determine the effect of irradiation time on cell survival. We then evaluated the effect of using 60 and 120 MeV electrons on cell survival using the Next Linear Collider Test Accelerator (NLCTA) beam line at the SLAC National Accelerator Laboratory. During irradiation, adherent cells were maintained at 37oC with 20%O2/5%CO2. Clonogenic assays were completed following irradiation to determine changes in cell survival due to dose delivery time and beam quality, and the survival data were fitted with the linear-quadratic model.

Results: Cell lines varied in radiosensitivity, ranging from two to four logs of cell kill at 10 Gy for both conventional and very rapid irradiation. Delivering radiation in shorter times decreased survival in all cell lines. Log differences in cell kill ranged from 0.2 to 0.7 at 10 Gy for the short compared to the long irradiation time. Cell kill differences between short and long irradiations were more pronounced as doses increased for all cell lines.

Conclusion: Our findings suggest that shortening delivery of therapeutic radiation doses to less than 1 minute may improve tumor cell kill. This study demonstrates the potential advantage of technologies under development to deliver stereotactic ablative radiation doses very rapidly.

Funding Support, Disclosures, and Conflict of Interest: Bill Loo and Peter Maxim have received Honoraria from Varian and Research Support from Varian and RaySearch.

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