Room: AAPM ePoster Library
Purpose: A spatially modulated proton minibeam has been developed on the preclinical small animal proton platform at our institution. In vitro studies using the human lung carcinoma cell line A549 were performed to compare the biological effects between the proton minibeam and open beam at the entrance of the beam.
Methods: A 6cmx6cm steel collimator was built for the 50MeV proton beamline to generate 300µm wide planar minibeams with a center-to-center spacing of 1mm. The dose output for the 6cm diameter open beam was measured using A16 microchamber with NIST traceable calibration certification. The output for the minibeam was determined by that of the open beam and Monte Carlo (MC) TOPAS simulations. Clonogenic survival assay (0Gy and 1.5Gy) and gamma H2AX assay (0Gy and 1Gy) for DNA double strand break (DSBs) were performed at the entrance of the open and minibeam. For minibeam, the collimator was placed 2cm away from the cells. Clonogenic survival data were analyzed at 14 days post irradiation and gamma H2AX staining started at 2-hour post irradiation. Gamma H2AX foci were counted using an open-source foci-counting software.
Results: The cell survival study revealed that for the minibeam, the 1.5Gy entrance mean dose had no detectable cell killing effect, while 1.5Gy open beam killed about 20% of the cells. The gamma H2AX assay determined a peak-to-valley dose ratio (PVDR) of 3.1 at the entrance of the minibeam, which agrees with the 3.7 obtained with the MC simulations.
Conclusion: We have developed a highly modulated proton minibeam. Initial in vitro cell survival study suggests cell killing sparing effects in the entrance of the minibeam. Gamma H2AX assay may be used as a biological dosimetry for minibeam PVDR. Further studies will be performed to verify the effects at different dose level and along the proton beam pathway.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by University of Washington Royalty Research Fund.