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Session: Therapy General ePoster Viewing [Return to Session]

Estimation of Uncertainties in the Distal Edge of Proton Beams Introduced by Inherent Variations in the Thickness of Plates Used to Perform Radiobiology Experiments

D Martinus*, D Flint, S Bright, U Titt, S Shaitelman, G Sawakuchi, MD Anderson Cancer Center, Houston, TX


PO-GePV-T-192 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To estimate dosimetric uncertainties introduced by the inherent variations in the thickness of dishes used to perform radiobiological experiments for a proton beam with high linear energy transfer.

Methods: We cut out the plastic at the bottom of 12-well plates from two different manufactures (#665180, Greiner; and #3513 Corning). For each manufacturer we generated 5 cutouts from each plate. The cutouts were then placed directly before the sensitive region of an Advance Markus ionization chamber. We used an unmodulated proton beam with range in water of 4.3 cm (R90%) to expose the upstream surface of the cutout at a water equivalent depth of 4.3 cm, which is the distal edge of the beam. A validated Monte Carlo model of the beam line was then used to obtain the percentage depth dose of the beam to determine the water equivalent thickness of each cutout. We also used the same Monte Carlo model to estimate the variation in LET introduced by the variation in the thickness across cutouts.

Results: The average water equivalent thicknesses of the bottom of Greiner and Corning plates was 1.1989 mm and 1.3691 mm with standard deviations of 0.0135 mm and 0.0332 mm, respectively. The Greiner well variation resulted in a 3.5% and 3.5% difference in LET and dose respectively. The Corning well variation resulted in an 8.3% and 12.2% difference in LET and dose respectively.

Conclusion: Our results indicate that variability within wells of the same plate degrades dosimetric certainty in the distal edge of proton beams. These findings suggest that detailed dosimetric characterization of the experimental setup is essential to conduct experiments in the distal edge of protons beams. Because the dose and LET gradients are even higher for heavy charged particles such as helium and carbon ions, detailed characterization of those beams is warranted.

Funding Support, Disclosures, and Conflict of Interest: GOS and SFS have research funds from Alpha Tau Medical and Artios Pharma. NIH funding: 1P01CA261669-01


Protons, Radiation Dosimetry, LET


TH- External Beam- Particle/high LET therapy: Proton therapy – experimental dosimetry

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