Program Information
Investigating the Linear Energy Transfer Dependency of Different PRESAGE Formulations in a Proton Beam
M Carroll1*, M Alqathami2 , A Blencowe3 , G Ibbott4 , (1) University of Texas MD Anderson Cancer Center, Houston, TX, (2) ,,,(3) The University of South Australia,, South Australia, SA, (4) UT MD Anderson Cancer Center, Houston, TX
Presentations
SU-E-T-515 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:
Previous studies have reported an under-response of PRESAGE in a proton beam as a result of the extremely high LET in the distal end of the spread out Bragg peak (SOBP). This work is a preliminary investigation to quantify the effect of the formulation, specifically the concentration of halocarbon radical initiator relative to leuco dye, on radical recombination resulting in LET dependence.
Methods:
The traditional PRESAGE formulation developed by Heuris Pharma was altered to constitute radical initiator concentrations of 5, 15, and 30% (low, medium, and high) by weight with all other components balanced to maintain proportionality. Chloroform was specifically examined in this study and all dosimeters were made in-house. Cylindrical PRESAGE dosimeters (3.5cm diameter and 6cm length) were made for each formulation and irradiated by a 200-MeV proton beam to 500 cGy across a 2cm SOBP. Dosimeters were read out using the DMOS optical-CT scanner. The dose distributions were analyzed and dose profiles were used to compare the relative dose response to find the stability across the high-LET region of the SOBP. LET dependence was measured by the variation to ion chamber measurements for the final 25% of the SOBP (~0.5cm) prior to the distal-90 of each profile.
Results:
Relative to ion chamber data, all PRESAGE dosimeters showed an under-response at the distal end of the SOBP. The medium concentration formulation matched most closely with an average 8.3% under-response closely followed by the low concentration at 12.2% and then the high concentration at 22.8%. In all three cases, the highest points of discrepancy were in the distal most regions.
Conclusion:
The radical initiator concentration in PRESAGE can be tailored to reduce the LET dependence in a proton beam. This warrants further study to quantify comprehensively the effect of concentration of different halocarbon radical initiators on LET dependency.
Funding Support, Disclosures, and Conflict of Interest: Grant number 5RO1CA100835
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