First Results Using Thermoluminescent Chips to Estimate Neutron Doses Near Proton Dose Delivery Regions in Solid Water Phantoms
C Allgower1*, C Reft2, (1) Indiana University Health Proton Radiotherapy Ctr, Bloomington, IN, (2) Univ Chicago, Chicago, ILSU-E-T-441 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: Demonstrate feasibility of using TLDs to estimate neutron doses near clinical proton dose delivery in solid water phantoms and compare relative readings for various conditions. The advantage of TLDs is their small size providing good spatial resolution. The issue of neutron levels adjuvant to proton therapy has been hotly debated for years. This effort aims at providing measured data of relevance to that question.
Methods: TLD-700 chips were irradiated in solid water stacks at locations a few cm distal and lateral to regions of proton dose delivered to 50 Gy. Readings were done at multiple beam energies (ranges in water) in a system that delivers beam via uniform scanning. A similar irradiation was done using a passive scattering system for further comparison. Absorbed doses were extracted from the two peak analysis of the TLD glow curves and cross calibration of the same chips in a proton beam and neutron therapy beams.
Results: Neutron dose estimates were surprisingly low for the uniform scanning system, being of order 0.2% of the proton dose at isocenter. Readings distal and lateral to the dose region were about equal, which was also somewhat surprising. Readings for the passive scattering system are expected to be higher than for the uniform scanning system, and will also be presented.
Conclusion: The feasibility of using TLDs to measure neturon levels near proton dose delivery regions is demonstrated, at least within the limitations of this method of data analysis. Additional work needs to be done, but initial results indicate that neutron levels appear to be lower than expected. Further study incorporating Monte Carlo simulations to estimate the neutron energy spectra at the locations of the chips will continue in the near future.