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Extracting a Neutron Dose Using Only TLDs (Thermoluminescent Detectors)

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A Dy

A Dy1*, K Shahnazi1,2, S Klein1, (1) Indiana University, Bloomington, IN, (2) Deaconess Health System, Evansville, IN

SU-E-T-35 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To test the use of TLDs for out-of-field neutron measurements and demonstrate the calibration and calculations necessary to extract a neutron dose by using TLD 600 chips, which measure photons plus neutrons, and TLD 700 chips, which measure only photons. For treatments requiring high-energy photons or protons, secondary neutron doses may become a factor and TLDs provide many advantages in a clinical setting over conventional neutron dosimeters.

Methods:A set of lithium fluoride TLDs (thermoluminescent detectors) consisting of 100, 600 and 700 series Rexon TLDs were arranged at set distances in and out of field of 6MV and 18MV photon beams from an Elekta Precise Treatment System. All TLD chips were read out using a Rexon System 310 reader and raw glow output data was exported for data analysis.

Results:Examination of the integrated TLD glow curves shows an energy dependent response and a higher reading for TLD 600 chips as the distance or angle from the beam field increases for the 18MV beam. At a low neutron dose, correct integration interval must be used extracted a signal above noise.

Conclusion:This work demonstrates the feasibility of neutron measurements using only TLDs as opposed to TLDs with CR39, bubble detectors, diamond detectors or WENDI detectors. TLDs are commercially available in different sensitivities and relatively cheap. We speculate that the TLD 600 chips will continue to read neutron doses at large distances to its neutron cross section. Furthermore they allow for spatial resolution and in vivo measurements. With calibration for neutron doses and photon energy ranges, a quantitative neutron dose is possible. This integration and subtraction method will be used in future investigation to directly quantify neutron doses spatially with respect to the beam and for different beam characteristics.

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