Room: Exhibit Hall
Purpose: To investigate the response of a commercial nanoDot optically stimulated luminescent dosimeter (OSLD) system in megavoltage photon and electron beams.
Methods: The nanoDot response was estimated by comparing with ionization chamber measurements for 4-18 MV photons and 6-20 MeV electrons in a solid water phantom. The photon and electron beams were obtained from a Varian Clinac iX linear accelerator (Varian Oncology Systems). The measured response was compared with that calculated using the BEAMnrc, egs_chamber, and cavity codes in the EGSnrc Monte Carlo (MC) code. The nanoDot response was analyzed as a function of energies, field sizes, depths, and angles. In addition, the response of the nanoDot cavity was analyzed according to Burlinâ€™s cavity theory. The perturbation correction factor, PQ, in the nanoDot cavity was also estimated from MC simulations.
Results: The nanoDot response was almost independent in the range of 4-18 MV photons at a 10 cm depth for a 10 x 10 cmÂ² field. The nanoDot response for 4 MV increased by 1.8% at a 15 cm depth for a 20 x 20 cmÂ² field. The angular response for 6 and 15 MV decreased by 5% and 3% at a parallel incident beam to the dosimeter plane, respectively. According to Burlinâ€™s cavity theory, the dose contributions from photon interactions (1-d) in the nanoDot cavity decreased by less than 0.05 as the mean photon energy increases. Values of PQ were almost constant between 0.96 and 0.97 at 10 MV or more. For 6-20 MeV electrons, the nanoDot response at a reference depth, dref, was constant within 0.9% relative to that of 6 MV photons.
Conclusion: The variation in energy response of the nanoDot was within 2% for 4-18 MV photons. The response at dref for 6-20 MeV electrons was an insignificant difference from that for 6 MV photons.
Funding Support, Disclosures, and Conflict of Interest: The measurement devices used in this study were provided by Nagase Landauer Ltd., Ibaraki, Japan