Author: Min Cheol Han, Chae-Seon Hong, Changhwan Kim, Dong Wook Kim, Hojae Kim, Hojin Kim, Jin Sung Kim, HO Lee, Kwangwoo Park, Ye-In Park, Junyoung Son 👨🔬
Affiliation: Department of Radiation Oncology, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine, Department of Radiation Oncology, Yongin Severance Hospital, Yonsei University College of Medicine 🌍
Purpose: Overresponse in surface in-vivo dosimetry using optically stimulated luminescence dosimeter (OSLD) depends on the beam incidence angle. This study aimed to investigate correction factors to determine the near-skin surface dose for two commercial OSLDs.
Methods: Surface dosimetry with two OSLDs, MyOSLchip (RadPro International GmbH, Germany) and nanoDot (Landauer, USA), was conducted on the solid water phantom using a 6 MV photon beam. A dose of 300 MU was delivered with various gantry angles ranging from 0° to 75° and five different field sizes of 3 × 3 cm2 to 20 × 20 cm2 with a source-to-surface distance of 100 cm. Gafchromic EBT4 film (Ashland, USA) measurements were performed on an identical beam delivery setup and applied as baseline of near skin surface dose. The measurements were repeated 3 times, and the relation between OSLD dose and film dose in surface dosimetry was assessed as a function of beam incidence angle and field size.
Results: Beam incidence angle and field size affected the degree of skin dose overestimation in surface dosimetry with MyOSLchip and nanoDot. For both OSLDs, correction factors for estimating near skin surface dose increased with increasing incidence angle and field size. The MyOSLchip to film correction factor in surface dosimetry ranged from 0.30 ± 0.01 to 0.71 ± 0.03. The nanoDot to film dose correction factor ranged from 0.47 ± 0.01 to 0.82 ± 0.01, which is larger than the correction factor for MyOSLchip under the same beam delivery conditions.
Conclusion: This study presents correction factors required for estimating near skin surface dose from OSLD measurements. Utilizing OSLD in surface in-vivo dosimetry should be performed considering beam incidence angle and field size.