Purpose: The nanoDot is a commercially available optically stimulated luminescence dosimeter (OSLD) and has been widely used for radiation therapy in-vivo dosimetry because of its high sensitivity, accuracy, and minimal energy dependence in the radiation therapy energy (i.e., MV) range. However, several studies have shown existence of energy dependence in the diagnostic energy (i.e., kV) range. The purpose of this study is to quantify the energy dependence of nanoDot OSLD response in the superficial radiation therapy (SRT) energy range (50 kV - 100 kV) used for treatment of skin lesions.
Methods: A 5 cm applicator mounted in the SRT-100 Vision was centered on a nanoDot placed on a solid water phantom (30 cm × 30 cm × 5 cm). Using 50 kV, a series of doses (approximately 50 cGy, 100 cGy, 200 cGy, 300 cGy, 400 cGy, 500 cGy and 600 cGy) were delivered to seven nanoDots (one nanoDot per dose level). Measurements were repeated using 70 kV and 100 kV. On the same day, the same doses were delivered to EBT3 films in the same setup. After several hours, the nanoDots and films were read. A correction factor (CF) for energy dependence relative to 70 kV was then calculated for each dose level: CF = [S/D]₅₀ ₒᵣ ₁₀₀/[S/D]₇₀ where S is the nanoDot’s sensitivity-corrected signal count and D is absolute dose (cGy) measured using the film.
Results: For the assessed dose range (50 cGy - 600 cGy), CF varied from 0.86 to 0.96, and the mean CF was 0.91 for 50 kV. For 100 kV, corresponding values were 0.82-1.09 and 0.95.
Conclusion: There exists energy dependence response (up to 9%) of nanoDot OSLDs in the SRT energy range. For accurate in-vivo dosimetry, nanoDots should be calibrated for each energy.