Determination of field output correction factors of radiophoto luminescent glass dosimeter in 6 mv small photon beams

Abstract

The objective of this study was to determine the field output correction factors of radiophotoluminescent glass dosimeter (RPLGD) for 6 MV photon beams by using Monte Carlo (MC) simulation. The ratios of absorbed dose of water and RPLGD were calculated using egs_chamber code for 6 MV, 90-cm SSD, 10-cm depth, and field size range from 0.5 × 0.5 to 10 × 10 cm2. Then the field output correction factors of RPLGD in perpendicular and parallel orientations were determined. Also, the volume averaging correction factors were discovered for supporting our results. Moreover, the comparison of measurement field output factors of RPLGD and that of CC01 determining using the field output correction factors from IAEA-AAPM TRS483 were performed to validate the field output correction factors in this study. For the results of the ratio of reading, the perpendicular RPLGD exhibited the underestimation for all field sizes. Parallel RPLGD showed underestimation for field size down to 1 × 1 cm2. In contrast, the overestimation was observed for lower field sizes. The field output correction factors of RPLGD were introduced. For the smallest field size, the field output correction factors of parallel RPLGD was within 5%, while perpendicular RPLGD was high up to 19%. The significant deviation of the field output correction factors in perpendicular RPLGD for the smallest field size because of a large volume averaging effect of 27%, while this effect was minimal in parallel RPLGD. The field output correction factor less than unity was observed in parallel orientation owing to the effect of the high density of RPLGD material. The percentage differences of field output factors comparing with CC01 were less than 3% for all field sizes, except the smallest field size of RPLGD in perpendicular. In conclusion, the field output correction factors of parallel RPLGD were practical for small field output factor measurement until field size down to 0.6 × 0.6 cm2. In comparison, RPLGD in perpendicular was practical for field size down to 1 × 1 cm2.