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MO‐EE‐A1‐02: Dosimetry for an Ophthalmic Applicator of P‐32
Author(s) -
Choi C,
Kim J,
Park J,
Park S,
Choi Y,
Kim H,
Park Y,
Kim H,
Ye S
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3469080
Subject(s) - dosimetry , ionization chamber , materials science , monte carlo method , percentage depth dose curve , nuclear medicine , extrapolation , absorbed dose , dose profile , dose rate , optics , ionization , physics , medicine , medical physics , mathematics , ion , mathematical analysis , statistics , quantum mechanics
Purpose : A 90 Sr/Y applicator has been used as a ‐source for postoperative irradiation after pterygium excision. As an alternative to 90 Sr/Y irradiation, we proposed treatments with 32 P. This study aims to provide the dosimetry for this new applicator. Method and Materials : In order to optimize the design and materials of 32 P ophthalmic applicators, Monte Carlo simulations were performed. The absorbed dose at the surface of a sealed beta source is often measured by using an extrapolation ionization chamber. Radiochromic film (RCF) was used to measure depth dose distributions and dose profiles at various depths. A micro‐MOSFET detector was used for depth dose measurements. Results : The absorbed dose rates to the reference point were 0.238 ± 0.012 cGy/s for an extrapolation ionization chamber, 0.280 ± 0.001 cGy/s for radiochromic films, and 0.257 ± 0.020 cGy/s for MOSFET. The axial depth dose rate was reduced into approximately 1/10 as 32 P betas penetrate every 2 mm depth. Measured data sets in depths of 1 mm to 3.5 mm agreed with Monte Carlo data. Due to non‐uniform absorption of 32 P into an absorbent disk, the dose at the center of transaxial plane were 2%–4% less than the peak dose around the periphery. We confirmed no leakage of 32 P activities and negligible exposure rate around the hand grip of the applicator. Conclusions : The 32 P applicator can deliver uniform therapeutic doses to the surface of the conjunctiva, while sparing the lens better than 90 Sr/Y applicators. The doses at any points from the 32 P applicator can be calculated by using these measured data sets. The safety of 32 P applicator was confirmed. However, prior to the clinical application of every new applicator, safety, dose uniformity, and absorbed dose rate at the reference point should be carefully evaluated by the method developed in this study.