title: Dosimetry of a new P-32 ophthalmic applicator.
abstract: OBJECTIVE
  The potential of P-32 ophthalmic applicator irradiation after pterygium excision has been demonstrated as an alternative to Sr∕Y-90 irradiation. This study aimed to provide the clinical dosimetry for this new applicator.
  
  
  METHODS
  The prototype of a cylindrical P-32 applicator was fabricated according to the Monte Carlo (MC)-based design study. At a nominal activity of 6 mCi (0.22 GBq), the absorbed dose rate at the front surface (i.e., reference dose rate) was measured by using an extrapolation ionization chamber (EC). The radiochromic film (RCF) was also used to measure the reference dose, axial depth dose distributions and transaxial dose profiles at various depths in water.
  
  
  RESULTS
  The reference dose rate was 3.89 ± 0.14 cGy∕s for EC and 3.84 ± 0.25 cGy∕s for RCF. The depth dose rate was reduced approximately by an order of magnitude for every 2 mm depth in water. Measured depth doses in depths of 0.5-2.5 mm agreed with Monte Carlo data within ±3%. Due to nonuniform absorption of P-32 into an absorbent disk, the dose profiles were not symmetric and decreased more rapidly toward the periphery than those predicted by the MC. The authors confirmed no leakage of P-32 activities and negligible exposure rate around the hand grip of the applicator.
  
  
  CONCLUSIONS
  The P-32 applicator can deliver therapeutic doses to the surface of the conjunctiva, while sparing the lens better than Sr∕Y-90 applicators. The doses at any points from the P-32 applicator could be calculated by using the measured dosimetry data. They also confirmed no leakage of the source, reliable integrity of the applicator, and negligible exposure level around the hand grip of the applicator. However, due to a possibility of nonuniform distributions of P-32 in an absorbent disk, measuring dose profiles as well as the reference dose rate for every new applicator would be recommended.
authors: Department of Radiation Oncology, Seoul National University, Seoul, Korea.
authors: Chang Heon
authors: CH
authors: Choi
authors: Hyon Soo
authors: HS
authors: Han
authors: Kwang-Jae
authors: KJ
authors: Son
authors: Ul Jae
authors: UJ
authors: Park
authors: Jun Sig
authors: JS
authors: Lee
authors: Won Ryang
authors: WR
authors: Wee
authors: Sung Whan
authors: SW
authors: Ha
authors: Il Han
authors: IH
authors: Kim
authors: Sung-Joon
authors: SJ
authors: Ye
mesh_terms: D005123:Eye; D009010:Monte Carlo Method; D010761:Phosphorus Radioisotopes; D011874:Radiometry / Q000295:instrumentation*; D013997:Time Factors
chemical_list: D010761:Phosphorus Radioisotopes