Direct measurement of absorbed dose to water in HDR 192Ir brachytherapy: water calorimetry, ionization chamber, Gafchromic film, and TG-43.
OBJECTIVE
Gafchromic film and ionometric calibration procedures for HDR 192Ir brachytherapy sources in terms of dose rate to water are presented and the experimental results are compared to the TG-43 protocol as well as with the absolute dose measurement results from a water calorimetry-based primary standard.


METHODS
EBT-1 Gafchromic films, an A1SL Exradin miniature Shonka thimble type chamber, and an SI HDR 1000 Plus well-type chamber (Standard Imaging, Inc., Middleton, WI) with an ADCL traceable Sk calibration coefficient (following the AAPM TG-43 protocol) were used. The Farmer chamber and Gafchromic film measurements were performed directly in water. All results were compared to direct and absolute absorbed dose to water measurements from a 4 degrees C stagnant water calorimeter.


RESULTS
Based on water calorimetry, the authors measured the dose rate to water to be 361 +/- 7 microGy/(h U) at a 55 mm source-to-detector separation. The dose rate normalized to air-kerma strength for all the techniques agree with the water calorimetry results to within 0.83%. The overall 1-sigma uncertainty on water calorimetry, ionization chamber, Gafchromic film, and TG-43 dose rate measurement amounts to 1.90%, 1.44%, 1.78%, and 2.50%, respectively.


CONCLUSIONS
This work allows us to build a more realistic uncertainty estimate for absorbed dose to water determination using the TG-43 protocol. Furthermore, it provides the framework necessary for a shift from indirect HDR 192Ir brachytherapy dosimetry to a more accurate, direct, and absolute measurement of absorbed dose to water.
Sarfehnia
Arman
A
Medical Physics Unit, McGill University, Montréal General Hospital, Montréal, Québec H3G 1A4, Canada.
Kawrakow
Iwan
I
Seuntjens
Jan
J
D000388:Air; D001918:Brachytherapy / Q000379:methods*; D002151:Calorimetry / Q000379:methods*; D003198:Computer Simulation; D004867:Equipment Design; D005373:Film Dosimetry / Q000379:methods; D006358:Hot Temperature; D006801:Humans; D007496:Iridium Radioisotopes / Q000737:chemistry*; D015233:Models, Statistical; D009369:Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D012984:Software; D013696:Temperature; D014867:Water / Q000737:chemistry
D007496:Iridium Radioisotopes; D014867:Water