Kiyotaka Kakei

Measurement of absorbed dose-to-water for an HDR 192Ir source with ionization chambers in a sandwich setup

PURPOSE In this study, a dedicated device for ion chamber measurements of absorbed dose-to-water for a Nucletron microSelectron-v2 HDR (192)Ir brachytherapy source is presented. The device uses two ionization chambers in a so-called sandwich assembly. Using this setup and by taking the average reading of the two chambers, any dose error due to difficulties in absolute positioning (centering) of the source in between the chambers is cancelled to first order. The methods accuracy was examined by comparing measurements with absorbed dose-to-water determination based on the AAPM TG-43 protocol. METHODS The optimal source-to-chamber distance (SCD) for (192)Ir dosimetry was determined from ion chamber measurements in a water phantom. The (192)Ir source was sandwiched between two Exradin A1SL chambers (0.057 cm(3)) at the optimal SCD separation. The measured ionization was converted to the absorbed dose-to-water using a (60)Co calibration factor and a Monte Carlo-calculated beam quality conversion factor, kQ, for (60)Co to (192)Ir. An uncertainty estimate of the proposed method was determined based on reproducibility of measurements at different institutions for the same type of source. RESULTS The optimal distance for the A1SL chamber measurements was determined to be 5 cm from the (192)Ir source center, considering the depth dependency of kQ for (60)Co to (192)Ir and the chamber positioning. The absorbed dose to water measured at (5 cm, 90°) on the transverse axis was 1.3% lower than TG-43 values and its reproducibility and overall uncertainty were 0.8% and 1.7%, respectively. The measurement doses at anisotropic points agreed within 1.5% with TG-43 values. CONCLUSIONS The ion chamber measurement of absorbed dose-to-water with a sandwich method for the (192)Ir source provides a more accurate, direct, and reference dose compared to the dose-to-water determination based on air-kerma strength in the TG-43 protocol. Due to the simple but accurate assembly, the sandwich measurement method is useful for daily dose management of (192)Ir sources.

Radiation exposure of operator performing interventional procedures using a flat panel angiography system: evaluation with photoluminescence glass dosimeters

PurposeUsing glass rod dosimeters we investigated the radiation dose to the operator performing interventional procedures in 43 patients with the aid of a monoplane flat detector-based angiography system.Materials and methodsDuring the procedures we recorded the number of radiographic frames and the radiographic conditions. After treatment we recorded the fluoroscopy time and the fluoroscopic, radiographic, and total air kerma. To obtain the total operator exposure dose we took measurements at five sites: left orbital fossa, thyroid, left hand, left chest, and pubic symphysis.ResultsThe mean operator exposure dose to the left hand was higher than at the other sites we measured; it was 387.0, 209.6, 174.3, and 237.1 μGy for the stentgraft, percutaneous transluminal arteriography, transarterial chemoembolization, and hepatic infusion port placement procedures. There was a positive correlation between the fluoroscopic and radiographic air kerma value and the operator exposure dose at the left orbital fossa, thyroid, and left hand.ConclusionThe operator exposure dose correlated with the radiographic and fluoroscopic air kerma. Exposure of the operator’s left hand was higher than at the other sites studied.

Absorbed dose-to-water measurement of an HDR 192Ir source with Farmer ionization chambers in a sandwich setup

This study extends a sandwich method for ion chamber measurements of absorbed dose to water of a Nucletron microSelectron-v2 high dose rate (HDR) 192Ir brachytherapy source presented in the previous paper (Araki et al 2013 Med. Phys. 40 092101) to Farmer-type ion chambers. The goal in this study is to verify the calculation dose based on the AAPM TG-43 protocol by direct absorbed dose-to-water measurement with the Farmer chamber. The measurement device uses two Farmer chambers in a so-called sandwich assembly. A microSelectron-v2 HDR 192Ir source and a PTW30013 Farmer chamber were modeled with the EGSnrc/egs_chamber code and its beam quality conversion factor, kIr, for 60Co to 192Ir was calculated as a function of a distance from the 192Ir source. From calculation results, the optimal distance for the Farmer chamber measurements was determined to be 8 cm from the 192Ir source center, considering the depth dependency of kIr and the chamber positioning, and the required measurement time. The developed device consists of 1 mm-thick poly-methyl methacrylate (PMMA) waterproof sleeves located at both sides of the 192Ir source with a separation of 16 cm. The chamber readings measured with the Farmer chambers inserted into the PMMA sleeves were converted to the absorbed dose to water using a 60Co calibration factor and kIr. The average dose of two Farmer chamber measurements was compared with values based on TG-43 for eight different 192Ir sources at four institutes. kIr for the PTW30013 Farmer chamber ranged from 1.174 to 0.985 at distances of 1.5–10 cm from the source and it was 0.992 at a distance of 8 cm. The measured dose to water was 0.73% lower than TG-43 values and its reproducibility, the chamber positioning accuracy, and the combined standard uncertainty were 0.28%, 0.25%, and 0.68%, respectively. The sandwich measurement with the more popular Farmer chamber is useful and convenient for daily dose management of 192Ir sources in clinics.

SU‐E‐T‐102: Measurement of Absorbed Dose‐To‐Water for An HDR Ir‐192 Source with a Farmer Ionization Chamber in a Sandwich Setup

PURPOSE This study developed a dedicated device for ion chamber measurements of absorbed dose-to-water for an HDR Ir-192 brachytherapy source. The device uses two Farmer chambers in a so-called sandwich assembly. The accuracy of the sundwich method was examined by comparing chamber measurements with absorbed dose-to-water determination based on the AAPM TG-43 protocol. METHODS A microSelectron-v2 HDR Ir-192 source was modeled with the EGSnrc/egs_chamber code. The accuracy of modeling was confirmed by comparing calculated results for gL(r) and F(r, θ) with those of TG-43. The PTW30013 Framer chamber was also modeled with the egs_chamber code and its beam quality conversion factors, kQ, of Ir-192 to Co-60 were calculated as a function of distance from the Ir-192 source. From calculation results, we developed a dedicated device for the sandwich setup with 1 mm PMMA waterproof sleeves located at both side of 8 cm from the Ir-192 source. The chamber readings measured with the Farmer chambers inserted into the 1 mm PMMA sleeves were converted to the absorbed dose to water using kQ. The average dose of two Farmer chamber measurements with the sandwich setup were compared with the TPS values based on TG-43 for eight Ir-192 sources at four institutes. RESULTS Calculated gL(r) and F(r, θ) values agreed well with those of TG-43. The calculated kQ values for the PTW30013 Framer chamber ranged from 1.103 to 0.986 at distance of 2∼10 cm from the source and it was 0.992 at distance of 8 cm. The doses to water measured with the sandwich setup were -0.73 +/- 0.28% (n=10) compared to TG-43 values. CONCLUSION The dose to water measurement by the Farmer chamber with the sandwich setup is useful for daily dose management for Ir-192 sources.

SU‐E‐T‐117: Absorbed Dose to Water Measurement with a Sandwich Method for High Dose‐Rate Ir‐192 Brachytherapy Sources

Purpose: This study aimed to establish a standard dosimetry protocol for HDR Ir‐192 sources using an ion chamber calibrated with a Co‐60 beam. We developed a dedicated device for ion chambermeasurements with a sandwich method and examined its measurement accuracy. Methods: A microSelectron‐v2 HDR Ir‐192 source was modeled with the EGSnrc/egs_chamber code. The accuracy of modeling was confirmed by comparing calculated results for gL (r) and F(r, angle) with those of TG‐43. First, an optimal source‐to‐chamber (SCD) separation for Ir‐192 dosimetry was determined from measurements with a PTW 31010 chamber at distances of 1.5–5 cm from the source center in water. The measuredionization chamber reading was corrected with the Monte Carlo‐calculated energy response for Co‐60 and Ir‐192, and was converted to the absorbed dose to water. The measureddoses were compared with TPS values based on TG‐43. We developed a dedicated device for ion chambermeasurements with a sandwich method at the optimal SCD separation. The average dosemeasured with two EXRADIN A1SL chambers was compared with the TPS value. Results: Calculated gL (r) and F(r, angle) values agreed well withthose of TG‐43. The absorbed dose to watermeasured with the PTW31010 chamber was 3% lower than that of TPS at a distance of 5 cm and was 3%– 7% lower at distances less than 5 cm. This was addressed to the uncertainty of the chamber positioning. We made a sandwich measurement device with the separation of 5 cm, considering the uncertainty of positioning and measurement time. The dose to water with the sandwich method was in agreement with that of TG‐43 within −1.2%. Conclusions: The optimal distance for ion chambermeasurements was at 5 cm from the Ir‐192 source. The dose to watermeasurement with the sandwich method is useful for daily dose management for Ir‐192 sources.