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Title: Quality assurance of HDR {sup 192}Ir sources using a Fricke dosimeter

Abstract

A prototype of a Fricke dosimetry system consisting of a 15x15x15 cm{sup 3} water phantom made of Plexiglas registered and a 11.3-ml Pyrex balloon fitted with a 0.2 cm thick Pyrex sleeve in its center was created to assess source strength and treatment planning algorithms for use in high dose rate (HDR) {sup 192}Ir afterloading units. In routine operation, the radioactive source is positioned at the end of a sleeve, which coincides with the center of the spherical balloon that is filled with Fricke solution, so that the solution is nearly isotropically irradiated. The Fricke system was calibrated in terms of source strength against a reference well-type ionization chamber, and in terms of radial dose by means of an existing algorithm from the HDR's treatment planning system. Because the system is based on the Fricke dosimeter itself, for a given type and model of {sup 192}Ir source, the system needs initial calibration but no recalibration. The results from measurements made over a 10 month period, including source decay and source substitutions, have shown the feasibility of using such a system for quality control (QC) of HDR afterloading equipment, including both the source activity and treatment planning parameters. The benefit ofmore » a large scale production and the use of this device for clinical HDR QC audits via mail are also discussed.« less

Authors:
; ; ; ;  [1];  [2];  [3]
  1. Brody School of Medicine, East Carolina University, Department of Radiation Oncology, 600 Moye Boulevard, Greenville, North Carolina 27858 (United States)
  2. (Brazil)
  3. (United States)
Publication Date:
OSTI Identifier:
20951152
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 4; Other Information: DOI: 10.1118/1.2714472; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; AFTERLOADING; ALGORITHMS; BRACHYTHERAPY; DOSEMETERS; DOSIMETRY; IONIZATION CHAMBERS; IRIDIUM; IRIDIUM 192; PHANTOMS; PLANNING; PLEXIGLAS; PYREX; QUALITY ASSURANCE; QUALITY CONTROL

Citation Formats

Austerlitz, C., Mota, H., Almeida, C. E., Allison, R., Sibata, C., Universidade Estadual do Rio de Janeiro, Rua Sao Franciso Xavier, 524-Maracana, Rio de Janeiro, RJ, and Brody School of Medicine, East Carolina University, Department of Radiation Oncology, 600 Moye Boulevard, Greenville, North Carolina 27858. Quality assurance of HDR {sup 192}Ir sources using a Fricke dosimeter. United States: N. p., 2007. Web. doi:10.1118/1.2714472.
Austerlitz, C., Mota, H., Almeida, C. E., Allison, R., Sibata, C., Universidade Estadual do Rio de Janeiro, Rua Sao Franciso Xavier, 524-Maracana, Rio de Janeiro, RJ, & Brody School of Medicine, East Carolina University, Department of Radiation Oncology, 600 Moye Boulevard, Greenville, North Carolina 27858. Quality assurance of HDR {sup 192}Ir sources using a Fricke dosimeter. United States. doi:10.1118/1.2714472.
Austerlitz, C., Mota, H., Almeida, C. E., Allison, R., Sibata, C., Universidade Estadual do Rio de Janeiro, Rua Sao Franciso Xavier, 524-Maracana, Rio de Janeiro, RJ, and Brody School of Medicine, East Carolina University, Department of Radiation Oncology, 600 Moye Boulevard, Greenville, North Carolina 27858. Sun . "Quality assurance of HDR {sup 192}Ir sources using a Fricke dosimeter". United States. doi:10.1118/1.2714472.
@article{osti_20951152,
title = {Quality assurance of HDR {sup 192}Ir sources using a Fricke dosimeter},
author = {Austerlitz, C. and Mota, H. and Almeida, C. E. and Allison, R. and Sibata, C. and Universidade Estadual do Rio de Janeiro, Rua Sao Franciso Xavier, 524-Maracana, Rio de Janeiro, RJ and Brody School of Medicine, East Carolina University, Department of Radiation Oncology, 600 Moye Boulevard, Greenville, North Carolina 27858},
abstractNote = {A prototype of a Fricke dosimetry system consisting of a 15x15x15 cm{sup 3} water phantom made of Plexiglas registered and a 11.3-ml Pyrex balloon fitted with a 0.2 cm thick Pyrex sleeve in its center was created to assess source strength and treatment planning algorithms for use in high dose rate (HDR) {sup 192}Ir afterloading units. In routine operation, the radioactive source is positioned at the end of a sleeve, which coincides with the center of the spherical balloon that is filled with Fricke solution, so that the solution is nearly isotropically irradiated. The Fricke system was calibrated in terms of source strength against a reference well-type ionization chamber, and in terms of radial dose by means of an existing algorithm from the HDR's treatment planning system. Because the system is based on the Fricke dosimeter itself, for a given type and model of {sup 192}Ir source, the system needs initial calibration but no recalibration. The results from measurements made over a 10 month period, including source decay and source substitutions, have shown the feasibility of using such a system for quality control (QC) of HDR afterloading equipment, including both the source activity and treatment planning parameters. The benefit of a large scale production and the use of this device for clinical HDR QC audits via mail are also discussed.},
doi = {10.1118/1.2714472},
journal = {Medical Physics},
number = 4,
volume = 34,
place = {United States},
year = {Sun Apr 15 00:00:00 EDT 2007},
month = {Sun Apr 15 00:00:00 EDT 2007}
}
  • A ring-shaped Fricke device was developed to measure the absolute dose on the transverse bisector of a {sup 192}Ir high dose rate (HDR) source at 1 cm from its center in water, D(r{sub 0},{theta}{sub 0}). It consists of a polymethylmethacrylate (PMMA) rod (axial axis) with a cylindrical cavity at its center to insert the {sup 192}Ir radioactive source. A ring cavity around the source with 1.5 mm thickness and 5 mm height is centered at 1 cm from the central axis of the source. This ring cavity is etched in a disk shaped base with 2.65 cm diameter and 0.90more » cm thickness. The cavity has a wall around it 0.25 cm thick. This ring is filled with Fricke solution, sealed, and the whole assembly is immersed in water during irradiations. The device takes advantage of the cylindrical geometry to measure D(r{sub 0},{theta}{sub 0}). Irradiations were performed with a Nucletron microselectron HDR unit loaded with an {sup 192}Ir Alpha Omega radioactive source. A Spectronic 1001 spectrophotometer was used to measure the optical absorbance using a 1 mL quartz cuvette with 1.00 cm light pathlength. The PENELOPE Monte Carlo code (MC) was utilized to simulate the Fricke device and the {sup 192}Ir Alpha Omega source in detail to calculate the perturbation introduced by the PMMA material. A NIST traceable calibrated well type ionization chamber was used to determine the air-kerma strength, and a published dose-rate constant was used to determine the dose rate at the reference point. The time to deliver 30.00 Gy to the reference point was calculated. This absorbed dose was then compared to the absorbed dose measured by the Fricke solution. Based on MC simulation, the PMMA of the Fricke device increases the D(r{sub 0},{theta}{sub 0}) by 2.0%. Applying the corresponding correction factor, the D(r{sub 0},{theta}{sub 0}) value assessed with the Fricke device agrees within 2.0% with the expected value with a total combined uncertainty of 3.43%(k=1). The Fricke device provides a promising method towards calibration of brachytherapy radiation sources in terms of D(r{sub 0},{theta}{sub 0}) and audit HDR source calibrations.« less
  • {sup 169}Yb has received a renewed focus lately as an alternative to {sup 192}Ir sources for high dose rate (HDR) brachytherapy. Following the results of a recent work by our group which proved {sup 169}Yb to be a good candidate for HDR prostate brachytherapy, this work seeks to quantify the radiation shielding requirements for {sup 169}Yb HDR brachytherapy applications in comparison to the corresponding requirements for the current {sup 192}Ir HDR brachytherapy standard. Monte Carlo simulation (MC) is used to obtain {sup 169}Yb and {sup 192}Ir broad beam transmission data through lead and concrete. Results are fitted to an analyticalmore » equation which can be used to readily calculate the barrier thickness required to achieve a given dose rate reduction. Shielding requirements for a HDR brachytherapy treatment room facility are presented as a function of distance, occupancy, dose limit, and facility workload, using analytical calculations for both {sup 169}Yb and {sup 192}Ir HDR sources. The barrier thickness required for {sup 169}Yb is lower than that for {sup 192}Ir by a factor of 4-5 for lead and 1.5-2 for concrete. Regarding {sup 169}Yb HDR brachytherapy applications, the lead shielding requirements do not exceed 15 mm, even in highly conservative case scenarios. This allows for the construction of a lead door in most cases, thus avoiding the construction of a space consuming, specially designed maze. The effects of source structure, attenuation by the patient, and scatter conditions within an actual treatment room on the above-noted findings are also discussed using corresponding MC simulation results.« less
  • Purpose: Accelerated partial breast irradiation via interstitial balloon brachytherapy is a fast and effective treatment method for certain early stage breast cancers. The radiation can be delivered using a conventional high-dose rate (HDR) {sup 192}Ir gamma-emitting source or a novel electronic brachytherapy (eBx) source which uses lower energy x rays that do not penetrate as far within the patient. A previous study [A. Dickler, M. C. Kirk, N. Seif, K. Griem, K. Dowlatshahi, D. Francescatti, and R. A. Abrams, ''A dosimetric comparison of MammoSite high-dose-rate brachytherapy and Xoft Axxent electronic brachytherapy,'' Brachytherapy 6, 164-168 (2007)] showed that the target dosemore » is similar for HDR {sup 192}Ir and eBx. This study compares these sources based on the dose received by healthy organs and tissues away from the treatment site. Methods: A virtual patient with left breast cancer was represented by a whole-body, tissue-heterogeneous female voxel phantom. Monte Carlo methods were used to calculate the dose to healthy organs in a virtual patient undergoing balloon brachytherapy of the left breast with HDR {sup 192}Ir or eBx sources. The dose-volume histograms for a few organs which received large doses were also calculated. Additional simulations were performed with all tissues in the phantom defined as water to study the effect of tissue inhomogeneities. Results: For both HDR {sup 192}Ir and eBx, the largest mean organ doses were received by the ribs, thymus gland, left lung, heart, and sternum which were close to the brachytherapy source in the left breast. eBx yielded mean healthy organ doses that were more than a factor of {approx}1.4 smaller than for HDR {sup 192}Ir for all organs considered, except for the three closest ribs. Excluding these ribs, the average and median dose-reduction factors were {approx}28 and {approx}11, respectively. The volume distribution of doses in nearby soft tissue organs that were outside the PTV were also improved with eBx. However, the maximum dose to the closest rib with the eBx source was 5.4 times greater than that of the HDR {sup 192}Ir source. The ratio of tissue-to-water maximum rib dose for the eBx source was {approx}5. Conclusions: The results of this study indicate that eBx may offer lower toxicity to most healthy tissues, except nearby bone. TG-43 methods have a tendency to underestimate dose to bone, especially the ribs. Clinical studies evaluating the negative health effects caused by irradiating healthy organs are needed so that physicians can better understand when HDR {sup 192}Ir or eBx might best benefit a patient.« less
  • In Brazil there are over 100 high dose rate (HDR) brachytherapy facilities using well-type chambers for the determination of the air kerma rate of {sup 192}Ir sources. This paper presents the methodology developed and extensively tested by the Laboratorio de Ciencias Radiologicas (LCR) and presently in use to calibrate those types of chambers. The system was initially used to calibrate six well-type chambers of brachytherapy services, and the maximum deviation of only 1.0% was observed between the calibration coefficients obtained and the ones in the calibration certificate provided by the UWADCL. In addition to its traceability to the Brazilian Nationalmore » Standards, the whole system was taken to University of Wisconsin Accredited Dosimetry Calibration Laboratory (UWADCL) for a direct comparison and the same formalism to calculate the air kerma was used. The comparison results between the two laboratories show an agreement of 0.9% for the calibration coefficients. Three Brazilian well-type chambers were calibrated at the UWADCL, and by LCR, in Brazil, using the developed system and a clinical HDR machine. The results of the calibration of three well chambers have shown an agreement better than 1.0%. Uncertainty analyses involving the measurements made both at the UWADCL and LCR laboratories are discussed.« less
  • New in vivo dosimetry methods would be useful for clinical HDR brachytherapy. An implantable MOSFET Dose Verification System designed by Sicel Technologies, Inc. was examined for use with {sup 192}Ir HDR applications. This investigation demonstrated that varying the dose rate from 22 to 84 cGy/min did not change detector response. The detectors exhibited a higher sensitivity to {sup 192}Ir energies than {sup 60}Co energies. A nonlinear accumulated dose effect was characterized by three third-order polynomials fit to data from detectors placed at three different distances from the source. The detectors were found to have minimal rotational angular dependence. A strongmore » longitudinal angular dependence was found when the detector's copper coil and electronics assembly were aligned between the MOSFETs and incident radiation. This orientation showed a 16% decrease in response relative to other orientations tested.« less