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Title: Dosimetric characterization of a novel intracavitary mold applicator for {sup 192}Ir high dose rate endorectal brachytherapy treatment

Abstract

The dosimetric properties of a novel intracavitary mold applicator for {sup 192}Ir high dose rate (HDR) endorectal cancer treatment have been investigated using Monte Carlo (MC) simulations and experimental methods. The 28 cm long applicator has a flexible structure made of silicone rubber for easy passage into cavities with deep-seated tumors. It consists of eight source catheters arranged around a central cavity for shielding insertion, and is compatible for use with an endocavitary balloon. A phase space model of the HDR source has been validated for dose calculations using the GEANT4 MC code. GAFCHROMIC trade mark sign EBT model film was used to measure dose distributions in water around shielded and unshielded applicators with two loading configurations, and to quantify the shielding effect of a balloon injected with an iodine solution (300 mg I/mL). The film calibration procedure was performed in water using an {sup 192}Ir HDR source. Ionization chamber measurements in a Lucite phantom show that placing a tungsten rod in the applicator attenuates the dose in the shielded region by up to 85%. Inserting the shielded applicator into a water-filled balloon pushes the neighboring tissues away from the radiation source, and the resulting geometric displacement reduces the dosemore » by up to 53%; another 8% dose reduction can be achieved when the balloon is injected with an iodine solution. All experimental results agree with the GEANT4 calculations within measurement uncertainties.« less

Authors:
; ; ; ;  [1];  [2];  [2]
  1. Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4 (Canada)
  2. (Canada)
Publication Date:
OSTI Identifier:
20853819
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 33; Journal Issue: 12; Other Information: DOI: 10.1118/1.2364054; (c) 2006 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; BRACHYTHERAPY; DOSE RATES; FUNGI; IODINE; IONIZATION CHAMBERS; IRIDIUM 192; LUCITE; MONTE CARLO METHOD; NEOPLASMS; PHANTOMS; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; RADIATION SOURCES; RODS; SILICONES; TUNGSTEN

Citation Formats

Poon, Emily, Reniers, Brigitte, Devic, Slobodan, Vuong, Te, Verhaegen, Frank, Department of Radiation Oncology, McGill University Health Center, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4, and Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4. Dosimetric characterization of a novel intracavitary mold applicator for {sup 192}Ir high dose rate endorectal brachytherapy treatment. United States: N. p., 2006. Web. doi:10.1118/1.2364054.
Poon, Emily, Reniers, Brigitte, Devic, Slobodan, Vuong, Te, Verhaegen, Frank, Department of Radiation Oncology, McGill University Health Center, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4, & Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4. Dosimetric characterization of a novel intracavitary mold applicator for {sup 192}Ir high dose rate endorectal brachytherapy treatment. United States. doi:10.1118/1.2364054.
Poon, Emily, Reniers, Brigitte, Devic, Slobodan, Vuong, Te, Verhaegen, Frank, Department of Radiation Oncology, McGill University Health Center, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4, and Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4. Fri . "Dosimetric characterization of a novel intracavitary mold applicator for {sup 192}Ir high dose rate endorectal brachytherapy treatment". United States. doi:10.1118/1.2364054.
@article{osti_20853819,
title = {Dosimetric characterization of a novel intracavitary mold applicator for {sup 192}Ir high dose rate endorectal brachytherapy treatment},
author = {Poon, Emily and Reniers, Brigitte and Devic, Slobodan and Vuong, Te and Verhaegen, Frank and Department of Radiation Oncology, McGill University Health Center, Montreal General Hospital, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4 and Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Quebec H3G 1A4},
abstractNote = {The dosimetric properties of a novel intracavitary mold applicator for {sup 192}Ir high dose rate (HDR) endorectal cancer treatment have been investigated using Monte Carlo (MC) simulations and experimental methods. The 28 cm long applicator has a flexible structure made of silicone rubber for easy passage into cavities with deep-seated tumors. It consists of eight source catheters arranged around a central cavity for shielding insertion, and is compatible for use with an endocavitary balloon. A phase space model of the HDR source has been validated for dose calculations using the GEANT4 MC code. GAFCHROMIC trade mark sign EBT model film was used to measure dose distributions in water around shielded and unshielded applicators with two loading configurations, and to quantify the shielding effect of a balloon injected with an iodine solution (300 mg I/mL). The film calibration procedure was performed in water using an {sup 192}Ir HDR source. Ionization chamber measurements in a Lucite phantom show that placing a tungsten rod in the applicator attenuates the dose in the shielded region by up to 85%. Inserting the shielded applicator into a water-filled balloon pushes the neighboring tissues away from the radiation source, and the resulting geometric displacement reduces the dose by up to 53%; another 8% dose reduction can be achieved when the balloon is injected with an iodine solution. All experimental results agree with the GEANT4 calculations within measurement uncertainties.},
doi = {10.1118/1.2364054},
journal = {Medical Physics},
number = 12,
volume = 33,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
  • Purpose: An integrated software platform was developed to perform a patient-specific dosimetric study on high-dose-rate {sup 192}Ir endorectal brachytherapy. Monte Carlo techniques were used to examine the perturbation effects of an eight-channel intracavitary applicator with shielding and a liquid-inflatable balloon. Such effects are ignored in conventional treatment planning systems that assume water-equivalent geometries. Methods and Materials: A total of 40 Task Group 43-based rectal patient plans were calculated using the PTRAN{sub C}T Monte Carlo photon transport code. The silicone applicator, tungsten or lead shielding, contrast solution-filled balloon, and patient anatomy were included in the simulations. The dose to water andmore » dose to medium were scored separately. The effects of heterogeneities and uncertainties in source positioning were examined. A superposition calculation method using pregenerated Monte Carlo dose distributions about the shielded applicator in water was developed and validated for efficient treatment planning purposes. Results: On average, metal shielding decreases the mean dose to the contralateral normal tissues by 24% and reduces the target volume covered by the prescribed dose from 97% to 94%. Tissue heterogeneities contribute to dose differences of <1% relative to the prescribed dose. The differences in the dose volume indices between dose to water and dose to medium-based calculations were <1% for soft tissues, <2% for bone marrow, and >20% for cortical bone. A longitudinal shift of {+-}2.5 mm and a rotational shift of {+-}15{sup o} in applicator insertion reduced the target volume receiving the prescribed dose by {<=}4%. Conclusion: The shielded applicator improved dose conformity and normal tissue sparing; however, Task Group 43-based treatment planning might compromise target coverage by not accounting for shielding.« less
  • Purpose: Historically, treatment of malignant surface lesions has been achieved with linear accelerator based electron beams or superficial x-ray beams. Recent developments in the field of brachytherapy now allow for the treatment of surface lesions with specialized conical applicators placed directly on the lesion. Applicators are available for use with high dose rate (HDR){sup 192}Ir sources, as well as electronic brachytherapy sources. Part I of this paper discussed the applicators used with electronic brachytherapy sources. Part II will discuss those used with HDR {sup 192}Ir sources. Although the use of these applicators has gained in popularity, the dosimetric characteristics havemore » not been independently verified. Additionally, there is no recognized method of output verification for quality assurance procedures with applicators like these. Methods: This work aims to create a cohesive method of output verification that can be used to determine the dose at the treatment surface as part of a quality assurance/commissioning process for surface applicators used with HDR electronic brachytherapy sources (Part I) and{sup 192}Ir sources (Part II). Air-kerma rate measurements for the {sup 192}Ir sources were completed with several models of small-volume ionization chambers to obtain an air-kerma rate at the treatment surface for each applicator. Correction factors were calculated using MCNP5 and EGSnrc Monte Carlo codes in order to determine an applicator-specific absorbed dose to water at the treatment surface from the measured air-kerma rate. Additionally, relative dose measurements of the surface dose distributions and characteristic depth dose curves were completed in-phantom. Results: Theoretical dose distributions and depth dose curves were generated for each applicator and agreed well with the measured values. A method of output verification was created that allows users to determine the applicator-specific dose to water at the treatment surface based on a measured air-kerma rate. Conclusions: The novel output verification methods described in this work will reduce uncertainties in dose delivery for treatments with these kinds of surface applicators, ultimately improving patient care.« less
  • Purpose: Historically, treatment of malignant surface lesions has been achieved with linear accelerator based electron beams or superficial x-ray beams. Recent developments in the field of brachytherapy now allow for the treatment of surface lesions with specialized conical applicators placed directly on the lesion. Applicators are available for use with high dose rate (HDR){sup 192}Ir sources, as well as electronic brachytherapy sources. Part I of this paper discussed the applicators used with electronic brachytherapy sources. Part II will discuss those used with HDR {sup 192}Ir sources. Although the use of these applicators has gained in popularity, the dosimetric characteristics havemore » not been independently verified. Additionally, there is no recognized method of output verification for quality assurance procedures with applicators like these. Methods: This work aims to create a cohesive method of output verification that can be used to determine the dose at the treatment surface as part of a quality assurance/commissioning process for surface applicators used with HDR electronic brachytherapy sources (Part I) and{sup 192}Ir sources (Part II). Air-kerma rate measurements for the {sup 192}Ir sources were completed with several models of small-volume ionization chambers to obtain an air-kerma rate at the treatment surface for each applicator. Correction factors were calculated using MCNP5 and EGSnrc Monte Carlo codes in order to determine an applicator-specific absorbed dose to water at the treatment surface from the measured air-kerma rate. Additionally, relative dose measurements of the surface dose distributions and characteristic depth dose curves were completed in-phantom. Results: Theoretical dose distributions and depth dose curves were generated for each applicator and agreed well with the measured values. A method of output verification was created that allows users to determine the applicator-specific dose to water at the treatment surface based on a measured air-kerma rate. Conclusions: The novel output verification methods described in this work will reduce uncertainties in dose delivery for treatments with these kinds of surface applicators, ultimately improving patient care.« less
  • Purpose: The aim of this work is the dosimetric validation of a deterministic radiation transport based treatment planning system (BRACHYVISION v. 8.8, referred to as TPS in the following) for multiple {sup 192}Ir source dwell position brachytherapy applications employing a shielded applicator in homogeneous water geometries. Methods: TPS calculations for an irradiation plan employing seven VS2000 {sup 192}Ir high dose rate (HDR) source dwell positions and a partially shielded applicator (GM11004380) were compared to corresponding Monte Carlo (MC) simulation results, as well as experimental results obtained using the VIP polymer gel-magnetic resonance imaging three-dimensional dosimetry method with a custom mademore » phantom. Results: TPS and MC dose distributions were found in agreement which is mainly within {+-}2%. Considerable differences between TPS and MC results (greater than 2%) were observed at points in the penumbra of the shields (i.e., close to the edges of the ''shielded'' segment of the geometries). These differences were experimentally verified and therefore attributed to the TPS. Apart from these regions, experimental and TPS dose distributions were found in agreement within 2 mm distance to agreement and 5% dose difference criteria. As shown in this work, these results mark a significant improvement relative to dosimetry algorithms that disregard the presence of the shielded applicator since the use of the latter leads to dosimetry errors on the order of 20%-30% at the edge of the ''unshielded'' segment of the geometry and even 2%-6% at points corresponding to the potential location of the target volume in clinical applications using the applicator (points in the unshielded segment at short distances from the applicator). Conclusions: Results of this work attest the capability of the TPS to accurately account for the scatter conditions and the increased attenuation involved in HDR brachytherapy applications employing multiple source dwell positions and partially shielded applicators.« less
  • Purpose: This retrospective study analyzed the effect of the activity of high-dose-rate (HDR) {sup 192}Ir source on late rectal bleeding after HDR intracavitary radiotherapy (ICRT) in patients with uterine cervix cancer. Methods and Materials: One hundred thirty-two patients who underwent HDR-ICRT and external beam radiotherapy (EBRT) were analyzed. The rectal point dose in ICRT was calculated by inserting a lead wire into the rectal lumen and summed with the whole-pelvic EBRT dose. The rectal biologic effective dose (BED) was calculated. The relationship between averaged source activity or the BED and late rectal bleeding were analyzed. Results: Three-year actuarial rectal bleedingmore » probabilities were 46% ({>=}100 Gy{sub 3}) and 18% ({<=} 100 Gy{sub 3}), respectively (p < 0.005). When patients were divided into four groups according to rectal BED ({>=} or {<=}100 Gy{sub 3}) and source activity ({>=} or {<=}2.4 cGy.m{sup 2}.h{sup -1}), the group with both a high BED and high activity showed significantly greater probability (58% at 3 years; p < 0.005). It was noted that the probability of the group with BED of 100 Gy{sub 3} or greater was high, but that was not the case with 2.4 cGy.m{sup 2}.h{sup -1} or less. Conclusion: This is the first clinical report concerning the source activity effect of HDR {sup 192}Ir on late rectal bleeding in patients undergoing HDR-ICRT. This suggests that when source activity is higher than 2.4 cGy.m{sup 2}.h{sup -1}, ICRT should be performed with more caution not to exceed 100 Gy{sub 3} in total.« less