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Title: SU-F-T-13: Transit Dose Comparisons for Co-60 and Ir-192 HDR Sources

Abstract

Purpose: The purpose of this study is to compare the transit dose due to the movement of high dose rate (HDR) Ir-192 and Co-60 sources along the transfer tube. This is performed by evaluating air-kerma differences in the vicinity of the transfer tube when both sources are moved with the same velocity from a HDR brachytherapy afterloader into a patient. Methods: Monte Carlo simulations have been performed using PENELOPE2014. mHDR-v2 and Flexisource sources have been considered. Collisional kerma has been scored. The sources were simulated within a plastic catheter located in an infinite air phantom. The movement of the seed was included by displacing their positions along the connecting catheter from z=−75 cm to z=+75 cm and combining them. Backscatter from the afterloader and the patient was not considered. Since modern afterloaders like Flexitron (Elekta) or Saginova (Bebig) are able to use equally Ir-192 and Co-60 sources it was assumed that both sources are displaced with equal speed. Typical content activity values were provided by the manufacturer (460 GBq for Ir-192 and 75 GBq for Co-60). Results: 2D distributions were obtained with type-A uncertainties (k=2) less than 0.01%. From those, the air kerma ratio Co-60/Ir-192 was evaluated weighted by theirmore » corresponding activities. It was found that it varies slowly with distance (less than 10% variation) but strongly in time due to the shorter half-life of the Ir-192 (73.83 days). The maximum ratio is located close to the catheter with a value of 0.57 when both sources are installed by the manufacturer, while increasing up to 1.25 at the end of the recommended working life (90 days) of the Ir-192 source. Conclusion: Air-kerma ratios are almost constant (0.51–0.57) in the vicinity of the source. Nevertheless, air-kerma ratios increase rapidly whenever the Ir-192 is approaching the end of its life.« less

Authors:
;  [1];  [2];  [3]
  1. University of Valencia, Burjassot (Spain)
  2. University of Valencia and IFIC(CSIC-UV), Burjassot (Spain)
  3. Hospital Clinica Benidorm, Benidorm, and Hospital Universitari i Politecnic La Fe, Valencia (Spain)
Publication Date:
OSTI Identifier:
22642263
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; BRACHYTHERAPY; COBALT 60; DOSE RATES; HALF-LIFE; IRIDIUM 192; KERMA; MONTE CARLO METHOD; PATIENTS; PHANTOMS; RADIATION DOSES

Citation Formats

Gimenez-Alventosa, V, Ballester, F, Vijande, J, and Perez-Calatayud, J. SU-F-T-13: Transit Dose Comparisons for Co-60 and Ir-192 HDR Sources. United States: N. p., 2016. Web. doi:10.1118/1.4956147.
Gimenez-Alventosa, V, Ballester, F, Vijande, J, & Perez-Calatayud, J. SU-F-T-13: Transit Dose Comparisons for Co-60 and Ir-192 HDR Sources. United States. doi:10.1118/1.4956147.
Gimenez-Alventosa, V, Ballester, F, Vijande, J, and Perez-Calatayud, J. 2016. "SU-F-T-13: Transit Dose Comparisons for Co-60 and Ir-192 HDR Sources". United States. doi:10.1118/1.4956147.
@article{osti_22642263,
title = {SU-F-T-13: Transit Dose Comparisons for Co-60 and Ir-192 HDR Sources},
author = {Gimenez-Alventosa, V and Ballester, F and Vijande, J and Perez-Calatayud, J},
abstractNote = {Purpose: The purpose of this study is to compare the transit dose due to the movement of high dose rate (HDR) Ir-192 and Co-60 sources along the transfer tube. This is performed by evaluating air-kerma differences in the vicinity of the transfer tube when both sources are moved with the same velocity from a HDR brachytherapy afterloader into a patient. Methods: Monte Carlo simulations have been performed using PENELOPE2014. mHDR-v2 and Flexisource sources have been considered. Collisional kerma has been scored. The sources were simulated within a plastic catheter located in an infinite air phantom. The movement of the seed was included by displacing their positions along the connecting catheter from z=−75 cm to z=+75 cm and combining them. Backscatter from the afterloader and the patient was not considered. Since modern afterloaders like Flexitron (Elekta) or Saginova (Bebig) are able to use equally Ir-192 and Co-60 sources it was assumed that both sources are displaced with equal speed. Typical content activity values were provided by the manufacturer (460 GBq for Ir-192 and 75 GBq for Co-60). Results: 2D distributions were obtained with type-A uncertainties (k=2) less than 0.01%. From those, the air kerma ratio Co-60/Ir-192 was evaluated weighted by their corresponding activities. It was found that it varies slowly with distance (less than 10% variation) but strongly in time due to the shorter half-life of the Ir-192 (73.83 days). The maximum ratio is located close to the catheter with a value of 0.57 when both sources are installed by the manufacturer, while increasing up to 1.25 at the end of the recommended working life (90 days) of the Ir-192 source. Conclusion: Air-kerma ratios are almost constant (0.51–0.57) in the vicinity of the source. Nevertheless, air-kerma ratios increase rapidly whenever the Ir-192 is approaching the end of its life.},
doi = {10.1118/1.4956147},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • The purpose was to measure the transit dose produced by a moving high dose rate brachytherapy source and assess its clinical significance. The doses produced from source movement during Ir-192 HDR afterloading were measured using calibrated thermoluminescent dosimeter rods. Transit doses at distances of 0.5-4.0 cm from an endobronchial applicator were measured using a Lucite phantom accommodating 1 x 1 x 6 mm thermoluminescent rods. Surface transit dose measurements were made using esophageal and endobronchial catheters, a gynecologic tandem, and an interstitial needle. No difference was detected in thermoluminescent dosimeter rod responses to 4 MV and Ir-192 spectra (427 nC/Gy)more » in a range of dose between 2 and 300 cGy. The transit dose at 0.5 cm from an endobronchial catheter was 0.31 cGy/(Curie-fraction) and followed an inverse square fall-off with increasing distance. Surface transit doses ranged from 0.38 cGy/(Curie-fraction) for an esophageal catheter to 1.03 cGy/(Curie-fraction) for an endobronchial catheter. Source velocity is dependent on the interdwell distance and varies between 220-452 mm/sec. A numeric algorithm was developed to calculate total transit dose, and was based on a dynamic point approximation for the moving high dose rate source. This algorithm reliably predicted the empirical transit doses and demonstrated that total transit dose is dependent on source velocity, number of fractions, and source activity. Surface transit doses are dependent on applicator diameter and wall material and thickness. Total transit doses within or outside the desired treatment volume are typically <100 cGy, but may exceed 200 cGy when using a large number of fractions with a high activity source. 9 refs., 8 figs., 1 tab.« less
  • In this paper the belief that machine energy consumption is now the major cause of environmental heat problems in working districts is questioned. Attention is drawn to the fact that more mechanization means not only more power but more coal and greater rates of advance. If the coal cools appreciably in transit it releases heat at a high rate. The misleading nature of heat analyses which fail to take account of the storage potential of steelwork in a modern district is discussed. The results of a field investigation to explore the contribution of transit coal seemed to show that whenmore » coal was being produced 60 percent of the heat transferred was from the coal, with the balance from the machinery. The authors conclude that in deep mines the strata and cooling coal could make major contributions in roadways in high-output districts, with face machinery performing an important topping-up function.« less