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SU‐F‐T‐13: Transit Dose Comparisons for Co‐60 and Ir‐192 HDR Sources
Author(s) -
GimenezAlventosa V,
Vijande J,
Ballester F,
PerezCalatayud J
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4956147
Subject(s) - kerma , brachytherapy , monte carlo method , nuclear medicine , imaging phantom , physics , dosimetry , transit (satellite) , materials science , environmental science , optics , mathematics , medicine , statistics , radiology , engineering , radiation therapy , public transport , transport engineering
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.