Characterization of a fiber‐coupled luminescence dosimetry system for online in vivo dose verification during brachytherapy

Abstract

A prototype of a new dose-verification system has been developed to facilitate prevention and identification of dose delivery errors in remotely afterloaded brachytherapy. The system allows for automatic online in vivo dosimetry directly in the tumor region using small passive detector probes that fit into applicators such as standard needles or catheters. The system measures the absorbed dose rate ͑0.1 s time resolution͒ and total absorbed dose on the basis of radioluminescence ͑RL͒ and optically stimulated luminescence ͑OSL͒ from aluminum oxide crystals attached to optical fiber cables ͑1 mm outer diameter͒. The system was tested in the range from 0 to 4 Gy using a solidwater phantom, a Varian GammaMed Plus 192 Ir PDR afterloader, and dosimetry probes inserted into stainless-steel brachytherapy needles. The calibrated system was found to be linear in the tested dose range. The reproducibility ͑one standard deviation͒ for RL and OSL measurements was 1.3%. The measured depth-dose profiles agreed well with the theoretical expectations computed with the EGSNRC Monte Carlo code, suggesting that the energy dependence for the dosimeter probes ͑relative to water͒ is less than 6% for source-to-probe distances in the range of 2-50 mm. Under certain conditions, the RL signal could be greatly disturbed by the so-called stem signal ͑i.e., unwanted light generated in the fiber cable upon irradiation͒. The OSL signal is not subject to this source of error. The tested system appears to be adequate for in vivo brachytherapy dosimetry.

A review of recent advances in optical fibre sensors forin vivodosimetry during radiotherapy

“…42 A further phantom-based study has indicated the suitability of fibre-coupled Al 2 O 3 : C for brachytherapy with an iridium-192 radiation source. 43 …”

Optical Fibers and Optical Fiber Sensors Used in Radiation Monitoring

“…That is: the RL signal is increasing with the total dose received, and does not depend on the dose rate, acquired dose history or the radiation quantity. If the measurements are done over well defined time intervals, the change of the RL signal corresponding to each time interval is proportional to the dose rate (Andersen , et al, 2009). The equipment was tested with good results (linearity, sensitivity to Cerenkov radiation, reproducibility, angular dependence) under gamma ray, X rays and electron beam irradiation.…”

On the use of a single‐fiber multipoint plastic scintillation detector for 192Ir high‐dose‐rate brachytherapy

“…Many groups have investigated the development of real-time detectors that can be inserted in catheters or anatomical orifices, and various types of detectors have been used (MOSFETs, RL/OSLDs, diodes, plastic scintillators). 3,5,6,[16][17][18][19][20][21][22][23] However, most of these detectors are limited to a single point of measurement, thereby limiting the number of dose measurements that can be performed simultaneously within a spatially constrained region (e.g., in a catheter).…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Since the treatment dose is delivered in a few fractions by a moving radioactive source and high dose gradients are involved, high-dose-rate (HDR) brachytherapy is among the main applications for real-time in vivo dosimetry systems. Many groups have investigated the development of real-time detectors that can be inserted in catheters or anatomical orifices, and various types of detectors have been used (MOSFETs, RL/OSLDs, diodes, plastic scintillators).…”