Thermoluminescence dosimetry for in-vivo verification of high dose rate brachytherapy for prostate cancer

Abstract

It was the aim of the study to verify dose delivered in urethra and rectum during High Dose Rate brachytherapy boost (HDRBB) of prostate cancer patients. During the first fraction of HDRBB measurement catheters were placed in the urethra and rectum of prostate cancer patients. These contained LiF:Mg,Ti Thermoluminescence Dosimetry (TLD) rods of 1 mm diameter, with up to 11 detectors positioned every 16 mm separated by radio-opaque markers. A Lorentzian peak function was used to fit the data. Measurements from 50 patients were evaluated and measured doses were compared with predictions from the treatment planning system (Plato Vs 13.5 to 14.1). Prospective urinary and rectal toxicity scores were collected following treatment. In more than 90% of cases, the Lorentzian peak function provided a good fit to both experimental and planning urethral data (r2 > 0.9). In general there was good agreement between measured and predicted doses with the average difference between measured and planned maximum dose being 0.1 Gy. No significant association between dose and any clinical endpoints was observed in 43 patients available for clinical evaluation. An average inferior shift of 2 mm between the plan and the measurement performed approximately 1 hour after the planning CT scan was found for the dose distribution in the cohort of patients for the urethra measurements. Rectal measurements proved to be more difficult to interpret as there is more variability of TLD position between planning and treatment. TLD in-vivo measurements are easily performed in urethra and rectum during HDR brachytherapy of prostate patients. They verify the delivery and provide information about the dose delivered to critical structures. The latter may be of particular interest if higher doses are to be given per fraction such as in HDR monotherapy.

AAPM TG 191: Clinical use of luminescent dosimeters: TLDs and OSLDs

“…TLDs have been used for patient measurements during brachytherapy, including in vivo measurements in the urethra and/or rectum, as well as measurements on the skin . However, the bulk of TLD use has related to verification of air kerma strength and measurement of other source parameters of the TG‐43 formalism.…”

In vivo real‐time dosimetric verification in high dose rate prostate brachytherapy

“…4,6 The study conducted by Waldhausl et al, 14 for example, found a difference in dose of greater than 10% in more than 65% of their clinical cases and determined that their method was sufficiently accurate and reproducible for clinical applications provided that the position of the diodes is determined accurately. Toye et al 5 showed a variation between À36 and þ101% for 31 patients with an average difference of 20%.…”

“…Dosimeters that have been used previously or have had their feasibility demonstrated include thermoluminescent dosimeters (TLDs), radiophotoluminescent glass dosimeters (RPLGDs), diamond detectors, semiconductors, scintillators, alanine dosimeters, and metal oxide semiconductor field effect transistors (MOSFETs). [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] A study incorporating TLD rods was performed by Das et al 4 where urethral and rectal dose measurements were performed for 50 patients undergoing a HDRB boost for treatment of prostate cancer. They found overall that the rectal readings have significantly more variability than the urethral measurements, which could be attributed to the possible movement of the catheter containing the detectors within the rectum between acquisition of planning images and treatment delivery.…”

Physics-aspects of dose accuracy in high dose rate (HDR) brachytherapy: source dosimetry, treatment planning, equipment performance and in vivo verification techniques

“…Das et al . [97] reported on the use of LiF:Mg,Ti TLD rods of 1 mm diameter, with up to 11 detectors positioned every 16 mm separated by radio-opaque markers, in catheters within the urethra and rectum of prostate cancer patients. Hsu et al .…”