Analysis of In-Vivo Dose Measurement of Urethra Using Array MOSFET Detectors and TPS-Calculated Dose in...

The urinary sub-structures, which lie in close proximity to the target, are often not contoured or evaluated during cervical cancer brachytherapy planning. This study aims to investigate the in vivo urethral dose during High-Dose-Rate Interstitial Brachytherapy applications using an array of Metal-Oxide-Semiconductor Field-Effect-Transistor detectors, and to compare the urethral dose recorded during brachytherapy planning with that calculated by the treatment planning system.

Twenty patients with cancer of the cervix, vagina, or vault, from Stage IB to Stage IV, who were treated with external beam radiotherapy (EBRT) and interstitial brachytherapy, were included in the study. The high-risk clinical target volume and organs at risk, such as the urinary bladder, rectum, sigmoid colon, urethra, and periurethra, were delineated. The commercially available linear array MOSFET detector, with each detector and its reader module, was characterized and used in this study. The detector channel was inserted into the Foley's catheter until it reached the neck of the bladder.

The maximum and mean doses received by the urethra were 486.32 ± 105.88 cGy and 246.73 ± 101.43 cGy per fraction, respectively, for the prescription dose of 700 cGy/fraction. The maximum dose received by the periurethra per fraction of brachytherapy was 697.43 ± 165.26 cGy, and the cumulative dose, in terms of Equivalent Dose at 200 cGy (EQD2) received by the periurethral region, including the EBRT dose, was found to be 13,406.1 ± 2,909.17 cGy. The urethral doses calculated by the Treatment Planning System (TPS) were compared with the doses measured by the detector per fraction of brachytherapy during treatment.

The urethral doses calculated by the Treatment Planning System (TPS) were comparable to the doses measured by the MOSFET detector. Urethral dose measurement using an array of MOSFET detectors in patients treated with the Interstitial Brachytherapy (ISBT) technique proved its suitability and ease for measuring urethral dose. A good correlation was observed between the MOSFET-measured dose and the TPS-calculated dose, with a P-value > 0.05.