Validation of an Individualized Home-Made Superficial Brachytherapy Mould Applied for Non-Melanoma Skin Cancer

Purpose: This study was conducted to evaluate the effect of a Brachytherapy (BT) customized mold (Condensation silicone elastomer (Protesil TM )) thickness ,on dose distribution pattern in deeper lesions used for nonmelanoma skin cancers (NMSC).Material and Method: MOSFET TM and GAFCHROMIC TM EBT3 film dosimeters were used for the different thicknesses of a Brachytherapy (BT) customized mold (up to 20 mm), skin dose and dose in different depths were evaluated.Result: The received dose to the surface is overestimated by TPS.Skin dose can be reduced from 250 to 150% of prescription dose by increasing mold thickness from 5 mm to 20 mm. There was a 7.7% difference in calculated dose by TPS and measured dose by MOSFET. Film dosimetry data was unreliable. There was a good agreement between film dosimetry, MOSFET detector, and TPS results, in the depth of 5mm<.Conclusion: Any individualized material chosen to use for making the customized surface BT mold should be validated at BT departments. Protesil TM can be selected as feasible material to make any form of superficial molds. For thicker NMSC lesions up to 20 mm using thicker molds up to 20 mm can be. Even for 10 mm lesions, by changing mold thickness from 5 mm to 20 mm, skin dose would reduce. Protesil TM can be used to make an individualized superficial BT mold. By increasing the mold thickness, lesions can be treated without overexposing the skin surface and skin dose reduced by increasing mold thickness. So, superficial BT can be recommended as an appropriate treatment option for NMSC lesions with some consideration.

Rectal and Bladder Dose Measurements in the Intracavitary Applications of Cervical Cancer Treatment with HDR Afterloading System: Comparison of TPS Data with MOSFET Detector

Background: Intracavitary brachytherapy plays a major role in management of cervical carcinoma. Assessment of dose received by OAR’s therefore becomes crucial for the estimation of radiation toxicities in high dose rate brachytherapy.Objective: The purpose of this study is to evaluate the role of in vivo dosimetry in HDR brachytherapy and to compare the actual doses delivered to OAR’s with those calculated during treatment planning.Materials and Methods: A total of 50 patients were treated with Microselectron HDR. Out of 50 patients, 26 were treated with a dose of 7 Gy and 24 with a dose of 9 Gy, prescribed to point A. Brachytherapy planning and evaluation of dose to the bladder and rectum was done on TPS & in vivo dosimetry was performed using portable MOSFET.Results: The calibration factors calculated for both the dosimeters are almost equal and are 0.984 cGy/mV and 1.0895 cGy/mV. For bladder, dose deviation was found to be within +/- 5% in 28 patients, +/- 5-10% in 14 patients, +/- 10-15% in 4 patients. The deviation between the TPS-calculated dose and the dose measured by MOSFET for rectum was within +/- 5% in 31 patients, +/- 5–10% in 8 patients, and +/- 10–15% in 7 patients.Conclusion: TPS calculated doses were slightly higher than that measured by MOSFET. The use of a small size of MOSFET dosimeter is an efficient method for accurately measuring doses in high-dose gradient fields typically seen in brachytherapy. Therefore, to reduce risk of large errors in the dose delivery, in vivo dosimetry can be done in addition to TPS computations.

Dosimetric impacts on skin toxicity for patients using topical agents and dressings during radiotherapy

Background and purposeSkin care practices for radiotherapy patients are complicated by dosimetric concerns. This study measures the effect on skin dose of various topical agents and dressings.Materials and methodsSuperficial doses were measured under 17 topical agents and dressings and three clinical materials for reference. Dose was measured using a MOSFET detector under a 1 mm polymethyl methacrylate slab, with 6 MV photon beams at 100 cm source to surface distance.ResultsRelative skin dose under reference materials was 128% (thermoplastic mask), 158% (5 mm bolus) and 171% (10 mm bolus). Under a realistic application of topical agent (0·5 mm), relative skin doses were 106–111%. All dry dressings yielded relative dose of ≤111%; two wet dressings yielded higher relative doses (133 and 141%).ConclusionsUnder clinically relevant conditions, no cream, gel or dry dressing increased the skin dose beyond that seen with a thermoplastic mask. Dressings soaked with water produced less skin dose than 5 mm bolus. This may be unacceptable if wet dressings are in place for the majority of the treatment course. Our results suggest that skin care practices should not be limited by dosimetric concerns when using a 6 MV photon beam.

Surface and Buildup Region Dose Measurements with Markus Parallel-Plate Ionization Chamber, GafChromic EBT3 Film, and MOSFET Detector for High-Energy Photon Beams

The aim of the study was to investigate surface and buildup region doses for 6 MV and 15 MV photon beams using a Markus parallel-plate ionization chamber, GafChromic EBT3 film, and MOSFET detector for different field sizes and beam angles. The measurements were made in a water equivalent solid phantom at the surface and in the buildup region of the 6 MV and 15 MV photon beams at 100 cm source-detector distance for 5 × 5, 10 × 10, and 20 × 20 cm2field sizes and 0°, 30°, 60°, and 80° beam angles. The surface doses using 6 MV photon beams for 10 × 10 cm2field size were found to be 20.3%, 18.8%, and 25.5% for Markus chamber, EBT3 film, and MOSFET detector, respectively. The surface doses using 15 MV photon beams for 10 × 10 cm2field size were found to be 14.9%, 13.4%, and 16.4% for Markus chamber, EBT3 film, and MOSFET detector, respectively. The surface dose increased with field size for all dosimeters. As the angle of the incident radiation beam became more oblique, the surface dose increased. The effective measurement depths of dosimeters vary; thus, the results of the measurements could be different. This issue can lead to mistakes at surface and buildup dosimetry and must be taken into account.