Validation of an individualized home-made superficial brachytherapy mold applied for deep nonmelanoma skin cancer

BACKGROUND: This study was conducted to evaluate the effect of brachytherapy (BT) customized mold [Condensation silicone elastomer (Protesil(TM))] and its thickness on the dose distribution pattern of deep nonmelanoma skin cancers (NMSC). MATERIALS AND METHODS: Four blocks of mold material were constructed in 5, 10, 15, and 20 mm thickness and 100 × 100 mm(2) area by a plastic cast. The high dose rate (HDR) plus treatment planning system (TPS) (Version 3, Eckert & Ziegler BEBIG Gmbh, Berlin, Germany) with a (60)Co source (model: Co0.A86, EZAG BEBIG, Berlin, Germany) as an high dose rate brachytherapy (HDR-BT) source was used. Solid phantom and MOSFET(TM) and GAFCHROMIC(TM) EBT3 film dosimeters were used for experimental dosimetry of the different thicknesses (up to 20 mm) of BT customized mold. Skin dose and dose to different depths were evaluated. RESULT: The TPS overestimated the calculated dose to the surface. Skin dose can be reduced from 250% to 150% of the prescription dose by increasing mold thickness from 5 mm to 20 mm. There was a 7.7% difference in the calculated dose by TPS and the measured dose by MOSFET. There was a good agreement between film dosimetry, MOSFET detector, and TPS’ results in depths less than 5 mm. CONCLUSION: Each BT department should validate any individualized material chosen to construct the customized surface BT mold. Increasing the mold thickness can treat lesions without overexposing the skin surface. Superficial BT can be recommended as an appropriate treatment option for some deep NMSC lesions (up to 20 mm) with pre-planning considerations employing thicker molds.