Room: Exhibit Hall
Purpose: Interstitial technique has been used to treat lip cancer. However, surface applicators have rarely been used since it is very difficult to make skin mold applicators to fit the irregular surface of the lip. We have developed customized surface mold applicators and compared dosimetry with interstitial implant method for HDR skin brachytherapy.
Methods: We retrospectively reviewed 4 patients treated for squamous cell carcinomas in situ of the lower lip. Custom skin mold applicators were made with traditional plaster dental mold or 3D-prining techniques in collaboration with Maxillofacial Prosthetics. The thicknesses of the applicators were 5-10 mm. A planar array of plastic brachytherapy catheters spaced 5-10 mm apart was affixed on the mold applicators. Since the patients were treated with only the surface applicators, interstitial implants were simulated by placing 2-3 virtual needles into the target with the Oncentra Brachy treatment planning system (Elekta Brachytherapy Solutions, Veenendaal, The Netherlands). CT simulation was used to contour the target and to determine the prescription depth. Inverse planning simulated annealing followed by graphical optimization was used to deliver 48-52.5 Gy in 10-16 fractions. Target coverage parameters (D90 and V100) and dose uniformity (V110-200) were obtained from each technique and compared with a paired t-test.
Results: The CTV volumes were measured to be 1-8cc. Similar target coverages were achieved (V100 = 96.7 Â± 2.4% from the custom molds vs. 96.4 Â± 2.3% from the interstitial, P>0.3). However, interstitial technique gave statistically significantly higher V110-V200 (hot spots P<<0.05) and higher D90 (120.6 Â± 13.1%), while the surface mold applicators were producing very uniform dose distributions (D90 = 107.2 Â± 6.7% and lower V110-V200).
Conclusion: Skin mold applicators provided better dosimetry than interstitial implant technique to treat superficial targets. The surface applicators can be customized for each individual patient with dental molding technique.