# Skin and Lip Brachytherapy: Superficial HDR Techniques ## Introduction Non-melanoma skin cancers (NMSC) affecting the face, scalp, and lip are most commonly treated with surgery. However, radiation therapy serves as an excellent alternative for patients who are poor candidates for surgery or when surgical intervention would cause significant cosmetic or functional impairment. Superficial high-dose-rate (HDR) brachytherapy, utilizing surface applicators and electronic brachytherapy devices, has gained popularity due to its ability to deliver highly conformal, hypofractionated treatment regimens that yield outstanding cosmetic outcomes. ## Indications for Skin Brachytherapy ### Appropriate Lesions Skin brachytherapy is primarily indicated for basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) of the skin. Ideal lesions are typically less than 5 cm in diameter and have a tumor depth of less than 5 mm, including superficial and nodular subtypes. Lesions with well-defined clinical margins are preferred. Additionally, brachytherapy is suitable for lip cancers involving the vermilion border and mucosal lip. ### Patient Selection Patients who are elderly or have significant comorbidities that preclude surgery are good candidates for skin brachytherapy. Lesions located in cosmetically sensitive areas such as the nose, eyelid, ear, and lip benefit from this approach. Brachytherapy is also appropriate for recurrent disease following prior surgery, for multiple synchronous lesions that can be treated sequentially, and for patients who prefer a non-surgical treatment option. ### Contraindications Brachytherapy is generally contraindicated for deeply infiltrative or morpheaform BCC and for lesions with perineural invasion extending beyond the planned treatment volume. Lesions overlying bone or cartilage without adequate soft tissue coverage represent a relative contraindication. Patients with connective tissue disorders such as lupus or scleroderma have increased radiation sensitivity, making brachytherapy less suitable. Prior radiation to the same site is also a relative contraindication, requiring careful evaluation before considering reirradiation. ## Applicator Systems ### Surface Mold Applicators The Leipzig applicator is a cone-shaped HDR surface applicator available in diameters ranging from 1 to 3 cm. It connects to a standard HDR afterloader via a catheter channel. The diameter is selected based on the lesion size plus an additional 0.5 to 1 cm margin. Its flat surface design ensures uniform dose delivery for flat lesions. ### Freiburg Flap Applicator The Freiburg flap applicator consists of a flexible mesh embedded with catheter channels at fixed spacing, allowing it to conform to irregular surfaces such as the nose, ear, and scalp. This design facilitates treatment of larger or irregularly shaped lesions. Treatment planning is CT-based, enabling dose optimization across multiple channels. ### Valencia Applicator Similar to the Leipzig applicator, the Valencia applicator incorporates an internal flattening filter that provides a more uniform dose distribution at the prescription depth. It is available in 2 cm and 3 cm diameters and offers simplified dosimetry compared to multi-channel systems. ### Electronic Brachytherapy Electronic brachytherapy systems, such as the Xoft Axxent, use low-energy x-rays (approximately 50 kV) delivered through a surface applicator. These systems do not require a radioactive source and have minimal shielding requirements, allowing treatments to be performed in office settings. The dose distribution achieved is similar to that of HDR Ir-192 surface applicators. ![Photographs of common skin brachytherapy applicators including Leipzig cones, Valencia applicator, and Freiburg flap system](images/skin-brachy-applicators.jpg) ## Treatment Planning and Dosimetry ### Target Volume The gross tumor volume (GTV) includes the visible or palpable tumor with its clinical margins. The clinical target volume (CTV) encompasses the GTV plus a 5 to 10 mm radial margin to account for microscopic disease. The prescription depth is typically set at 3 to 5 mm from the applicator surface, depending on tumor thickness. For superficial BCC, a depth of 3 mm is standard, whereas thicker SCC lesions may require a 5 mm depth. ### Dose and Fractionation Several dose regimens are acceptable. Common schedules include 40 Gy delivered in 10 fractions (4 Gy per fraction, twice weekly), 36 Gy in 6 fractions (6 Gy per fraction, twice weekly), and 42 Gy in 6 fractions (7 Gy per fraction, twice weekly). In select cases using electronic brachytherapy, a regimen of 34 Gy in 2 fractions (17 Gy per fraction) may be employed. According to the American Brachytherapy Society (ABS) consensus, these regimens deliver a biologically effective dose (BED) roughly equivalent to 60 to 66 Gy in 2 Gy fractions. ### Planning Considerations For single-channel applicators such as Leipzig and Valencia, dose calculations are based on commissioning data. Multi-channel applicators like the Freiburg flap require CT-based three-dimensional planning with dose optimization. It is essential to verify dose uniformity across the treatment surface and to document the dose delivered at depth as well as to underlying structures such as cartilage and bone. ## Lip Cancer Brachytherapy ### Anatomy and Considerations Squamous cell carcinomas of the vermilion border and mucosal lip are ideal candidates for brachytherapy. The interstitial technique involves placing parallel needles or plastic tubes through the lip, while superficial lesions may be treated with surface applicators. This approach yields excellent functional and cosmetic outcomes, preserving oral competence. ### Interstitial Lip Implant Interstitial implants are performed under local or general anesthesia, with plastic tubes or needles placed in parallel and equidistant fashion according to the Paris system dosimetry. The dose typically ranges from 60 to 65 Gy in low-dose-rate (LDR) equivalent or an HDR equivalent delivered in fractionated regimens. HDR lip implants usually involve 40 to 50 Gy delivered in 10 to 15 fractions, with 3 to 4 Gy per fraction. The active length of the implant covers the tumor plus a 1 cm margin. ### Outcomes for Lip Cancer Local control rates for T1-T2 lip cancers treated with brachytherapy range from 90 to 95%. Cosmetic outcomes are often superior to surgery, with preservation of lip function and sensation. Late effects may include mild fibrosis, telangiectasia, and mucosal atrophy. ![Clinical photograph showing interstitial brachytherapy needle placement for lower lip squamous cell carcinoma with treatment plan overlay](images/lip-brachy-implant.jpg) ## Clinical Outcomes ### Local Control For basal cell carcinoma, local control rates at 5 years range from 95 to 98%, while squamous cell carcinoma achieves 90 to 95% local control at 5 years. These outcomes are comparable to those achieved with surgical excision and Mohs surgery. Recurrence is more common in SCC cases with perineural invasion or positive surgical margins. ### Cosmetic Results Excellent or good cosmetic outcomes are reported in 85 to 95% of patients. The best cosmetic results are observed with moderate hypofractionation, typically 3 to 4 Gy per fraction. Very high doses per fraction exceeding 7 Gy may increase the risk of late fibrosis and telangiectasia. Overall, cosmetic results with brachytherapy are generally superior to those achieved with external beam radiation therapy (EBRT) for comparable lesions. ### Toxicity Acute toxicities include erythema and moist desquamation, which are expected and usually heal within 2 to 4 weeks. Late toxicities may involve hypopigmentation, telangiectasia, and soft tissue atrophy, but these effects are generally mild. Cartilage necrosis is rare when appropriate dose constraints are observed, occurring in less than 3 to 5% of nasal lesions. ![Before and after photographs showing cosmetic outcomes at 6 months following HDR surface brachytherapy for nasal basal cell carcinoma](images/skin-brachy-cosmetic-results.jpg) ## Key Clinical Pearls Superficial HDR brachytherapy is an excellent treatment option for non-melanoma skin cancers smaller than 5 cm located in cosmetically sensitive areas, achieving local control rates between 90 and 98%. The choice of applicator depends on lesion size, location, and surface contour; Leipzig and Valencia applicators are preferred for small, flat lesions, while the Freiburg flap is suited for larger or irregular surfaces. The standard prescription depth ranges from 3 to 5 mm based on tumor thickness, with an adequate margin of 5 to 10 mm around the GTV being essential. Moderate hypofractionation, delivering 3 to 4 Gy per fraction, optimizes the balance between local control and cosmetic outcome. Lip cancers are particularly well suited for interstitial brachytherapy, which preserves function and achieves excellent cosmetic results. ## References 1. Ouhib Z, Kasper M, Perez Calatayud J, et al. Aspects of dosimetry and clinical practice of skin brachytherapy: the American Brachytherapy Society working group report. *Brachytherapy*. 2015;14(6):840-858. 2. Guinot JL, Rembielak A, Perez-Calatayud J, et al. GEC-ESTRO ACROP recommendations in skin brachytherapy. *Radiother Oncol*. 2018;126(3):377-385. 3. Delishaj D, Rembielak A, Manfredi B, et al. Non-melanoma skin cancer treated with high-dose-rate brachytherapy: a review of literature. *J Contemp Brachytherapy*. 2016;8(6):533-540. 4. Mazeron JJ, Ardiet JM, Haie-Meder C, et al. GEC-ESTRO recommendations for brachytherapy for head and neck squamous cell carcinomas. *Radiother Oncol*. 2009;91(2):150-156.