Superficial tumours of head and neck region (T1-T2N0 M0) over accessible sites like hard palate, hard-soft palate junction or over the skin like cheek, nose, and ear were considered for treatment with SMB. The decision of treating with SMB was undertaken after reviewing the disease site, and discussing with the medical physicist and mould room technician regarding feasibility of the procedure and possibility of adequate target volume coverage. For patients with primary over hard palate or soft palate, additional consultation with the dental department was done regarding preparation of the dental carrier material.

The workflow of procedure for SMB is shown in Figure 1. Customized mould was made for each patient. Gross tumour with 1 cm margin was considered as the clinical target volume and was marked on the patient. First component of SMB included preparation of the carrier material. The area, over which the cast was to be prepared, was marked over the skin. For tumours located over skin, a negative impression was made using dental alginate material (Alginate Dental Impression Material, The Bombay Burmah Trading Corporation Ltd.) (Figure 2A). Stone cast or plaster of Paris cast was used to remove the alginate. The negative impression was obtained by removing the assembly after 15 to 20 minutes. The positive cast using stone cast (kalstone) powder was made by filling the hollow of the alginate cast, which was then kept for 10-15 hours. The carrier material (2 mm thick) was made by use of self-curing dental acrylic material to cover the target area and a part of the body contour surrounding it. As per necessities, velcro straps were attached to the carrier for comfortable fitting during treatment (Figure 2B). For intra-oral tumours, the carrier prosthesis was made using similar procedure of negative and positive cast making in the dental department (Figure 2C). A dental obturator was made over the positive cast, which was used as a carrier material.

Wax sheets were applied over the carrier material for reinforcement of the catheters to obtain a distance of 5 mm from the surface. Nylon catheters were placed over the wax at a spacing of 10 mm to ensure coverage of the target volume. After the catheters were fixed to the carrier, the entire assembly was tested over the patient for proper fitting (Figure 2B, 2D).

Three dimensional computed tomography (CT) based planning was done using thin CT slices of 1 to 1.25 mm slice thickness on Somatom Emotion (Siemens Medical Systems, Germany). To ensure proper visualization, metallic markers or thin copper wires were placed at the edges of the tumour and in the tubes. On the planning scan, the proper fitting of the mould material was verified, and in case of improper fitting with intervening air gaps, repeat images were undertaken or the entire procedure was repeated on some occasions. Planning was done using Oncentra brachytherapy version 3.3 and 4.1 (Nucletron, an Elekta company, Elekta AB, Stockholm, Sweden). Catheter reconstruction was done using multiplanar reconstruction, and loading was decided based on the target volume marked on patient. Dose points were defined at 5-7 mm from the source and dose distribution was obtained. Dose point optimization was done for all the patients. Evaluation of the plan was done with slice-by-slice visualization of the target coverage. Dose was prescribed at 100% isodose line in 33 patients and at 85% in 2 patients. Parameters such as V₁₀₀, V₁₅₀, V₂₀₀, and dose homogeneity index (DHI) were evaluated for each patient. In SMB, majority of V₁₅₀ and V₂₀₀ were observed inside the carrier prosthesis, and hence had little impact on the plan evaluation process. Dose per fraction of 3-4 Gy, twice daily, 6 hours apart was considered. Total dose ranged from 38.5 Gy to 52.5 Gy in 11-15 fractions in radical setting, and 15-30 Gy in 5-10 fractions as boost.

Radical brachytherapy was considered for tumours of skin and T1 tumours of intraoral region. The aim was to deliver doses of 54-60 Gy equivalent dose of 2 Gy (EQD₂) (Table 1). Combined external beam radiotherapy (EBRT) and SMB boost was considered in intraoral tumours with T2 lesions. The external beam radiotherapy was considered prior to SMB to a dose ranging from 44 to 60 Gy (median, 50 Gy) at 2 Gy per fraction. In these patients, the aim was to achieve total combined dose of 66-72 Gy EQD₂ (Table 1). The appropriate fitting of the mould was verified and presence of airgap checked clinically before each fraction by the treating radiation oncologist.

On completion of the treatment, in case of skin reactions, patients were prescribed topical steroid creams. The radiation related toxicities were classified according to the Radiation Therapy Oncology Group (RTOG) grading system. The first review was done at 2 weeks from completion, then at 6 weeks, and subsequently every 3 months, till 2 years and then 6 monthly. On follow-up, detailed clinical examination was undertaken and further investigations were done only if warranted clinically. Pre-radiotherapy and post-radiotherapy visual evaluation of cosmetic outcome was done in all patients. The outcomes were subjectively scored as excellent, good, fair, or poor by the treating radiation oncologist. For assessment of function preservation for skin or hard palate tumours, integrity of the organ without any complication was taken as desired end point.

Statistical analysis was done using Statistical Package for the Social Sciences (SPSS V21) software. Kaplan Meier methods were used for analysis of survival outcomes and curves were plotted accordingly. The date of starting radiotherapy was taken for calculation of the survival, and date of recurrence was the date of clinically or radiologically relapsed disease. The prognostic factors for survival were compared using log-rank test (Mantel-Cox) for univariate analysis, and Cox regression for multivariate analysis. A p-value of less than 0.05 was considered to be of statistical significance. Χ² test was performed for assessment of toxicity and relation with various factors.

The patient characteristics and treatment details are summarized in Table 1. The median time from onset of symptoms to diagnosis was 5 months (range, 1-36 months). In 31 patients, SMB was used as the primary treatment modality, and in four patients, for disease recurrence as the second primary. The growth was ulcerative in 13 patients, ulceroproliferative in 12, proliferative in 6, infiltrative and superficial creeping in 2 patients each.

In 8 patients, SMB was used as boost after EBRT. Of these, 7 patients had lesions in palate (3 soft palate, 2 hard palate, and 2 over the soft palate/hard palate junction), and 1 over tonsil. Seven patients were treated using parallel opposed portals, while in 1 patient IMRT (soft palate primary) was considered. Median gap between EBRT and BT was 14 days (range, 8 to 28 days). Concurrent weekly chemotherapy with cisplatinum (30 mg/m²) was used during EBRT in 2 patients with carcinoma soft palate due to bulky disease. For patients treated with brachytherapy alone, the treatment duration ranged from 5 to 11 days (median, 7 days). Dosimetric data was available for 30 patients and has been summarized in Table 1.