Field-based radiotherapy using volumetric modulated arc therapy (VMAT) for skin field cancerisation (SFC)–outcomes from 100 consecutive fields

Abstract

Introduction: Skin field cancerisation (SFC) arises from prolonged sun exposure and increases with age, especially in fair skinned individuals. Multiple areas of the skin can be involved, resulting in poor quality of life and cosmesis. Invasive skin cancer can arise causing morbidity and even death. The long-term efficacy of traditional treatments is disappointing. Volumetric modulated arc therapy (VMAT) allows efficient definitive radiotherapy treatment of large convex skin fields. This retrospective, single-institution study presents a case series of 100 consecutive SFC fields in 74 patients. Methods: The first 100 fields treated with VMAT for SFC by the same clinician (GBF) were identified through departmental medical records. Patient, field, treatment, and outcome factors were collected for analysis. The date of the first consultation was collected to calculate the rate of referrals over time. Results: The first patient completed treatment in October 2013 and the last patient in May 2020. Seventy-four mostly male (84%) patients with a median age of 76 years were identified. At least 75% had previously undergone treatment for SFC and 11% were immunosuppressed. Twenty percent of patients had more than one field treated with VMAT. Ninety-three fields of keratinocytic lineage were found with most involving the legs (27), scalp (23) or nose (20). Average planning target volume (PTV) size was 175 (range 5 - 1282) cm3. Average prescribed dose was 50 (range 15 - 72) Gy, average delivered dose was 45 (range 4 - 72) Gy. Sixty-four (69%) of fields completed the prescribed course. There were 15 (16%) in-field recurrences. In-field control on an intention-to-treat basis was 89% at 12 months. For those who completed the prescribed treatment, in-field control at 12 months was 98% as compared with 71% for those who did not (p <.0001). PTV size did not impact treatment completion. In those who completed the prescribed treatment, recurrence was not associated with PTV size nor dose. The rate of referrals increased over time. Conclusion: VMAT for SFC is feasible and effective if the whole course is completed. These findings support our national protocol. More research is warranted to predict radiosensitivity so that treatment can be better tailored. Research to identify patients at risk of lower leg lymphoedema before they become symptomatic is also needed to ensure treatment completion thereby reducing the risk of recurrence.