Re-irradiation of recurrent head and neck cancers using pulsed reduced dose-rate radiotherapy: an institutional series

Purpose: Patients diagnosed with recurrent tumors are often faced with limited treatment options that will prolong their life expectancy. Re-irradiation of the original tumor site has been shown to offer palliative benefits in some patient populations, but it does not come without risks. The patients undergoing re-irradiation have an increased risk of experiencing severe toxicities and late effects from the radiotherapy. A re-irradiation technique, called pulsed reduced dose-rate radiotherapy (PRDR), has been used in an attempt not only to avoid the adverse side effects associated with conventional re-irradiation, but also to prolong the life expectancy in these patients. PRDR is typically delivered in a series of 0.2Gy pulses, each separated by 3-minute time intervals. PRDR takes advantage of the differences in the repair thresholds of tumor cells and normal tissue by allowing tissue repair in the normal tissue only. While this technique has shown to be effective in patients with recurrent gliomas and breast cancer, there is limited literature describing its effect in patients with recurrent head and neck cancers.

Methodology: Data was collected from the medical records of five patients diagnosed with recurrent head and neck cancers who received PRDR radiotherapy between August 2020 and August 2021. All patients received prior radiation as a part of their initial treatment, with some patients undergoing surgery and chemotherapy. All patients received salvage surgery prior to re-irradiation. Acute toxicities and late effects of PRDR radiotherapy were recorded and compared.

Results: All five patients had histologically confirmed squamous cell carcinoma recurrences and had received at least 63Gy from their prior courses of radiotherapy. During re-irradiation using PRDR radiotherapy, all patients were prescribed 200 cGy per fraction (given as ten 0.2Gy pulses) and 30 total fractions delivered. Four patients completed radiation as prescribed; one patient discontinued radiation due to issues with transportation. Three patients also received concurrent systemic therapy. There were no grade 4 or 5 acute toxicities. One patient had grade 3 radiation dermatitis managed with silver sulfadiazine. In terms of late toxicities, there were no grade 4 or 5 toxicities. One patient had grade 3 esophageal stenosis requiring esophageal dilation. No patients had evidence of recurrent disease. The median follow-up was 3 months (range 1-13).

Conclusions: In this single institution, retrospective study, PRDR re-irradiation for recurrent head and neck cancers demonstrated acceptable toxicity rates and encouraging cancer control rates. Additional study is needed to define the role of PRDR in the re-irradiation of head and neck cancers.

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