Introduction

Most dogs with intranasal neoplasia show a favorable tumor response to radiotherapy (RT); however, the long-term prognosis is poor. The progression-free interval (PFI) of hypofractionated RT is shorter than that of fractionated RT. Re-irradiation may be indicated after hypofractionated RT. The purpose of this study was to investigate re-irradiation after hypofractionated RT for recurrent intranasal tumors.

Methods

This was a retrospective study on re-irradiation after hypofractionated RT in dogs with intranasal tumors.

Results

Eighteen dogs met the selection criteria. Tumor types were adenocarcinoma (n=13), transitional cell carcinoma (n=2), papillary adenocarcinoma (n=2), chondrosarcoma (n=1). Tumor stages were I (n=1), II (n=5), III (n=8), and IV (n=4). The median number of fractions and dose/fraction of the first course of RT were 4 and 7.5 Gy, respectively. The median number of re-irradiation courses and dose/fraction were 2 and 7.5 Gy, respectively. The median total isocenter dose, total number of fractions, PFI, and overall survival were 58 Gy, 9,383 days (range, 84–1,433 days), and 1,600 days (range, 262–1,606 days), respectively. The early side effect of re-radiation was alopecia (grade 1), and late side effects were skin problems (grade 1) and vision changes (grades 1 and 2). Dogs with a PFI exceeding 1 year survived longer than dogs with a PFI of less than 1 year (P=0.0291).

Conclusion: Re-irradiation after hypofractionated RT was effective in dogs with recurrent intranasal tumors.