Clinical outcomes and prognostic factors of repeated conventional hypofractionated radiotherapy for recurrent intranasal tumors in dogs.

BACKGROUND

Despite an initial favorable response to hypofractionated radiotherapy (RT), intranasal neoplasia has a poor long-term prognosis. Re-irradiation (re-RT) has been shown to result in clinical remission in dogs with recurrent intranasal tumors. Hypofractionated re-RT is indicated in cases of recurrence.

AIM

This study aimed to investigate the response of patients with recurrent intranasal tumors who were initially treated with repeated hypofractionated RT and subsequently underwent re-RT.

METHODS

Medical records of dogs with intranasal tumors that relapsed after undergoing hypofractionated RT at Azabu University Veterinary Teaching Hospital and who underwent re-RT between 2008 and 2022 were retrospectively analyzed.

RESULTS

Among the 30 dogs included, 20 had adenocarcinomas. Eleven patients underwent a second re-RT, and five patients underwent a third re-RT. The median total isocenter dose and total number of fractions were 56 Gy (range, 37.5-102) and 8 fractions (range, 5-14), respectively. The first, second, and third progression-free intervals (PFIs) were 315 ( = 30), 185 ( = 11), and 218 days ( = 4), respectively. Overall survival (OS) was 504 days ( = 30). Adverse events such as alopecia ( = 7), white hair ( = 8), cataracts ( = 9), pigmentation ( = 5), keratitis ( = 3), and corneal ulceration ( = 1) were limited to grades 1 and 2. The medians of the first PFI for one course and two or more courses of re-RT were 298 and 331 days, respectively, indicating no significant differences between the groups. The OS after two or more courses of re-RT (758 days) was significantly longer than after one course of re-RT alone (414 days) ( = 0.048). However, the cases were not randomized, and most of the tumor types were adenocarcinomas.

CONCLUSION

Since it is expected to prolong survival time with few life-threatening adverse events, the findings of the present study suggest that hypofractionated re-RT can be used in dogs with recurrent intranasal tumors initially treated with hypofractionated RT. Therefore, repeated hypofractionated re-RT may be a reasonable option for young dogs with a good initial response and recurrent intranasal tumors.