Rabbit’s Thymoma

Introduction/Purpose
Thymomas represent 7% of neoplastic diseases in rabbits. Because of the risks connected with surgery, various protocols of radiotherapy have been proposed most encumbered by high morbidity and mortality. In this work, hypofractionated AHSR-VMAT technique has been tested for rabbit’s thymoma as the elective treatment also for resectable patients. The aim was to compare AHSR-VMAT with the traditional RT treatment protocols and to assess feasibility, efficacy and side effects of this protocol.

Methods and Materials
A dual-step single institution study based on linear accelerator (LINAC) stereotactic hypofractionated radiotherapy for thymoma in rabbits was conducted. In the first retrospective phase, five rabbits suffering from thymoma present in our database were considered in order to evaluate the feasibility of a treatment with a dose of 40 Gy in six fractions over nine days. In the second prospective phase, 15 rabbits suffering from thymoma diagnosed by CT/MRI and confirmed by cytology and histology were enrolled. Patients were treated with LINAC-based hypofractionated stereotactic Volumetric Modulated Arc Therapy (VMAT). Patients were placed in a stereotactic cradle in simple sedation and positioning was verified with cone beam CT; each session lasted less than 1 minute. Throughout treatment 3 subsequent CT scans were performed in order to redefine the planning target volume (PTV) according to the tumor shrinkage.

Results
During the follow up (mean 22 months) all the treated patients showed a complete response and no relevant radiotoxicity. The treatment was well tolerated and no comorbidity interruption occurred.
Discussion/Conclusions
AHSR-VMAT is particularly indicated for tumors that shrink rapidly. Results show the feasibility and efficacy of this treatment as the elective and exclusive solution, with a complete disease control rate and fewer complications with respect to traditional RT.