●Surrene                                             Timoma nel coniglio                                           Stent tracheale                                 ●La Cittadina a Bergamo●                                  

Veterinary Radiology and Ultrasound

accepted November 2, 2015

FEASIBILITY FOR USING HYPOFRACTIONATED STEREOTACTIC VOLUMETRIC MODULATED ARC RADIOTHERAPY (VMAT) WITH ADAPTIVE PLANNING FOR TREATMENT OF THYMOMA IN RABBITS: 15 CASES

MARIO DOLERA, LUCA MALFASSI, GIOVANNI MAZZA, GAETANO URSO, MASSIMO SALA, SILVIA MARCARINI, NANCY CARRARA, SIMONE PAVESI, SARA FINESSO, MICHAEL S. KENT 

Abstract

Thymoma is a relatively common tumor in rabbits. Treatment with surgery, radiation therapy, and chemother- apy alone or in combination has been reported with varying outcomes. Stereotactic volumetric modulated arc radiotherapy delivered in a hypofractionated manner allows high doses of radiation to be delivered to the target volume while allowing sparing of adjacent critical structures. This therapy is ideally suited for thymomas in rabbits given their size, the difficulty of multiple anesthesia episodes and the complex- ity of the radiotherapy plans required due to the tumor’s proximity to the heart, lungs, and mediasti- nal structures. Fifteen rabbits with thymoma were prospectively recruited for this observational, single in- stitution, single arm clinical study. All rabbits were imaged with both computed tomography (CT) and magnetic resonance imaging (MRI). A total dose of 40 Gy in six fractions was delivered using a sin- gle arc over an 11-day period with repeat CT simulation done every other fraction for adaptive planning. Follow-up evaluation was done through repeat CT and MRI imaging and revealed complete responses us- ing the Response Evaluation Criteria in Solid Tumors (RECIST) criteria. Two rabbits had died at 618 and 718 days, 10 were alive and three were lost to follow-up. Observed acute and late effects were graded accord- ing to the Veterinary Radiation Therapy Oncology Group (VRTOG) criteria and were found to be minimal.

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