Safety and feasibility of stereotactic radiotherapy using computed portal radiography for canine intracranial tumors

Abstract

Stereotactic radiotherapy is a highly conformal treatment option for intracranial and extracranial malignancies. Stereotactic radiotherapy utilizes specialized equipment specifically designed to avoid normal tissue while delivering ablative treatments with submillimeter precision and accuracy. Linear accelerator based stereotactic radiotherapy incorporates on-board image guidance utilizing cone beam computed tomography (CT). Many institutions lack the ability to provide image guidance with cone beam CT but delivery of highly conformal treatments with submillimeter precision and accuracy is still feasible. The purpose of this retrospective, pilot study was to describe clinical outcomes for a group of dogs with neurological disease that were treated with an stereotactic radiotherapy technique utilizing intensity modulated radiation therapy, megavoltage computed portal radiography, a bite plate, thermoplastic mold, and mask based positioning system. Twelve dogs with neurological clinical signs were included. The diagnosis of intracranial tumor was made based on advanced imaging (12/12) and confirmed via histopathology (3/12). Twelve courses of stereotactic radiotherapy, utilizing three fractions of 8.0 Gy, were delivered on alternating days. Self-resolving neurological deterioration was observed in two patients during stereotactic radiotherapy. Neurological progression free interval and median survival time were 273 days (range: 16-692 days) and 361 days (range: 25-862 days). Stereotactic radiotherapy using computed portal radiography may be a safe treatment option for dogs with intracranial tumors.

Long‐term survival with stereotactic radiotherapy for imaging‐diagnosed pituitary tumors in dogs

“…Stereotactic radiotherapy limits normal tissue dose, in part by use of advanced on‐board imaging and reliable positioning for patients, and also by use of advanced planning systems . To the authors’ knowledge, there are only two peer‐reviewed veterinary studies that describe stereotactic radiotherapy for very few canine pituitary cases . In one study, four dogs received a median dose of 16.25 Gy and had a median survival of 118 days .…”

“…In this stereotactic radiotherapy study, four dogs had pituitary masses and received a median dose of 16.25 Gy (range 15 – 25 Gy), with a median survival of 118 days . Stereotactic radiotherapy was also used in another study that included three dogs with pituitary masses; they received 24 Gy in three fractions of 8 Gy every other day, and they had survival times ranging from 255 to 342 days …”

“…Although chemotherapy has been used with some intracranial tumors, a survival benefit has not clearly been demonstrated, including for pituitary masses . The potential benefits of stereotactic radiotherapy for a variety of intracranial tumor types in dogs have previously been described, but pituitary tumors have accounted for very few stereotactic radiotherapy patients in the literature …”

A survey of stereotactic radiation therapy in veterinary medicine

“…In the 2010 survey, 28% of facilities indicated the capacity to deliver stereotactic radiotherapy but details of the planning, quality assurance, and treatment techniques utilized were not reported . Over the past few years, a number of manuscripts have been published suggesting a more widespread adoption of stereotactic radiotherapy …”

Radiotherapy isocenters verified by matching to bony landmarks of the canine and feline head differ when localized using volumetric versus planar imaging

“…However, kV‐CBCT is not uniformly available . To improve accessibility and meet current clinical demands, orthogonal megavoltage (MV) portal imaging is used for pre‐SRT position verification in some facilities that do not have CBCT . This practice pattern is mirrored in physician‐based medicine, particularly in rural areas or countries that do not currently have linear accelerators equipped with modern kilovoltage on‐board imaging systems .…”