Radiation therapy planning using MRI-CT fusion in dogs and cats with brain tumors.

INTRODUCTION: Volume definition is a delicate step within the radiation treatment planning process and the precision of defining the volumes to irradiate is important for the success of the radiation treatment. Traditionally, radiation plans are created using computed tomography (CT) studies. Due to its different mechanism of action, magnetic resonance imaging (MRI) is more sensitive for detection of brain lesions. Therefore, using fused images of both imaging modalities should result in a more precise definition of the volumes to irradiate. The feasibility to fuse CT and MRI studies performed at different institutions was tested to subsequently analyse the influence of the fused images on target volume definition. MATERIALS AND METHODS: Fourteen dogs and four cats with brain lesions having MR- and CT-imaging were included. Contrast-enhanced radiotherapy planning CT scans were fused to T1-weighted post-contrast and T2-weighted MRI scans. The gross tumor volume (GTV), the clinical tumor volume (CTV) and the planning target volume (PTV) were delineated on CT- and MRI studies. CT and MRI volumes were compared with regard to volumetric and spatial differences. RESULTS: The mean GTV was larger on MRI than on CT (2.15 vs.1.54 cm3). Also the mean CTV was larger on MRI than on CT (5.34 vs. 4.38 cm3). Consequently, the mean PTV was larger on MRI than on CT (14.20 vs. 10.82 cm3) as well. None of the differences in defined volumes were significant. Fusion images were accepted showing mean errors of 1.32 mm (mean error) and 1.73 mm (maximal error). CONCLUSION: CT-MRI fusion was feasible especially when defined, reliable, and consistent anatomic landmarks were used as registration points. Volumetric differences between CT and MRI were insignificant. In general, GTV and CTV were easier identified on MRI.

Proton spot scanning radiotherapy of spontaneous canine tumors.

Thirty dogs with spontaneous tumors were irradiated with proton therapy using a novel spot scanning technique to evaluate the safety and efficacy of the system, and to study the acute and late radiation reactions. Nasal tumors, soft tissue sarcomas, and miscellaneous tumors of the head were treated with a median total dose of 52.5 Gy given in 3.5 Gy fractions. Acute effects, late effects, tumor response, and outcome were analyzed. No unexpected radiation reactions were seen, however two dogs did develop in-field osteosarcoma, and one dog developed in-field bone necrosis. Complete response to therapy was seen in 40% (12/30), partial response in 47% (14/30), and no response in 13% (4/30). Median survival for all dogs was 385 days (range of 14-4583 days). Dogs with nasal cavity tumors had a median survival of 385 days (range of 131-1851 days) and dogs with soft tissue sarcomas had a median survival time of 612 days (range of 65-4588 days). Treatment outcome was similar to historical controls. This new proton spot scanning technique proved to be safe and reliable.

Ki67 reactivity in nasal and periocular squamous cell carcinomas in cats treated with electron beam radiation therapy.

Squamous cell carcinomas of sparsely haired skin are relatively common tumors in cats, and these tumors likely exhibit a rapid growth rate. Thus, we evaluated response and duration of response in relation to the Ki67 proliferative reactivity in such tumors. Seventeen cats with confirmed squamous cell carcinomas and treated with an accelerated, hypofractionated electron beam radiation protocol were included in the study. For all of them histologic grading, Ki67 reactivity, response, and disease-free interval (DFI) were evaluated. Response to therapy was excellent (94% complete response rate) with a median DFI of 414 days. Only moderate acute and few long-term adverse effects were seen. Cats with tumors with a low Ki67 reactivity had markedly shorter DFIs than cats with tumors with high Ki67 reactivity. We concluded that an accelerated, hypofractionated electron beam radiation therapy protocol is well suited for feline squamous cell carcinomas. The protocol appears especially efficacious in tumors with a high Ki67 reactivity.

Irradiation of brain tumors in dogs with neurologic disease.

Radiation therapy is the treatment of choice for many primary canine brain tumors. The radiation dose tolerated by surrounding healthy brain tissue can be a limiting factor for radiation treatment and total dose as well as fractionation schedules, and volume effects may play a role in the outcome of patients undergoing radiation therapy. The purpose of this retrospective study was to evaluate the efficacy of radiation therapy in dogs with brain tumors that showed signs of neurologic disease. Forty-six dogs with brain tumors were included in the analysis. In 34 dogs, computer-generated treatment plans were available, and dose-volume data could be obtained. The totally prescribed radiation therapy doses ranged from 35 to 52.5 Gy (mean = 40.9 [SD +/- 2.91) applied in 2.5- to 4-Gy fractions (mean = 3.2). The median overall survival time calculated for deaths attributable to worsening of neurologic signs was 1,174 days (95% confidence interval [CI], 693-1,655 days). Assuming that all deaths were due to disease or treatment consequences, the median survival time was 699 days (95% CI, 589-809 days). No prognostic clinical factors such as the location or size of the tumor or neurologic signs at presentation were identified. With computerized treatment planning and accurate positioning, high doses of radiation (> 80% of the total dose) could be limited to mean relative brain volumes of 35.3% (+/- 12.6). These small volumes may decrease the probability of severe late effects such as infarction or necrosis. In this study, very few immediate or early delayed adverse effects and no late effects were noted, and quality of life was good to excellent.

Combining magnetic and optical tracking for computer aided therapy.

A fast and accurate magnetic tracking system was developed for applications in real-time tumor tracking, computer-aided surgery, and endoscopy. The tracking is based on the application of miniaturized sensors. Once implanted in the patient, the sensors receive signals from an external field generator. The fast evaluation of the signals allows the online determination of position and orientation of each sensor. With the help of optical tracking, the sensor coordinates are transformed in the reference system used by the clinician. The effects of eddy currents in nearby electrically-conducting objects are taken into account using special computational methods. The present paper presents the results of a first experiment in a canine model.

Assessment of a radiotherapy patient immobilization device using single plane port radiographs and a remote computed tomography scanner.

Radiation treatment requires a precise procedure for interfraction repositioning of the patient. The purpose of this study was to determine the accuracy of our fixation device in treatment position and to evaluate the setup accuracy with two different methods. The positioning data of 19 canine patients with tumors in the head region (oral, nasal, cerebral) treated with photon or proton irradiation were included in this study. The patients were immobilized by means of an individualized fixation device. Focus was set upon interfraction displacement with systematic and random components. In one method, treatment position was evaluated using single plane port radiographs and megavoltage x-rays. In the other method, two orthogonal CT-topograms were acquired to evaluate the precision of positioning of the patient in the immobilization device. Systematic and random displacements were calculated and presented as mean values with corresponding 95% confidence intervals. In spite of a difference between both methods, the positioning seemed to be accurate within the expected range. It seems that a safety margin of 3.7 mm would be enough for both methods to take into account systematic and random position variability in the fixation device, thereby preventing geometric inaccuracies of treatment delivery. The reported immobilization protocol provides accurate patient immobilization for photon and conformal proton radiation therapy.

A comparison of normal tissue complication probability of brain for proton and photon therapy of canine nasal tumors.

This study compared the calculated normal tissue complication probability of brain in dogs with a nasal tumor, which had both photon and proton treatment planning. Nine dogs diagnosed with a variety of histologies, but all with large, caudally located nasal tumors were studied. Three-dimensional (3-D) photon dose distribution, and a proton dose distribution was calculated for each dog. To calculate the normal tissue complication probability (NTCP) for brain, the partial brain volume irradiated with the prescribed dose was determined, then a mathematic model relating complications to partial volume and radiation dose was used. The NTCP was always smaller for proton plans as compared to photon plans, indicating conformation of the dose to the target allows a higher dose to be given. If a 5% NTCP were accepted, the mean applicable dose for this group of dogs was 50.2 Gy for photons, but 58.3 Gy for protons. Not all dogs would benefit the same from proton irradiation. If a large partial brain volume has to be irradiated, the advantage becomes minimal. There is also a minimal advantage if the planning target volume (PTV) includes a small, superficial brain volume. However, for a complex PTV shape the degree of conformation is clearly superior for protons and results in smaller calculated NTCPs.