Detecting Selection on Temporal and Spatial Scales: A Genomic Time-Series Assessment of Selective Responses to Devil Facial Tumor Disease.

Detecting loci under selection is an important task in evolutionary biology. In conservation genetics detecting selection is key to investigating adaptation to the spread of infectious disease. Loci under selection can be detected on a spatial scale, accounting for differences in demographic history among populations, or on a temporal scale, tracing changes in allele frequencies over time. Here we use these two approaches to investigate selective responses to the spread of an infectious cancer--devil facial tumor disease (DFTD)--that since 1996 has ravaged the Tasmanian devil (Sarcophilus harrisii). Using time-series 'restriction site associated DNA' (RAD) markers from populations pre- and post DFTD arrival, and DFTD free populations, we infer loci under selection due to DFTD and investigate signatures of selection that are incongruent among methods, populations, and times. The lack of congruence among populations influenced by DFTD with respect to inferred loci under selection, and the direction of that selection, fail to implicate a consistent selective role for DFTD. Instead genetic drift is more likely driving the observed allele frequency changes over time. Our study illustrates the importance of applying methods with different performance optima e.g. accounting for population structure and background selection, and assessing congruence of the results.

Assessment of the accuracy and precision of a patient immobilization device for radiation therapy in canine head and neck tumors.

The positioning accuracy and precision of a head and neck immobilization device for radiation therapy of tumors in the canine skull was evaluated. Nineteen dogs with a spontaneous tumor of the head were enrolled including 12 with an intracranial mass and seven with an intranasal or maxillary tumor. Three hundred thirty-three pairs of orthogonal digital portal radiographs were analyzed to assess patient displacement in the cranial-caudal, lateral, and dorso-ventral directions. The mean systematic displacement was 0.8, 1, and 0.9 mm. The mean random displacement was 1.9, 1.6, and 1.5 mm. These values resulted in an overall displacement of 2.1 mm in the cranial-caudal direction, 1.8mm in the lateral direction, and 1.7 mm in the dorsal-ventral direction. The mean displacement value of the three dimensional (3D) vector was 2.4 mm with a standard deviation of 2.1. Ninety-five percent of all vectors were < 6.4 mm. This study quantifies the precision and accuracy of this particular positioning device. Knowing the limitations and setup variability of the system being used to set patients up for daily radiotherapy is paramount to planning and delivering appropriate radiation doses, especially as more complex treatment methods are used.

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.

Ultrasonic hyperthermia for animal tumor treatment: CT assessment.

The effect of cancer treatment by ultrasound-induced hyperthermia in domestic pets was evaluated by computed tomography (CT) regarding changes in tumor volume and x-ray attenuation after intravenous contrast material. CT scanning is more accurate in measuring tumor volume than estimates after surface measurements. A decrease inn tumor volume and x-ray attenuation after contrast medium seems to be a valuable index of tumor response to hyperthermia.