Gibbon Aggression During Introductions: An International Survey.

Little is known regarding the prevalence of aggression seen during introductions of captive gibbons (Hylobatidae). In this study, an online survey was developed to quantify and collect contextual details regarding the frequency and types of aggression seen during introductions of captive gibbons (Hylobatidae). Nineteen percent of institutions (17 institutions) reported observing aggression, and 6 of these institutions recorded multiple instances of aggression, though a vast majority of these cases resulted in mild injuries or none at all. The female was the primary aggressor in 23% of cases, the male was the primary aggressor in 58% of cases, and both were the primary aggressor in 1 case. Although these aggressive interactions were often not associated with a known cause, 27% of cases were associated with food displacement. In most cases, management changes, including trying new pairings, greatly reduced situational aggression, suggesting that individual personalities may play a factor in aggression. These data begin to explain the extent of aggression observed in captive gibbons; future studies will address possible correlations with aggression and introduction techniques.

Electromagnetic detection and real-time DMLC adaptation to target rotation during radiotherapy.

PURPOSE: Intrafraction rotation of more than 45° and 25° has been observed for lung and prostate tumors, respectively. Such rotation is not routinely adapted to during current radiotherapy, which may compromise tumor dose coverage. The aim of the study was to investigate the geometric and dosimetric performance of an electromagnetically guided real-time dynamic multileaf collimator (DMLC) tracking system to adapt to intrafractional tumor rotation. MATERIALS/METHODS: Target rotation was provided by changing the treatment couch angle. The target rotation was measured by a research Calypso system integrated with a real-time DMLC tracking system employed on a Varian linac. The geometric beam-target rotational alignment difference was measured using electronic portal images. The dosimetric accuracy was quantified using a two-dimensional ion chamber array. For each beam, the following five delivery modes were tested: 1) nonrotated target (reference); 2) fixed rotated target with tracking; 3) fixed rotated target without tracking; 4) actively rotating target with tracking; and 5) actively rotating target without tracking. Dosimetric performance of the latter four modes was measured and compared to the reference dose distribution using a 3 mm/3% γ-test. RESULTS: Geometrically, the beam-target rotational alignment difference was 0.3° ± 0.6° for fixed rotation and 0.3° ± 1.3° for active rotation. Dosimetrically, the average failure rate for the γ-test for a fixed rotated target was 11% with tracking and 36% without tracking. The average failure rate for an actively rotating target was 9% with tracking and 35% without tracking. CONCLUSIONS: For the first time, real-time target rotation has been accurately detected and adapted to during radiation delivery via DMLC tracking. The beam-target rotational alignment difference was mostly within 1°. Dose distributions to fixed and actively rotating targets with DMLC tracking were significantly superior to those without tracking.

Electromagnetic-guided dynamic multileaf collimator tracking enables motion management for intensity-modulated arc therapy.

PURPOSE: Intensity-modulated arc therapy (IMAT) is attractive because of high-dose conformality and efficient delivery. However, managing intrafraction motion is challenging for IMAT. The purpose of this research was to develop and investigate electromagnetically guided dynamic multileaf collimator (DMLC) tracking as an enabling technology to treat moving targets during IMAT. METHODS AND MATERIALS: A real-time three-dimensional DMLC-based target tracking system was developed and integrated with a linear accelerator. The DMLC tracking software inputs a real-time electromagnetically measured target position and the IMAT plan, and dynamically creates new leaf positions directed at the moving target. Low- and high-modulation IMAT plans were created for lung and prostate cancer cases. The IMAT plans were delivered to a three-axis motion platform programmed with measured patient motion. Dosimetric measurements were acquired by placing an ion chamber array on the moving platform. Measurements were acquired with tracking, without tracking (current clinical practice), and with the phantom in a static position (reference). Analysis of dose distribution differences from the static reference used a γ-test. RESULTS: On average, 1.6% of dose points for the lung plans and 1.2% of points for the prostate plans failed the 3-mm/3% γ-test with tracking; without tracking, 34% and 14% (respectively) of points failed the γ-test. The delivery time was the same with and without tracking. CONCLUSIONS: Electromagnetic-guided DMLC target tracking with IMAT has been investigated for the first time. Dose distributions to moving targets with DMLC tracking were significantly superior to those without tracking. There was no loss of treatment efficiency with DMLC tracking.

Evaluation of linear accelerator gating with real-time electromagnetic tracking.

PURPOSE: Intrafraction organ motion can produce dosimetric errors in radiotherapy. Commonly, the linear accelerator is gated using real-time breathing phase obtained by way of external sensors. However, the external anatomy does not always correlate well with the internal position. We examined a beam gating technique using signals from implanted wireless transponders that provided real-time feedback on the tumor location without an imaging dose to the patient. METHODS AND MATERIALS: An interface was developed between Calypso Medical's four-dimensional electromagnetic tracking system and a Varian Trilogy linear accelerator. A film phantom was mounted on a motion platform programmed with lung motion trajectories. Deliveries were performed when the beam was gated according to the signal from the wireless transponders. The dosimetric advantages of beam gating and the system latencies were quantified. RESULTS: Beam gating using on internal position monitoring provided up to a twofold increase in the dose gradients. The percentage of points failing to be within +/-10 cGy of the planned dose (maximal dose, approximately 200 cGy) was 3.4% for gating and 32.1% for no intervention in the presence of motion. The mean latencies between the transponder position and linear accelerator modulation were 75.0 +/-12.7 ms for beam on and 65.1 +/- 12.9 ms for beam off. CONCLUSION: We have presented the results from a novel method for gating the linear accelerator using trackable wireless internal fiducial markers without the use of ionizing radiation for imaging. The latencies observed were suitable for gating using electromagnetic fiducial markers, which results in dosimetric improvements for irradiation in the presence of motion.