A novel restrainer device for acquistion of brain images in awake rats.

Functional neuroimaging methods like fMRI and PET are vital in neuroscience research, but require that subjects remain still throughout the scan. In animal research, anesthetic agents are typically applied to facilitate the acquisition of high-quality data with minimal motion artifact. However, anesthesia can have profound effects on brain metabolism, selectively altering dynamic neural networks and confounding the acquired data. To overcome the challenge, we have developed a novel head fixation device designed to support awake rat brain imaging. A validation experiment demonstrated that the device effectively minimizes animal motion throughout the scan, with mean absolute displacement and mean relative displacement of 0.0256 (SD: 0.001) and 0.009 (SD: 0.002), across eight evaluated subjects throughout fMRI image acquisition (total scanning time per subject: 31 min, 12 s). Furthermore, the awake scans did not induce discernable stress to the animals, with stable physiological parameters throughout the scan (Mean HR: 344, Mean RR: 56, Mean SpO2: 94 %) and unaltered serum corticosterone levels (p = 0.159). In conclusion, the device presented in this paper offers an effective and safe method of acquiring functional brain images in rats, allowing researchers to minimize the confounding effects of anesthetic use.

Dorsal Raphe Dopamine Neurons Signal Motivational Salience Dependent on Internal State, Expectation, and Behavioral Context.

The ability to recognize motivationally salient events and adaptively respond to them is critical for survival. Here, we tested whether dopamine (DA) neurons in the dorsal raphe nucleus (DRN) contribute to this process in both male and female mice. Population recordings of DRNDA neurons during associative learning tasks showed that their activity dynamically tracks the motivational salience, developing excitation to both reward-paired and shock-paired cues. The DRNDA response to reward-predicting cues was diminished after satiety, suggesting modulation by internal states. DRNDA activity was also greater for unexpected outcomes than for expected outcomes. Two-photon imaging of DRNDA neurons demonstrated that the majority of individual neurons developed activation to reward-predicting cues and reward but not to shock-predicting cues, which was surprising and qualitatively distinct from the population results. Performing the same fear learning procedures in freely-moving and head-fixed groups revealed that head-fixation itself abolished the neural response to aversive cues, indicating its modulation by behavioral context. Overall, these results suggest that DRNDA neurons encode motivational salience, dependent on internal and external factors.SIGNIFICANCE STATEMENT Dopamine (DA) contributes to motivational control, composed of at least two functional cell types, one signaling for motivational value and another for motivational salience. Here, we demonstrate that DA neurons in the dorsal raphe nucleus (DRN) encode the motivational salience in associative learning tasks. Neural responses were dynamic and modulated by the animal's internal state. The majority of single-cells developed responses to reward or paired cues, but not to shock-predicting cues. Additional experiments with freely-moving and head-fixed mice showed that head-fixation abolished the development of cue responses during fear learning. This work provides further characterization on the functional roles of overlooked DRNDA populations and an example that neural responses can be altered by head-fixation, which is commonly used in neuroscience.

Respond of the different human cranial bones to pin-type head fixation device.

BACKGROUND: At this juncture, there is no consensus in the literature for the use and the safety of pin-type head holders in cranial procedures. METHODS: The present analysis of the bone response to the fixation of the instrument provides data to understand its impact on the entire skull as well as associated complications. An experimental study was conducted on fresh-frozen human specimens to analyze the puncture hole due to the fixation of each single pin of the pin-type head holder. Cone-beam CT images were acquired to measure the diameter of the puncture hole caused by the instrument according to several parameters: the pin angle, the clamping force, and different neurosurgical approaches most clinically used. RESULTS: The deepest hole, 2.67 ± 0.27 mm, was recorded for a 35° angle and a clamping force of 270 N at the middle fossa approach. The shallowest hole was 0.62 ± 0.22 mm for the 43° angle with a pinning force of 180 N in the pterional approach. The pterional approach had a significantly different effect on the depth of the puncture hole compared with the middle fossa craniotomy for 270 N pinning at 35° angle. The puncture hole measured with the 43° angle and 180 N force in prone position is significantly different from the other approaches with the same force. CONCLUSIONS: These results could lead to recommendations about the use of the head holder depending on the patient's history and cranial thickness to reduce complications associated with the pin-type head holder during clinical applications.

Intraoperative radiographic method of locating the radial head safe zone: the bicipital tuberosity view.

HYPOTHESIS: The proximal radius is asymmetrical, is mostly articular, and rotates through a large arc of motion. Because of these anatomic factors, there is limited space for hardware. This is magnified in the setting of complex fractures. The portion of the radial head where a radial head plate can be placed without compromising forearm motion has been termed the "safe zone." We hypothesized that the bicipital tuberosity could be used as a reproducible intraoperative fluoroscopic landmark to confirm radial head plate position in the safe zone. METHODS: Seventeen cadaveric radii were evaluated. First, the anatomic safe zone was identified using the method previously described by Caputo et al. A proximal radial plate was then placed in the center of this safe zone. The relationship of the plate to the tuberosity was evaluated, and the angle from the point of the greatest tuberosity profile to the center of the safe zone was measured. RESULTS: The maximum profile of the bicipital tuberosity is 166° ± 10° from the center of the safe zone as described by Caputo et al. By use of radiographic imaging, a radial head plate placed directly opposite the bicipital tuberosity will be within the safe zone. This position can be ascertained fluoroscopically with an anteroposterior view of the proximal forearm, in which the surgeon rotates the forearm into full supination. The plate should be placed opposite the bicipital tuberosity as seen on the greatest profile at maximum supination. With this method, the plate will be consistently placed within the safe zone. CONCLUSION: The bicipital tuberosity can be used as a consistent radiographic anatomic landmark to ensure proximal radial plate placement within the safe zone. If the proximal radial head plate is placed 166° ± 10° opposite the bicipital tuberosity, a landmark easily identified on intraoperative imaging, the implant will be in the safe zone and will not impinge on the ulna in rotation.

The EC90 of remifentanil for blunting cardiovascular responses to head fixation for neurosurgery under total intravenous anesthesia with propofol and remifentanil based on bispectral index monitoring: estimation with the biased coin up-and-down sequential method.

BACKGROUND: Head fixation can induce hemodynamic instability. Remifentanil is commonly used with propofol for total intravenous anesthesia (TIVA) during neurosurgery. This study investigated the 90% effective concentration (EC90) of remifentanil for blunting of cardiovascular responses to head fixation during neurosurgery via bispectral index (BIS) monitoring. METHODS: Fifty patients undergoing neurosurgery requiring head fixation were enrolled. This study was performed using the biased coin up-and-down design sequential method (BCD). After tracheal intubation, the effect-site target concentration (Ce) of remifentanil was adjusted to achieve hemodynamic stability and reset to the level preoperatively assigned to each patient, according to the BCD method, approximately 10 min before head fixation. Baseline hemodynamic values were recorded before head fixation. An ineffective response was defined as a case with a > 20% increase in hemodynamic values from baseline. Otherwise, the response was determined to be effective. The EC90 of remifentanil was calculated as a modified isotonic estimator. RESULTS: Forty-three patients completed this study. The EC90 of remifentanil for blunting cardiovascular responses to head fixation was estimated to be 6.48 ng/mL (95% CI, 5.94-6.83 ng/mL). CONCLUSIONS: Adjustment of the Ce of remifentanil to approximately 6.5 ng/mL before head fixation could prevent noxious cardiovascular responses in 90% of neurosurgical ASA I-II patients aged 20 to 65 years old during propofol target-controlled infusion titrated to maintain BIS between 40 and 50. TRIAL REGISTRATION: ClinicalTrials.gov Identifier NCT01489137 , retrospectively registered 5 December 2011.

Customizable rigid head fixation for infants: technical note.

INTRODUCTION: The need and advantages of rigid fixation of the head in cranial surgeries are well documented (Berryhill et al., Otolaryngol Head Neck Surg 121:269-273, 1999). Head fixation for neurosurgical procedures in infants and in early years has been a challenge and is fraught with risk. Despite the fact that pediatric pins are designed, rigid head fixation involving direct application of pins to the head of infants and slightly older children is still generally not safe (Agrawal and Steinbok, Childs Nerv Syst 22:1473-1474, 2006). Yet, there are some surgeries in which some form of rigid fixation is required (Agrawal and Steinbok, Childs Nerv Syst 22:1473-1474, 2006). We describe a simple technique to achieve rigid fixation of the head in infants for neurosurgical procedures. TECHNICAL NOTE: This involves applying a head band made of Plaster of Paris (POP) around the head and then applying the fixation pins of the fixation frame directly on to the POP. CONCLUSION: We have used this technique of head fixation successfully for infants with no complications.

Comparison between radial head arthroplasty and open reduction and internal fixation in patients with radial head fractures (modified Mason type III and IV): a meta-analysis.

PURPOSE: Open reduction and internal fixation (ORIF) and radial head arthroplasty (RHA) are the most common operative treatments in patients with radial head fractures. The purpose of this study was to determine the efficacy of RHA and ORIF treatments in patients with radial head fractures (modified Mason type III and IV). METHODS: We conducted a computerized search of five electronic databases from their inception to July 2015. All clinical trials comparing ORIF versus RHA treatment in patients with radial head fractures were included. We evaluated the primary outcomes included elbow functional evaluation criteria by Broberg and Morrey, elbow score (Broberg and Morrey), Mayo Elbow Performance Score (MEPS) and QuickDASH score. Secondary outcomes included Visual Analog Scale (VAS), range of motion, operation time and complications. The "assessing risk of bias" table was applied to assess the risk of bias of the included studies. RESULT: Eight studies were included in this meta-analysis, which consisted of 138 cases of ORIF and 181 RHA. Methodological quality of the studies was moderate to low. RHA afforded significantly higher satisfaction rate, better elbow score (Broberg and Morrey) and MEPS, shorter operation time, lower incidence of bone nonunion or absorption and internal fixation failure when compared to ORIF. There were no significantly differences in QuickDASH score and other complications. CONCLUSIONS: RHA has better outcome in patients with radial head fractures (modified Mason type III and IV) than ORIF with medium-short-term follow-up period, but longer-term studies will be required to ascertain whether the apparent benefits of RHA were offset by late complications. LEVEL OF EVIDENCE: Therapeutic decision analysis; a meta-analysis, Level III.

Push-in Head Restraining Apparatus for Intracranial Self Stimulation Tasks in Rats.

Head restraining is an experimental technique that firmly secures the animal's head to a fixation apparatus for the precise control and sensing of behaviors. However, procedural and surgical difficulties and limitations have been obstructing the use of the technique in neurophysiological and behavioral experiments. Here, we propose a novel design of the head-restraining apparatus which is easy to develop and convenient for practical use. Head restraining procedure can be completed by sliding the head mounter, which is molded by dental cement during implantation surgery, into the port, which serves as matching guide rails for the mounter, of the fixation bar. So neither skull-attached plates nor screws for fixation are needed. We performed intracranial self stimulation experiment in rats using the newly designed device. Rats were habituated to acclimatize the head-restraint environment and trained to discriminate two spatially distinguished cues using a customized push-pull lever as an operandum. Direct electrical stimulation into the medial forebrain bundle served as reward. We confirmed that head restraining was stable throughout experiments and rats were able to learn to manipulate the lever after successful habituation. Our experimental framework might help precise control or sensing of behavior under head fixed rats using direct electrical brain stimulation as a reward.

Pin penetration depths in the neurocranium using a three-pin head fixation device.

In estimated 10-15% of neurosurgical interventions employing a conventional three-pin head fixation device (HFD) the patient's head loses position due to slippage. At present no scientifically based stability criterion exists to potentially prevent the intraoperative loss of head position or skull fractures. Here, data on the skull penetration depth both on the single and two-pin side of a three-pin HFD are presented, providing scientific evidence for a stability criterion for the invasive three-pin head fixation. Eight fresh, chemically untreated human cadaveric heads were sequentially pinned 90 times in total in a noncommercially calibrated clamp screw applying a predefined force of 270 N (approximately 60 lbf) throughout. Three head positions were pinned each in standardized manner for the following approaches: prone, middle fossa, pterional. Titanium-aluminum alloy pins were used, varying the pin-cone angle on the single-pin side from 36° to 55° and on the two-pin side from 25° to 36°. The bone-penetration depths were directly measured by a dial gauge on neurocranium. The penetration depths on the single-pin side ranged from 0.00 mm (i.e., no penetration) to 6.17 mm. The penetration depths on the two-pin side ranged from 0.00 mm (no penetration) to 4.48 mm. We measured a significantly higher penetration depth for the anterior pin in comparison to the posterior pin on the two-pin side in prone position. One pin configuration (50°/25°) resulted in a quasi-homogenous pin depth distribution between the single- and the two-pin side. Emanating from the physical principle that pin depths behave proportionate to pin pressure distribution, a quasi-homogenous pin penetration depth may result in higher resilience against external shear forces or torque, thus reducing potential complications such as slippage and depressed skull fractures. The authors propose that the pin configuration of 50°/25° may be superior to the currently used uniform pin-cone angle distribution in common clinical practice (36°/36°). However, future research may identify additional influencing factors to improve head fixation stability.

Non-consummatory behavior signals predict aversion-resistant alcohol drinking in head-fixed mice.

A key facet of alcohol use disorder is continuing to drink alcohol despite negative consequences (so called "aversion-resistant drinking"). In this study, we sought to assess the degree to which head-fixed mice exhibit aversion-resistant drinking and to leverage behavioral analysis techniques available in head-fixture to relate non-consummatory behaviors to aversion-resistant drinking. We assessed aversion-resistant drinking in head-fixed female and male C57BL/6 J mice. We adulterated 20% (v/v) alcohol with varying concentrations of the bitter tastant quinine to measure the degree to which mice would continue to drink despite this aversive stimulus. We recorded high-resolution video of the mice during head-fixed drinking, tracked body parts with machine vision tools, and analyzed body movements in relation to consumption. Female and male head-fixed mice exhibited heterogenous levels of aversion-resistant drinking. Additionally, non-consummatory behaviors, such as paw movement and snout movement, were related to the intensity of aversion-resistant drinking. These studies demonstrate that head-fixed mice exhibit aversion-resistant drinking and that non-consummatory behaviors can be used to assess perceived aversiveness in this paradigm. Furthermore, these studies lay the groundwork for future experiments that will utilize advanced electrophysiological techniques to record from large populations of neurons during aversion-resistant drinking to understand the neurocomputational processes that drive this clinically relevant behavior. This article is part of the Special Issue on "PFC circuit function in psychiatric disease and relevant models".

Design and manufacturing of a head mask for fixation in stereotactic radiosurgery by the Gamma Knife® Icon™.

Background: This study evaluates an alternative to the classical method of head fixation during Gamma Knife radiosurgery using a Leksell head frame. In the Gamma Knife® Icon™ model, a new method of head fixation is used by utilizing a thermal molded polymer mask that takes the shape of the patient's head before fixing the head to the table. However, this mask is for single use and quite expensive. Methods: We describe a new, very economical method to fix the head of the patient during radiosurgery. We used commercial, quite cheap material [polylactic acid (PLA)] plastic and made a 3D printing model for the patient's face, taking special measurements to put this mask and fix it on the Gamma Knife. The actual material cost is only $4 (100 times less than the original mask cost). Results: The new mask efficiency was tested using the movement checker software, the same one used to measure the efficiency of the original mask. Conclusion: The newly designed and manufactured mask is quite effective for use with the Gamma Knife® Icon™, with a much lower cost, and it can be manufactured locally.

Non-Consummatory Behavior Signals Predict Aversion-Resistant Alcohol Drinking in Head-Fixed Mice.

A key facet of alcohol use disorder is continuing to drink alcohol despite negative consequences (so called "aversion-resistant drinking"). In this study, we sought to assess the degree to which head-fixed mice exhibit aversion-resistant drinking and to leverage behavioral analysis techniques available in head-fixture to relate non-consummatory behaviors to aversion-resistant drinking. We assessed aversion-resistant drinking in head-fixed female and male C57BL/6J mice. We adulterated 20% (v/v) alcohol with varying concentrations of the bitter tastant quinine to measure the degree to which mice would continue to drink despite this aversive stimulus. We recorded high-resolution video of the mice during head-fixed drinking, tracked body parts with machine vision tools, and analyzed body movements in relation to consumption. Female and male head-fixed mice exhibited heterogenous levels of aversion-resistant drinking. Additionally, non-consummatory behaviors, such as paw movement and snout movement, were related to the intensity of aversion-resistant drinking. These studies demonstrate that head-fixed mice exhibit aversion-resistant drinking and that non-consummatory behaviors can be used to assess perceived aversiveness in this paradigm. Furthermore, these studies lay the groundwork for future experiments that will utilize advanced electrophysiological techniques to record from large populations of neurons during aversion-resistant drinking to understand the neurocomputational processes that drive this clinically relevant behavior.

Endoscopic microvascular decompression without the use of rigid head fixation.

BACKGROUND: Rigid fixation using a three-point skull clamp is a common practice during cranial surgery. Despite its frequency of use, rigid fixation is not without risk of complications including hemodynamic changes, skull fractures and venous thromboembolism. Given this, alternative head fixation should be considered when clinically appropriate. OBJECTIVE: We sought to demonstrate a safe and effective "pinless" head fixation system during endoscopic microvascular decompression (E-MVD). METHODS: Patients undergoing E-MVD were placed in the lateral position with a doughnut pillow under the head, providing support and reducing lateral neck flexion. The vertex of the cranium was angled 10 degrees downward and tape placed circumferentially in an X-shaped fashion around the head, avoiding direct pressure on the ears or eyes. The ipsilateral shoulder was pulled caudally away from the operative field and taped in place to ensure a maximal working corridor. RESULTS: Fifty-two patients underwent the E-MVD procedure with pinless head fixation without any clinical complications. Indications included trigeminal neuralgia type 1 (63.5%), trigeminal neuralgia type 2 (5.8%), hemifacial spasm (19.2%), geniculate neuralgia (7.7%) and glossopharyngeal neuralgia (3.8%). There were no intraoperative or post operative complications and operative time for patients with three-point skull clamp fixation were similar compared to pinless head fixation. CONCLUSIONS: Pinless head fixation is a suitable alternative for certain patients undergoing E-MVD and provides a way to minimize complications that can occur secondary to rigid fixation. If pinless fixation is used, diligent and continued communication with the anesthetist is necessary to ensure there is no intraoperative patient movement.

Refinements to rodent head fixation and fluid/food control for neuroscience.

The use of head fixation in mice is increasingly common in research, its use having initially been restricted to the field of sensory neuroscience. Head restraint has often been combined with fluid control, rather than food restriction, to motivate behaviour, but this too is now in use for both restrained and non-restrained animals. Despite this, there is little guidance on how best to employ these techniques to optimise both scientific outcomes and animal welfare. This article summarises current practices and provides recommendations to improve animal wellbeing and data quality, based on a survey of the community, literature reviews, and the expert opinion and practical experience of an international working group convened by the UK's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs). Topics covered include head fixation surgery and post-operative care, habituation to restraint, and the use of fluid/food control to motivate performance. We also discuss some recent developments that may offer alternative ways to collect data from large numbers of behavioural trials without the need for restraint. The aim is to provide support for researchers at all levels, animal care staff, and ethics committees to refine procedures and practices in line with the refinement principle of the 3Rs.

3D pose estimation enables virtual head fixation in freely moving rats.

The impact of spontaneous movements on neuronal activity has created the need to quantify behavior. We present a versatile framework to directly capture the 3D motion of freely definable body points in a marker-free manner with high precision and reliability. Combining the tracking with neural recordings revealed multiplexing of information in the motor cortex neurons of freely moving rats. By integrating multiple behavioral variables into a model of the neural response, we derived a virtual head fixation for which the influence of specific body movements was removed. This strategy enabled us to analyze the behavior of interest (e.g., front paw movements). Thus, we unveiled an unexpectedly large fraction of neurons in the motor cortex with tuning to the paw movements, which was previously masked by body posture tuning. Once established, our framework can be efficiently applied to large datasets while minimizing the experimental workload caused by animal training and manual labeling.

Development of a Real-Time Thermoplastic Mask Compression Force Monitoring System Using Capacitive Force Sensor.

Purpose: Thermoplastic masks keep patients in an appropriate position to ensure accurate radiation delivery. For a thermoplastic mask to maintain clinical efficacy, the mask should wrap the patient's surface properly and provide uniform pressure to all areas. However, to our best knowledge, no explicit method for achieving such a goal currently exists. Therefore, in this study, we intended to develop a real-time thermoplastic mask compression force (TMCF) monitoring system to measure compression force quantitatively. A prototype system was fabricated, and the feasibility of the proposed method was evaluated. Methods: The real-time TMCF monitoring system basically consists of four force sensor units, a microcontroller board (Arduino Bluno Mega 2560), a control PC, and an in-house software program. To evaluate the reproducibility of the TMCF monitoring system, both a reproducibility test using a micrometer and a setup reproducibility test using a head phantom were performed. Additionally, the reproducibility tests of mask setup and motion detection tests were carried out with a cohort of six volunteers. Results: The system provided stable pressure readings in all 10 trials during the sensor unit reproducibility test. The largest standard deviation (SD) among trials was about 36 gf/cm2 (∼2.4% of the full-scale range). For five repeated mask setups on the phantom, the compression force variation of the mask was less than 39 gf/cm2 (2.6% of the full-scale range). We were successful in making masks together with the monitoring system connected and demonstrated feasible utilization of the system. Compression force variations were observed among the volunteers and according to the location of the sensor (among forehead, both cheekbones, and chin). The TMCF monitoring system provided the information in real time on whether the mask was properly pressing the human subject as an immobilization tool. Conclusion: With the developed system, it is possible to monitor the effectiveness of the mask in real time by continuously measuring the compression force between the mask and patient during the treatment. The graphical user interface (GUI) of the monitoring system developed provides a warning signal when the compression force of the mask is insufficient. Although the number of volunteers participated in the study was small, the obtained preliminary results suggest that the system could ostensibly improve the setup accuracy of a thermoplastic mask.

The head fixation based on skull cap: An improved protocol used in single unit recording in the vestibular system.

Single unit recording has an important application in neuroscience, especially in the vestibular system such as visual stabilization, posture maintenance, spatial orientation and cognition. However, single unit recording conducted in living animals is a demanding technique and non-ideal mechanical stability between the recording location of nerve tissues and the tip of microelectrode always results in failure to obtain successful recordings in the vestibular system. In order to improve the mechanical stability during single unit recording, we constructed a novel head fixation method based on skull cap. This article describes in detail how to construct this novel head fixation. Following the step-by-step procedure mentioned in this article will provide a high-quality mechanical stability for single unit recording in the vestibular system, allowing us to successfully record the nonlinear neural dynamic response over a big magnitude motion stimulation. This improvement of head fixation contributes to the in-depth understanding of the vestibular system.

Bilateral skull fracture with massive epidural hematoma secondary to pin-type head fixation in a pediatric patient: Case report and review of the literature.

INTRODUCTION: A head fixation device containing pins is common equipment used in neurosurgical procedures. Previous reports analysed some of the complications associated with the application of this device for adults and children, even the indications for the use in pediatric are not well defined. CASE PRESENTATION: An 11-year-old girl diagnosed with non-communicating hydrocephalus, caused by posterior fossa tumor. During the surgery, complications were found in the form of acute epidural hematoma due to head fixation pins. So, the operation was stopped. Emergent CT scan was carried out and showed a bilateral skull fracture and a massive right-sided epidural hematoma. An emergency craniotomy for clot removal was performed and five days later, a second surgery was carried out uneventfully for the residual tumor. The patient fully recovered after the second surgery. DISCUSSION: Complications due to the use of a pin head fixation are easier to occur in pediatric patients, because the bones are thinner and need more carefull strategy when pinning. With promp identification of any complications and earlier treatment, the good outcome will be achieved. We compared our case report with published literature in order to suggest the way to prevent this complication. CONCLUSION: Skull fractures and associated epidural hematomas in pediatric patients need to be considered as possible complications of the pin-type head fixation application. The head fixation devices in pediatric need to be used with great caution and knowing the risk factors, safe technique for application and management of complications will prevent worse outcome.

Intrafractional 6D head movement increases with time of mask fixation during stereotactic intracranial RT-sessions.

BACKGROUND: The present study investigates the intrafractional accuracy of a frameless thermoplastic mask used for head immobilization during stereotactic radiotherapy. Non-invasive masks cannot completely prohibit head movements. Previous studies attempted to estimate the magnitude of intrafractional inaccuracy by means of pre- and postfractional measurements only. However, this might not be sufficient to accurately map also intrafractional head movements. MATERIALS AND METHODS: Intrafractional deviation of mask-fixed head positions was measured in five patients during a total of 94 fractions by means of close-meshed repeated ExacTrac measurements (every 1.4 min) conducted during the entire treatment session. A median of six (range: 4 to 11) measurements were recorded per fraction, delivering a dataset of 453 measurements. RESULTS: Random errors (SD) for the x, y and z axes were 0.27 mm, 0.29 mm and 0.29 mm, respectively. Median 3D deviation was 0.29 mm. Of all 3D intrafractional motions, 5.5 and 0.4% exceeded 1 mm and 2 mm, respectively. A moderate correlation between treatment duration and mean 3D displacement was determined (rs = 0.45). Mean 3D deviation increased from 0.21 mm (SD = 0.26 mm) in the first 2 min to a maximum of 0.53 mm (SD = 0.31 mm) after 10 min of treatment time. CONCLUSION: Pre- and post-treatment measurement is not sufficient to adequately determine the range of intrafractional head motion. Thermoplastic masks provide both reliable interfractional and intrafractional immobilization for image-guided stereotactic hypofractionated radiotherapy. Greater positioning accuracy may be obtained by reducing treatment duration (< 6 min) and applying intrafractional correction. TRIAL REGISTRATION: Clinicaltrials.gov, NCT03896555, Registered 01 April 2019 - retrospectively registered.