Rotational Discrepancies Research Articles

SU‐GG‐I‐26: A Simple Technique to Improve Image Quality of CBCT for Brain

Purpose: Improve the image quality of Cone‐Beam CT from the Elekta Synergy Linear Accelerator for its use for radio surgery system or external radiation therapy for small brain tumors. Method and Materials: The image quality of the CBCT images using manufacturer‐recommended preset value are not adequate to take full advantage of image fusion with planned CT and CBCT images for daily setup, especially for small targets or organs with low contrast in the brain. To resolve this issue various parameters, including the gantry rotational settings and the XVI image panel are experimentally optimized to improve image contrast in the CBCT images of the brain. Results: Choosing a voltage of 120KVp instead of 100KVp reduced the bony artifacts, especially in the region of skull base. Increasing gantry rotation from 200° to 300° reduced streak artifacts. Increasing the x‐ray tube current by a factor of 2 or 4 increased the signal‐to‐noise ratio (SNR) while minimizing the radiation dosage to a patient. Reducing the collimator setting for x‐ray generator from a size of ∼25cm by 25cm (at the Isocentre) to 25cm by 10cm minimized scattered radiation and radar artifacts, while covering whole brain independent of tumor position in the brain. Using 0.1 to 2mm thick aluminum filter effectively reduced scattered radiation from the head of the patient. Conclusion: New protocol qualitatively improves low contrast of the brain. This setup is especially useful to correlate the targets in the middle of the brain when there are rotational discrepancies between CT and CBCT images. Further investigation of the this technique is required to qualitatively improve the CBCT image quality.

Near simultaneous computed tomography image-guided stereotactic spinal radiotherapy: An emerging paradigm for achieving true stereotaxy

Purpose To report treatment setup data from an emerging technique using near-simultaneous computed tomography (CT) image-guided stereotactic radiotherapy for the treatment of spinal and paraspinal tumors. Methods and materials A targeting system that integrates a CT-on-rails scanner with a linear accelerator (LINAC) was evaluated in the lead-in portion of a Phase I/II protocol for treating patients with paraspinal metastases. Patients were immobilized in supine position by a moldable body cushion vacuum wrapped with a plastic fixation sheet. Planning CT and immediately repeated CT were performed on the LINAC/CT-on-rails unit to assess respiratory-related vertebral body motion. Coplanar intensity-modulated radiotherapy (IMRT) using 7–9 beams was used to deliver 30 Gy in five fractions to the target volume, while limiting the spinal cord dose to <10 Gy. Pretreatment CT scans were fused with the planning CT scans to determine the correct target isocenter by accounting for any translational and roll (axial) rotational discrepancies from the planning CT. (Corrections caused by yaw and pitch rotations have not yet been implemented.) The reproducibility of the treatment isocenter as compared with the planned isocenter was measured with digitally reconstructed radiographs (DRRs), portal film imaging, and immediate post-treatment verification CT scans. Phantom measurements were taken for dose verification for each IMRT plan. Results Based on a total of 36 CT scans (3 for planning, 3 for respiration study, 15 pretreatment, and 15 post-treatment) from 3 patients, no respiration-associated vertebral body motion was seen. A comparison of the corrected daily anterior-posterior (AP) and lateral (LAT) digital portal images with the planning AP and LAT DRRs confirmed that the isocenter setup accuracy for the 15 treatments was within 1 mm of the planning isocenter. The results from the immediate post-treatment CT scans reconfirmed the findings from the portal images and verified the absence of spinal movement during the treatment. The ion-chamber measurement for the high-dose region was within 2% of the planning dose for three patient treatment plans. Film dose measurement in an IMRT quality assurance phantom demonstrated good agreement from 90% to 30% isodose lines between the planned and measured results. Conclusion Preliminary experience suggests that the near-simultaneous CT image-guided verification technique can be used as a new platform technology for extracranial applications of stereotactic radiotherapy and radiosurgery to spinal and paraspinal tumors.

Interindividual reproducibility in perioperative rotational alignment of femoral components in knee prosthetic surgery using the transepicondylar axis.

Femoral component malalignment is one of the main causes of persisting anterior knee pain after knee replacement. This study examined interindividual reproducibility in perioperative definition of the transepicondylar axis (TEA) as a reference for measuring the rotational alignment of the femoral component. Eight surgeons experienced in knee prosthetic surgery marked on Thiel-embalmed cadaver specimens the reference points that they would normally use to define the TEA during knee replacement. These were digitized by a video system, and all the spots defined by the surgeon were translated into a reference picture, allowing a digital analysis of the distances between all the spots marked. The maximal distance between the spots that the participants had marked as relevant for the TEA was 13.8 mm at the lateral and 22.3 mm at the medial epicondyle. Projecting all spots marked into one picture resulted in an area of 116 mm2 on the lateral and 102 mm2 on the medial epicondyle. The median range of the fault between two different participants was 6.4 mm on the lateral side (range 13.2 mm) and 9.7 mm on the medial (range 21.6 mm). Because the rotational alignment of the femoral component is extremely relevant for successful implantation of total knee prosthesis, the interindividual discrepancy in defining the TEA as reference is rather high. As this reference line is commonly used, the perioperative variance and the resulting rotational discrepancy of the femoral component must be considered.

Rotational injuries of the cervical spine

Injuries which are caused in part by a rotational mechanism include atlantoaxial rotatory fixation (AARF), traumatic isolation of the articular pillar (TIAP), and unilateral interfacetal dislocation (UID). The anatomy, classification, radiographic findings, and frequency of neurological signs are reviewed. Key points include: AARF: (1) Mild injury is not diagnosed radiographically since the appearance is the same as for physiologic rotation. More significant injuries demonstrate widening of the atlanto-dens interval ( > 3 mm in adults) and/or abnormal rotation ( > 45 °) of C1 on C2. (2) AARF refers to an inability to return the head to a neutral position. This may be due to trauma resulting in subluxation or dislocation or may be due to muscle spasm in torticollis. TIAP: (1) Radiographic diagnosis depends on visualizing ipsilateral pedicle and lamina fractures. (2) Rotation of an articular mass from its normal orientation on radiographs implies the presence of this injury. However, rotation of the articular mass is not always present, and the ipsilateral pedicle and lamina fractures must be seen on radiographs or CT. UID: (1) Less rotational discrepancy than expected can occur in two circumstances: articular mass fracture with dislocation or significant subluxation on the contralateral side. (2) Less anterolisthesis than expected can occur if there is articular mass fracture with dislocation.

Technique of minimally invasive retrograde instrumentation of femoral shaft fractures. Indications, procedure and first results

In a consecutive series of 12 cases a newly developed minimally invasive technique was performed using a specially designed retrograde dilator system (RDS) for the insertion of the retrograde femoral nail (ACE®-DePuy), the reaming of the femoral canal and the locking of the distal screws. The mean age of the patients (4 men and 8 women) was 48 (±26) years. 3 type A, 7 type B and 2 type C fractures of the femoral shaft according to the AO classification were stabilized. 4 of the patients had sustained a severe polytrauma. (All values are given as mean (standard deviation). The ISS (injury severity score) of the total collective was 15 (± 12). The follow-up time was 12 (± 8) months. No severe complications were observed. All fractures healed unevent-fully, all patients were mobilzed under full weight-bearing and regained a full range of motion without pain. The performed minimally invasive technique minimizes damages to the patella ligament and the articular cartilage. It facilitates the control of rotational deformities and length discrepancies of the femur also under difficult conditions, e.g. polytrauma and obese patients.

Patient position reproducibility in fractionated stereotactic radiotherapy: an update after changing dental impression material

The reproducibility of patient positioning within the Gill–Thomas–Cosman relocatable stereotactic frame was re-evaluated following the substitution of a new, softer, dental impression material for the original hard acrylic compound. The average total displacement for a series of 10 patients was 1.1 mm (±0.6 mm). Rotational discrepancies were small. This technique cannot deliver accurate repositioning in the absence of patient co-operation.

A comparison of the dimensional accuracy of the splinted and unsplinted impression techniques for the Bone-Lock implant system

Statement of problem. The precise transfer of intraoral relationships of implants to laboratory working models is central to the success of implant prostheses. Purpose. In this study a stone master model incorporating five implants (Bone-Lock) was used to compare the dimensional accuracy of a splinted impression technique with an unsplinted impression technique. Methods. A three-factor analysis of variance was used to examine the effect of technique, relative position of the implant on the cast, and plane of measurement. Results. All three factors had a significant effect on dimensional accuracy. Conclusions. The splinted technique exhibited more deviation from the master model than the unsplinted technique did. This was primarily associated with rotational discrepancies around the long axes of the implants for the splinted technique. (J Prosthet Dent 1997;77:68-75.)

Accuracy of field alignment in abdominal radiation therapy

To assess the accuracy of field alignment in a homogeneous group of patients undergoing radiotherapy of the abdomen (adjuvant treatment of the paraaortic region in Stage I testicular seminoma). To evaluate the predictive value of the first verification on field placement errors during subsequent treatment delivery. In 45 patients, linear and rotational discrepancies were measured between simulation and first check and between 10 consecutive verification films. For the total group of patients, the distribution of all deviations showed mean values between 2.3 mm and -2.7 mm with standard deviations of 3.9 mm to 4.7 mm for linear discrepancies, and -0.5 degree to 0.3 degree with standard deviations of 1.2 degrees to 2.1 degrees for rotational discrepancies, respectively. For all patients, deviations for the transition from simulator to the treatment machine were similar to deviations during subsequent treatment delivery, with 95% of all absolute deviations < 10.0 mm and 4 degrees, respectively. When performing correlation analysis between deviations at first check and during treatment delivery, a correlation for lateral displacements and a borderline correlation for caudal displacements could be found. There was no correlation for cranial and rotational displacements. Although a trend of deviations for subsequent treatment delivery may be shown at first check, our analysis indicates that the first verification cannot reliably predict inaccuracies during treatment delivery. Random fluctuations of field displacements of up to 1.0 cm prevail. They must be considered when prescribing the safety margins of the planned target volume and determining cutoff points for corrective actions in abdominal radiation therapy.

Is the standardized helmet technique adequate for irradiation of the brain and the cranial meninges?

Purpose : To evaluate whether the standardized helmet technique is adequate to reliably cover the clinical target volume (whole brain including cranial meninges) during treatment planning and treatment delivery. Methods and Materials : In 21 patients undergoing irradiation of the brain in acute lymphoblastic leukemia or primary cerebral lymphoma, the coverage of the clinical target volume was checked with a repeat computed tomography (CT) in the treatment position (head fixation with face mask). The accuracy of field alignment was quantitatively assessed with sequential verification films. For each patient, linear and rotational discrepancies were measured between the simulation and first check film, and between five consecutive verification films. Results : Coverage of clinical target volume. In 11 cases (52%), the CT examinations showed that parts of the subfrontal region and midcranial fossa were not included by the field assigned under simulation. Accuracy of field alignment. For the total group of patients, all deviations were normally distributed with mean values between –1.2 mm and 1.5 mm and standard deviations of 2.9 mm to 3.7 mm for linear discrepancies, and 0.3 degrees ± 3.2 degrees for rotational discrepancies. For all patients, deviations were similar for the transition from simulation to the treatment machine and for subsequent treatment delivery, with 50% and 95% of absolute differences being less than 2.0 mm and 6.5 mm, respectively. Maximum linear deviations were less than 9.5 mm. Conclusions : The currently used helmet technique is inadequate to cover the clinical target volume. Repeat CT examinations are a useful method to delineate the clinical target volume on an individual patient basis. In addition, statistical fluctuations of field displacements up to 1.0 cm have to be considered when prescribing safety margins for reliable coverage of the clinical target volume during treatment planning and delivery.

Reproducibility of field alignment in difficult patient positioning

Purpose : Quantitative assessment of the accuracy of field alignment in a homogeneous group of patients with difficult positioning (postoperative irradiation after total hip replacement). Methods and Materials : In 95 patients linear and rotational discrepancies were measured between the simulation and first check film and between five consecutive verification films. Results : For the total group of patients, all deviations were normally distributed with mean values of approximately zero and standard deviations of 4.0–8.0 mm (linear discrepancies) and 3.5–5 degrees (rotational discrepancies). Deviations were similar for the transition from simulator to the treatment machine and for subsequent treatment delivery, with 50% and 95% of absolute differences being less than 5 mm and 15 mm, respectively. Conclusions : Our analysis indicates that statistical fluctuations are considerably more important than errors introduced at start of treatment. Therefore, a first check film seems to be inadequate to predict the expected inaccuracies for the whole course of treatment. In addition, our results should help to prescribe appropriate safety margins for patients with difficult positioning.