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PubMed2006

[Accuracy of total knee replacement bone cuts using a conventional ancillary system: 300 Innex total knee arthroplasties].

PURPOSE OF THE STUDY: Short-term functional results and long-term outcome in terms of stability and wear greatly depend on the precision of the bone cuts. We wanted to know whether conventional ancillaries are still competitive in terms of accuracy in comparison with computer-assisted navigation systems. A few comparative studies favor navigation, but have generally only included a small number of patients. We studied radiographically a prospective consecutive series of 300 total knee prostheses (Innex, Zimmer) implanted with the conventional technique by the same operator. MATERIAL AND METHODS: A telegonometric view in the upright position and a short lateral view were obtained in all patients. In the AP view, implants were measured in comparison with the mechanical axis of the femur (F) and the tibia (T). On the lateral view, the prosthesis-tibial shaft angle (PT) was measured from the proximal portion of the tibial shaft and the prosthesis-femoral shaft angle (PF) from the distal portion of the femur. The same operator made all measurements using the same optimal conditions. The series included 178 women and 122 men, mean age 72 +/- 8 years who presented genu varum (n = 248 knees) and genu valgum (n = 52 knees): degenerative disease (n = 238), polyarthritis (n = 4), hemophilic arthropathy (n = 3), necrosis (n = 3), revision of unicompartmental prosthesis (n = 8), and osteotomy (n = 44). RESULTS: The standard x-ray protocol was performed at two months in all patients. The mechanical axis (HKA) was 179.4 +/- 2.4 degrees (range 173-186 degrees) and was +/- 3 degrees in 87% of knees with no difference for varum and valgum. F was 90.1 +/- 1.4 degrees (87-95), with +/- 3 degrees for 98.7%. T was 89.3 +/- 1.5 degrees (85-94) with +/- 3 degrees for 95.6%. PF was 88.6 +/- 1.6 degrees (84-93) for 87%, PT was 87 +/- 2 degrees (81-93) with +/- 3 degrees for 94%. The four cuts were within +/- 3 degrees for 227 prostheses (77%), within +/- 2 degrees for 156 (52%) and within +/- 1 degrees for 56 (18%). Measurements made again one year after implantation for 203 knees gave the same results. Operative time for implantation was 68 +/- 23 minutes for implantation and 85 +/- 23 minutes including complete closure (less than 60 minutes for 68 knees). DISCUSSION: The accuracy of each cut was satisfactory on average with a small standard deviation. Recent data in the literature show that the accuracy in our series is comparable with that obtained currently with navigation systems. In light of this experience, it can be seen that better precision can be achieved for each of the cuts. CONCLUSION: The accuracy of conventional instrumentation systems is still comparable with that obtained with computer-assisted surgery. The purpose of this study was not to question the benefit of navigation, but to establish a basis upon which progress can be measured. The results enabled a more realistic comparison of the precision of navigation systems and also can be comforting for operators still using conventional ancillaries.

Adult↗
PubMed2003

Accuracy of self-reports of fecal occult blood tests and test results among individuals in the carpentry trade.

BACKGROUND: Inaccuracy in self-reports of colorectal cancer (CRC) screening procedures (e.g., over- or underreporting) may interfere with individuals adhering to appropriate screening intervals, and can blur the true effects of physician recommendations to screen and the effects of interventions designed to promote screening. We assessed accuracy of self-report of having a fecal occult blood test (FOBT) within a 1-year window based on receipt of FOBT kits among individuals aged 50 and older in the carpentry trade (N = 658) who were off-schedule for having had a FOBT. METHOD: Indices of evaluating accuracy of self-reports (concordance, specificity, false-positive and false-negative rates) were calculated relative to receipt of a mailed FOBT. Among those who mailed a completed FOBT, we assessed accuracy of reporting the test result. RESULTS: Participants underestimated having performed a FOBT (false-negative rate of 44%). Accuracy was unrelated to perceptions of getting or worrying about CRC or family history. Self-reports of having a negative FOBT result more consistently matched the laboratory result (specificity 98%) than having a positive test result (sensitivity 63%). CONCLUSIONS: Contrary to other findings, participants under- rather than over reported FOBT screening. Results suggest greater efforts are needed to enhance accurate recall of FOBT screening.

Aged↗
PubMed1998

A SEM study of in vivo accuracy of the Root ZX electronic apex locator.

Twenty-nine unprepared, vital teeth were used to evaluate the accuracy of the Root ZX in locating the root canal foramen. After extraction of the teeth, a scanning electron microscope analyzed the relation of the file tip to the foramen. The sample was divided into two groups (Group A and Group B) according to the presence of a normal apical foramen (along the root main axis) or of a lateral foramen (deviating from the root main axis). With a tolerance level of +/- 0.5 mm, a clinical accuracy rate of 82.75% was recorded in the total sample. With a +/- 1.0-mm tolerance level, an accuracy of 100% was found. The error in locating the apex was significantly smaller in cases with a normal apical foramen (Group A) than in cases with a lateral foramen (Group B) (p < 0.001). An accuracy of 100% at the +/- 0.5-mm tolerance level was registered in Group A.

Dental Instruments↗
PubMedDate not supplied

The effect of changing gamma count threshold on sentinel lymph node accuracy.

PURPOSE: Sentinel lymph node (SLN) biopsy has been increasingly accepted in many centers as an alternative to axillary lymph node dissection in the nodal staging of breast cancer. The goal of SLN biopsy is to accurately stage the axilla while minimizing postoperative morbidity. Theoretically, the continuing search for SLNs disrupts additional lymphatics and impacts on operative time. The gamma count threshold is a predefined threshold percentage of the ex vivo count of the "hottest" SLN, which when applied to each individually excised lymph node determines whether a given lymph node is the SLN or a non-SLN. The higher the threshold percentage, the less the number of lymph nodes will meet the criteria of being an SLN. This study examines the hypothesis that changing the gamma count threshold from 10% to 50% will not significantly affect accuracy or the false-negative rate. METHODS: We retrospectively reviewed the charts of patients who underwent SLN biopsy with or without completion axillary lymph node dissection from March 1995 to January 2001 at Walter Reed Army Medical Center. Data were collected on gamma counts for each SLN and histopathology of each SLN. For each SLN ex vivo gamma count, percentage of the ex vivo gamma count of the "hottest" SLN was calculated. RESULTS: The SLN identification success rate was 94% (163 out of 174 patients). On average, 2.07 SLNs were removed per patient and 58% of patients had more than 1 SLN removed (94 out of 163 patients). Only 10% had 4 or more SLNs removed (17 out of 163 patients). Sentinel lymph node metastasis was found in 21% of patients (35 of 163 patients). Of these 35 patients with positive SLNs, 8 patients had a negative "hottest" SLN when a less radioactive SLN was positive for metastasis. Changing the gamma count threshold from 10% to 50% lowers the extrapolated accuracy from 98% to 95% and increases the extrapolated false-negative rate from 8% to 21%. CONCLUSIONS: The accuracy and false-negative rate of SLN biopsy varies based on the lower limit gamma threshold. Maintaining our 10% gamma count threshold results in acceptable accuracy and false-negative rates comparable to reported literature.

Journal Article↗
PubMed1999

A 6-dof device to measure head movements in active vision experiments: geometric modeling and metric accuracy.

This work describes a technique for measuring human head movements in 3D space. Rotations and translations of the head are tracked using a light helmet fastened to a multi-joint mechanical structure. This apparatus has been designed to be used in a series of psycho-physiological experiments in the field of active vision, where position and orientation of the head need to be measured in real time with high accuracy, high reliability and minimal interference with subject movements. A geometric model is developed to recover the position information and its parameters are identified through a calibration procedure. The expected accuracy, derived on the basis of the pure geometric model and the sensor resolution, is compared with the real accuracy, obtained by performing repetitive measurements on a calibration fixture. The outcome of the comparison confirms the validity of the proposed solution which turns out to be effective in providing measurement of head position with an overall accuracy of 0.6 mm and sampling frequency above 1 kHz.

Calibration↗
PubMed2003

A Bayesian approach to the accuracy of clinical observations.

The accuracy of clinical observations was estimated using Bayesian latent-class models with two or more independent tests. Four veterinarians carried out systematic independent clinical examinations on 155 pigs in three herds. Based on the results of binary recordings of clinical observations on dullness, poor body condition (PBC), skin lesions, lameness, respiratory disease, and diarrhea, a latent disease state for each clinical disease was estimated using Gibbs sampling. The accuracy of the clinical observations differed for the four observers and for different clinical signs. Population parameters were estimated from a Bayesian hierarchical model, and the accuracy of a random observer was calculated. We concluded that the accuracy of the veterinarians in this study substantiated the need to pursue more-precise definitions of the clinical findings and that larger sample sizes would be needed to provide reasonable variance estimates. Finally, we concluded that the uncertainty in the clinical decision-making process (starting with the clinical examination) needs to be represented fully.

Animals↗
PubMed2005

Accuracy of intelligent medical systems.

Intelligent medical systems are a special kind of medical software in general, and just as any medical software system they should make accurate presumptions. However, accuracy of intelligent medical systems is highly dependent on various factors such as: choosing an appropriate basic method (i.e. decision trees, neural networks), induction method (i.e. purity measures) and appropriate support methods (i.e. discretization, pruning, boosting). In this paper we present the results of extensive research of the above alternatives on 54 UCI databases and their influence on the accuracy of decision trees, which constitute one of the most desirable forms of intelligent medical systems. We also introduce new hybrid purity measures that on some databases outperform other purity measures. The results presented here show that the selection of the right purity measure with the proper discretization method and application of the boosting method can really make a difference in terms of higher accuracy of induced decision trees. Thereafter choosing the appropriate factors that can increase the accuracy of the induced decision tree is a very demanding and time-consuming task.

Algorithms↗
PubMed1983

Accuracy of standard radiographic views in detecting cervical spine fractures.

Recent studies have challenged the accuracy of standard radiographs for detecting cervical spine injuries. We used thin-section tomography to determine the accuracy of the cross-table lateral view (CTLV) alone, and the three standard emergency department views (CTLV, anteroposterior, and open-mouth) together, for detecting acute cervical spine fractures. Seventy-one patients with blunt cervical spine injuries had thin-section tomography performed for the following indications: fracture, dislocation, or suspicious findings on standard radiographs; or persistent severe pain or neurologic deficit. Tomography detected acute fractures in 44 of the 71 patients. The CTLV had a sensitivity of 82%, specificity of 70%, and accuracy of 77% for detecting patients with fractures. The three standard views had a corresponding sensitivity, specificity, and accuracy of 93%, 71%, and 84%, respectively. Eight patients with fractures had the CTLV interpreted as normal, and three patients with fractures had all three standard views interpreted as normal. The use of thin-section tomography is recommended when there are suspicious radiographic or clinical findings suggesting a severe cervical spine injury.

Cervical Vertebrae↗
PubMedDate not supplied

[Diagnostic accuracy of semiquantitative analysis of positron emission tomography in radiologically indeterminate lung lesions].

OBJECTIVE: The objective of this work was to assess the Standardized Uptake Value (SUV) in the differential diagnosis of radiologically indeterminate lung lesions by means of ROC curves. MATERIAL AND METHOD: Forty seven patients were studied by Positron Emission Tomography with 18-fluorine-2-desoxy-D-glucose (FDG PET) analyzing the value of maximum SUV. The patients were classified into three groups. Group 1 = patients without previous neoplasia (WPN) + patients with previous neoplasia (PN). Group 2 = WPN. Group 3 = PN. RESULTS: The ROC curves showed a high diagnostic accuracy in the three groups, with area under the curve (AUC) values of 0.96, 0.98 and 0.91 respectively. The typical error was 0.03, 0.02 and 0.08. The maximum SUV cutoffs with the best diagnostic accuracy for the three groups were: 2.6; 3 and 2.4, with an accuracy (A) of 93.6%, 97% and 92.3%, respectively. Analyzing all the patients globally (group 1), we obtained one false positive result in a patient with hamartoma (max SUV = 2.8) and two false negative results in one patient with lung metastases from malignant fibrohistiocytoma (max SUV = 0.7) and in another patient with lung metastases from unknown origin adenocarcinoma (max SUV = 1.9). CONCLUSIONS: FDG PET permits differentiation with a very high diagnostic accuracy of benign and malignant lung lesions using the maximum SUV. The differences observed between the different groups are due to the different disease prevalence, obtaining a lower negative predictive value of max SUV in patients with previous neoplasia.

Adult↗
PubMed2003

Reliability and accuracy of different sensors of a flexible electrogoniometer.

OBJECTIVE: To describe a gauging device for electrogoniometer sensors and to evaluate the reliability and accuracy of different sensors including two similar sensors. DESIGN: Repeated measurement design for reliability. BACKGROUND: Despite being considered reliable equipment, several aspects of electrogoniometer reliability and accuracy have not been reported so far. METHOD: Five repeated measurements of each electrogoniometer sensor were performed in 1 degrees increments, during the whole uniplanar amplitudes of flexion, extension, lateral deviations and rotational movements, totaling 6380 measurements. RESULTS: Values from the coefficient of variation and mean square error, respectively indicated that the reliability and accuracy of the sensors varied between sensors and movements, with goniometers being more reliable and accurate than torsiometers. A significant difference between identical sensors was identified. CONCLUSIONS: No similar pattern of variation was found between the sensors evaluated, indicating that every sensor should be tested for its reliability and accuracy when highly precise measurements are needed, and particularly when bilateral limbs are being compared. RELEVANCE: Research on movement recordings demands precise methodology for quantifying angular variations.

Calibration↗
PubMed1999

Digital image analysis: improving accuracy and reproducibility of radiographic measurement.

OBJECTIVE: To assess the accuracy and reproducibility of a digital image analyser and the human eye, in measuring radiographic dimensions. DESIGN: We experimentally compared radiographic measurement using either an image analyser system or the human eye with digital caliper. BACKGROUND: The assessment of total hip arthroplasty wear from radiographs relies on both the accuracy of radiographic images and the accuracy of radiographic measurement. METHODS: Radiographs were taken of a slip gauge (30+/-0.00036 mm) and slip gauge with a femoral stem. The projected dimensions of the radiographic images were calculated by trigonometry. The radiographic dimensions were then measured by blinded observers using both techniques. RESULTS: For a single radiograph, the human eye was accurate to 0.26 mm and reproducible to +/-0.1 mm. In comparison the digital image analyser system was accurate to 0.01 mm with a reproducibility of +/-0.08 mm. In an arthroplasty model, where the dimensions of an object were corrected for magnification by the known dimensions of a femoral head, the human eye was accurate to 0.19 mm, whereas the image analyser system was accurate to 0.04 mm. CONCLUSIONS: The digital image analysis system is up to 20 times more accurate than the human eye, and in an arthroplasty model the accuracy of measurement increases four-fold. We believe such image analysis may allow more accurate and reproducible measurement of wear from standard follow-up radiographs.

Hip Prosthesis↗
PubMed2000

Accuracy of decrease in blood flow in predicting hemodialysis graft thrombosis.

We recently showed that a single low graft blood-flow measurement (Qa) does not accurately predict graft thrombosis. In this study, we prospectively determined whether percentage of decrease in Qa (DeltaQa) or adjustment of Qa for mean arterial pressure (Qa/MAP; Delta(Qa/MAP)) provides greater predictive accuracy than a single Qa. We monitored 83 grafts from 80 patients for thrombosis over periods up to 12 months. Qa (by ultrasound dilution) and MAP were measured monthly during the study. Receiver operating characteristic curves were used to determine whether Qa, DeltaQa, Qa/MAP, or Delta(Qa/MAP) provided the combination of high sensitivity (>80%) and low false-positive rate (FPR; <20%) needed for clinical use. This level of predictive accuracy requires an area under the curve (AUC) of approximately 0.90. We analyzed the four predictors by a number of criteria and found that all AUCs were less than 0.90 and adjustment for MAP reduced the AUC. In predicting thrombosis within 1 month, for example, AUCs for Qa and net DeltaQa (over 3 months) were 0.84 and 0.82, respectively, whereas AUCs for Qa/MAP and net Delta(Qa/MAP) were 0.78 and 0.75, respectively. At a sensitivity of 80%, FPRs for all predictors were at least 30%. Thus, a high sensitivity always required a high FPR. These results show that DeltaQa and adjustment for MAP are not more accurate than a single low Qa in predicting thrombosis. None of these predictors provide enough predictive accuracy to be the sole criterion for clinical decision making. A successful monitoring and intervention program will likely require the inclusion of other predictors that, together with Qa, may provide the needed accuracy.

Area Under Curve↗
PubMed2000

Assessment of arterial stenosis in a flow model with power Doppler angiography: accuracy and observations on blood echogenicity.

The objective of the project was to study the influence of various hemodynamic and rheologic factors on the accuracy of 3-D power Doppler angiography (PDA) for quantifying the percentage of area reduction of a stenotic artery along its longitudinal axis. The study was performed with a 3-D power Doppler ultrasound (US) imaging system and an in vitro mock flow model containing a simulated artery with a stenosis of 80% area reduction. Measurements were performed under steady and pulsatile flow conditions by circulating, at different flow rates, four types of fluid (porcine whole blood, porcine whole blood with a US contrast agent, porcine blood cell suspension and porcine blood cell suspension with a US contrast agent). A total of 120 measurements were performed. Computational simulations of the fluid dynamics in the vicinity of the axisymmetrical stenosis were performed with finite-element modeling (FEM) to locate and identify the PDA signal loss due to the wall filter of the US instrument. The performance of three segmentation algorithms used to delineate the vessel lumen on the PDA images was assessed and compared. It is shown that the type of fluid flowing in the phantom affects the echoicity of PDA images and the accuracy of the segmentation algorithms. The type of flow (steady or pulsatile) and the flow rate can also influence the PDA image accuracy, whereas the use of US contrast agent has no significant effect. For the conditions that would correspond to a US scan of a common femoral artery (whole blood flowing at a mean pulsatile flow rate of 450 mL min(-1)), the errors in the percentages of area reduction were 4.3 +/- 1.2% before the stenosis, -2.0 +/- 1.0% in the stenosis, 11.5 +/- 3.1% in the recirculation zone, and 2.8 +/- 1.7% after the stenosis, respectively. Based on the simulated blood flow patterns obtained with FEM, the lower accuracy in the recirculation zone can be attributed to the effect of the wall filter that removes low flow velocities. In conclusion, the small errors reported in vitro may support the clinical use of this technique.

Algorithms↗
PubMed2000

Accuracy of the extent of axillary nodal positivity related to primary tumor size, number of involved nodes, and number of nodes examined.

PURPOSE: While a number of studies have evaluated the minimum number of axillary nodes that need to be examined to accurately determine nodal positivity or negativity, there is little information on the number of nodes which must be examined to determine the extent of nodal positivity. This study attempts to determine for patients with 1-3 positive nodes the probability that the number of positive nodes reported is the true number of positive nodes as well as the probability that 4 or more nodes could be positive based on primary tumor size and number of nodes examined. MATERIALS AND METHODS: From 1979 to 1998, 1652 women with Stages I-II invasive breast cancer underwent an axillary dissection as part of their breast conservation therapy and had more than 10 lymph nodes examined. The mean and median number of nodes identified in the dissection was 19 and 17 (range, 11-75). The median age was 55 years. A total of 1155 women had T1 tumors and 497 had T2 tumors. Of the 459 node-positive women, 72% had 1-3 positive nodes, 18% had 4-9 positive nodes, and 10% had 10 or more positive nodes. A mathematical model based on tumor size and number of nodes examined was created using the hypergeometric distribution and Bayes Theorem. The resulting model was used to estimate the accuracy of the reported number of positive nodes and the probability of 4 or more positive nodes based on various observed sampling combinations. RESULTS: For patients with T1 tumors and 1, 2, or 3 positive nodes, the minimum number of nodes examined needed for a 90% probability of accuracy is 19, 20, and 20. For T2 tumors and 1, 2, or 3 positive nodes, a minimum of 20 nodes is required. The probability of 4 or more positive nodes increases as tumor size and the number of reported positive nodes increase and as the number of examined nodes decreases. For a 10% or less probability of 4 or more positive nodes, a patient with a T1 tumor and 1, 2, or 3 observed positive nodes would require a minimum of 8, 15, and 20 nodes removed. For a T2 tumor and 1, 2, or 3 observed positive nodes, the corresponding numbers are 10, 16, and 20. CONCLUSION: The accuracy of the extent of axillary nodal positivity is influenced by the number of observed positive nodes, tumor size, and the number of nodes examined. Underestimation of the number of positive nodes will result in errors in the assessment of an individual's risk for locoregional recurrence, distant disease, and breast cancer death and will adversely impact on treatment recommendations. This model provides the clinician with a means for assessing the accuracy of the number of positive nodes reported in patients with 1-3 positive nodes.

Adult↗
PubMed2001

The TALON removable head frame system for stereotactic radiosurgery/radiotherapy: measurement of the repositioning accuracy.

PURPOSE: To present the TALON removable head frame system as an immobilization device for single-fraction intensity-modulated stereotactic radiosurgery (IMRS) and fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT); and to evaluate the repositioning accuracy by measurement of anatomic landmark coordinates in repeated computed tomography (CT) examinations. METHODS AND MATERIALS: Nine patients treated by fractionated stereotactic intensity-modulated radiotherapy underwent repeated CTs during their treatment courses. We evaluated anatomic landmark coordinates in a total of 26 repeat CT data sets and respective x, y, and z shifts relative to their positions in the nine treatment-planning reference CTs. An iterative optimization algorithm was employed using a root mean square scoring function to determine the best-fit orientation of subsequent sets of anatomic landmark measurements relative to the original image set. This allowed for the calculation of the x, y, and z components of translation of the target isocenter for each repeat CT. In addition to absolute target isocenter translation, the magnitude (sum vector) of isocenter motion and the patient/target rotation about the three principal axes were calculated. RESULTS: Anatomic landmark analysis over a treatment course of 6 weeks revealed a mean target isocenter translation of 0.95 +/- 0.55, 0.58 +/- 0.46, and 0.51 +/- 0.38 mm in x, y, and z directions, respectively. The mean magnitude of isocenter translation was 1.38 +/- 0.48 mm. The 95% confidence interval ([CI], mean translation plus two standard deviations) for repeated isocenter setup accuracy over the 6-week period was 2.34 mm. Average rotations about the x, y, and z axes were 0.41 +/- 0.36, 0.29 +/- 0.25, and 0.18 +/- 0.15 degrees, respectively. Analysis of the accuracy of the first repeated setup control, representative of single-fraction stereotactic radiosurgery situations, resulted in a mean target isocenter translation in the x, y, and z directions of 0.52 +/- 0.38, 0.56 +/- 0.30, and 0.46 +/- 0.25 mm, respectively. The mean magnitude of isocenter translation was 0.99 +/- 0.28 mm. The 95% confidence interval for these radiosurgery situations was 1.55 mm. Average rotations at first repeated setup control about the x, y, and z axes were 0.24 +/- 0.19, 0.19 +/- 0.17, and 0.19 +/- 0.12 degrees, respectively. CONCLUSION: The TALON relocatable head frame was seen to be well suited for immobilization and repositioning of single-fraction stereotactic radiosurgery treatments. Because of its unique removable design, the system was also seen to provide excellent repeat immobilization and alignment for fractionated stereotactic applications. The exceptional accuracy for the single-fraction stereotactic radiosurgical application of the system was seen to deteriorate only slightly over a 6-week fractionated stereotactic treatment course.

Algorithms↗
PubMed1998

Repositioning accuracy: comparison of a noninvasive head holder with thermoplastic mask for fractionated radiotherapy and a case report.

PURPOSE: To compare accuracy, clinical feasibility, and subjective patient impression between a noninvasive head holder (Vogele Bale Hohner [VBH]; Wellhoefer Dosimetry, Schwarzenbruck, Germany) developed at the University of Innsbruck and the thermoplastic mask fixation system for use in fractionated external radiotherapy. We present a case report of an actual patient fixated in the VBH head holder during radiation therapy. MATERIALS AND METHODS: The VBH head holder consists of an individualized vacuum dental cast connected to a head plate via two hydraulic arms allowing noninvasive, reproducible head fixation of even uncooperative patients. Accuracy was tested and compared with that of the thermoplastic mask using the Phillips EasyGuide navigation system on five volunteers. Specific external registration points served as landmarks and their positions were compared after each repositioning. System and operator inaccuracy were also taken into account. The times taken for production and repositioning of the respective fixation devices were compared, and subjective impressions were noted. RESULTS: Mean VBH head holder repositioning accuracy was 1.02 mm while that of the thermoplastic mask was 3.05 mm. 69% of mask repositionings showed a deviation > 2 mm and 41% > 3 mm (as opposed to 8% and 1% respectively for the VBH head holder) Those points located farthest away from the respective plane of fixation showed the largest deviations. Both production and repositioning times were similar between the systems; depending upon the patient, the VBH head holder was generally better tolerated than the mask system. CONCLUSION: Due to its significantly better repositioning accuracy compared to that of the thermoplastic mask, the VBH head holder is especially suited for external radiation requiring precise repositioning due to critical tissues in immediate surrounding of the area to be irradiated.

Adult↗
PubMed1999

Geometric accuracy of field alignment in fractionated stereotactic conformal radiotherapy of brain tumors.

PURPOSE: To assess the accuracy of field alignment in patients undergoing three-dimensional (3D) conformal radiotherapy of brain tumors, and to evaluate the impact on the definition of planning target volume and control procedures. METHODS AND MATERIALS: Geometric accuracy was analyzed in 20 patients undergoing fractionated stereotactic conformal radiotherapy for brain tumors. Rigid head fixation was achieved by using cast material. Transfer of stereotactic coordinates was performed by an external positioning device. The accuracy during treatment planning was quantitatively assessed by using repeated computed tomography (CT) examinations in treatment position (reproducibility of isocenter). Linear discrepancies were measured between treatment plan and CT examination. In addition, for each patient, a series of 20 verifications were taken in orthogonal projections. Linear discrepancies were measured between first and all subsequent verifications (accuracy during treatment delivery). RESULTS: For the total group of patients, the distribution of deviations during treatment setup showed mean values between -0.3-1.2 mm, with standard deviations (SD) of 1.3-2.0 mm. During treatment delivery, the distribution of deviations revealed mean values between 0.7-0.8 mm, with SDs of 0.5-0.6 mm, respectively. For all patients, deviations for the transition to the treatment machine were similar to deviations during subsequent treatment delivery, with 95% of all absolute deviations between less than 2.8 and 4.6 mm. CONCLUSION: Random fluctuations of field displacements during treatment planning and delivery prevail. Therefore, our quantitative data should be considered when prescribing the safety margins of the planning target volume. Repeated CT examination are useful to detect operator errors and large random or systematic deviations before start of treatment. Control procedures during treatment delivery appear to be of limited importance. In addition, our findings should help to determine "cut-off points" for corrective actions in stereotactic conformal radiotherapy of brain tumors.

Brain Neoplasms↗
PubMed1997

Tolerance and cross tolerance to the accuracy- and rate-decreasing effects of mu opioids in rats responding under a fixed-consecutive-number schedule.

The purpose of the present investigation was to examine the development of tolerance to the effects of morphine and other mu opioids in rats responding under a fixed-consecutive-number (FCN) schedule of food presentation. To this end, five rats were trained under an FCN schedule and subsequently tested with a variety of mu opioids both before and during chronic exposure to a 0.4 mg/ml morphine drinking solution. Morphine, fentanyl, buprenorphine, butorphanol and nalbuphine produced dose-dependent decreases in both accuracy and response rate when tested prior to the chronic regimen. In most instances, doses of these drugs that decreased accuracy also decreased response rate. During chronic treatment, tolerance developed to the effects of morphine and cross-tolerance was conferred to the effects of fentanyl, buprenorphine and butorphanol. A greater degree of tolerance was conferred to the effects of butorphanol than to the other opioids examined, and the degree of tolerance conferred to butorphanol's rate-decreasing effects was greater than the degree of tolerance conferred to its accuracy-decreasing effects. Doses of naloxone that had no effect prior to morphine treatment produced large decreases in accuracy and response rate when tested during the chronic regimen. In contrast to the other opioids examined, the potency of nalbuphine was not altered by chronic morphine administration. These data emphasize the importance of both pharmacological and procedural variables in the development of tolerance and cross tolerance to the behavioral effects of opioids.

Animals↗