Reliability of software-based assessment of paediatric preparations for preformed metal crowns in the simulation laboratory.

PURPOSE: Using software for assessment of restorative work on typodonts in the simulation laboratory may enhance the objective evaluation of student work. The study aimed to evaluate the inter-rater and intra-rater reliability using 3-D scans from the Planmeca Emerald™ intra-oral scanner with Romexis Compare® software for assessing preparations for preformed metal crowns (PMCs). METHODS: Three operators independently recorded 3-D scans and digitally measured the features of 30 PMC preparations on typodont primary teeth (# 75). Using Romexis Compare® software, preparations were measured from mesial, distal and occlusal aspects. Measurements were repeated after 2 weeks. The intraclass correlation coefficient (ICC) was used to measure the reliability of measurements between operators and within the one operator. RESULTS: For measuring the extent of tooth reduction, there was excellent intra-rater reliability for each operator (ICC 0.96-0.99). The highest inter-rater reliability was for measurements of the occlusal surface (0.946 and 0.956), followed by the mesial surface (0.852 and 0.862) and then the distal surface (0.746 and 0.724). CONCLUSION: This method was useful and reliable for measuring features of PMC preparation, but with some limitations. Improving the software to provide specific assistance tools would empower greater uptake of this method as an adjunct to traditional visual grading tool in paediatric dentistry preclinical teaching.

Splenic rupture in a premature neonate.

Splenic injuries are very rare in neonates. We report a case of splenic injury in a premature neonate, highlighting the importance of a high-index suspicion in early recognition of this rare but potentially fatal intra-abdominal injury. We also review the literature on possible aetiologies and mechanism of splenic injury, as well as its management. This is the first reported case of a very low-birth-weight neonate with splenic rupture who survived with intact neurology.

Scattered radiation from linear accelerator and cobalt-60 collimator jaws.

PURPOSE: Solid state diodes and/or thermoluminescent dosimeters (TLDs) are often used to measure scattered radiation doses to critical organs immediately adjacent to radiation field sites. The energy-dependent response of these commonly used in vivo dosimeters sometimes makes the interpretation of measured values uncertain. This study investigates scattered radiation arising from the collimator jaws of linear accelerators and the treatment head of a cobalt-60 teletherapy unit. METHODS AND MATERIALS: A thin window Markus-type parallel-plate ionization chamber placed in a polystyrene phantom was employed to document the magnitude, energy composition, and sources of scattered radiation at surfaces near radiation fields. Measurements were taken both with and without additional phantom material covering the ionization chamber, as well as with various distances between the ionization chamber and edges of the radiation fields tested. RESULTS: Data was collected, analyzed and compared for treatment units produced by different manufacturers. It was found that the magnitude of scattered radiation to surfaces immediately adjacent to radiation fields ranged from 1% to 15% of the maximum dose along the beam central axis. These values showed a strong dependence upon distance from the edge of the radiation field, beam energy, collimator setting (field size), and the presence of externally mounted accessories. Teletherapy unit differences due to manufacturing firm origins were found to only slightly affect scattered radiation magnitude, while the orientation of upper and lower collimator jaws had absolutely no effect. CONCLUSIONS: Percent depth dose curves of scattered radiation were obtained and analyzed. The shapes of these depth dose curves suggest the presence of complex energy spectra from secondary electrons and scattered x-rays. Because of the presence of these complex energy spectra in areas immediately adjacent to radiation fields, caution should be observed when interpreting patient doses near radiation fields, if dose values have been measured in vivo using thermoluminescent dosimeters (TLDs) or solid state diodes. Many of these on-patient dosimetry devices are strongly energy dependent and may demonstrate large over- or under-responses in areas dominated by scattered radiation. The results of this study, thus, suggest that ionization chambers are preferred for determination of scattered radiation doses in such regions.

Dose-volume histograms for bladder and rectum.

PURPOSE: A careful examination of the foundation upon which the concept of the Dose-Volume Histogram (DVH) is built, and the implications of this set of parameters on the clinical application and interpretation of the DVH concept has not been conducted since the introduction of DVHs as a tool for the quantitative evaluation of treatment plans. The purpose of the work presented herein is to illustrate problems with current methods of implementing and interpreting DVHs when applied to hollow anatomic structures such as the bladder and rectum. METHODS AND MATERIALS: A typical treatment plan for external beam irradiation of a patient with prostate cancer was chosen to provide a data set from which DVH curves for both the bladder and rectum were calculated. The two organs share the property of being shells with contents that are of no clinical importance. DVHs for both organs were computed using a solid model and using a shell model. Typical treatment plans for prostate cancer were used to generate DVH curves for both models. The Normal Tissue Complication Probability (NTCP) for these organs is discussed in this context. RESULTS: For an eight-field conformal treatment plan of the prostate, a bladder DVH curve generated using the shell model is higher than the corresponding curve generated using the solid model. The shell model also has a higher NTCP. A six-field conformal treatment plan also results in a higher DVH curve for the shell model. A treatment plan consisting of bilateral 120-degree arcs, results in a higher DVH curve for the shell model, as well as a higher NTCP. CONCLUSION: The DVH concept currently used in evaluation of treatment plans is problematic because current practices of defining exactly what constitutes "bladder" and "rectum." Commonly used methods of tracing the bladder and rectum imply use of a solid structure model for DVHs. In reality, these organs are shells and the critical structure associated with NTCP is obviously and indisputably the shell, as opposed to its contents. Treatment planning algorithms for DVH computation should thus be modified to utilize the shell model for these organs.

Tissue compensation using dynamic collimation on a linear accelerator.

PURPOSE: The availability of computer-controlled collimators on some accelerators has led to techniques for dynamic beam modification, mainly to simulate beam wedge filters. This work addresses the practical aspects of dynamic tissue compensation in one dimension using available treatment-planning software. METHODS AND MATERIALS: Data derived from the treatment-planning program is used with an iterative calculational routine to determine the monitor unit settings needed for the collimator-controlling computer. The method was first tested by simulating a 60 degrees physical wedge. Further studies were carried out on a specially fabricated plastic phantom that modeled the sagittal contour of the upper torso, neck, and lower head regions. RESULTS: Dynamic wedge point doses generated by the planning program agreed within 1% with the values directly measured in a polystyrene phantom. In the patient phantom, dynamic collimation achieved calculated dose uniformity within 0.5% in a reference plane near the phantom midline. A comparison of computer-generated and measured point doses in this case showed agreement within 3%. CONCLUSIONS: Dynamic collimation can provide effective compensation for contours that vary primarily along one direction. A conventional treatment-planning program can be used to plan dynamic collimation and deliver a prescribed dose with reliable accuracy.

A quantitative assessment of standard vs. customized midline shield construction for invasive cervical carcinoma.

PURPOSE: An individualized midline shield (MLS) has been advocated for delivering homogeneous radiotherapy for patients with invasive cervical carcinoma. Yet, many radiation oncologists continue to employ a standard block. In the latter instance, any deviation of the cranial-caudal central axis of he tandem from the patient's midline could result in dose inhomogeneity to tumor. A retrospective review of a single university medical center's experience with constructing the MLS was initiated to determine the outcome of using a standard block vs. a customized block that conforms to the "Point A" isodose line. In addition, participating radiation oncologists associated with the Gynecologic Oncology Group (GOG) were polled to assess if there exists a consensus regarding midline block utilization in the management of cervical cancer patients which could be compared to the institutional study. METHODS AND MATERIALS: From January 1, 1990 through December 31, 1992, 32 patients with invasive cervical carcinoma who underwent low dose rate brachytherapy at a single institution were identified. Patients were grouped as having a standard block (18 cases), customized block (5 cases), or no block (9 cases). The "Point A" isodose distribution from the implant was superimposed onto the whole pelvic simulation film and quantitatively compared to the actual or a hypothetical standard block outlined on the same radiograph. In September of 1995, 56 member and affiliated institutions in the GOG were surveyed concerning their use of a MLS, and the results were tabulated in December of 1995. RESULTS: Approximately 72% of all cases (23 out of 32) at the single institution had tandem deviation ranging from 0-230 with a median of 50. This translated into a median percent overdosage to "Point A" Right of 15% and "Point A" Left of 12.5%. Although overall survival and incidence of chronic complications have not been affected by type of shielding, patient follow-up is limited with a median of 17.7 months (range: 4.2-58.9 months). Of the 56 surveyed radiation facilities in the GOG, 34 (61%) responded. One center was subsequently excluded as it performs only high dose rate brachytherapy. Of the evaluable respondents, 88% (29 out of 33) utilize a MLS in treating their patients with invasive cervical carcinoma. Of the latter group, 76% (22 out of 29), 21% (6 out of 29), and 3% (1 out of 29) employ a standard block, customized block, and a "step-wedge," respectively. For those using a standard block, 77% (17 out of 22) align the central cranial-caudal axis of the MLS along the corresponding midplane of the patient's pelvis on an anteroposterior radiograph rather than along the superior-inferior central axis of the tandem. CONCLUSIONS: This study suggests that the use of a standard midline shield could result in potential tumor dose inhomogeneity and should be avoided. A national survey of major academic centers further suggests that the majority of these facilities also utilize a rectangular central block that is not positioned with respect to possible tandem deviation. Further investigation concerning the techniques of midline shield construction should be considered.

A comparison of 3-D data correlation methods for fractionated stereotactic radiotherapy.

PURPOSE: Stereotactic radiosurgery is currently used to treat patients who are not good candidates for conventional neurosurgical procedures. For treatments of nonvascular tumor cells, it appears that fractionation offers a radiobiological advantage between tumor and normal tissues. Therefore, fractionated stereotactic radiotherapy (FSR) is preferred because it minimizes normal tissue complications and maximizes local tumor control probability. We have implemented a methodology clinically to perform the noninvasive patient repositioning technique. The 3-D data correlation method for high-precision and multiple fraction stereotactic treatments has been presented. METHODS AND MATERIALS: Three different optimization algorithms (Hooke and Jeeves optimization, simplex optimization, and simulated annealing optimization) are evaluated to calculate the transformation parameters necessary for FSR. A least-square object function is created to perform the 3-D data matching process. By minimizing the unconstrained object function value the best fit can be approached for the reference 3-D data sets. Simulation shows that these algorithms deliver results that are comparable to the previously published correlation algorithm (1,2) (singular value decomposition [SVD] method). The advantage for optimization algorithms is easily understood and can be readily implemented by using a personal computer (PC). The mathematical framework provides a tool to calculate the transformation matrix which can be used to adjust patient position for fractionated treatments. Therefore, using these algorithms for a high-precision fractionated treatment is possible without an invasive repeat fixation device and has been implemented clinically. A bite plate system was incorporated to acquire 3-D patient data. With a 3-D digital camera localization device, the patient motion can be followed in real time with the system calibrated to the isocenter. RESULTS: Two types of data sets are utilized to study the correlation results. One is using the digitized patient data which were retrieved clinically. The other is using the randomly generated data sets. Simulation errors for the optimization algorithms are all less than 1 mm in translation and less than 1 degree in rotation. Currently, FSR is performed using special designed repeat fixation devices which assure reproducible patient position for multiple fractions of radiation treatment. Clinical results indicated that this technique provided excellent treatment results. CONCLUSION: Three optimization algorithms have been applied and evaluated in calculating the transformation parameters between two 3-D contours or digitized data points. The mathematical functions behind these optimization algorithms are straightforward and can be easily implemented. When incorporated with the proper CT/MR image data with an electronic portal imaging (EPI) system, this process can possibly verify the patient's treatment position whenever there is doubt about the movement during the treatment procedure.

Improvements in obtaining and characterizing mouse cerebrospinal fluid. Application to mouse hepatitis virus-induced encephalomyelitis.

This report describes advances in techniques for analyzing cellular and humoral immune components in the cerebrospinal fluid (CSF) of the mouse that are applicable to other laboratory animals. CSF studies undertaken during experimental infection of mice with JHM strain virus (JHMV) of mouse hepatitis virus are presented. A critical pitfall which can lead to erroneous or invalid results is contamination of the CSF by even minute quantities of blood. Means of avoiding this contamination are attention to anatomical reference points, the use of a micropipet, and prior intracardiac perfusion of animals with phosphate-buffered saline. Cells in the CSF were typed as either B, T, polymorphonuclear, or mononuclear cells by the combination of a microcytotoxicity assay and histologic stains. A radioimmunoassay (RIA) allowed quantification of antibodies to JHMV in the CSF and indicated the presence of intrathecal synthesis of antibody in chronically infected mice. The combined use of these sensitive methods makes possible CSF analysis in individual mice rather than in pooled groups.

Small-field electron dosimetry for the Philips SL25 linear accelerator.

Electron-beam characteristics of a Philips SL25 linear accelerator have been studied. Central-axis percentage depth doses, cross-beam profiles and beam output factors of 6-, 10-, and 20-MeV beams, selected from the available energy range of 4 to 22 MeV, are reported in this paper. The main thrust of this work is to determine the systematic variation of beam characteristics, especially the output factor, with standard cone sizes and cerrobend beam-shaping cutouts down to a field size of 2 X 2 cm Output factors for the standard cones (open field) are energy dependent in a complex manner, increasing with the cone size for the 6-MeV beam whereas decreasing for 10- and 20-MeV beams. The output factor falls below unity at lower energies (6 and 10 MeV) for fields with at least one side smaller than 6 cm, and stays nearly constant for the 20-MeV beam. Measured output factors of small fields are least squares fitted by a second-order polynomial function. Output factors for small rectangular fields have been derived from the one-dimensional and square-root formulas, and the equivalent-square method. Only the one-dimensional formula predicts the measured output factors of highly elongated fields to within +/- 1% experimental uncertainties. Different cones with the same size electron cutout show a varied dose response, primarily due to variation in scattered electron contamination from the cones.

Measurements and calculations of the influence of thin inhomogeneities on charged particle beams.

The predictions of an analytic technique for calculating fluence and dose distributions beneath thin inhomogeneities are presented for a number of structures, including a rectangular cavity or bar, a cylinder, a disk, and an angled or diffuse edge. Experiments with both electrons and protons for several geometries are presented and compared with predictions based on this technique. We offer some clinical guidelines for avoiding large perturbations due to scattering effects.

Management of stage I-B, II-A, and II-B carcinoma of the cervix with high-dose-rate brachytherapy: initial results of an institutional clinical trial.

In 1989, the University of Miami began a program incorporating high-dose-rate (HDR) brachytherapy into the definitive treatment of patients with invasive carcinoma of the cervix. Patients received an average total dose to point A of 5,511 cGy (range 4,280-6,360 cGy) in an average of 57 days (range 39-84 days). An analysis of the first 24 cases found 11 FIGO Stage I-B, four Stage II-A, and nine Stage II-B tumors. At the end of all radiation therapy, 19/24 patients' tumors (79.2%) had undergone a clinical complete response (CR). With median follow-up of 26 months (range 14-63 months), three have relapsed locally, two regionally, and six in extrapelvic sites. Almost two-thirds of all failures occurred in patients with tumors >4 cm, who also took more than 8 weeks to complete their treatment. Overall 2-year actuarial survival for the entire study group is approximately 74%. A univariate analysis determined that clinical stage (P = 0.02), overall treatment time (P = 0.03), tumor size (P = 0.05), and response at the end of therapy (P = 0.005) were significant prognostic factors. Multivariate analysis showed that tumor response to therapy was the most important prognosticator of outcome (P = 0.001). Besides five cases of apical vaginal stenosis, there have been no reported chronic complications in this cohort of patients. A prospectively randomized trial is recommended to compare the efficacy of HDR vs. low-dose-rate brachytherapy in cervical carcinoma.

Ciguatera poisoning: an example of a public health challenge.

Ciguatera is a common form of fish poisoning, endemic in all nations of the Pacific region. Several thousand cases have been notified to Queensland authorities over a 10-year period. However, many cases remain undiagnosed and most go unreported. The public health implications include raising awareness of the condition, ensuring that ciguatera is considered in differential diagnosis and promoting better documentation and reporting.

Hyperosmolar diabetic non-ketotic coma, hyperkalaemia and an unusual near death experience.

Generally, cardiac arrest due to pulseless electrical activity has a poor outcome, except when reversible factors such as acute hyperkalaemia are identified and managed early. Hyperosmolar diabetic non-ketotic coma may lead to acute hyperkalaemia. Hyperosmolar diabetic non-ketotic coma is a metabolic emergency usually seen in elderly non-insulin dependent diabetics, characterized by severe hyperglycaemia, volume depletion, altered consciousness, confusion and less frequently neurological deficit. Cerebrovascular accident or transient ischaemic attack may be mistakenly diagnosed, particularly if the patient has no history of diabetes mellitus. Delays in diagnosis and management of glycaemic emergencies presenting as a constellation of neurological abnormalities can be avoided by routine early measurement of blood glucose. Hyperosmolar diabetic non-ketotic coma should be considered in any patient with altered consciousness or neurologic deficit in conjunction with hyperglycaemia. As hyperosmolar diabetic non-ketotic coma results in severe fluid depletion, electrolyte disturbance, profound hyperglycaemia and an altered mental state, the guiding principles of therapy include aggressive rehydration, insulin therapy, correction of electrolyte abnormalities and treatment of any underlying illnesses. Treatment of acute hyperkalaemia includes calcium ions, insulin with dextrose, salbutamol and haemodialysis.

Ciguatera poisoning: a global issue with common management problems.

Ciguatera poisoning, a toxinological syndrome comprising an enigmatic mixture of gastrointestinal, neurocutaneous and constitutional symptoms, is a common food-borne illness related to contaminated fish consumption. As many as 50000 cases worldwide are reported annually, and the condition is endemic in tropical and subtropical regions of the Pacific Basin, Indian Ocean and Caribbean. Isolated outbreaks occur sporadically but with increasing frequency in temperate areas such as Europe and North America. Increase in travel between temperate countries and endemic areas and importation of susceptible fish has led to its encroachment into regions of the world where ciguatera has previously been rarely encountered. In the developed world, ciguatera poses a public health threat due to delayed or missed diagnosis. Ciguatera is frequently encountered in Australia. Sporadic cases are often misdiagnosed or not medically attended to, leading to persistent or recurrent debilitating symptoms lasting months to years. Without treatment, distinctive neurologic symptoms persist, occasionally being mistaken for multiple sclerosis. Constitutional symptoms may be misdiagnosed as chronic fatigue syndrome. A common source outbreak is easier to recognize and therefore notify to public health organizations. We present a case series of four adult tourists who developed ciguatera poisoning after consuming contaminated fish in Vanuatu. All responded well to intravenous mannitol. This is in contrast to a fifth patient who developed symptoms suggestive of ciguatoxicity in the same week as the index cases but actually had staphylococcal endocarditis with bacteraemia. In addition to a lack of response to mannitol, clinical and laboratory indices of sepsis were present in this patient. Apart from ciguatera, acute gastroenteritis followed by neurological symptoms may be due to paralytic or neurotoxic shellfish poisoning, scombroid and pufferfish toxicity, botulism, enterovirus 71, toxidromes and bacteraemia. Clinical aspects of ciguatera toxicity, its pathophysiology, diagnostic difficulties and epidemiology are discussed.

Dose verification for patients undergoing IMRT.

At Emory Clinic intensity-modulated radiation therapy (IMRT) was started by using dynamic multileaf collimators (dMLC) as electronic tissue compensators in August 1998. Our IMRT program evolved with the inclusion of a commercially available inverse treatment planning system in September 1999. While the introduction of electronic tissue compensators into clinical use did not affect the customary radiation oncology practice, inverse treatment planning does alter our basic routines. Basic concepts of radiation therapy port designs for inverse treatment planning are different from conventional or 3D conformal treatments. With inverse treatment planning, clinicians are required to outline a gross tumor volume (GTV), a clinical target volume (CTV), critical normal structures, and to design a planning target volume (PTV). Clinicians do not designate the volume to be shielded. Because each IMRT radiation portal is composed of many beamlets with varying intensities, methods and practice used to verify delivered dose from IMRT portals are also different from conventional treatment portals. Often, the validity of measured data is in doubt. Therefore, checking treatment planning computer output with measurements are confusing and fruitless, at times. Commissioning an IMRT program and routine patient dose verification of IMRT require films and ionization chamber measurements in phantom. Additional specialized physics instrumentation is not required other than those available in a typical radiation oncology facility. At this time, we consider that routine quality assurance prior to patient treatments is necessary.

A case of severe haemolytic disease of the newborn due to anti-Di(a) antibody.

Red cell allo-antibodies directed against the Diego (Di) blood group antigen have rarely been reported to cause a haemolytic reaction against transfusion or haemolytic disease of the newborn. The frequency of the Di(a+) phenotype among the Hong Kong Chinese population is estimated to be 4.4%. We report on a case of severe haemolytic disease of the newborn due to anti-Di(a) antibody--the first local case to the best of our knowledge. Rare but clinically significant antibodies targeting red blood cells have to be considered in the investigation of haemolytic disease of the newborn when common underlying factors have been eliminated.

Exposures to patient and personnel in computed axial tomography.

Distribution of radiation exposure circumcranially for patients undergoing brain scanning with EMI computed tomographic equipment was measured using thermoluminescent dosimeters. The exposures are found to lie in the range of 1-5 R depending on position relative to tube motion. The maximum exposure of 5 R in CT scanning lies between the estimated exposure of 1.2 R for skull radiography and approximately 10 R for angiographic examination. Measured exposures are reported corresponding to locations of the patients' eyes, thyroid, chest and gonads, and at various locations in the vicinity of the unit.

Stereotactic dose computation and plan optimization using the convolution theorem. I. Dose computation.

With Leksell Gamma Knife stereotactic radiosurgery, the dose distribution delivered by a specific helmet can be assumed to remain as a fixed-dose distribution when the shot is moved to different locations within the predefined dose calculation matrix. The convolution theorem may be implemented to take advantage of this fact for fast dose computation and plan construction. Using this technique, the shot spatial arrangement is formulated as a convolution kernel, which is theoretically a three-dimensional multi-delta function. The dose distribution is computed by the convolution of this single-shot dose distribution with the shot convolution kernel. To determine the shot arrangement, an ideal dose distribution is generated based upon the target structure. Deconvolution is then applied to find the convolution kernel which best fits the proposed ideal dose distribution. The primary task of this presentation is to focus on and describe in detail the dose computation using the convolution theorem.

Bladder and rectal doses from external-beam boosts after gynecologic brachytherapy.

PURPOSE: To establish a typical value for radiation doses under pelvic midline shields. MATERIALS AND METHODS: Three methods were used to determine bladder and rectal doses under 5- or 6-half-value layer (HVL) shields for 10- and 24-MV external beams. First, dose was computed with a standard irregular field routine in 25 consecutive patients (aged 35-70 years) with stage IIB or IIIB disease treated with cesium-137 brachytherapy followed by a parametrial external-beam boost. Second, in vivo measurements with a solid-state probe were recorded during the first boost after completion of brachytherapy in each patient. Third, measurements obtained with an ionization chamber in a solid phantom (water-equivalent material) were compared with computed and in vivo results. RESULTS: All three dosimetric methods yielded bladder and rectal doses higher than the commonly assumed 5% of the unshielded primary beam dose. Doses within the shielded volume may be as high as 15% of the unshielded dose. Doses are similar under 5- and 6-HVL midline shields. Often, the actual bladder and rectal doses exceeded the planned dose limits and their corresponding maximum radiation dose tolerance levels. CONCLUSION: Bladder and rectal doses are higher than previously understood. Parametrial boosts may contribute as much as 3.0 Gy to the bladder and rectal doses.