Radiation incidents with a cobalt-60 teletherapy unit

To separate fact from fiction regarding the susceptibility of women athletes to injury, three surveys were conducted. The initial data were collected from the athletic departments of collegiate institutions, and the final material was assembled from certified athletic trainers at these institutions, plus an extensive computer search of applicable publications. The collected statistical data were tabulated, and a written commentary was evaluated by the authors. It was established that injuries sustained by female athletes, aside from those related to different biological structures, were essentially no different than those of men, nor are well-trained women athletes more prone to injury. Ankle and knee injuries are most frequent, and women sustain many contusions, sprains, and shin splints. It is anticipated that the overall number of injuries will decrease as better coaches and trainers become available to women athletes.     

Monte Carlo dosimetry study of a 6 MV stereotactic radiosurgery unit

Small-field and stereotactic radiosurgery (SRS) dosimetry with radiation detectors, used for clinical practice, have often been questioned due to the lack of lateral electron equilibrium and uncertainty in beam energy. A dosimetry study was performed for a dedicated 6 MV SRS unit, capable of generating circular radiation fields with diameters of 1.25-5 cm at isocentre using the BEAM/EGS4 Monte Carlo code. With this code the accelerator was modelled for radiation fields with a diameter as small as 0.5 cm. The radiation fields and dosimetric characteristics (photon spectra, depth doses, lateral dose profiles and cone factors) in a water phantom were evaluated. The cone factor (St) for a specific cone c at depth d is defined as St(d, c) = D(d, c)/D(d, c(ref)), where c(ref) is the reference cone. To verify the Monte Carlo calculations, measurements were performed with detectors commonly used in SRS such as small-volume ion chambers, a diamond detector, TLDs and films. Results show that beam energies vary with cone diameter. For a 6 MV beam, the mean energies in water at the point of maximum dose for a 0.5 cm cone and a 5 cm cone are 2.05 MeV and 1.65 MeV respectively. The values of St obtained by the simulations are in good agreement with the results of the measurements for most detectors. When the lateral resolution of the detectors is taken into account, the results agree within a few per cent for most fields and detectors. The calculations showed a variation of St with depth in the water. Based on calculated electron spectra in water, the validity of the assumption that measured dose ratios are equal to measured detector readings was verified.     

Monte Carlo treatment planning for stereotactic radiosurgery

A position-dependent pattern of epidermal cell types is produced during root development in Arabidopsis thaliana. This pattern is reflected in the expression pattern of GLABRA2 (GL2), a homeobox gene that regulates cell differentiation in the root epidermis. GL2 promoter::GUS fusions were used to show that the TTG gene, a regulator of root epidermis development, is necessary for maximal GL2 activity but is not required for the pattern of GL2 expression. Furthermore, GL2-promoter activity is influenced by expression of the myc-like maize R gene (35S::R) in Arabidopsis but is not affected by gl2 mutations. A position-dependent pattern of cell differentiation and GL2-promoter activity was also discovered in the hypocotyl epidermis that was analogous to the pattern in the root. Non-GL2-expressing cell files in the hypocotyl epidermis located outside anticlinal cortical cell walls exhibit reduced cell length and form stomata. Like the root, the hypocotyl GL2 activity was shown to be influenced by ttg and 35S::R but not by gl2. The parallel pattern of cell differentiation in the root and hypocotyl indicates that TTG and GL2 participate in a common position-dependent mechanism to control cell-type patterning throughout the apical-basal axis of the Arabidopsis seedling.     

Anaesthetic considerations for children undergoing stereotactic radiosurgery

An anaesthetic case report of children undergoing stereotactic radiosurgery is presented, with a review of the inherent unique anaesthetic challenges. Twelve stereotactic radiosurgery procedures performed at The Prince of Wales Hospital, Sydney, were retrospectively reviewed. Despite differences in approach by individual anaesthetists to managing these children, an overall safe sequence may be evolved. The use of stereotactic radiosurgery for paediatric neuropathology is reviewed. The potential anaesthetic problems related to the paediatric patient and the peculiarities of the procedure are discussed and related to our series.     

Initial clinical results of LINAC-based stereotactic radiosurgery and stereotactic radiotherapy for pituitary adenomas

PURPOSE: To retrospectively evaluate the initial clinical results of stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (SRT) for pituitary adenomas with regard to tumor and hormonal control and adverse effects of the treatment. SUBJECTS AND METHODS: Forty-eight patients with pituitary adenoma who underwent SRS or SRT between September 1989 and September 1995 were analyzed. Of these, 18 received SRS and 30 received SRT. The median tumor volumes were 1.9 cm3 for SRS and 5.7 cm3 for SRT. Eleven of the SRS and 18 of the SRT patients were hormonally active at the time of the initial diagnosis. Four of the SRS and none of the SRT patients had a history of prior radiation therapy. Both SRS and SRT were performed using a dedicated stereotactic 6-MV linear accelerator (LINAC). The dose and normalization used for the SRS varied from 1000 cGy at 85% of the isodose line to 1500 cGy at 65% of the isodose line. For SRT patients, a total dose of 4500 cGy at 90% or 95% of the isodose line was delivered in 25 fractions of 180 cGy daily doses. RESULTS: Disease control-The three year tumor control rate was 91.1% (100% for SRS and 85.3% for SRT). Normalization of the hormonal abnormality was achieved in 47% of the 48 patients (33% for SRS and 54% for SRT). The average time required for normalization was 8.5 months for SRS and 18 months for SRT. Adverse effects-The 3-year rate of freedom from central nervous system adverse effects was 89.7% (72.2% for SRS and 100% for SRT). Three patients who received SRS for a tumor in the cavernous sinus developed a ring enhancement in the temporal lobe as shown by follow-up magnetic resonance imaging. Two of these cases were irreversible and were considered to be radiation necrosis. None of the 48 patients developed new neurocognitive or visual disorders attributable to the irradiation. The incidence of endocrinological adverse effects were similar in the two groups, resulting in 3-year rates of freedom from newly initiated hormonal replacement of 78.4% (77.1% for SRS and 79.9% for SRT). CONCLUSION: Considering the relatively high incidence of morbidity observed in the SRS group, we recommend SRT as the primary method of radiation therapy for pituitary tumors. When treating a lesion in the cavernous sinus with SRS, special attention should be paid to dose distribution in the adjacent brain parenchyma. Longer follow-up is necessary before drawing any conclusions about the advantages of these techniques over conventional external beam radiation therapy.     

Preoperative cortical localization with functional MRI for use in stereotactic radiosurgery

Accurate localization of the lesion with respect to functionally significant brain is essential to safe stereotactic radiosurgical dose planning. We report the use of functional MR imaging in 3 patients to identify critical areas of surrounding brain and to provide assistance with dose planning, especially with regard to shaping the peripheral isodose around the lesion. We used a functional MRI system employing a conventional 1.5-tesla MRI unit that can detect decreases in deoxyhemoglobin concentration occurring with performance of specific tasks. Two of the patients had supratentorial arteriovenous malformations and 1 patient had a recurrent parasagittal meningioma. Functional MRI provided information on the location of speech, motor, and sensory cortex in these patients. Radiosurgical dose plans were constructed that kept these cortical areas outside of the 30% isodose curves. We believe that the safety of supratentorial parenchymal radiosurgery will be enhanced by the localization of critical brain regions around the target.     

Reduction of hippocampal-kindled seizure activity in rats by stereotactic radiosurgery

The development of a noninvasive imaging procedure for identifying atherosclerotic lesions is extremely important for the clinical management of patients with coronary artery and peripheral vascular disease. Although numerous radiopharmaceuticals have been proposed for this purpose, none has demonstrated the diagnostic accuracy required to replace invasive angiography. In this report, we used the radiolabeled purine analog, 99mTc diadenosine tetraphosphate (Ap4A; AppppA, P1,P4-di(adenosine-5')-tetraphosphate) and its analogue 99mTc AppCHClppA for imaging experimental atherosclerotic lesions in New Zealand White rabbits. Serial gamma camera images were obtained after intravenous injection of the radiolabeled dinucleotides. After acquiring the final images, the animals were sacrificed, ex vivo images of the aortas were recorded, and biodistribution was measured. 99mTc-Ap4A and 99mTc AppCHClppA accumulated rapidly in atherosclerotic abdominal aorta, and lesions were clearly visible within 30 min after injection in all animals that were studied. Both radiopharmaceuticals were retained in the lesions for 3 hr, and the peak lesion to normal vessel ratio was 7.4 to 1. Neither of the purine analogs showed significant accumulation in the abdominal aorta of normal (control) rabbits. The excised aortas showed lesion patterns that were highly correlated with the in vivo and ex vivo imaging results. The present study demonstrates that purine receptors are up-regulated in experimental atherosclerotic lesions and 99mTc-labeled purine analogs have potential for rapid noninvasive detection of plaque formation.     

An efficient method for small field treatment dose calculation for stereotactic radiosurgery using a LINAC

The normal procedure for a physician-physicist team designing a treatment plan for multiarc stereotactic radiosurgery is the trial-and-error approach of changing the collimator size and the location of the isocenter of radiation and viewing the isodose curves on two-dimensional computed tomography (CT) or magnetic resonance imaging (MRI) image planes. Automatic optimization procedures have also been used to optimize beam weight or beam size. However, either process is very time consuming. To improve the speed of the dose calculation, a random sampling method has been proposed. Unfortunately, the sampled values of an objective function are different from one sample to another. Such a sampling method cannot be used in automatic optimization because the next move in an optimization process is based on the current and past objective function values. To this end, an adaptive method based on the size of the collimators is proposed and used to determine a small volume in the shape of a hollow sphere for which the dose is calculated. With an appropriate choice of an adaptive hollow sphere, the objective function calculated based on such a hollow sphere is the same as that calculated with the traditional three-dimensional (3-D) cube matrix. However, with the new adaptive method, the speed of calculating a dose can be improved by a factor of 4 to a factor of 100. Because of the improvement in the speed of calculating a treatment dose, the new adaptive hollow sphere method for calculating a treatment dose can be used routinely in designing a treatment plan.     

Comparison of stereotactic radiosurgery and brachytherapy in the treatment of recurrent glioblastoma multiforme

The purpose of this study was to compare the efficacy of stereotactic radiosurgery (SRS) and brachytherapy in the treatment of recurrent glioblastoma multiforme (GBM). The patients had either progressive GBM or pathologically proven GBM at recurrence after previous treatment for a lower grade astrocytoma. Thirty-two patients were treated with interstitial brachytherapy, and 86 received treatment with stereotactic radiosurgery (SRS). The patient characteristics were similar in the two groups. Those patients treated with SRS had a median tumor volume of 10.1 cm3 and received a median peripheral tumor dose of 13 Gy. Patients treated with brachytherapy had a median tumor volume of 29 cm3. Median dose to the periphery of the tumor volume was 50 Gy delivered at a median dose rate of 43 cGy/hour. Twenty-one patients (24%) treated with SRS were alive, with a median follow-up of 17.5 months. Median actuarial survival, measured from the time of treatment for recurrence, for all patients treated with SRS was 10.2 months, with survivals of 12 and 24 months being 45 and 19%, respectively. A younger age and a smaller tumor volume were predictive of better outcome. The tumor dose, the interval from initial diagnosis, and the need for reoperation were not predictive of outcome after SRS. Five patients (16%) treated with brachytherapy were alive, with a median follow-up of 43.3 months. The median actuarial survival for all patients treated with brachytherapy was 11.5 months. Survivals of 12 and 24 months were 44 and 17%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

The role of stereotactic radiosurgery in the treatment of malignant skull base tumors

PURPOSE: To determine the efficacy and toxicity of stereotactic radiosurgery in the treatment of malignant skull base tumors. METHODS AND MATERIALS: Thirty-two patients with 35 newly diagnosed or recurrent malignant skull base tumors < or = 33.5 cm3 were treated using the Leksell Gamma unit. Tumor histologies included: adenoid cystic carcinoma [12], basal cell carcinoma [1], chondrosarcoma [1], chordoma [8], nasopharyngeal carcinoma [3], osteogenic sarcoma [2], and squamous cell carcinoma [8]. RESULTS: After a median follow-up of 2.3 years, 83% +/- 15% (+/-95% confidence interval) of patients experienced a symptomatic response to treatment. Local control at the skull base was 95 +/- 9% at 2 years and 78 +/- 23% at 3 years. Local-regional control above the clavicles was 75 +/- 15% at 1 year and 51 +/- 20% at 2 years. Overall and cause specific survival were identical, 82 +/- 13% at 1 year, 76 +/- 14% at 2 years, and 72 +/- 16% at 3 years. One patient developed a radiation-induced optic neuropathy 12 months after radiosurgery. CONCLUSION: Stereotactic radiosurgery using the Leksell Gamma Unit can provide durable tumor control and symptomatic relief with acceptable toxicity in the majority of patients with malignant tumors 4 cm or less in size involving the skull base. Further evaluation of more patients with longer follow-up is warranted.     

Use of an open stereotactic ring for neurosurgical procedures

We describe an open ring as a new design to the Zamorano-Dujovny (Z-D) stereotactic unit. The titanium base ring has an opening of 45 degrees that can be located in any chosen position. Imaging studies such as computed tomography, X-ray, positron emission tomography, digital angiography, and digital substraction angiography can be performed with the open stereotactic ring for multimodality image localization. Preoperatively and intraoperatively, this open design provides the anesthesiologist with an unobstructed pathway for airway management. During the surgical procedure, it facilitates approach to any intracranial lesion, including orbitozygomatic, combined supra-infratentorial, and others. During awake craniotomies it not only allows for easy airway management, but also provides good access to the patient's face for intraoperative evaluation of speech and visual functions. Accuracy and reliability of this unit were similar to results obtained with the original circular ring. This system can be used in conventional stereotaxis with the Z-D arc, as well as a reference for intraoperative registration with any digitizer system. The open stereotactic unit is a relatively inexpensive, reliable, and easy-to-use solution for resections using conventional stereotaxis or interactive image guidance in any intracranial site.     

A semi-empirical formula for approximate estimation of the fall-off of intensity in the penumbra region of 60co teletherapy beam

The nature of the observed fall-off of intensity across the teletherapy beams for two different 60Co therapy units has been studied. The fall-offs for various field sizes have been compared and an empirical function derived to represent the fall-off. This function is of trigonometric tan inverse form and makes use of only one parameter. The value of this parameter is directly related to the geometrical penumbra width, which can be calculated from the source diameter, the source-to-diaphragm distance and the source-to-skin distance.     

Development of an MRI-compatible needle insertion manipulator for stereotactic neurosurgery

At the University of California, San Francisco, 17 patients who met the following criteria-hepatic tumor unresectable because of location or inadequate liver reserve, no metastases, HBsAg negative, no tumor larger than 5 cm in diameter, and no more than three tumors--were enrolled prospectively in a protocol employing preoperative chemoembolization to assess whether orthotopic liver transplantation (OLT) could cure a majority of highly selected patients with hepatocellular carcinoma (HCC). Thirteen patients had biopsy-proven HCC, 2 had the fibrolamellar variant, and 2 had radiological findings of HCC but no biopsy confirmation. Fourteen had underlying liver disease. All arteriographically apparent lesions were chemoembolized using a mixture including Gelfoam powder, doxorubicin, mitomycin-c, and cisplatin. Eight patients with poor hepatic reserve were chemoembolized when a donor organ became available, whereas 9 patients were chemoembolized and then placed on the waiting list. The only complication of chemoembolization was a gangrenous gallbladder in 1 patient. Thirteen patients underwent liver transplantation (2 patients without prior histological confirmation of carcinoma had no identifiable tumor at OLT); 3 patients developed metastases between the time of enrollment and donor organ availability and subsequently died; and 1 patient underwent a trisegmentectomy. Ten of the 11 patients with biopsy-proven HCC who underwent transplantation remain free of recurrent cancer at a median of 40 months; 1 patient died at 6 months of lymphoproliferative disease with no cancer found at autopsy. Although the role of chemoembolization is uncertain, these data show that the majority of carefully selected patients with HCC may achieve long-term survival with OLT.     

Treatment of arteriovenous malformations with stereotactic radiosurgery employing both magnetic resonance angiography and standard angiography as a database

Twenty-one arteriovenous malformations were prospectively evaluated using magnetic resonance angiography and compared with stereotactic angiography. The goals were to establish the feasibility of magnetic resonance angiography, compare it to stereotactic angiography, employ magnetic resonance angiography in follow-up, and semiquantify flow. A correlative evaluation between flow and response to stereotactic radiosurgery was carried out. Phase contrast angiograms were obtained at flow velocities of 400, 200, 100, 60, and 20 cm/sec. The fractionated velocities provided images that selectively demonstrated the arterial and venous components of the arteriovenous malformations. Qualitative assessment of the velocity within the arteriovenous malformations and the presence of fistulae were also determined by multiple velocity images. In addition, 3-dimensional time-of-flight magnetic resonance angiograms were obtained to define the exact size and shape of the nidus. This technique also permitted evaluation of the nidus and feeding arteries for the presence of low flow aneurysms. Correlation between the two imaging modalities was carried out by subjective and semiquantitative estimation of flow velocity and estimation of nidus size. The following velocity parameters were employed: fast, intermediate, slow, and none (arteriovenous malformation obliterated). In 19 of 21 (90.5%) arteriovenous malformations, magnetic resonance angiography was equal or superior to stereotactic angiography for flow quantification and visualization of the nidus. Only 2 of 21 arteriovenous malformations were better demonstrated by stereotactic angiography than by magnetic resonance angiography (failure rate of 9.5%). The nidus size in one case was clearly underestimated by stereotactic angiography and would have resulted in a geographic miss without magnetic resonance angiography. Seven post-radiosurgery arteriovenous malformations were evaluated for follow-up with both magnetic resonance angiography and stereotactic angiography. In 6 of 7 arteriovenous malformations, magnetic resonance angiography response matched stereotactic angiography response. Correlation of flow with outcome was carried out for 14 arteriovenous malformations using magnetic resonance angiography only. Interestingly, all nine arteriovenous malformations with intermediate or slow flow demonstrated partial or complete obliteration; whereas only 3 of 5 fast flow arteriovenous malformations achieved a response with a median follow-up of 10 months. This early analysis suggests that slower flowing arteriovenous malformations may obliterate faster after stereotactic radiosurgery and flow parameters could be employed to predict response. In conclusion, magnetic resonance angiography permits semiquantitative flow velocity assessment and may therefore be superior to stereotactic angiography. An additional advantage of magnetic resonance angiography is the generation of serial transverse images which can replace the conventional CT scan employed for stereotactic radiosurgery treatment planning.(ABSTRACT TRUNCATED AT 400 WORDS)     

Assimilation, excretion and distribution of cobalt-60 in the rat after daily ingestion of contaminated marine food products

An unusual electrocardiogram (ECG) is presented which demonstrates two mechanisms of communication between the atria and the ventricles. The first appears to reflect ordinary atrio-ventricular impulse propagation. The second appears likely to represent stimulation of the ventricles by mechanical atrial systole.     

Viability of Designing for Construction Worker Safety

Designing for construction safety entails consideration of the safety of construction workers in the design of a project. Research studies have identified the design aspect of projects as being a significant contributing factor to construction site accidents. Designing to eliminate or avoid hazards prior to exposure on the jobsite is also listed as the top priority in the hierarchy of controls common to the safety and health professions. Widespread implementation of the concept in the United States by engineering and architecture firms, however, is lacking due to perceived industry and project barriers. Given its absence from standard design practice, a question arises as to the viability of designing for safety as an intervention in the construction industry. This paper presents a pilot study that was conducted to investigate the practice of addressing construction worker safety when designing a project and to determine the feasibility and practicality of such an intervention. Through interviews of architects and engineers, the study found that a large percentage of design professionals are interested and willing to implement the concept in practice. Among the perceived impacts of implementation, project cost and schedule were mentioned most often along with limitations being placed on design creativity. The results of the pilot study indicate that designing for safety is a viable intervention in construction. The factors that impact the consideration of safety in the design of a project do not entirely prohibit its implementation or make its implementation extremely impractical and therefore not feasible. Additionally, the outcomes of implementation provide sufficient motivation to implement the concept in practice. The paper describes the key changes needed for implementation of the concept in practice which include: a change in designer mindset toward safety; establishment of a motivational force to promote designing for safety; increase designer knowledge of the concept; incorporate construction safety knowledge in the design phase; utilize designers knowledgeable about design-for-safety modifications; make design for safety tools and guidelines available for use and reference; and mitigate designer liability exposure.     

Evaluation of an assessment and training unit for developmentally delayed children

The Rata villa assessment and training unit is intended to provide a short term community service for the evaluation and treatment of developmentally delayed children who are becoming difficult to manage at home or in community educational or training facilities. Since it opened the unit has dealt with 102 first admissions with a wide variety of problems, ranging in age from two to 15 years and varying in intellectual level from normal intelligence to profoundly retarded. In 71 percent of these cases permanent improvements have been made in at least one of the problem areas identified by the child's parents on admission. The treatment programmes are considered to have contributed to maintaining the child in the community as only 28 percent of those treated are currently long term residents in psychopaedic hospitals.