Dosimetric intercomparison for multicenter clinical trials using a patient-based anatomic pelvic phantom.

PURPOSE: To assess dose delivery accuracy to clinically significant points in a realistic patient geometry for two separate pelvic radiotherapy scenarios. METHODS: An inhomogeneous pelvic phantom was transported to 36 radiotherapy centers in Australia and New Zealand. The phantom was treated according to Phase III rectal and prostate trial protocols. Point dose measurements were made with thermoluminescent dosimeters (TLDs) and an ionisation chamber. Comprehensive site-demographic, treatment planning, and physical data were collected for correlation with measurement outcomes. RESULTS: Dose delivery to the prescription point for the rectal treatment was consistent with planned dose (mean difference between planned and measured dose - 0.1 ± 0.3% std err). Dose delivery in the region of the sacral hollow was consistently higher than planned (+1.2 ± 0.2%). For the prostate treatment, dose delivery to the prostate volume was consistent with planned doses (-0.49 ± 0.2%) and planned dose uniformity, though with a tendency to underdose the PTV at the prostate-rectal border. Measured out-of-field doses were significantly higher than planned. CONCLUSIONS: A phantom based on realistic anatomy and heterogeneity can be used to comprehensively assess the influence of multiple aspects of the radiotherapy treatment process on dose delivery. The ability to verify dose delivery for two trials with a single phantom was advantageous.

Design, manufacture, and evaluation of an anthropomorphic pelvic phantom purpose-built for radiotherapy dosimetric intercomparison.

PURPOSE: An anthropomorphic pelvic phantom was designed and constructed to meet specific criteria for multicenter radiotherapy dosimetric intercomparison. METHODS: Three dimensional external and organ outlines were generated from a computed tomography image set of a male pelvis, forming the basis of design for an anatomically realistic phantom. Clinically relevant points of interest were selected throughout the dataset where point-dose values could be measured with thermoluminescence dosimeters and a small-volume ionization chamber. Following testing, three materials were selected and the phantom was manufactured using modern prototyping techniques into five separate coronal slices. Time lines and resource requirements for the phantom design and manufacture were recorded. The ability of the phantom to mimic the entire treatment chain was tested. RESULTS: The phantom CT images indicated that organ densities and geometries were comparable to those of the original patient. The phantom proved simple to load for dosimetry and rapid to assemble. Due to heat release during manufacture, small air gaps and density heterogeneities were present throughout the phantom. The overall cost for production of the prototype phantom was comparable to other commercial anthropomorphic phantoms. The phantom was shown to be suitable for use as a "patient" to mimic the entire treatment chain for typical external beam radiotherapy for prostate and rectal cancer. CONCLUSIONS: The phantom constructed for the present study incorporates all characteristics necessary for accurate Level III intercomparison studies. Following use in an extensive Level III dosimetric comparison over a large time scale and geographic area, the phantom retained mechanical stability and did not show signs of radiation-induced degradation.

Comprehensive Australasian multicentre dosimetric intercomparison: issues, logistics and recommendations.

The present paper describes the logistics of the 2004-2008 Australasian Level III Dosimetry Intercomparison. Dosimetric intercomparisons (or 'audits') can be used in radiotherapy to evaluate the accuracy and quality of radiation delivery. An intercomparison was undertaken in New Zealand and Australia to evaluate the feasibility and logistics of ongoing dosimetric intercomparisons that evaluate all steps in the radiotherapy treatment process, known as a 'Level III' intercomparison. The study commenced in 2002 with the establishment of a study team, definition of the study protocol, acquisition of appropriate equipment and recruitment of participating radiotherapy centres. Measurements were undertaken between October 2004 and March 2008, and included collation of data on time, costs and logistics of the study. Forty independent Australian and New Zealand radiotherapy centres agreed to participate. Measurement visits were made to 37 of these centres. Data is presented on the costs of the study and the level of support required. The study involved the participation of 16 staff at the study centre who invested over 4000 hours in the study, and of over 200 professionals at participating centres. Recommendations are provided for future phantom-based intercomparisons. It is hoped that the present paper will be of benefit to any centres or groups contemplating similar activities by identifying the processes involved in establishing the study, the potential hazards and pitfalls, and expected resource requirements.

Effects of an internal escape channel on a castable ceramic crown.

This study evaluated the adaptation and strength of Dicor castable ceramic crowns cemented using an internal escape channel on the axial wall of the preparation. Twenty-eight crown wax patterns were made on 14 machined brass dies. The adaptation of the crowns was evaluated by measuring the combined height of the die and crown. The results revealed a significant difference in the mean and standard deviation of 16 +/- 13 micron in the experimental group and 85 +/- 31 microns in the control group. The differences between the force to fracture of 2155 +/- 1188 N and 1040 +/- 658 N, respectively, was also significant. The findings suggested that having an internal escape channel during cementation significantly improved the fit and strength of Dicor castable ceramic crowns. This technique would be particularly beneficial for cementation of posterior castable ceramics.

Zinc deficiency in anorexia nervosa.

Adolescents with anorexia nervosa were evaluated for clinical and biochemical evidence of zinc deficiency. To assess whether these patients would benefit from zinc supplementation, a double-blind, randomized, controlled trial was conducted. The mean zinc intake of the anorexic group calculated on the basis of three-day dietary records was 7.7 +/- 5.2 mg/day, which is significantly below the recommended daily allowance of 15 mg for adolescents (p less than 0.001). The mean urinary zinc excretion in the anorexic group was 257.1 +/- 212.7 micrograms/24 hours compared to 749.9 +/- 897.8 micrograms/24 hours in the control group (p less than 0.005). This result suggests that the zinc status of anorexia nervosa patients may be compromised due to an inadequate zinc intake. Zinc supplementation (50 mg elemental zinc/day) was followed by a decrease in the level of depression and anxiety as assessed by the Zung Depression Scale (p less than 0.05) and the State-Trait Anxiety Inventory (p less than 0.05), respectively. Our data suggest that individuals with anorexia nervosa may be at risk for zinc deficiency and may respond favorably after zinc supplementation.

Spinal cord compression in breast cancer.

Myelography was performed on 78 patients with breast cancer who had signs or symptoms compatible with spinal cord compression. Of 42 patients (54%) with extradural defects, 21 (50%) had a complete block. All patients with positive myelograms (M+) had a positive bone scan and 41 of 42 (97%) had positive skeletal x-rays. Except for paraplegia, paraparesis, or a sensory level abnormality, signs and symptoms were usually not precise enough to accurately predict patients with cord lesions; however, back pain, paresthesias, and bladder or bowel dysfunction were significantly more common in M+ patients. Cerebrospinal fluid (CSF) protein was elevated in almost all M+ patients but also in approximately half of the M- group. Cytology and glucose analysis of CSF were not of value in predicting cord involvement. Response to treatment was better for patients with fewer sites of metastatic disease and a shorter time from diagnosis to treatment. There was no notable difference in survival between M+ and M- patients. Myelography remains the most precise tool for diagnosing spinal cord lesions. Unfortunately, the prognosis of patients with metastatic breast cancer is poor regardless of whether spinal cord compression is present.

Neurogenic pulmonary oedema.

Two young patients with head injuries subsequently developed neurogenic pulmonary oedema. The origin and pathways of the reflex response to cerebral trauma are discussed, with emphasis on the role of raised intracranial pressure and the sympathetic division of the autonomic nervous system in precipitating movement of systemic circulatory volume into the pulmonary circulation. Therapeutic measures are discussed which correct the progression of this condition by reducing intracranial pressure and blocking the systemic effects of autonomic reflex activity. This leads to the basis of a simple regime to treat future cases.

Platelet adhesiveness after blood donation.

Platelet adhesiveness to glass was measured in healthy blood donors at the time of and eight days after donating 500 ml of blood. By a whole blood method a highly significant increase was found whereas by a method using platelet-rich plasma with added adenosine diphosphate there was only a slightly significant increase. The discrepancy suggested that changes in the red cell population might influence the results. Packed red cells from 19 blood donors obtained at the time of donation and eight days later were mixed with fresh pooled platelets from the same independent persons on each occasion. The whole blood platelet adhesiveness on this mixture showed an increase in every case after blood donation. It is postulated that the increased adhesiveness is influenced by the presence of young red cells.