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.

Linear-accelerator X-ray output: a multicentre chamber-based intercomparison study in Australia and New Zealand.

This paper describes the process and results of a survey of linear accelerator outputs as part of an Australasian Level III Dosimetry Intercomparison. This study involved the measurement of accelerator output under reference conditions ('Level I') with a small-volume ionisation chamber in water for 47 beams at 36 radiotherapy centres using the IAEA TRS 398 dose-to-water protocol. The mean ratio of measured to locally-determined accelerator output was 1.003 +/- 0.009 (1 standard deviation) with a range from 0.981 to 1.024. No correlation could be found between output ratio and accelerator type or local output calibration protocol. The small-volume chamber used satisfied most requirements for the study though showed some variation in sensitivity via repeated cross-calibration with a chamber calibrated at a primary standards laboratory.

Enhanced dynamic wedge and independent monitor unit verification.

Some serious radiation accidents have occurred around the world during the delivery of radiotherapy treatment. The regrettable incident in Panama clearly indicated the need for independent monitor unit (MU) verification. Indeed the International Atomic Energy Agency (IAEA), after investigating the incident, made specific recommendations for radiotherapy centres which included an independent monitor unit check for all treatments. Independent monitor unit verification is practiced in many radiotherapy centres in developed countries around the world. It is mandatory in USA but not yet in Australia. This paper describes development of an independent MU program, concentrating on the implementation of the Enhanced Dynamic Wedge (EDW) component. The difficult case of non centre of field (COF) calculation points under the EDW was studied in some detail. Results of a survey of Australasian centres regarding the use of independent MU check systems is also presented. The system was developed with reference to MU calculations made by Pinnacle 3D Radiotherapy Treatment Planning (RTP) system (ADAC - Philips) for 4MV, 6MV and 18MV X-ray beams used at the Newcastle Mater Misericordiae Hospital (NMMH) in the clinical environment. A small systematic error was detected in the equation used for the EDW calculations. Results indicate that COF equations may be used in the non COF situation with similar accuracy to that achieved with profile corrected methods. Further collaborative work with other centres is planned to extend these findings.

Functional symptoms in neurology: questions and answers.

Between 10 and 30% of patients seen by neurologists have symptoms for which there is no current pathophysiological explanation. The objective of this review is to answer questions many neurologists have about disorders characterised by unexplained symptoms (functional disorders) by conducting a multidisciplinary review based on published reports and clinical experience. Current concepts explain functional symptoms as resulting from auto-suggestion, innate coping styles, disorders of volition or attention. Predisposing, precipitating, and perpetuating aetiological factors can be identified and contribute to a therapeutic formulation. The sympathetic communication of the diagnosis by the neurologist is important and all patients should be screened for psychiatric or psychological symptoms because up to two thirds have symptomatic psychiatric comorbidity. Treatment programmes are likely to be most successful if there is close collaboration between neurologists, (liaison) psychiatrists, psychologists, and general practitioners. Long term, symptoms persist in over 50% of patients and many patients remain dependent on financial help from the government. Neurologists can acquire the skills needed to engage patients in psychological treatment but would benefit from closer working relationships with liaison psychiatry or psychology.

Evaluation of P-type semiconductor diodes for in-vivo dosimetry in a 6MV x-ray beam.

The importance of dose verification in radiotherapy has long been recognised. Semiconductor diodes used for in-vivo dosimetry are well suited for this purpose. It was the aim of the present study to investigate the performance of a commercially available set of diodes (Rainbow diodes by Nuclear Associates) which had been in use for two years in our department. The reading of the diodes proved to be reproducible within +/- 0.5% and recalibration was necessary approximately every month. While no marked influence of field size or beam modifiers was found, SSD proved to be a significant factor influencing diode response. Using various radiation qualities in air and phantom experiments, it could be shown that dose rate was not the contributing factor to the SSD dependence of the diode reading, as has been reported by some authors. The results reinforce the need to thoroughly assess diode response prior to clinical use. Using a correction for SSD this work has resulted in the implementation of an accurate and reliable system for diode entrance dose measurements in our 6MV x-ray beams, allowing an action level of +/- 4% to be set in patient measurements.

Evaluation of rectal shielding in a Henschke system applicator.

PURPOSE: To assess the effectiveness of avoid shielding in the Henschke intracavitary gynaecologic 3-channel applicator. MATERIAL AND METHODS: An acrylic phantom was used with our locally modified 3-channel Henschke applicator so that standard treatments with caesium-137 sources could be simulated. Thermoluminescent dosimeters were used to measure point A and rectal doses with and without ovoid shielding to assess the benefits of this shielding. Unshielded measurements were also compared to our planning computer calculations to assess its accuracy. The thermoluminescent dosimeters were calibrated against a caesium teletherapy unit. An estimate of shielding effect produced by the ovoid shielding when using iridium-192 wire was also determined. RESULTS: Doses received at points in the plane containing the rectal point as defined by the ICRU in its report 38 [4] show a reduction ranging from 5% to 15% over the area measured due to the ovoid shielding. As expected this benefit is more pronounced when using iridium-192 sources. Given the steep dose gradients, good agreement is found between computed and measured values of point A doses. CONCLUSION: While ovoid shielding will never provide a large reduction in rectal dose using caesium-137 sources, our results indicate that it can be a worthwhile option when using the Henschke applicator.

The pharmacology of excitatory transmission in the rat olfactory cortex slice.

The pharmacology of excitatory transmission in slices of olfactory cortex of the rat, perfused with solution containing picrotoxin, has been studied by assessing the effects of cis-2,3-piperidine dicarboxylate, a nonselective antagonist of excitatory amino acid receptors, 2-amino-5-phosphonopentanoate, a selective antagonist of N-methyl-D-aspartate (NMDA) receptors and 2-amino-4-phosphonobutyrate (APB) and baclofen, which act at APB and GABAB sites, respectively, on evoked surface field potentials. Monosynaptic excitatory transmission was monitored by measuring the amplitude of the N'a'-wave, evoked on stimulation of the lateral olfactory tract, whilst di-/polysynaptic excitatory transmission was evaluated by calculating the areas of the potentials evoked on direct stimulation of the superficial and deep-lying association fibre systems. On the basis of the effects of the drugs in this and earlier studies, it is concluded that: (i) transmission at the lateral olfactory tract-pyramidal cell synapse is mediated by kainate/quisqualate but not NMDA receptors and is regulated by inhibitory APB receptors, located on the tract terminals; (ii) NMDA receptors are involved in mediating excitatory transmission at the synapses of superficial association fibres with the proximal apical dendrites of pyramidal cells with inhibitory APB receptors playing a regulatory role; (iii) transmission at synapses of association fibres with basal dendrites of pyramidal cells, is mediated in part by NMDA receptors with (presynaptic?) GABAB receptors exerting a strong inhibitory influence. These proposed roles of NMDA receptors have been confirmed in experiments in which the effects of magnesium ions on field potentials evoked in slices perfused in magnesium-free solution were monitored.