Semiconductor real-time quality assurance dosimetry in brachytherapy

With the increase in complexity of brachytherapy treatments, there has been a demand for the development of sophisticated devices for delivery verification. The Centre for Medical Radiation Physics (CMRP), University of Wollongong, has demonstrated the applicability of semiconductor devices to provide cost-effective real-time quality assurance for a wide range of brachytherapy treatment modalities. Semiconductor devices have shown great promise to the future of pretreatment and in vivo quality assurance in a wide range of brachytherapy treatments, from high-dose-rate (HDR) prostate procedures to eye plaque treatments. The aim of this article is to give an insight into several semiconductor-based dosimetry instruments developed by the CMRP. Applications of these instruments are provided for breast and rectal wall in vivo dosimetry in HDR brachytherapy, urethral in vivo dosimetry in prostate low-dose-rate (LDR) brachytherapy, quality assurance of HDR brachytherapy afterloaders, HDR pretreatment plan verification, and real-time verification of LDR and HDR source dwell positions.     

Output factor calculations for intensity modulation radiation therapy as dosimetry quality assurance

Because intensity-modulated radiation therapy (IMRT) is complicated by many small, irregular, and off-center fields, dosimetry quality assurance (QA) is extremely important. QA is performed with verifications of both dose distributions and some arbitrary point doses. In most institutes, verifications are carried out in comparison with dose values generated from radiation treatment planning systems (RTPs) and actually measured doses. However, the estimation of arbitrary point doses without RTPs should be feasible in order to perform IMRT delivery more safely and accurately in terms of the clinical aspect. In this paper, we propose a new algorithm for calculating output factors at the center point of the collimations in an IMRT field with step and shoot delivery machines in which the lower jaws were replaced with multileaf collimators (MLC). We assumed that output is independently affected by collimator scatter and total scatter according to the position of the upper jaws and each of the MLC leaves (lower jaws). Then, the two scatter factors are accurately measured when changing their position. Thus, the output factor for an irregular field could be calculated with the new algorithm. We adopted this technique for some irregular fields and actual IMRT fields for head-and-neck cancer and found that the differences between calculated and measured output values were both small and acceptable. This study suggests that our methods and this algorithm are useful for dosimetry quality assurance.     

Performance assessment of patient dosimetry services and X-ray quality assurance instruments used in diagnostic radiology.

Experiences of the Regional Radiation Physics and Protection Service (RRPPS) in performance assessment of diagnostic X-ray QA instrumentation and on-patient dosemeters are recounted. Issues relating to the provision of realistic and reproducible reference conditions for calibrated X-irradiations are considered and summary statistics from test measurements of dose and kVp meters are provided. For both dose and kVp meters it is indicated that as many as 25% of instruments used in routine use in the U.K. may require some adjustment before they can truly be said to be performing as the manufacturer intended. Results from intercomparison exercises for patient dosimetry services are also discussed. It is apparent that, for those centres participating in the exercise, dose assessments are generally being obtained to within a bias and a relative standard deviation of less then 10%.     

An investigation into the performance of an automated quality assurance and dosimetry system in diagnostic radiology

A system has been developed to undertake automatic quality assurance and dosimetry for diagnostic radiology examinations. The accuracy and reproducibility of the measurements and calculations made by the system have been investigated in a laboratory study and compared with concurrent measurements of exposure parameters made using standard techniques. In a later set of experiments, doses measured using a RANDO phantom and thermoluminescent dosimeters were compared with those calculated by the automated system. Assessment was carried out over a wide range of exposure factors and for a number of different radiological examinations. It is deduced from the results that exposure parameters can be measured with comparable accuracy to standard techniques, and that the automated system is suitable for performing on-line dosimetry.     

Routine quality assurance and results of a diagnostic radiology quality assurance programme

Routine testing of diagnostic radiology equipment performance has shown that more than 10% of equipment has not been properly setup. It also identifies equipment which is deteriorating in use as well as faults which need immediate correction. There is little doubt it is cost-effective and has also been shown to be effective in reducing the collective dose to the population from diagnostic radiology.     

Selective in vivo dosimetry in radiotherapy using P-type semiconductor diodes: a reliable quality assurance procedure.

Since 1994, our center has conducted entrance dose measurements on selected patients receiving 6MV x-ray therapy by utilizing a commercial set of p-type semiconductor diodes. We report on three years results representing 386 patients having 1005 measurements and the usefulness of such a system in a radiotherapy department. The 386 patients represent approximately 20% of our total radical treatments. Minimal disruption to patient treatment was achieved. Measurements showed an average variation from expected dose of 0.5% +/- 2.2%. Specific treatment site groups were investigated. Our results show that in vivo dosimetry on a selected group of patients is an effective method of providing an independent verification of dose delivery accuracy.     

Instrumentation quality assurance and performance

Summary  In summary, a thorough QA program involves all aspects of image acquisition, processing, and interpretation and is essential to the high-quality practice of nuclear cardiology.     

Patient dosimetry measurement methods.

This article reviews patient dosimetry measurement methods applied to diagnostic radiology examinations. Various dose quantities and their relevance to patient dose surveys are described. When contemplating a patient dose survey it is important to develop a clear measurement strategy. This involves a detailed consideration of the most applicable dose measurement method for the intended survey. Various approaches to patient dosimetry are described and reviewed.     

Physical dosimetry of volumetric modulated arc therapy (VMAT) using EPID and 2D array for quality assurance

Outline

To address the correspondence of measured and predicted doses for different malignant tumours utilizing various gamma criteria and QA for confirmation of VMAT with an EPID and 2D array detector.

Mammography processor quality assurance

After completing this article on mammographic processing, readers will: Understand the relationship between mammography and breast cancer survival. Define quality assurance and quality control. Discuss the history of the Mammography Quality Standards Act. List the important considerations in processor setup. Name the tests in the medical physicist survey. Know how to perform daily processor quality control. Understand the importance of continuous quality improvement.     

Hyperthermia: principles and quality assurance

The methods of energy deposition, the power absorbtion properties of biological tissues and the basic components of a typical hyperthermia system are described. In addition, the clinical requirements of hyperthermia treatment are discussed. A perspective on treatment planning and quality control is presented.     

The Reference Man in diagnostic radiology dosimetry.

Following the legislation for radiation protection in Europe, increasing interest has been given to patient dosimetry in diagnostic radiology. Dose comparisons between groups of patients have demonstrated considerable discrepancies. The equipment, as well as the procedures used, have been scrutinized in order to find the reasons for the variation and to reduce it. In this work, patient size and shape are considered in patient dose evaluations in diagnostic radiology. The size, shape and constitution of the patients are shown to relate exponentially to the energy imparted during examination of the trunk. The equivalent cylindrical diameter of the patient body is used as the independent variable. Exponential functions are created by linear regression. The ICRP Reference Man with an equivalent diameter of 22.9 cm is used as a body-size standard. A method is suggested by which coordinate transformations reduce data to a base line defined by the Reference Man. It is shown that the method reduces the range of energy imparted by between 30% and 60% for six common X-ray examinations of the trunk. Resulting data constitute a finer instrument for intercomparisons between hospitals for the same examination. Further, it is suggested that adipose tissues should not be included when detrimental effects of radiologic exposure are determined. The Reference Man, stripped of 10 kg subcutaneous adipose tissue, is used as the non-fat standard dimension corresponding to the equivalent cylindrical diameter 21.2 cm. The suggested method is used to estimate the fraction of energy imparted to vital organs only. The results show that the energy imparted is reduced by between 30% and 60% according to this model. Consequently, predicted deaths are reduced by the same amount.