Biomedical subjects

M C Kirby

Publications and source records attributed to M C Kirby.

14 recordsLinked to original sources

PubMed2006

Design and implementation of an electronic data recording and processing system for physics quality control checks in external beam radiotherapy.

Quality control (QC) of external beam radiotherapy equipment ensures that commissioning performance is maintained. Paper based data recording is still used for QC, but this is resource intensive in terms of data calculation and processing. Electronic systems of data recording have many advantages; for example, they facilitate the analysis of data on a regular basis, allowing the user to examine the "health" of each machine; they help review and audit local frequencies of each check and can possibly predict component failure. They also allow for secure calculation of results and automatic charting for routine trend analysis. Initially, data recording at our centre was paper-based for daily, weekly and monthly checks. This paper system has been successfully replaced with an electronic system for QC data recording and processing for linear accelerators and superficial units. The system makes use of personal digital assistants and networked laptops for online recording of data, and networked desktop PCs for offline work. The systems of data recording have been designed using the power of macros within Microsoft Excel, which automatically calculate each QC parameter and charts the data recorded for long-term analysis of trends. As of the beginning of 2006, these systems have been fully implemented. The benefits of implementing such a system are numerous, for example, central storage, backup and archiving of data, for greater security and reducing operator errors in calculations. Other benefits are discussed within the paper. In the future, we hope to develop similar systems of data recording for QC checks on other radiotherapy equipment.

Computers, Handheld↗

PubMed2006

Developments in electronic portal imaging systems.

Verification of geometric accuracy at the time of treatment delivery has always been a necessary part of the radiotherapy process. Since the introduction of conformal and intensity-modulated radiotherapy, the consequences of patient positioning errors are more serious. Portal imaging has played a large part in fulfilling the need for improved geometric accuracy. This review examines how portal imaging has progressed through the development and evolution of electronic portal imaging devices (EPIDs). Changes in technology, including the current commercial systems, and how image quality has changed are presented. The clinical usage of EPIDs and the technological innovations being devised for further improvements in image quality and systems are considered.

Artifacts↗

PubMed2005

Dosimetric characteristics of the Elekta Beam Modulator.

The dosimetric characteristics of a production pilot multi-leaf collimator (Elekta Beam Modulator, Elekta Oncology Systems, Crawley, UK) having a 4 mm leaf width (at isocentre) have been investigated. Characteristics explored included leaf bank set-up, penumbra width (80-20%) as a function of leaf position, leaf positioning reproducibility, interleaf leakage and leaf transmission. The penumbra values for leaf ends were measured to be between 4.2 and 4.8 mm for various large rectangular fields studied using Kodak X-omat V film at isocentre (1.5 cm deep). Similar films were taken with a standard 1 cm width multi-leaf collimator (MLC) and the penumbra for leaf ends was found to range from 4.3 to 5.2 mm. Other results showed that the rounded leaf tip provided tight control of the penumbra across the leaves' full range of travel. The positioning of the leaves was within a 0.5 mm range when approaching from the same direction. The maximum interleaf leakage was found to be 1.7% and the average leaf transmission less than 1.0%. No major differences were observed in leakage and transmission with changing gantry angle.

Film Dosimetry↗

PubMed2000

Verification of dynamic multileaf collimation using an electronic portal imaging device.

High standards of treatment verification are necessary where complex new delivery techniques, such as intensity modulated radiation therapy using dynamic multileaf collimation, are being developed. This paper describes the use of a fluoroscopic electronic portal imaging device (EPID) to provide real-time qualitative verification of leaf position during delivery of a dynamic MLC prescription in addition to off-line quantitative verification. A custom-built circuit triggers the EPID to capture a series of snap-shot images at equally spaced dose points during a dynamic MLC prescription. Real-time verification is achieved by overlaying a template of expected leaf positions onto the images as they are acquired. Quantitative off-line verification is achieved using a maximum gradient edge detection algorithm to measure individual leaf positions for comparison with required leaf positions. Investigations have been undertaken to optimize image acquisition and assess the edge detection algorithm for variations in machine dose rate, leaf velocity and beam attenuation. On-line verification enables the operator to monitor the progress of a dynamic delivery and has been used for independent confirmation of accurate dynamic delivery during intensity modulated treatments. Off-line verification allows measurement of leaf position with a precision of 1 mm although image acquisition times must be less than or equal to 140 ms to ensure coincidence of the maximum gradient in the image with the 50% dose level.

Algorithms↗

PubMed1999

The performance of a fluoroscopic electronic portal imaging device modified for portability.

Advances in external beam therapy technology have made routine, efficient conformal therapy a reality. With it comes the increasing need for online treatment verification, which is only achievable at present through the use of electronic portal imaging devices (EPIDs). For a large radiotherapy centre, the provision of one EPID per treatment machine proves extremely expensive. This paper details modifications to the design of a commercial fluoroscopic EPID (the SRI-100) to produce a portable system, capable of providing quick, high quality imaging on more than one treatment machine. We describe the necessary hardware and software changes made to the system, as well as the variety of mechanical and quality control checks performed for testing the stability and quality of the imaging. The modified system has been found to be both electronically and mechanically robust, with associated image quality, scaling, distortion and movement similar to other EPIDs in the department. Although the modification was designed specifically to allow for the acquisition of images from multiple treatment machines, it may also enable the operation of the EPID for other uses such as total body irradiation (TBI) treatment verification and a further range of quality control procedures on the linear accelerator itself.

Ambulatory Care↗

PubMed1997

Use of electronic portal imaging to assess cardiac irradiation in breast radiotherapy.

An audit was performed to assess the frequency of cardiac irradiation in patients receiving radiotherapy for left-sided breast cancer. Images from an 'online' electronic portal imaging device were reviewed in patients who were treated with a tangential pair of megavoltage fields. In 169 consecutive patients treated on a Philips SL25 6 MV linear accelerator equipped with an SRI 100 imaging device, the cardiac apex was included in the radiotherapy field in 15 patients (9%). The long term sequelae of such cardiac irradiation is uncertain. The results of this audit suggest that careful treatment technique and quality control with portal imaging can minimize unnecessary cardiac irradiation in the majority of patients.

Breast Neoplasms↗

PubMed1996

The consequences of fixed-pattern noise and image movement on electronic portal images.

Fixed-pattern noise in electronic portal images (EPIs) is normally eliminated by dividing raw image data by an open-field calibration image (OFCI). However, for successful elimination, there must be exact registration between the two image sets. Any movement within the imaging system, such as that which occurs with gantry angle, will result in misregistration and a subsequent increase in noise. This paper describes, both qualitatively, by way of example, and quantitatively, by way of variance analysis, the consequences of misregistration and its effects on image quality. Our results show that image quality is found to degrade significantly with change in gantry angle, when a single OFCI is used, with a loss of low-contrast, fine detail. Variance is observed to increase over 2.5-fold. A simple solution of using multiple OFCIs is described, along with a technique for optimizing the number of images required, and the gantry angles at which they are acquired. When five OFCIs are used, the variance changes with gantry angle are limited to less than 20%. These changes are observed in both long and very short exposures (5 MU or 1 s).

Analysis of Variance↗

PubMed1995

The use of an electronic portal imaging device for exit dosimetry and quality control measurements.

PURPOSE: To determine ways in which electronic portal imaging devices (EPIDs) could be used to (a) measure exit doses for external beam radiotherapy and (b) perform quality control checks on linear accelerators. METHODS AND MATERIALS: When imaging, our fluoroscopic EPID adjusts the gain, offset, and frame acquisition time of the charge coupled device (CCD) camera automatically, to allow for the range of photon transmissions through the patient, and to optimize the signal-to-noise ratio. However, our EPID can be programmed to act as an integrating dosemeter. EPID dosemeter measurements were made for 20 MV photons, for different field sizes and thicknesses of unit density phantom material placed at varying exit surface to detector distances. These were compared with simultaneous Silicon diode exit dose measurements. Our exit dosimetry technique was verified using an anthropomorphic type phantom, and some initial measurements have been made for patients treated with irregularly shaped 20 MV x-ray fields. In this dosimetry mode, our EPID was also used to measure certain quality control parameters, x-ray field flatness, and the verification of segmented intensity modulated field prescriptions. RESULTS: Configured for dosimetry, our EPID exhibited a highly linear response, capable of resolving individual monitor units. Exit doses could be measured to within about 3% of that measured using Silicon diodes. Field flatness was determined to within 1.5% of Farmer dosemeter measurements. Segmented intensity modulated fields can be easily verified. CONCLUSIONS: Our EPID has the versatility to assess a range of parameters pertinent to the delivery of high quality, high precision radiotherapy. When configured appropriately, it can measure exit doses in vivo, with reasonable accuracy, perform certain quick quality control checks, and analyze segmented intensity modulated treatment fields.

Humans↗

PubMed1995

Clinical applications of composite and realtime megavoltage imaging.

The versatility of electronic portal imaging devices (EPIDs) is best demonstrated by their ability to perform novel megavoltage imaging protocols, which are still pertinent to good radiotherapy practice. This paper examines two such techniques: composite and realtime imaging. Our EPID can be programmed to acquire and manipulate images very easily, allowing images from segmented treatment protocols to be mixed and displayed, giving a composite image of the effective treatment result. Its use for verifying the efficacy of spinal shielding using a segmented, offset collimator technique is described. By acquiring images very quickly, realtime imaging sequences can be obtained and used to analyse anatomical movement within a single treatment field. The technique is employed here to investigate movement in radical lung, breast, abdomen, pelvis and thyroid treatments. Our results show that the protocol is vital for treatment sites involving the lungs; changes up to 5 mm have been observed in the maximum lung depth for breast treatments, and displacements up to 16 mm for radical lung treatments. It is also useful in other anatomical sites for ensuring that no movement occurs.

Fluoroscopy↗

PubMed1995

A multipurpose phantom for use with electronic portal imaging devices.

A simple, low-cost, multipurpose phantom has been designed for use with electronic portal imaging devices (EPIDS). Making use of the high spatial resolution of an EPID, together with the built in software tools for measuring distances, it is possible to verify x-ray/light field size and congruence, at any gantry angle, for fields up to 200 mm x 200 mm. Being of an accurate construction, it can help analyse the distance measuring capabilities of an EPID, ensuring that they are accurate and remain so with time. It can also be used to quantify, and monitor, image displacement and rotation with gantry angle.

Equipment Design↗

PubMed1993

Measurement possibilities using an electronic portal imaging device.

A vital role in the quality control of radiotherapy is the use of portal imaging for verifying field size, shape, orientation and patient set-up. Coincidence of treated volume and target volume is imperative. Electronic portal imaging devices are effective at providing this verification. However, these devices are versatile enough to be used in other ways pertinent to the delivery of high quality, high precision radiotherapy. This paper examines two such ways: in assessing the reproducibility of a multileaf collimator system, and in determining exit doses in vivo. Configured as a dosimeter, the system shows a linear response with good dynamic range. Its high spatial resolution was used to show that leaf positioning was reproducible to within 0.5 mm for all tested gantry and collimator angles. Our preliminary results from this exit dosimetry technique demonstrate that, under specific conditions, doses can be determined to within 2.5% of that measured using silicon diodes or ion chambers.

Humans↗

PubMed1991

Portal imaging for the verification of breast treatments.

Increasing demands are being made for more accurate versatile and precise methods of quality control for radiation therapy, in general. To this end, we have used a digital, on-line, megavoltage imaging system for the verification of breast treatments, in particular. Quick, high-quality images are produced from which the depth of lung irradiated during treatment is very easily determined using the system software. We describe how this quantitative clinical information has been used to assess critical aspects of the treatment technique, and also patient orientated criteria, throughout the course of treatment.

Breast Neoplasms↗

PubMed1990

Comparison of structure, mechanical properties, and functions of lumbar spinal ligaments.

The organization of collagen in the supraspinous, interspinous, and longitudinal ligaments, as well as the ligamenta flava, in lumbar spines from human cadavers has been investigated by polarized light microscopy, scanning electron microscopy, and x-ray diffraction. These experiments were performed on ligaments in situ, with their bony attachments undisturbed, and on excised ligaments at a range of applied strains. Results were related to the composition (investigated by standard histologic techniques) and gross structures (investigated by light microscopy) of the ligaments. More importantly, the results were related to the mechanical properties of the ligaments, which include stiffness, failure conditions, stress relaxation, and hysteresis. Where necessary, results were supplemented by or compared with those obtained from pig ligaments. Mechanical properties were related to postural changes by ligament strains induced in cadaveric specimens, using results from the literature. Thus, ligament structures could be related to their physiologic functions.

Biomechanical Phenomena↗

PubMed1989

Structure and mechanical properties of the longitudinal ligaments and ligamentum flavum of the spine.

Stress-strain curves were recorded from anterior and posterior longitudinal ligaments and ligamenta flava dissected from pig lumbar spines. Ligaments were examined during extension by light microscopy, to observe crimp structure, and by X-ray diffraction, to determine collagen fibril orientations. Scanning electron microscopy (SEM) was used to examine ligaments fixed at high and low strains. Initial stages of ligament extension involved alignment of collagen fibrils. Collagen fibrils in unstrained ligamentum flavum were much more disoriented than in the longitudinal ligaments. Thus, fibril alignment, and consequent stiffening, occurred at much higher strains than for longitudinal ligaments, allowing ligamentum flavum to exploit the extensibility of its elastin.

Animals↗