Ethical considerations regarding the effects of climate change and planetary health on children

Climate change represents one of the most significant health challenges and global inequities of our generation. As a 'wicked' problem, climate change imposes an involuntary exposure on vulnerable individuals and societies that is regressive in its nature, with those least responsible for destroying planetary health at greatest risk of suffering the direct and indirect health consequences of unabated warming of the planet. The current and future generations of children are the most vulnerable population to suffer the effects of climate change. By 2030, there will be 131 000 additional child deaths each year if climate mitigation strategies are not enacted, driven by the synergy of an increasing burden of infectious diseases, food insecurity and political instability. Over half a billion of the world's children live in areas vulnerable to extreme weather events, and there is a pressing risk that our current lack of action to mitigate and adapt to climate change will result in today's children, and future generations, being the first to have poorer physical and mental health than previous generations - creating a significant intergenerational ethical dilemma. Child health-care professionals need to advocate for policies to address climate change that consider the complex health, planetary and ethical considerations necessary to solve the most significant risk to our children's health today. Without immediate action, the health of the current and future generations of children is perilous.

Impact of climate change and biodiversity collapse on the global emergence and spread of infectious diseases

The reality of climate change and biodiversity collapse is irrefutable in the 21st century, with urgent action required not only to conserve threatened species but also to protect human life and wellbeing. This existential threat forces us to recognise that our existence is completely dependent upon well-functioning ecosystems that sustain the diversity of life on our planet, including that required for human health. By synthesising data on the ecology, epidemiology and evolutionary biology of various pathogens, we are gaining a better understanding of factors that underlie disease emergence and spread. However, our knowledge remains rudimentary with limited insight into the complex feedback loops that underlie ecological stability, which are at risk of rapidly unravelling once certain tipping points are breached. In this paper, we consider the impact of climate change and biodiversity collapse on the ever-present risk of infectious disease emergence and spread. We review historical and contemporaneous infectious diseases that have been influenced by human environmental manipulation, including zoonoses and vector- and water-borne diseases, alongside an evaluation of the impact of migration, urbanisation and human density on transmissible diseases. The current lack of urgency in political commitment to address climate change warrants enhanced understanding and action from paediatricians - to ensure that we safeguard the health and wellbeing of children in our care today, as well as those of future generations.

Potential of fosfomycin in treating multidrug-resistant infections in children

In an era of increasing antimicrobial resistance, there are limited treatment options available to treat multidrug-resistant organisms in paediatric patients. Fosfomycin is an antibiotic defined as 'critically important' by The World Health Organization due to its potential efficacy against multidrug-resistant bacteria and is increasingly cited in the international literature as a promising antimicrobial for combating sepsis in an era of increasing antimicrobial resistance. With broad-spectrum cover that includes both Gram-positive and Gram-negative organisms and both parenteral and oral formulations available, fosfomycin provides a promising treatment option for paediatric patients. This review summarises fosfomycin's spectrum of activity, published efficacy in paediatric patients, safety considerations and pharmacokinetic data, as well as identifying current clinical trials delineating pharmacokinetic parameters and safety parameters in neonatal sepsis which will provide further information regarding the use of fosfomycin in neonatal and paediatric infections. Limitations regarding the current standards for fosfomycin susceptibility definitions, variations in dosing regimens and the potential mechanisms for resistance are also discussed.

Measurement of Total Starch in Cereal Products by Amyloglucosidase-α-Amylase Method: Collaborative Study

American Association of Cereal Chem- ists/AOAC collaborative study was conducted to evaluate the accuracy and reliability of an enzyme assay kit procedure for measurement of total starch in a range of cereal grains and products. The flour sample is incubated at 95°C with thermostable α-amylase to catalyze the hydrolysis of starch to maltodextrins, the pH of the slurry is adjusted, and the slurry is treated with a highly purified amyloglucosidase to quantitatively hydrolyze the dextrins to glucose. Glucose is measured with glucose oxidase-peroxidase reagent. Thirty-two collaborators were sent 16 homogeneous test samples as 8 blind duplicates. These samples included chicken feed pellets, white bread, green peas, high- amylose maize starch, white wheat flour, wheat starch, oat bran, and spaghetti. All samples were analyzed by the standard procedure as detailed above; 4 samples (high-amylose maize starch and wheat starch) were also analyzed by a method that requires the samples to be cooked first in dimethyl sulfoxide (DMSO). Relative standard deviations for repeatability (RSDr) ranged from 2.1 to 3.9%, and relative standard deviations for reproducibility (RSDr) ranged from 2.9 to 5.7%. The RSDr value for high amylose maize starch analyzed by the standard (non-DMSO) procedure was 5.7%; the value

Shading correction algorithm for improvement of cone-beam CT images in radiotherapy

Cone-beam CT (CBCT) images have recently become an established modality for treatment verification in radiotherapy. However, identification of soft-tissue structures and the calculation of dose distributions based on CBCT images is often obstructed by image artefacts and poor consistency of density calibration. A robust method for voxel-by-voxel enhancement of CBCT images using a priori knowledge from the planning CT scan has been developed and implemented. CBCT scans were enhanced using a low spatial frequency grey scale shading function generated with the aid of a planning CT scan from the same patient. This circumvents the need for exact correspondence between CBCT and CT and the process is robust to the appearance of unshared features such as gas pockets. Enhancement was validated using patient CBCT images. CT numbers in regions of fat and muscle tissue in the processed CBCT were both within 1% of the values in the planning CT, as opposed to 10-20% different for the original CBCT. Visual assessment of processed CBCT images showed improvement in soft-tissue visibility, although some cases of artefact introduction were observed.

Real-time noninvasive assessment of pancreatic ATP levels during cold preservation

31P-NMR spectroscopy was utilized to investigate rat and porcine pancreatic ATP:P(i) ratios to assess the efficacy of existing protocols for cold preservation (CP) in maintaining organ quality. Following sacrifice, rat pancreata were immediately excised or left enclosed in the body for 15 minutes of warm ischemia (WI). After excision, rat pancreata were stored at 6 degrees C to 8 degrees C using histidine-tryptophan-ketoglutarate solution (HTK) presaturated with air (S1), HTK presaturated with O2 (S2), or the HTK/perfluorodecalin two-layer method (TLM) with both liquids presaturated with O2 (S3). 31P-NMR spectra were sequentially collected at 3, 6, 9, 12, and 24 hours of CP from pancreata stored with each of the three protocols examined. The ATP:Pi ratio for rat pancreata exposed to 15 minutes of WI and stored with S3 increased during the first 9 hours of CP, approaching values observed for organs procured with no WI. A marked reduction in the ATP:Pi ratio was observed beyond 12 hours of CP with S3. After 6 hours of CP, the ATP:Pi ratio was highest for S3, substantially decreased for S2, and below detection for S1. In sharp contrast to the rat model, ATP was barely detectable in porcine pancreata exposed to minimal warm ischemia (<15 minutes) stored with the TLM regardless of CP time. We conclude that 31P-NMR spectroscopy is a powerful tool that can be used to (1) noninvasively evaluate pancreata prior to islet isolation, (2) assess the efficacy of different preservation protocols, (3) precisely define the timing of reversible versus irreversible damage, and (4) assess whether intervention will extend this timing.

Developments in and experience of kilovoltage X-ray cone beam image-guided radiotherapy

This paper offers a realistic review of kilovoltage X-ray cone beam tomography integrated with the treatment machine for image-guided radiotherapy in the light of experience taking a commercial system from prototype development into clinical use. It shows that key practicalities cannot be ignored, in particular the regular characterization of mechanical flex during gantry rotation, the mapping of defects in flat panel image transducers and their response to X-ray exposure. The number of X-ray projections and the doses required for clinically useful cone beam reconstruction at different therapy sites are considered in the context of imaging that is fit for purpose. Three roles for cone beam tomography in radiotherapy are identified: patient setup in three dimensions (3D), where even low dose cone beam tissue detail is superior to megavoltage imaging; disease targeting where, despite wide field scatter and slow scanning, it is possible to generate images that are suitable for tumour delineation even at challenging sites; adaptive treatment planning, where calibrated cone beam images have been shown to provide sufficient target detail to support "plan of the day" selection and have the potential for planning with bulk corrections. With frequent use in mind, the need to limit patient dose during setup, yet maximize much needed image quality in the target zone, is considered. Finally, it is noted that the development of cone beam tomography for radiotherapy is far from complete, with X-ray source, image transducer, reconstruction algorithms and techniques for image profile collection still being researched.

IMRT: delivery techniques and quality assurance

Intensity modulated radiotherapy (IMRT) is a major development in the delivery of radiation therapy that has the potential to improve patient outcome by reducing morbidity or increasing local tumour control. Delivery techniques include those based on purpose built devices and treatment machines together with those utilizing the capabilities of computer controlled multileaf collimators which are more widely available. The complexity of IMRT techniques demands a high level of quality control both in the operation of the equipment and in the delivery of treatment to individual patients. The purpose of this paper is therefore to review the techniques available, concentrating on the use of multileaf collimators, and to consider the necessary quality control requirements for clinical application. It demonstrates that the technology is mature and sufficiently well understood so that IMRT can be safely implemented in the general clinical environment rather than being limited to application in the research environment.

Indexing artefacts using a tertiary collimator and a method to avoid them

A tertiary, slotted grid collimator has been proposed as a method by which the spatial resolution of radiation fields shaped using a multileaf collimator (MLC) may be improved. The prototype device previously reported in the literature allowed each slot in the grid to be aligned with each pair of opposing leaves in the MLC. Irradiation through the collimator resulted in a regular pattern of high dose strips, with the width of each strip defined by the width of the slot and the length by the relative separation of the MLC leaf pair. To complete the field, the patient must be indexed relative to the collimator, with the number of sub-fields required determined by the width of the slots and the spacing between them. This indexing is achieved by rotation of the collimator along a radius centred on the radiation source, thus avoiding the effects of beam divergence on the uniformity of delivered composite beams. However, rotation of the tertiary collimator has been shown to result in artefacts in field definition. The source of such artefacts is the proximity of the long edge of a slot to the junction between two MLC leaves, if one leaf is withdrawn with respect to the next. A simple cause for such artefacts was identified as a small misalignment between the slot edge and the leaf junction. Another source of such effects is the finite size of the radiation source, which allows for partial shielding effects beyond the leaf edge. Finally, the effect of the leaf edge penumbra was identified as the cause of potential areas of underdose within the field boundary. Measurements were performed using a mini-diode of the potential magnitude of the last two effects for slot widths of 2.5 and 5.0 mm beneath a single open MLC leaf. For both slot widths, the unwanted overdose due to partial shielding by neighbouring leaves did not exceed 8% of the dose with the slot at the centre of the single open leaf. The potential for underdose within the field was a much more significant effect, especially for the narrower slot, with the peak intensity through the 2.5 mm slot positioned just inside the open leaf only reaching 41% of that measured with it positioned centrally. Such an arrangement of slots and leaves is unavoidable if the separation between neighbouring slots is identical to that of the MLC leaves (1 cm at isocentre). An alternative arrangement is proposed, and has been demonstrated to avoid the generation of the artefacts detailed above.

Optimizing the indexing of a resolution-enhancing tertiary collimator for radiotherapy

A method for improving the resolution of multileaf collimator (MLC) defined radiotherapy fields using a tertiary, slotted grid collimator has been investigated and developed further. The original concept was for each slot to be aligned with each leaf pair of opposing MLC leaves. The total treated area is composed of a series of sub-fields, a pattern of irradiated strips, with the width of each strip defined by the width of the slot and the length by the relative separation of the MLC leaf pair. To complete the field, the patient must be indexed relative to the collimator, with the number of sub-fields required determined by the width of the slots and the spacing between them. Two methods were considered by which this indexing could be achieved: movement of the patient while holding the tertiary collimator fixed, or rotating the grid with the point of rotation defined as the radiation source. Consideration of the movement resolution and precision required for the patient support system for non-cardinal gantry, collimator and table angles cast doubt on the practicality of the use of such a strategy. To assess the effect of divergence on the abutting sub-fields, measurements were also performed to assess the uniformity of single fields generated by the tertiary collimator in planes above and below the isocentre using both methods of indexing. As expected, rotation of the collimator resulted in a similar degree of non-uniformity for any plane chosen, whereas significant dose heterogeneities were introduced to treatment planes within 5 cm above and below the isocentre if the patient support system was used. Therefore, the rotation strategy will be implemented with all future versions of the device.

The required number of treatment imaging days for an effective off-line correction of systematic errors in conformal radiotherapy of prostate cancer--a radiobiological analysis

BACKGROUND AND PURPOSE

To use radiobiological modelling to estimate the number of initial days of treatment imaging required to gain most of the benefit from off-line correction of systematic errors in the conformal radiation therapy of prostate cancer.

MATERIALS AND METHODS

Treatment plans based on the anatomical information of a representative patient were generated assuming that the patient is treated with a multi leaf collimator (MLC) four-field technique and a total isocentre dose of 72 Gy delivered in 36 daily fractions. Target position variations between fractions were simulated from standard deviations of measured data found in the literature. Off-line correction of systematic errors was assumed to be performed only once based on the measured errors during the initial days of treatment. The tumour control probability (TCP) was calculated using the Webb and Nahum model.

RESULTS

Simulation of daily variations in the target position predicted a marked reduction in TCP if the planning target volume (PTV) margin was smaller than 4 mm (TCP decreased by 3.4% for 2 mm margin). The systematic components of target position variations had greater effect on the TCP than the random components. Off-line correction of estimated systematic errors reduced the decrease in TCP due to target daily displacements, nevertheless, the resulting TCP levels for small margins were still less than the TCP level obtained with the use of an adequate PTV margin of approximately 10 mm. The magnitude of gain in TCP expected from the correction depended on the number of treatment imaging days used for the correction and the PTV margin applied. Gains of 2.5% in TCP were estimated from correction of systematic errors performed after 6 initial days of treatment imaging for a 2 mm PTV margin. The effect of various possible magnitudes of systematic and random components on the gain in TCP expected from correction and on the number of imaging days required was also investigated.

CONCLUSIONS

Daily variations of target position markedly reduced the TCP if small margins were used. Off-line correction of systematic errors can only partly compensate for these TCP reductions. The adequate number of treatment imaging days required for systematic error correction depends on the magnitude of the random component compared with the systematic component, and on the size of PTV margin used. For random components equal to or smaller than the systematic component, 3 consecutive treatment imaging days are estimated to be sufficient to gain most of the benefit from correction for current clinically used margins (6-10 mm); otherwise more days are required.

Vanquishing virtue: the impact of medical education

North American physicians emerge from their medical training with a wide array of professional beliefs and values. Many are thoughtful and introspective. Many are devoted to patients' welfare. Some bring to their work a broad view of social responsibility. Nonetheless, the authors contend that North American medical education favors an explicit commitment to traditional values of doctoring-empathy, compassion, and altruism among them-and a tacit commitment to behaviors grounded in an ethic of detachment, self-interest, and objectivity. They further note that medical students and young physicians respond to this conflict in various ways. Some re-conceptualize themselves primarily as technicians and narrow their professional identities to an ethic of competence, thus adopting the tacit values and discarding the explicit professionalism. Others develop non-reflective professionalism, an implicit avowal that they best care for their patients by treating them as objects of technical services (medical care). Another group appears to be "immunized" against the tacit values, and thus they internalize and develop professional virtue. Certain personal characteristics of the student, such as gender, belief system, and non-medical commitments, probably play roles in "immunization," as do medical school features such as family medicine, communication skills courses, medical ethics, humanities, and social issues in medicine. To be effective, though, these features must be prominent and tightly integrated into the medical school curriculum. The locus of change in the culture of medicine has now shifted to ambulatory settings and the marketplace. It remains to be seen whether this move will lessen the disjunction between the explicit curriculum and the manifestly contradictory values of detachment and entitlement, and the belief that the patient's interest always coincides with the physician's interest.

High-resolution field shaping utilizing a masked multileaf collimator

Multileaf collimators (MLCs) have become an important tool in the modern radiotherapy department. However, the current limit of resolution (1 cm at isocentre) can be too coarse for acceptable shielding of all fields. A number of mini- and micro-MLCs have been developed, with thinner leaves to achieve approved resolution. Currently however, such devices are limited to modest field sizes and stereotactic applications. This paper proposes a new method of high-resolution beam collimation by use of a tertiary grid collimator situated below the conventional MLC. The width of each slit in the grid is a submultiple of the MLC width. A composite shaped field is thus built up from a series of subfields, with the main MLC defining the length of each strip within each subfield. Presented here are initial findings using a prototype device. The beam uniformity achievable with such a device was examined by measuring transmission profiles through the grid using a diode. Profiles thus measured were then copied and superposed to generate composite beams, from which the uniformity achievable could be assessed. With the average dose across the profile normalized to 100%, hot spots up to 5.0% and troughs of 3% were identified for a composite beam of 2 x 5.0 mm grids, as measured at Dmax for a 6 MV beam. For a beam composed from 4 x 2.5 mm grids, the maximum across the profile was 3.0% above the average, and the minimum 2.5% below. Actual composite profiles were also formed using the integrating properties of film, with the subfield indexing performed using an engineering positioning stage. The beam uniformity for these fields compared well with that achieved in theory using the diode measurements. Finally sine wave patterns were generated to demonstrate the potential improvements in field shaping and conformity using this device as opposed to the conventional MLC alone. The scalloping effect on the field edge commonly seen on MLC fields was appreciably reduced by use of 2 x 5.0 mm grids, and still further by the use of 4 x 2.5 mm grids, as would be expected. This was also achieved with a small or negligible broadening of the beam penumbra as measured at Dmax.

Requirements for leaf position accuracy for dynamic multileaf collimation

Intensity modulated radiation therapy can be achieved by driving the leaves of a multileaf collimator (MLC) across an x-ray therapy beam. Algorithms to generate the required leaf trajectories assume that the leaf positions are exactly known to the MLC controller. In practice, leaf positions depend upon calibration accuracy and stability and may vary within set tolerances. The purpose of this study was to determine the effects of potential leaf position inaccuracies on intensity modulated beams. Equations are derived which quantify the absolute error in delivered monitor units given a known error in leaf position. The equations have been verified by ionization chamber measurements in dynamically delivered flat fields, comparing deliveries in which known displacements have been applied to the defined leaf positions with deliveries without displacements applied. The equations are then applied to two clinical intensity modulations: an inverse planned prostate field and a breast compensating field. It is shown that leaf position accuracy is more critical for a highly modulated low-dose intensity profile than a moderately modulated high-dose intensity profile. Suggestions are given regarding the implications for quality control of dynamic MLC treatments.

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.

Customised compensation using intensity modulated beams delivered by dynamic multileaf collimation

BACKGROUND AND PURPOSE

This paper describes the development of customised compensation by intensity modulated radiation therapy (IMRT), delivered by dynamic application of a multileaf collimator (MLC), in order to improve dose homogeneity in treatments of the pelvic region. The introduction of this simple IMRT procedure will help facilitate the clinical implementation of more complex 3D conformal therapy techniques.

MATERIALS AND METHOD

Computer software is used to generate profiles of the intensity modulated beams which are required to deliver a uniform dose in a plane, passing through the isocentre and normal to the beam axis, under an irregular surface contour. These profiles are then operated on by interpreter software which determines the leaf trajectories that are necessary to deliver these beam profiles using a single, unidirectional sweep of the MLC leaves. A full dose calculation based on the calculated leaf positions is subsequently performed, allowing further fine adjustments to the modulation where required.

RESULTS AND CONCLUSION

The compensation procedure has been successfully tested using films placed under a test phantom. The effect of the compensation procedure on dose distributions in the transverse plane has been investigated using an anthropomorphic phantom. Overall dose homogeneity has been improved through the use of customised compensation delivered by dynamic multileaf collimation.

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.

The design and performance characteristics of a multileaf collimator

A multileaf collimator, which has been in routine clinical use for both conventional and conformal radiotherapy for over four years, is described in detail. The collimator replaces the conventional treatment head of a Philips SL series linear accelerator and comprises 80 tungsten leaves and two orthogonal pairs of back-up collimators. Each leaf projects a width of 1 cm in the isocentric plane, allowing shaped photon treatment beams of up to 40 cm square. The performance of the prototype and first production model have been thoroughly tested against the design specifications and the requirements of IEC standards. Radiation attenuation by the collimator components has been measured and substantially exceeds those requirements. The irregular portion of a field (shielded by the leaves only) receives, on average, a dose of less than 2% of the tumour dose. The effect on the penumbra of using leaves which translate linearly and have curved faces has been assessed and found not to degrade the sharpness of the beam fall-off significantly. The reproducibility of the video system used in positioning the leaves has been measured and gave a root mean square deviation of less than 0.3 mm in repeat setting of a 10 cm square field, and an accuracy always within 1 mm. The rationale for clinical use of the device is discussed and its effect on treatment quality control and reliability, is considered.

An experimental investigation of the tongue and groove effect for the Philips multileaf collimator

The tongue and groove effect is an underdosing effect which can occur in certain applications of multileaf collimators. It results from the need to overlap adjacent leaves of a multileaf collimator in order to limit leakage between leaves. The applications in which the effect can occur are the abutment of fields where the beam edges are defined by the leaf edge and the production of intensity-modulated fields by dynamic collimation. The effect has been measured for the 'worst case' when just two MLC fields are matched along leaf edges which have overlapping steps. Measurements of the dose have been made at d(max) and also at a more clinically relevant depth of 87 mm in Perspex for beam energies of 6 MV, 8 MV and 20 MV on two Philips SL series accelerators. Dose distributions were recorded on radiographic film which was subsequently digitized for analysis. The dose reduction of the tongue and groove effect was found to be 15-28% and spread over a width of 3.8 to 4.2 mm. This is somewhat shallower and wider than would be expected from a simple, idealized model of the effect which would predict a dose reduction of 80% over a width of 1 mm.

Quality assurance of the dose delivered by small radiation segments

The use of intensity modulation with multiple static fields has been suggested by many authors as a way to achieve highly conformal fields in radiotherapy. However, quality assurance of linear accelerators is generally done only for beam segments of 100 MU or higher, and by measuring beam profiles once the beam has stabilized. We propose a set of measurements to check the stability of dose delivery in small segments, and present measured data from three radiotherapy centres. The dose delivered per monitor unit, MU, was measured for various numbers of MU segments. The field flatness and symmetry were measured using either photographic films that are subsequently scanned by a densitometer, or by using a diode array. We performed the set of measurements at the three radiotherapy centres on a set of five different Philips SL accelerators with energies of 6 MV, 8 MV, 10 MV and 18 MV. The dose per monitor unit over the range of 1 to 100 MU was found to be accurate to within +/-5% of the nominal dose per monitor unit as defined for the delivery of 100 MU for all the energies. For four out of the five accelerators the dose per monitor unit over the same range was even found to be accurate to within +/-2%. The flatness and symmetry were in some cases found to be larger for small segments by a maximum of 9% of the flatness/symmetry for large segments. The result of this study provides the dosimetric evidence that the delivery of small segment doses as top-up fields for beam intensity modulation is feasible. However, it should be stressed that linear accelerators have different characteristics for the delivery of small segments, hence this type of measurement should be performed for each machine before the delivery of small dose segments is approved. In some cases it may be advisable to use a low pulse repetition frequency (PRF) to obtain more accurate dose delivery of small segments.

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.

Predicting late rectal complications following prostate conformal radiotherapy using biologically effective doses and normalized dose-surface histograms

A model to predict the late normal tissue complication probability (NTCP) of the rectum following conformal therapy is described. The model evaluates the biological consequence of inhomogeneities in the physical dose by computing dose histograms of the biologically effective dose to the surface of the rectum for a given fractionation scheme. A method of normalizing the surface area of the rectum is employed so that the predicted NTCP is independent of the differing cross-sectional size of sections of the rectum, ensuring the NTCP is dependent only on the dose delivered to sensitive rectal tissues. The model has been used to assess severe late rectal complications and the milder RTOG grades 2 and 3 reactions. This model was found to predict severe toxicity levels of 1.7 +/- 0.6% for an accelerated treatment of 50 Gy in 16 fractions commonly employed at this centre. This result lies between the severe toxicities predicted for 60 and 62 Gy delivered in 2 Gy fractions. The model predicts that the average NTCP for severe late effects for nine prostate patients becomes greater than 5% with a fractionation scheme of 70 Gy in 35 fractions, for the four fields treatment. The effects of not treating all fields at each therapy session on rectal toxicity were also investigated. Biologically effective dose-surface histograms show that the dose to the lower surface of the rectum is increased by not treating all fields at each therapy session, but the predicted differences in rectal NTCP are negligible.

Changes in the cellularity of the cortex of human hairs as an indicator of radiation exposure

Growing hair follicles with their rapid cell proliferation would be expected to be sensitive organs to cytotoxic agents such as radiation. Various abnormalities in the hair and hair follicles have been reported in the past. Changes in the number of cells in the newly forming hair cortex have been shown in the mouse to be one of the more sensitive assays for radiation effects, and this approach could provide a basis for a biological dosimeter. Here we show for the first time using hair cortex cell counts some preliminary data indicating that the number of cell nuclei in a unit of length (140 microns) of the cortex of human hairs from the chest and scalp of patients undergoing fractionated radiotherapy falls significantly (P = 0.005) by 5%-10% 3 days after the first dose in a fractionated sequence of irradiations. The first dose was delivered on a Friday, and no further exposures were delivered until after the hair sample was taken on the 3rd day (Monday). No significant effect of radiation dose could be detected over the available. limited range of doses studied (5-6.5 Gy with one exit dose sample at 2.6 Gy). Also, the width varies from hair to hair. If the width of the hair is taken into account and the cortical nuclei counts are normalised to the width of each hair, the effects seen at day 3 become slightly more significant (P = 0.002), and those at day 5 also become significant (P = 0.012). Samples taken on the 5th day after the first (Friday) exposure were also 2 days after the second exposure and 1 day after the third exposure. However, little expression of damage attributable to the 2nd and 3rd exposures was anticipated since their effects would take some time to be expressed in the cortical region examined, which is some distance from the proliferative region of the follicle.

Ethical principles in federal regulations: the case of children and research risks

Ethical principles play an important part not only in the promulgation of regulations but also in their application, i.e., enforcement and adjudication. while traditional ethical principles--promotion of welfare, freedom, and fairness--play an important role in both elements of regulation, some other kinds of ethical principles are significant as well. Principles governing the structure of decision processes should shape the structure and actions of agencies; principles of wise application should govern the work of those whose responsibility it is to apply regulatory language to particular situations. These points are demonstrated by investigating a case study: federal regulations designed to protect children involved in scientific research applied to a placebo study of the effects of recombinant human growth hormone on children of extremely short stature.

Educating medical students about law and the legal system

The study of jurisprudence--law, legal reasoning, and the legal system--has become progressively more common in medical school curricula. Familiarity with jurisprudence helps physicians practice medicine well, collaborate productively with lawyers, and be more effective in public discourse about health care delivery. Moreover, the study of jurisprudence can help physicians polish the methods and clarify the purposes common to law and medicine. Empirical studies over the last 30 years demonstrate patterns of change in the frequency and focus of jurisprudence teaching in medical school curricula that can guide contemporary efforts to devise or refine curricula in medical jurisprudence. The general goal of such curricula should be to enhance physicians' clinical, institutional, and public effectiveness. These curricula should adhere to principles of sound pedagogy and be based on informed answers to the central questions of what should be taught, when, how, and by whom, and how the curriculum should be evaluated. Developing skills and changing attitudes are more important than imparting information about particular doctrines and laws. Curriculum planners should take into account the intellectual styles of the learners; integrate, not just coordinate, the new courses with the rest of the curriculum; build on features that medicine and law share and where they collaborate; and ensure intra- and inter-curricular coherence and continuity. Even though limitations of time, people, and money and differences in educational goals will influence what, when, and how medical jurisprudence is taught, the effort should be made if physicians are to be better empowered to use the law and their law colleagues to serve patients and promote public welfare.

Toxicity and efficacy of carboplatin and etoposide in conjunction with disruption of the blood-brain tumor barrier in the treatment of intracranial neoplasms

CARBOPLATIN AND ETOPOSIDE have been investigated in preclinical studies and a limited toxicity study in 13 patients; these studies have established carboplatin and etoposide as a tolerable combination when administered with blood-brain barrier disruption. The studies also found a predictable dose-limiting toxicity of myelosuppression. Subsequently, a broad efficacy trial of this regimen was carried out. A total of 34 patients, ranging in age from 7 to 72 years, underwent a combination chemotherapy regimen of carboplatin (200 mg/m2 administered intra-arterially) and etoposide (200 mg/m2 administered intravenously) administered with blood-brain barrier disruption on each of 2 consecutive days every 28 days. The diagnoses included glioblastoma multiforme (n = 3), malignant astrocytoma (n = 8), malignant astrocytoma-oligodendroglioma (n = 1), primitive neuroectodermal tumor (n = 4), disseminated germ cell tumor of the central nervous system (CNS) (n = 6), CNS lymphoma (n = 7), and metastatic carcinoma (n = 5). The major toxicity observed in patients treated with multiple courses of this regimen was the expected reversible myelosuppression and an unexpected, irreversible high-frequency hearing loss. Of these 34 patients, 22 had measurable disease, and 9 radiographic responses (50% or more decrease in enhancing tumors) were observed in these patients. Carboplatin and etoposide with blood-brain barrier disruption is an active regimen in the treatment of malignant astrocytomas and has shown dramatic responses in primitive neuroectodermal tumors and CNS lymphoma. Additionally, the durability of responses in patients with disseminated CNS germ cell tumors is encouraging. However, such therapy is associated with unexpected high-frequency hearing loss; even so, on the basis of the favorable responses in patients with primitive neuroectodermal tumors, germ cell tumors, and lymphomas, the study of this regimen for those tumors is being extended in a multiinstitutional trial that also includes cytoxan to further evaluate the potential enhanced drug delivery.

MR and cognitive testing of patients undergoing osmotic blood-brain barrier disruption with intraarterial chemotherapy

PURPOSE

To determine whether osmotic blood-brain barrier disruption is associated with MR abnormalities or cognitive deterioration and, if so, whether the MR findings correlate with cognitive test results.

METHODS

Fifteen brain tumor patients who had a complete tumor response (nine central nervous system lymphoma, three germ cell and two astrocytoma, and one primitive neuroectodermal tumor) treated with blood-brain barrier disruption procedures (318 total procedures) with intraarterial chemotherapy were included. MR images were evaluated for the development of white matter hyperintensity, vascular lesions, or atrophy. Cognitive testing was performed to assess deterioration caused by this therapy.

RESULTS

In two patients white matter hyperintensity developed, in two small vascular lesions developed, and in one mild atrophy developed. One infarct was asymptomatic and the second one resulted in mild dysesthesia in one upper extremity. No patient showed diminished cognitive function on the posttherapy evaluation.

CONCLUSION

In patients undergoing blood-brain barrier disruption with intraarterial chemotherapy, new abnormalities on MR imaging may develop. These patients maintain the same level of cognitive and neurologic function and MR findings do not correlate with the results of cognitive testing.

Duties and decency

Though we should help improve the lives of those with disabilities, it is not because we owe them help. The paper begins with a discussion of some features of disabilities: they are defining, ubiquitous, mutable, context dependent, and normative. The moral meaning of "owing" is analyzed and sources of moral duties set out and related to the moral claims of the disabled. Finally the paper suggests that decency--a minimal concern for the welfare of those whose lot we can improve--is a richer way to explain the moral propriety of helping the handicapped.

Using electronic mail for a small-group curriculum in ethical and social issues

PURPOSE

To initiate an electronic mail (e-mail) program as a supplement to a medical humanities curriculum focusing on ethical and social issues.

METHOD

In 1991-92 an e-mail track (called NET) was established for second-year students participating in Medicine in Contemporary Society, a four-year curriculum in medical humanities at the State University of New York at Stony Brook School of Medicine. In 1991-92 ten students volunteered to form a NET group; in 1992-93 22 students, forming two groups, were randomly selected from a volunteer pool of 76 students (from a class of 100). In both study years, the NET students analyzed and discussed electronically a series of cases posted sequentially through the academic year. Faculty tutors reviewed the students' responses, interacting with the groups and with individual students by e-mail. NET was evaluated in two ways: at the end of the course, the students completed e-mail questionnaires that included quantitative and qualitative assessments; and throughout the course, the tutors assessed the students' participation, quality of case analysis and discussion, and quality of writing.

RESULTS

The students' assessments indicated that they considered NET to be more educational than the lectures, "live" group discussions, problem-based learning exercises, and formal papers in the medical humanities curriculum; that they made gains in computer literacy; and that NET enhanced their abilities to think about ethical and social issues. The tutors judged that the students had improved their written self-expression as the course progressed.

CONCLUSION

NET adequately accomplished the goals set for it as an adjunct to the small-group sessions and other components of the medical humanities curriculum.

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.

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.

High technology to simplify the planning and delivery of radiotherapy

Two techniques for the automatic selection of individual leaf positions of a Philips multi-leaf collimator are described. Target volumes are identified either on simulator images or on cross-sectional images from CT or MR scanners. The setting of each leaf is computed to position the beam edge to cover the target with an appropriate, user defined, margin. An important consideration in the development of the system was its robustness and so the applications initially implemented have been relatively simple, comprising single field, parallel opposed fields and coplanar 4 field box techniques. Attention has been paid to the overall integrity of the planning and treatment delivery process. Before treatment commences, the beam shapes, which have been generated by the computer and transferred to the MLC control computer over a local area network, are checked against a printed template representing each beam. All data used for planning is archived and is accessible for review or, if necessary, for treatment modification.

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.

Computer-assisted generation of multi-leaf collimator settings for conformation therapy

Techniques for the automatic set up of the individual leaf positions of a Philips multi-leaf collimator system to cover a defined target volume are described. Tumour outline data for multi-field treatments may be obtained from one of two techniques, either from simulator images or from cross-sectional computed tomography (CT) slices. In the first technique, simulator images are digitized directly from image intensifier video signals or from conventional film radiographs using a CCD camera. Corrections for image distortion are carried out before reformatting the digitized images to a common data structure. Target outlines are subsequently traced interactively on the digital image to create an outline file. In the second technique, target volumes are defined on several individual CT slices and these are then used to obtain projected graphical views from any desired angle. In both techniques, a scaled graphical representation of leaf positions is then displayed and set relative to the outer edge of the target outline. Both techniques allow interactive repositioning of single leaves when required, or the operator can specify a margin around the projected target volume. Leaf prescription data files are created and are transferred via a Decnet-OSI-Opennet network link to an Intel microcomputer, which is used to drive the device itself. Examples of both techniques are given.

A dosimetric intercomparison of megavoltage photon beams in UK radiotherapy centres

A dosimetry intercomparison has been carried out for all 64 radiotherapy centres in the UK. Doses were measured with an ionization chamber in an epoxy resin water-substitute phantom of relatively simple geometry. Reference-point measurements were made for all MV photon beams. For 61 Co-60 beams, a mean ratio of measured-to-stated dose of 1.002 was observed with a standard deviation of 0.014, whilst for 100 MV x-ray beams, the corresponding figures were 1.003 and 0.015. 97% of beams lay within a +/- 3% deviation. One measurement was instrumental in discovering a large discrepancy. Doses were also investigated in two planned three-field distributions at one beam quality in each centre. One of these was in a homogeneous phantom, whilst the second included a lung-equivalent insert. Doses were measured at the central point and at four other points in the high dose volume. In both situations, the mean ratio of measured-to-calculated doses for all points was 1.008, with standard deviations of 0.027 and 0.035 for the uniform and non-uniform phantoms, respectively. Discrepancies over 5% were followed up. The work must be viewed in the context of other international intercomparisons and is an essential part of wider radiotherapy audit processes.