Consensus recommendations for incident learning database structures in radiation oncology.

PURPOSE: Incident learning plays a key role in improving quality and safety in a wide range of industries and medical disciplines. However, implementing an effective incident learning system is complex, especially in radiation oncology. One current barrier is the lack of technical standards to guide users or developers. This report, the product of an initiative by the Work Group on Prevention of Errors in Radiation Oncology of the American Association of Physicists in Medicine, provides technical recommendations for the content and structure of incident learning databases in radiation oncology. METHODS: A panel of experts was assembled and tasked with developing consensus recommendations in five key areas: definitions, process maps, severity scales, causality taxonomy, and data elements. Experts included representatives from all major North American radiation oncology organizations as well as users and developers of public and in-house reporting systems with over two decades of collective experience. Recommendations were developed that take into account existing incident learning systems as well as the requirements of outside agencies. RESULTS: Consensus recommendations are provided for the five major topic areas. In the process mapping task, 91 common steps were identified for external beam radiation therapy and 88 in brachytherapy. A novel feature of the process maps is the identification of "safety barriers," also known as critical control points, which are any process steps whose primary function is to prevent errors or mistakes from occurring or propagating through the radiotherapy workflow. Other recommendations include a ten-level medical severity scale designed to reflect the observed or estimated harm to a patient, a radiation oncology-specific root causes table to facilitate and regularize root-cause analyses, and recommendations for data elements and structures to aid in development of electronic databases. Also presented is a list of key functional requirements of any reporting system. CONCLUSIONS: Incident learning is recognized as an invaluable tool for improving the quality and safety of treatments. The consensus recommendations in this report are intended to facilitate the implementation of such systems within individual clinics as well as on broader national and international scales.

Towards an objective evaluation of tolerances for beam modeling in a treatment planning system.

The performance of a convolution/superposition based treatment planning system depends on the ability of the dose calculation algorithm to accurately account for physical interactions taking place in the tissue, key components of the linac head and on the accuracy of the photon beam model. Generally the user has little or no control over the performance of the dose calculation algorithm but is responsible for the accuracy of the beam model within the constraints imposed by the system. This study explores the dosimetric impact of limitations in photon beam modeling accuracy on complex 3D clinical treatment plans. A total of 70 photon beam models was created in the Pinnacle treatment planning system. Two of the models served as references for 6 MV and 15 MV beams, while the rest were created by perturbing the reference models in order to produce specific deviations in specific regions of the calculated dose profiles (central axis and transverse). The beam models were then used to generate 3D plans on seven CT data sets each for four different treatment sites (breast and conformal prostate, lung and brain). The equivalent uniform doses (EUD) of the targets and the principal organs at risk (OARs) of all plans ( approximately 1000) were calculated and compared to the EUDs delivered by the reference beam models. In general, accurate dosimetry of the target is most greatly compromised by poor modeling of the central axis depth dose and the horns, while the EUDs of the OARs exhibited the greatest sensitivity to beam width accuracy. Based on the results of this analysis we suggest a set of tolerances to be met during commissioning of the beam models in a treatment planning system that are consistent in terms of clinical outcomes as predicted by the EUD.

Intensity modulated and three-dimensional conformal radiation therapy plans for oropharyngeal cancer: a comparison of their sensitivity to set-up errors and uncertainties.

We compared the effect of set-up error and uncertainty on two radiation therapy treatment plans for head and neck cancer: one using intensity modulated radiation therapy (IMRT) and one using conventional three-dimensional conformal radiation therapy (3D-CRT). We used a Pinnacle3 (Philips Medical Systems, Markham, Ontario) system to create the two treatment plans (7-beam IMRT and 5-beam 3D-CRT) for the same volumetric data set, based on the objectives and constraints defined in the Radiation Therapy Oncology Group H-0022 protocol. In both plans, the dose-volume constraints for the targets and the organs at risk (oars) were met as closely as the beam geometries would allow. Monte Carlo-based simulations of set-up error and uncertainty were performed in three orthogonal directions for 840 simulated "courses of treatment" for each plan. A systematic error (chosen from distributions characterized by standard deviations ranging from 0 mm to 6 mm) and random uncertainties (2 mm standard deviation) were incorporated. We used a probability approach to compare the sensitivities of the IMRT and the 3D-CRT plans to set-up error and uncertainty in terms of equivalent uniform dose (EUD) to targets and oars.Based on the EUD analysis, the targets and oars showed considerably greater sensitivity to set-up error with the IMRT plan than with the 3D-CRT plan. For the IMRT plan, target EUDS were reduced by 4%, 7.5%, and 10% for 2-mm, 4-mm, and 6-mm set-up errors respectively. However, even with set-up error, the mandible, spinal cord, and parotid EUDS always remained lower with the IMRT plan than with the 3D-CRT plan.We conclude that, when quantified by EUD, IMRT-plan doses to oars and targets are more sensitive to set-up error than are 3D-CRT-plan doses. However, as judged by the differences between target and OAR doses, IMRT retains its superiority over 3D-CRT, even in the presence of set-up error.

HERO (Health Economics in Radiation Oncology): a pan-European project on radiotherapy resources and needs.

Radiotherapy continues to evolve at a rapid rate in technology and techniques, with both driving up costs in an era in which health care budgets are of increasing concern at every governmental level. Against this background, it is clear that the radiotherapy community needs to quantify the costs of state of the art practice and then to justify those costs through rigorous cost-effectiveness analyses. The European Society for Radiotherapy and Oncology-Health Economics in Radiation Oncology project is directed towards tackling this issue in the European context. The first step has been to provide a validated picture of the European radiotherapy landscape in terms of the availability of equipment, personnel and guidelines. An 84-item questionnaire was distributed to the 40 countries of the European Cancer Observatory, of which 34 provided partial or complete responses. There was a huge variation in the availability and sophistication of treatment equipment and staffing levels across Europe. The median number of MV units per million inhabitants was 5.3, but there was a seven-fold variation across the European countries. Likewise, although average staffing figures per million inhabitants were 12.8 for radiation oncologists, 7.6 for physicists, 3.5 for dosimetrists, 26.6 for radiation therapists and 14.8 for nurses, there was a 20-fold variation, even after grouping personnel with comparable duties in the radiotherapy process. Guidelines for capital and human resources were declared for most countries, but without explicitly providing metrics for developing capital and human resource inventories in many cases. Although courses delivered annually per resource item ­ be it equipment or staff ­ increase with decreasing gross national income (GNI) per capita, differences were observed in equipment and staff availability in countries with a higher GNI/n, indicating that health policy has a significant effect on the provision of services. Although more needs to be done to increase access to radiotherapy in Europe, the situation has improved considerably since the comparable RadioTherapy for Cancer: QUAnification of Infrastructure and Staffing Needs (QUARTS) study reported in 2005.

A cost-outcome analysis of adjuvant postmastectomy locoregional radiotherapy in premenopausal node-positive breast cancer patients.

PURPOSE: To calculate cost-effectiveness and cost-utility ratios for adjuvant postmastectomy locoregional radiotherapy in premenopausal node-positive breast cancer patients and to place these ratios in the context of generally accepted medical expenditures. MATERIALS AND METHODS: A spreadsheet-based activity costing model using 1997 Canadian (cdn) capital, operating, and administrative costs has been used to identify, from the institutional perspective, the incremental cost of adding radiotherapy to surgery and chemotherapy for this group of patients. Outcome data were derived from two recently published clinical trials and were converted to discounted incremental life years and quality-adjusted life years gained. Recommended health economics principles were employed in the quantification of both costs and outcomes, and a sensitivity analysis was performed. Three referenced publications provide a context within which to evaluate the calculated cost-effectiveness and cost-utility ratios. RESULTS: The incremental cost of adjuvant radiotherapy for this group of patients is calculated to be approximately $7,000cdn in 1997 Canadian dollars and in the Canadian socialized health-care environment. Based on published work the discounted incremental outcome benefit is calculated to be 0.5 life years or 0.45 quality-adjusted life years at ten years. Thus, cost effectiveness and cost-utility ratios are estimated to be $14,000cdn and $15,600cdn, respectively. CONCLUSION: Within the context of generally accepted medical expenditures, adjuvant postmastectomy locoregional radiotherapy for premenopausal node-positive breast cancer patients would be regarded as a cost-effective treatment strategy.

Quantitative vs. subjective portal verification using digital portal images.

PURPOSE: Off-line, computer-aided prescription (simulator) and treatment (portal) image registration using chamfer matching has been implemented on PC based viewing station. The purposes of this study were (a) to evaluate the performance of interactive anatomy and field edge extraction and subsequent registration, and (b) to compare observer's perceptions of field accuracy with measured discrepancies following anatomical registration. METHODS AND MATERIALS: Prescription-treatment image pairs for 48 different patients were examined in this study. Digital prescription images were produced with the aid of a television camera and a digital frame grabber, while the treatment images were obtained directly from an on-line portal imaging system. To facilitate perception of low contrast anatomical detail, on-line portal images were enhanced with selective adaptive histogram equalization prior to extraction of anatomical edges. Following interactive extraction of anatomical and field border information by an experienced observer, the identified anatomy was registered using chamfer matching. The degree of conformity between the prescription and treatment fields was quantified using several parameters, which included relative prescription field coverage and overcoverage, as well as the translational and rotational displacements as measured by chamfer matching applied to the boundaries of the two fields. These quantitative measures were compared with subjective evaluations made by four radiation oncologists. RESULTS: All the images in this series that included a range of the most commonly seen treatment sites were registered and the conformity parameters were found. The mean treatment/prescription field coverage and overcoverage were approximately 95 and 7%, respectively before registration. The mean translational displacement in the transverse and cranio-caudal directions were 2.9 and 3.4 mm, respectively. The mean rotational displacement was approximately 2 degrees. For all four oncologists, the portals classified as unacceptable, in terms of the field placement, exhibited significantly higher (p < 0.03) translational errors in the transverse direction. The field coverages were significantly lower (p < 0.05) and the translational errors in the cranio-caudal direction were significantly higher (p < 0.05) for the portals rated as unacceptable by two of the oncologists. CONCLUSIONS: From the parameters that were used to quantify the degree of conformity between the prescription and treatment fields, the translational error in the transverse direction correlated best with the oncologists' assessments on the field placement. Field coverage and translational error in the cranio-caudal direction correlated well with assessments of only two out of the four participating oncologists. This can be explained by the fact that for the majority of treatment sites included in the study the positioning of field borders was more critical for the transverse direction. A conclusion for the design of future quantitative and automated on-line portal verification systems is that they will have to model different perceived significances of different types of localization errors intrinsic to oncologist evaluation of portal images.

The investigation and rectification of field placement errors in the delivery of complex head and neck fields.

PURPOSE: To evaluate a novel technique for resolving field placement errors into their components and to quantify the improvement in accuracy potentially achievable by translation and rotation of the radiation beam. METHODS AND MATERIALS: One hundred and eighty-five films (both simulator and portal) from seventeen patients receiving radiotherapy to the head and neck region were analyzed in pairs. The computer based comparisons of complex fields with curved edges employed the intersections of perpendiculars from two reference points with the field periphery to define field match points. Field placement errors were resolved into those due to patient motion within the immobilization shell and those due to incorrect beam position, orientation, or shape. RESULTS: The median and the 95 percentile of the distribution of differences between prescribed (simulator) fields and treated (portal) fields referenced to the patients anatomy were 4.4 mm and 8.9 mm, respectively. The analysis suggests that with appropriate translation and rotation of the beam with respect to the immobilization shell these figures could be reduced to 3.1 mm and 8.2 mm, respectively, confirming the large contribution of patient motion within the shell to field placement accuracy. Comparisons between treated fields indicated smaller variability during treatment than between simulation and treatment. CONCLUSION: The perpendicular intersection method described here was found appropriate for the identification of field match points. The distributions of field placement errors were similar to those in a published study of straight edged fields. Translation and rotation of the applied field with respect to the immobilization shell would generally result in only a small improvement in field placement accuracy.

Physical aspects of external beam radiotherapy for the treatment of malignant pleural mesothelioma.

The optimization of radiotherapy for the treatment of malignant mesothelioma highlights many of the currently outstanding problems in clinical radiation physics. The experimental investigation of an intuitively attractive irradiation technique with combined photon and electron beams using a specially constructed phantom has established that, due to the penetration in low density material of both primary electrons and those secondary to photon irradiation, the normal lung tissue is not spared to any significant degree by such a technique. Furthermore, great care needs to be exercised in the treatment planning calculations for this approach if absolute dosimetry errors as large as 50% are to be avoided.

Sizes and sources of field placement error in routine irradiation for prostate cancer.

Discrepancies between prescribed and treated field edges have been measured from 76 film pairs taken on 29 patients being treated for prostate cancer. The distribution of field edge discrepancies is described by a standard deviation of 4.5 mm and has an average absolute value of 3.5 mm. The observed discrepancies are shown to be attributable to field position errors and hence, in principle, are easily rectifiable.

The sensitivity of the thoracolumbar spinal cord of the mouse to hyperthermia.

Twelve millimeters of the thoracolumbar spinal cord of mice has been treated with a radiofrequency heating system which has been shown previously to produce localized and controllable elevation of temperature. The severity of neurological damage was assessed by measuring the reduction in the reflex leg extension of the hind legs of the mice from video-recorded images and by scoring the performance of the mice by a negative geotaxis test. The response to treatment was rapid with maximum paralysis occurring within a few days after treatment. Only minor symptoms were observed in those animals which had not developed paralysis within 2 weeks. A 40% reduction in the reflex leg extension was chosen as an end point, and the percentage of mice having reached the end point for different thermal doses was determined in groups of nine mice. The ED50 for heating for 1 h was 43.1 degrees C and for heating at 45 degrees C was 10.8 min. An increase in temperature by 1 degree C required a decrease in time by a factor of 2.25 to produce the same effect. Thermotolerance was observed 24 h after preheating at 45 degrees C for 1.9 min with a thermotolerance ratio of 1.7. The rapid response and high sensitivity of the spinal cord will have to be taken into consideration in the clinical application of hyperthermia.

A search for nonthermal effects of 434 MHz microwave radiation on whole human blood.

Whole human blood was subjected to a microwave environment at 434 MHz for 6 hr with external electric fields corresponding to free space power densities up to 598 mW cm-2 and the levels of hemoglobin, sodium, and potassium in the plasma were monitored. Under geometrical conditions in which the field strength within the samples was unknown, measurements indicated increased red cell membrane fragility following irradiation. It was not possible to exclude localized heating as an explanation of this effect. However, with a known and reasonably uniform electric field distribution within spherical specimens, increased membrane fragility was not observed. We are therefore unable to confirm previously reported results which indicate a nonthermal deleterious effect of microwave radiation on erythrocytes.

Detection of campylobacter by immunofluorescence in stools and rectal biopsies of patients with diarrhoea.

Rabbit antiserum, elicited by the intravenous injection of a strain of Campylobacter jejuni heated to 100 degrees C, cross reacted strongly with all other thermophilic campylobacters tested as well as with "C pyloridis" and could be detected by indirect fluorescence with labelled anti-rabbit serum. Antisera to formalin killed cells did not do so. The correlation of positive stool culture with positive immunofluorescence of stools and rectal biopsies from patients with diarrhoea was 70-80%. Some inconsistent, weak reactions showing differently shaped organisms have been seen with some strains of Bacteroides fragilis. Wolinella spp reacted weakly, but one strain of Vibrio cholerae tested did not. Other intestinal organisms, commensals, and pathogens tested were negative.

Jaws 2: a description of in-air beam profiles for half blocked and dynamically wedged radiation fields.

In a recent paper [Med. Phys. 19, 1441 (1992)] it was shown that the field size dependence of on-axis relative output from a linear accelerator can be well described by a model comprising two components. One component represents radiation emanating from a point source and the other represents radiation from a field size dependent distributed source. In this communication the application of the model is extended to off-axis situations and demonstrates that a good description of the dependence of off-axis output on collimator configuration can be obtained. Of particular clinical relevance in this regard is the beam profile of half blocked fields which are adequately reproduced. The model has also been applied to the study of profiles generated by simulated dynamic wedging.

A technique for the evaluation of a missing tissue compensator system.

A two dimensional approach to the evaluation of a missing tissue compensator system has been developed and implemented. Quantitative descriptors of the dose area histograms generated by scanning films irradiated under a variety of compensated and uncompensated conditions are proposed. The method has been found to be useful during the acceptance testing of a commercial compensator system and the results of this exercise are presented.

On the field-size dependence of relative output from a linear accelerator.

The radiation output in air on the central axis of a linac photon beam has been modeled as the sum of two components. These are a point source representing radiation direct from the target and a distributed source representing scatter in the flattening filter and primary collimator. By fitting only two parameters, the ratio of the two components for a 20 x 20 field and a width parameter for the distributed source this semi-empirical model describes the relative outputs of square, symmetric rectangular, and asymmetric rectangular fields with an average error of 0.25% for the field sizes studied.

A test tool for the visual verification of light and radiation fields using film or an electronic portal imaging device.

We describe the design and evaluation of a simple test tool which can be used in conjunction with either film or an electronic portal imaging device (EPID) to verify light and radiation fields and their congruence. The precision of the technique is better than 0.5 mm under all conditions tested. When used with film the accuracy or offset of the technique (the difference between test tool observations and a scanned conventional film) is better than 0.5 mm but, with an EPID as the image receptor, the accuracy dropped to, in one trial, 0.86 mm. The offset may be due to a systematic observer bias in determining the 50% O.D. level on the image, compounded, in the case of EPID measurements, by image acquisition and display parameters. Thus, when used with an EPID, calibration of the system will be required if absolute field dimensions are required. When used with film, the test tool method described here is of sufficient accuracy and precision to confirm the compliance of light and radiation field parameters with currently accepted quality control protocols.

The characterization of a promising new optical source for use with a radiotherapy treatment simulator.

We report on an experimental examination of a new powerful optical source with potential application in radiotherapy treatment simulation. The illuminance, effective source position, and source size have been measured for this new source and, for comparison, for conventional sources on a simulator and a linear accelerator. This new source is considerably brighter than those in common use in radiotherapy. Its effective optical source size is larger than that on the linear accelerator tested but comparable with that on a conventional simulator.

Heat production in microwave-irradiated thermocouples.

It has been known for some time that the irradiation of metallic thermometers by microwaves during clinical hyperthermia can lead to artifactual readings. We describe here a series of measurements in which this effect has been quantitatively studied. In particular, the data yield values for the conversion coefficient describing the rate of heat production per unit length of a thermocouple array per watt applied power which can be compared with the rate of heat production in the same volume of tissue. The degree of artifact in the temperature recording depends on the thermal resistance of the protective materials surrounding the array, and this thermal resistance has also been determined. It has been shown that measures taken to reduce the temperature artifact do not compromise the response time of the probe.

Matching photon and electron fields in the treatment of head and neck tumors.

Radiotherapy of head and neck tumors frequently involves joining photon and electron fields. In such situations narrow penumbras combined with relatively small positioning errors can lead to significant "hot" and "cold" spots in the vicinity of the join-up. The objective of this work was to devise penumbra spreading techniques which lead to a relatively uniform dose distribution in the join-up region of these fields and which reduce the effect of positioning errors on dose uniformity. A stepped edge attenuator was used to obtain a wider penumbra for the 4-MV x-ray beam and a Lucite scatterer was used for the 10-MeV electron beam. The resulting composite beam profiles from these "modified" abutting photon and electron fields are provided and the effects of positioning errors on dose uniformity across the junction are illustrated. These profiles are compared with those resulting from "unmodified" adjacent electron and photon beams.

Perturbation of the temperature distribution in microwave irradiated tissue due to the presence of metallic thermometers.

To date, satisfactory thermal dosimetry during the clinical application of localized hyperthermia can only be achieved using invasive thermometry. However the presence of commonly used metallic thermometers, such as thermocouples, may lead to the distortion of the temperature field due to self-heating of the probe under microwave irradiation. A computer simulation of the effect of this self-heating on the steady-state temperature distribution in plane-microwave irradiated homogeneous tissue has been undertaken and the significance of the effect for clinical hyperthermia dosimetry is assessed. The results indicate that a distortion of the temperature field in the neighborhood of the thermometer by several degrees can occur under adverse conditions.