James A. Purdy

Bio: James A. Purdy is an academic researcher from Washington University in St. Louis. The author has contributed to research in topics: Radiation therapy & Radiation treatment planning. The author has an hindex of 52, co-authored 188 publications receiving 13514 citations. Previous affiliations of James A. Purdy include University of California, Davis.

A technique for the quantitative evaluation of dose distributions

Abstract: The commissioning of a three-dimensional treatment planning system requires comparisons of measured and calculated dose distributions. Techniques have been developed to facilitate quantitative comparisons, including superimposed isodoses, dose-difference, and distance-to-agreement (DTA) distributions. The criterion for acceptable calculation performance is generally defined as a tolerance of the dose and DTA in regions of low and high dose gradients, respectively. The dose difference and DTA distributions complement each other in their useful regions. A composite distribution has recently been developed that presents the dose difference in regions that fail both dose-difference and DTA comparison criteria. Although the composite distribution identifies locations where the calculation fails the preselected criteria, no numerical quality measure is provided for display or analysis. A technique is developed to unify dose distribution comparisons using the acceptance criteria. The measure of acceptability is the multidimensional distance between the measurement and calculation points in both the dose and the physical distance, scaled as a fraction of the acceptance criteria. In a space composed of dose and spatial coordinates, the acceptance criteria form an ellipsoid surface, the major axis scales of which are determined by individual acceptance criteria and the center of which is located at the measurement point in question. When the calculated dose distribution surface passes through the ellipsoid, the calculation passes the acceptance test for the measurement point. The minimum radial distance between the measurement point and the calculation points (expressed as a surface in the dose–distance space) is termed the γ index. Regions where γ>1 correspond to locations where the calculation does not meet the acceptance criteria. The determination of γ throughout the measured dose distribution provides a presentation that quantitatively indicates the calculation accuracy. Examples of a 6 MV beam penumbra are used to illustrate the γ index.

Clinical dose-volume histogram analysis for pneumonitis after 3D treatment for non-small cell lung cancer (NSCLC)

Abstract: Purpose: To identify a clinically relevant and available parameter upon which to identify non-small cell lung cancer (NSCLC) patients at risk for pneumonitis when treated with three-dimensional (3D) radiation therapy. Methods and Materials: Between January 1991 and October 1995, 99 patients were treated definitively for inoperable NSCLC. Patients were selected for good performance status (96%) and absence of weight loss (82%). All patients had full 3D treatment planning (including total lung dose–volume histograms [DVHs]) prior to treatment delivery. The total lung DVH parameters were compared with the incidence and grade of pneumonitis after treatment. Results: Univariate analysis revealed the percent of the total lung volume exceeding 20 Gy ( V 20 ), the effective volume ( V eff ) and the total lung volume mean dose, and location of the tumor primary (upper versus lower lobes) to be statistically significant relative to the development of ≥ Grade 2 pneumonitis. Multivariate analysis revealed the V 20 to be the single independent predictor of pneumonitis. Conclusions: The V 20 from the total lung DVH is a useful parameter easily obtained from most 3D treatment planning systems. The V 20 may be useful in comparing competing treatment plans to evaluate the risk of pneumonitis for our individual patient treatment and may also be a useful parameter upon which to stratify patients or prospective dose escalation trials.

Comprehensive QA for radiation oncology: report of AAPM Radiation Therapy Committee Task Group 40.

Abstract: Published by the American Association of Physicists in Medicine DISCLAIMER: This publication is based on sources and information believed to be reliable, but the AAPM and the editors disclaim any warranty or liability based on or relating to the contents of this publication. The AAPM does not endorse any products, manufacturers, or suppliers. Nothing in this publication should be interpreted as implying such endorsement. PREFACE This document is the report of a task group of the Radiation Therapy Committee of the American Association of Physicists in Medicine and supersedes the recommendations of AAPM Report 13 (AAPM, 1984). The purpose of the report is twofold. First, the advances in radiation oncology in the decade since AAPM Report 13 (AAPM, 1984) necessitated a new document on quality assurance (QA). Second, developments in the principles of quality assurance and continuing quality improvement necessitated a report framed in this context. The title \" Comprehensive Quality Assurance for Radiation Oncology \" may need clarification. While the report emphasizes the physical aspects of QA and does not attempt to discuss issues that are essentially medical (e.g., the decision to treat, the prescription of dose), it by no means neglects issues in which the physical and medical issues intertwine, often in a complex manner. The integrated nature of QA in radiation oncology makes it impossible to consider QA as limited to, for example, checking machine output or calibrating brachytherapy sources. QA activities cover a very broad range, and the work of medical physicists in this regard extends into a number of areas in which the actions of radiation oncologists, radiation therapists, 1 dosimetrists, accelerator engineers, and medical physicists are important. Moreover, this is true for each of the disciplines-each has special knowledge and expertise which affects the quality of treatment , and each discipline overlaps the others in a broad \" gray zone. \" It is important not only to understand each discipline's role in QA, but to clarify this zone so that errors do not \" fall between the cracks. \" This report therefore attempts to cover the physical aspects of QA both in a narrow or traditional sense and in a more integrated sense. The report comprises 2 parts: Part A is for administrators, and Part B is a code of practice in six sections. The first section of Part B describes a comprehensive quality assurance program in which the importance of a written procedural …

Radiation pneumonitis as a function of mean lung dose: An analysis of pooled data of 540 patients

Abstract: Purpose: To determine the relation between the incidence of radiation pneumonitis and the three-dimensional dose distribution in the lung. Methods and Materials: In five institutions, the incidence of radiation pneumonitis was evaluated in 540 patients. The patients were divided into two groups: a Lung group, consisting of 399 patients with lung cancer and 1 esophagus cancer patient and a Lymph./Breast group with 78 patients treated for malignant lymphoma, 59 for breast cancer, and 3 for other tumor types. The dose per fraction varied between 1.0 and 2.7 Gy and the prescribed total dose between 20 and 92 Gy. Three-dimensional dose calculations were performed with tissue density inhomogeneity correction. The physical dose distribution was converted into the biologically equivalent dose distribution given in fractions of 2 Gy, the normalized total dose (NTD) distribution, by using the linear quadratic model with an α/β ratio of 2.5 and 3.0 Gy. Dose–volume histograms (DVHs) were calculated considering both lungs as one organ and from these DVHs the mean (biological) lung dose, NTD mean , was obtained. Radiation pneumonitis was scored as a complication when the pneumonitis grade was grade 2 (steroids needed for medical treatment) or higher. For statistical analysis the conventional normal tissue complication probability (NTCP) model of Lyman (with n = 1) was applied along with an institutional-dependent offset parameter to account for systematic differences in scoring patients at different institutions. Results: The mean lung dose, NTD mean , ranged from 0 to 34 Gy and 73 of the 540 patients experienced pneumonitis, grade 2 or higher. In all centers, an increasing pneumonitis rate was observed with increasing NTD mean . The data were fitted to the Lyman model with NTD 50 = 31.8 Gy and m = 0.43, assuming that for all patients the same parameter values could be used. However, in the low dose range at an NTD mean between 4 and 16 Gy, the observed pneumonitis incidence in the Lung group (10%) was significantly ( p = 0.02) higher than in the Lymph./Breast group (1.4%). Moreover, between the Lung groups of different institutions, also significant ( p = 0.04) differences were present: for centers 2, 3, and 4, the pneumonitis incidence was about 13%, whereas for center 5 only 3%. Explicitly accounting for these differences by adding center-dependent offset values for the Lung group, improved the data fit significantly ( p −5 ) with NTD 50 = 30.5 ± 1.4 Gy and m = 0.30 ± 0.02 (± 1 SE) for all patients, and an offset of 0–11% for the Lung group, depending on the center. Conclusions: The mean lung dose, NTD mean , is relatively easy to calculate, and is a useful predictor of the risk of radiation pneumonitis. The observed dose–effect relation between the NTD mean and the incidence of radiation pneumonitis, based on a large clinical data set, might be of value in dose-escalating studies for lung cancer. The validity of the obtained dose–effect relation will have to be tested in future studies, regarding the influence of confounding factors and dose distributions different from the ones in this study.

A prospective study of salivary function sparing in patients with head-and-neck cancers receiving intensity-modulated or three-dimensional radiation therapy: initial results

Abstract: Objectives: In a prospective clinical study, we tested the hypothesis that sparing the parotid glands may result in significant objective and subjective improvement of xerostomia in patients with head-and-neck cancers. The functional outcome 6 months after the completion of radiation therapy is presented. Methods and Materials: From February 1997 to February 1999, 41 patients with head-and-neck cancers were enrolled in a prospective salivary function study. Inverse-planning intensity-modulated radiation therapy (IMRT) was used to treat 27 patients, and forward-planning three-dimensional radiation therapy in 14. To avoid potential bias in data interpretation, only patients whose submandibular glands received greater than 50 Gy were eligible. Attempts were made to spare the superficial lobe of the parotid glands to avoid underdosing tumor targets in the parapharyngeal space; however, the entire parotid volume was used to compute dose–volume histograms (DVHs) for this analysis. DVHs were computed for each gland separately. Parotid function was assessed objectively by measuring stimulated and unstimulated saliva flow before and 6 months after the completion of radiation therapy. Measurements were converted to flow rate (mL/min) and normalized relative to that before treatment. The corresponding quality-of-life (QOL) outcome was assessed by five questions regarding the patient's oral discomfort and eating/speaking problems. Results: We observed a correlation between parotid mean dose and the fractional reduction of stimulated saliva output at 6 months after the completion of radiation therapy. We further examined whether the functional outcome could be modeled as a function of dose. Two models were found to describe the dose–response data well. The first model assumed that each parotid gland is comprised of multiple independent parallel functional subunits (corresponding to computed tomography voxels) and that each gland contributes equally to overall flow, and that saliva output decreases exponentially as a quadratic function of irradiation dose to each voxel. The second approach uses the e quivalent u niform d ose (EUD) metrics, which assumes loss of salivary function with increase in EUD for each parotid gland independently. The analysis suggested that the mean dose to each parotid gland is a reasonable indicator for the functional outcome of each gland. The corresponding exponential coefficient was 0.0428/Gy (95% confidence interval: 0.01, 0.09). The QOL questions on eating/speaking function were significantly correlated with stimulated and unstimulated saliva flow at 6 months. In a multivariate analysis, a toxicity score derived from the model based on radiation dose to the parotid gland was found to be the sole significant predictive factor for xerostomia. Neither radiation technique (IMRT vs. non-IMRT) nor chemotherapy (yes or no) independently influenced the functional outcome of the salivary glands. Conclusion: Sparing of the parotid glands translates into objective and subjective improvement of both xerostomia and QOL scores in patients with head-and-neck cancers receiving radiation therapy. Modeling results suggest an exponential relationship between saliva flow reduction and mean parotid dose for each gland. We found that the stimulated saliva flow at 6 months after treatment is reduced exponentially, for each gland independently, at a rate of approximately 4% per Gy of mean parotid dose.

Tolerance of normal tissue to therapeutic irradiation.

Abstract: The importance of knowledge on tolerance of normal tissue organs to irradiation by radiation oncologists cannot be overemphasized. Unfortunately, current knowledge is less than adequate. With the increasing use of 3-D treatment planning and dose delivery, this issue, particularly volumetric information, will become even more critical. As a part of the NCI contract N01 CM-47316, a task force, chaired by the primary author, was formed and an extensive literature search was carried out to address this issue. In this issue. In this manuscript we present the updated information on tolerance of normal tissues of concern in the protocols of this contract, based on available data, with a special emphasis on partial volume effects. Due to a lack of precise and comprehensive data base, opinions and experience of the clinicians from four universities involved in the contract have also been contributory. Obviously, this is not and cannot be a comprehensive work, which is beyond the scope of this contract.

sources and effects of ionizing radiation

Abstract: NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …

A technique for the quantitative evaluation of dose distributions

Abstract: The commissioning of a three-dimensional treatment planning system requires comparisons of measured and calculated dose distributions. Techniques have been developed to facilitate quantitative comparisons, including superimposed isodoses, dose-difference, and distance-to-agreement (DTA) distributions. The criterion for acceptable calculation performance is generally defined as a tolerance of the dose and DTA in regions of low and high dose gradients, respectively. The dose difference and DTA distributions complement each other in their useful regions. A composite distribution has recently been developed that presents the dose difference in regions that fail both dose-difference and DTA comparison criteria. Although the composite distribution identifies locations where the calculation fails the preselected criteria, no numerical quality measure is provided for display or analysis. A technique is developed to unify dose distribution comparisons using the acceptance criteria. The measure of acceptability is the multidimensional distance between the measurement and calculation points in both the dose and the physical distance, scaled as a fraction of the acceptance criteria. In a space composed of dose and spatial coordinates, the acceptance criteria form an ellipsoid surface, the major axis scales of which are determined by individual acceptance criteria and the center of which is located at the measurement point in question. When the calculated dose distribution surface passes through the ellipsoid, the calculation passes the acceptance test for the measurement point. The minimum radial distance between the measurement point and the calculation points (expressed as a surface in the dose–distance space) is termed the γ index. Regions where γ>1 correspond to locations where the calculation does not meet the acceptance criteria. The determination of γ throughout the measured dose distribution provides a presentation that quantitatively indicates the calculation accuracy. Examples of a 6 MV beam penumbra are used to illustrate the γ index.

The management of respiratory motion in radiation oncology report of AAPM Task Group 76.

Abstract: This document is the report of a task group of the AAPM and has been prepared primarily to advise medical physicists involved in the external-beam radiation therapy of patients with thoracic, abdominal, and pelvic tumors affected by respiratory motion. This report describes the magnitude of respiratory motion, discusses radiotherapy specific problems caused by respiratory motion, explains techniques that explicitly manage respiratory motion during radiotherapy and gives recommendations in the application of these techniques for patient care, including quality assurance (QA) guidelines for these devices and their use with conformal and intensity modulated radiotherapy. The technologies covered by this report are motion-encompassing methods, respiratory gated techniques, breath-hold techniques, forced shallow-breathing methods, and respiration-synchronized techniques. The main outcome of this report is a clinical process guide for managing respiratory motion. Included in this guide is the recommendation that tumor motion should be measured (when possible) for each patient for whom respiratory motion is a concern. If target motion is greater than 5 mm, a method of respiratory motion management is available, and if the patient can tolerate the procedure, respiratory motion management technology is appropriate. Respiratory motion management is also appropriate when the procedure will increase normal tissue sparing. Respiratory motion management involves further resources, education and the development of and adherence to QA procedures.