Arthur J. Olch

Code of practice for brachytherapy physics: Report of the AAPM Radiation Therapy Committee Task Group No. 56

Recommendations of the American Association of Physicists in Medicine (AAPM) for the practice of brachytherapy physics are presented. These guidelines were prepared by a task group of the AAPM Radiation Therapy Committee and have been reviewed and approved by the AAPM Science Council.

Dosimetric performance of an enhanced dose range radiographic film for intensity-modulated radiation therapy quality assurance.

Film-based quality assurance (QA) is an important element of any intensity modulated radiation therapy (IMRT) program. XV2 film is often used for IMRT QA, however, it has saturation and energy response limitations which hinder accurate film dosimetry. A new commercially released ready-pack film has been introduced that has an extended dose range (EDR2), reportedly allowing measured doses above 600 cGy without saturation. Also, this film may have less energy dependence due to its composition. The purpose of this paper is to study and compare the two types of film with respect to absolute dose accuracy for IMRT plans, percent depth dose accuracy for square fields between 2 and 20 cm, ability to measure composite plan isodoses and single beam fluence maps for IMRT cases, and sensitivity to processor variations over time. In 19 IMRT patient QA tests, the EDR2 film was able to achieve an absolute dose accuracy of better than 2% vs over 4% for XV2 film. The EDR2 film was able to reproduce ionization chamber and diode-measured percent depth doses to 20 cm depth generally to within 1% over the range of field sizes tested compared to about 10% for the XV2 film. When compared to calculations, EDR2 film agreed better than XV2 film for both composite plan isodoses and single beam fluence intensity maps. The EDR2 film was somewhat more resistant to processor changes over time than the XV2 film, with a standard deviation of dose reproducibility of less than 2% compared to 6%, respectively.

TG-69 : Radiographic film for megavoltage beam dosimetry

TG-69 is a task group report of the AAPM on the use of radiographic film for dosimetry. Radiographic films have been used for radiation dosimetry since the discovery of x-rays and have become an integral part of dose verification for both routine quality assurance and for complex treatments such as soft wedges (dynamic and virtual), intensity modulated radiation therapy (IMRT), image guided radiation therapy (IGRT), and small field dosimetry like stereotactic radiosurgery. Film is convenient to use, spatially accurate, and provides a permanent record of the integrated two dimensional dose distributions. However, there are several challenges to obtaining high quality dosimetric results with film, namely, the dependence of optical density on photon energy, field size, depth, film batch sensitivity differences, film orientation, processing conditions, and scanner performance. Prior to the clinical implementation of a film dosimetry program, the film, processor, and scanner need to be tested to characterize them with respect to these variables. Also, the physicist must understand the basic characteristics of all components of film dosimetry systems. The primary mission of this task group report is to provide guidelines for film selection, irradiation, processing, scanning, and interpretation to allow the physicist to accurately and precisely measure dose with film. Additionally, we present the basic principles and characteristics of film, processors, and scanners. Procedural recommendations are made for each of the steps required for film dosimetry and guidance is given regarding expected levels of accuracy. Finally, some clinical applications of film dosimetry are discussed.

Evaluation of the accuracy of 3DVH software estimates of dose to virtual ion chamber and film in composite IMRT QA

PURPOSE A novel patient-specific intensity modulated radiation therapy (IMRT) QA system, 3DVH software and mapcheck 2, purports to be able to use diode array-measured beam doses and the patients DICOM RT plan, structure set, and dose files to predict the delivered 3D dose distribution in the patient for comparison to the treatment planning system (TPS) calculated doses. In this study, the composite dose to an ion chamber and film in phantom predicted by the 3DVH and mapcheck 2 system is compared to the actual measured chamber and film doses. If validated in this context, then 3DVH can be used to perform an equivalent dose analysis as that obtained with film dosimetry and ion chamber-based composite IMRT QA. This is important for those losing their ability to perform film dosimetry for true composite IMRT QA and provides a measure of confidence in the accuracy of 3DVH 3D dose calculations which may replace phantom-based IMRT QA. METHODS The dosimetric results from 15 consecutive patient-specific IMRT QA tests performed by composite field irradiation of ion chamber and EDR2 film in a solid water phantom were compared to the predicted doses for those virtual detectors based on the calculated 3D dose by the 3DVH software using mapcheck 2 measured doses of each beam within each plan. For each of the 15 cases, immediately after performing the ion chamber plus film measurements, the mapcheck 2 was used to measure the dose for each beam of the plan. The dose to the volume of the virtual ion chamber and the dose distribution in the plane of the virtual film calculated by the 3DVH software was extracted. The ratio of the measured to 3DVH or eclipse-predicted ion chamber doses was calculated. The same plane in the phantom measured using film and calculated with eclipse was exported from 3DVH and the 2D gamma metric was used to compare the relationship between the film doses and the eclipse or 3DVH predicted planar doses. Also, the 3D gamma value was calculated in the 3DVH software which compares the eclipse dose to the 3DVH predicted dose distribution. For the 2D and 3D gamma metrics, 2% dose and 2 mm distance to agreement (DTA) were used. In addition, a simple dose difference was performed using either a 2% or 3% dose difference tolerance. RESULTS The mean ratio ± standard deviation of the measured vs 3DVH or vs eclipse-predicted dose to the ion chamber was 1.013 ± 0.015 and 1.003 ± 0.012, respectively. For 3DVH vs eclipse, the mean percentage of pixels failing the 3D gamma metric was 1.2% ± 1.4% while the failure rate for the 2D gamma metric was 1.1% ± 0.9%. When either 3DVH or eclipse was compared to EDR2 film, the gamma failure rate was 2.3% ± 2.0% and 1.6% ± 1.7%, respectively. Mean dose difference failures were 9%-27% ± 5%-15% for 2 or 3% dose difference tolerances, depending on the combination of systems tested. No statistically significant differences were found for any of the planar dosimetric comparisons. CONCLUSIONS 3DVH + mapcheck 2 predicts the same absolute dose, the percent of pixels failing the gamma metric, and the percent of pixels failing 2% or 3% dose difference tolerance tests as one would have obtained had one made measurements in solid water phantom using an ion chamber and coronal film instead of a diode array. This is also a necessary although not sufficient condition for validation of the accuracy of 3DVH predictions of the 3D dose using beam-by-beam measurements.

Evaluation of a computed radiography system for megavoltage photon beam dosimetry

Computed radiography (CR) systems have been gaining adoption as digital replacements for film for diagnostic and therapy imaging. As a result, film processors are being removed from service, leaving a void for the medical physicists who use film and processors for two-dimensional mega-voltage beam dosimetry. This is the first report to evaluate the ability of a commercial CR reader and storage phosphor plate system to accurately quantitate absolute dose and dose distributions from a 6 MV photon beam. There are potential advantages and disadvantages of current CR systems compared to film systems. CR systems inherently produce a linear dose-response over several logs of dose. However, the barium in the storage phosphor has a higher atomic number than the silver in film, resulting in significant energy sensitivity. The purpose of this work is to fully characterize the impact of these and other features of this CR system relevant to dosimetry. The tests performed and reported on in this study include uniformity of readout across a uniform field, geometrical accuracy, intra- and interday reproducibility, signal decay with time and with light exposure, dose-to-signal calibration, high dose effects, obliquity effects, perpendicular and parallel calibration results, field size and depth of measurement effects and the use of lead filters to minimize them, and intensity modulated radiation therapy quality assurance test results compared to that for film. Practical techniques are provided to optimize the accuracy of the system as a dosimetric replacement for film.

Clinical outcomes of radiation therapy in the management of Langerhans cell histiocytosis.

Objectives:Langerhans cell histiocytosis (LCH) is a rare disease with variable clinical presentation. In the present study, we report on the effectiveness and clinical complications of radiation therapy in children with LCH. Materials and Methods:We retrospectively reviewed all patients with LCH treated with radiation therapy over a 6-decade period at a single institution. Radiotherapy data, clinical features, radiographic data, and vital status were analyzed. Results:The mean age at diagnosis for 69 patients was 5.3 years (3 mo to 37 y) and the median duration of follow-up was 6 years (7 d to 32 y). Radiation therapy was performed for 169 sites, primarily bone lesions. The median radiotherapy dose was 10 Gy (2.5 to 45 Gy). Radiographic follow-up data were available for 139 of the sites treated and clinical follow-up was available for 156 of sites treated. The radiographic local control was 91.4%, and 13% of lesions showed complete sclerosis or reconstitution of bone. A total of 90.4% of patients reported stabilization or improvement in lesion-related symptoms, most often pain. Twelve patients had diabetes insipidus at diagnosis or during follow-up. Eight of these patients received radiation treatment to the pituitary and none experienced a reduction in desmopressin dosage posttreatment. Radiation complications were few, including femoral neck fracture in 1 patient and facial asymmetry in 3 patients. No secondary malignancies were observed. Conclusions:Radiotherapy for LCH has high rates of local control and symptomatic improvement. Importantly, however, there is evidence of short-term and long-term morbidity when children are treated with low-dose irradiation.

Correlation of Clinical and Dosimetric Factors With Adverse Pulmonary Outcomes in Children After Lung Irradiation

PURPOSE To identify the incidence and the risk factors for pulmonary toxicity in children treated for cancer with contemporary lung irradiation. METHODS AND MATERIALS We analyzed clinical features, radiographic findings, pulmonary function tests, and dosimetric parameters of children receiving irradiation to the lung fields over a 10-year period. RESULTS We identified 109 patients (75 male patients). The median age at irradiation was 13.8 years (range, 0.04-20.9 years). The median follow-up period was 3.4 years. The median prescribed radiation dose was 21 Gy (range, 0.4-64.8 Gy). Pulmonary toxic chemotherapy included bleomycin in 58.7% of patients and cyclophosphamide in 83.5%. The following pulmonary outcomes were identified and the 5-year cumulative incidence after irradiation was determined: pneumonitis, 6%; chronic cough, 10%; pneumonia, 35%; dyspnea, 11%; supplemental oxygen requirement, 2%; radiographic interstitial lung disease, 40%; and chest wall deformity, 12%. One patient died of progressive respiratory failure. Post-irradiation pulmonary function tests available from 44 patients showed evidence of obstructive lung disease (25%), restrictive disease (11%), hyperinflation (32%), and abnormal diffusion capacity (12%). Thoracic surgery, bleomycin, age, mean lung irradiation dose (MLD), maximum lung dose, prescribed dose, and dosimetric parameters between V22 (volume of lung exposed to a radiation dose ≥22 Gy) and V30 (volume of lung exposed to a radiation dose ≥30 Gy) were significant for the development of adverse pulmonary outcomes on univariate analysis. MLD, maximum lung dose, and Vdose (percentage of volume of lung receiving the threshold dose or greater) were highly correlated. On multivariate analysis, MLD was the sole significant predictor of adverse pulmonary outcome (P=.01). CONCLUSIONS Significant pulmonary dysfunction occurs in children receiving lung irradiation by contemporary techniques. MLD rather than prescribed dose should be used to perform risk stratification of patients receiving lung irradiation.

AAPM Medical Physics Practice Guideline 2.a: Commissioning and quality assurance of X-ray-based image-guided radiotherapy systems.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized.

A retrospective analysis of recurrent intracranial ependymoma

Recurrence occurs in almost 50% of patients with intracranial ependymoma, and their outcome following recurrence is poor.

Dosimetric accuracy of the ITP inverse treatment planning system.

The dosimetric accuracy of the ITP system for intensity modulated radiation therapy was determined for 19 patient plans. Treatments were given with a Varian 2100C and a 120-leaf multileaf collimator using step and shoot delivery. Both absolute dose, determined by an ionization chamber, and relative dose, determined by film, were assessed. It was found that absolute dose agreement was within 0.1% +/- 1.5%, isodoses in the high dose-low gradient region were within 1.7% +/- 2%, and the distance to agreement for isodoses between 20% and 90% was 1.4 mm +/- 1 mm. This agreement is at least as good as that found for standard wedged fields in most treatment planning systems.