Radiological Physics Center Research Articles

TH-D-352-05: Optically Stimulated Luminescence (OSL) Dosimeters Can Be Used for Remote Dosimetry Services

Purpose: To evaluate aluminum-oxide optically stimulated luminescence (OSL) dosimeters as a potential alternative to thermoluminescent dosimeters (TLDs) for remote dosimetry services provided by the Radiological Physics Center (RPC) at the University of Texas M. D. Anderson Cancer Center. Method and Materials: OSL dosimeters were placed equidistant (< 1 cm) from the center of a 20 cm × 20 cm Solid Water™ (SW) phantom which provided backscatter and build-up. OSL dosimeters were also irradiated in an acrylic mini-phantom based on the RPC's mailable TLD system mini-phantom. For modality-dependence measurements, dosimeters were irradiated to doses of either 100 or 300 cGy with 6 or 15 MV photons or 8 or 15 MeV electrons. All other irradiations were performed with a Co-60 unit. A Landauer microStar™ reader was used to measure the dosimeter responses. Results: The calculated percent standard deviation of the reproducibility readings was less than 1.4% for doses of 50 cGy and 300 cGy, and less than 0.9% for a dose of 1000 cGy. The measured dose response was linear at doses less than 600 cGy, and independent of modality. Field-size output factors measured with OSL dosimeters agreed with those measured with an ion chamber within 1.5%. Heat, cold and humidity had no effect on the dosimeters, but exposure to light significantly decreased their response. Measurements of fading demonstrated that a 4% loss of signal occurs over the first ten days after irradiation, after which the response changes less than 1% up to 90 days. The dosimeters lost 0.2% of signal with each successive reading. Conclusion: The precision of OSL dosimeters is comparable to that provided by TLDs used for remote dosimetry and warrants further investigation. Conflict of Interest: This work was supported in part by Landauer Corporation and by PHS grant CA10953 from the NCI, DHHS.

TU‐C‐AUD B‐03: A Comparison of Heterogeneity Correction Algorithms

Purpose: To compare the measured dose distribution to the planned distribution over a PTV centrally located within the lung when heterogeneity corrections are taken into account. Method and Materials: The Radiological Physics Center has constructed an anthropomorphic thorax phantom that includes a target (∼ 1 g/cm3) centrally located in the left lung (∼ 0.33 g/cm3). The phantom was irradiated by 33 institutions with results that meet criteria established for the RTOG 0236 protocol. TLDs and radiochromic films were used as dosimeters within the target region. Institutions were asked to design plans using 3D‐CRT and IMRT techniques. The TLD dose was compared to the dose calculated by the TPS at the center of the target. Film response was normalized to TLD doses and a 2D‐gamma analysis comparison to the planned distribution was performed. Institutions whose irradiation of the phantom did not meet the RTOG 0236 criteria were not included. Results: A 2D‐Gamma analysis was done in the axial, sagittal and coronal planes through the PTV. 5% / 5mm criteria were applied. Due to limitations of the analysis software only the comparison over the axial plane is reported. 21 of the cases were planned with a superposition/convolution or AAA algorithm. For these cases, 92% ± 12% of the pixels in the analyzed region met the criteria. 12 of the cases were planned with a pencil beam or Clarkson algorithm. 74% ± 25% of the pixels meet the criteria for these cases. Conclusion: The superposition convolution heterogeneity correction algorithm showed better agreement with the measured dose distribution across the PTV than the pencil beam and Clarkson algorithms.Work supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.

SU‐GG‐T‐287: Deformable Lung Phantom for Verification of 4D Dose Calculations

Purpose: 4D dose calculations have been developed that explicitly incorporate patient motion and deformation in the calculation of dose. Before these calculations can be used in the clinic it is necessary to evaluate and verify their accuracy. The purpose of this study was to develop a deformable lung phantom for verification of 4D dose calculations. Method and Materials: The Radiological Physics Center (RPC) had previously developed an anthropomorphic thoracic phantom with inhomogeneities and an imageable target. An insert was built for the lung cavity of this phantom to incorporate motion and deformation. The insert was composed of disks of sponges of different compressabilities and a computer controlled motor‐driven piston to compress the sponges. The control system is capable of reproducing measured respiratory motion traces as well as simple sinusoidal motions. A tissue‐equivalent target was placed in one of the sponge disks and planes of films were distributed throughout the target and between sponge disks. Results: The choice of sponge compressibility, thickness, and order has allowed us to shape the lung motion to mimic clinically observed deformations. In addition the design of the deformable phantom offers flexibility of target position and motion, film placement and diaphragm motion pattern. Conclusion: The deformable lung insert for the RPC phantom provides an anthropomorphic phantom that can be used to verify the accuracy of 4D dose calculations. Conflict of Interest: This work is partially supported through a Sponsored Research Agreement with Philips Healthcare.

TH‐SAMS‐AUD B‐03: Requirements for Addressing Respiratory Motion in Cooperative Group Clinical Trials (SAM Session)

In mid‐2006, the National Cancer Institute (NCI) published updated guidelines for the use of intensity‐modulated radiation therapy (IMRT) on clinical trials, specifically when the target volume included the thoracic region or other areas in which respiratory motion could have a significant effect. In addition to requiring heterogeneity corrections, the NCI now requires that the clinical protocol address the localization and immobilization of both the patient and the tumor. Imaging must be performed in a manner that provides a representation of the target volume without motion artifact. Procedures must be defined to document reproducible daily position of the patient and target. Some form of credentialing is required.The Radiological Physics Center (RPC) has been enlisted to participate in the credentialing process for institutions participating in certain cooperative group trials in which respiratory motion is an issue. To accomplish this, the RPC has constructed several phantoms that mimic the thoracic and abdominal region, and which can be placed on a moving platform to simulate respiratory motion. The combination of phantom and moving platform have been used to evaluate compensation techniques for respiratory motion at several institutions. The techniques employed and the results of these measurements will be described as well as those reported in the literature.Educational Objectives:1. Review the structure supporting cooperative group clinical trials in the US.2. Become familiar with the NCI guidelines for the use of IMRT in clinical trials.3. Learn about the effects of respiratory motion during thoracic treatments.4. Understand the information derived from the RPC's moving anthropomorphic phantoms.This research is supported by grants CA 10953 and 81647 awarded by NCI, DHHS.

Dosimetry in an IMRT phantom designed for a remote monitoring program

An accurate delivery of prescribed dose is essential to ensure the most successful outcome from advanced radiation treatments such as intensity modulated radiation therapy (IMRT). An anthropomorphic phantom was designed and constructed to conduct a remote-audit program for IMRT treatments. The accuracy of the dosimetry in the phantom was assessed by comparing the results obtained from different detectors with those from Monte Carlo calculations. The developed phantom has a shape of a cylinder with one target and three organs at risk (OARs) inside the unit. The target and OARs were shaped similar to those of nasopharyngeal cancer patients, and manufactured for their identification during computed tomography imaging. The phantom was designed with thermoluminescent dosimeter (TLD) holders that were inserted inside the target and the OARs for the measurements of absolute dose. In addition, the phantom allowed measurements with ionization chambers placed at the TLD locations. As a result, an inter-comparison between the two types of dosimeters was possible. For the measurement of the relative dose distribution across the target and OARs, two film slots were orthogonally placed near the center of the phantom, which also enabled the insertion of inhomogeneities near the target. Measurements with TLDs, provided by Korea Food and Drug Administration and Radiological Physics Center, and measurements with an ionization chamber (IC) were performed in four cases. The first case was one anterior field of 6 MV x rays delivered to the phantom; the second case used the same anterior field, but with inhomogeneities inserted into the phantom. The third case was three fields of 6 MV beams at an equi-gantry angle for the homogeneous phantom, and the fourth case was IMRT delivery to the phantom without inhomogeneities. For each case, measurements with both TLDs and IC were performed. For cases 1-3, theoretical predictions were obtained by using the Monte Carlo (MC) codes (BEAMnrc and DOSXYZnrc6.0). The TLD measurements were larger than the IC readings by 2.2% (1.3-2.5%), 2.2% (1.2-2.9%), and 2.1% (0-3.3%) on average for case 1, case 2 and case 3, respectively. The average deviation between TLDs and MC results was 0.97% (-0.13-2.07%) for the first case, 1.27% (0.34-2.18%) for the second case, and 1.13% (0.31-1.94%) for the third case. The IC reading was less than the MC results; the average deviations were -1.2% (-2.44--0.43%), -0.96% (-1.74 - -0.54%) and -0.94% (-1.53-0.27%) for the first, second, and third cases, respectively. For the IMRT case, the average deviation between IC readings and TLD measurements was 0.5% (-7.0-3.9%). In conclusion, the TLD measurements in the developed phantom agreed with IC and MC results with less than 3% of an average difference. The developed phantom with TLD dosimeters should be useful for remote monitoring of IMRT.

Challenges in Credentialing Institutions and Participants in Advanced Technology Multi-institutional Clinical Trials

The Radiological Physics Center (RPC) has functioned continuously for 38 years to assure the National Cancer Institute and the cooperative groups that institutions participating in multi-institutional trials can be expected to deliver radiation treatments that are clinically comparable to those delivered by other institutions in the cooperative groups. To accomplish this, the RPC monitors the machine output, the dosimetry data used by the institutions, the calculation algorithms used for treatment planning, and the institutions' quality control procedures. The methods of monitoring include on-site dosimetry review by an RPC physicist and a variety of remote audit tools. The introduction of advanced technology clinical trials has prompted several study groups to require participating institutions and personnel to become credentialed, to ensure their familiarity and capability with techniques such as three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, stereotactic body radiotherapy, and brachytherapy. The RPC conducts a variety of credentialing activities, beginning with questionnaires to evaluate an institution's understanding of the protocol and their capabilities. Treatment-planning benchmarks are used to allow the institution to demonstrate their planning ability and to facilitate a review of the accuracy of treatment-planning systems under relevant conditions. The RPC also provides mailable anthropomorphic phantoms to verify tumor dose delivery for special treatment techniques. While conducting these reviews, the RPC has amassed a large amount of data describing the dosimetry at participating institutions. Representative data from the monitoring programs are discussed, and examples are presented of specific instances in which the RPC contributed to the discovery and resolution of dosimetry errors.

Quality Assurance Issues in Conducting Multi-Institutional Advanced Technology Clinical Trials

The National Cancer Institute-sponsored Advanced Technology Quality Assurance (QA) Consortium, which consisted of the Image-Guided Therapy QA Center, Radiation Therapy Oncology Group, Radiological Physics Center, Quality Assurance Review Center, and Resource Center for Emerging Technologies, has pioneered the development of an infrastructure and QA method for advanced technology clinical trials that requires volumetric digital data submission of a protocol patient's treatment plan and verification data. In particular, the Image-Guided Therapy QA Center has nearly 15 years experience in facilitating QA review for Radiation Therapy Oncology Group advanced technology clinical trials. This QA process includes (1) a data integrity review for completeness of protocol required elements, the format of data, and possible data corruption, and recalculation of dose-volume histograms; (2) a review of compliance with target volume and organ-at-risk contours by study chairs; and (3) a review of dose prescription and dose heterogeneity compliance by the Radiation Therapy Oncology Group Headquarters Dosimetry Group or the Radiological Physics Center dosimetrists (for brachytherapy protocols). This report reviews the lessons learned and the QA challenges presented by the use of advanced treatment modalities in clinical trials requiring volumetric digital data submission.

Siemens Multileaf Collimator Characterization and Quality Assurance Approaches for Intensity-Modulated Radiotherapy

Application of the multileaf collimator (MLC) has evolved from replacing blocks to create treatment fields to creating photon fluence modulation for intensity-modulated radiotherapy (IMRT). Multileaf collimator system performance requirements are far more stringent for such applications and will require increased performance for future applications, such as motion tracking. This article reviews Siemens MLC systems, including a technical description and dosimetric characteristics of 56-, 82-, and 160-leaf designs. Routine quality assurance of MLC for IMRT necessitates frequent and critical assessment of MLC leaf position calibration errors that can present in many different ways (e.g., accuracy, reproducibility, longevity, hysteresis, and collimator/gantry angle dependencies). Several techniques for measuring these errors are presented, along with qualitative and quantitative techniques for analyzing results. In particular, increased accuracy of leaf position measurement at variable gantry angles is enabled by spatial transformations to electronic portal imaging device position quantified by calibration protocols introduced with megavoltage cone beam. Measured values of X-ray transmission (intra-leaf, inter-leaf, and through abutting leaf pairs) and penumbra (leaf end, leaf tongue, leaf groove) are presented with an evaluation of their characterization by a treatment-planning system. The dosimetric impact of planning system model inadequacies is demonstrated for collimator scatter, dose profile values within 30 mm of the field edge, and the resultant effect demonstrated on clinical cases. Finally, a description of automated quality assurance delivery, analysis, and calibration protocols applicable for the specific vendor's system is provided.

Anniversary Paper: Fifty years of AAPM involvement in radiation dosimetry

This article reviews the involvement of the AAPM in various aspects of radiation dosimetry over its 50 year history, emphasizing the especially important role that external beam dosimetry played in the early formation of the organization. Topics covered include the AAPM's involvement with external beam and x-ray dosimetry protocols, brachytherapy dosimetry, primary standards laboratories, accredited dosimetry chains, and audits for machine calibrations through the Radiological Physics Center.

Dose Specification and Quality Assurance of Radiation Therapy Oncology Group Protocol 95-17; a Cooperative Group Study of Iridium-192 Breast Implants as Sole Therapy

The Radiation Therapy Oncology Group (RTOG) protocol 95-17 was a Phase I/II trial to evaluate multicatheter brachytherapy as the sole method of adjuvant breast radiotherapy for Stage I/II breast carcinoma after breast-conserving surgery. Low- or high-dose-rate sources were allowed. Dose prescription and treatment evaluation were based on recommendations in the International Commission on Radiation Units and Measurements (ICRU), Report 58 and included the parameters mean central dose (MCD), average peripheral dose, dose homogeneity index (DHI), and the dimensions of the low- and high-dose regions. Three levels of quality assurance were implemented: (1) credentialing of institutions was required before entering patients into the study; (2) rapid review of each treatment plan was conducted before treatment; and (3) retrospective review was performed by the Radiological Physics Center in conjunction with the study chairman and RTOG dosimetry staff. Credentialing focused on the accuracy of dose calculation algorithm and compliance with protocol guidelines. Rapid review was designed to identify and correct deviations from the protocol before treatment. The retrospective review involved recalculation of dosimetry parameters and review of dose distributions to evaluate the treatment. Specifying both central and peripheral doses resulted in uniform dose distributions, with a mean dose homogeneity index of 0.83 +/- 0.06. Vigorous quality assurance resulted in a high-quality study with few deviations; only 4 of 100 patients were judged as representing minor variations from protocol, and no patient was judged as representing major deviation. This study should be considered a model for quality assurance of future trials.

WE‐B‐M100F‐01: RPC Programs

Purpose: To describe the mission and activities of the Radiological Physics Center (RPC). Method and Materials: The RPC was founded in 1968 under an agreement between the AAPM and the Committee for Radiation Therapy Studies (CRTS). The agreement called for the AAPM to solicit applications to form a QA center that would be a resource in radiation dosimetry and physics for cooperative clinical trial groups and all radiotherapy facilities that deliver radiation treatments to patients entered onto cooperative group protocols. The RPC has functioned continuously for 38 years to support medical physicists and radiation therapy departments. Results: The RPC's mission has changed only slightly over the years. The primary responsibility is to assure NCI and the cooperative groups that the participating institutions have adequate quality assurance procedures and no major systematic dosimetry discrepancies, so that they can be expected to deliver radiation treatments that are clinically comparable to those delivered by other institutions in the cooperative groups. To accomplish this, the RPC monitors the basic machine output and brachytherapy source strengths, the dosimetry data utilized by the institutions, the calculation algorithms used for treatment planning, and the institutions' quality control procedures. The methods of monitoring include on‐site dosimetry review by an RPC physicist, and a variety of remote audit tools. During the on‐site evaluation, the institution's physicists and radiation oncologists are interviewed, physical measurements are made on the therapy machines, dosimetry and quality assurance data are reviewed, and patient dose calculations are evaluated. The remote audit tools include 1) mailed dosimeters (TLD) evaluated on a periodic basis to verify output calibration and simple questionnaires to document changes in personnel, equipment, and dosimetry practices, 2) comparison of dosimetry data with RPC “standard” data to verify the compatibility of dosimetry data, 3) evaluation of reference and actual patient calculations to verify the validity of treatment planning algorithms, and 4) review of the institution's written quality assurance procedures and records. Mailable anthropomorphic phantoms are also used to verify tumor dose delivery for special treatment techniques. Any discrepancies identified by the RPC are pursued to help the institution find the origin of the discrepancies and identify and implement methods to resolve them. Conclusion: While conducting these reviews, the RPC has amassed a large amount of data describing the dosimetry at participating institutions. Representative data from the monitoring programs will be discussed and examples will be presented of specific instances in which the RPC contributed to the discovery and resolution of dosimetry errors.The RPC is supported by PHS grants CA 10953 and CA 81647 awarded by NCI, DHHS, and by an educational grant from Varian Medical Systems.Educational Objectives:1. Become familiar with the activities of the Radiological Physics Center.2. Know how to contact the RPC for assistance or collaboration.3. Understand the role of the RPC in monitoring institutions that participate in clinical trials.4. Review common errors and misconceptions regarding dosimetry, credentialing requirements, and other issues.

TH-A-M100E-03: Requirements for Addressing Respiratory Motion in Cooperative Group Clinical Trials

In mid-2006, the National Cancer Institute (NCI) published updated guidelines for the use of intensity-modulated radiation therapy (IMRT) on clinical trials, specifically when the target volume included the thoracic region or other areas in which respiratory motion could have a significant effect. In addition to requiring heterogeneity corrections, the NCI now requires that the clinical protocol address the localization and immobilization of both the patient and the tumor. Imaging must be performed in a manner that provides a representation of the target volume without motion artifact. Procedures must be defined to document reproducible daily position of the patient and target. Some form of credentialing is required. The Radiological Physics Center (RPC) has been enlisted to participate in the credentialing process for institutions participating in certain cooperative group trials in which respiratory motion is an issue. To accomplish this, the RPC has constructed several phantoms that mimic the thoracic and abdominal region, and which can be placed on a moving platform to simulate respiratory motion. The combination of phantom and moving platform have been used to evaluate compensation techniques for respiratory motion at several institutions. The techniques employed and the results of these measurements will be described as well as those reported in the literature. Learning Objectives: 1. Review the structure supporting cooperative group clinical trials in the US. 2. Become familiar with the NCI guidelines for the use of IMRT in clinical trials. 3. Learn about the effects of respiratory motion during thoracic treatments. 4. Understand the information derived from the RPC's moving anthropomorphic phantoms. This research is supported by grants CA 10953 and 81647 awarded by NCI, DHHS.

MO‐D‐AUD‐01: A Comprehensive Study On the Heterogeneity Dose Calculation Accuracy in IMRT Using An Anthropomorphic Thorax Phantom

Purpose: To provide a comprehensive study on the accuracy of many commonly used Intensity Modulated Radiation Therapy (IMRT) treatment planning systems using the Radiological Physics Center's (RPC) anthropomorphic thorax phantom. Method and Materials: Treatment planning systems (TPSs) from Corvus, Eclipse, Pinnacle, and Tomotherapy were evaluated using the RPC anthropomorphic phantom. Treatment plans were designed using the same clinical constraints and prescriptions so that 96% of the planning target volume (PTV) was covered by the prescription dose. The phantom is equipped with TLD located in the tumor, heart, and spinal cord and radiochromic film located in three anatomical planes intersecting the tumor center and extending into the lung. IMRT QA was performed to adjust the calculated dose distributions in order to isolate the effects of heterogeneity. Comparisons were made between each TPS calculation and measurement. In two instances, re‐calculations of the original correction based pencil beam (PB) plans were performed using the superposition convolution (SC) method. Results: TPSs employing superposition convolution algorithms predicted dose within 3.6% of the target TLD, while TPSs using correction based pencil beam algorithms predicted dose within 5.0% of the target TLD. Both algorithm types showed variations (2% to 38% in the cord and heart) in predicting low dose to normal structures. The dose distributions within the PTV and penumbra lung regions showed good agreement when using an SC algorithm. However, TPSs using the PB type algorithm overestimated dose in the PTV and underestimated the extent of penumbra broadening corresponding to the surrounding lung. Conclusion: This work demonstrated that superposition convolution algorithms found in widely used IMRT treatment planning systems are able to calculate the dose accurately to the PTV and penumbra regions when low density heterogeneities are involved. Conflict of Interest: This work supported by PHS CA010953 and CA081647 awarded by NCI, DHHS.

MO‐D‐AUD‐04: A Comparison of Heterogeneity Correction Algorithms Within a Lung PTV

Purpose: To compare the measured dose distribution with the planned distribution over a PTV centrally located within the lung when heterogeneity corrections are taken into account. Method and Materials: The Radiological Physics Center's anthropomorphic thorax phantom includes a target (∼ 1 g/cm3) centrally located in the left lung (∼ 0.33 g/cm3). The phantom was sent to 25 institutions, each of which was instructed to design and deliver a stereotactic treatment plan. The plan was intended to deliver 20Gy (homogeneous calculation) to ⩾ 95% of the PTV and limit the lung dose at point 2 cm from the PTV edge to 11.7 Gy. The institutions were asked to recalculate the dose distribution with the heterogeneity correction using the monitor units determined from the homogeneous calculated plan. TLD and radiochromic films were used as dosimeters within the target region. Results: A total of 17 institutions met the phantom irradiation criteria: +/− 5% for DTLD/DInst, and +/−5mm DTA on all sides of the PTV, based on the heterogeneous calculated plan. For these irradiations, the delivered doses over the central 80% of the PTV were compared to the planned doses along 3 orthogonal profiles through the PTV. An average of 85% of the points in the profiles from the cases calculated with the superposition/convolution algorithm were within 5% of the calculation, while only 69% of the points from the plans using pencil beam and Clarkson were within the 5% of the plan. Conclusions: The superposition/convolution heterogeneity correction algorithm showed better agreement with the measured dose distribution across the PTV than the pencil beam and Clarkson algorithms because it more accurately accounted for the lack of lateral scatter.Work supported by PHS grant CA10953 and CA081647 from the NCI, DHHS.

Design, development, and implementation of the Radiological Physics Center's pelvis and thorax anthropomorphic quality assurance phantoms

The Radiological Physics Center (RPC) developed two heterogeneous anthropomorphic quality assurance phantoms for use in verifying the accuracy of radiation delivery: one for intensity-modulated radiation therapy (IMRT) to the pelvis and the other for stereotactic body radiation therapy (SBRT) to the thorax. The purpose of this study was to describe the design and development of these two phantoms and to demonstrate the reproducibility of measurements generated with them. The phantoms were built to simulate actual patient anatomy. They are lightweight and water-fillable, and they contain imageable targets and organs at risk of radiation exposure that are of similar densities to their human counterparts. Dosimetry inserts accommodate radiochromic film for relative dosimetry and thermoluminesent dosimetry capsules for absolute dosimetry. As a part of the commissioning process, each phantom was imaged, treatment plans were developed, and radiation was delivered at least three times. Under these controlled irradiation conditions, the reproducibility of dose delivery to the target TLD in the pelvis and thorax phantoms was 3% and 0.5%, respectively. The reproducibility of radiation-field localization was less than 2.5 mm for both phantoms. Using these anthropomorphic phantoms, pelvic IMRT and thoracic SBRT radiation treatments can be verified with a high level of precision. These phantoms can be used to effectively credential institutions for participation in specific NCI-sponsored clinical trials.

3D dosimetry by optical-CT scanning

The need for an accurate, practical, low-cost 3D dosimetry system is becoming ever more critical as modern dose delivery techniques increase in complexity and sophistication. A recent report from the Radiological Physics Center (RPC) (1), revealed that 38% of institutions failed the head-and-neck IMRT phantom credentialing test at the first attempt. This was despite generous passing criteria (within 7% dose-difference or 4mm distance-to-agreement) evaluated at a half-dozen points and a single axial plane. The question that arises from this disturbing finding is – what percentage of institutions would have failed if a comprehensive 3D measurement had been feasible, rather than measurements restricted to the central film-plane and TLD points? This question can only be adequately answered by a comprehensive 3D-dosimetry system, which presents a compelling argument for its development as a clinically viable low cost dosimetry solution. Optical-CT dosimetry is perhaps the closest system to providing such a comprehensive solution. In this article, we review the origins and recent developments of optical-CT dosimetry systems. The principle focus is on first generation systems known to have highest accuracy but longer scan times.

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The Radiological Physics Center (RPC) has performed credentialing of institutions to participate in a number of protocol studies. The purpose of credentialing is to verify that the radiation oncologist and other personnel involved are familiar with the protocol prior to enrolling patients with the goal of limiting the number of deviations. Credentialing has been performed for high and low dose rate brachytherapy studies, stereotactic studies and IMRT studies. Credentialing has also been done for several different study groups and for a variety of disease sites including eye, brain, breast, and cervix.

Radiation therapy facilities in the United States

About half of all cancer patients in the United States receive radiation therapy as a part of their cancer treatment. Little is known, however, about the facilities that currently deliver external beam radiation. Our goal was to construct a comprehensive database of all radiation therapy facilities in the United States that can be used for future health services research in radiation oncology. From each state's health department we obtained a list of all facilities that have a linear accelerator or provide radiation therapy. We merged these state lists with information from the American Hospital Association (AHA), as well as 2 organizations that audit the accuracy of radiation machines: the Radiologic Physics Center (RPC) and the Radiation Dosimetry Services (RDS). The comprehensive database included all unique facilities listed in 1 or more of the 4 sources. We identified 2,246 radiation therapy facilities operating in the United States as of 2004-2005. Of these, 448 (20%) facilities were identified through state health department records alone and were not listed in any other data source. Determining the location of the 2,246 radiation facilities in the United States is a first step in providing important information to radiation oncologists and policymakers concerned with access to radiation therapy services, the distribution of health care resources, and the quality of cancer care.

Independent Evaluations of IMRT through the Use of an Anthropomorphic Phantom

Intensity-modulated radiation therapy (IMRT) has gained rapid and wide-spread acceptance in the radiation oncology community for its ability to create dose distributions that conform to the convoluted shapes of many tumors. It is a complicated treatment technique, for which quality assurance procedures are correspondingly complicated and labor intensive. Several of the cooperative cancer study groups that conduct clinical trials under the auspices of the National Cancer Institute have required participating institutions to seek credentialing before enrolling patients in trials involving IMRT. The Radiological Physics Center has conducted such credentialing programs through the use of anthropomorphic phantoms that evaluate the planning and delivery of IMRT. The experience obtained through the irradiation of the phantoms by a number of institutions demonstrates that institutions vary significantly in their ability to deliver doses and dose distributions that agree with their own treatment plans.

A descriptive analysis of postimplant dosimetric parameters from Radiation Therapy Oncology Group P0019

Background To date, there are few descriptive analyses of postimplant dosimetry from multi-institutional clinical trials. The purpose of this report is to describe the postimplant dosimetry achieved in Radiation Therapy Oncology Group (RTOG) 0019. Methods and materials Patients were treated with external beam radiation therapy (45 Gy/25 fractions) followed by a prostate implant (I-125, prescription dose 108 Gy). Postimplant dosimetric assessment was accomplished by obtaining a CT scan of the prostate 1 month after the date of the implant procedure. Prostate volume was outlined by the first author. Dose–volume histograms were calculated by the Radiologic Physics Center. Four dosimetric quantifiers (DQs) were examined: D 90 is the dose (reported as percentage of the prescription dose) received by 90% of the prostate; V 100, V 150, V 200 is the percentage of the prostate volume receiving 100%, 150%, and 200% of the prescription dose, respectively. For the purposes of analysis, institutions were divided into three groups according to accrual (<5, 6–9, 10–12). Results One hundred thirty-eight patients from 27 institutions were registered in the study. Nineteen patients were excluded from this analysis; 14 who had no data and 5 who were ineligible, leaving 119 for analysis. The mean, median, and range of the four DQs are as follows: D 90 105.6%, 106.0%, 57.6–174.8%; V 100 89.8%, 92.6%, 11.2–100%; V 150 58.4%, 59.6%, 0.9–93.7%; and V 200 27.9%, 25.1%, 0.3–85.2%. Statistically significant differences according to institutional accrual were observed for D 90 ( p = 0.0283) and V 200 ( p = 0.0075), but not for V 100 ( p = 0.1534) and V 150 ( p = 0.0509). Conclusions The DQ observed in this multi-institutional prospective study are roughly comparable to series from single institutions with considerable brachytherapy experience. Differences in DQs were observed according to institutional accrual. These data could be used to determine a community standard with respect to postimplant dosimetry.