Radiological Physics Center

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Mission Statement

The mission of the Radiological Physics Center (RPC) is to assure NCI and the Cooperative Groups that institutions participating in clinical trials deliver prescribed radiation doses that are clinically comparable and consistent.

We do this by assessing the institution's radiotherapy programs, helping the institutions implement remedial actions, assisting the study groups in developing protocols and QA procedures, and informing the community of our finding.


The Radiological Physics Center 1 (RPC) has been funded by the National Cancer Institute (NCI) continuously since 1968 to provide quality auditing of dosimetry practices at institutions participating in NCI cooperative clinical trials. The RPC was formed at the urging of radiation physicists through the American Association of Physicists in Medicine (AAPM), and radiation oncologists through the Committee on Radiation Therapy Studies. The AAPM Radiation Therapy Committee has been, and continues to be, the scientific advisory body to the RPC.

Housed at M. D. Anderson Cancer Center since its inception, the RPC was first led by Robert J. Shalek, Ph.D., who served as director from 1968 until 1985. William F. Hanson, Ph.D., became director in 1985 and served until August 2001. Geoffrey S. Ibbott, Ph.D., is the present director.

The primary responsibility of the RPC is to assure the NCI and the cooperative clinical trial groups that all participating institutions have the equipment, personnel, and procedures necessary to administer radiation doses that are clinically comparable to those of other participating institutions. The monitoring tools used include on-site dosimetry reviews; remote auditing tools, including thermoluminescent dosimeter (TLD) and anthropomorphic phantoms; and review of benchmarks and actual protocol patient treatments.

The historical development of cooperative clinical trial groups, the creation of the RPC, and the development of group specific quality assurance offices, have all been interconnected. The following is an overview of the main events in this chronicle.

A brief history of cooperative group clinical trial quality assurance

In 1969 there were three cooperative groups, each with one protocol involving radiation therapy. Thirty-five megavoltage therapy facilities were participating in studies, and the RPC was the only group identified by NCI to monitor quality assurance.

In the early 1970s there was a major expansion in the number of cooperative groups and participating institutions. In 1974 there were 20 multidisciplinary cooperative groups with more than 200 megavoltage therapy institutions participating. In that same year the NCI Division of Cancer Control and Rehabilitation established six Centers of Radiological Physics (CRPs) to monitor the extension of modern diagnosis and radiotherapy to community hospitals. Although the originally defined functions and responsibilities were distinct from the RPC, very quickly community hospitals became involved in cooperative trials and the responsibilities of the CRPs and the RPC began to overlap. In 1977 the Quality Assurance Review Center (QARC) was established to assure quality of the radiotherapy treatment of individual patients entered onto the Cancer and Leukemia Group B (CALGB) studies. Other such quality assurance offices (QAO) were also funded, and by 1983 there were nine QAOs serving various cooperative groups.

Consolidation began at this time. In 1986 the NCI terminated the CRP contracts and subsequently supplemented the RPC to cover their institutions. In addition, only six QAO’s were left. There were now 600 radiotherapy facilities participating in clinical trials. Over the next ten years, cooperative group activity changed so that by 1996 there were only 9 cooperative groups and 4 QAO’s remaining, but more than 1050 participating radiotherapy facilities. In addition, the Proton Working Group and the 3-D QA Center were established to monitor high technology studies. In 2001, there were 8 cooperative groups, 3 QAO’s, and nearly 1300 radiotherapy facilities monitored by the RPC. The Image Guided Radiotherapy QA Center in St. Louis and the Resource Center for Emerging Technologies (RCET) in Gainesville were funded to establish databases of image guided radiotherapy treatments for cooperative groups and make that data available for evaluation.

From its beginning, the RPC quality assurance tools have included on-site dosimetry review visits to institutions, protocol patients’ chart reviews, and remote dose monitoring by TLD. In the early clinical protocols, only megavoltage photon therapy was allowed, so quality auditing by the RPC was limited to this modality. By 1977, electron beam therapy and brachytherapy had been introduced into cooperative studies, and, consequently, the RPC began to audit these modalities routinely. Today, with advances in therapy equipment including multileaf collimators and dynamic wedges, and advances in treatment techniques, including high dose rate brachytherapy, three-dimensional conformal radiotherapy, and intensity-modulated radiation therapy, the RPC has had to develop new auditing techniques. These include expanded measurements during on-site visits, mailable anthropomorphic phantoms, and increased computerization of all RPC activities.

When clinical trials involve advanced technologies, study groups often require institutions to pass an evaluation to demonstrate their ability to deliver the new technology safely and accurately. The RPC participates in developing and administering such evaluations, to credential institutions to participate in trials involving the use of three-dimensional conformal radiotherapy (3D CRT), high- and low-dose rate brachytherapy, intensity-modulated radiation therapy (IMRT), stereotactic radiosurgery (SRS), and other new technologies. Credentialing is conducted through the completion of questionnaires, performance of calculation benchmarks, and irradiation of anthropomorphic phantoms 2. The RPC's phantom evaluation program has proven to be a valuable and thorough test of an institution's ability to perform imaging procedures, develop a treatment plan, and deliver the plan to a phantom or patient using IMRT or SRS techniques.

When the RPC first started, there were no nationally or internationally promulgated calibration protocols. The first such protocols were SCRAD 3 (1971) for photon beams and ICRU #21 4(1972) for electron beams. In Apri1 1984, the RPC adopted the AAPM Task Group 21 5 (1983) calibration protocol for photon and electron beams. In 1990, nearly 95% of institutions monitored by the RPC were using the AAPM Task Group 21 (TG-21), or equivalent, protocol. On January 1, 2000, the RPC implemented the new AAPM dosimetry calibration protocol, popularly known as TG-51 6 protocol (1999). RPC TLD results suggest that by April 2006, approximately 79% of RPC monitored facilities have converted to TG-51.

There has been a marked improvement in radiation dosimetry over the past three decades, and the RPC has been monitoring it through its auditing tools. Between 1970 and 1980, the compliance rate (±3%) for beam calibration increased from approximately 70% to 90%. Improvement since then has been gradual, with compliance now near 98%, for both photons and electron beam calibrations. With the complexity of therapy increasing, discrepancies in other components of the treatment are more prevalent. Over the past four years, at approximately 45% of the institutions reviewed by an on-site review, the RPC found at least one clinical situation where patients could be at risk to receive a dose more than 5% different from that intended.

As of April 2006 the RPC staff includes eight physicists, five dosimetrists, six TLD technologists, three computer system analysts, six administrative support staff, and three graduate students. The RPC currently monitors nearly 1,450 radiation therapy facilities. Discrepancies detected by the RPC are investigated to help the institution resolve them. Thus, the RPC’s overall quality assurance program has an impact not only on the treatment received by patients enrolled in clinical trials, but also on the quality of treatment administered to all patients treated at the institution.


1. Hanson WF, Shalek RJ, Kennedy P. Dosimetry quality assurance in the United States from the experience of the Radiological Physics Center. In: Starkschall G, Horton J, editors. Proceedings of the American College of Medical Physics Symposium. Madison, WI: Medical Physics Publishing, 1991:255-279.

2. Design and implementation of an anthropomorphic quality assurance phantom for intensity-modulated radiation therapy for the Radiation Therapy Oncology Group. Molineu A, Followill DS, Balter PA, Hanson WF, Gillin MT, Huq M S, Eisbruch A, Ibbott GS International Journal of Radiation Oncology*Biology*Physics 01 October 2005 (Vol. 63, Issue 2, Pages 577-583)

3. Scientific Committee on Radiation Dosimetry (SCRAD) of the American Association of Physicists in Medicine. "Protocol for the Dosimetry of X-rays and Gamma Ray Beams with Maximum Energies Between 0.6 and 50 MeV." Of Physics in Medicine and Biology 16:379-396, 1971.

4. ICRU Report #21 Radiation Dosimetry: Electron with Initial Energies Between 1 and 50 MeV. International Commission of Radiation Units and Measurements, Washington, DC, 1972.

5. Task Group 21, Radiation Therapy Committee, American Association of Physicists in Medicine. "A Protocol for the Determination of Absorbed Dose from High-energy Photon and Electron Beams", Med. Phys. 10 :741-771 (1983).

6. Task Group 51, Radiation Therapy Committee, American Association of Physicists in Medicine: “Protocol for clinical reference dosimetry of high-energy photon and electron beams”, Med. Phys. 26 : 1847-1870 (1999).

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