Background: The Patterns of Care Study (PCS), started in the 1970's, is a well-known study used for clinical quality assurance (QA) in radiation oncology in the United States. PCS has been introduced in Japan since 1996. Methods: Three national PCS surveys have been performed by means of external audit to evaluate patterns of care for the patients with carcinoma of any of esophagus and cervix treated with radiation between 1992 and 1994, for those with carcinoma of any of esophagus, cervix, breast, lung and prostate between 1995 and 1997, and for those with any of the five disease sites between 1999 and 2001. In the first PCS, feasibility of the study was confirmed. In the second PCS, two-stage cluster sampling of institutions and patients was performed and national averages for the survey items were calculated as QA measures. In the third PCS, additional imaging data were collected. The Japan/USA PCS workshops were held at San Francisco in 2001 and at Tokyo in 2003. Results: Significant variations in process and structure were observed according to institutional stratification. In academic institutions, external beam energy ≥6 MV for deep-seated tumors of esophagus, lung, prostate and cervix, and brachytherapy for those of cervix and esophagus were used more frequently. There was an average of less than one full-time equivalent radiation oncologist in most non-academic institutions. These variations influenced the outcomes. There were also significant differences between USA and Japan in various aspects, e.g. a difference in radiation dose of 20% for uterine cervix cancer patients. It is higher in the USA. The number of new cancer patients requiring radiation is increasing steeply (120 000 in 2000 and 170 000 in 2005). Based on PCS data, structural guidelines were published and distributed throughout Japan. Conclusion: PCS is useful for establishing the clinical QA for radiation oncology as well as other specialties through detailed monitoring and evaluation of their structures, processes and outcomes.
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