Purpose: The Kaiser Permanente (KP) Breast Cancer Survivors Study is a retrospective cohort study for evaluating late health effects among breast cancer patients. This paper describes the characteristics of the radiotherapy received by a subset of patients in the cohort.
Methods: This analysis included 6274 women diagnosed with first primary unilateral invasive breast cancer at KP Colorado (1994-2014) or KP Northwest (1990-2008). Eligible subjects were women treated with surgery for breast cancer and were alive and second cancer free one year after diagnosis. Scanned copies of paper radiotherapy summaries were collected for 85% of patients who received radiotherapy, from which relevant treatment details were abstracted including fields, prescribed dose, fractionation, and beam energy. Trends in these treatment variables were evaluated as a function of year of breast cancer diagnosis, age at diagnosis, and cancer stage with special attention to the prevalence of hypofractionated treatments (15 or 16 fractions) which are increasingly becoming the standard of care.
Results: The most common prescribed dose to the breast was ~50 Gy usually delivered in 25 or 28 fractions. Only 12% of patients received hypofractionated treatments and these were observed mostly between 2010-2014, but as early as 2002 and the typical dose was 42.56 Gy. Hypofractionated treatments were observed mostly for stage 1 and some stage 2 breast cancers, but not stage 3. The energy of the photon treatment beams has changed over the years, with 4 MV being predominately used between 1990-1994, 6 MV between 1995-2009, and 6 MV in combination with 16 MV or 23 MV between 2010-2014.
Conclusion: Radiotherapy treatments continue to evolve. The KP cohort has relatively few patients who received hypofractionated therapy, but will nonetheless provide valuable information on risk of treatments using conventional fractionation which are still quite common around the world.
Not Applicable / None Entered.