SUMMARY: Breast cancer is the most common cancer among women in the US and about 1 in 8 women (12%) will develop invasive breast cancer during their lifetime. Approximately 266,120 new cases of invasive breast cancer will be diagnosed in 2018 and about 40,920 women will die of the disease. When it comes to adjuvant radiation therapy in breast cancer, the standard of care has been Whole Breast Irradiation (WBI), administered in Conventional Fractions (CF-WBI) of 180 to 200 cGy daily, to approximately 4500 to 5000 cGy, with or without a tumor bed boost. More recently, with clinical trials supporting the safety and effectiveness of HypoFractionated Whole Breast Irradiation (HF-WBI), the American Society for Radiation Oncology (ASTRO) task force, has issued a new clinical guideline for the use of whole-breast radiation therapy for breast cancer, which replaces the existing ASTRO Whole Breast Irradiation guideline published in 2011. With HypoFractionated Whole Breast Irradiation, patients receive larger doses of radiation over a shorter period of time, typically completing treatment in 3-4 weeks, compared with 5-7 weeks for CF-WBI.
The guideline recommendations were based on a systematic literature review, between January 2009 and May 2016, and created using ASTRO-approved tools, for grading evidence quality and recommendation strength. The ASTRO convened a task force to address 5 key questions focused on dose-fractionation for WBI, indications and dose fractionation for tumor bed boost, and treatment planning techniques for WBI and tumor bed boost. The recommendations are summarized below.
Whole-Breast Irradiation (without irradiation of regional lymph nodes) – Delivery and Dosing
1) Treatment decisions, including radiation techniques (Hypofractionated versus Conventional Fractions) should be a shared decision between patient and physician and should be individualized to each patient.
2) For women with invasive breast cancer receiving WBI with or without inclusion of the low axilla, the preferred dose-fractionation scheme is HF-WBI to a dose of 4000 cGy in 15 fractions or 4250 cGy in 16 fractions.
3) The decision to offer HF-WBI should be independent of age, tumor grade, hormone receptor status, HER2 receptor status, surgical margin status, breast size, breast cancer laterality, chemotherapy received prior to radiation and trastuzumab or endocrine therapy received prior to or during radiation.
4) HF-WBI may be used as an alternative to CF-WBI in patients with DCIS.
5) CF-WBI may be preferred over HFWBI when treating primary breast cancers with rare histologies that are most commonly treated with CF when arising in other parts of the body.
6) In patients with breast augmentation, either HF-WBI or CF-WBI may be used.
Tumor Bed Boost
1) A tumor bed boost is recommended for patients with invasive breast cancer 50 years or younger with any grade tumor, age 51-70 years with high grade tumor, or a positive margin. Omitting a tumor bed boost is suggested in patients with invasive breast cancer who are older than 70 years with hormone receptor-positive tumors of low or intermediate grade, resected with widely negative (2 or more mm) margins.
2) A tumor bed boost may be used for patients with DCIS, 50 years and younger, high grade tumors, or close (less than 2 mm) or positive margins following resection. A tumor bed boost may be omitted for patients with DCIS who are older than 50 years, screen detected tumor, total size 2.5 cm or less, low to intermediate nuclear grade, and have widely negative surgical margins (3 mm or more).
3) The decision to use a tumor bed boost should be based on the clinical indications for a boost and should be independent of whether the patient received Conventional or Hypofractionated WBI.
Preferred Techniques for WBI Treatment Planning
1) Three-dimensional conformal radiotherapy planning with a field-in-field technique is recommended to achieve radiation dose homogeneity and full coverage of the tumor bed.
2) Techniques that incorporate deep inspiration breath hold, prone positioning, and/or heart blocks are recommended to minimize heart dose. Treatment techniques should also minimize dose to the contralateral breast, lung, and other normal tissues.
3) Treatment plans should be individualized after consideration of many factors, including tumor characteristics, patient anatomy and comorbidities.
Radiation therapy for the whole breast: Executive summary of an American Society for Radiation Oncology (ASTRO) evidence-based guideline. Smith BD, Bellon JR, Blitzblau R, et al. DOI: https://doi.org/10.1016/j.prro.2018.01.012