Postmastectomy radiotherapy just got a major update. A new guideline released by the American Society for Radiation Oncology, American Society of Clinical Oncology, and Society of Surgical Oncology is far more comprehensive than the groups’ last offering in 2016.

With advances in diagnostic imaging, radiotherapy, systemic treatments, and axillary surgery de-escalation, it was time to revisit the guideline, said authors led by Rachel Jimenez, MD, a breast radiation oncologist at Massachusetts General Hospital, Boston.

“The goal is to provide more specificity around treatment recommendations and treatment planning with modern treatment techniques,” Jimenez told Medscape Medical News.

There’s nothing too surprising for radiation oncologists who have been following the field, but the push toward 3-dimensional conformal planning — rather than older 2D approaches — along with specific dose constraints for the heart, lungs, and other critical structures “is far more proscriptive than has been available in the literature and gives a lot of guidance on treatment planning,” Jimenez said.

A call for moderately hypofractionated regimens in most settings is also “likely to have a large impact on clinical practice,” senior author Kathleen Horst, MD, a radiation oncologist at Stanford University, California, said in a video explaining the new guideline.

The recommendations are based on a multidisciplinary review of randomized trials, meta-analyses, and large observational cohorts from 2005-2024 that involved tens of thousands of women. They aim to reduce the risk of breast cancer recurrence while maximizing postmastectomy radiotherapy safety. Focused updates are planned as new study results come in. 

Although the authors offered the following general recommendations, each one comes with nuances and caveats depending on the specifics of each patient.

Postmastectomy radiotherapy after upfront mastectomy

• Recommended for patients with positive lymph nodes or large pT4 tumors
• Not recommended for node-negative pT1-2 tumors
• Omission is reasonable in patients with low nodal burdens (pN1mic or pN1a disease) who undergo axillary dissection and have favorable clinicopathologic features 

In the context of neoadjuvant systemic therapy

• Recommended for patients presenting with advanced disease (cT4 or cN2-3) regardless of pathologic response, and those who have positive surgical margins or residual nodal disease after neoadjuvant systemic therapy
• Not recommended for patients with smaller tumors (cT1-2N0) that are node-negative after neoadjuvant systemic therapy
• Individualize decisions for patients with smaller tumors and low nodal burden (cT1-3N1 or cT3N0) who are node-negative at surgery; factors such as young age, lymphovascular invasion, and residual breast disease favor postmastectomy radiotherapy 

Radiotherapy delivery

• Use moderately hypofractionated regimens for most patients; oncologic outcomes with 3-week courses are similar those of standard 5-week courses and toxicity is lower
• Consider internal mammary node irradiation based on tumor location (medial/central), tumor size, and extent of nodal involvement
• Use 3D planning with CT-based contouring to define targets and organs-at-risk; dose guidance and limitations are provided
• Use intensity-modulated radiotherapy when conventional techniques offer inadequate coverage or risk healthy tissue
• Use deep inspiration breath-holds with real-time image guidance to reduce heart and lung exposure
• Limit bolus use to patients with skin involvement, positive superficial margins, and/or lymphovascular invasion