ASTRO Guidelines Support Accelerated Whole Breast Radiation for Most Patients

Benjamin Smith, MD

A new American Society for Radiation Oncology (ASTRO) guideline calls for hypofractionated whole breast irradiation (HF-WBI) for patients with breast cancer regardless of age, tumor stage, and previous chemotherapy treatment.

The update from a 2011 guideline also recommends that patients be encouraged to play a larger role in the choice of HF-WBI, observing that HF-WBI has not been widely adopted despite delivering results that are comparable to and more convenient than longer courses of radiotherapy.

Whereas the previous guideline restricted HF-WBI to women aged ≥50 years with T1-2 N0 disease, the new guideline recommends offering HF-WBI to patients regardless of tumor grade, hormone receptor (HR) status, and HER2 status. Previously, women who had received chemotherapy were not candidates for WBI.

“The evidence base has matured since our last guideline, so this new guideline is more expansive in the types of patient for whom it endorses the use of hypofractionated whole breast radiation,” Benjamin Smith, MD, co-chair of the guideline task force and an associate professor of radiation oncology at The University of Texas MD Anderson Cancer Center in Houston, told OncologyLive®.

“Rather than just saying that the evidence base is more or less equivalent, which is what we said in the last guideline for certain patients, now we’re saying these shorter courses of whole breast radiation are preferred compared to the more standard or conventional longer courses of radiation,” he added. Smith said that this new guideline is broader, more comprehensive, and, he hopes, more helpful to clinicians.

Previously, the guideline recommended accelerated treatment for only certain patients, including older patients and those with less advanced disease. Recent long-term results from several large trials have added to the body of evidence that HF-WBI can yield outcomes that are similar to those of conventional fractionation (CF) WBI, and the task force now strongly supports the use of WBI for a broader patient population.

Physicians can also offer HF-WBI as an alternative to CF-WBI for women with ductal carcinoma in situ (DCIS). Women with breast augmentation or collagen vascular disease can chose either treatment in consultation with their physicians.

HF-WBI is administered over 3 to 4 weeks rather than the 5 to 7 weeks required for conventional radiation treatment. The new guidelines strongly recommend a dose of 40 Gy of HF-WBI administered in 15 fractions or 42.5 Gy in 16 fractions for women with invasive breast cancer with or without inclusion of the low axilla. The new guidelines also say the volume of breast tissue receiving >105% of WBI should be minimized regardless of dose fractionation. The previous guidelines established dose homogeneity at ± 7% in the central axis.

“Hypofractionated radiation therapy offers patients a more convenient and lower-cost option for their treatment” without increasing the likelihood that their cancer will return or their risk of adverse effects, Reshma Jagsi, MD, DPhil, co-chair of the task force and a professor of radiation oncology at the University of Michigan in Ann Arbor, said in a statement. “A shorter course of radiation equates to more time with family, less time away from work, and lower treatment costs. We hope that this guideline encourages providers to counsel their patients on options including hypofractionation.”

The authors noted that patients should feel empowered to make treatment decisions in collaboration with oncologists. “[We] are very sensitive to the fact that the best medical decisions are made in the context of a shared decision between the physician and the patient,” Smith said. “We wanted to encourage that and always frame our recommendations within that larger narrative.”

To update these recommendations, a 15-member ASTRO work group reviewed study results published from January 2009 to May 2016. Overall, the work group screened 528 abstracts and reviewed data from 100 articles.

The authors stressed that treatment should be individualized and take factors such as tumor characteristics, patient anatomy, and comorbidities into account. That said, Smith hopes that this new guideline will spur further adoption of these shorter courses of radiation that require fewer trips for therapy.

“There’s been increasing use of hypofractionated whole breast radiation—the evidence base has really been growing since 2004,” he said. “But even among patients who are declared eligible for hypofractionated whole breast radiation based on the prior ASTRO guideline, only about a third of them were receiving this shorter course of radiation.”

Although ASTRO favors a short course of radiation for most patients, Smith said there are times when a conventional course might be appropriate. The evidence supporting HF-WBI is weaker in some patient groups, such as women with DCIS who weren’t typically included in clinical trials comparing conventional radiation with HF-WBI.

In addition, the guidelines strongly recommend a tumor bed boost for patients with a positive margin, women aged ≤50 years with any grade of invasive breast cancer, and women aged 51 to 70 years with high-grade disease.

The guidelines offer a moderate recommendation to avoid a tumor bed boost in women aged >70 years with low- or intermediate-grade HR-positive tumors resected with widely negative (≥2 mm) margins.

Women with DCIS can receive a tumor bed boost if they are aged ≤50 years, have a high-grade tumor, or have close (<2 mm) or positive margins. Women aged >50 years can forgo a boost if their tumor is screen detected, ≤2.5 cm in total size, low-to-intermediate nuclear grade, and surgical margins are widely negative (≥3 mm).

A patient with DCIS who does not meet any of these criteria should decide whether to have a tumor bed boost in consultation with her physician. The guidelines say that the decisions regarding tumor bed boost should be made irrespective of the whole breast fractionation scheme.

For patients who do opt for tumor bed boost, the guidelines recommend administering the boost sequentially following whole breast treatment. Furthermore, physicians should take care to limit the volume of ipsilateral breast included in the boost field and minimize radiation exposure to healthy tissues, including the heart, the lungs, and the opposite breast.

The guidelines recommend deep inspiration breath hold, target and organ-at-risk contouring, and optimal patient positioning to reduce the radiation dose affecting nearby organs and normal tissue.

Smith said more research is needed to determine the ideal course of treatment for patients who require radiation to the breast and regional lymph nodes. Oncologists are still using conventional schedules that last about 6 weeks, and investigators will need to determine when and whether administering shorter courses of radiation in this population is appropriate.

He added that ASTRO currently has guidelines for both whole and partial breast radiation. Although the guideline for partial breast radiation lays out a framework for when that treatment approach is acceptable, it doesn’t take a position on when to use one or the other.

“There’s now starting to be a consolidating evidence base that looks at a comparison between partial breast radiation and whole breast radiation and starts to draw some conclusions about the trade-offs between the two,” he said. “That’s certainly a topic that merits additional study and reflection.”

Smith BD, Bellon JR, Blitzblau R, et al. Radiation therapy for the whole breast: executive summary of an American Society for Radiation Oncology (ASTRO) evidence-based guideline. Pract Radiat Oncol. 2018;8(3):145- 152. doi: 10.1016/j.prro.2018.01.012.