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The American Society for Radiation Oncology (ASTRO) updated their guidelines on partial breast irradiation (PBI) for patients with early-stage invasive breast cancer or ductal carcinoma in situ (DCIS).

These new take into account results from multiple randomized controlled trials that have been published since ASTRO last issued recommendations for PBI in 2017. The trials included more than 10,000 women with about 10 years of follow-up, and, according to ASTRO guideline task force members, demonstrated "oncologic equivalence" between PBI and whole-breast irradiation (WBI) for the treatment of early-stage breast cancer and DCIS.

"For patients with early-stage breast cancer, many are eligible for consideration of partial breast irradiation," Task Force Chair Janice Lyons, MD, of the University Hospitals Seidman Cancer Center in Cleveland, told MedPage Today. "This is a conversation radiation oncologists should have with their patients and they can use the guidelines as a framework on how to have that discussion and how to deliver partial breast irradiation safely."

According to Lyons, one of the key differences in the updated guidelines is that they are "more liberal" regarding the age at which PBI may be appropriate.

The 2017 guidelines recommended that women ages 50 and older be considered "suitable" for PBI outside a clinical trial, while women ages 40 to 49 were included in the "cautionary" group, and those ages 40 and under be included in the "unsuitable" group.

The updated guidelines state that, for patients with early-stage, node-negative invasive breast cancer, PBI is strongly recommended as an alternative to WBI if the patient has favorable clinical features and tumor characteristics, including grade 1 to 2 disease, estrogen receptor (ER)-positive status, age 40 or older, and small tumor size.

PBI is conditionally recommended if the patient has an indication of higher recurrence risk, including grade 3 disease, ER-negative histology, or larger tumor size. It is not recommended for patients with positive lymph nodes, positive surgical margins, or germline BRCA1/2 mutations, or those who are younger than 40, and is conditionally not recommended for patients with less favorable risk features (e.g., lymphovascular invasion or lobular histology), due to the lack of robust data on these patient subsets.

For patients with DCIS, the recommendations align with those for early-stage breast cancer. PBI is strongly recommended as an alternative to WBI for patients with favorable clinical and tumor features outlined in the guideline, conditionally recommended for those with higher-grade disease or larger tumors, and not recommended for patients with positive surgical margins, BRCA mutations, or age less than 40.

"At this point so many randomized controlled trials have been conducted that we were able to really drill down into the subgroups of patients to better define those represented sufficiently enough to strongly recommend partial breast radiation rather than whole breast radiation," said Simona F. Shaitelman, MD, of the University of Texas MD Anderson Cancer Center in Houston, who served as the task force's vice chair.

Shaitelman pointed out that the updated guidelines also dealt with issues related to the delivery of PBI.

Recommended techniques for PBI include 3-D conformal radiation therapy, intensity-modulated radiation therapy, and multi-catheter interstitial brachytherapy, based on studies showing similar long-term rates of ipsilateral breast recurrence compared with WBI.

Single-entry catheter brachytherapy is conditionally recommended, while intraoperative radiation therapy (IORT) techniques, including electron IORT and photon (kV) IORT without WBI, are not recommended unless part of a clinical trial or multi-institutional registry.

The guideline also outlines the optimal dose-fractionation regimens, target volume delineation, and treatment planning parameters for different PBI techniques.

A daily or every-other-day course of PBI is recommended over twice-daily regimens, and the guidelines also pay particular attention to clinical and cosmetic side effects of PBI.

"I think the guidelines highlight how in certain scenarios, partial breast irradiation is actually more favorable than whole-breast irradiation," said Shaitelman. "And that's an important point to highlight to patients in order to improve their overall quality of life if they require radiation as part of their oncologic care."

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