As the leading organization representing radiation oncologists, ASTRO takes seriously any public mischaracterization of radiation therapy. We are deeply disturbed by a recent NBC News story on intraoperative radiation therapy for breast cancer that presented inaccurate and misleading information, because such reporting risks confusing patients and undermining trust in evidence-based medicine. In response, ASTRO’s Breast Cancer Resource Panel offers the following clarification of what current data show:

The ASTRO guideline development process is rigorous, involving standardized methodology, independent data review, multidisciplinary input and thorough peer review.

The guideline panel for “Partial Breast Irradiation for Patients with Early-Stage Invasive Breast Cancer or Ductal Carcinoma In Situ” was comprised of a multidisciplinary team of academic and community-based radiation, surgical, and medical oncologists; a medical physicist; and a patient representative. The guideline was developed in collaboration with the Society of Surgical Oncology and American Society of Clinical Oncology and is endorsed by Canadian Association of Radiation Oncology, European Society for Radiotherapy and Oncology, Royal Australian and New Zealand College of Radiologists, and Society of Surgical Oncology

ASTRO guidelines are published based on robust data evaluating clinical data and patient outcomes. At no point are financial considerations factored in, and there is a strict firewall between the data analysis and any financial implications for the physician practice. As data evolves and we have more evidence, ASTRO guidelines also evolve, and many now recommend shorter courses of radiation therapy for patients, including those with breast cancer as in the recent ASTRO/ASCO/SSO guideline on post-mastectomy radiation therapy. The highest-value, most cost-effective treatment for people with breast cancer is a radiation therapy course that balances optimal control of the cancer with minimal side effects and factors in patient cost and convenience. As of now, IORT has not been proven to have the value of other methods of partial breast irradiation.

The mission of the ASTRO Breast Resource Panel is to ensure that patients receive the most effective and evidence-based care tailored to their individual needs. Accelerated partial breast irradiation (APBI) is a valuable treatment option for many patients that offers a shorter course of radiation while maintaining oncologic efficacy and safety. APBI can be delivered through several modalities, including external beam radiation therapy (EBRT), brachytherapy and intraoperative radiation therapy (IORT). The key decision point for radiation oncologists and patients is first between PBI and whole breast irradiation (WBI) — it is not a decision about IORT versus WBI. Once a patient is deemed to be a good candidate for APBI, appropriate APBI techniques should be discussed with the patient.

The guideline reflects our endorsement of EBRT and brachytherapy-based APBI techniques, while withholding support for IORT due to specific concerns. Our recommendations are grounded in long-term, high-quality data. The randomized controlled trials (RCTs) supporting EBRT and brachytherapy APBI include more than 10,000 patients with up to 10 years of follow-up. These trials demonstrate local control and side effect profiles comparable to WBI, validating their use in appropriately selected patients. In contrast, the data supporting IORT — particularly the TARGIT and ELIOT trials — raise significant concerns:

• Limited Follow-Up: The TARGIT trial has only published results with a median follow-up of less than three years for the full pre-specified population. This is insufficient to assess long-term recurrence and toxicity outcomes.

• Higher Recurrence Rates: The ELIOT trial showed significantly higher local recurrence rates with IORT compared to WBI, even when re-analyzed for patients with very low risk disease. This suggests that the technique itself may be inherently less effective.

• Technical Concerns: IORT, particularly TARGIT-IORT, uses a proprietary device with a unique delivery method. Despite claims of distinct technique, the target volumes are similar or even smaller than those used in other APBI methods, which may contribute to inferior outcomes.

• Need for Additional Treatment: Approximately 20% of patients in the TARGIT trial required subsequent WBI, undermining the premise of a single-treatment approach and introducing additional side effect risks. While acute skin toxicity is less severe with IORT compared to external beam radiation, long-term toxicity such as breast fibrosis is significantly higher in patients that receive IORT+WBI compared to IORT alone (38% vs. 6%). Breast fibrosis is permanent and impacts patient quality of life as well. For all other APBI techniques, final pathology results are available to help the patients and physicians make an informed treatment decision — no patients receive APBI + WBI but instead receive one treatment or the other. However, proceeding with IORT at the time of surgery introduces a 20% chance that patients will need to add WBI with the significantly increased risk of breast fibrosis.

ASTRO strongly supports partial breast irradiation for a growing population of patients with early-stage breast cancer. The ASTRO APBI guideline reflects this support, expanding eligibility based on maturing data. However, our endorsement is reserved for techniques with proven efficacy and patient safety. TARGIT-IORT, while promising in concept, has not yet met the evidentiary threshold required for guideline inclusion as the current body of evidence supporting IORT remains insufficient. This position was also formally reflected in a resource guide from the American Society of Breast Surgeons which published their own statement on the use of Accelerated Partial Breast Irradiation.

Should future long-term data demonstrate that IORT offers comparable outcomes to other APBI techniques, ASTRO would consider revisiting the recommendations accordingly.