Catheryn Yashar, MD
The SAVI Collaborative Research Group (SCRG) studies the long-term outcomes of women treated with strut-based brachytherapy with the SAVI® applicator. At the 56th annual meeting of the American Society for Radiation Oncology (ASTRO) in September 2014, researchers from the SCRG presented excellent five-year outcomes for the first 200 patients treated with SAVI. The study is the most mature follow-up of the largest cohort of patients treated with strut-based brachytherapy to date.
Radiation oncologist Catheryn Yashar, MD, of UC San Diego’s Moores Cancer Center in La Jolla, Calif., is the co-principal investigator of the SCRG. She discusses the data, the study’s significance, and why she believes strut-based brachytherapy is the optimal method for delivering accelerated partial breast irradiation (APBI).
What are the most significant conclusions that can be drawn from your study of the first 200 patients treated with strut-based brachytherapy?
This was a large, multi-center study with five years of follow up; both the size of the cohort and the length of follow-up make the results very meaningful. The data showed excellent local control, low toxicity, and great cosmetic results. Over the years, our data have continually shown strut-based brachytherapy to be a safe and effective treatment for lower risk breast cancers. This study confirms that it be can be used to treat appropriately selected patients with an efficacious and low toxicity regimen for APBI. Physicians should feel comfortable offering strut-based brachytherapy as a standard option to any APBI-eligible patient – in fact, I would say it’s the optimal option for delivering APBI.
Based on your data, how does strut-based brachytherapy compare to other forms of APBI?
It’s the superior choice with the widest applicability of any APBI method. Based on our data, it’s equally efficacious – there’s no indication the recurrence rates are higher than other modes of APBI. Compared to other single-entry brachytherapy devices, strut-based brachytherapy has far better dose modulation, making it easier to conform to normal tissue with few long-term toxicities. While interstitial brachytherapy is effective and also conforms well to normal tissue, it’s far more invasive than is necessary for most women. It’s also incredibly skill-dependent, which limits its availability.
Compared to external APBI, whether it’s 3D conformal or IMRT, strut-based brachytherapy is markedly better. External methods of radiation delivery treat significantly more tissue, resulting in much greater toxicity and inferior cosmetic outcomes.
How do the results compare to other accelerated forms of radiation, such as intraoperative radiation therapy (IORT) or hypofractionated whole breast irradiation (WBI)?
While hypofractionated WBI shortens treatment time from six weeks to three weeks – or four weeks if a boost is required – there’s just no comparison when you look at the amount of normal tissue irradiated unnecessarily. This includes the ribs, lung, potentially the heart, and other healthy parts of the breast. In this day and age when we are trying to increase efficacy, decrease cost and minimize toxicity, it seems inconsistent to irradiate tissue that the data suggest doesn’t need irradiation.
When looking at IORT, there are several different methods to consider. With IORT via Intrabeam, the data is still very immature and the population is so low risk that we don’t have any evidence at this time that it’s as efficacious as other methods of APBI. While IORT with electrons has a large randomized dataset, it has begun to show an increased recurrence rates and higher toxicity compared to other methods.
How do the results of your study demonstrate the benefits of targeted radiation like brachytherapy?
The benefits of a highly targeted treatment are that it can treat the area most at risk while reducing unnecessary radiation exposure to healthy tissue and other critical structures, which are reflected in the excellent local control, low toxicity and great cosmetic outcomes as reported in the study. In addition, it offers women a shorter course of treatment. All of these factors combined make a targeted form of radiation like this a superior alternative to other forms of treatment for early-stage breast cancer.
Dr. Yashar is an associate professor of radiation oncology at the UC San Diego School of Medicine and chief of breast and gynecological radiation services at the Moores UCSD Cancer Center.