Accelerated partial-breast radiation after lumpectomy was pretty close, but a little less effective, than whole-breast radiation at reducing the risk of breast cancer recurrence in the same breast in women diagnosed with early-stage disease, according to long-term study results.
The research was presented on Dec. 6, 2018, at the San Antonio Breast Cancer Symposium. Read the abstract of “Primary results of NSABP B-39/RTOG 0413 (NRG Oncology): A randomized phase III study of conventional whole breast irradiation (WBI) versus partial breast irradiation (PBI) for women with stage 0, I, or II breast cancer.”
Watch study investigator Frank Vicini, M.D., of the MHP Radiation Oncology Institute/21st Century Oncology, discuss the two key things you should know about this study.
Accelerated partial- vs. whole-breast radiation
Women diagnosed with early-stage breast cancer who have lumpectomy to remove the cancer usually have radiation therapy after surgery. Radiation therapy after lumpectomy lowers the risk of the cancer coming back (recurrence) and makes lumpectomy as effective as mastectomy.
Radiation can be delivered to the entire breast — called whole-breast radiation — or to just the area of the breast where the cancer was — called accelerated partial-breast radiation.
Traditional whole-breast external beam radiation therapy aims cancer-destroying energy at the whole breast. The source of the radiation is outside the breast, which is why it's called "external beam." Whole-breast radiation therapy is usually given as one treatment per day, 5 days a week, for 5 to 7 weeks. A Gray (Gy) is the unit radiation oncologists use to measure the dose of radiation therapy; if you’re on a 5-week treatment schedule, 50 Gy is the usual amount given during the 5 weeks (2 Gy at each treatment). A supplemental “boost” dose may be included at the end of the treatment regimen that targets the area where the cancer was.
Radiation treatment schedules were developed based on research results. But a 5- to 7-week nearly daily commitment may be difficult for some women, especially if they live far away from a treatment center.
To overcome the drawbacks of traditional whole-breast radiation therapy, doctors have developed different ways to deliver radiation. Accelerated partial-breast radiation delivers a higher dose of radiation to a smaller area of the breast over a shorter period of time compared to traditional whole-breast radiation therapy.
There are three types of accelerated partial-breast radiation:
- 3-D conformal external beam radiation therapy (3DCRT) uses a linear accelerator, the same machine used to deliver whole-breast external beam radiation. But instead of aiming radiation at the whole breast, a special MRI or CAT scan of the breast is done and used to map out small treatment fields for the area at risk. The type and distribution of radiation are designed to maximize the dose of radiation to the area that needs to be treated and avoid or minimize radiation to tissue near the area. Radiation treatments are done once or twice a day for 1 week.
- Multi-catheter internal radiation, also called interstitial needle-catheter brachytherapy. This approach uses radioactive "seeds" to deliver radiation directly to the area where the cancer was. The seeds are placed in very small tubes (catheters) that are stitched into place under the skin. The seeds are left in the tubes for a few hours or a few days, and you remain in the hospital during treatment. Once the treatment is completed, the seeds, tubes, and stitches are removed and you go home.
- Balloon internal radiation, known by the brand name MammoSite, places a special tube with a balloon on one end in the breast where the cancer was. The tube comes out of the skin through a small hole. The tube and balloon are placed either during lumpectomy or afterward in a surgeon's office. During each treatment, a machine places a radioactive seed into the center of the balloon for 5 to 10 minutes — just long enough to deliver the required dose of radiation. After the seed is removed, you may leave the treatment center. A total of 10 treatments are usually given over 5 days. That means two treatments per day, about 6 hours apart. When the final treatment is done, the balloon and tube are removed through the small hole in the skin.
Comparing the two types of radiation therapy
In the study, called NSABP B-39/RTOG 0413, 4,216 women diagnosed with stage 0, stage I, or stage II breast cancer who had lumpectomy to remove the cancer between 2005 and 2013 were randomly assigned to receive either whole-breast radiation or accelerated partial-breast radiation after surgery:
- 2,107 women were treated with accelerated partial-breast radiation
- 2,109 women were treated with whole-breast radiation
The accelerated partial-breast radiation was given as 3.4–3.85 Gy twice per day for 1 week using either 3-DCRT or brachytherapy. About 70% of the women in this group were treated with 3-DCRT.
The whole-breast radiation was given as 2 Gy per day, 5 days per week, for 5 weeks, plus a supplemental boost to the area where the cancer was.
Other characteristics of the study:
- 61% of the women were postmenopausal.
- 29% of the women were schedule to be treated with chemotherapy.
- 81% of the breast cancers were hormone-receptor-positive.
- 25% of the cancers were ductal carcinoma in situ (DCIS; stage 0).
- 65% of the cancers were stage I.
- 10% of the cancers were stage II.
- Half the women were followed for longer than about 10 years and half the women were followed for shorter periods of time.
During follow-up, 161 women were diagnosed with a breast cancer recurrence in the same breast:
- 90 women had been treated with accelerated partial-breast radiation.
- 71 women had been treated with whole-breast radiation.
In the study, the researchers called breast cancer recurrence in the same breast as the original cancer “ipsilateral breast tumor recurrence.”
This difference in the risk of recurrence was very small — less than 1% — and was not statistically significant. This means that it was likely due to chance and not because of the difference in treatment. Still, the results did not meet the statistical standards needed to say the two types of radiation therapy were equal.
“Despite only small differences in ipsilateral breast tumor recurrence between the two treatment arms at 10 years, we could not declare that whole-breast radiation and partial-breast radiation were equivalent in controlling local in-breast tumor recurrence because the hazard ratio between arms fell short of meeting statistical equivalence,” said Frank Vicini, M.D., of the MHP Radiation Oncology Institute/21st Century Oncology, who presented the results. “On the other hand, we also could not claim that it is inferior.”
There were no differences between the two groups in:
- overall survival (how long the women lived, with or without the cancer recurring)
- disease-free survival (how long the women lived without the cancer recurring)
- distant disease-free survival (how long the women lived without the cancer recurring in a part of the body away from the breast, such as the bones or liver)
Women treated with accelerated partial-breast radiation had a slightly higher rate of side effects compared to women treated with whole-breast radiation: 9.6% vs. 7.1%, respectively. Rates of severe side effects, while low, were also slightly higher in women treated with accelerated partial breast radiation compared to whole-breast radiation: 0.5% vs. 0.3%, respectively.
What do the results mean for you?
“The results show that partial-breast radiation is pretty close to whole-breast radiation, but not exactly the same,” said Marisa Weiss, M.D., radiation oncologist and Breastcancer.org chief medical officer and founder. “Recurrence was a little higher in women treated with partial-breast radiation, but the difference was small. Partial-breast radiation remains an important option for certain women.”
If you’ve been diagnosed with stage 0, stage I, or stage II breast cancer and will be having lumpectomy followed by radiation, you and your doctor may be considering accelerated partial-breast radiation as an alternative to traditional whole-breast radiation therapy. Perhaps the daily trips to the treatment center would be a burden because of distance, your job, or other commitments. Talk to your doctors about the various types of accelerated partial-breast radiation and their experience with each of the delivery methods.
The Breastcancer.org Radiation Therapy section has more information on both whole-breast and accelerated partial-breast radiation therapy.
To discuss all types of radiation therapy and its effects with others, join the Breastcancer.org Discussion Board forum Radiation Therapy - Before, During, and After.
Written by: Jamie DePolo, senior editor