Abstract
BackgroundThere are limited data on accelerated partial breast irradiation (APBI) using external beam techniques. Moreover, there are recent reports of increased fibrosis and unacceptable cosmesis with APBI using external beam with BID fractionation. We adopted a once daily regimen of APBI with fractionation similar to that shown to be effective in a Canadian randomized trial of whole breast irradiation. It is unclear whether patients with DCIS or invasive lobular carcinoma (ILC) are suitable for APBI.MethodsThe retrospective cohort included 310 patients with 312 tumors of T1-T2N0-N1micM0 invasive ductal carcinoma (IDC), ILC, or Tis (DCIS) treated with APBI via external beam. Most patients were treated using IMRT with 16 daily fractions of 270 cGy to a dose of 4320 cGy. The target volume included the lumpectomy cavity plus 1.0 cm to account for microscopic disease and an additional 0.5 to 1.0 cm for setup uncertainty and breathing motion. Ipsilateral breast failure (IBF) was pathologically confirmed as a local failure (LF) or an elsewhere failure (EF).ResultsMedian follow-up was 49 months. Among the 312 cases, 213 were IDC, 31 ILC, and 68 DCIS. Median tumor size was 1.0 cm. There were 9 IBFs (2.9%) including 5 LFs and 4 EFs. The IBF rates among patients with IDC, ILC, and DCIS were 2.4%, 3.2%, and 4.4%, respectively, with no significant difference between histologies. When patients were analyzed by the ASTRO APBI consensus statement risk groups, 32% of treated cases were considered suitable, 50% cautionary, and 18% unsuitable. The IBF rates among suitable, cautionary, and unsuitable patients were 4.0%, 2.6%, and 1.8%, respectively, with no significant difference between risk groups. Acute skin reactions were rare and long-term cosmetic outcome was very good to excellent.ConclusionsExternal beam APBI with once daily fractionation has a low rate of IBF consistent with other published APBI studies. The ASTRO risk stratification did not differentiate a subset of patients with a higher rate of IBF. APBI may be an appropriate treatment for women with DCIS and ILC.
Highlights
accelerated partial breast irradiation (APBI) can be delivered by several techniques and has been explored to treat early stage breast cancer patients in recent years without definitive long-term data from randomized clinical trials
There is no uniform agreement about which patients are suitable candidates for APBI
The clinical target volume (CTV) was limited to 3-5 mm from the skin surface and manually edited to exclude the anterior chest wall and pectoralis muscle or, alternatively, limited to 5 mm from the lung-chest wall interface
Summary
APBI can be delivered by several techniques and has been explored to treat early stage breast cancer patients in recent years without definitive long-term data from randomized clinical trials. Many investigators limit APBI to early stage invasive ductal carcinoma (IDC) < 3 cm in size with lymph node negative disease It is not clear whether patients with DCIS or invasive lobular carcinoma (ILC) are suitable for APBI. ASTRO has formulated a consensus statement on APBI based on limited published literature and divided patients into suitable, cautionary, and unsuitable groups [12] Factors such as age, T stage, N stage, margin status, ER status, LVI, ductal or lobular histology, presence of pure DCIS, EIC, and multifocality/multicentricity were used to classify patients. We adopted a once daily regimen of APBI with fractionation similar to that shown to be effective in a Canadian randomized trial of whole breast irradiation It is unclear whether patients with DCIS or invasive lobular carcinoma (ILC) are suitable for APBI
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