Partial Breast Irradiation for Breast Cancer
Authors: Shumway Dean A. , Corbin Kimberly S. , Farah Magdoleen H. , Viola Kelly E. , Nayfeh Tarek , Saadi Samer , Shah Vishal , Hasan Bashar , Shah Sahrish , Mohammed Khaled , Bin Riaz Irbaz , Prokop Larry J. , Wang Zhen , Murad M. Hassan 
Published: January 2023

Objectives. To evaluate the comparative effectiveness and harms of partial breast irradiation (PBI) compared with whole breast irradiation (WBI) for early-stage breast cancer, and how differences in effectiveness and harms may be influenced by patient, tumor, and treatment factors, including treatment modality, target volume, dose, and fractionation. We also evaluated the relative financial toxicity of PBI versus WBI. Data sources. MEDLINE®, Embase®, Cochrane Central Registrar of Controlled Trials, Cochrane Database of Systematic Reviews, Scopus, and various grey literature sources from database inception to June 30, 2022. Review methods. We included randomized clinical trials (RCTs) and observational studies that enrolled adult women with early-stage breast cancer who received one of six PBI modalities: multi-catheter interstitial brachytherapy, single-entry catheter brachytherapy (also known as intracavitary brachytherapy), 3-dimensional conformal external beam radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), proton radiation therapy, intraoperative radiotherapy (IORT). Pairs of independent reviewers screened and appraised studies. Results. Twenty-three original studies with 17,510 patients evaluated the comparative effectiveness of PBI, including 14 RCTs, 6 comparative observational studies, and 3 single-arm observational studies. PBI was not significantly different from WBI in terms of ipsilateral breast recurrence (IBR), overall survival, or cancer-free survival at 5 and 10 years (high strength of evidence [SOE]). Evidence for cosmetic outcomes was insufficient. Results were generally consistent when PBI modalities were compared with WBI, whether compared individually or combined. These PBI approaches included 3DCRT, IMRT, and multi-catheter interstitial brachytherapy. Compared with WBI, 3DCRT showed no difference in IBR, overall survival, or cancer-free survival at 5 and 10 years (moderate to high SOE); IMRT showed no difference in IBR or overall survival at 5 and 10 years (low SOE); multi-catheter interstitial brachytherapy showed no difference in IBR, overall survival, or cancer-free survival at 5 years (low SOE). Compared with WBI, IORT was associated with a higher IBR rate at 5, 10, and over 10 years (high SOE), with no difference in overall survival, cancer-free survival, or mastectomy-free survival (low to high SOE). There were significantly fewer acute adverse events (AEs) with PBI compared with WBI, with no apparent difference in late AEs (moderate SOE). Data about quality of life were limited. Head-to-head comparisons between the different PBI modalities showed insufficient evidence to estimate an effect on main outcomes. There were no significant differences in IBR or other outcomes according to patient, tumor, and treatment characteristics; however, data for subgroups were insufficient to draw conclusions. Eight studies addressed concepts closely related to financial toxicity. Compared with conventionally fractionated WBI, accelerated PBI was associated with lower transportation costs and days away from work. PBI was also associated with less subjective financial difficulty at various time points after radiotherapy. Conclusions. Clinical trials that compared PBI with WBI demonstrate no significant difference in the risk of IBR. PBI is associated with fewer acute AEs and may be associated with less financial toxicity. The current evidence supports the use of PBI in appropriately selected patients with early-stage breast cancer. Further investigation is needed to evaluate the outcomes of PBI in patients with various clinical and tumor characteristics, and to define optimal radiation treatment dose and technique for PBI.