Unacceptable Cosmesis in a Protocol Investigating Intensity-Modulated Radiotherapy With Active Breathing Control for Accelerated Partial-Breast Irradiation

Abstract

Purpose To report interim cosmetic results and toxicity from a prospective study evaluating accelerated partial-breast irradiation (APBI) administered using a highly conformal external beam approach. Methods and Materials We enrolled breast cancer patients in an institutional review board–approved prospective study of APBI using beamlet intensity-modulated radiotherapy (IMRT) at deep-inspiration breath-hold. Patients received 38.5 Gy in 3.85 Gy fractions twice daily. Dosimetric parameters in patients who maintained acceptable cosmesis were compared with those in patients developing unacceptable cosmesis in follow-up, using t-tests. Results Thirty-four patients were enrolled; 2 were excluded from analysis because of fair baseline cosmesis. With a median follow-up of 2.5 years, new unacceptable cosmesis developed in 7 patients, leading to early study closure. We compared patients with new unacceptable cosmesis with those with consistently acceptable cosmesis. Retrospective analysis demonstrated that all but one plan adhered to the dosimetric requirements of the national APBI trial. The mean proportion of a whole-breast reference volume receiving 19.25 Gy (V50) was lower in patients with acceptable cosmesis than in those with unacceptable cosmesis (34.6% vs. 46.1%; p = 0.02). The mean percentage of this reference volume receiving 38.5 Gy (V100) was also lower in patients with acceptable cosmesis (15.5% vs. 23.0%; p = 0.02). Conclusions The hypofractionated schedule and parameters commonly used for external beam APBI and prescribed by the ongoing national trial may be suboptimal, at least when highly conformal techniques such as IMRT with management of breathing motion are used. The V50 and V100 of the breast reference volume seem correlated with cosmetic outcome, and stricter limits may be appropriate in this setting.

Accelerated Partial Breast Irradiation: Executive summary for the update of an ASTRO Evidence-Based Consensus Statement

“…4 Single-arm studies have also reported higher rates of fair to poor cosmetic outcomes in approximately 20% of patients treated with EBRT-based APBI. 29,36,37 However, other clinical series of APBI delivered with 3D-CRT or IMRT reported acceptable cosmetic outcomes. 9,[38][39][40][41][42][43][44][45] These conflicting studies raise the hypothesis that subtle variations in planning techniques and/or dose constraints may substantially modify the therapeutic ratio of EBRT-based APBI.…”

Is the simultaneously integrated boost (SIB) technique for early breast cancer ready to be adopted for routine adjuvant radiotherapy?

“…Moreover, opinions are dissenting on how to adopt the LQ model for prediction of late reactions. For instance, some studies on accelerated partial breast irradiation (AP-BI) show markedly higher rates of fibrosis and unacceptable cosmetic results following zonal single doses of 3.85 Gy in 10 fractions over 5 consecutive dayseven without WBI [15]. This observation was interpreted by Bentzen and Yarnold [3] as a possible overestimation of cell repair capacities within the interval of a hypofractionated RT and/or as consequence of overvaluated α/β ratios for the estimation of cosmetically relevant late effects.…”

Proton Therapy for Breast Cancer: Progress & Pitfalls

“…The APBI dose-fractionation regimen in that study remains the most commonly employed regimen in North America. Of note, deterioration of cosmesis has been correlated with irradiated breast volume [54][55][56]. The relationship between irradiated breast volume and cosmesis supports a potential advantage of PBT, which markedly lowers the volume of normal breast exposed [57][58][59].…”