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.

Fig. 1

Volumes contoured on an axial image of a sample patient. The lumpectomy cavity is contoured in red. Margins were added as described in the text to create a planning target volume, as depicted in green. The contoured breast is depicted in pink and excludes the pectoral musculature, excludes 5 mm of skin and tissue from the body surface, and extends to 5 mm inside the medial and lateral catheters denoting the borders of the tangent fields. For comparison with the Radiation Therapy Oncology Group (RTOG) 0413/National Surgical Adjuvant Breast and Bowel Project (NSABP) B-39 study (11), a breast reference volume was created retrospectively to include the region encompassed by traditional tangential portals; the large yellow contour corresponds to this volume.

Fig. 2

Isodose distributions achieved in 2 patients. Both cases illustrate the conformality of the treatment. The cases differ with respect to the volume of the lumpectomy cavity and the proportion of normal breast irradiated.

Fig. 3

Visible impairment in cosmesis observed in 3 patients deemed to have unacceptable cosmesis after treatment.

Fig. 4

Distribution of the proportion of the breast reference volume in each case receiving 50% of prescribed dose (V50), by cosmetic outcome, among patients with good or excellent cosmesis at baseline.