Clinical Investigation
A Prospective Pathologic Study to Define the Clinical Target Volume for Partial Breast Radiation Therapy in Women With Early Breast Cancer

https://doi.org/10.1016/j.ijrobp.2012.02.038Get rights and content

Purpose

To determine an appropriate clinical target volume for partial breast radiation therapy (PBRT) based on the spatial distribution of residual invasive and in situ carcinoma after wide local excision (WLE) for early breast cancer or ductal carcinoma in situ (DCIS).

Methods and Materials

We performed a prospective pathologic study of women potentially eligible for PBRT who had re-excision and/or completion mastectomy after WLE for early breast cancer or DCIS. A pathologic assessment protocol was used to determine the maximum radial extension (MRE) of residual carcinoma from the margin of the initial surgical cavity. Women were stratified by the closest initial radial margin width: negative (>1 mm), close (>0 mm and ≤1 mm), or involved.

Results

The study population was composed of 133 women with a median age of 59 years (range, 27-82 years) and the following stage groups: 0 (13.5%), I (40.6%), II (38.3%), and III (7.5%). The histologic subtypes of the primary tumor were invasive ductal carcinoma (74.4%), invasive lobular carcinoma (12.0%), and DCIS alone (13.5%). Residual carcinoma was present in the re-excision and completion mastectomy specimens in 55.4%, 14.3%, and 7.2% of women with an involved, close, and negative margin, respectively. In the 77 women with a noninvolved radial margin, the MRE of residual disease, if present, was ≤10 mm in 97.4% (95% confidence interval 91.6-99.5) of cases. Larger MRE measurements were significantly associated with an involved margin (P<.001), tumor size >30 mm (P=.03), premenopausal status (P=.03), and negative progesterone receptor status (P=.05).

Conclusions

A clinical target volume margin of 10 mm would encompass microscopic residual disease in >90% of women potentially eligible for PBRT after WLE with noninvolved resection margins.

Introduction

Partial breast radiation therapy (PBRT) as a component of breast conservation therapy is an emerging paradigm in the treatment of women with early breast cancer (1). The rationale for PBRT is based on the premise that limiting the radiation target volume to the breast tissue immediately surrounding the surgical cavity where the majority of local recurrences are observed will achieve local control equivalent to whole breast radiation therapy.

The clinical target volume (CTV) for PBRT defines the volume of breast tissue that encompasses the residual microscopic carcinoma after wide local excision (WLE) of the primary breast cancer. However, the optimal CTV margin surrounding the surgical cavity remains uncertain and there is a paucity of contemporary pathologic data to validate current approaches. Clinical trials investigating PBRT have mostly defined a radial CTV margin of 10-15 mm based on studies describing the clinical patterns of local recurrence and historical retrospective series that examined the patterns of residual disease in mastectomy and re-excision specimens 2, 3, 4.

The primary objective of the present study was to determine an appropriate margin surrounding the surgical cavity after WLE to form the CTV for PBRT based on the spatial distribution of residual carcinoma in a prospective cohort of women with early breast cancer or ductal carcinoma in situ (DCIS) who were potential candidates for PBRT. The secondary objective was to determine the clinicopathologic factors associated with the presence and extent of residual carcinoma in the re-excision or completion mastectomy specimens.

Section snippets

Study schema

We performed a prospective pathologic assessment of a cohort of women who underwent re-excision or completion mastectomy after WLE for early breast cancer or DCIS. The study was approved by the ethics boards of the Peter MacCallum Cancer Centre and St. Vincent's Hospital in Melbourne, Australia. Patients who required re-excision or completion mastectomy were identified and their eligibility for entry to the study was assessed. The re-excision or completion mastectomy was performed at the

Results

The study population comprised 133 women with a median age of 59 years (range, 27-82 years). Re-excision was performed at the time of initial WLE in 65 patients or as a second procedure in 61 patients. Completion mastectomy after WLE was performed in 7 patients and after re-excision in 5 patients.

Table 1 shows the pathologic stage of the cases that are presented by the initial WLE margin status (involved or noninvolved), since an involved margin typically excluded patients from PBRT. The

Discussion

To our knowledge, this study is the first prospective pathologic analysis of the spatial distribution of residual carcinoma in re-excision or completion mastectomy specimens from a cohort of women who were potential candidates for PBRT.

Early retrospective studies examining mastectomy specimens reported a high incidence of multifocal and multicentric disease. The largest series, by Holland et al, included 314 cases in which multifocal disease was present in 63% and tumor foci were found more

Conclusions

Our study showed that a CTV margin of 10 mm would encompass microscopic residual disease in >90% of patients who had a noninvolved surgical margin after WLE for unifocal DCIS or T1/2 invasive breast cancer. This finding supports the American Society for Radiation Oncology (ASTRO) consensus recommendation for a 10-20mm CTV margin for PBRT (1). An involved margin, tumor size >30 mm, and premenopausal status were associated with larger MRE of residual disease. Patients with an involved surgical

References (19)

There are more references available in the full text version of this article.

Cited by (12)

  • What is the dosimetric impact of isotropic vs anisotropic safety margins for delineation of the clinical target volume in breast brachytherapy?

    2021, Brachytherapy
    Citation Excerpt :

    Accurate delineation of the TB and clinical target volume (CTV) is therefore important (13, 14). In the past, various authors have studied about the appropriate safety margins that should be generated for target coverage in APBI (15–17). As a routine practice, the CTV was delineated by uniform 1- to 2-cm expansion of the TB guided by the surgical cavity and clips to cover the microscopic disease adequately.

  • Treatment constraints for single dose external beam preoperative partial breast irradiation in early-stage breast cancer

    2017, Clinical and Translational Radiation Oncology
    Citation Excerpt :

    An MRI and histopathology correlation study showed that in the absence of extensive intraductal component, no subclinical invasive disease was present in 93% of lumpectomy cases more than 10 mm beyond the edge of the lesion as measured on MRI [28]. In a recent prospective pathology study on the appropriate CTV margin for APBI, the maximum radial extension of residual carcinoma was assessed in 133 women requiring re-excision or completion mastectomy after initial lumpectomy [29]. In the 58% patients with non-involved initial margins, residual disease, if present, was ≤10 mm in 97.4% of the cases.

  • Breast Cancer: Stages I-II

    2015, Clinical Radiation Oncology
  • Recommendations from GEC ESTRO Breast Cancer Working Group (I): Target definition and target delineation for accelerated or boost Partial Breast Irradiation using multicatheter interstitial brachytherapy after breast conserving closed cavity surgery

    2015, Radiotherapy and Oncology
    Citation Excerpt :

    The size of the proposed total safety margins (resection margins and, “added” safety margins) should to be at least 1–2 cm (Fig. 2). The corresponding pathological data [12,30,32,55] are controversial (8–30 mm), and the clinical guidelines in USA and Europe are different. The optimal value of total safety margins (sum of the resection margin size and “added” safety margins size) is about 2 cm for both APBI and boost irradiation.

View all citing articles on Scopus

Conflict of interest: none.

View full text