Prone vs Supine Positioning for Breast Cancer Radiotherapy FREE

To the Editor: Adjuvant radiotherapy to the breast contributes to improved outcomes in breast cancer patients after breast preservation surgery.¹ However, whole breast radiotherapy is associated with damage to the heart and lung, increased cardiovascular mortality, and lung cancer development, with risks that remain 15 to 20 years after treatment.² These consequences occur when breast cancer patients are treated supine. Preliminary data on prone positioning suggest that radiation exposure to the heart and lung can be reduced compared with supine positioning^3- 4 with similar efficacy.⁵ To test the hypothesis that prone positioning is superior to standard supine positioning, we compared the volume of heart and lung within the radiation field in a prospective study of patients who underwent simulation in both positions.

From November 15, 2005, to December 26, 2008, patients with stage 0-IIA breast cancer, segmental mastectomy, negative surgical margins, and 3 or fewer involved lymph nodes referred to New York University Radiation Oncology were eligible for the study. Each patient underwent 2 computed tomography (CT) simulation scans, first supine and next prone. The dose from the second CT was justified ethically because additional imaging enabled the treating physician to choose the position that best spared heart and lung. The treating physician contoured target and normal structures and placed the treatment fields. Comparable coverage of the breast regardless of position was ensured by placing the posterior edge of the field on a plane connecting the midline to the anterior extent of the latissimus dorsi muscle, visualized at CT (Figure). In-field heart and lung volumes were then measured by 2 physicists (J.K.D. and G.J.) as reliable surrogates for dose.⁴ Three breast volume groups were defined (<750 cm³, 750-1500 cm³, and >1500 cm³).

Two hundred patients per stratum (left and right breast cancer) were enrolled to detect differences smaller than ±0.30 SD for each volume parameter between the supine and prone positions, using paired t tests with a 2-sided α of .05 and power of 80%. Differences in in-field lung and heart volumes (and 95% confidence intervals) between the supine and prone positions for patients with left breast cancer and in lung volumes for patients with right breast cancer were estimated. Data analysis was performed using SAS software version 9.2 (SAS Institute Inc).

All patients provided written informed consent. The New York University institutional review board approved the study.

Four hundred consecutive patients were prospectively accrued, approximately 60% of those eligible. Median age was 56.3 years (range, 30.7-94.3 years). Ethnicity was 322 (80.5%) white, 22 (5.5%) black, 21 (5.2%) Hispanic, 28 (7%) Asian, and 7 (1.7%) of other ethnicity. The primary insurance carrier was private in 310 (77%) patients, Medicare in 76 (19%), and Medicaid in 14 (4%). Eighty-six (21.5%) patients had ductal carcinoma in situ. Among the 314 (78.5%) patients with invasive breast cancer, 47 (14.96%) had involved sentinel or axillary lymph nodes.

In all patients, the prone position was associated with reduced in-field lung volumes compared with supine (Table) (mean difference: 104.6 cm³ [95% CI, 94.26-114.95 cm³], an 86.2% reduction for right breast cancer; 89.85 cm³ [95% CI, 80.16-99.55 cm³], a 91.1% reduction for left breast cancer). In patients with left breast cancer, the prone position was associated with a reduction of in-field heart volumes compared with supine (mean difference: 7.5 cm³ [95% CI, 5.16-9.85 cm³], an 85.7% reduction). However, in 15% of patients with left breast cancer, the supine position was associated with less in-field heart volume compared with prone (mean difference: 6.15 cm³; 95% CI, 2.97-9.33 cm³). These reductions were statistically significant regardless of breast volume (with the exception of heart in women with breast size <750 cm³).

Prone positioning was associated with a reduction in the amount of irradiated lung in all patients and in the amount of heart volume irradiated in 85% of patients with left breast cancer.

The study is limited to a single institution. A multi-institutional prospective trial with outcome measures is warranted to confirm these findings. If prone positioning better protects normal tissue adjacent to the breast, the risks of long-term deleterious effects of radiotherapy may be reduced.