Abstract
BackgroundProne breast positioning reduces skin reaction and heart and lung dose, but may also reduce radiation dose to axillary lymph nodes (ALNs).MethodsWomen with early stage breast cancer treated with whole breast irradiation (WBI) in the prone position were identified. Patients treated in the supine position were matched for treating physician, laterality, and fractionation. Ipsilateral breast, tumor bed, and Level I, II, and III ALNs were contoured according to the RTOG breast atlas. Clips marking surgically removed sentinel lymph nodes (SLN)s were contoured. Treatment plans developed for each patient were retrospectively analyzed. V90% and V95% was calculated for each axillary level. When present, dose to axillary surgical clips was calculated.ResultsTreatment plans for 46 women (23 prone and 23 supine) were reviewed. The mean V90% and V95% of ALN Level I was significantly lower for patients treated in the prone position (21% and 14%, respectively) than in the supine position (50% and 37%, respectively) (p < 0.0001 and p < 0.0001, respectively). Generally, Level II & III ALNs received little dose in either position. Sentinel node biopsy clips were all contained within axillary Level I. The mean V95% of SLN clips was 47% for patients treated in the supine position and 0% for patients treated in the prone position (p < 0.0001). Mean V90% to SLN clips was 96% for women treated in the supine position but only 13% for women treated in the prone position.ConclusionsStandard tangential breast irradiation in the prone position results in substantially reduced dose to the Level I axilla as compared with treatment in the supine position. For women in whom axillary coverage is indicated such as those with positive sentinel lymph node biopsy who do not undergo completion axillary dissection, treatment in the prone position may be inappropriate.
Highlights
Prone breast positioning reduces skin reaction and heart and lung dose, but may reduce radiation dose to axillary lymph nodes (ALNs)
The eight-year results of the American College of Surgeons Oncology Group (ACOSOG) Z0011 study evaluating locoregional recurrence after sentinel lymph node dissection (SLND) with or without axillary lymph node dissection (ALND) in patients with positive sentinel lymph nodes suggest that completion ALND may be unnecessary for selected early stage breast cancer patients [1,2]
Breast volumes tended to be larger in the prone position than in the supine position, but this difference did not reach statistical significance
Summary
Prone breast positioning reduces skin reaction and heart and lung dose, but may reduce radiation dose to axillary lymph nodes (ALNs). Prone breast positioning for WBI has become more popular in efforts to decrease radiation dose to the heart and lungs and to decrease acute skin reaction in women with pendulous breasts [9,14,15,16,17] while maintaining acceptable long-term outcomes [18]. Prone positioning increases the anatomic distance of the breast from the heart and lungs, eliminates the bolus effect created by the inframammary fold, and improves dose homogeneity as compared to WBI in the prone position. Recent work has shown decreased coverage of the ALNs in the prone position when treatment plans were created for each patient in both the prone and supine position [9]. The current work explores dosing to axillary lymph nodes in patients thought to be ideal candidates for prone positioning
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