Axillary lymph node dose with tangential whole breast radiation in the prone versus supine position: a dosimetric study

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.

Evaluation of axillary dose coverage following whole breast radiotherapy: Variation with the breast volume and shape

“…Leonard et al compared both stances and observed a mean A1 V95 of 37% and 14% both for supine and prone positions, respectively, meaning a substantial dose reduction in the axilla with supine [23]. Nevertheless this study showed no therapeutic dose levels to the axilla regardless of the patient stance.…”

“…The impact of patient positioning in a prone or supine stance during RT, and its influence on axillary dose coverage with standard TgF has also been addressed [22,23]. Leonard et al compared both stances and observed a mean A1 V95 of 37% and 14% both for supine and prone positions, respectively, meaning a substantial dose reduction in the axilla with supine [23].…”

Axillary Coverage by Whole Breast Irradiation in 1 to 2 Positive Sentinel Lymph Nodes in Breast Cancer Patients

“…Leonard et al (25) evaluated the difference between supine and prone positions and observed a lower coverage with supine position. Mean L1 V95 was 37% and 14%, respectively.…”

Radiation dose to the nodal regions during prone versus supine breast irradiation

“…Alonso-Basanta et al studied the radiation-treatment plans (prone or supine) of 20 patients,21 and Leonard et al compared the plans for 23 patients in the prone and 23 patients in the supine position 22. Both studies led to the conclusion that the coverage of the three axillary nodal levels was inadequate in either position, but the doses were even lower in the prone than in the supine position.…”

“…A number of research groups have demonstrated that the dose to the axillary or sentinel lymph-node areas during supine breast irradiation with tangential fields is usually insufficient “therapeutically” 21–26. In the prone position, the axillary nodal doses are further decreased 21,22…”