Coverage of axillary lymph nodes with high tangential fields in breast radiotherapy

Abstract

ABSTRACT. The aim of this study is to evaluate the coverage of axillary nodal volumes with high tangent fields (HTF) in breast radiotherapy and to determine the utility of customised blocking. The treatment plans of 30 consecutive patients with early breast cancer were evaluated. The prescription dose was 50 Gy to the whole breast. Axillary level I-II lymph node volumes were delineated and the cranial border of the tangential fields was set just below the humeral head to create HTF. Dose-volume histograms (DVH) were used to calculate the doses received by axillary nodal volumes. In a second planning set, HTF were modified with multileaf collimators (MLC-HTF) to obtain an adequate dose coverage of axillary nodes. The mean doses of the axillary nodes, the ipsilateral lung and heart were compared between the two plans (HTF vs MLC-HTF) using a paired sample t-test. The doses received by 95% of the breast volumes were not significantly different for the two plans. The doses received by 95% of the level I and II axillary volumes were 16.79 Gy and 11.59 Gy, respectively, for HTF, increasing to 47.2 Gy and 45.03 Gy, respectively, for MLC-HTF. Mean lung doses and per cent volume of the ipsilateral lung receiving 20 Gy (V20) were also increased from 6.47 Gy and 10.47%, respectively, for HTF, to 9.56 Gy and 16.77%, respectively, for MLC-HTF. Our results suggest that HTF do not adequately cover the level I and II axillary lymph node regions. Modification of HTF with MLC is necessary to obtain an adequate coverage of axillary levels without compromising healthy tissue in the majority of the patients. Sentinel lymph node (SLN) biopsy for clinically nodenegative breast cancer has become the standard approach for the surgical evaluation of the axilla [1,2]. If the final pathology report reveals metastatic involvement of the sentinel lymph node(s), then axillary lymph node dissection (ALND) is considered. Irradiation of the axillary lymph nodes is also an option for regional treatment. Axillary radiation and surgery have provided equivalent local control in early breast cancer patients [3,4]. Randomised trials to evaluate the efficacy and toxicity of surgical or radiotherapeutic management of axilla with positive sentinel lymph node biopsy have been planned, and the results are pending [5]. Irradiation of the axilla can be performed via separate anteriorposterior fields; alternatively a portion of the axilla (the most likely levels I and II) can be covered by the tangential fields; Irradiating the lower levels of the axilla through tangential fields is considered to be more practical. In the era of CT-based three dimensional (3D) radiotherapy planning, however, concerns have been raised about the adequacy of coverage of the axillary levels in the tangential fields [6][7][8][9][10].In this study, we evaluated the coverage of the axillary nodal levels administered using modified high tangential fields in patients without axillary dissection and the effect of this modification on the doses received by the ipsilateral lung. Methods ...

Axillary Irradiation with High Tangent Fields for Clinically Node-Negative Breast Cancer: Can 3-D Conformal Radiotherapy with a Field-in-Field Technique Better Control the Axilla?

“…However, dosedistribution analysis indicated that the entire volume of the axilla is not irradiated with the entire prescribed dose. It is now estimated that, using standard tangential fields, more than 50% of level I and 20-30% of level II nodes receive 95% of the prescribed radiation dose [8,9,11,12]. The advantage of the field-in-field plan over the conventional wedge-inserted plan was also demonstrated in other reports [7,13].…”

“…In contrast, the strength of this study is that it shows the clinical use of 3-D treatment planning to irradiate intentionally the large volume of level I and II nodes. While retrospective dosimetric studies have suggested the technical use of high tangent fields [7,11,12,13], this is the first study to demonstrate the impact of improved dose distribution on regional control in breast cancer management.…”

Comparison of Incidental Radiation Dose to Axilla and Internal Mammary Nodal Area by Conventional, 3DCRT, and IMRT Technique in Carcinoma of Breast

“…That can have direct correlation, with standard tangents, the axilla receives a significant incidental dose but still adequate for clinical control of disease is unknown [18,19]. Substantial variability was observed in contouring the targets and organ at risk between observers and the structure overlaps were as low as 10% and volume variation had standard variation up to 60% [20].…”

Radiotherapy of the Lymphatic Pathways in Early Breast Cancer

“…This approach was based on several studies investigating the dose delivered to the ALNs by conventional tangential fields, and the exploration of techniques yielding an improved coverage of level I by minor field extensions in cranial direction [29,30,31]. This technique is also recommended in the new textbook on Radiation Oncology edited by Perez and Brady [18].…”