Clinical investigation: breast
Evaluation of level I and II axillary nodes included in the standard breast tangential fields and calculation of the administered dose: results of a prospective study

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Abstract

Purpose: To evaluate if Level I and II axillary nodes are included in the standard breast tangential fields, and to calculate the dose administered.

Methods and Materials: In 35 patients treated with conservative surgery and axillary dissection, three clips were surgically positioned: one at the beginning of Level I, one between Level I and II, and another at the end of Level II. The breast was irradiated with two tangential fields. On simulation films, the volume between the clips was scored as “entirely included” or “not entirely included” in the treatment fields. Computed tomography (CT) scans were performed; CT data were imported into a treatment planning system, and three-dimensional plans were devised. Axillary Levels I and II were delineated on CT slices on the basis of anatomic landmarks. Fields and isodose curves previously obtained were superimposed to calculate the dose administered to the first two axillary node levels and to 90% of both volumes.

Results: On X-rays, the volume between clips corresponding to Level I was completely included in the medial field in 66.7% of cases and in the lateral field in 63.7% of cases, whereas the volume of Level II was entirely included in the medial field in 54.5% of cases and in the lateral field in 45.4% of cases. The median dose administered to Level I and II was 38.58 Gy ± 11.01 (range 3.46–47.14) and 20.65 Gy ± 14.07 (range 0.95–38.94), respectively. The median dose to 90% of both volumes of Level I and II was 6.75 Gy ± 14.01 (range 1.9–39) and 1.75 Gy ± 9.72 (range 0.8–29), respectively.

Conclusion: The standard tangential fields do not entirely include Levels I and II axillary nodes.

Introduction

After conservative surgery, the breast is usually irradiated with two tangential fields. Although it is generally believed that the lower portion of the axilla is adequately treated with the same fields used for the breast 1, 2, only a few studies have been conducted to ascertain if this assumption is valid 3, 4, 5.

We carried out a prospective study to evaluate if the standard breast tangential fields include the first two axillary node levels. Furthermore, we calculated the dose administered to these nodes and the dose to 90% of both volumes.

Section snippets

Methods and materials

Thirty-five patients treated with conservative surgery and axillary dissection for early-stage breast cancer were enrolled. Three clips were positioned during surgery; the patient lay supine with the ipsilateral arm extended laterally at 90° respective to the trunk. The first and second clips were put on the internal and external borders of the pectoralis minor muscle; the third was positioned at the lowest point of surgical dissection (Fig. 1). According to this clip placement, Level I begins

Results

On simulation films, the volume between the clips corresponding to Level I was completely included in the medial field in 66.7% of cases and in the lateral field in 63.7% of cases; the volume of Level II was entirely included in the medial field in 54.5% of cases and in the lateral field in 45.4% of cases. None of the parameters taken into account with the Pearson test (field length, gantry angle, and collimator angle) were significantly correlated with the percentage of clips defining the

Discussion

Although it is commonly assumed that nodes of axillary Levels I and II are included in the standard breast tangential fields, only a few studies have been conducted to ascertain if this assumption is valid 3, 4, 5. In two of these studies, the evaluation was retrospective 3, 4. Simulator films were reviewed, and the clips, placed to obtain hemostasis in the axilla at the time of axillary dissection, were considered surrogate locations for the axillary nodes. Results from both studies showed

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