Evaluation of apical clips placed during axillary dissection demonstrates potential under‐coverage of axillary radiation therapy target volumes during breast cancer regional nodal irradiation

Abstract

INTRODUCTION Evidence-based Australian guidelines (eviQ) recommend adjuvant supraclavicular fossa irradiation after axillary lymph node dissection (ALND) in node-positive breast cancer patients. Disparity between surgically determined versus computed tomography (CT) determined nodal volumes may result in discontiguous nodal volumes and untreated nodal tissue. We examine the extent of untreated nodal tissue in women with breast cancer post-level II or III ALND and adjuvant radiation therapy (RT) using ESTRO contouring guidelines.

METHODS Female breast cancer patients who underwent level II and III ALND with apical clip placement from 2016 to 2020 and CT simulated in supine position were included. CT-defined axillary level II-IV volumes were contoured using ESTRO guidelines. The distance between the apical clip and RT nodal volumes was measured to indicate extent of untreated tissue.

RESULTS Of 34 eligible patients treated by 7 surgeons, 76% had level II ALND and 24% level III ALND. Only 5.9% of clips entirely encompassed the corresponding RT nodal volumes. 55.9% of clips fell within and 44.1% fell inferolaterally outside the corresponding RT nodal volumes. A median 3.6 cm (range 0-7.5 cm) of undissected nodal tissue would not be included within standard RT target volumes following eviQ recommendations.

CONCLUSION There is a disparity between surgically determined versus CT determined axillary nodal volumes, leading to discontiguous nodal volumes and untreated axillary nodal tissue, despite following standard radiation contouring guidelines. Intraoperatively placed apical axillary clips may assist radiation oncologists to accurately delineate undissected nodal tissues at risk.