Glandular tissue-based versus anatomical landmark-based CTV delineation in postoperative breast cancer radiotherapy:...

Precise delineation of clinical target volume (CTV) in postoperative breast cancer radiotherapy to ensure adequate target coverage while limiting radiation exposure to organs at risk (OARs). Anatomical landmark-based and glandular tissue-based approaches are widely used, but their dosimetric differences and practical implications remain under discussion.

This retrospective dosimetric study included breast cancer patients who underwent breast-conserving surgery with normal bilateral breast morphology. CT simulations (3-mm slice thickness) were imported into the Monaco 5.0 planning system. Two CTV delineation strategies were compared: anatomical landmark-based (CTV _an ) following ESTRO guidelines, and glandular tissue-based (CTV _gl ) using CT visualization. Planning target volume (PTV) was generated by applying a 0.5-cm retraction from the skin and a 0.5-cm uniform expansion. All contours were generated by a single senior radiation oncologist, and treatment plans were created by an experienced physicist. Dosimetric parameters for the heart, left lung, and contralateral breast were evaluated.

A total of 48 patients (age 32-67 years; mean 49.35 ± 8.57) were included. CTV _gl volumes were significantly smaller than CTV _an volumes (432.87 ± 184.09 cc vs. 582.59 ± 232.55 cc; P < 0.001). Glandular-based delineation was associated with lower D _max , higher D₉₈, and reduced OARs exposure. Left lung V₂₀, mean heart dose, heart V₄₀, and contralateral breast(CB) D _mean were all significantly lower in the CTV _gl group (P < 0.001). CTV volume showed significant positive associations with heart and contralateral-breast dose, whereas left-lung dose demonstrated weaker and more variable associations, reflecting the influence of anatomical and planning-related factors.

Glandular tissue-based delineation produced smaller target volumes and lower radiation exposure to adjacent organs compared with anatomical landmark-based delineation. These findings provide quantitative dosimetric evidence of differences between the two approaches; however, the clinical implications of these reductions cannot be inferred from this dosimetric analysis alone. Further studies incorporating normal tissue complication probability (NTCP) modeling and clinical outcomes are needed to determine their relevance for long-term toxicity and treatment decision-making.