BREAST CANCER-TARGET VOLUME DELINEATION

• 3D conformal radiation therapy (3D CRT) with field‑in‑field or mixed‑energy beams is standard for early‑stage breast cancer, ensuring homogeneous dose distribution.
• Hypofractionated whole breast irradiation has the strongest supporting evidence.
• Tumor bed (lumpectomy cavity) boost reduces recurrence risk but may be omitted in select low‑risk patients.
• Boost typically delivered with en‑face electron fields; beam energy selected based on tumor bed depth and margin without extending beyond anterior pectoralis surface. Mini‑tangents may be used for deep beds.
• Accelerated partial breast irradiation (APBI) is acceptable for select low‑risk, unifocal cases.
• Multiple RT techniques are available including 3D CRT and IMRT.
• Thorough physical exam, pre‑operative imaging, and pathological assessment are required before radiation planning.
• Mammography is universal; ultrasound common; MRI reserved for specific early‑stage cases.
• All pre‑operative imaging must be reviewed to ensure adequate margins for whole‑breast RT and accurate boost targeting.
• Image‑guided biopsy confirms diagnosis; SLNB recommended for early invasive cancer. Pathology must confirm adequate margins (no tumor on ink for invasive; ≥2 mm for DCIS).
• Surgical clips are preferred for accurate tumor‑bed delineation but not mandatory.
• Whole‑breast CT planning: ≤3 mm slices; APBI: 1.5–2 mm slice thickness through lumpectomy cavity.
• Supine simulation: patient positioned on breast board with both arms elevated. DIBH is recommended for left‑sided disease.
• Pendulous breasts may benefit from prone technique to reduce separation and dose heterogeneity. Prone positioning reduces lung and heart dose.
• Prone patients must be positioned on a dedicated prone breast board with attention to comfort and reproducibility.
• OARs include heart and lungs. Heart contouring extends superiorly to PA bifurcation and includes pericardium and epicardial fat (but not pericardial fat outside pericardium). LAD and LV doses should be minimized.
• Target volumes include breast tissue and lumpectomy cavity. For APBI, delineate lumpectomy CTV and PTV.

• CT simulation is performed with both arms elevated using breast‑board immobilization; IV contrast is optional.
• In intact breast cases, borders of the breast and lumpectomy scar should be wired on skin before scanning.
• Scan from the cricoid to 5 cm below the inferior field border; include the entire lungs.
• PTV includes:
  • Breast or chest wall.
  • Ipsilateral level I–III axillary lymph nodes.
  • Ipsilateral supraclavicular nodes.
  • Ipsilateral interpectoral nodes.
  • Ipsilateral internal mammary lymph nodes.
• Daily bolus of 3 mm used over chest wall for VMAT/IMRT.
• 1‑cm bolus applied for inflammatory breast cancer when ≥100% skin GTV dose is required.

• APBI is suitable for select low-risk, unifocal early breast cancers.
• CT simulation slice thickness should be 1.5–2 mm through the lumpectomy cavity.
• CTV includes tumor bed, seroma, surgical clips, and glandular distortion.
• CTV to PTV margin: 0.5–1.0 cm depending on setup uncertainty.
• APBI volumes should remain within the breast; avoid extension into ribs/pectoralis unless for dose reporting.
• APBI techniques include 3D CRT, IMRT, VMAT, and brachytherapy.

• IMNs lie in first three intercostal spaces adjacent to internal thoracic vessels.
• CTV includes vessels and surrounding lymphatic tissue while respecting anatomic boundaries.
• Posterior IMN CTV margin: 0 mm to reduce lung dose.
• PTV expansion: 5–10 mm except posteriorly (0 mm).
• Aim for D95 ≥ 90% while maintaining heart/LAD constraints.
• Use DIBH for left-sided IMN irradiation to reduce cardiac exposure.

Breast VMAT Dosimetric Planning Guidelines

IMRT/VMAT (Non‑DIBH vs DIBH)