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Postoperative Radiation Treatment of the Breast

Definitions

Target Volume

Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)

GTV (= Gross Tumor Volume)

Tumor volume

Palpable or visible/identifiable area of malignant growth. Confirmed lymph nodes may be reported as GTV-N, other metastases as GTV-M.

CTV (= Clinical Target Volume)

Clinical target volume

Tissue volume containing GTV and/or subclinical microscopic malignant disease.

ITV (= Internal Target Volume)

Target volume

Volume containing CTV and an internal margin taking into account internal movements and changes in  CTV. This is the volume that should receive an optimal dose.

PTV (= Planning Target Volume)

Planning volume

Geometric volume containing ITV and one Set-up margin taking into account variation for patient movements, variations in patient positioning, and field modeling.

Planning contour: Beams-Eye-View projection of PTV.

 IM (= Inner margin) and SM (= Setup margin)

IM and SM cannot be summed linearly. Total margin must be given specifically for different tumor localizations.

GTV

Gross tumor volume is not applicable for postoperative radiation.

CTV breast

Includes breast and the axillary process of the breast,

Limits

  • Ventrally: 5 mm under skin layer
  • Dorsally: fascia covering the pectoral muscle, possibly anterior surface of ribs in deeply located tumors.

CTV boost

With CT as reference, this volume includes the tumor bed defined as the operative cavity and the visible postoperative reaction, with additional 5-10 mm surrounding tissue, or alternatively as visible operation cavity and possibly staples with about 2 cm surrounding tissue. The scar is not part of the target.

CTV parasternal lymph nodes

Routine radiation is no longer necessary. The method should be considered for:

  • large, medially or centrally localized tumors
  • positive parasternal sentinel lymph node

Limits

  • Medially: lateral border of sternum 
  • Laterally: 2 cm laterally to the medial limit
  • Dorsally: pleura
  • Ventrally: anterior edge of ribs
  • Cranially: immediately caudally to the sternoclavicular joint
  • Caudally: cranial border of ribs IV (often equals 1 cm below carina)

CTV periclavicular lymph nodes

Limits

  • Medially: 1,5 cm from trachea
  • Caudally/laterally: border to the axilla
  • Cranially: equals 1 cm caudal to vocal cords or the lower part of C6
  • Caudally: lower part of the sternoclavicular joint
  • Anteriorly: 5 mm deep to the skin
  • Dorsally: anterior to the transverse process in upper part, the ribs more caudally.

CTV axilla

Level I lateral to pectoralis minor muscle 

Level II posterior to pectoralis minor muscle 

Level III medially to pectoralis minor muscle. Lateral to the supra/infraclavicular region.

CTV thoracic wall

  • Includes the area underlying the breast as well as the operation scar. The outer 5 mm of the skin is not included in the clinical target volume. Over the scar itself and 20 mm to the sides of the scar, the clinical target volume includes the surface of the skin when the distance from the tumor to the skin is short (use of bolus). In the depth the target volume reaches the anterior rib surface. The medial border mimics the edge of the remaining breast. If this is not possible to identify, the medial border should be 25 mm lateral to the lateral edge of the sternum.

ITV=CTV

PTV

Margins are set to 5-7mm, towards the heart 0 mm. The minimum dose in PTV should be 90% of the target dose.

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