6.3 Target Volume
There will be one gross target volume (GTV) to be treated by both AP/PA and off-cord fields (or any other field arrangement), which includes the primary tumor plus any enlarged hilar and/or mediastinal lymph nodes, defined as measuring >1.5 cm in largest dimension on a thoracic CT scan. If lymph nodes measuring <1.5 cm by the thoracic CT scan are known to contain tumor by means of other diagnostic tests (mediastinoscopy, mediastinotomy, PET scan), then they also should be included in the gross target volume. In a rare patient without obvious lymph node involvement, it is recommended that the ipsilateral hilum/mediastinum be included as part of CTV1 to a dose of at least 36 Gy (Sequence A) or 40-46 Gy (Sequence B), which would constitute the only departure from the general policy of omitting elective nodal irradiation.
6.3.1 There will be two different clinical target volumes (CTV) required:
6.3.1.1 CTV1: In the initial AP/PA fields, the primary tumor and the enlarged lymph nodes will be treated with a 2.0 cm margin (as measured to the edge of the block), constituting CTV1. If multiple field arrangement is used throughout the entire treatment course, the margin should be 2.0 cm until 36.0 Gy is reached (Sequence A) or 40-46.0 Gy (Sequence B), at which point the margin should be 1.5 cm for the remainder of therapy. Planning target volume 1
(PTV1) therefore will be the same as CTV1.
6.3.1.2 CTV2: In the off-cord (oblique/other) fields, the primary tumor and the enlarged lymph nodes will be treated with a 1.5 cm margin (as measured to the edge of the block), constituting CTV2. An even smaller margin is allowed in the off-cord fields, if so dictated by the proximity of the spinal cord. Planning target volume 2 (PTV2) therefore will be the same as CTV2.
Note: more margin may be necessary (particularly in the cranio-caudad direction) if the tumor movement is increased because of respiratory movement which should be checked by fluoroscopy.
6.3.1.3 Ipsilateral supraclavicular irradiation is allowed when necessary for primary tumor or nodal coverage only.
6.3.2 It is required that target volume for antero-posterior (AP), postero-anterior (PA) and oblique/lateral ports be simulated before initiation of radiotherapy.
6.3.3 Target volumes for AP/PA treatment also define target volumes to be included in oblique or multi-field volume.