Gross tumour volume (GTV) – is the gross palpable or visible/demonstrable extent and location of the malignant growth.

Clinical target volume (CTV) – is a tissue volume that contains a GTV and/or subclinical microscopic malignant disease, which has to be eliminated. This volume thus has to be treated adequately in order to achieve the aim of therapy: cure or palliation.

Planning target volume (PTV) – is a geometrical concept, and it is defined to select appropriate beam size and beam arrangement, taking into consideration the net effect of all the possible geometrical variations and inaccuracies in order to ensure that the prescribed dose is actually absorbed in the CTV.

Treatment volume – is the volume enclosed by an isodose surface, selected and specified by the radiation oncologist as being appropriate to achieve the purpose of treatment.

Organs at risk (OAR) — are normal tissues whose radiation sensitivity may significantly influence treatment planning and/or prescribed dose.