This document discusses key concepts and volumes used in radiotherapy planning according to ICRU reports 50 and 62. It defines the gross tumour volume (GTV), clinical target volume (CTV), planning target volume (PTV), treated volume (TV), irradiated volume (IV) and organs at risk (OARs). Inter-observer variation can lead to differences in delineating the GTV and PTV. Advances in imaging may help define volumes for ill-defined tumors in the future.

1. TARGET
DEFINITION

2. INTRODUCTION :
 The therapeutic use of radiation (radiotherapy) is an
established method of treating malignant tumours.
Radiotherapy is local treatment and is complementary to
systemic treaments such as chemotherapy and hormone
therapies. It is important appreciate that the desired anti-cancer
activity of radiotherapy is only seen in the tissue irradiated by
the primary beam.

3. The International Commission On
Radiation Units And Measurements
Volumes :
 The (ICRU) 50 report
stipulates standard protocols
for recording and reporting
radiotherapy treatments of all
degrees of complexity. The
adoption of these terms serves
several purpose.
 Improves clarity of thought
and encourages a logical
approach to planning.
 Promotes consistency in
physics planning and clinical
practice.
 Allows standardisation of
clinical trial protocols,
particularly for complex,
multi-phase treatments.
 Facilities Communication
between different centres and
within clinical trials.

4. GROSS TUMOUR VOLUME (GTV) :
 The volume that includes palpable, visible or
demonstrable extent of a tumour. It may consist of the
primary tumour, metastatic disease, or
lymphadenopathy. The GTV usually represents the part
of the maligrant growth where the tumour cell density is
the largest.

5. CLINICAL TARGET VOLUME (CTV) :
 CTV includes the GTV as well as the region of direct,
local subclinical spread of disease hat must be treated.
The CTV often has a high tumor cell density nearest the
GTV with decreasing density toward the periphery. The
CTV volume may not contain demonstrable tumor but
are considered at risk, such as regional lymph node and
their volumes for subclinical spread.

6. PLANNING TARGET VOLUME (PTV) :
 PTV includes the gross tumor volume (GTV) the clinical
target volume (CTV), and a region to account for setup
error, movements and any possible geometric variations.
 The volume that includes the CTV with any ITV (if
presents) as well as a setup margin to account for patient
movement and daily setup uncertainties.

7. Figure :
The concept of
radiotherapy
Plan

8. TREATED VOLUME (TV) :
 Additional margin must be provided around the target
volume to allow for limitations of the treatment
technique. Thus, the minimum target dose be
represented by on isodose surface that adequately cover
the PTV provide that margin.The volume enclosed by
this isodose surface is called treated volume. The treated
volume is as general larger than the planning target
volume and depends as a particular treatment technique.

9. IRRADIATED VOLUME (IV) :
 The irradiated volume (IV) is the tissue volume
receiving a radiation absorbed dose that is considered
significant in relation to normal tissue tolerance.
 The concepts is not often considered in practice but may
be useful when comparing one or more competing plans.

10. ORGANS AT RISK (OARs) :
 Organs at risk is a crucial task for radiation oncologists
when aiming to optimize the benefit of radiation therapy,
with delivery of the maximum dose to the tumor volume
while sparing healthy tissues.

11. Most Common OARs :
 Brain : Lens of eye, optic chiasm, brain stem.
 Head & neck : Lens of eye, parotid glands.
 Thorax : Spinal cord, lungs.
 Abdomen : Spinal cord, large bowel, small bowel,
kidneys.
 Pelvis : Bladder, rectum, femoral heads, large
bowel, small bowel.

12. POOR ORGAN :
For some malignancies , it is the usual
practice to treat the whole of the organ
from which the tumour originates.
Some tumour are well circumscribed
with an easily defined margin of
demarcation from the surrounding normal
tissue.
Some tumour are far less well
defined,this may be because of diffuse
infiltration at the tumour periphery has a
similar radiographic density compared to
the surrounding normal tissue.

13. INTER-OBSERVER VARIATION :
 Some tumour there can be some considerable inter-
observer variation.
 Comparison of the GTVs and PTVs suggested
considerable variation from person to person in the GTV
contour, in some cases with a substantial difference in
tumour volumes.

14. ICRU 62 ADDITIONS TO ICRU 50 :
 ICRU report 62 (1999) has
been introduced as a
supplement to ICRU report
50 . The definitions of GTV
and CTV remain unchanged
as these are oncological
concepts independent of any
technical developments.

15. INTERNAL - ORGAN MOVEMENTS :
 The tissue containing the tumour has very little scope for
movements, the emergence of precision radiation
delivery techniques such as conformal radiotherapy,
these issues have had to be considered.
 The variability of the result may have been greater than
would have been obtained by a group of experienced
oncologists alone because of the different criteria being
used by the different groups.

16. CONCLUSIONS :
 The increasing sophistication of treatment planning and radiation
delivery has outstripped our capability to delineate the ICRU
volumes with precision and consistency.
 To consider uncertainties in daily practice will undermine the
treatment and ultimately will lead to an undesirable shift in the
balance between tumour control and normal tissue morbidity.
 Future improvements in medical imaging such as functional PET ,
SPECT and their incorporation into the planning process will
contribute to delineation of the GTV for ill-defined tumours.

17. THANK YOU