Variation in the Definition of Clinical Target Volumes for Pelvic Node Conformal Radiation Therapy o

1
Variation in the Definition of Clinical Target
Volumes for Pelvic Node Conformal Radiation
Therapy of Prostate Cancer
C Lawton1, J Michalski2, I El-Naqa2, D Kuban3, RW
Lee4, S Rosenthal5, A Zietman6, H Sandler7, M
Roach8
1 Medical College of Wisconsin, 2 Washington
University St. Louis, MO, 3MD Anderson Cancer
Center Houston, TX, 4Duke University, Durham, NC,
5University of California Sacramento, CA,
6Massachucetts General Hospital, Boston MA,
7University of Michigan Ann Arbor, MI, 8
University of California San Francisco, CA
PURPOSE
RESULTS

• CONCLUSIONS
• Significant disagreement exists in the definition
  of the CTV for pelvic nodal radiation therapy
  amongst GU radiation oncology specialists. A
  consensus for future trials employing conformal
  or IMRT techniques needs to be developed so as to
  accurately assess the merit and safety of such
  treatment.
• A consensus meeting was held on October 3, 2007
  which is resulting in a manuscript and CT images
  of consensus on pelvic lymph node volumes for
  appropriate radiation therapy treatment of high
  risk adenocarcinoma of the prostate.

Pelvic nodal radiation therapy may improve the
outcome in patients with high risk of nodal
metastases and is a requirement of many RTOG
protocols including the current 05-21. With the
advent of IMRT, the question of target volume
becomes paramount. We conducted a comparative
study of pelvic nodal clinical target volumes
(CTV) definitions by multiple GU radiation
oncology specialists.
Significant variation in the definition of the
iliac and presacral CTVs were seen amongst
physicians. The minimum, maximum, mean, (SD)
iliac volumes (cc) were 81.8, 876.6, 337.6 203
for case 1 and 60.3, 627.7, 251.8 159. 3 for
case 2. The volume of 100 agreement was 30.6
and 17.4 for case 1 and 2 and the volume of the
union of all contours was 1012.0 and 807.4 for
case 1 and 2 respectively. The overall agreement
was judged to be moderate in both cases kappa
0.53 (plt0.0001) and kappa 0.48 (plt0.0001)
respectively as shown below. The estimated
experts sensitivities and specificities were
0.63 and 0.99 0.03 for case 1 and 0.59
0.21 and 0.99 0.02 for case 2 indicating higher
agreement levels with increased volumes. The
minimum, maximum, mean (SD) presacral volumes
(cc) were 24.3, 157.3, 63.9 38.2 for case 1 and
26.6, 98.8 55.6 24.1 for case 2. There was no
volume of 100 agreement for either of the two
presacral volumes. These variations were
confirmed in the responses to the associated
questionnaire. For example the superior limit
of the nodal volume ranged from the L4/5
interspace to the bottom of the SI joints, with
only half of the physicians requiring treatment
of the presacral lymph nodes.
METHODS AND MATERIALS

• DICOM contrast enhanced pelvic CT scans from two
  men referred for definitive treatment were
  distributed to eleven RTOG GU radiation
  oncologists with instructions to define CTVs for
  the iliac and pre-sacral lymph node regions. The
  CT data with contours was then returned for
  comparative data analysis. In addition, a
  questionnaire was completed that described the
  physicians method for target volume definition.
  Statistical analysis of physicians agreement was
  measured using Kappa-statistics (Fleiss, 1981).
  Probabilistic estimate of true contour and
  variations in contouring performance sensitivity
  and specificity were analyzed using an iterative
  algorithm for simultaneous truth and performance
  level estimations (STAPLE) (Warfield 2004).

• REFERENCES
• Fleiss JL. Statistical Methods for Rates and
  Proportions, New York, Wiley, 1981
• Warfield SK, Zou KH, Wells WM. Simultaneous
  Truth and Performance Level Estimation (STAPLE)
  An Algorithm for the Validation of Image
  Segmentation. Medical Imaging, IEEE Transactions
  23903-921

This work supported by NIH U24 grant CA81647,
Advanced QA Center