Scientific poster

1
4D PET/CT - Early Observations on Integration and
Impact in Radiation Therapy Planning for Lung
Cancer
Allan Caggiano, M.S. , Charles Vialotti, M.D.
Department of Radiation Oncology, Holy Name
Hospital, Teaneck, New Jersey Jacqueline
Brunetti, M.D. Department of Radiology, Holy
Name Hospital, Teaneck, New Jersey
Purpose/Objective To investigate the feasibility
and benefits/drawbacks of utilizing 4D PET/CT for
the purpose of treatment planning in Radiation
Therapy and present this time-sequenced
structural/functional data visually to clinicians
for incorporation into the treatment planning
process.
Two representative cases of patients with NSCL
cancer with well-correlated respiratory patterns
are shown in the time sequences below
The breakdown of the motion analysis of the tumor
centroids are given in the table below
Holy Name 4D PET/CT Imaging Protocol Our imaging
protocol was broken into two separate sessions
due to the large amount of data that was required
for our IRB protocol comparison of gated and
ungated imaging. The protocol was as
follows Day 1 Part 1 RT Sim 1. Creation of
immobilization device (wingboard with
Alpha-cradle a requirement). Must fit through
PET bore! 2. Identification of patient
isocenter. 3. Breathing assessment and training
session 4. Fluoroscopy assessment of motion. 5.
Establish baseline breathing pattern and
intra-fraction reproducibility. 6. Selection of
candidates for gated RT. 7. Simulator films
taken at middle of gating interval (50 phase).
These films will be compared to daily port
films. Day 2 Ungated PET/CT 1. Whole body
PET/CT (15-20 mCi FDG/60 min uptake). 2. 1-2 bed
position ungated PET/CT RT Sim (for study
comparison to gated imaging as per IRB
protocol). Gated PET/CT 3. Passive reflective
marker is placed on abdomen of patient. 4.
Re-validate baseline breathing pattern and assess
inter-fraction reproducibility. 5. 4D PET
(Prospective gating) A. 1 FOV 2D acquisition
B. Data acquisition is triggered by RPM C.
Acquired during multiple RPM coached-breathing
cycles (5-8 minute duration) D. 6.5 sec
breathing cycle 6. 4D CT (Retrospective
gating) A. Area scanned larger than gated 4D
PET for full lung volumes. B. Cine
acquisition/4 slices per revolution C. Acquired
during multiple RPM coached-breathing cycles
(4-5 minute duration) D. RPM breathing traces
saved to floppy and ftpd to Advantage
Workstation.
Materials and methods We have accrued eighteen
patients into an IRB-approved study that
investigates the Varian RPM respiratory gating
system on a GE Discovery LS PET/CT scanner. A
simulation protocol was created to compare the
differences in ungated PET/CT versus gated PET/CT
(4D). Both sets of CT and PET images were
utilized on a Varian Eclipse treatment planning
computer and incorporated into the treatment
planning for these patients. The tumor motion
during all phases of respiration were assessed
and broken into three groups high (gt2.0 cm),
medium (1.0-2.0 cm), and low (lt1.0 cm). New
methods of display of these gated images on our
treatment planning system were investigated for
clinical use.
Pre-RT, SUV 16.0
Post-RT Post-RT (7 months), SUV 4.1
Fig. 1. Picture of a volunteer with an abdominal
marker block in position on the GE Discovery LS
PET/CT scanner and the Varian RPM gating system
attached to the treatment table.
Fig. 3. An example of a lung patient with 4
discrete activity areas on PET/CT. The maximum
motion ranged from 1 to 2 cm.
Fig. 5. Comparison of initial PET from PET/CT
prior to radiotherapy to the PET scan at the
6-month follow-up for a lung patient treated with
gated radiotherapy using the RPM gating system.
The tumor centroid motion for this case was 3.0
cm.
Conclusions 4D PET/CT is a useful clinical
assessment tool for determining BTV/GTV and/or
organ motion in properly selected radiation
therapy patients, especially when used in
conjunction with dynamic displays on treatment
planning computers. Breathing reproducibility is
the most important factor for respiratory gating.
Breath synchronization methods, such as audio and
video prompting, are important methods of
ensuring this reproducibility of both amplitude
and phase. In patients with large tumor motion,
large uncertainties in tumor localization can
occur on standard ungated CT scans. The range of
tumor centroid motion varied from 0 to 3.0 cm in
our current series of patients.
An example of a NSCLC patient imaged with gated
PET/CT that was overlaid with the dose
distribution from the treatment planning system.
Note the excursion of tumor close to the inferior
and superior edges of the field. The MLC blocking
used for this case was based the ungated PET/CT
acquisition.
Fig. 2a. An illustration of retrospective CT
gating on the GE PET/CT scanner. In this type of
gating, the sorting of the respiratory phases
does not occur during image acquisition, but is
performed separately after the imaging study is
completed. This type of gating is prone to errors
caused due to variations in the patients
respiratory motion.
Literature cited S. A. Nehmeh, Y. E. Erdi, G.
Mageras, T. Pan, E. Yorke, H. Mostavi, D. Hurley,
O. Squire, J. L. Ham, H. Schroeder, S. M. Larson,
K. E. Rosenzweig, Improved accuracy in image
co-registration and tumor quantitation of
pulmonary lesions of NSCL patients by respiratory
correlated acquisition on PET/CT, J. Nucl. Med.
44, No. 124 (2003).
Results 15 of the 18 patients (83.3) were able
to fully complete the imaging protocol. All ten
phases of the gated PET and CT were successfully
registered to each other and presented to
clinicians for evaluation of respiratory motion
in the form of fused PET/CT movie loops, which
the clinicians thought were highly useful in
determining whether patients were candidates for
respiratory gating.
Acknowledgments We thank Cynthia Mento for her
help with the PET/CT acquisitions. Some of the
software used for this presentation was provided
by GE Medical Systems, and Varian Medical
Systems.
Fig. 4. An example of a lung patient with a large
primary lesion plus nodal chain activity. The
maximum motion was 3.0 cm.
For further information Please contact
caggiano_at_holyname.org. An online version of
poster is available at the ASTRO electronic
poster website.
Fig. 2b. An illustration of prospective PET
gating on the GE PET/CT scanner. In this type of
gating, the sorting of the respiratory phases
occurs during image acquisition. This type of
gating is performed with a trigger generated from
the RPM system and the PET counts are deposited
in bins of a fixed time duration.