Position Corrections During Tracking with the Calypso System During External Radiation Therapy Deliv

1
Position Corrections During Tracking with the
Calypso System During External Radiation Therapy
Delivery in Patients with Localized Prostate
Cancer
T Willoughby1, P. Kupelian1, A. Mahadevan2, C.
Enke3, G. Weinstein4, D. Beyer 5 , M L Levine6
1M. D. Anderson Cancer Center Orlando, Orlando,
FL, 2The Cleveland Clinic, Cleveland, OH,
3Nebraska Medical Center, Omaha, NE, 4Sharp
Memorial Hospital, San Diego, CA, 5Scottsdale
Healthcare/Arizona Oncology Services, Scottsdale,
AZ, 6Calypso Medical Technologies, Inc.,
Seattle, WA
Materials and Methods
Introduction The Calypso 4D Localization System
(Calypso System, Calypso Medical, Seattle, WA)
is a patient positioning device to be used as an
adjunct for radiation therapy. The Calypso
System includes implanted markers (Beacon
transponders) and external electronics consisting
of a movable console and electromagnetic array,
user interface, infrared cameras, and tracking
station. The external electronics continuously
localize the implanted transponders using
electromagnetic signals. See Fig 1 2 This
system was used for treatment positioning for
patients with prostate cancer.
Method and Materials The Calypso System was
used to position and continuously track 35
patients participated in a trial for prostate
cancer radiation therapy positioned using this
system. During the tracking session The use of
the system was analyzed retrospectively to
evaluate the usefulness of the system in
incorporating changes to radiation therapy based
on tracking information. A total of 1157
sessions were available for analysis (average 33
per patient). Following individual institutional
preferences, 4 different responses were observed
for patients whose target tracking exceeded
either the 3mm or 5mm limit (institutionally
dependant). These responses were as follows 1.)
Do nothing, 2.) Delay initiation of radiation
portal until target come back to within limits.
3.) Realign patient between radiation portals.
4.) Stop Radiation, wait or realign as necessary
to be within limits.
Fig. 1. Plain X-ray and CT showing the implanted
transponders.
Fig. 2. Calypso system with Beacon transponder
and cart holding the detector array.
Results
Results Target motion exceeded tracking limits
(either 3 mm or 5 mm) at some point during
radiation therapy in 34 of 35 patients. This
occurred during 31 (362/1157) of all fractions
ranging from 0 to 85 of fractions for individual
patients. In 131 of the 362 fractions that
exceeded tracking limit, some form of
intervention occurred The following
interventions occurred 1) the radiation
delivery was stopped during actual delivery in
0.4 of fractions (max 7 of fractions for
individual patient), 2) the actual radiation
delivery was delayed in 2.7 of fractions waiting
for a spontaneous resolution of the prostate
gland motion or drift (max 18 in individual
patients) 3) the patient was realigned in 8.2
of all fractions (max 50 in individual
patients). Fig. 1A shows a real-time track of the
prostate gland during which the prostate gland
gradually drifted out of position no correction
was made during that session. Fig. 1B is from a
session during which the prostate did drift twice
by gt5 mm the patient was repositioned twice by
adjusting the treatment couch using the Calypso
system. As seen by comparing Fig. 3A versus Fig.
3B, two correction procedures added only 2
minutes to the entire treatment period
(approximately 9 versus 11 minutes).
Conclusion Different therapeutic interventions
can be implemented now that the motion can be
observed and quantified during the actual
delivery of radiotherapy with the patient in the
treatment position. Position correction
strategies would include options such as
interrupting treatment if target is off-line,
delaying the radiation delivery till target is
on-line, with or without patient realignment.
Using electromagnetic signals from implanted
transponders within the prostate gland, these
corrections can be rapidly and accurately
performed.