Patient study of in vivo verification of beam delivery and range, using positron emission tomography and computed tomography imaging after proton therapy.
OBJECTIVE
To investigate the feasibility and value of positron emission tomography and computed tomography (PET/CT) for treatment verification after proton radiotherapy.


METHODS
This study included 9 patients with tumors in the cranial base, spine, orbit, and eye. Total doses of 1.8-3 GyE and 10 GyE (for an ocular melanoma) per fraction were delivered in 1 or 2 fields. Imaging was performed with a commercial PET/CT scanner for 30 min, starting within 20 min after treatment. The same treatment immobilization device was used during imaging for all but 2 patients. Measured PET/CT images were coregistered to the planning CT and compared with the corresponding PET expectation, obtained from CT-based Monte Carlo calculations complemented by functional information. For the ocular case, treatment position was approximately replicated, and spatial correlation was deduced from reference clips visible in both the planning radiographs and imaging CT. Here, the expected PET image was obtained from an analytical model.


RESULTS
Good spatial correlation and quantitative agreement within 30% were found between the measured and expected activity. For head-and-neck patients, the beam range could be verified with an accuracy of 1-2 mm in well-coregistered bony structures. Low spine and eye sites indicated the need for better fixation and coregistration methods. An analysis of activity decay revealed as tissue-effective half-lives of 800-1,150 s.


CONCLUSIONS
This study demonstrates the feasibility of postradiation PET/CT for in vivo treatment verification. It also indicates some technological and methodological improvements needed for optimal clinical application.
Parodi
Katia
K
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. Katia.Parodi@med.uni-heidelberg.de
Paganetti
Harald
H
Shih
Helen A
HA
Michaud
Susan
S
Loeffler
Jay S
JS
DeLaney
Thomas F
TF
Liebsch
Norbert J
NJ
Munzenrider
John E
JE
Fischman
Alan J
AJ
Knopf
Antje
A
Bortfeld
Thomas
T
D000465:Algorithms; D005240:Feasibility Studies; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D009369:Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*; D049268:Positron-Emission Tomography / Q000379:methods*; D061766:Proton Therapy; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*; D011522:Protons
D011522:Protons