Accuracy of proton beam range verification using post-treatment positron emission tomography/computed tomography as function of treatment site.
OBJECTIVE
For 23 patients, an off-line positron emission tomography scan and a computed tomography scan after proton radiotherapy was performed at the Massachusetts General Hospital to assess in vivo treatment verification. A well-balanced population of patients was investigated to assess the effect of the tumor location on the accuracy of the technique.


METHODS
Range verification was achieved by comparing the measured positron emission tomography activity distributions with the corresponding Monte Carlo-simulated distributions. Observed differences in the distal end of the activity distributions were analyzed as potential indicators for the range differences between the actual delivered and planned dose.


RESULTS
The average spatial agreement between the measured and simulated activity distribution was within ±3 mm, and the corresponding average absolute agreement was within ±45% (derived from gamma index analysis). The mean absolute range deviation at 93 randomly chosen positions in 17 treatment fields delivered to 11 patients was 3.6 mm. Characteristic differences in the agreement of the measured and simulated activity distribution for the different tumor/target sites were found. This resulted from the different effect of factors such as biologic washout effects, motion, or limitations in the Monte Carlo-simulated activity patterns.


CONCLUSIONS
We found that intracranial and cervical spine patients can greatly benefit from off-line positron emission tomography and computed tomography range verification. However, for the successful application of the method to patients with abdominopelvic tumors, major technological and methodologic improvements are needed. Among the intracranial and cervical spine target sites, patients with arteriovenous malformations or metal implants represent groups that could especially benefit from the approach.
Knopf
Antje-Christin
AC
Department of Radiation Oncology, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA. antje-christin.knopf@psi.ch
Parodi
Katia
K
Paganetti
Harald
H
Bortfeld
Thomas
T
Daartz
Juliane
J
Engelsman
Martijn
M
Liebsch
Norbert
N
Shih
Helen
H
D000008:Abdominal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D000465:Algorithms; D005134:Eye Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006801:Humans; D008297:Male; D009010:Monte Carlo Method; D009068:Movement; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D049268:Positron-Emission Tomography / Q000379:methods*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D061766:Proton Therapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012447:Sacrum; D013125:Spinal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D014057:Tomography, X-Ray Computed / Q000379:methods*; D011522:Protons
D011522:Protons