Maximum likelihood estimation of proton irradiated field and deposited dose distribution.
In proton therapy, it is important to evaluate the field irradiated with protons and the deposited dose distribution in a patient's body. Positron emitters generated through fragmentation reactions of target nuclei can be used for this purpose. By detecting the annihilation gamma rays from the positron emitters, the annihilation gamma ray distribution can be obtained which has information about the quantities essential to proton therapy. In this study, we performed irradiation experiments with mono-energetic proton beams of 160 MeV and the spread-out Bragg peak beams to three kinds of targets. The annihilation events were detected with a positron camera for 500 s after the irradiation and the annihilation gamma ray distributions were obtained. In order to evaluate the range and the position of distal and proximal edges of the SOBP, the maximum likelihood estimation (MLE) method was applied to the detected distributions. The evaluated values with the MLE method were compared with those estimated from the measured dose distributions. As a result, the ranges were determined with the difference between the MLE range and the experimental range less than 1.0 mm for all targets. For the SOBP beams, the positions of distal edges were determined with the difference less than 1.0 mm. On the other hand, the difference amounted to 7.9 mm for proximal edges.
Inaniwa
Taku
T
Department of Energy Sciences, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8502, Japan.
Kohno
Toshiyuki
T
Yamagata
Fumiko
F
Tomitani
Takehiro
T
Sato
Shinji
S
Kanazawa
Mitsutaka
M
Kanai
Tatsuaki
T
Urakabe
Eriko
E
D000465:Algorithms; D004583:Electrons; D005720:Gamma Rays / Q000627:therapeutic use; D006801:Humans; D010315:Particle Accelerators; D049268:Positron-Emission Tomography / Q000379:methods; D011522:Protons; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*
D011522:Protons