Physiologic reactions after proton beam therapy in patients with prostate cancer: significance of urinary autoactivation.
OBJECTIVE
Proton therapy is a sophisticated treatment modality for prostate cancer. We investigated how physiologic factors affected the distribution of autoactivation as detected by positron emission tomography (PET) after proton beam therapy.


METHODS
Autoactivation was evaluated in 59 patients treated with a 210-MeV proton beam. Data acquisition for autoactivation by PET started 5 minutes after proton irradiation to assess activation. In the first 29 patients, five regions of interest were evaluated: planning target volume (PTV) center, urinary bladder inside the PTV, urinary bladder outside the PTV, rectum (outside the PTV), and contralateral femoral bone head (outside the PTV). In the remaining 30 patients, urine activity was measured directly. In a phantom study autoactivation and its diffusion after proton beam irradiation were evaluated with water or an ice block.


RESULTS
Mean activities calculated by use of PET were 629.3 Bq in the PTV center, 555.6 Bq in the urinary bladder inside the PTV, 332.5 Bq in the urinary bladder outside the PTV, 88.4 Bq in the rectum, and 23.7 Bq in the femoral bone head (p < 0.001). Mean urine activity was 679.4 Bq, recorded 10 minutes after therapy completion, and the half-life for urine autoactivation was 4.5 minutes.


CONCLUSIONS
Urine is a major diffusion mediator of autoactivation after proton beam therapy. Our results indicate that physiologic factors can influence PET images of autoactivation in the context of proton beam therapy verification.
Shimizu
Masakazu
M
Department of Radiation Technology, Hyogo Ion Beam Medical Center, Tatsuno, Japan.
Sasaki
Ryohei
R
Miyawaki
Daisuke
D
Nishimura
Hideki
H
Demizu
Yusuke
Y
Akagi
Takashi
T
Suga
Daisaku
D
Sakamoto
Hidenobu
H
Murakami
Masao
M
Sugimura
Kazuro
K
Hishikawa
Yoshio
Y
D000368:Aged; D000369:Aged, 80 and over; D005270:Femur Head / Q000000981:diagnostic imaging; D006207:Half-Life; D006801:Humans; D008297:Male; D008875:Middle Aged; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D061766:Proton Therapy; D011874:Radiometry / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012007:Rectum / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden; D001743:Urinary Bladder / Q000000981:diagnostic imaging; D014556:Urine; D011522:Protons
D011522:Protons