Proton therapy coverage for prostate cancer treatment.
OBJECTIVE
To determine the impact of prostate motion on dose coverage in proton therapy.


METHODS
A total of 120 prostate positions were analyzed on 10 treatment plans for 10 prostate patients treated using our low-risk proton therapy prostate protocol (University of Florida Proton Therapy Institute 001). Computed tomography and magnetic resonance imaging T(2)-weighted turbo spin-echo scans were registered for all cases. The planning target volume included the prostate with a 5-mm axial and 8-mm superoinferior expansion. The prostate was repositioned using 5- and 10-mm one-dimensional vectors and 10-mm multidimensional vectors (Points A-D). The beam was realigned for the 5- and 10-mm displacements. The prescription dose was 78 Gy equivalent (GE).


RESULTS
The mean percentage of rectum receiving 70 Gy (V(70)) was 7.9%, the bladder V(70) was 14.0%, and the femoral head/neck V(50) was 0.1%, and the mean pelvic dose was 4.6 GE. The percentage of prostate receiving 78 Gy (V(78)) with the 5-mm movements changed by -0.2% (range, 0.006-0.5%, p > 0.7). However, the prostate V(78) after a 10-mm displacement changed significantly (p < 0.003) with different movements: 3.4% (superior), -5.6% (inferior), and -10.2% (posterior). The corresponding minimal doses were also reduced: 4.5 GE, -4.7 GE, and -11.7 GE (p < or = 0.003). For displacement points A-D, the clinical target volume V(78) coverage had a large and significant reduction of 17.4% (range, 13.5-17.4%, p < 0.001) in V(78) coverage of the clinical target volume. The minimal prostate dose was reduced 33% (25.8 GE), on average, for Points A-D. The prostate minimal dose improved from 69.3 GE to 78.2 GE (p < 0.001) with realignment for 10-mm movements.


CONCLUSIONS
The good dose coverage and low normal doses achieved for the initial plan was maintained with movements of < or = 5 mm. Beam realignment improved coverage for 10-mm displacements.
Vargas
Carlos
C
University of Florida Proton Therapy Institute, Jacksonville, FL 32206, USA. c2002@ufl.edu
Wagner
Marcus
M
Mahajan
Chaitali
C
Indelicato
Daniel
D
Fryer
Amber
A
Falchook
Aaron
A
Horne
David
D
Chellini
Angela
A
McKenzie
Craig
C
Lawlor
Paula
P
Li
Zuofeng
Z
Lin
Liyong
L
Keole
Sameer
S
D000368:Aged; D000369:Aged, 80 and over; D005269:Femur; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009068:Movement; D010388:Pelvis; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D012007:Rectum; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden; D001743:Urinary Bladder; D011522:Protons
D011522:Protons