Image guidance based on prostate position for prostate cancer proton therapy.
OBJECTIVE
To determine the target coverage for proton therapy with and without image guidance and daily prebeam reorientation.


METHODS
A total of 207 prostate positions were analyzed for 9 prostate cancer patients treated using our low-risk prostate proton therapy protocol (University of Florida Proton Therapy Institute 001). The planning target volume was defined as the prostate plus a 5-mm axial and 8-mm superoinferior extension. The prostate was repositioned using 5- and 10-mm shifts (anteriorly, inferiorly, posteriorly, and superiorly) and for Points A-D using a combination of 10-mm multidimensional movements (anteriorly or inferiorly; posteriorly or superiorly; and left or right). The beams were then realigned using the new prostate position. The prescription dose was 78 Gray equivalent (GE) to 95% of the planning target volume.


RESULTS
For small movements in the anterior, inferior, and posterior directions within the planning target volume (< or =5 mm), treatment realignment demonstrated small, but significant, improvements in the clinical target volume (CTV) coverage to the prescribed dose (78 GE). The anterior and posterior shifts also significantly increased the minimal CTV dose (Delta +1.59 GE). For prostate 10-mm movements in the inferior, posterior, and superior directions, the beam realignment produced larger and significant improvements for both the CTV V(78) (Delta +6.4%) and the CTV minimal dose (Delta +8.22 GE). For the compounded 10-mm multidimensional shifts, realignment significantly improved the CTV V(78) (Delta +11.8%) and CTV minimal dose (Delta +23.6 GE). After realignment, the CTV minimal dose was >76.6 GE (>98%) for all points (A-D).


CONCLUSIONS
Proton beam realignment after target shift will enhance CTV coverage for different prostate positions.
Vargas
Carlos
C
Department of Radiation Oncology, University of Florida Proton Therapy Institute, 2015 N. Jefferson Street, Jacksonville, FL 32206, USA. c2002@ufl.edu
Wagner
Marcus
M
Indelicato
Daniel
D
Fryer
Amber
A
Horne
David
D
Chellini
Angela
A
McKenzie
Craig
C
Lawlor
Paula
P
Mahajan
Chaitali
C
Li
Zuofeng
Z
Lin
Liyong
L
Keole
Sameer
S
D005240:Feasibility Studies; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000473:pathology; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D047368:Tumor Burden; D011522:Protons
D011522:Protons