Dosimetric changes resulting from patient rotational setup errors in proton therapy prostate plans.
OBJECTIVE
To evaluate the dose changes to the target and critical structures from rotational setup errors in prostate cancer patients treated with proton therapy.


METHODS
A total of 70 plans were analyzed for 10 patients treated with parallel-opposed proton beams to a dose of 7,600 (60)Co-cGy-equivalent (CcGE) in 200 CcGE fractions to the clinical target volume (i.e., prostate and proximal seminal vesicles). Rotational setup errors of +3 degrees , -3 degrees , +5 degrees , and -5 degrees (to simulate pelvic tilt) were generated by adjusting the gantry. Horizontal couch shifts of +3 degrees and -3 degrees (to simulate longitudinal setup variability) were also generated. Verification plans were recomputed, keeping the same treatment parameters as the control.


RESULTS
All changes shown are for 38 fractions. The mean clinical target volume dose was 7,780 CcGE. The mean change in the clinical target volume dose in the worse case scenario for all shifts was 2 CcGE (absolute range in worst case scenario, 7,729-7,848 CcGE). The mean changes in the critical organ dose in the worst case scenario was 6 CcGE (bladder), 18 CcGE (rectum), 36 CcGE (anterior rectal wall), and 141 CcGE (femoral heads) for all plans. In general, the percentage of change in the worse case scenario for all shifts to the critical structures was <5%. Deviations in the absolute percentage of volume of organ receiving 45 and 70 Gy for the bladder and rectum were <2% for all plans.


CONCLUSIONS
Patient rotational movements of 3 degrees and 5 degrees and horizontal couch shifts of 3 degrees in prostate proton planning did not confer clinically significant dose changes to the target volumes or critical structures.
Sejpal
Samir V
SV
Division of Radiation Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030-4009, USA.
Amos
Richard A
RA
Bluett
Jaques B
JB
Levy
Lawrence B
LB
Kudchadker
Rajat J
RJ
Johnson
Jennifer
J
Choi
Seungtaek
S
Lee
Andrew K
AK
D005270:Femur Head / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging / Q000528:radiation effects; D012399:Rotation; D012669:Seminal Vesicles / Q000528:radiation effects; D036542:Tomography, Spiral Computed; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000528:radiation effects; D011522:Protons
D011522:Protons