Effect of anatomic motion on proton therapy dose distributions in prostate cancer treatment.
OBJECTIVE
To determine the dosimetric impact of interfraction anatomic movements in prostate cancer patients receiving proton therapy.


METHODS
For each of the 10 patients studied, 8 computed tomography (CT) scans were selected from sets of daily setup CT images that were acquired from a cohort of prostate cancer patients. The images were acquired in the treatment room using the CT-on-rails system. First, standard proton therapy and intensity-modulated radiation therapy (IMRT) plans were designed for each patient using standard modality-specific methods. The images, the proton plan, and the IMRT plan were then aligned to the eight CT images based on skin marks. The doses were recalculated on these eight CT images using beam from the standard plans. Second, the plans were redesigned and evaluated assuming a smaller clinical target volume to planning target volume margin (3 mm). The images and the corresponding plans were then realigned based on the center of volume of the prostate. Dose distributions were evaluated using isodose displays, dose-volume histograms, and target coverage.


RESULTS
For the skin-marker alignment method, 4 of the 10 IMRT plans were deficient, whereas 3 of 10 proton plans were compromised. For the alignment method based on the center of volume of the prostate, only the proton plan for 1 patient was deficient, whereas 3 of the 10 IMRT plans were suboptimal.


CONCLUSIONS
A comparison of passively scattered proton therapy and highly conformal IMRT plans for prostate cancer revealed that the dosimetric impact of interfractional anatomic motions was similar for both modalities.
Zhang
Xiaodong
X
Department of Radiation Physics, The University of Texas M D Anderson Cancer Center, Houston, TX 77030, USA. xizhang@mdanderson.org
Dong
Lei
L
Lee
Andrew K
AK
Cox
James D
JD
Kuban
Deborah A
DA
Zhu
Ron X
RX
Wang
Xiaochun
X
Li
Yupeng
Y
Newhauser
Wayne D
WD
Gillin
Michael
M
Mohan
Radhe
R
D002138:Calibration; D005270:Femur Head / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D009068:Movement; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D001743:Urinary Bladder / Q000000981:diagnostic imaging; D011522:Protons
D011522:Protons