Influence of organ motion on conformal vs. intensity-modulated pelvic radiotherapy for prostate cancer.
OBJECTIVE
To compare an intensity-modulated radiotherapy (IMRT) planning approach for prostate pelvic RT with a conformal RT (CRT) approach taking into account the influence of organ-at-risk (OAR) motion.


METHODS
A total of 20 male patients, each with one planning computed tomography scan and five to eight treatment computed tomography scans, were used for simulation of IMRT and CRT for delivery of a prescribed dose of 50 Gy to the prostate, seminal vesicles, and pelvic lymph nodes. Planning was done in Eclipse without correcting for OAR motion. Evaluation was performed using the CRT and IMRT dose matrices and the planning and treatment OAR outlines. The generalized equivalent uniform dose (gEUD) was calculated for 894 OAR volumes using a volume-effect parameter of 4, 12, and 8 for bowel, rectum and bladder, respectively. For the bowel, the gEUD was normalized to a reference volume of 200 cm(3). For each patient and each OAR, an average of the treatment gEUDs (gEUD(treat)) was calculated for CRT and IMRT. The paired t test was used to compare IMRT with CRT and gEUD(treat) with gEUD(plan).


RESULTS
The mean gEUD(treat) was reduced from 43 to 40 Gy, 47 to 46 Gy, and 48 to 45 Gy with IMRT for the bowel, rectum, and bladder, respectively (p < 0.001). Differences between the gEUD(plan) and gEUD(treat) were not significant (p > 0.05) for any OAR but was >6% for the bowel in 6 of 20 patients.


CONCLUSIONS
Intensity-modulated RT reduced the bowel, rectum, and bladder gEUDs also under influence of OAR motion. Neither CRT nor IMRT was robust against bowel motion, but IMRT was not less robust than CRT.
Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway. liv.bolstad.hysing@gmail.com
Liv Bolstad
LB
Hysing
Tone Nybø
TN
Skorpen
Markus
M
Alber
Lise Bauge
LB
Fjellsbø
Svein Inge
SI
Helle
Ludvig Paul
LP
Muren
D000368:Aged; D000369:Aged, 80 and over; D002295:Carcinoma, Transitional Cell / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D007422:Intestines / Q000528:radiation effects; D008198:Lymph Nodes; D015182:Lymphatic Irradiation; D008297:Male; D008875:Middle Aged; D009068:Movement; D010388:Pelvis; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011832:Radiation Injuries / Q000517:prevention & control; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000528:radiation effects; D012669:Seminal Vesicles / Q000528:radiation effects; D001743:Urinary Bladder / Q000528:radiation effects