Reduction of small and large bowel irradiation using an optimized intensity-modulated pelvic radiotherapy technique in patients with prostate cancer.
OBJECTIVE
To investigate the role of intensity-modulated radiation therapy (IMRT) to irradiate the prostate gland and pelvic lymph nodes while sparing critical pelvic organs, and to optimize the number of beams required.


METHODS
Target, small bowel, colon, rectum, and bladder were outlined on CT planning scans of 10 men with prostate cancer. Optimized conventional (RT) and 3-dimensional conformal radiotherapy (3D-CRT) plans were created and compared to inverse-planned IMRT dose distributions using dose-volume histograms. Optimization of beam number was undertaken for the IMRT plans.


RESULTS
With RT the mean percentage volume of small bowel and colon receiving >45 Gy was 21.4 +/- 5.4%. For 3D-CRT it was 18.3 +/- 7.7% (p = 0.0043) and for 9-field IMRT it was 5.3 +/- 1.8% (p < 0.001 compared to 3D-CRT). For 7, 5, and 3 IMRT fields, it was 6.4 +/- 2.9%, 7.2 +/- 2.8%, and 8.4 +/- 3.8% (all p < 0.001 compared to 3D-CRT). The rectal volume irradiated >45 Gy was reduced from 50.5 +/- 16.3% (3D-CRT) to 5.8 +/- 2.1% by 9-field IMRT (p < 0. 001) and bladder from 52.2 +/- 12.8% to 7 +/- 2.8% (p < 0.001). Similar benefits were maintained for 7, 5, and 3 IMRT fields.


CONCLUSIONS
The reduction in critical pelvic organ irradiation seen with IMRT may reduce side effects in patients, and allow modest dose escalation within acceptable complication rates. These reductions were maintained with 3-5 IMRT field plans which potentially allow less complex delivery techniques and shorter delivery times.
Nutting
C M
CM
Academic Department of Radiotherapy, Institute of Cancer Research and The Royal Marsden NHS Trust, Sutton, Surrey, UK. chrisnutting@cs.com
Convery
D J
DJ
Cosgrove
V P
VP
Rowbottom
C
C
Padhani
A R
AR
Webb
S
S
Dearnaley
D P
DP
D003106:Colon; D006801:Humans; D007420:Intestine, Large; D007421:Intestine, Small; D008297:Male; D010388:Pelvis; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011835:Radiation Protection / Q000379:methods*; D011878:Radiotherapy / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D012007:Rectum; D001743:Urinary Bladder