Influence of treatment technique on dose-volume histogram and normal tissue complication probability for small bowel and bladder. A prospective study using a 3-D planning system and a radiobiological model in patients receiving postoperative pelvic irradiation.
OBJECTIVE
A prospective study was undertaken to evaluate the influence of pelvic irradiation techniques on the dose-volume histograms of organs at risk and to analyze its possible clinical relevance using radiobiological models.


METHODS
For 20 patients receiving postoperative pelvic irradiation because of rectal cancer a 3-field technique (3-FT), a 4-field technique (4-FT) and an opposing field technique (OFT) were designed by a 3-D planning system (Helax, TMS). Dose-volume histograms (DVH) of small bowel, urinary bladder and planning target volume (PTV) were analyzed. The normal tissue complication probability (NTCP) was determined by the radiobiological model of Lyman and Kutcher using the tolerance data of Emami.


RESULTS
Median dose to the PTV did not differ between the 3 techniques (3-FT/4-FT/OFT: 99.2%/98.6%/98.1% of the prescribed dose; p > 0.05). Although the median dose to the urinary bladder was lower for the 3-FT than for the 4-FT (44.7% vs 60.3%; p < 0.001), there was no difference in the calculated NTCP (0.0% vs 0.0%; p > 0.05). Using multiple field techniques both the dose to and the treated volume of the urinary bladder were significantly lower than using the OFT. As a consequence of this the late NTCP of the bladder was higher for the OFT (5.46%). Although the median dose to the small bowel was lower for the 3-FT than for the 4-FT (30.8% vs 54.5%; p < 0.005), the fractional part of small bowel within the high-dose region (90% isodose) was higher for the 3-FT (10.6% vs 8.2%; p > 0.05). Thus the calculated NTCP was higher for the 3-FT (0.79 vs 0.44) than for 4-FT. For the OFT the median dose to small bowel was 69.9% and the small bowel volume within the high-dose region was 57.8% resulting in a late NTCP of 9.36% (OFT vs 3-FT/4-FT: p < 0.05).


CONCLUSIONS
Using multiple field techniques both the dose to the organs of risk and the fractional part of risk organs within the high-dose region can be reduced significantly. As a consequence of this a lower NTCP was calculated for the 3-FT and the 4-FT than for the OFT. Using the biological model a small, but significant difference between a 3-FT and a 4-FT was demonstrated in favor to the 4-FT.
Kölbl
O
O
Department for Radiotherapy, University of Würzburg, Germany. koelbl@strahlentherapie.uni-wuerzburg.de
Richter
S
S
Flentje
M
M
D000328:Adult; D000368:Aged; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007421:Intestine, Small / Q000528:radiation effects*; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000528:radiation effects*; D011182:Postoperative Care / Q000379:methods* / Q000706:statistics & numerical data; D011336:Probability; D011446:Prospective Studies; D011878:Radiotherapy / Q000009:adverse effects / Q000379:methods / Q000706:statistics & numerical data; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D018714:Radiotherapy, Adjuvant / Q000379:methods / Q000706:statistics & numerical data; D012004:Rectal Neoplasms / Q000532:radiotherapy / Q000601:surgery; D001743:Urinary Bladder / Q000528:radiation effects*