The Different Volume Effects of Small-Bowel Toxicity During Pelvic Irradiation Between Gynecologic Patients With and Without Abdominal Surgery: A Prospective Study With Computed Tomography-Based Dosimetry

Purpose To evaluate the effect of abdominal surgery on the volume effects of small-bowel toxicity during whole-pelvic irradiation in patients with gynecologic malignancies. Methods and Materials From May 2003 through November 2006, 80 gynecologic patients without (Group I) or with (Group II) prior abdominal surgery were analyzed. We used a computed tomography (CT) planning system to measure the small-bowel volume and dosimetry. We acquired the range of small-bowel volume in 10% (V10) to 100% (V100) of dose, at 10% intervals. The onset and grade of diarrhea during whole-pelvic irradiation were recorded as small-bowel toxicity up to 39.6 Gy in 22 fractions. Results The volume effect of Grade 2–3 diarrhea existed from V10 to V100 in Group I patients and from V60 to V100 in Group II patients on univariate analyses. The V40 of Group I and the V100 of Group II achieved most statistical significance. The mean V40 was 281 ± 27 cm3 and 489 ± 34 cm3 ( p < 0.001) in Group I patients with Grade 0–1 and Grade 2–3 diarrhea, respectively. The corresponding mean V100 of Group II patients was 56 ± 14 cm3 and 132 ± 19 cm3 ( p = 0.003). Multivariate analyses revealed that V40 ( p = 0.001) and V100 ( p = 0.027) were independent factors for the development of Grade 2–3 diarrhea in Groups I and II, respectively. Conclusions Gynecologic patients without and with abdominal surgery have different volume effects on small-bowel toxicity during whole-pelvic irradiation. Low-dose volume can be used as a predictive index of Grade 2 or greater diarrhea in patients without abdominal surgery. Full-dose volume is more important than low-dose volume for Grade 2 or greater diarrhea in patients with abdominal surgery.