Purpose: To identify dosimetric factors correlated with acute gastrointestinal (GI) toxicity in gynecology patients undergoing intensity-modulated whole pelvic radiation therapy (IM-WPRT).
Material and methods: Fifty gynecology patients received IM-WPRT (45-1.8Gy/fraction) between 2/00 and 3/02. All patients were treated to a clinical target volume (CTV) consisting of the upper vagina, parametria, uterus, presacral region and pelvic lymph nodes. Grade 2 acute GI toxicity requiring frequent medications and grade 3-5 toxicities were designated as clinically significant and analyzed as a function of patient and dosimetric variables. The most significant volumetric factors were fit to a normal tissue complication probability (NTCP) function.
Results: Fourteen women (28%) developed clinically significant acute GI toxicity. None of the patient factors were correlated with acute GI toxicity. In addition, the volume of rectum receiving 25, 50, 75, 90, 100 and 110% of the prescription dose did not reach statistical significance. In contrast, a correlation was observed between the volume of small bowel (SB) irradiated and acute GI toxicity, particularly the SB volumes receiving 90 and 100% of the prescription dose (p=0.009 and p=0.009, respectively). Controlling for patient and other dosimetric factors, the SB volume receiving the 100% (Vol(SB,100)) of the prescription dose remained the sole significant factor on multivariate analysis (p=0.012). Subsequently, a NTCP curve, quantifying the risk of acute GI toxicity, was generated based on the Vol(SB,100).
Conclusions: The most significant factor correlated acute GI toxicity in gynecology patients undergoing IM-WPRT is Vol(SB,100).