Visceral Adipose Volume as a Predictor for Acute Bowel Toxicity in Patients Receiving Adjuvant Intensity-Modulated Radiation Therapy for Cervical or Endometrial Cancer

Abstract

Relative to 3D conformal radiation therapy (RT), intensity modulated radiation therapy (IMRT) is associated with decreased acute bowel toxicity during adjuvant RT for gynecologic cancers. Delineating the peritoneal space as a 'bowel bag' is a common method to assess RT dose and volume parameters during treatment planning. However, there is a relative lack of evidence-based bowel bag dose/volume constraints that can be used to guide clinicians. Previously, we described a method to normalize dose/volume measures based on the proportion of adipose tissue within the bowel bag contour and demonstrated this technique more closely correlates with acute toxicity than standard measures. This work was criticized for including a heterogenous patient population of gastrointestinal and gynecologic cancer patients treated with definitive and adjuvant RT. Here, we report an updated analysis, limiting our patient population to those receiving adjuvant IMRT for gynecologic cancers.Eighteen consecutive patients treated with adjuvant pelvic +/- para-aortic IMRT following hysterectomy for a diagnosis of endometrial or cervical cancer at a single academic medical center were included. As previously described by Ganju et al, simulation CT scans were retrieved and the bowel bag was contoured per RTOG guidelines. Dosimetric data for V45 Gy (cc) and V40 Gy (%) was collected. Adipose tissue was auto-contoured using Hounsfield Unit thresholds. Visceral adipose ratio was defined as the volume of non-adipose tissue within the bowel bag divided by the total volume. This was multiplied by the above dosimetric variables to correct for uninvolved adipose tissue. Bowel function was assessed weekly during therapy using the Expanded Prostate Cancer Index Composite (EPIC) questionnaire. Baseline bowel scores were defined as those obtained at CT simulation or week 1 of therapy, and final scores were those occurring during week 4 of 5 of treatment. One-tailed spearman correlation coefficients were used to identify significant associations between acute bowel toxicity and bowel bag dose/volume measures.Eighteen patients met criteria for inclusion. Fifteen patients were treated for endometrial and three for cervical cancer. The median dose of radiation was 45 Gy. V40 Gy (%) and V45 Gy (cc) measures were not correlated with decline in EPIC bowel function, bother, or composite measures. However, adipose corrected V45 Gy(cc) showed significant correlation with bowel function decline (P = 0.04) and overall decline in bowel composite measure (P = 0.03).Adipose corrected bowel bag dose/volume measures (V45 Gy cc) may be used to predict acute bowel toxicity in patients receiving post-operative IMRT following a hysterectomy in endometrial and cervical cancers. Future studies will require validation in a larger patient population.D. Nganga: None. A. Hoover: None.