RCR9: Refining proximal gastrointestinal tract radiotherapy tolerance parameters using published clinical data
1Department of Oncology, University of Oxford, Oxford, UK
The limited tolerance of the abdominal organs to radiotherapy results in significant toxicity for many patients and precludes delivery of sufficient dose for local control of some malignancies, such as pancreatic cancer. We conducted a systematic review to identify published datasets of paired toxicity outcomes and dose-volume parameters for the duodenum and small bowel in order to refine radiobiological models.
SCOPUS, EMBASE & MEDLINE databases were searched and 952 unique results screened to identify 29 publications reporting delivered dose-volumes and toxicity (23 for small-bowel and 6 for duodenum) incorporating outcomes for over 1500 patients. A cubic spline was fitted to dose-volume datapoints to reconstruct a continuous DVH and the Kutcher-Burman DVH reduction method used to derive effective volume: V(eff).
Published analyses report significant relationships between dose-volume and toxicity incidence for both duodenum and small-bowel. Low incidence of small-bowel toxicity relative to V(eff) was seen when no concomitant chemotherapy was given and vice versa. The highest incidence of toxicity was seen in papers reporting highest absolute volumes at low dose (V5Gy), and increases in both low and high dose volumes appear to correlate with increased incidence of toxicity while mid-range dose volumes did not. On pooled analysis, small-bowel mean effective volume, V(eff), was higher for patients suffering ?G3 (302.7 cc vs 128.1 cc; data from 203 patients) or ?G2 acute GI toxicity (243.8 cc vs 127.9 cc; 121 patients) than for those who did not.
There is strong evidence for a consistent radiotherapy dose-volume-toxicity relationship for the small-bowel modified by clinical parameters, such as chemotherapy. Analysis for the duodenum was hindered by sparse data and incomplete reporting of dose-volume parameters. Existing parameters appear to be overly conservative and revised toxicity thresholds and refined Normal Tissue Complication Probability parameters will be presented.