The Dosimetric Analysis of Duodenal and Intestinal Toxicity After a Curative Dose Re-irradiation Using the...

This study aimed to examine the influence of dosimetric factors on gastrointestinal toxicity after radical re-irradiation for lymph node recurrence in the abdominopelvic region using a composite plan.

Between January 2008 and March 2017, 33 patients underwent radical re-irradiation for lymph node recurrence in the abdominopelvic region with a complete overlap with previous radiation therapy (RT) with the median prescription dose of the second RT of 71.7 Gy₁₀. Re-irradiation planning protocol for target volume and organs at risk (OARs) (duodenum, small and large intestines) was decided as follows: more than equal to 97% of the prescription dose was administered to the D95 (percentage of the minimum dose that covered 95% of the target volume) of planning target volume (PTV); minimal dose to the maximally irradiated doses delivered to 1cc [D1 cc] and 5cc [D5 cc] of OARs was set below 70 Gy₃ and 50 Gy₃, respectively; and D1 cc and D5 cc in the cumulative plans to OARs were 120 Gy₃ and 100 Gy₃. Kaplan-Meier analyses were performed to evaluate overall survival (OS) and univariate log-rank and multivariate Cox proportional hazards model analyses were performed to explore predictive factors. Using dose summation of the first and re-irradiation plans, we conducted a dosimetric analysis for grade ≥ 3 toxicities of the duodenum and intestine.

With a median follow-up of 18 months, the two-year OS rate was 45.5%. The number of RT fields (localized or multiple) was a significant predisposing factor for OS rate with a hazard ratio of 0.23 (95% confidence interval 0.07-0.73). The two-year OS of the patients with a localized RT field was 63.6% and 9.1% for multiple RT fields (p= 0.00007). Four patients experienced grade ≥3 gastrointestinal toxicity related to re-irradiation (4/33=12.1%). We could not find any predisposing dosimetric value in the comparisons with and without toxicity.

The dose constraints presented in this study are relatively low rates of toxicity, which may be useful when planning re-irradiation. Especially, for the patients who could be treated with localized RT field, radical re-irradiation with a high curative dose is a good option. No dosimetric predisposing factor was found for radical re-irradiation of abdominopelvic lesions in the composite plan.