After external beam radiotherapy (ERTx) and intraluminal high-dose-rate brachytherapy (BRTx), 4 of 10 patients developed Grade 3 or 4 ulcers at the posterior wall of the duodenal bulb (PWDB) (compromised group); the remainder exhibited no duodenal complications (spared group) for 14 (range, 7–59) months after radiotherapy. The radiation exposure to the duodenal volume at risk (Vduod) in ERTx and BRTx was individually analyzed using dose–volume histograms in terms of the mean doses (the average dose of Vduod[Dave] and the median dose of Vduod [Dmedian]), dose covering 1 % or 5 % of Vduod (dose covering 1 % of the Vduod [D1] and dose covering 5 % of the Vduod [D5], respectively), and the Vduod receiving 100 % or 150 % of the prescribed radiation dose (V100 and V150, respectively) in ERTx (Dave, Dmedian, D5) and BRTx (Dave, D1, D5, V100, V150). Dave and D5 were converted to biologically effective doses (BEDs), and each corresponding values of ERTx and BRTx were summed presenting as BEDave_sum and BED5_sum.
The PWDB was consistently involved in 100 % of the prescription dose area in ERTx. The compromised group had smaller exposure doses without significant difference (SD). In BRTx, the PWDB was exposed to higher doses. The compromised group had larger dose exposures without SD and larger volume exposures (V100, V150) with SD in BRTx. The BEDave_sum and BED5_sum showed no difference between the groups.
Measuring the duodenal volume exposed to determine doses that exceed the prescription in BRTx may be useful for predicting intractable complications in the combined radiotherapy.