Small time.

In this study of nearly 500 patients receiving long-course chemoradiation for locally advanced rectal cancer, the volume of small bowel receiving 30 Gy (V30) was the single best predictor of late grade 2+ and 3+ toxicity. Importantly, “small bowel” was contoured as individual loops (not bowel bag) and excluded large bowel. The dose volume threshold with a <5% risk of late grade 2+ and grade 3+ GI toxicity was V30 < ~100cc and V30 < ~200 cc, respectively. | Abraham, Pract Radiat Oncol 2020


  1. The above study plays along very nicely with the meta-analysis of small bowel dose. However, the meta includes those who contours of small bowel as a bag or as loops. Note how V30 is nearly 100 cc! Coincidence? Likely not!

    -V10 < 240 cc appears to keep risk of acute toxicity to less than 20%.
    -Vdose from 5-40 Gy were significantly greater for patients with G3+ toxicity than those without.
    -Logistic regression of Vdose demonstrated V5, V10, V30-V45 to be predictive of G3+ toxicity, with V10 demonstrating the strongest association.
    -To maintain a projected risk of acute toxicity of 20% or less, the volume of small bowel irradiated should be kept within the following thresholds: V5 < 363 cc, V10 < 240 cc, **V30 < 92 cc**, V35 < 80 cc, V40 < 69 cc, and V45 < 44 cc.


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