What are your constraints when treating an abdominal site with SBRT?

This includes duodenum, stomach, small bowel, colon, kidney, liver, etc.

1 Answer

Mednet MemberInvited Expert

Radiation Oncology · Brigham and Women's Hospital

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There are many published guidelines and no single "right" answer for dose constraints when treating patients with abdominal SBRT. Guidelines should also always be taken with a grain of salt, as there may be relevant clinical factors for a specific patient that would make the general guidelines inappropriate. With those and other caveats in mind, here are the constraints we are currently using at my institution. Please note that these are always a work in progress, with continued adjustments as new data or guidelines become available.

We use the same constraints for all luminal structures in the GI tract, including the esophagus, stomach, duodenum, small and large bowel. When treating in five fractions, these are V33 < 0.5cc and V35 < 0.03 cc. In addition, we use an esophageal constraint of V19.5 < 5 cc.

Our heart constraint is V32 < 15cc and D0.035cc < 38 Gy.

For kidneys, we just set a mean dose below 1000 cGy.

There are a number of liver constraints. For patients with HCC, we follow the sliding scale used in Dr. @Dr. First Last's trial of Sorafenib +/- SBRT, RTOG/NRG 1112

Mean Liver Dose Prescription Dose If the Max Allowed MLD is Exceeded:

13 Gy 50 Gy Reduce to 45 Gy and re-evaluate

15 Gy 45 Gy Reduce to 40 Gy and re-evaluate

15 Gy 40 Gy Reduce to 35 Gy and re-evaluate

15.5 Gy 35 Gy Reduce to 30 Gy and re-evaluate

16 Gy 30 Gy Reduce to 27.5 Gy and re-evaluate

17 Gy 27.5 Gy Ineligible

(There are two entries for an MLD of 15 Gy reflecting different Liver Veff, which is more detailed than appropriate for this entry).

For non-HCC patients, we aim to spare 700 cc below 15 Gy in 3 fractions or 21 Gy in 5 fractions, and keep the mean liver dose below 15 Gy.

Our spinal canal constraints are V14.5 < 1.2cc, V23 < 0.35cc and D0.035cc < 30 Gy.