For gyn cancers receiving chemoradiation, how high can you boost grossly positive nodes with SIB if not near bowel?

I typically will give a simultaneous integrated boost (SIB) of 60 Gy in 30 fractions to the pelvic and para-aortic nodal CTV, which is the PET positive GTV plus a 3 mm margin. If possible I will boost the GTV of larger gross nodes (>1 cm) to 66 Gy (2.2 Gy/fx) with no margin, if constraints can be met.

At the same time, I give 51 Gy in 30 fractions (1.7 Gy/fx) to the grossly normal para-aortic and pelvic nodal volumes. 51 Gy in 30 is a little hotter than 45 Gy in 25 fractions but seems generally well tolerated in the IMRT era. Nearly this same regimen has been published in the 2008 Red Journal by Dr. Perry Grigsby's team at University of Washington. In their series, less than 1% of bowel received 60 Gy and less than 10% received 50 Gy.

Invest...

I have not attempted to push the dose further than it is written in EMBRACE II. Keep in mind that this is at a higher dose per fractionation (as high as 2.3Gy per fraction) than we typically use. Assuming an alpha/beta of 10 for SCC this calculates to a BED ~ 58Gy for the diseased node, but a higher BED for any nearby GI OARs which would have a lower alpha/beta value. In my experience, para-aortic nodes often reside near bowel loops, especially the higher PA nodes that can abut the duodenum. In addition, for cervical cancer, I am more concerned for failures outside of the radiation field than I am outside of the region of treatment, especially the boost region.

EQ2 calculation doesn’t take time factor into account and also contributions from brachytherapy for pelvic nodes.

I will usually go for 55-60 Gy in 25 fractions based on location with 45 in 25 to the remainder of elective nodal regions. GTV + 5mm to PTV. Goal is to keep the treatment isotoxic, however, so will turn down the dose at interface of bowel, always, and bladder/rectum as necessary.

While Dr. @Dr. First Last is correct that most of the time the concern is about progression outside of the field, I think we do underestimate how much our regions of nodal boost fail, and try to not only go to at least 55/25 to all gross nodes, but will attempt higher as feasible.

A reminder that there is a lot we don't know about ureteral stenosis dose tolerance in regards to dose escalation, which can be an extra point of concern for lymph nodes in close proximit...