Pelvic Nodal Recurrence in Awkward Location

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Haybrant

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The non-standard cases continue to pour in. This one is a guy that had Gleason 8 prostate cancer underwent surgery in 2014 with persistent post op PSA of 0.4, then had RT to the prostate bed adjuvantly. PSA nadird at 0.6 ng/ml then started rising. He was put on some trial of abi + Lupron for a couple years. now he was taken off ADT as his PSA had been undetectable on this systemic therapy and PSA started going up fast, in November 2017 it was 0.4 now it is 1.5 ng/ml. The med onc got an auxumin PET and bone scan. There is a pelvic node in a pretty random location (attaching picture, see arrow). Does legit appear to be the only radiological area of concern. This area would have gotten RT before (im guessing something like 35-45 Gy, was done at diff hosptial). Would you offer RT for this lesion now and if so what would you give?

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I had a somewhat similar case recently with an Axumen scan showing a small proximal femur met (not seen on regular CT, MRI, or Bone scan); PSA around 1.7 just like your guy. I presented him at tumor board and talked to some academic guys who thought SBRT was reasonable so that's what I went for.

My patient had been on 2 years ADT with his salvage prostate bed XRT and had rising PSA about a year after coming off of ADT. He knew he was probably destined for more ADT but didn't want it long term right now. I ended up treating his bone met with SBRT with 2 months concurrent/adjuvant short term ADT. Too early to tell what his PSA is going to do, but I hope it gives him some time off of of ADT now.

For your case, I would probably offer treatment with this same goal. Probably can't get truly ablative doses of XRT in there (I think given prior XRT there's a myositis risk at that obturator internus if you're looking at like 40 Gy in 5 or something), but I think 30-36.25 Gy in 5 may be OK (Stanford/RTOG SBRT is 36.25 in 5, so some dose rationale there). Kind of wimpy I know (I'm sure braver people would go higher), but probably what I'd consider with hopes of temporary pause in PSA rise and given probably no survival benefit I'd hate to give him a major side effect.

Really it's a Wild West out there with what to do with these super sensitive Axumen/PSMA tests. Are we really changing the natural history of this of zapping these small mets or not? I'd like to think so, but maybe not.
 
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Any possibility of image misregistration? Obturator nodes should, naturally, be located medially to the muscle.
 
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Any possibility of image misregistration? Obturator nodes should, naturally, be located medially to the muscle.

Ct actually does show prominence there. I prob would get mri if He opted for treatment to be sure about it and to see if anything in the bed
 
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Any possibility of image misregistration? Obturator nodes should, naturally, be located medially to the muscle.

True. This could be the issue or it's a soft tissue met or a bone met at the anterior acetabulum. You're right though - that area is not even in the contouring atlas for a pelvic lymph node.

Or it's not a met at all. These scans are very sensitive but hard to know for sure specificity.
 
Uncommon to see a node past the obturator foramen. Obturator node with retrograde flow? Regardless, if you get the Auxumin scan and it's positive in this patient with PSA 1.5, i'd treat it, otherwise why get the scan. I think my main concern would be the femoral head (need to review previous plan and develop some form of EQD2 dose constraint) and some consideration of bladder, but otherwise blast away. I wouldn't overtly worry about myositis from reirradiation.

I think MRI prior to treatment is certainly reasonable. Just be careful about contrast as it's right where those hypogastric vessels would flow.

Certainly one of the weirdest places I've seen a prostate cancer go.

I would caution him of maybe a theoretical risk of lymphedema in weird places of his thigh, but don't have any real expectation of that. Unknown because this area is not routinely dissected or radiated for pretty much anything I can think of.
 
I'd treat that too. It seems to be some misplaced obturator node. SBRT?
 
I have seen gross nodes in this location in prostate and bladder cancer.
 
Uncommon to see a node past the obturator foramen. Obturator node with retrograde flow? Regardless, if you get the Auxumin scan and it's positive in this patient with PSA 1.5, i'd treat it, otherwise why get the scan. I think my main concern would be the femoral head (need to review previous plan and develop some form of EQD2 dose constraint) and some consideration of bladder, but otherwise blast away. I wouldn't overtly worry about myositis from reirradiation.

I think MRI prior to treatment is certainly reasonable. Just be careful about contrast as it's right where those hypogastric vessels would flow.

Certainly one of the weirdest places I've seen a prostate cancer go.

I would caution him of maybe a theoretical risk of lymphedema in weird places of his thigh, but don't have any real expectation of that. Unknown because this area is not routinely dissected or radiated for pretty much anything I can think of.


i also think the biggest concern is fem head/acetabulum. What is appropriate bone constraints anyway? Like we talk bout keeping the fem heads small volume to <45. But then people SBRT bone lesions 10 x 3 which is way higher. Where would you get a an appropriate fem head/acetabulum bone constraint for a situation like this? And what % would you put that risk at?

Im essentially telling this guy ok we can do this but your risk of fracture is 10-15+%(?) and we're not even going to ablative doses?
 
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Are people really SBRTing 10Gy x 3 to the femoral head? I wouldn't feel comfortable doing that. I'd do a lit search and see if hypofractionated RT dose constraints to femoral head have been published. Otherwise, I'd convert to EQD2 45 and try to keep it below that as much as possible.
 
I wouldn't do 3 fractions, that's probably risky.

Something like 6 x 6 Gy should work well, in my opinion.
If 60 /3 can heal cancer in the prostate, 36 / 6 sounds reasonable.
 
Are people really SBRTing 10Gy x 3 to the femoral head? I wouldn't feel comfortable doing that. I'd do a lit search and see if hypofractionated RT dose constraints to femoral head have been published. Otherwise, I'd convert to EQD2 45 and try to keep it below that as much as possible.

Actually im asking what would be the constraint for the pelvic bone that is adjacent to the lesion, that I think is at highest risk and would have gotten a higher dose than fem head in the past.
 
Actually im asking what would be the constraint for the pelvic bone that is adjacent to the lesion, that I think is at highest risk and would have gotten a higher dose than fem head in the past.

Not overtly familiar with pelvic bone (but not femoral head) constraints in terms of fracture. Maybe some pelvic re-RT series (MD Anderson with recurrent rectal/anal) mentioned something?
 
Not overtly familiar with pelvic bone (but not femoral head) constraints in terms of fracture. Maybe some pelvic re-RT series (MD Anderson with recurrent rectal/anal) mentioned something?

not necessarily pelvic bone, like bone in general is there a constraint. I think the fem head has distance here but the part of the ischium that is next to the lesion is at most risk. I suspect a fracture there could cause instability and long term issues?
 
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