Re-irradiation of OARs

[Gfunk6]

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I was curious what you guys use as a model to quantitatively determine recovery of normal organs from XRT. Also, is there a time period long enough to say that an organ has effectively returned to a “radiation naive state?”

5, 10, 15, 20 years?

When I do this myself, there is a lot of hemming and hawing and obsessing over the composite plans.

 

[Mandelin Rain]

5-10% per year, up to a 50% discount.

This is based on next to nothing. Like much of radbio.

 

[RANDO_Phantom]

Never easy, and always have a gnawing feeling. For spinal cord, go-to reference to extrapolate from is KK Ang's paper from early 2000s (rhesus monkeys) --> substantial (60%) recovery of occult spinal cord injury from 44 Gy in 2-Gy fractions occurred within first 1-2 years.

 

[seper]

I presume no discount and counsel patients as such. I you re-irradiate in your practice routinely (helps a lot of patients), inevitably a catastrophic RT complication will occur. It helps to have everybody's expectations aligned.

 

[thecarbonionangle]

Never easy, and always have a gnawing feeling. For spinal cord, go-to reference to extrapolate from is KK Ang's paper from early 2000s (rhesus monkeys) --> substantial (60%) recovery of occult spinal cord injury from 44 Gy in 2-Gy fractions occurred within first 1-2 years.

Can you please post PMID for this reference? Thank you!

 

[RANDO_Phantom]

Can you please post PMID for this reference? Thank you!

There are antecedent ones from the late KK Ang, too, as his lab studied this extensively, but in residency always referred to this one.

Extent and kinetics of recovery of occult spinal cord injury. - PubMed - NCBI

 

[scarbrtj]

The monkey data showed the cord forgives more than dogma states, prob has higher alpha/beta than we think. Have re-irradiated several head/neck patients to lifetime 65-70 (45 initial, 20 in second course) cord dose with no CNS effects.

You can hyperfractionate to equivalent doses and always be assured of less late effects; radbio has taught us that. Also keep in mind nowadays with IMRT most head neck patients actually receive something like 45 Gy in 33 fx versus in old days they got 45 in 25. Thus the IMRT era has baked in more cord tolerance for reirradiation... also a radbio deducement.

When reirradiating you just have to be super anal about conformality, and hyperfx when possible. I think that produces success.

 

[evilbooyaa]

I generally do the up to 50% recovery for spinal cord, although I try to plan as if there is NO recovery. I would rather overestimate the toxicities of re-irradiation than underestimate.

Despite what is shown in rhesus monkeys, I prefer human evidence even if it's not as good as the monkey data:

Proposal of human spinal cord reirradiation dose based on collection of data from 40 patients. - PubMed - NCBI - fractionated
https://www.redjournal.org/article/S0360-3016(10)03067-1/pdf - SBRT

 

[scarbrtj]

I generally do the up to 50% recovery for spinal cord, although I try to plan as if there is NO recovery. I would rather overestimate the toxicities of re-irradiation than underestimate.

Despite what is shown in rhesus monkeys, I prefer human evidence even if it's not as good as the monkey data:

Proposal of human spinal cord reirradiation dose based on collection of data from 40 patients. - PubMed - NCBI - fractionated
https://www.redjournal.org/article/S0360-3016(10)03067-1/pdf - SBRT

This human data suggests even more forgiveness than the monkey data. Take home message: reirradiating the cord to modest doses after several months break is pretty safe. But to Gfunks original question, nothing ever returns radiation naive after therapeutic dose exposure. There are many unknown unknowns in this arena (like second malignancies decades later etc) and hemming and hawing is appropriate. Have you seen Michael Douglas in the movies lately? You think his neck looks radiation naive? I think not. Hank Pym survived radiation and the quantum realm. Both can change a man.

 

[ramsesthenice]

Being perfectly honest, except for cord I really don’t do formal calculations. Too much BS goes in the the process for it to be meaningful. In most cases they don’t have other good options so I make it sound as scary as possible, document the worst possible outcomes, then pick a number that can reasonably have a chance of accomplishing what I am hoping for. If that number is not in the ball park of what I feel comfortable doing, I shouldn’t be treating.