SRS without an MRI?

[thesauce]

Has anyone done it? I could really use an MRI for this case but patient has a cochlear implant. Is there another imaging option to fuse?

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[Palex80]

Yes, I've done it before.
My patient had a pacemaker and was dependent on it. An older model, not MRI compatible and I couldn't get the cardiologists to find an alternate solution.
In the end she passed away from extracerebral tumor progression, the treated lesion was well controlled.

Think about talking to you radiologists about ways to enhance the quality of your planning CT.

 

[RadOncDoc21]

Has anyone done it? I could really use an MRI for this case but patient has a cochlear implant. Is there another imaging option to fuse?

I'm sure the older trials didn't always use an MRI... I'm too lazy to verify though!

 

[Gfunk6]

I've also done it with pacemakers. I use a high-res CT Brain with contrast using stealth protocol. For an added margin of safety I fractionate treatment into 3-5 fractions since it is hard to justify a GTV=CTV paradigm without MRI; thereby increasing your treatment volume.

 

[thesauce]

Thanks so much, guys

 

[Palex80]

I've also done it with pacemakers. I use a high-res CT Brain with contrast using stealth protocol. For an added margin of safety I fractionate treatment into 3-5 fractions since it is hard to justify a GTV=CTV paradigm without MRI; thereby increasing your treatment volume.

So what do you usually give?
3 x ?
5 x ?

I have seen a couple of recurrences after 5 x 6 Gy, so I've been treating with 6 x 6 Gy lately to the PTV (95% isodose).

 

[ramsesthenice]

I've also done it with pacemakers. I use a high-res CT Brain with contrast using stealth protocol. For an added margin of safety I fractionate treatment into 3-5 fractions since it is hard to justify a GTV=CTV paradigm without MRI; thereby increasing your treatment volume.

I use high res CT with contrast fairly often. I do contour a little bigger but still do single fraction if size is appropriate. Haven't had any problems yet. Control seems to be as good (though havnt specifically gone back and looked). Rest of our group feels pretty good about it too (when we have to).

 

[Gfunk6]

So what do you usually give?
3 x ?
5 x ?

I have seen a couple of recurrences after 5 x 6 Gy, so I've been treating with 6 x 6 Gy lately to the PTV (95% isodose).

8 Gy x 3
or 5-6 Gy x 5

Whenever possible I try to Rx to a lower isodose line (typically low to mid 80%).

 

[ramsesthenice]

Whenever possible I try to Rx to a lower isodose line (typically low to mid 80%).

Agree. 75-85% IDL most of the time (most often 80-82%).

 

[Damn_Daniel]

Why the 3-5 fractions?
I've been doing 1 (20-24 Gu)
I have a linac based system. Treating to 80-90% IDL.
Should I be fractionating ? Does this have to do with the CT vs MRI?
I'm not up to date on this stuff, and nobody does stuff right here at Third Rate Academic Center anyway, so appreciate some guidance.

 

[ramsesthenice]

Why the 3-5 fractions?
I've been doing 1 (20-24 Gu)
I have a linac based system. Treating to 80-90% IDL.
Should I be fractionating ? Does this have to do with the CT vs MRI?
I'm not up to date on this stuff, and nobody does stuff right here at Third Rate Academic Center anyway, so appreciate some guidance.

I do 20 Gy x 1 for up to 2 cm, and 18 Gy x 1 for 2-3 cm unless it is near something critical or its a retreatment. Almost all of this is based on RTOG I cant remember the numbers single fraction dose escalation study from the 90s. There are also a fair number of large single-institution studies (mostly out of Pitt) which suggest this is reasonable right now. Collectively these all suggest that the risk of seizures and symptomatic necrosis goes up with single Frx when the V12 gets over 10 Gy or the tumor volume gets over 3 cm. Biggest caveat, a lot of these are mostly for AVMs. May be a little more wiggle room depending on what you consider tumor vs normal brain (it is different with AVMs).

The only people I know I hurt were on a trial for which I did single frx to large volumes post-op per protocol. It happened in 2/5 patients and I quit enrolling.