lung SBRT 34 Gy in 1fx

[seper]

Is anybody considering switching your SBRT prescription to 34 Gy in 1 fraction, given preliminary results of RTOG 0915?

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[napoleondynamite]

Is there a more recent update than the ASTRO Atlanta? I remember the control rates and toxicity were equivalent with 1 year follow-up, so if there's something more recent I'm assuming it's with 2 years follow-up (I couldn't find anything with a quick search, so if have a link please post if you can). Even still, we should be "curing" a fair amount of early stage lung cancer so I would need pretty compelling superiority rather than equivalence to switch - would still worry about late toxicity personally. Some would argue we still don't fully know the late toxicity even with the 4 fraction approach..

 

[ramsesthenice]

Is there a more recent update than the ASTRO Atlanta? I remember the control rates and toxicity were equivalent with 1 year follow-up, so if there's something more recent I'm assuming it's with 2 years follow-up (I couldn't find anything with a quick search, so if have a link please post if you can). Even still, we should be "curing" a fair amount of early stage lung cancer so I would need pretty compelling superiority rather than equivalence to switch - would still worry about late toxicity personally. Some would argue we still don't fully know the late toxicity even with the 4 fraction approach..

I agree and then some. We have done a couple but it makes me nervous. We have good control and I love lung SBRT. When we do have local failures the tend to look more like marginal misses than in field failures. Every time someone does single fraction anything all of the contours get a little tighter, consciously or otherwise. I'm curious to see how the data works out but unless there is a really compelling reason I don't plan to jump ship either. 4 fractions isn't that much to go through.

 

[Palex80]

I agree ramsesthenice.

Not only the tighter contours are the problem however. The considerably longer treatment time when delivering such a high dose (and u dont own a flattening-free-Linac) means potentially more intrafractional movement of the patient and tumor during a long radiation treatment. Event with 4D-CT-planning and CBCT, I am scared about that. I always found it nice to have several "chances" to hit the tumor with high doses.

Furthermore, I just don't believe that 1x 34 Gy equals 3 x 20 Gy in terms of BED.

 

[seper]

Actually, BED model does not apply to extreme hypofractionation...
Agree, would like 3 y f/u to switch, despite RTOG's decision.

 

[Palex80]

Actually the linear-quadratic model does not apply. There is however still a BED. There is always a BED. We just can't calculate it with the models we have.

However my feeling says, that 1x34 Gy is "less BED" than 3x20 Gy.

Get my point?