First report of SBRT performed as rescue treatment in a cardiac ICU patient

[scarbrtj]

I realized (re)watching 'Star Wars' this weekend that Princess Leia says that something is her/our "only hope" two times, but re: two different things. Sort of logically inconsistent. That said, perhaps cardiac SBRT is radiation oncology's only hope.

We report here an intensive care patient suffering from an electrical storm due to incessant VT, unresponsive to catheter ablation and anti-arrhythmic drugs, showing an immediate and durable response to electrophysiology-guided cardiac SBRT.

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[evilbooyaa]

Cool stuff. Rare but new avenue for treating benign disease with radiation.

 

[seper]

I'm really curious about proposed pathophysiology of rapid SBRT effect here.

 

[RO2019]

I mean i'm pretty sure in these cases the cardiologist IS highly involved in contouring the target and understanding their own cardiac imaging and how it fuses with CT?

That's not really an issue here. I would hope rad oncs aren't trying to target ablation zones on their own. God Help us if so.

 

[Palex80]

I'm really curious about proposed pathophysiology of rapid SBRT effect here.

Aside radiation therapy the cardiologists use RFTA to treat these lesions.

I presume high dose SBRT induces vascular damage and ultimately local necrosis in the ablated area.

Interestingly, patients after RFTA often experience arrhythmias and need to be overwatched in ICU for 2 days or so after ablation. It‘s probably because RFTA induces all damage immediately. SBRT effect on the other hand happens over time and reported results sofar show very little amount of post–procedural problems.

In this sense, SBRT may be safer for immediately induced effects?

 

[scarbrtj]

Aside radiation therapy the cardiologists use RFTA to treat these lesions.

I presume high dose SBRT induces vascular damage and ultimately local necrosis in the ablated area.

Interestingly, patients after RFTA often experience arrhythmias and need to be overwatched in ICU for 2 days or so after ablation. It‘s probably because RFTA induces all damage immediately. SBRT effect on the other hand happens over time and reported results sofar show very little amount of post–procedural problems.

In this sense, SBRT may be safer for immediately induced effects?

The patients who are responding to SBRT have not responded to RFTA. The effect of SBRT seems to be rather immediate as well as in this article patient went immediately after procedure with no further episodes. In general it seems like >90% reduction over 4 weeks and >99% reduction 4+ weeks in vtach is more common after SBRT; but again, effects can be immediate. If this is not making you think about new radiobiology you aren't thinking hard enough!

I hypothesize that the cardiac DNA has more twisted-knot DNA vs double helix DNA, which would mean cardiac cells would not respond in a linear-quadratic "two hit" fashion but have linear-quadratic-cubic-quartic response and a "four hit" response, and of course then an alpha/beta/gamma/delta type dose response at high dose (ie traditional radiobiology and alpha/beta would need revision with twisted-knot DNA cells). My reasoning for this is that arrhythmia is associated with relative cardiac cellular acidosis, and cellular acidosis is associated with twisted-knot DNA. Thus, arrhythmic cardiac cells may be exquisitely sensitive to high dose radiotherapy. And only arrhythmic cells would show this sensitivity; non-arrhythmic/non-acidic cells would be more high dose tolerant. Just my thoughts but you heard it here first

 

[nkmiami]

I am not sure how a post mitotic non dividing cell could respond acutely to radiation.

 

[evilbooyaa]

Right now cardiac SBRT is for patients who don't respond to RFTA. Similar to how SBRT started in NSCLC for patients who couldn't get surgery.

Definitely needs cardiologist assistance in contouring the lesion, at least at this initial stage, not dissimilar to how brain SRS started with neurosurgeons coming and contouring the lesion. Maybe if it gets big enough it'll become as routine as brain mets, where neurosurg involvement isn't 100% (at my institution, more like 5-10%). Probably not, but maybe.

 

[scarbrtj]

I am not sure how a post mitotic non dividing cell could respond acutely to radiation.

"New" radiobiology. (It's "new" because we don't understand it lol.) Unknown unknowns etc.