Femoral Head/Neck Fracture

[Thaiger75]

Does anybody know of any data supporting a dose response of risk of femoral head/neck fracture?

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[Thaiger75]

Does anybody know of any data supporting a dose response of risk of femoral head/neck fracture?

Let me rephrase that, is there any dose volume effect? There's data on "max" dose, but is giving 40 Gy to the entire structure any different that 50 Gy to 1/3 of the structure?

 

[Palex80]

TD 5/5: 52 Gy
TD 50/5: 65 Gy

I find these figures quite high, I am sure that in daily practice most of us like to keep the dose below 46 Gy.

On the other hand, we should not forget that those doses are meant to be with 2 Gy/d. Most of our patients would only receive a fraction of that per day.

 

[Thaiger75]

TD 5/5: 52 Gy
TD 50/5: 65 Gy

I find these figures quite high, I am sure that in daily practice most of us like to keep the dose below 46 Gy.

On the other hand, we should not forget that those doses are meant to be with 2 Gy/d. Most of our patients would only receive a fraction of that per day.

Where does this data come from?

 

[qwert]

Emami tables of course. Always refer to the Emami paper before asking a question like that.

Where does this data come from?

 

[bobloblaw]

If you look at the Emami paper, the authors concede that the dose guidelines are estimations and all of the data are very imprecise (with no volume data at all). Emami's paper was great because it gave us standard guidelines but asking "where does the data come from" is still a relevant question.

In the Emami paper they quote a book from 1983, Shimanovskaya K, Radiation injury of the bone: bone injuries following radiation therapy of tumors. I don't know if it's available at your library, but it may have more information.

Just in my opinion, there probably is a dose volume effect that also relates to which part of the femoral head/neck is receiving high doses. I don't know if anyone has ever studied this, though. It's a pretty specific question and it's probably easier for us to just limit the dose fo 45 Gy and not worry about it.

 

[radiaterMike]

THe Emami paper (and the 1983 book) aren't quite useful for dose-volume constraints since they were written in the pre-3D planning era. So the 1/3, 2/3 and 3/3 structures reflect an estimation based upon 2D planning. I have not seen anything written about dose-volume constraints for femoral neck fracture. I agree, that it is probably a more complicated matter with regional volumes of femoral neck exposure being relevant, and perhaps a slew of other variables such as age, gender, hormonal therapy, chemotherapy ....

If you look at the Emami paper, the authors concede that the dose guidelines are estimations and all of the data are very imprecise (with no volume data at all). Emami's paper was great because it gave us standard guidelines but asking "where does the data come from" is still a relevant question.

In the Emami paper they quote a book from 1983, Shimanovskaya K, Radiation injury of the bone: bone injuries following radiation therapy of tumors. I don't know if it's available at your library, but it may have more information.

Just in my opinion, there probably is a dose volume effect that also relates to which part of the femoral head/neck is receiving high doses. I don't know if anyone has ever studied this, though. It's a pretty specific question and it's probably easier for us to just limit the dose fo 45 Gy and not worry about it.

 

[cdf95cro]

Femoral neck fracture following groin irradiation.

Grigsby PW, Roberts HL, Perez CA.

Int J Radiat Oncol Biol Phys. 1995 Apr 30;32(1):63-7.

We try to keep femoral neck dose under 42 Gy, but it is (obviously) a soft constraint.

 

[Thaiger75]

Emami tables of course. Always refer to the Emami paper before asking a question like that.

I know where that particular data comes from. But most of the data (including the Grigsby paper just mentioned) as pointed out are pretty imprecise. The Grisgby paper, which I think gives strong clinical data for the total threshold dose, does not give any data related to volume effects in relation to dose.

I don't think it has been studied very well or much and I suspect that that total threshold dose is probably good enough, but it might have implications when comparing IMRT plans versus conventional plans.

As I stated before: does treating the entire femoral head/neck to say 48 Gy differ from treating only 50% of the volume to that dose?

 

[Thaiger75]

THe Emami paper (and the 1983 book) aren't quite useful for dose-volume constraints since they were written in the pre-3D planning era. So the 1/3, 2/3 and 3/3 structures reflect an estimation based upon 2D planning. I have not seen anything written about dose-volume constraints for femoral neck fracture. I agree, that it is probably a more complicated matter with regional volumes of femoral neck exposure being relevant, and perhaps a slew of other variables such as age, gender, hormonal therapy, chemotherapy ....

The other issue is that at least in my training, we rarely hear about a patient with a femoral neck/head fracture from radiation, because they either don't come back to us or, well, we don't hear about it. Suspect it would be a difficult thing to study unless done in a prospective fashion or with good communication with the orthopods.

 

[Brim]

As I stated before: does treating the entire femoral head/neck to say 48 Gy differ from treating only 50% of the volume to that dose?

Good dose/volume effect data is lacking for the majority of organs that we consider dose limiting structures. It's unfortunate that we lack specific knowledge of the partial volume tolerance of the femoral head, but that's partly due to the fact that fractures following RT are rare, and that's fortunate for us. It means the way we've been doing things, with the techniques and doses we used, are fairly safe. But we just don't have any data to guide us about how we can push the limits with new techniques. Giving 48 Gy to a small portion of the femoral head is probably okay, but how much of 70 Gy can we give? Or 80 Gy? Nobody knows the real answer because there haven't been enough patients treated with high doses to portions of the femoral head because we always have been able to avoid this.

To answer your specific question above, while there may not be reliable data to answer that directly, the question can be approached logically. Is the femoral head a serial organ or a parallel organ? While it may not be purely one or the other, it should be viewed mostly as a parallel organ, since it has a structural function.

As long as most of the structure is strong and intact, it should continue to "work."

So, yes, giving a high dose to more of the organ is going to cause more damage than giving that dose to less of the organ.

Giving very high doses to very small volumes, on the other hand, may not do enough damage to cause the organ to fail. As an analogy using something mechanical: you can remove one or two rivets from a bridge, but the bridge will still likely be standing. You have weakened it some, but if you only weaken it by a small amount, it doesn't matter. It takes a certain amount of damage or damage to a critical structural element to cause the bridge to collapse.

For something like the femoral head, we don't know what the critical amount of damage is or if there's a critical structural element. Probably different parts of the femoral head respond differently to RT (cortex vs. marrow; neck vs epiphysis) and how they are grouped spatially is also probably important (irradiating 100% of the circumference vs 10% of the circumference).

These relationships can be complex and may preclude us from being able to come up with a simple one-variable model to predict damage, which is frustrating for us since we like to have these numbers or formulas to tell us "yes! good plan" or "no! bad plan." It may be similar to pneumonitis where the models may not explain everything (there's likely more going on biologically than just the V20 or the MLD).

Until we learn more specifics about dose-volume effects, we just have to play it safe, doing the best we can to keep the partial organ doses less than the whole organ tolerance.