Pelvic immobilization

[probiotic]

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Is it feasible to perform a pelvic 3D CRT without any immobilization?
And if it is what is the acceptable CTV to PTV margin for example for a 6 field prostate conformal treatment.

Thanks

 

[Gfunk6]

Is it feasible to perform a pelvic 3D CRT without any immobilization?
And if it is what is the acceptable CTV to PTV margin for example for a 6 field prostate conformal treatment.

Thanks

Feasible, yes. Acceptable? No.

At a minimum you should use a knee sponge or a vac-lok.

Your CTV to PTV expansion is totally dependent on your institutional variability and what kind of image guidance you are using. Are you using fiducials, daily CBCT, daily CT on rails, Calypso, or U/S guided setup?

In the US, the range of CTV to PTV expansion is ~ 3-10 mm except posteriorly where it is slightly less ~3-7 mm. I'd expect the low end of PTV expansion in centers that use fiducials w/ daily orthogs and the high end of PTV in centers who don't do daily image guidance.

 

[deleted4401]

In the NCCN defined "very-low" risk group, no immobilization and keeping beam off would lead to very high control rates.
S

 

[probiotic]

At our institution we routinely use Orfit thermoplastic masks for pelvic fixation.
but it doesn't make good immobilization in craniocaudal direction and its a very time consuming process.