Clarification re: RTOG 1016

[Gfunk6]

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I was reading the protocol for RTOG 1016 (RT + CDDP vs RT + cetuximab for HPV positive oropharyngeal cancer) and had a question.

There is no "GTV" written in the entire protocol, so am I to assume that there are no expansions from GTV1 --> CTV1? It sounds like you just draw the primary tumor and gross LNs and that constitutes your CTV1. Then you contour the lymphatic space in high risk regions and that constitutes your CTV2. I didn't see CTV2 defined anywhere, so I guess it is at the attending's discretion?

Then you expand both by ~ 3-5 mm with daily IGRT and that constitutes your PTV1 and PTV2.

Am I on track here?

 

[Pointless]

That doesn't seem correct. The end result of that would be a boost volume of tumor + 3-5 mm??

 

[Gfunk6]

That's what I thought but it seems one of the main purposes of this trial is to put a check on the "increasing target volume creep" and "increasing doses with IMRT creep" that is happening in treatment of HPV positive SCC.

 

[Pointless]

If that's the protocol, local control is gonna take a serious nosedive. Good luck with that RTOG.

 

[temujim]

Under Section 6.1.1 CTV1 = GTV + 5-10mm

CTV2 = "anatomic compartment" encompassing PTV1 (whatever that means; probably a reference to the seminars in rad onc paper from 8-10 yrs ago) + first echelon nodes (again, whatever that means).

I know of only one clinical paper regarding what should be the high risk CTV expansion size, and that showed no difference in the local control based on smaller vs larger expansion.

 

[Gfunk6]

Temujim, could you provide a citation for that paper?

So I guess you could draw your GTV1, expand by 5 mm to create a CTV1 and expand 3 mm to create a PTV1.

If you are using daily image guidance, that sounds a bit more reasonable.

 

[Pointless]

Agreed.

 

[temujim]

PMID: 12118389 for the "anatomic compartments"
PMID: 19386438 for the total expansion
PMID: 20932680 for PTV expansion

Caveats abound.