What RT margins do you use when treating Grade III anaplastic gliomas?

While there are clearly well-defined margin guidelines for GBM (which nonetheless differ between RTOG and other groups), little has been written about the optimal GTV/CTV definitions when treating anaplastic glioma in the modern treatment planning era.

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Radiation Oncology · Cleveland Clinic

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At the Cleveland Clinic, we extrapolate from the GBM literature and from the Cairncross RTOG 9402 and Van den Bent EORTC trials showing the benefit of chemotherapy, and thus deliver radiation with concurrent temozolomide. We typically treat to 5940 cGy in 33 fractions. We treat PTV1 to 5040 cGy and then boost a smaller region (PTV2) by 9 Gy to reach 5940 cGy. GTV1 includes the resection cavity + any T1 enhancement + T2 changes. We add 2 cm to GTV1 to create CTV1 and restrict the margin along barriers such as the falx and tentorium. Using daily image guidance, we then add 3 mm to generate PTV1 which, as above, we treat to 5040 cGy. We then create GTV2 which includes the resection cavity + T1 enhancement alone. We add a 1 cm margin to create CTV2 and add another 3 mm to create PTV2. Again, with daily image guidance, we then deliver a boost of 900 cGy in 5 fx to CTV2.

Alternatively, when enrolling patients on CODEL trial, we adhere to their slightly different protocol. This protocol instructs radiation oncologists to create a GTV1 that includes the surgical resection cavity and any T2/FLAIR changes. This is expanded by 1 cm to create CTV1. CTV1 is further expanded by 3-5 mm to create PTV1, which receives 5940 cGy in 33 fractions. If 3D conformal radiotherapy is used, the protocol states that another 5-7 mm block margin is generally added to account for penumbra

Special thanks to Camille Berriochoa, MD for assisting with this answer.