Model of Novotny et al for Predicting the Probability of Intracranial Edema Following Gamma Knife Surgery on a Meningioma

 

Parameters:

(1) history of previous surgery

(2) presence of intracranial edema before gamma knife surgery (GKS)

(3) tumor volume in cubic cm

(4) tumor location

(5) radiation dose to the tumor margin in Grays

 

Parameter	Finding	Points
previous surgery	no	0
	yes	1
intracranial edema before surgery	no	0
	yes	1
tumor volume		(volume in cc)
tumor location	no risk (middle cranial fossa, posterior cranial fossa, tentorium, cerebellum)	0
	at risk (anterior cranial fossa, convexity, falx)	1
dose to margin		(dose in Grays)

 

where:

• The risk of edema was lower with a radiation dose to the margin was <= 16 Grays than if it was higher.

• The relative risks for edema based on location are shown in Figure 6.

 

Z =

= (-0.786 * (points for previous surgery)) + (3.896 * (points for edema before)) + (0.104 * (tumor volume)) + (0.855 * (points for tumor location)) + (0.17 * (radiation dose to margin)) - 5.080

 

probability of intracranial edema after the surgery =

= 1 / (1 + EXP((-1) * Z))

 

Interpretation:

• If the estimated probability is < 05 it is assumed that edema will not occur.

• If the estimated probability is > 05 it is assumed that edema will occur.