Why and how to spare the hippocampus during brain radiotherapy: the developing role of hippocampal avoidance in cranial radiotherapy

Table 2 Acceptable and unacceptable variations from per protocol IMRT treatment planning according to RTOG 0933 trial[11]

Treatment component	Parameter	Per protocol	Variation acceptable	Unacceptable deviation
MRI/CT Fusion and Contouring	MRI-CT fusion	No corrections to MRI/CT fusion requested	No corrections to MRI/CT fusion requested	Corrections to MRI/CT fusion requested
MRI/CT Fusion and Contouring	Hippocampal Contouring	≤ 2 mm deviation using the Hausdorff distance*	> 2 and ≤ 7 mm deviation using the Hausdorff distance*	> 7 mm using the Hausdorff distance*
HA WBRT IMRT Planning	PTV	D_2% ≤ 37.5 Gy	D_2% > 37.5 Gy ≤ 40 Gy	V₃₀ < 90%
	PTV	D_98% ≥ 25 Gy	D_98% < 25 Gy	D_2% > 40 Gy
	Hippocampus	D_100% ≤ 9 Gy	D_100% ≤ 10 Gy	D_100% > 10 Gy
	Hippocampus	D_max ≤ 16Gy	D_max ≤ 17 Gy	D_max > 17 Gy
OARs constraints	Optic nerves and chiasm	D_max ≤ 37.5 Gy	D_max ≤ 37.5 Gy	D_max > 37.5 Gy
Unscheduled break days	-	0 break days	1–3 break days	> 3 break days

*according to comparison with contours prepared by co-principal investigators.
PTV: planning target volume; D_2%: dose in 2% of volume; D_98%: dose in 98% of volume; D_100%: dose in 100% of volume; D_max: maximal dose; V₃₀: volume irradiated by 30 Gy.

ISSN: 1748-717X