Table 2.

Necessary dose–volume constraints for planning approval of Hom (D_2% ≤ 37.5 Gy) and Het (D_2% ≤ 40.2 Gy) plans

Volume	Hom plans	Any plan	Het plans
sub-PTV	D98% ≥ 33.2 Gy		D98% ≥ 35 Gy
	Dmean = 35 Gy		Dmean = 37.5 Gy
	D2% ≤ 37.5 Gy		D2% ≤ 40.2 Gy
PTV		$V_{33.2}^{\text{PTV}}$ ≥ 95%
	D2% ≤ 37.5 Gy		D2% ≤ 40.2 Gy
OVLrectum, OVLbladder, OVLPRV-u		$D_{{1\text{cm}}^3}$ < 35 Gy
		D98% ≥ 32 Gy
Rectuma		$D_{{1\text{cm}}^3}$ < 35 Gy
		$V_{32}^{\text{r}}$ < 5%
		$V_{28}^{\text{r}}$ < 10%
		$V_{18}^{\text{r}}$ < 35%
Femoral heads		$D_{{1\text{cm}}^3}$ < 20 Gy

D_mean, mean dose of the structure; D_n%, minimum dose to n% of the structure; OVL_bladder, overlap between PTV and bladder; OVL_PRV-u, overlap between PTV and urethral-PRV; OVL_rectum, overlap between PTV and rectum; PRV, planning at risk volume; PTV, planning target volume; sub-PTV, planning target volume minus OVL_rectum, OVL_bladder, and OVL_PRV-u; $V_{\text{m}}^{\text{PTV}}$, percentage of PTV structure receiving ≥m (Gy); $V_{\text{m}}^{\text{r}}$, percentage of rectal structure receiving ≥m (Gy).

^aFor plans computed on a CT study which was scanned after the insertion of a rectal spacer, a <1 cm³ extension for OVL_rectum may result. In this case, the $D_{{1\text{cm}}^3}$ < 35 Gy constraint is applied to the whole rectum. As the extensions of OVL_bladder and OVL_PRV-u are always >1 cm³, the use of the $D_{{1\text{cm}}^3}$ < 35 Gy constraint to the overlaps assures the fulfilment of the same constraint to the whole organ.