Table 1.

Optimal uniform block margin sizes used for virtual phantom plans for spherical GTVs of 15 mm, 30 mm, and 50 mm diameters, planned individually with 90%, 80%, 70%, and 60% prescription isodose lines and with 6 MV photon beams, as based on PB calculation

Block Margin (mm)	$Rx\hspace{0.17em}Line=90\%$	$Rx\hspace{0.17em}Line=80\%$	$Rx\hspace{0.17em}Line=70\%$	$Rx\hspace{0.17em}Line=60\%$
${\mathrm{D}}_{\text{GTV}}=15\hspace{0.17em}\text{mm}$	0.5	$-0.5$	$-1.5$	$-2.5$
${\mathrm{D}}_{\text{GTV}}=30\hspace{0.17em}\text{mm}$	0	$-0.5$	$-1.5$	$-3.5$
${\mathrm{D}}_{\text{GTV}}=50\hspace{0.17em}\text{mm}$	$-0.5$	$-1.5$	$-3$	$-5$