Table 1.

Volumes of the irradiated breast (PTV) and the nodal regions in the prone and supine positions

Volumes	Prone (mean ± SE, mm3)	Supine (mean ± SE, mm3)	P (paired t-test)
PTV	971.6±44.0	967.3±44.4	0.380
Level I	61.6±2.0	62.7±2.2	0.306
Level II	14.2±0.4	13.9±1.2	0.792
Level III	6.0±0.2	5.9±0.2	0.451
IM	4.7±0.1	4.7±0.1	0.450

Note: The volumes of the PTV or the nodal regions did not differ in the prone versus the supine position.

Abbreviations: PTV, planning target volume; SE, standard error; IM, internal mammary.