Although optical imaging of electron beams and X-rays from
medical linear accelerators (LINAC) is a possible method for dose
distribution measurements, it has been limited to two-dimensional
(2D) projection images. For the precise measurement of an optical
image of electron beams and X-rays, three-dimensional (3D) imaging
is desired. To measure 3D dose distributions, we conducted imaging
of electron beams and X-rays using a plastic scintillator plate set
in a water phantom. When this plate was immersed in the water
phantom, irradiation with electron beams or X-rays was carried out
from along the plate's sides. Optical images of the scintillator
plate were acquired using a charge-coupled device (CCD) camera from
the side during irradiation with electron beams and
X-rays. Measurements were conducted at 6 MeV, 9 MeV and 12 MeV
for electron beams and at 6 MV and 10 MV for X-rays. The imaging
system was set on the bed of the LINAC and moved at 10-mm steps
perpendicular to the beam direction to acquire a set of sliced
optical images of the beams. A set of these sliced images were
stacked and interpolated to form 3D optical images. For the 3D
images, after the correction of the Cherenkov-light component in the
images, the relative depth and lateral doses were evaluated. From
the relative depth doses of electron beams, the half-value depths
could be evaluated within an error of 1.3 mm. Lateral widths could
be evaluated within an error of less than 2 mm parallel to the
plastic scintillator and less than 6.5 mm perpendicular to it. From
the relative depth doses of X-rays, the average difference between
the measured value and that by a planning system was within an error
of 2 %. Lateral widths could be evaluated within an error of less
than 0.68 mm parallel to the plastic scintillator and less than
2.6 mm perpendicular to it. We confirmed that 3D imaging of
electron beams and X-rays using plastic scintillator plate is
feasible and is a promising method for measuring dose images at any
position.