The ornamental design for a radiotherapydevice, as shown and described.
FIG. 1 is a front perspective view of a radiotherapy device showing the new design;
FIG. 2 is a right perspective view thereof;
FIG. 3 is a left perspective view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a front elevation view thereof; and,
FIG. 6 is a rear right perspective view thereof.
The even-length broken lines shown in the drawings illustrate portions of the radiotherapy device that form no part of the claimed design. The uneven length broken lines represent the bounds of the claim and form no part of the claimed design.