<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _create_plot(tumor, in_glob, out_ext, page=1):
 """Create an output plot for the given PDF in the images directory. """

    out_dir = utils.safe_makedir("images")
    out_name = os.path.join(out_dir, "%s-%s" % (tumor, out_ext))
    in_file = glob.glob(in_glob)[0]
    cmd = ["pdftoppm", in_file, out_name, "-png", "-f", page, "-singlefile"]
    if not os.path.exists(out_name + ".png"):
        subprocess.check_call([str(x) for x in cmd])
    return out_name + ".png"