Fig. 3.

Placement of peripheral needles and readjustment of the target volume. (a) Step ③‐1, at this step, peripheral (bilateral, anterior, and posterior) needles, including the needles anterior to the rectum, are placed. Lateral and anterior needles should be placed just inside the prostatic capsule. The distance to the nearby needles should be 5‐7mm (not more than 7mm). Needles should also be placed at the bottom of bilateral corners (right and left). As described in Step ①, the distance between the needles above the rectum (c‐1.5 and d‐1.5) and those at the posterior surface of the prostate should be kept at 5–7 mm: care must be taken “not to get too close to the posterior surface of the prostate in order to avoid overdosing the anterior rectal wall (blue arrow). (b) Step ③‐2, after completing insertion of the peripheral needles, reacquisition of the transverse images should be conducted from the base to the apex. Then, the final target volume (red line) is determined by the alignment with the sagittal image.