Figure 1. Representative dose distribution of WPRT and WPRT-CS field in IMRT and 3D-CRT. A) WP field in IMRT (upper) and 3D-CRT (lower). B) WP-CS field in IMRT (upper) and 3D-CRT (lower). Red line: tumor; Yellow line: bladder; Light blue line: rectum. 3D-CRT plan was made for the planning study to compare the dose distribution to that of the IMRT plan. C) Central shielding. The central shielding (CS, light blue line) was defined as a 4-cm wide structure in the center of PTV 3 (pink line). Three nested virtual structures (light violet line, light green line, and green line) were established within the CS by contracting its outline in 5-mm steps. WPRT: Whole pelvic radiation therapy; WPRT-CS: WPRT with central shielding; IMRT: intensity-modulated radiation therapy; 3D-CRT: three-dimensional conformal radiation therapy.