Poster - Thur Eve - 60: Physical and dynamic wedges in radiotherapy for rectal cancer: A dosimetric comparison.

Abstract

The aim of this study is to compare the dosimetry of the physical wedge (PW) and enhanced dynamic wedge (EDW) in radiotherapy of rectal cancer. Two wedge angles of 45° and 60° were used in the comparison due to the size of the pelvis contour. 6 and 15 MV photon beams produced from a Varian 21 CD linear accelerator were used. Thirty rectum patients were investigated using the three-field technique. Treatment plans using the PWs and EDWs were created using the Eclipse treatment planning system. Monitor units, plan normalization value, maximum and minimum doses in the planning target volume (PTV), dose conformity index, dose homogeneity index and uniformity index were determined for each treatment plan. The average dose coverage for the PTV with EDW and PW plans were compared. The PTV received prescription doses of 100.9±0.74%, 101.01±1.63% for the EDW (45°, 60°) compared to 101.2±1.65%, 101.3±1.33% for the PW (45°, 60°). Homogeneity indices were (0.11±0.02%, 0.11±0.05%) for the EDW (45°, 60°), and (0.15±0.1%, 0.16±0.11%) for the PW (45°, 60°), respectively. The EDW at 45° had better target coverage with higher conformity index value of 0.98 ± 0.01 compared to the other wedges. A statistically significant (p < 0.01) change in plan normalization values and fewer monitor units were found using the EDW at 45°. We conclude that the EDW at 45° results in an improvement to the plan evaluation parameters presented and thus increases dose efficacy for radiotherapy of rectal cancer.