Study of dose variations induced by MLC weight effect for IMRT delivery / 医疗卫生装备

ABSTRACT

Objective To evaluate dose variations induced by gravity of multi-leaf collimator to provide references for clinical intensity-modulated radiotherapy.Methods Two-dimensional dose distributions in the central plane of IMRT fields were measured by use of a 2D ion chamber array.All measurements were repeated at two collimator angles (C=0 and 90°),for each of the following gantry anglesG=0 and 270°.Comparisons were made to dose distributions generated at G=0°and their differences were analyzed using gamma index analysis (3％/3 mm and 1％/1 mm).Results Under the radiation field of 10 cm×10 cm,the gamma passing rate was higher than 99％ for 3％ 3 mm anch close to 95％ for 1％/1mm Under a 3％/3mm error standard,the average matching rate for step & shoot fields was (96.46±0.33)％ and for DMLC fields was (94.67±0.54)％ at C=0°;The average matching rate for step & shoot fields was (94.59±0.47)％ and for DMLC fields was (92.60±0.52)％ at C=90°.Under a 1％/1mm error standard,the average matching rate for step & shoot fields was (89.83 ±1.06)％ and for DMLC fields was (85.84±0.57)％ at C=0°;The average matching rate for step & shoot fields was (86.91 ±1.71)％ and for DMLC fields was (83.89±0.69)％ at C=90°.Concusion MLC weight effect affects IMRT delivery dose,and DMLC fields are more sensitive to gravity than step & shoot fields.