Intensity modulated radiation therapy (IMRT) plans can be further
customized to each patient with the use of a four-dimensional (4D) respiratorygated
computed tomography (CT), with time being the fourth dimension. The 4D
respiratory-gated CT allows for the internal margin (IM), the expansion of the
tumor volume that accounts for physiologic motions, to be addressed in the
treatment planning process and no longer assumes that the treatments will be
delivered to a fixed or rigid patient anatomy. Delivering the IMRT plan with a
gated technique limits the treatment to a duty cycle when the target motion is at a
minimum.
The goal of this project is to study respiratory-gated IMRT quality
assurance (QA) results for tumor motion in two dimensions and develop a
guideline for acceptable limits on tumor motion and field size. Respiratory-gated
IMRT QA was performed for four field sizes and varying amounts of motion with a
fixed duty cycle using Sun Nuclear¿¿¿¿s MapCHECK and MotionSIM XY/4D
products. The treated and planned dose planes were compared and errors were
evaluated using standard acceptance conditions.