Abstract:
As the field of radiation therapy evolves new treatment techniques will be
established. An example of an evolving treatment technique is respiratory gated
radiation therapy (RGRT). Research and studies have shown that RGRT can be used
to account for tumor motion as a result of respiratory motion. With evolving
technology and advanced treatment techniques comes complexity, as is the case with
RGRT.
One step used to prove the validity of RGRT as a treatment technique is
dosimetric verification. This study is performed on a Varian Trilogy linear accelerator
coupled with Varian's Real-time Position Management™ (RPM) system. The
dosimetric verification is based on the measurements taken using a dynamic
respiratory motion phantom with an ionization chamber and MapCHECK™. The
ionization chamber and MapCHECK™ measurements are then compared to predicted
values of the treatment planning system (TPS) and RadCalc® (independent monitor
unit calculation).
After the dosimetric verification was completed on a dynamic respiratory
motion phantom, the dosimetry of several RGRT patient treatments plans was also
evaluated and verified.
The dosimetric verification in the study confirmed our ability to accurately
measure the predicted or calculated dose from the TPS, validated the dose calculation
algorithm used in the TPS and validated RadCalc®. The agreement between measured
and predicted central axis point doses fell within the distance to agreement (DTA)
acceptance criteria of 3% and 3 mm or 1 cGy. The agreement between measured
and predicted planar doses also fell within the DTA acceptance criteria with a
minimum of 94% of the points passing with an exception of one beam with 91.2% of
the points passing.
