Quality assurance of inhomogeneity correction algorithm in the intensity modulated radiotherapy and dynamic conformal arc radiotherapy using multiple heterogeneous head and neck phantoms

To quantify the differences between heterogeneous dose estimates from the calculation algorithm of 3-D treatment planning systems and dosimetry measurements, radiation was delivered in accordance with IMRT and dynamic conformal arc radiotherapy (DCART) QC procedures using multiple heterogeneous head & neck phantoms. The multiple inhomogeneous head and neck phantoms were constructed by various materials such as water equivalent homogeneous (acryl), air equivalent (cavity), bone equivalent (teflon) materials. The absolute and relative dosimetry were done using pinpoint ionization chamber, film and TLD (Harshaw 100). With custom-written software modules, the measured and calculated dose distributions were superimposed and compared. The point dose measured at the interface between water and air material region shows about 7% mismatch with the treatment planning system in IMRT. This dose difference is even increased at the interface between bone and water material region reaches up to 18% under-dose comparative to planned value. Our results suggest that the effectiveness of the imhomogeneity corrections used in IMRT and DCART planning should be evaluated in order to ensure meaningful quality assurance and delivery.