The aim of this study was to show that the optimum dosage can be delivered to the target organs at risk (OAR) by radiotherapy, which becomes more complicated because of technical difficulties arising from irregular, convex, and complex geometrical structure of the target, such as scalp irradiation, and because of situations resulting from the necessity of bolus of the lesion and immobilization as well as the proximity to neighboring critical organs using the VMAT-SIB technique.
METHODS
Five different VMAT-SIB schemes were designed using the Varian Trilogy IX linear accelerator (Varian
Medical Systems) for total scalp irradiation and bilateral neck irradiation. These different VMAT scehemes
were compared with respect to a dose volume histogram of obtained data, homogeneity, indices,
conformity index, OAR, and doses of target volumes.
RESULTS
The patient-designed bolus plan 1 with two isocenters was chosen as the most appropriate plan. Plans 2, 3,
4, and 5 were inappropriate plans because the application of the virtual bolus in plan 2 was difficult, plan
3 with one isocenter was unacceptable with respect to the value of conformity index, plan 4 with three
isocenters had a matching field, and plan 5 in which different priority values were used had an increase
in OAR doses.
CONCLUSION
VMAT-SIB can be preferred as an appropriate radiotherapy technique as it can provide optimum and
allowable OAR doses in tumors requiring an intensive treatment planning effort.