Investigation of dose optimization of stereotactic body radiotherapy techniques in lung cancer treatment

In this study, the dose optimization of stereotactic body radiotherapy (SBRT) techniques were compared in the treatment of lung cancer. Treatment plans of 15 patients prepared using Intensity Modulated Radiotherapy (IMRT), Volumetric Modulated Arc Therapy (VMAT), Helical Tomotherapy (HT) and CyberKnife Radiosurgey (CK) techniques. For all treatment plans, 18 Gy dose per fraction with a total of three fractions, 54 Gy was given to the target volume. For each technique, the planned target volume (PTV) was normalized to 95% with a minimum prescribed dose of 54 Gy. The treatment plans of four different treatment techniques were prepared using computerized tomography (CT) images of 15 patients with lung cancer treated with radiotherapy before at Istanbul University, Institute of Health Science. Conformity index (CI), homogeneity index (HI), monitor unit (MU) values and doses of critical organs were evaluated. Mean CI95% values were found 1.89(±0,36), 1,39(±0,08), 1,51(±0,18) and 1,43(±0,11) for IMRT, VMAT, HT and CK, respectively. It has been determined the VMAT technique provides the best uniform dose distribution. The mean HI5/95 values were found 1.05(±0.03), 1.06(±0.03), 1.10(±0.02) and 1.16(±0,05) for IMRT, VMAT, HT and CK respectively. It has been determined that the IMRT technique provides the best homogeneous dose distribution. The maximum percent dose values at 2 cm above the PTV, D2cm, which is the parameter of the dose reduction, were found 85%(±9.05), 66.6%(±9.5), 57.9%(±6,5) and 55%(±8) for IMRT, VMAT, HT and CK respectively. It was found that the IMRT technique had the lowest value of MU, which means IMRT technique provides shorter treatment time. When all the techniques were evaluated, the mean values of all parameters of PTV and critical organs met the desired criteria for all techniques. Key Words: SBRT, lung cancer, lineer accelerator, HT, CK