The superiority of a novel treatment planning approach in treatment of locally advanced non-small cell cancer (nsclc) by using intensity-modulated radiation therapy (İMRT) and volumetric-modulated arc therapy (VMAT)

Non small cell lung cancer (NSCLC) is the most common cancer in man both worldwide and at our country. Beside conventional 3 dimensional (3D) conformal radiotherapy techniques, new treatment techniques such as intensity-modulated radiation therapy (IMRT) and volumetric-modulated arch therapy (VMAT) started to use in treatment of NSCLC. Major difference of these new techniques is to use optimization in order to reach desired dose distribution. Optimization mainly depends on the iteration concept in order to have optimal dose distribution both at target volumes (TV) and critical organs at risk (OAR). After each iteration process, an ideal dose volume histogram (IDVH) and ideal fluence map (IFM) was obtained. After reaching the DVH and FM objective values, optimization process was terminated and the treatment planning system start to calculate the actual DVH (ADVH) and actual fluence map (AFM) by 3D calculation. If IDVH and ADVH compared, a major difference can be easily observed. Main reason for this difference is optimization does not to include various parameters like heterogeneity effect, leaf leakage, leaf transmission and effective SSD in the iteration process, while these parameters are included to the by 3D calculation. We tried to solve this problem by using the AFM as a "base plan" for a second optimization. In this study, we selected 15 locally advanced non small lung cancer patients and generated optimal IMRT and VMAT plans. After obtaining these plans, we generated 5 different plans for each method and compared them with each other. These plans were obtained by following methods: 1) Original IMRT plan is used as a base plan for a second optimization and reach a new IMRT plan.(A-IMRT), 2) "Intermediate dose" calculation mode of the treatment planning is used for a new plan.(B-IMRT), 3) A modifed IMRT plan by using alternative gantry angles is generated and used as a "base plan" and a second optimization is generated to reach a final plan.(C-IMRT) 4) A 3 Dimensional conformal plan is generated and used as a "base plan" and make a second optimization by using IMRT and reach a final plan.(D-IMRT) 5) Original IMRT plan is summed with plan A with equal weighting. (E-IMRT) All above mentioned plans were generated also for VMAT plans and reached A-VMAT, B-VMAT, C-VMAT, D-VMAT and E-VMAT plans. Only in C-VMAT plan original IMRT plan is used as a "base plan". All plans are evaluated and compared with each other in terms of PTV evaluation parameters (Dmin, Dmax, Dmean, V110%, V107%,V95%, CI, HI values) and for critical organ doses (V5Gy, V10Gy, V20Gy, V30Gy, Dmean for lung; Dmax, D1cc for spinal cord; V30Gy, V40Gy, V45Gy,V60Gy, Dmean for heart; and V55Gy, V66Gy, Dmean values for esophagus.. Our results demonstrated that A-IMRT and B-VMAT plans are superior in terms of all PTV evaluation criterias within for both IMRT and VMAT groups. (p<0.001). In terms of critical organ doses; A-IMRT plan have better V5Gy and V10Gy (p =0.027, p =0.014) for lung, have better V55Gy, V66Gy, Dmean criteria for esophagus, (p =0.001, p=0.001, p= 0.001), V60Gy and Dmean criteria for heart, (p =0.037, p =0.032) and, Dmax and D1cc criteria for spinal cord (p=0.019, p=0.014) doses compared to the original IMRT plan values. In terms of critical organ doses; D-VMAT plan have better V5Gy and V10Gy (p =0.011, p =0.037) for lung, compared to the original VMAT plan. A-VMAT plan values have better V55Gy, V66Gy, Dmean criteria for esophagus, (p =0.001, p=0.001, p= 0.001). B-VMAT plan values have better V30Gy and V40Gy criteria for heart (p =0.01, p =0.044) compared to the original VMAT plan. A-VMAT plan values have better D1cc criteria for spinal cord (p=0.032) doses compared to the original IMRT plan values. Briefly, the basis of this new planning method is to use the first optimization dose map as a "base plan" and make a second optimization to reach a better final dose distribution. Our results have indicated that all investigated plans have better PTV and organ at risk parameters compared to the original plans. Best results were obtained for A-IMRT and for B-VMAT for both PTV and critical organ criterias. D-VMAT have the best results in terms of lung critical organ criterias.