Analysis Of Radiotherapy Techniques In Three-dimensional Dosimetric Planning For Limited-stage Small Cell Lung Cancer

Objective To assess and delineate the dosimetric shortcomings of conventional radiotherapy planning, as compared with the three-dimensional treatment planning system, and to obtain a better technique in the treatment of limited-stage small cell lung cancer. To analyze the feasibility and the practicability of combining two-course treatment plans of one patient who was localized in different position during two-course.Methods Ten patients with ]imited-stage small cell lung cancer were chosen in the present study (The patients was treated [rom February 2006 to May 2006). According to the clinical requirement, all patients were localized twice with different position in total course. Using the Cadplan R 3. 1. 2 treatment planning system, two different methods of radiotherapy planning: conventional planning, and conformal planning were designed for each patient in two-course. The radiation dose was 36Gy in the first course and 14Gy in the second course, then the dose volume histograms(DVH) were used to assess the dosimetric distribution in theplanning target volume and the surrounding organs at risk; Using the Cadplan R 3. 1. 2 treatment planning system, treatment plans in the first course superposed treatment plans in the second course. The total radiation dose was 50Gy. To evaluate the dosimetric distribution in the planning target volumes and the surrounding organs at risk, a comparison was made between the conventional planning and the conformal planning. This study was analyzed with SPSS 13.0 statistic software package. In order to guarantee normality of sampling, Shapiro-Wilk (S-W) method was used to prove normality plots. Significant dosimetric disparities between the conventional planning and the conformal planning were analyzed by paired-samples t test. As compared with the linearity correlations of volumes and dosimetric parameters between reproductive plans and original plans, pearson correlation analysis was used.Results 1. Significant dosimetric disparities in relative dose homogeneity indices of PTV1, conformal indices of PTV2, contralateral lung V30 and contralateral mean lung dose were found between the conventional planning and the conformal planning in thefirst course. 2. Significant dosimetric disparities in relative dose homogeneity indices of PTVl, conformal indices of PTV1, mean PTV1 dose, conformal indices of PTV2 and mean PTV2 dose were found between the conventional planning and the conformal planning in the second course. 3. The variation ofcaring' s position was 6±2.01mm between two courses and the movements of caring in three-dimensional directions were closely correlated between two courses(r＞0.7, P＜0.05). No significant disparities in target volume and normal tissue volumes were found except for the volume of PTV2. Except for dosimetric parameter of spinal cord (r=0.337, P=0.341), positive correlations of dosimetric parameters were displayed between reproductive plans and original plans. 4. Significant dosimetric disparities in conformal indices of PTV1, mean PTV1 dose, contralateral lung V_dose(5,10,20,40), contralateral mean lung dose, esophagus V40 and the maximum dose of heart were found between the conventional planning and the conformal planning in the total course.Conclusions By comparison with conventional radiotherapy planning, the three dimensional conformal radiation therapy planning system is able to meet the demands of dosimetric requirements better for radiation therapy of limited-stage small cell lung cancer. No significant dosimetric disparities were found among the surrounding normal tissue and organs. To assure the accuracy of isocenter' s coordinate in combined treatment plans and the positive correlations of dosimetric parameters between reproductive plans and original plans, it is feasible and the practicable to combine two-course treatment plans of one patient who was localized in different position during two-course.