RESUMO
Objective:To explore a new technique for lung dose reduction in esophageal cancer radiotherapy based on the dose distribution characteristics of the half-field combined with intensity-modulated radiotherapy (IMRT) technique.Methods:A three-dimensional water tank was used to measure the dose distribution at the edge of the symmetrical field and half-field, which was then compared and analyzed. Twenty patients with the middle and lower thoracic esophageal cancer receiving radiotherapy with prescription doses of 50.4-60.0 Gy were selected. Based on the Varian Vital beam linear accelerator and Eclipse planning system, flattening filter (FF) technique symmetrical field and half-field beam design and the flattening filter-free (FFF) technique symmetrical field and half-field design were adopted to compare and analyze various dose data and treatment MU numbers for the target area and the endangered organs. The field settings were chosen in the front 1 and back 4 mode.Results:Compared with the symmetrical field plan, the half-field plan significantly improved the irradiated dose to the lung with a statistically significant difference ( P<0.05), and the half-field FFF was slightly better than the half-field FF mode. Compared with the total lung V 5Gy, V 20Gy, V 30Gy, and D mean dosimetric parameters (Gy), the FF symmetric field and FFF half-field were (49.64±5.39)% vs.(42.70±5.53)%, (15.99±3.93)% vs.(13.32±3.06)%, (9.24±2.77)% vs.(8.50±2.62)%, and (10.45±1.76)% vs.(9.50±1.53)%, respectively. There was a significant reduction in the volume dose values for all structures of the lung (all P<0.05). For other comparative data, the irradiated dose for the heart of the symmetrical field was better than that of the half-field mode ( P<0.05), and the differences in conformity index (CI) and homogeneity index (HI), number of treated MU, and spinal cord associated with the target area were not statistically significant (all P>0.05). Conclusions:During radiotherapy for esophageal cancer, target area coverage and dose volume data of the lung are the main parameters affecting the efficacy and side effects. IMRT treatment based on the half-field mode can give full play to the advantages of half-field and IMRT, and significantly improve the irradiated dose to the lung, which can offer an additional clinical option.
RESUMO
Objective:To explore a new technology that can protect the lungs and heart better by utilizing the dose distribution attributes of the half-field and the characteristics of the VMAT (volumetric modulated arc therapy) technology.Methods:A three-dimensional water tank was used to measure the dose of symmetrical field and half field edge and analyze them comparatively. A total of 50 patients with left breast cancer receiving the postoperative radiotherapy were selected. Among them, 25 patients were performed conserving surgery and 25 patients were performed radical mastectomy. After the operation, all the patients received the prescription dose of 50 Gy in 25 fractions. Based on the Eclipse system, the symmetrical field continuous arc VMAT technology and the semi-field segmented arc VMAT technology were used to design the plan. Besides, the dose suitability data and the treatment efficiency of target areas and organs at risk were compared and analyzed.Results:The radiation size of half-field did not increase with the increased depth in the water mode. The symmetric field gradually enlarged due to the angle of tensor factor, increased to about 2 cm at the depth of 30 cm, and the delivery dose in the half-field was lower than that in the symmetric field. The closer the field edge is, the more obvious it is. Compared with the symmetric field continuous arc plan, the half-field segmental arc VMAT plan significantly improved the delivery dose of the lungs and heart ( t=-4.11, -4.42, P=0.00), in which the mean values of V5, V30, and Dmean for the whole structure of the heart were reduced by 52.5%, 65.5%, and 47%, respectively. The left anterior descending coronary artery, which was closely related to the target area, had a decrease of more than 20%. The mean values of V5, V10, V20, and Dmean of the affected lung were reduced by 21.6%, 24.8%, 25.0%, and 23.2%, respectively. The mean values of the doses of other endangered healthy organs, and the execution time of half-field segment arc plan were also better than the continuous arc plan. Conclusions:For breast cancer radiotherapy, the combination of half-field and VMAT can give full play to the advantages of half-field and VMAT, and significantly reduce the irradiated dose of the heart, affected lung, and healthy side of the breast.
RESUMO
Objective:To analyze the setup and residual errors of spinal cord during online CT-guided radiotherapy for patients with esophageal cancer, and to discuss the necessity of segmental extension of spinal cord.Methods:According to the radiotherapy site, 60 cases of esophageal cancer were divided into the neck, chest and abdomen groups, 20 cases in each group. Cervical pleura or vacuum bag was fixed, IMRT technology was adopted, and pre-treatment CT images were obtained by CT Vision, and 20 consecutive CT scans were collected for each case. CT images were imported into MIM software. The parameters of the setup errors were processed and extracted. The CT spinal cord was delineated for verification and planning, and the Dice coefficient, Hausdorff maximum distance and centroid coordinate of the delineated spinal cord were processed and extracted. Compatibility anova data were adopted. The calculation formula of the extension margin is M PRV= 1.3 ∑ total+ 0.5 σ total. Results:Residual centroid method was employed. Non-on-line and on-line CT-guided radiotherapy, the extension margins of neck, chest, abdominal spinal cord in the x-, y-and z-axis were 3.86, 5.37, 6.36 mm; 3.45, 3.83, 4.51 mm; 4.05, 4.83, 7.06 mm, vs, 2.85, 2.19, 2.83 mm; 2.32, 2.20, 2.16 mm; 2.86, 2.21, 2.83 mm, respectively. During residual Hausdorff distance method, non-on-line and on-line CT guided radiotherapy, the extension margins of neck, chest, abdominal spinal cord in the x-, y-and z-axis were 3.10, 5.33, 6.15 mm; 3.30, 3.77, 4.61 mm; 3.35, 4.76, 6.87 mm, vs, 2.12, 2.06, 2.32 mm; 2.12, 2.06, 2.32 mm; 2.12, 2.06, 2.32 mm, respectively.Conclusion:The setup errors and residual errors are different in each segment of spinal cord. Henc, different extension margins should be given.