Objective To investigate the impact of accelerator′s multi-leaf collimator (MLC) on the radiotherapy dose with different gantry angles.Methods Measured with Mapcheck 2D diode array and 30 cm×30 cm×3 cm solid water, Pre-selecting the 30 appropriate single fields and 0°,45°,90°,270°,315° gantry angles of static and dynamic intensity modulated radiation therapy (IMRT), quantification analysis of the passing rate with MapCheck γ(3%/3 mm) and (5%/3 mm) analysis methods, and the same method to 30 examples static and dynamic IMRT plans.Results When the accelerator collimator angle is 0°,the 30 appropriate single fields′ passing rate of between 0°gantry angle and 45°,90°,270°,315°gantry angles of static and dynamic IMRT accordingly is 97.71% and 96.25%(t=1.70, P=0.389), 96.34% and 93.72%(t=2.95, P=0.002), 96.65% and 92.98%(t=2.87, P=0.005), 95.87% and 93.15%(t=2.71, P=0.006), 96.09% and 93.51%(t=2.89, P=0.004) with MapCheck γ(3%/3 mm) analysis methods, however, the passing rate also does not have the difference, respectively is 99.31%-99.73% and 98.89-99.68%(t=0.57-1.90, P=0.913-0.725) with MapCheck γ(5%/3 mm) analysis methods;the passing rate of 30 examples static and dynamic IMRT plans accordingly is 96.11%-96.76% and 94.88%-95.78%(t=1.02-1.61, P=0.317-0.235).Conclusions When the accelerator collimator angle is 0°, at different gantry angles, MLC leaves due to gravity, friction, inertia, etc caused by errors in place, the physical penumbra and leakage radiation will indeed affect the IMRT dose, however, the deviation of dose distribution is within acceptable 5%.

OBJECTIVETo discuss the influence of setup errors on the accuracy of pelvic cancer in IGRT, analysis setup errors and determine the CTV-to-PTV margins.

METHODS60 pelvic cancer patients treated with Varian 23IX, all of them were performed by CBCT before and after-correction three times in the first week and after that once a week. Then, to measure the setup errors at X(left-right), Y(superior-inferior), Z(anterior-posterior) axis and E(coronal), F(sagittal), G(axial) rotation directions.

RESULTS530 scans obtained in all, the setup errors in X, Y, Z, E, F, G were (-0.52 ± 4.18) mm, (0.73 ± 4.86) mm, (-0.36 ± 3.62) mm, (0.14 ± 1.20)degrees, (0.13 ± 1.34)degrees, (0.21 ± 1.73)degrees respectively and were much lower after correction at X, Y, Z axis, besides, CTV-to-PTV margins decrease a lot.

CONCLUSIONThe accuracy of radiotherapy can be highly increased with the use of IGRT in pelvic cancer.

Humans ; Pelvic Neoplasms ; radiotherapy ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted ; Radiotherapy, Image-Guided

Objective: To compare the dosimetric differences among Target-Segmented Plan (TSP), Non-TSP, and conventional static 8-field intensity modulated radiation therapy (8F-IMRT) plan for post-mastectomy irradiation of left-sided breast cancer patients. Methods: This study enrolled thirty consecutive breast cancer patients who underwent radical mastectomy and treated with post-op radiation in Department of Radiation Oncology, Renmin Hospital of Wuhan University from June 2017 to November 2018.The clinical target volume (CTV) included the ipsilateral chest wall, supra/infra-clavicular, high-risk partial axillary in high risk, and internal mammary nodes (IMN). The organs at risk (OARs) near the targets, including ipsilateral lung, heart, contralateral breast, ipsilateral humeral head and spinal cord, were contoured as well. The maximum distance of PTV′s tangent to the outermost side of the affected lung was more than 2 cm. Depending on the maximum distance, the patients were classified into three groups: A(<3 cm), B(3~4 cm) and C(>4 cm), respectively. Three types of treatment plans (TSP, Non-TSP and 8F-IMRT) were created for each patient using the Eclipse treatment planning system with the same dose optimization objective . The dose-volume histograms were compared for the PTVs and OARs. Results: All plans achieved the intended dose criteria.The D_98% of TSP was lower than that of Non-TSP and 8F-IMRT (Z=-3.294, -3.266, P<0.05). However, the homogeneity index (HI) and conformal index (CI) of the three plans had no statistically significant difference among the three plans (P>0.05). Non-TSP required more Monitor Units (MUs)than the other two plans (Z=-3.04, -2.669, P<0.05). The D_mean of TSP was higher than that of 8F-IMRT (Z=-3.181, P<0.05). Compared with Non-TSP and 8F-IMRT plans, TSP significantly reduced V_{5 Gy}, V_{10 Gy}, V_{20 Gy} and D_meanof ipsilateral lung and heart in all patients (lung: V_{5 Gy}: Z=-3.408, -3.408; V_{10 Gy}: Z=-3.408, -3.408; V_{20 Gy}: Z=-3.408, -3.124; D_mean: Z=-3.408, -3.408, P<0.05; heart: V_{5 Gy}: Z=-3.408, -3.408; V_{10 Gy}: Z=-3.408, -3.408; V_{20 Gy}: Z=-2.499, -3.067; D_mean: Z=-3.408, -3.408, P<0.05). The D_mean of contralateral breast in Non-TSP was higher than that in TSP and 8F-IMRT (Z=-2.954, -2.215, P<0.05), and the D_maxhas no significant difference in (P>0.05). There was no significant difference in spinal cord D_max among the three plans, but the D_mean of humeral head in 8F-IMRT was higher than that in TSP and Non-TSP (Z=-3.01, -2.442, P<0.05). In the three groups, the mean amplitude of difference comparing Non-TSP and 8F-IMRT with TSP in ipsilateral lung(V_{5 Gy}, V_{10 Gy}, V_{20 Gy}) and heart(V_{5 Gy}, V_{10 Gy}, D_mean) satisfied the relation: D(N-T, A)<D(N-T, B) <D(N-T, C)和D(8F-T, A)<D(8F-T, B) <D(8F-T, C). Conclusions For post-mastectomy left-sided breast cancer patients, TSP is not only dosimetrically feasible as Non-TSP and 8F-IMRT treatment techniques, but also could effectively reduce the irradiation volume of the ipsilateral lung and heart in the low dose area with minimum adverse dosimetric impact on the treatment targets and other OARs.The advantage of TSP is more prominent with increasing curvature of the clinic target volume.