ABSTRACT
Objective To evaluate the performance of progressive optimization algorithm-based Auto-Planning module in automated volumetric-modulated arc therapy(VMAT)planning for nasopharyngeal carcinoma. Methods Thirteen treated VMAT plans of nasopharyngeal carcinoma were re-planed with Auto-Planning module. Only one cycle of automated optimization of the Auto-Planning module was performed for each plan without any manual intervention. The dosimetric parameters of the automated treatment plans were compared with those of the manual plans. Paired t-test was used for statistical analysis. The time required for automated planning using the Auto-Planning module was also measured. Results All plans generated with the Auto-Planning module met the routine dosimetric requirements and were acceptable for clinical use. The homogeneity index of targets was superior in the automated plans than in manual plans(P= 0.000).In addition,the automated plans had significantly improved protection for some organs at risk than the manual plans. The mean dose to the left and right parotids were reduced by 7.75 Gy(P=0.000)and 5.79 Gy(P=0.000)in the automated plans,respectively. Furthermore,the V60(0.58% vs. 3.12%,P=0.000)and Dmean(34.11 Gy vs. 40.78 Gy,P= 0.000)of the mandible were also significantly lower with Auto-Planning than with manual planning. Conclusions Auto-Planning module can improve the overall quality and consistency of treatment plans,and reduce the workload and time of treatment planning,resulting in substantially enhanced treatment planning efficiency.
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Objective To investigate the influence of treatment table with C-arm and immobilization device in IMRT planning accuracy, and to explore methods to solve this problem.Methods The solid water slabs and the ionization chamber was scanned and images were transmitted to the treatment planning system (TPS).Beam parameters in the TPS were set with 6 MV beam and 100 MU exposures were used.Measurements were performed at two different sizes of 5 cm×5 cm and 10 cm×10 cm.The gantry was rotated through angles from 0° to 180° with measurements taken at 5° increments.The measure point was set at center of the ionization chamber' measure point, which was also the central point of planning.The center axis of Matrix was aligned with the center of couch and was irradiated in accordance with the same conditions.OmniPro-FmRT software was used to compare and analyze the dose distribution of the radiation field of measurement and the treatment planning system output.Using the function of add constant value to find the appropriate coefficient to improve the plan total dose.The dose distributions for each beam in IMRT plans which was increased or unincreased total dose were measured for 6 patients with pelvic tumor respectively.Results In radiation therapy, treatment couch and immobilization device may attenuate radiotherapy dose.The impact of the incident range from 65°-70° and 115°-125° were the largest.Increasing the total dose of the treatment plan by 2％ could compensate the attenuation of the treatment table and immobilization device.Conclusions In radiation therapy, the impact of the incident range from 65°-70°, 115°-125° and another side of 290°-295° and 230°-245° should be avoided.The attenuation should not be neglected in the TPS and dose should be compensated by adjusting beams' MU.
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Objective To analyze the impact of dose calculation resolution on Gamma pass rate for planar dose distribution verification of intensity-modulated radiotherapy (IMRT),and to find out the appropriate calculation resolution value with specific applied criteria.Methods 25 IMRT plans were selected for the planar dose verification.The Gamma pass rates with 3 mm/3％,2 mm/2％ and 1 mm/1％ criteria were compared and analyzed.The planar dose distributions were calculatedand exported from TPS with different resolutions of 0.5,1,2,3,4 and 5 mm.The pass rates of Gamma analysis between the computed dose distributions with different resolutions and the dose distributions measured by Mapcheck device were compared and analyzed.Results The average Gamma pass rates of all the 225 fields decreased with the increment of calculation resolution.When the pass rates of Gamma analysis were calculated using 3 mm/3％ criteria,the gamma pass rate with 1 mm and 0.5 mm calculation resolution were (98.3±1.3)％ and (98.3±1.2)％,respectively.The results were almost the same and the difference wasn't statistically significant (P＞0.05).The gamma pass rates with greater than or equal to3 mm calculation resolution were significantly less than the pass rate with 0.5 mm calculation resolution (P＜0.05).When the pass rates of Gamma analysis were calculated using 2 mm/2％ criteria,all the pass rates with greater than 0.5 mm calculation resolution were significantly less than the pass rate with 0.5 mm calculation resolution (P＜0.05).Conclusions The Gamma pass rates of planar dose verification reduce significantly with the increment of calculation resolution.In order to reduce the effect of calculation resolution on Gamma pass rate,the lower calculation resolution should be used.When using the 3 mm/3％ criteria for the Gamma analysis,1 mm calculation resolution is recommended.When using the 2 mn/2％ criteria for the Gamma analysis,0.5 mm calculation resolution is recommended.The appropriate calculation resolution will ensure the reliability of planar dose verification.
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Objective To analyze the anatomic changes and dosimetric variations of patients with head-and-neck cancer during intensity-modulated radiotherapy and to assess the necessity of re-planning the treatment course.Methods Twenty-one nasopharyngeal carcinoma patients were selected to receive the second CT scan in the course of intensity-modulated radiotherapy,targets and organs at risk were re-contoured on the new CT images with the help of deformable registration software.Actual dose distribution delivered by the original treatment plan was calculated on the second CT image,and then the volume and doses of targets and organs at risk were compared between the planning CT and second CT.Results The volume of patient's head-and-neck outlines and GTVnd decreased significantly,the volume of cord and brainstem didn't change much,while the volume of left and right parotids decreased significantly by (24.23 ± 12.15)％ and (25.82± 10.46)％,respectively.The parameters D95％ and Dmean of PGTVnx kept stable,but the parameters D1cc of spinal cord PRV and brainstem PRV increased by (8.12± 10.32)％ and (14.60±18.85)％ respectively.The mean dose of the left and right parotids increased significantly by (27.43±17.67)％ and (26.76±12.46)％,respectively.Conclusion The anatomical changes of patients undergoing intensity-modulated radiotherapy will cause significant dosimetric variations of the cord,brainstem and parotids,so it's meaningful and necessary to re-design the treatment plan in the course of radiotherapy.Repeat CT imaging and replanning during the course of IMRT is essential to ensure adequate doses to target volumes and safe doses to normal tissue.
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Objective To study the impact of accelerator's gantry angle on MLC position accuracy. Methods Kodak X-omat-V Films were used, appropriate multi-leaf collimator positions and gantry angles were chosen, precise setup was needed , and the exposal films were analyzed by RIT113 software. Results At all conditions, most of the leaf position errors were less than 0. 5 mm. There were 2 pairs of leaf position errors larger than 1 mm when the gantry angle was 270° and the leaves moved from left to right. Conclu-sions Gantry angle can affect the accuracy of multi-leaf collimator position. Gravity and inertia increase the uncertainty of leaf position accuracy. Prieise setup is critical for the dose measurement.