ABSTRACT
Objective To analyze the effect of the fixed-jaw technique on dosimetric parameters during dynamic intensity-modulated radiotherapy (DIMRT) planning. Methods Ten patients each with nasopharyngeal carcinoma, postoperative cervical cancer, and right breast cancer after radical surgery were selected for this study; all patients underwent DIMRT in our hospital in 2020. After administration at the prescribed dose, two methods were used to design the radiotherapy plan for each patient: split-field technique (SFT) and fixed-jaw technique (FJT). The two plans were compared for the differences in the dosimetric parameters and plan verification pass rate. Results Compared with SFT, FJT showed significant decreases (P <0.05) in the following parameters for patients with nasopharyngeal carcinoma, postoperative cervical cancer, and right breast cancer after radical surgery: number of radiation fields (down by 41.5%, 47.3%, and 34.9%, respectively, t = 7.954, 24.2, and 4.949, respectively), total number of monitor units (MUs) (down by 5.6%, 5.3%, and 13.5%, respectively, t = 3.211, 2.423, and 5.481, respectively), and actual beam-on time (down by 25.3%, 23.8%, and 13.6%, respectively, t = 5.814, 9.208, and 5.655, respectively). There were significant differences in some of the dosimetric parameters for all three types of cancer patients between the two plans (P <0.05). There were no significant differences in the plan verification pass rate (P >0.05). Conclusion FJT can reduce the total number of MUs and actual beam-on time while meeting the requirements for clinically prescribed doses in DIMRT planning.
ABSTRACT
Objective The purpose of this study is to provide a reference for the selection of clinical radiotherapy plan by comparing the difference of dosimetry between coplanar dynamic intensity modulation dIMRT and coplanar VMAT plan in hippocampal protective whole brain radiotherapy (WBRT). Methods 10 patients were selected whose hippocampal were protected by WBRT, dIMRT and VMAT plans were designed for each patient, the differences of target dose, organ-endangering dose and machine hop count were compared between the two groups. Results The two technical plans PTV V30 Gy, D98% and D2% all meet the standard of RTOG 0933, which is better than the dIMRT group for the PTV HI VMAT group (P = 0.004). The hippocampal dose of dIMRT group was better than that of VMAT group, but it did not meet the standard of RGOT 0933. The average Dmax of hippocampus in dIMRT group and VMAT group was 18.44 Gy and 19.30 Gy, respectively (P = 0.004). The average value of hippocampal Dmin was 10.03 Gy and 10.77 Gy, respectively (P = 0.013), and the mean value of hippocampal Dmean was 14.20 Gy and 15.12 Gy, respectively (P = 0.002). The doses of lens, eyeball and optic nerve all met the standard of RTOG0933, and the dose of dIMRT group was significantly better than that of VMAT group (P = 0.000). The treatment time in VMAT group was significantly lower than that in dIMRT group. The treatment time in VMAT group was significantly lower than that in dIMRT group. Conclusion Varian dIMRT has more advantages in controlling hippocampal dose and protecting lens than VMAT, but PTV HI and treatment efficiency are higher in VMAT group.
ABSTRACT
Objective:To evaluate the dosimetric effect of multi-leaf collimator (MLC) position error on dynamic intensity-modulated radiotherapy (dMLC-IMRT), aiming to provide guidance for the establishment of MLC quality control accuracy and operation tolerance.Methods:In the phantom study, the virtual water phantom established in the treatment planning system (TPS), and three dynamic sliding window test fields with gap width of 5 mm, 10 mm and 20 mm were designed. Clinical treatment plans of 7 common tumor types were extracted, including nasopharyngeal carcinoma, glioma, lung cancer, esophageal cancer, cervical cancer, prostate cancer, and breast cancer, with 6 cases in each. MLC errors were introduced into the copy from original plan to generate the simulation plans. MLC errors included systematic open/close error, systematic deviation error and random error. The dosimetric differences between the original and simulation plans were compared.Results:The phantom study showed that the symbol of dose deviation was the same as that of systematic open/close error, and the value was increased with the increase of MLC error and decreased with the increase of gap width. The results of patient study showed that the systematic open/close error had a significant effect on dosimetry, the target volume dose sensitivities of different plans were 7.258-13.743%/mm, and were negatively correlated with the average field width. The dosimetric deviation caused by the systematic shift error below 2 mm was less than 2%. The dosimetric change caused by the random error below 2 mm could be neglected in clinical treatment.Conclusions:The minimal gap width should be limited in TPS, whereas the quality control of MLC should be strengthened. In addition, for the dynamic intensity-modulated treatment technology, 2 mm random error was suggested to be the operation tolerance during treatment delivery, and 0.2 mm alignment accuracy on each side (or 0.4 mm unilateral) is recommended to be the MLC quality control accuracy to ensure the dose accuracy of radiotherapy for different tumors.