ABSTRACT
Objective:To explore the clinical application value of Bodyfix fixation device in stereotactic body radiotherapy (SBRT) for elderly patients with lung cancer.Methods:The clinical data of 63 elderly patients with lung cancer who received SBRT in Tongji Hospital Affiliated to Tongji Medical College of Huazhong University of Science and Technology from January to October 2021 were retrospectively analyzed. According to different fixation methods, the patients were divided into Bodyfix combined with vacuum bag fixation device group (Bodyfix group, 20 cases) and 4D respiratory gating technology combined with vacuum bag fixation device group (vacuum bag group, 43 cases). Cone beam CT (CBCT) was used for position verification before each treatment, linear and rotational errors in the horizontal (X), head-to-foot (Y), front-to-back (Z) directions were recorded.Results:The linear errors of Bodyfix group in the X, Y and Z directions were 1.7 mm (1.3 mm, 3.0 mm), 4.6 mm (4.3 mm, 5.3 mm) and 1.3 mm (0.8 mm, 2.8 mm), and the rotational errors were (0.46±0.04)°, (-0.48±0.05)° and 0.64°(0.38°, 1.07°); the linear errors of vacuum bag group in the X, Y and Z directions were 2.1 mm (1.6 mm, 3.3 mm), 2.8 mm (1.8 mm, 3.7 mm) and 3.0 mm (2.3 mm, 3.8 mm), and the rotational errors were (0.69±0.04)°, (-0.70±0.04)° and 0.64° (0.42°, 0.86°). The differences in linear errors in the Y and Z directions and rotational errors in the X and Y directions between the two groups were statistically significant ( P values were <0.001, <0.001, 0.003 and 0.007). Conclusions:Compared with the 4D respiratory gating technology, the Bodyfix fixation device has smaller rotational errors in the X and Y directions and linear errors in the Z direction. It can be used as an effective method of postural fixation for SBRT in elderly patients with lung cancer.
ABSTRACT
Objective To evaluate dose variations induced by gravity of multi-leaf collimator to provide references for clinical intensity-modulated radiotherapy.Methods Two-dimensional dose distributions in the central plane of IMRT fields were measured by use of a 2D ion chamber array.All measurements were repeated at two collimator angles (C=0 and 90°),for each of the following gantry angles:G=0 and 270°.Comparisons were made to dose distributions generated at G=0°and their differences were analyzed using gamma index analysis (3％/3 mm and 1％/1 mm).Results Under the radiation field of 10 cm×10 cm,the gamma passing rate was higher than 99％ for 3％ 3 mm anch close to 95％ for 1％/1mm Under a 3％/3mm error standard,the average matching rate for step & shoot fields was (96.46±0.33)％ and for DMLC fields was (94.67±0.54)％ at C=0°;The average matching rate for step & shoot fields was (94.59±0.47)％ and for DMLC fields was (92.60±0.52)％ at C=90°.Under a 1％/1mm error standard,the average matching rate for step & shoot fields was (89.83 ±1.06)％ and for DMLC fields was (85.84±0.57)％ at C=0°;The average matching rate for step & shoot fields was (86.91 ±1.71)％ and for DMLC fields was (83.89±0.69)％ at C=90°.Concusion MLC weight effect affects IMRT delivery dose,and DMLC fields are more sensitive to gravity than step & shoot fields.
ABSTRACT
Objective To investigate the design and manufacture of 3D printed compensator in electron radiation therapy for Merkel cell carcinoma,and to verify the feasibility of this technique in electron radiation therapy.Methods Computed tomography was used to collect images of a human head phantom.The delineation of target volume of Merkel cell carcinoma was simulated in the planning system and a radiotherapy plan was formulated after adding the compensator.The compensator was printed out by a 3D printer and fixed on the head phantom.A second CT scan was performed to make a new treatment plan.For the two plans,several planes parallel to the beam were selected to calculate gamma passing rates.The actual dose distribution was measured using disposable films.The gamma passing rate was compared between the film system and the planning system.The conformity index (CI) and the heterogeneity index (HI) of target volume were compared between the plans using the printed compensator and the conventional compensator of the same thickness.Comparison between the two plans was made by paired t test.Results Using the dose distribution of the plan with simulated compensator,the gamma passing rate was 94.7±2.3％ in the plan with 3D printed compensator.Using the dose distribution measured by the film,the gamma passing rate was 96.6％ in the plan with 3D printed compensator.Compared with the conventional compensator,the 3D printed compensator achieved a significantly elevated CI (0.85 vs.0.69,P=0.004) and a slightly improved HI (1.30 vs.1.26,P=0.001).Conclusions The conformal dose distribution provided by 3D printed compensator for tumors at different depths meets the clinical need.