Objective To develop a new type of locating rod with easy installation and high reliability for radiotherapy.Methods The locating rod was composed of a joining beam,two clamping buckles and buckle holders.The joining beam had the length being 530+03 mm.One of the buckles was put at one end of the beam,and the other slided along a stool.An eccentric wheel drove the sliding buckle to determine the space between two buckles,and a returning spring was involved in to enhance the compliance of the sliding buckle.Results The rod gained easy installation and operation,and was compatible with the bed board with the width of 5300 mm.There was no sideslip occurred after locking the rod,and the sideslip shift was not more than 1 mm in case of 20 kgf (1 kgf=9.8 N) lateral traction.Conclnsion The rod has high performances and meets clinical requirements.

Objective:To compare the dosimetric differences between the VenusX accelerator with an orthogonal dual-layer multi-leaf collimator (MLC) and the Varian′s CLINAC IX and EDGE accelerators with a single-layer MLC for hippocampus protection in the whole-brain radiotherapy (WBRT).Methods:Forty patients with multiple brain metastases admitted to the Radiotherapy Department of the Shanghai General Hospital from June 2021 to February 2023 were selected in this study. Three whole-brain treatment plans were designed based on the above three accelerators for each patient. Under the same prescription dose, radiation field, and plan constraints, the three plans were compared in terms of the dosimetric differences in target volumes, hippocampi, and adjacent organs at risk (OARs), as well as the execution efficiency.Results:For the planning target volume (PTV), there were statistically significant differences in approximate maximum dose ( D2) between the VenusX and IX plans ( t = 4.94, P < 0.05), in approximate minimum dose ( D98) between the VenusX and EDGE plans ( t = 5.98, P < 0.05), in the target conformity indices (CIs) between VenusX plan and EDGE plans, and between the VenusX and IX plans ( t = -6.84, -14.30; P < 0.05), and dose homogeneity indices (HIs) between the VenusX and IX plans ( t = 3.48, P < 0.05). For OARs, the maximum doses ( Dmax) and average doses ( Dmean) to bilateral hippocampi of the VenusX plan were lower than those of the EDGE and IX plans ( t = 8.59-17.11, P < 0.05); the maximum doses ( Dmax) to bilateral lenses, bilateral optic nerves, and optic chiasma of the VenusX plan were lower than those of the other two plans ( t = 2.10-20.80, P < 0.05); and the differences between the maximum doses ( Dmax) to the brain stem of the VenusX and EDGE plans were statistically significant ( t = 3.86, P < 0.05). In terms of plan execution efficiency, the number of machine jumps (MU) and the treatment time of the VenusX plan were higher than those of the EDGE and IX plans, with statistically significant differences ( t = -56.48, -56.90, P < 0.05). Conclusions:The doses to target volumes of the three treatment plans all meet the prescription requirements, and the VenusX plan outperforms the EDGE and IX plans in the protection of OARs. Despite the reduced execution efficiency, the VenusX plan shortens the actual treatment time by improving the dosage rate, thus meeting the clinical requirements.

Objective To compare the effects of different respiratory signal acquisition methods on the delineation of moving tumor targets. Methods A cube phantom containing a sphere was placed on a motion platform to simulate respiratory movement by setting motion period, frequency, and direction. Respiratory signal was acquired by real-time position management (RPM) method and GE method independently. Target delineation was conducted using the maximum intensity projection (MIP) sequence. The difference between the reconstructed volume and the theoretical moving volume was compared under the two respiratory signal acquisition methods for cube and sphere targets. Results Under the same respiratory signal acquisition method, the same respiratory amplitude, and different respiratory frequencies, reconstructed volume changes were relatively small. For the sphere target, the deviation between the reconstructed volume and the theoretical moving volume was −1.5% to 5.7% with the RPM method and −1.3% to −13.8% with the GE method (both P < 0.05). For the cube target, the deviation between the reconstructed volume and the theoretical moving volume was 0.2% to 0.9% with the RPM method and −2.6% to 0.9% with the GE method, with no statistical significance. Conclusion For small-volume sphere targets, the target volumes obtained from MIP images by the two respiratory signal acquisition methods are both smaller than the actual moving volume. For large-volume cube targets, there is no significant difference between the reconstructed and theoretical results with any respiratory signal acquisition method. The RPM method produces smaller deviation and better image quality when reconstructing small-volume targets.