In the treatment of primary liver cancer and metastatic liver cancer,stereotactic body radiotherapy(SBRT)can be utilized to administer high doses of radiation for achieving ablative therapeutic effects.Given the singular nature of delivering high-dose radiation through SBRT,a higher level of precision is required in radiation therapy.Particularly,liver cancer is susceptible to positioning errors and respiratory motion,necessitating the implementation of respiratory motion management and image guidance techniques.However,existing accuracy verification methods for radiation therapy primarily rely on phantom studies,making it challenging to conduct in-vivo verification during treat-ment execution.Research has indicated that the liver exhibits corresponding morphological changes in magnetic reso-nance imaging following exposure to specific doses of radiation therapy,thereby serving as an indicator for assessing treatment accuracy.This article aims to discuss and analyze the principles underlying magnetic resonance imaging alterations after stereotactic body radiotherapy for liver cancer,including their manifestations,timing of appearance,evaluation methodologies for accuracy assessment,clinical challenges encountered during implementation,as well as future directions for development.

Objective:To evaluate the accuracy of the optical surface imaging system (OSI) using stereotactic radiosurgery (SRS) algorithm in single-center non-coplanar treatment of multiple brain metastases.Methods:Data of phantom and 15 patients with multiple brain metastases who underwent single-center non-coplanar radiotherapy in West China Hospital of Sichuan University from February to April 2022 were retrospectively analyzed. kV/MV and OSI imaging were used for imaging of the patients and phantoms under the same non-coplanar couch angle, respectively. The accuracy of OSI imaging of the phantoms and patients was evaluated using kV/MV imaging as reference image. The difference between the OSI and kV/MV systems is defined as accuracy, and the percentage of the absolute difference ≤1.00 mm in the translational direction or ≤0.50° in the rotational direction is defined as the threshold pass rate. Origin software was used to draw radar maps and Bland-Altman plots for statistical analysis.Results:When OSI images were used for the phantom imaging, the average differences in six-dimensional directions of lateral, long, vertical, rotational, roll and pitch were 0.03 mm, -0.09 mm, -0.27 mm, 0.04°, 0.17° and -0.19°, respectively. The maximum values were -2.20 mm, -2.30 mm, -1.20 mm, 0.60°, -1.00°, and -1.00°, respectively. When OSI system was utilized for the imaging of 15 patients, the average differences in six-dimensional directions were 0.44 mm, 0.16 mm, -0.20 mm, -0.11°, 0.10°, and -0.12°, respectively. The maximum values were -1.80 mm, 2.00 mm, 0.90 mm, -0.90°, -0.70°, and 0.80°, respectively. The translational errors mainly occurred in the lateral and long directions. The qualified rates of the threshold values of the phantoms and patients were 77% and 75% in the lateral direction, 82% and 89% in the long direction, respectively. In addition, 57% and 56% of patients met the threshold conditions of ±1.00 mm and ±0.50° in the six-dimensional directions, respectively.Conclusions:The OSI system using new SRS algorithm cannot meet the high accuracy requirements of single-center non-coplanar radiotherapy for multiple brain metastasis, especially in the lateral and long directions. It is not recommended for non-coplanar image guidance.

This paper describes the design of an innovative linear accelerator image-guided radiosurgery(IGRS)device,which is based on a composite twofold rotary gantry structure.The paper discusses five aspects of the innovative device:its overall composition,the safety net space created by the accelerator radiation head as it rotates around the patient's longitudinal axis,the non-coplanar spherical coverage in the direction of the incidence angle for quasi-4π delivery,the structural features of the composite twofold rotary gantry,and the processes of treatment planning and implementation.It elaborates on the device's manufacturing feasibility,safety,effectiveness,accuracy,and efficiency.The conclusion is that this innovative device design holds significant development value and market promotion potential.

Objective:To evaluate the accuracy and stability of stereotactic radiosurgery (SRS) algorithm in optical surface imaging (OSI) system in non-coplanar radiotherapy.Methods:Three OSI imaging systems were used to measure the phantom repeatedly at different couch rotation angles to analyze the accuracy and stability of OSI system. Seven patients with multiple brain metastases who underwent single-center non-coplanar radiotherapy were randomly selected, and the accuracy and stability of OSI for patient imaging were analyzed. Stability is defined as the difference between the two OSI measurements when the couch is turned from 0° to a non 0° angle, and then back to 0°, using the 0° cone beam CT (CBCT) as the "gold standard". Accuracy is defined as the difference between OSI and CBCT (at 0° couch angle) measurement data. The measurement data with normal distribution were described as Mean ± SD. The data with non-normal distribution were expressed as M (Q). The difference of the former data was compared by one-way ANOVA, and the difference of the latter data was assessed by Kruskal-Wallis H nonparametric test. Results:For non-coplanarity, the translation accuracy of the phantom and the patient was ≤ 1.30 mm and ≤ 1.00 mm, and the rotation accuracy was ≤ 0.50° and ≤ 0.60°, respectively. The translation errors mainly occurred in the left-right and head-foot directions. In terms of stability, the maximum standard deviation of phantom coplanar translation and rotation was 0.06 mm and 0.06°. The maximum standard deviation of patient translation and rotation was 0.17 mm and 0.19°.Conclusions:Although the new SRS algorithm improves the non-coplanar accuracy, it still cannot meet the precise requirements of non-coplanar single isocenter radiotherapy for multiple brain metastases, especially in the left-right and head-foot directions. When the couch rotation angle is large, OSI is not recommended for image-guided radiotherapy. However, its high stability can be used to monitor the intrafractional motion of patients.

In case of ischemic stroke(IS),thrombus in the vascular system can cause ischemia and hypoxia in brain tissue,produce inflammatory cytokines and cause brain tissue damage,while reactive oxygen species during ischemia-reperfusion cause stress injury.Conventional drug administra-tion is limited by the selective permeability of the blood-brain barrier and the low bioavailability of the drug itself,and its therapeutic effect against IS is unsatisfactory.Nanomedicine is expected to bring hope in that it has a unique mechanism of action and can cross the blood-brain barrier to reach the periphery of the infarct,release drugs or therapeutic genes,and exert a therapeutic effect.Nanomedi-cine inhibits platelet aggregation,enhances the efficacy of thrombolytic drugs,dissolves thrombus,increases blood supply to ischemic areas,eliminates reactive oxygen species and weakens injury response by fighting inflammatory cytokines.Loaded therapeutic genes regulate the differentiation pro-cess of neural stem cells,increase the number of neurons,induce the occurrence of blood vessels,and enhance the repair function of brain tissue.Nanomedicines can not only improve pharmacokinetics and pharmacodynamics to achieve more effective drug treatment,but also use nanoimaging technology to achieve real-time monitoring and condition assessment of therapy.

Objective:To introduce the stereotactic cardiac radioablation (SCRA) based on the stereotactic body radiotherapy (SBRT), and comprehensively evaluate the new approach by short-term effectiveness and safety.Methods:Patients with ventricular arrhythmia (VA) were evaluated and included in this clinical trial, who were immobilized by vacuum bag and performed simulation with 4-dimensional computed tomography (4DCT). In this study, the planning target volume (PTV) was set as the target to design a SBRT plan using volumetric modulated arc therapy (VMAT), which was evaluated by dose parameters such as R 50%, homogeneity index and conformity index, etc. The results of Holter and echocardiography were monitored during the follow-up and compared with the data before treatment. Results:Three subjects with ventricular tachycardia (VT) and one with premature ventricular contraction (PVC) received the same prescription of 25 Gy in a single fraction. The average volume of PTV was 71.4 cm 3(60.3-89.4 cm 3). The average time of beam delivery was 12.0 min (4.5-21.0 min). And the short-term follow-up lasted for an average of 18 weeks (14-25 weeks), which showed significant decrease in both VT and PVC load without complications. Conclusion:This study reports the implementation method of SCRA and proves its short-term effectiveness and safety, but the effects and standards of the key radiotherapy techniques still need to be explored.

Objective:To evaluate the effects of orthogonal magnetic fields on the dose distribution of 6 MeV X-ray in a uniform water and heterogeneous phantoms.Methods:The Monte Carlo simulation software Gate v8.2 was used to investigate the dose distribution of X-ray beams of different field sizes in a uniform water phantom, water-air/bone-water layer phantom and" custom lung model" in the magnetic field strength of 0.0, 0.5, 1.0, 1.5, 3.0 T, respectively. The relationship between the intensity of magnetic field and the dose distribution of X-rays in the phantoms was analyzed.Results:The existence of a magnetic field would cause the X-ray to shorten the built-up area in the water phantom; when the field was 10 cm×10 cm, the maximum dose on the central axis could change by up to 56.22%(3.0 T). The transverse dose distribution of the radiation field in the direction of the vertical magnetic field shifted to one side by up to 43.64%(-44.55%). The average dose of the air layer in the water-air-water phantom could be reduced by 57.4%(3.0 T). In the water-bone-water phantom, the dose at the proximal end of the bone layer was decreased by 16.5%, whereas the dose at the distal end was increased by 22.6%(1.5 T). The dose change in each layer in the customed lung model was positively correlated with the magnetic field strength.Conclusion:The existence of the orthogonal magnetic field will cause the change of X-ray dose distribution on the built-up area and both sides of the radiation field in the phantoms, which is more obvious adjacent to the interface of heterogeneous phantom.

Objective:To quantify the registration deviation between CT and cone-beam computed tomography (CBCT) images with different breathing rates and motion amplitudes under free breathing state.Methods:Using the QUASAR respiratory motion phantom, breathing rate and motion amplitude in the superior-inferior (SI) direction were changed to simulate free breathing motion under different states. The CT and CBCT images were acquired under different breathing rates and motion amplitudes, and static states, then the registration errors between CT and CBCT images and CT target volume were obtained and subject to quantitative analysis.Results:Using the static CT image as a reference, the changes in breathing rate exerted no significant effect on the registration error when the motion amplitude was constant. When the motion amplitude was 0.5, 1.0, 2.0, and 3.0 cm, the average registration errors were (0.213±0.020), (0.351±0.009), (0.654±0.010), and (0.972±0.022) cm, respectively. When the motion amplitude was 0.5 and 1.0 cm, the CT target volume varied from -16.92% to 18.78%. When the motion amplitude was 2.0 and 3.0 cm, the CT target volume changed from -16.44% to 81.78%.Conclusions:The changes in breathing rate under free-breathing state has no significant effect on the registration error between CBCT and CT images. When the motion amplitude is 0.5 and 1.0 cm, the CT target volume changes and the registration errors are small. When themotion amplitude is 2.0 and 3.0 cm, the registration errors exceed 0.5 cm and the CT target volume changes may exceed 20%.

Radiotherapy is a vital treatment method for pancreatic cancer. However, the therapeutic effect of radiotherapy is significantly limited by the influence of pancreatic motion. More efficient radiotherapy for pancreatic cancer depends upon the improvement of motion management and high-quality image guidance. The emerging MR-guided radiotherapy (MRgRT) can perform functional imaging with high soft tissue resolution and no additional radiation. Multiple researches have demonstrated that MRgRT has significant advantages in terms of precise delineation of target area and organ at risk, motion management and adaptive radiotherapy, which assists radiotherapy to play a better role in the treatment of pancreatic cancer. In this paper, the application of MRgRT in pancreatic cancer was reviewed and prospected.

Stereotactic radiotherapy (SRT), also known as stereotactic ablative radiotherapy (SABR), includes stereotactic radiosurgery and stereotactic body radiotherapy (SBRT). This technique has the characteristics of large single fractional dose, few fractions, high equivalent biological doses, and rapid fall off-target doses. It can be implemented by relatively special equipment such as Gamma knife, Cyberknife, Tomotherapy and Vero 4D RT system, etc. In many cases, SBRT technique is employed based on linear accelerators. SRT differs from conventional radiotherapy in terms of the plan design and plan evaluation. Consequently, it is necessary to discuss the differences and provide guidance for clinical application and research.