As the lateral amplitude of the fuel assembly grows, it exhibits nonlinear characteristics, including a decrease in stiffness, a decrease in frequency, and an increase in the damping ratio. This study aims to simulate the aforementioned phenomena by introducing the Bouc-Wen nonlinear hysteresis model to develop a nonlinear mechanical model for the lateral vibration of fuel assemblies. Additionally, a multi-objective genetic optimization algorithm (NSGA-II) is employed to determine the model's unknown parameters. The computational results indicate that the nonlinear model effectively simulates the phenomena of decreased stiffness, decreased frequency, and increased damping ratio observed in the tests. Based on this nonlinear mechanical model, this study developed an impact analysis model for a single group of fuel assemblies using the Kelvin impact element. The model was then utilized to simulate fuel assembly single-point and multi-point impact tests. The calculation results indicate that the maximum impact force Fmax at each grid position closely aligns with the test results, exhibiting a maximum relative error of less than 2%. This proves that the impact analysis model effectively simulates the collision behavior of the fuel assembly. Simultaneously, the effects of parameters like impact stiffness, impact gap, and impact impulse on the computational results are also thoroughly researched in this study. Some conclusions that are helpful for fuel assembly impact simulation studies are summarized, such as the discovery that impact stiffness and impact gap have a significant non-linear effect on the grid's Fmax.

With the development of social economy and radiotherapy technique, proton/heavy ion radiotherapy has been applied widely to clinical practices. At present, there are at least 29 hospitals in China at various stages of planning, construction, commissioning or clinical operation of medical proton/heavy ion beam radiotherapy equipment. Compared with common radiotherapy accelerators used in conventional external beam radiotherapy, the proton/heavy ion therapy system has more stringent requirements for quality control so as to achieve an optimum therapeutic effect. In order to protect the health rights of patients undergoing radiotherapy, to facilitate the relevant administrative supervision departments to carry out standard-based approval and routine supervision and to promote the development of related medical undertakings, the standard for testing of quality control for medical proton/heavy ion beam radiotherapy equipment is drafted to fill the gap in this regard in China and even worldwide. The standard contains five indicators and corresponding testing methods for radiological protection and safety and 16 indicators for quality control of equipment performance. The standard is a mandatory standard and is based on the relevant Chinese legal requirements for the testing of radiotherapy equipment, so all the indicators listed in the standard shall be tested. During the drafting of the standard, the opinions from hospitals that are currently using proton/heavy ion medical accelerators for radiotherapy purpose and from the related equipment manufacturers were taken into account. The draft standard was revised with reference to these opinions and the feasibility of the related quality control requirements. The official version of the standard was released on March 7, 2023, and implementation is scheduled to begin on March 1, 2024.

Abstract Aims Adjuvant chemotherapy (ACT) plays an important role in improving the survival of stage II-III colorectal cancer (CRC) patients after curative surgery. However, the prognostic role of irregular delay of ACT (IDacT) for these patients has been less studied. Materials and methods A total of 117 stage II-III CRC patients who underwent radical resection and received at least 3 months ACT were enrolled retrospectively. The significance of IDacT, including total delay (TD) and delay per cycle (DpC), in predicting disease-free survival (DFS) was determined using receiver operating characteristic curve (ROC) analysis. The survival differences between the TD, DpC-short and DpC-long subgroups were tested using Kaplan–Meier analysis, and risk factors for prognosis were determined using a Cox proportional hazards model. Results Using 35.50 and 3.27 days as the optimal cut-off points for TD and DpC, respectively, ROC analysis revealed that TD and DpC had sensitivities of 43.60% and 59.00% and specificities of 83.30% and 62.80%, respectively, in predicting DFS (both P < 0.05). No differences in the clinicopathological parameters were found between the TD, DpC-short or -long subgroups except histological differentiation in different TD subgroups and combined T stages in different DpC subgroups (both P = 0.04). Patients in the TD or DpC-long group exhibited significantly worse survival than in the -short group (TD: Log rank = 9.11, P < 0.01; DpC: Log rank = 6.09, P = 0.01). DpC was an independent risk factor for prognosis (HR = 2.54, 95% CI: 1.32–4.88, P = 0.01). Conclusions IDacT had a profound effect on the outcome for stage II-III CRC. Although TD and DpC were significant for the prognosis, DpC was more robust, and patients who presented DpC for a long time had a significantly worse DFS.

Background Robotic linac is ideally suited to deliver hypo-fractionated radiotherapy due to its compact head and flexible positioning. The non-coplanar treatment space improves the delivery versatility but the complexity also leads to prolonged optimization and treatment time. Methods In this study, we attempted to use the deep learning (pytorch) framework for the plan optimization of circular cone based robotic radiotherapy. The optimization problem was topologized into a simple feedforward neural network, thus the treatment plan optimization was transformed into network training. With this transformation, the pytorch toolkit with high-efficiency automatic differentiation (AD) for gradient calculation was used as the optimization solver. To improve the treatment efficiency, plans with fewer nodes and beams were sought. The least absolute shrinkage and selection operator (lasso) and the group lasso were employed to address the "sparsity" issue. Results The AD-S (AD sparse) approach was validated on 6 brain and 6 liver cancer cases and the results were compared with the commercial MultiPlan (MLP) system. It was found that the AD-S plans achieved rapid dose fall-off and satisfactory sparing of organs at risk (OARs). Treatment efficiency was improved by the reduction in the number of nodes (28%) and beams (18%), and monitor unit (MU, 24%), respectively. The computational time was shortened to 47.3 s on average. Conclusions In summary, this first attempt of applying deep learning framework to the robotic radiotherapy plan optimization is promising and has the potential to be used clinically.

574 Objectives: Prompt gamma (PG) imaging technique has been demonstrated to be very promising in real-time proton range monitoring in proton therapy. Despite the high correlation between PG and proton dose (PD) distribution, the detected PG cannot represent the delivered PD and be directly comparable with the planned PD. Here, we propose a deep learning based method to estimate the absolute PD from PG distribution. Methods: Monte Carlo simulation was performed using GATE v8.0 with the physics list QGSP_BERT_HP_EMY. Head and neck CT scans were performed on 14 volunteers, and the data were used to generate the heterogeneous medium distribution in the simulation. For each volunteer, incident monenergistic pencil beams with the energy of 150±0.8 MeV was simulated from two different positions. The spot size of proton beam was 6 mm ×10 mm. The total number of protons for each incidence was 1.2×108. The 3D PD deposited in each volunteer’s brain and the emitted PG with energy ranging from 2 MeV to 8 MeV were stored in a 300×234×300 image with 1 mm ×1 mm ×1 mm voxel size. 31 2D slices were extracted from the each 3D image. A U-net model was implemented to learn the PG-to-PD transform. Integrated CT and simulated PG distribution were used as two input channels for training, while the simulated PD was used as the label. Patches with size of 200×200 were randomly extracted from the images and then flipped both horizontally and vertically to augment the data and avoid over-fitting. L2 was chosen as the loss function to obtain stable solution. 480 epochs with size of 1600 were trained. Each epoch contained 100 batches with mini-batch size of 16. The model was trained with 744 pairs from 12 volunteers and tested with the remaining 2 volunteers. To investigate the performance of this proposed method, the estimated PD was first visually compared with simulated PD. The mean projected range equal the depth of the distal 80% point of the Bragg peak in different slices, D80, was calculated to measure the range accuracy of estimated PD. Also, the relative error of the cumulative dose in 3D ROI was calculated to compare the estimated PD and simulated PD quantitatively by rendering 2D slices together. Results: We observe very similar distribution between estimated PD and simulated PD. The range D80 bias is less than 0.5 mm for volunteer #1, where the Bragg peak locates in homogeneous brain regions. In volunteer #2, when the Bragg peak is near the nasal cavity, the range bias is less than 2.0 mm. The relative error of cumulative dose in a 3D ROI is less than 5% for all cases. Conclusion: The proposed deep learning based method satisfactorily recovers PD distribution from PG and corresponding CT data. This method shows great potential not only for range verification but also for quantitative 3D dose monitoring using PG in proton therapy. Further investigations are under way to implement the polyenergetic pencil beam scanning plans in simulation and estimation. Research Support: The research was supported by the National Natural Science Foundation of China (No. 81727807, No.11575096, No. 11605008) and National Key Research and Development (R&D) Plan of China (Grant ID. 2019YFF0302503 and 2016YFC0105405).

Objective To evaluate the feasibility and clinical efficacy of preoperative simultaneous integrated boost intensity-modulated radiotherapy (SIB-IMRT) combined with neoadjuvant chemotherapy of capecitabine in patients with locally-advanced low rectal cancer.Methods Between 2015 and 2016,26 patients admitted to 301 Hospital who were diagnosed with locally-advanced low rectal cancer,which was located within 5 cm from the anal verge,were enrolled in this investigation.Dose fractionation pattern was delivered:58.75 Gy in 25 fractions (2.35 Gy/fraction) for rectal cancer and lymph node metastasis and 50 Gy in 25 fractions for the pelvic lymphatic drainage area and simultaneously combined with capecitabine chemotherapy (825 mg/m2,bid d 1-5 weekly).One cycle of capecitabine (1 250 mg/m2,twice daily,d 1-14)was given at one week after the completion of chemoradiotherapy (CRT).Total mesorectal excision (TME)was performed at 6 to 8 weeks after the completion of CRT.The primary endpoints included pathological complete response rate (ypCR) and sphincter-preserving rate.The secondary endpoints included acute toxicity,tumor downstaging rate and postoperative complications.Results Twenty-six patients successfully completed neoadjuvant CRT,25 of them underwent surgical resection and one patient failed to receive surgery due to pxrianal edema.Postoperative ypCR rate was 32％ (8/25),the sphincter-preserving rate was 60％ (15/25),the tumor downstaging rate was 92％ (23/25) and the R0 resection rate was 100％.During the period of CRT,grade 1 and 2 adverse events occurred in 24 patients,grade 3 radiation dermatitis was noted in 2 cases.No ≥ grade 4 acute adverse event was observed.Postoperative complications included ureteral injury in one case and intestinal obstruction in one patient.Conclusions Preoperative SIB-IMRT combined with neoadjuvant chemotherapy of capecitabine is a feasible and safe treatment for patients with locallyadvanced low rectal cancer,which yields expected ypCR rate,R0 resection rate and sphincter-preserving rate.Nevertheless,the long-term clinical benefits remain to be elucidated.Clinical Trial Registry Chinese Clinical Trial Registry,registration number:ChiCTR-ONC-12002387.

The treatment plans were designed based on planning CT of Catphan phantom's homogenic and heterogenetical module, respectively. With the OBI system, Catphan phantom was scanned under different scanning conditions. The dose was recalculated by applying treatment plans based on planning CT to the CBCT images with its individual hounsfield unit-electron density calibration curve. The dose distributions were compared with those of the original plan, the results of HI showed a good agreement. CIs in the homogenic module were superior to those in the heterogenetical one. There is a good dose distribution for CBCT images under different scanning conditions. It is helpful for CBCT images directly used for dose re-calculation in adaptive radiation therapy (ART).

Objective To investigate the plan quality between two treatment planning systems (TPSs) for volumetric modulated arc therapy (VMAT). Methods VMAT plans based on Varian Eclipse and Philips Pinnacle TPS were designed for 10 cervical cancer patients (2, 3 Arcs) and 10 prostate cancer patients ( 1, 2 Arcs) . The delivery system of VMAT was Varian ClinaciX machine, and RapidArc was used. The treatment plan quality between the two TPSs was evaluated based on dose distribution, delivery efficiency, and parameter settings. The differences between the two TPSs were compared using paired t-test. Results For cervical cancer patients, the 2-Arc VMAT plans based on the Pinnacle was slightly better than those based on the Eclipse in terms of the conformal index ( CI) of planning target volume ( PTV) , rectum V30 and V40 , and bladder V30 and V40 , and the homogeneity index ( HI) of PTV and PTV1 as well as CI of PTV1 in the Eclips were slightly better than those in the Pinnacle( P<005) Pinnacle were slightly worse than those in the Eclipse ( P>005) . The number of monitor units with 2-Arcs and 3-Arcs plans of the Eclipse was significantly smaller than those in the Pinnacle (P<005). For prostate cancer patients, The 1-arc VMAT plans of the Pinnacle TPS were slightly superior to those of the Eclipse TPS in terms of the HI of PTV, rectumV30 and V40 , and bladderV30 and V40 , but the former was slight inferior to the latter in terms of the CI of PTV (P<005). The number of monitor units of 1-arc and 2-Arcs plans showed no significant difference between the two TPSs (P>005). Conclusions For patients with cervical cancer and prostate cancer, the VMAT plans based on Varian Eclipse and Philips Pinnacle TPS can achieve a clinically acceptable dose distribution and show a little difference in the treatment plan quality. However, we will still need more cases to further study and determine the performance characteristics of the commercial TPSs for optimizing VMAT.

Objective To review our initial experience in selecting patients to undergo robotic pancreatic surgery.Methods This is a retrospective study on 100 patients who underwent robotic pancreatic operations at the Chinese PLA General Hospital from September 2009 to March 2015.Results 89 patients underwent robotic pancreatic body and tail resection,5 patients superficial enucleation of pancreatic lesions,3 patients middle pancreatic resection,1 patient pancreaticoduodenectomy,1 patient pancreatico-gastric anastomosis,and 1 patient pancreatico-jejunal anastomosis.Conclusions Robotic pancreatic surgery was safe and feasible.Lesions located in pancreatic body and tail could be treated with resection of pancreatic body and tail,and this appeared to be the best indication for robotic pancreatic surgery.Focal lesions on the surface of pancreas could be enucleated using the Da Vinci robotic surgical system.Extreme care should be exercised in selecting patients for robotic pancreaticoduodenectomy,because the surgical risk is high.

Objective To compare the characteristics and discuss on the dosimetric advantages and efficiencies of tangential field three-dimensional conformal radiotherapy(TF-3DCRT), field-in-field intensity-modulated radiotherapy(FIF-IMRT) and fixed-field inversely optimized intensity-modulated radiotherapy(FFIO-IMRT) after breast conserving surgery. Methods The treatment plans for 16 breast cancer patients in need of adjuvant radiotherapy after breast conserving surgery were analyzed,including 8 right breast cancer patients and 8 left breast cancer patients. The prescription dose was 50 Gy/25 f. Varian Eclipse Ver10.0 planning system was applied to design TF- 3DCRT plan. Based on TF- 3DCRT plan, the low dose region in target volume was contoured and FIF-IMRT plan was designed. Pinnacle planning system was used to design FFIO-IMRT plan. The dose distribution of organs at risk(OARs) and target volume were compared, and the clinical efficiencies were evaluated.Results Statistically significant differences were found among TF- 3DCRT, FIF- IMRT and FFIO- IMRT. The monitor units(MUs) of TF-3DCRT, FIF-IMRT and FFIO-IMRT were respectively(244.9±8.3) MU,(285.9±20.3) MU,(534.0±56.2) MU(P<0.001). The conformity index(CI) of target volume of TF-3DCRT, FIF-IMRT and FFIO-IMRT were respectively 0.40±0.12,0.48±0.12, 0.57±0.12(P≤0.01), and the homogeneity index(HI) were respectively 0.20±0.02, 0.13±0.02, 0.17±0.02(P≤0.01).All the compared results of D2, V107, V110 of target volume were FIF-IMRT