ABSTRACT
Objective:To understand the components, performance, acceptance test and quality assurance (QA) protocols of the new Varian Halcyon accelerator through the procedures of installation product acceptance (IPA).Methods:Per Varian IPA protocol, TG-142 for LINAC and TG-148 for tomotherapy QA protocols, the software license, safety interlock, mechanical accuracy, dosimetric performance and imager system were checked thoroughly. Some parameters were benchmarked to the conventional TrueBeam system.Results:The system has been fully licensed. Safety interlock was normal. Mechanical accuracy: The maximum deviation of beam stability per gantry rotation was 1.13%. The size of isocenter was>0.59mm. The offsets of MV imager, collimation rotation and absolute gantry rotation were 0.09mm, -0.21° and 0.11°, respectively. The maximum offsets of couch, virtual-to-isocenter were 0.15mm (vertical) and -0.04mm (vertical), respectively. Beam performance: The depth deviation of maximum dose was 0.1cm. The offset of percentage depth dose at 10cm was 0.5%. The maximum deviations of off-axis-intensity, symmetry, and repeatability were 0.9%, 0.94% and -0.44%, respectively. MV imager: The dark field mean pixel value, noise, corrected pixels, defective lines, sensitivity and linearity disparity of dose were 614, 4.4, 3626, 0, 19177, and 0.47%, respectively. All values were within the range of tolerance. Visual check of contrast resolution and small object detection was all satisfactory.Conclusions:Without Halcyon-specific TG report or guidelines, manufacture-provided IPA manual can be helpful with the installation of acceptance and QA protocols. IPA has been successfully performed for Halcyon at Peking University Cancer Hospital. The automated workflow improves the clinical efficiency by simplifying the operations.
ABSTRACT
Objective:To develope an automatic volumetric modulated arc therapy (VMAT) planning for rectal cancer based on a dose-prediction model for organs at risk(OARs) and an iterative optimization algorithm for objective parameter optimization.Methods:Totally 165 VMAT plans of rectal cancer patients treated in Peking University Cancer Hospital & Institute from June 2018 to January 2021 were selected to establish automatic VMAT planning. Among them, 145 cases were used for training the deep-learning model and 20 for evaluating the feasibility of the model by comparing the automatic planning with manual plans. The deep learning model was used to predict the essential dose-volume histogram (DVH) index as initial objective parameters(IOPs) and the iterative optimization algorithm can automatically modify the objective parameters according to the result of protocol-based automatic iterative optimization(PBAIO). With the predicted IOPs, the automatic planning model based on the iterative optimization algorithm was achieved using a program mable interface.Results:The IOPs of OARs of 20 cases were effectively predicted using the deep learning model, with no significantly statistical difference in the conformity index(CI) for planning target volume(PTV)and planning gross tumor volume(PGTV)between automatic and manual plans( P>0.05). The homogeneity index (HI) of PGTV in automatic and manual plans was 0.06 and 0.05, respectively( t=-6.92, P< 0.05). Compared with manual plans, the automatic plans significantly decreased the V30 for urinary bladder by 2.7% and decreased the V20 for femoral head sand auxiliary structure(avoidance)by 8.37% and 15.95%, respectively ( t=5.65, 11.24, P< 0.05). Meanwhile, the average doses to bladder, femoral heads, and avoidance decreased by 1.91, 4.01, and 3.88 Gy, respectively( t=9.29, 2.80, 10.23, P< 0.05) using the automatic plans. The time of automatic VMAT planning was (71.49±25.48)min in 20 cases. Conclusions:The proposed automatic planning based on dose prediction and an iterative optimization algorithm is feasible and has great potential for sparing OARs and improving the utilization rate of clinical resources.
ABSTRACT
Objective:To assess the three-dimensional dose distribution in radiotherapy plans using the structural similarity index(SSIM), compare the performance of SSIM with commonly used quality assessment indices, and develop a SSIM-based quality assessment method of multiple prescribed doses.Methods:The SSIM was introduced to providea quality score of various voxels by comparing actual and ideal three-dimensional dose data and combining the spatial location information of the voxels. Then the average value in a region of interest (ROI) was calculated as the quality score of the region. Fifty-three cases of cervical cancer were selected to analyze the correlation of the SSIM with the uniformity index (HI), conformity index (CI) of the dose distribution in various ROIs and to explore the capability of the SSIM to reflect the uniformity and conformity of dose distribution.Two types of quality defects were individually introduced into two of 53 radiotherapy plans. Then the two plans were compared with normal plans to characterize the response of the SSIM.Results:There was no correlation between HI and SSIM in positive lymph nodes(PGTVnd) due to the decrease in the HI sensitivity, while there was a significant negative correlation between them in regions where PGTVnd was removed from the planning target volume(PTV, R=-0.86, P<0.01). Meanwhile, there was a significant positive correlation between CI and SSIM in PGTVnd ( R=0.83, P<0.01). Therefore, the SSIM can be used to identify the artificial design defects in plans by determining abnormal dose gradients. Conclusions:Apart from reducing the defects of previous assessment parameters, the SSIM has the capability to assess the quality of radiotherapy plans by combining the uniformity and conformity of dose distribution and can provide accurate feedback on the spatial locations of quality defects.
ABSTRACT
Objective:To investigate the performance of W2 plastic scintillator in megavolt photon and electron beams.Methods:The photon and electron beam energy provided by linear accelerator was used to collect data of the W2 scintillator. The parameters include the electrometer reading stability, W2 dose and dose rate linearity, and angular response. And the dose uncertainty of the W2 correction factors was also investigated.Results:The standard deviation of the electrometer reading stability was between 0.03 and 0.47. The linear regression factors of W2 dose were all 1.0; the maximum deviation of the dose rates was 0.61%. The Cerenkov light radiation correction factor(CLR) for 6 and 10 MV were 0.741 and 0.746, respectively, and the CLR for 6, 9, 12 and 15 MeV were 0.750, 0.753, 0.757 and 0.757, respectively. The maximum deviation of dose uncertainty for 15 MeV was 3.15%.Conclusions:The signal obtained by the blue and green channel was no angular dependence, the same as the high-energy electron beam, which verified that the Cerenkov radiation correction factor has good linearity. W2 plastic scintillator can be applied to non-coplanar radiotherapy dosimetry.
ABSTRACT
Objective:To solve the problems in intensity-modulated radiation therapy (IMRT) planning, such as large labor cost and high dependence on the experience of physicists and great inconsistency in the quality of plan, and to discuss an unsupervised automatic treatment planning procedure of IMRT.Methods:The eclipse scripting application programming interface (ESAPI) within the Eclipse treatment planning system (TPS) 15.6 and optimization parameters tree search algorithm (OPTSA) were used to emulate and realize the whole planning process. Interacted with the TPS through ESAPI, relevant dosimetric parameters were input and output. The OPTSA evaluated the plan qualities based on dosimetric parameters of the targets and organs at risk (OARs) and iteratively adjusted the optimization objective parameters to achieve a progressively improving IMRT plan. In order to verify the effectiveness of the automatic planning, twenty historical rectum cancer cases were selected from the clinical database, and the dose distribution and specific dosimetric parameters were compared between the plans generated by the OPTSA and the manual plans under the same constraints.Results:All the auto plans have met clinical requirements. Furthermore, 90% and 10% of the auto plans were deemed as clinically improved and equally compared with the manual plans, respectively. The average CI for the PTV was 0.88 and 0.80 for the auto and manual plans respectively. Compared with the manual plans, the mean doses of all the OARs in the auto plans were reduced by 11% in average. The average elapsed time of automatic planning and manual planning was (28.15±3.61) and (36.7±4.6) min, respectively.Conclusions:The plans created by the proposed algorithm have been shown to be at least as good as the manual plans. In addition, this method can shorten the labor time in plan designing while ensuring the plan quality and consistency of the plan.
ABSTRACT
The present study aims to investigate the impact of hydrogen-rich water on the lactic acid level in metformin-treated diabetic rats under hypoxia. Thirty Sprague–Dawley rats were randomly divided into five groups, including normal diet group, and diabetes model (DM) group, DM + metformin treatment (DMM) group, DMM + hypoxia treatment (DMMH) group and DMMH + hydrogenrich water (DMMHR) group. We found that the levels of lactic acid, pyruvate and lactate dehydrogenase were significantly lower in the blood of DMMHR group than DMMH group. Superoxide dismutase and glutathione levels in liver and heart were significantly higher in DMMH group after hydrogen-rich water treatment, while malondialdehyde and oxidized glutathione levels were decreased in DMMHR group when compared with DMMH group, which indicates that hydrogen-rich water could reduce oxidative stress. qPCR analysis demonstrated that that pro-apoptotic genes Bax/Caspase-3 were upregulated in DM group and metformin treatment suppressed their upregulation (DMM group). However, hypoxic condition reversed the effect of metformin on apoptotic gene expression, and hydrogen-rich water showed little effect on these genes under hypoxia. HE staining showed that hydrogen-rich water prevented myocardial fiber damages under hypoxia. In summary, we conclude that hydrogen-rich water could prevent lactate accumulation and reduce oxidant stress in diabetic rat model to prevent hypoxia-induced damages. It could be served as a potential agent for diabetes patients with metformin treatment to prevent lactic acidosis and reduce myocardial damages under hypoxic conditions.
ABSTRACT
Objective:To characterize the key dose response properties of the novel presage sheet dosimeters for radiotherapy dose verification, including absorption spectra, linearity, dose range and stability.Methods:The same batch of presage sheet dosimeters were irradiated by a radiotherapy linac. The absorption spectra within 400-700 nm were read out with a spectrophotometer, and the R-G-B3 absorption changes read out with a film flatbed scanner was compared before and after irradiation.Results:An absorption peak was clearly identified at 628 nm, where absorptions change in high linearity with delivered doses ( R2=0.9999). A flat valley region is identified around 490 nm, where dose induced absorption changes were negligible. The readout sensitivity of the R-channel of the flatbed scanner was higher than both in green and blue channels. In the dose range below 10 Gy, the R-channel absorptions are in significant linearity with doses ( R2=0.9999), with absorptions change in an obvious quadratic trend in the range beyond 10 Gy ( R2=0.9999). The dose range of presage sheets was more than 94.6 Gy. The absorptions were well preserved within 1 h post-irradation, and then are shown to increase gradually, where the increase speeds are dose-related. The post-irradiation integrity of dose falloff gradients are shown with negligible gradient blurring. Conclusions:The novel presage sheets shown to have reasonable dose response linearity, large dose range, desirable post-irradiation dose gradient integrity and negligible fractionation effect, which indicates its great potentials in integral dose verification of high-dose and multiple target radiotherapy deliveries.
ABSTRACT
Objective To evaluate the relationship between the changes in gray matter volume ( GMV) in different brain regions in the early postoperative period and the development of chronic pain after radical mastectomy. Methods Forty-four American Society of Anesthesiologists physical status Ⅰ or Ⅱpatients, aged 25-64 yr, scheduled for elective radical mastectomy, were divided into 3 groups according to the numeric rating scale ( NRS) score within 3 months after surgery: severe chronic pain group ( NRS score≥3, group SEP), slight chronic pain group (NRS score=1 or 2, group SLP) and no chronic pain group ( NRS score=0, group NP ) . All the patients underwent whole brain MRI scan within 7 days after surgery. MRI data processing and analysis were carried out using SPM8-based VBM software package and REST 1. 8 software. Results There were 17 cases in group SEP, 10 cases in group SLP and 17 cases in group NP. Compared with group NP, GMV in the right postcentral gyrus was significantly decreased, and GMV in the right superior frontal gyrus was increased in group SEP ( P＜0. 01) . Conclusion The changes in GMV in the right postcentral and superior frontal gyrus in the early postoperative period may be related to the development of chronic pain after radical mastectomy.
ABSTRACT
Dose verification, as part of the radiotherapy QA chain, is a significant method to ensure the patients' safety and efficacy of treatment. The increasing application of precision radiotherapy techniques in clinic has advanced the need of three-dimensional ( 3D) dose verification. Gel dosimeters, prevailing for its intrinsic 3D high-resolution measurement and good tissue equivalence, can serve as effective supplement to the clinical radiotherapy dosimetric system. This paper reviews the method ology, dose response mechanism, characterizations of the state-of-the-art gel dosimeters. Gel dosimeters, outstanding for 3D dose measurement, have a great potential to explore both for clinical application and academic research.
ABSTRACT
Objective The aim of this study was to investigate the response in health-related epidemiological investigation among Chinese population aged 15 and over.We analyzed the specific causes of non-response,and explored the effective ways to improve the response rate,so as to provide reference for future epidemiological studies of this kind.Methods Two modes of studies regarding the prevalence of important cardiovascular diseases were used in Chongqing,during the 12th Five-Year Plan period in oder to find out the cause related to non-response.Intervention programs were carried out to evaluate the effects.Results When using the concentrated mode (CM),the completion rate to the questionnaires was only 20.00％ in the pre-investigation,with the response rate as 13.48％.In the deconcentrated mode (DM),the completion rate was 31.16％,with the response rate as 25.19％.After a series of incentives provided to both the respondents and the project-related core staff in the two modes,response rates of the two modes increased to the expected 60％.Conclusions CM appeared having advantages on quality control,but was more time consuming,with higher cost,and without effective follow-up measures to improve the response rate.However,DM had the advantages on controlling the cost and could increase the response rate through making advanced appointment with the households but quality control remained difficult.Two key points should be strengthened to improve the response rates,which including:Precisely finding out the research objects and providing incentives to the respondents to attract their interests of participating in the investigation.
ABSTRACT
Objective The aim of this study was to investigate the response in health-related epidemiological investigation among Chinese population aged 15 and over.We analyzed the specific causes of non-response,and explored the effective ways to improve the response rate,so as to provide reference for future epidemiological studies of this kind.Methods Two modes of studies regarding the prevalence of important cardiovascular diseases were used in Chongqing,during the 12th Five-Year Plan period in oder to find out the cause related to non-response.Intervention programs were carried out to evaluate the effects.Results When using the concentrated mode (CM),the completion rate to the questionnaires was only 20.00％ in the pre-investigation,with the response rate as 13.48％.In the deconcentrated mode (DM),the completion rate was 31.16％,with the response rate as 25.19％.After a series of incentives provided to both the respondents and the project-related core staff in the two modes,response rates of the two modes increased to the expected 60％.Conclusions CM appeared having advantages on quality control,but was more time consuming,with higher cost,and without effective follow-up measures to improve the response rate.However,DM had the advantages on controlling the cost and could increase the response rate through making advanced appointment with the households but quality control remained difficult.Two key points should be strengthened to improve the response rates,which including:Precisely finding out the research objects and providing incentives to the respondents to attract their interests of participating in the investigation.
ABSTRACT
This study was aimed to establish rat bladder tumor animal models to investigate the in viva antitumor effect of polyanhydride-pirarubicin (PAD-THP), a long-lasting anti-cancer implant, in the bladder tumor of animal models. The model of bladder cancer was set up with N-butly-N-(4 hydroxybutyl) nitrosamine (BBN) feeding into rats. The PAD-THP long-acting anti-cancer implants containing the drugs and the same dose of the THP naked drug were placed under the bladder mucosa of bladder tumor model in vivo. The pirarubicin plasma concentration was measured with high performance liquid chromatography (HPLC) detection in vivo. The effective drug concentration and lasting period were observed and compared in the animal bodies. The tumor sizes were measured before and after the treatment. The in viva antitumor effects were analyzed and compared. The results showed that more significant antitumor effect of PAD-THP implants on the local drug release characteristics were presented compared with that of the same dose of THP bare drug group and there were significant differences (P<0. 05) between the two methods. All the results indicated that the PAD-THP anti-cancer implants in the postoperative local treatment of bladder tumors would show prosperous in the future for clinical application.