Objective:To study the changing characteristics and impact factors of helical tomotherapy (HT)for longitudinal dose fall-off outside the target, in order to guide the plan junction or pretreatment target and implementation efficiency in clinical.Methods:Eight patients with head and neck tumors admitted to the Department of Oncology Radiotherapy of the First Affiliated Hospital of Zhengzhou University in December 2019 were retrospectively selected as the research objects. The planning target area and dose drop structure were outlined in the head and neck images with a thickness of 1 mm obtained by Siemens SOMATOM Definition AS positioning computerized tomography (CT). Different field widths (FW, 5.0 cm/2.5 cm/1.0 cm) and pitches (0.430/0.287/0.215) were assembled for planning with the same modulation factor (1.8), finest does calculation grid (0.195 cm ×0.195 cm) and other planning parameters were consistent. The plans were designed by different parameters, and the result was analyzed by univariate analysis.Results:The that different pitch curves coincided under the same field width by comparative analyzing, so pitchs had no effect on dose drop. The different field width curves were independent of each other, indicating that the field width had an effect on dose drop in the head and foot direction. The relationship between the longitudinal dose drop speed outside the target and the change of the field width was inversely correlated: the larger field widths meant the slower dose fall-off and the larger penumbra, while the smaller field widths meant the faster fall-off and the smaller penumbra. When the dose fall-off to 50% of the prescribed dose, the distance from the target was approximately equal to half the field widths, and the pitchs had not affect the rate of dose-drop, while the dose at different distances from the target boundary could be calculated by the fitting formulas. The field widths and pitchs had little effect on the CI and HI index of the target, relatively, the target area was best when the field width was 2.5 cm. The total beam-on time gradually decreased with the increase of the field widths and pitches.Conclusions:When segment target therapy needs to consider planning junction, execution efficiency, and controlling longitudinal dose fall-off and considered the execution, the optimal planned parameters such as field widths and pitches could be selected or the target at the junction regions could be adducted according to the longitudinal dose drop formula, so as to achieve the ideal dose distribution.

Objective To explore the impact factors of liver uptake of 18F-FDG in PET/CT imaging,and to preliminary analyze the application of maximum standardized uptake values corrected by conventional body mass,lean body mass and body surface area (SUVmax-B,SUVmax-L,SUVmax-S).Methods A retrospective analysis was performed on 67 healthy subjects who underwent 18F-FDG PET/CT.SUVmax-B,SUVmax-L and SUVmax-S were measured,and the impact of age,levels of fasting blood glucose,body mass index (BMI),CT value of liver,gender and the fatty liver on SUVmax-B,SUVmax-L and SUVmax-S were analyzed.Results The liver SUVmax-B,SUVmax-L,SUVmax-S were positively correlated with the levels of fasting blood glucose (r=0.329,0.336,0.353,P =0.012,0.010,0.007).There was a positive correlation between BMI and SUVmax-B (r=0.543,P＜0.01),SUV-L (r=0.328,P=0.007),while BMI value had no correlation with SUVmax-S (r=0.026,P=0.833).There was no correlation between age,CT value of the liver nor SUVmax-B,SUVmax-L and SUVmax-S (all P＞0.05).The liver SUVmax-B (t=2.608,P=0.011) and SUVmax-L (t=5.272,P=0.001) of male were significantly higher than those of female,while there was no difference between male's and female's liver SUVmax-S and liver SUVmax-S (t=0.759,P=0.450).There was no difference in SUVmax-B,SUVmax-L nor SUVmax-S between fatty liver subjects and non-fatty liver subjects (P=0.646,0.775,0.068).Conclusion The fasting blood glucose level,BMI and sex are the impact factors of liver uptake of 18F-FDG in PET/CT imaging.SUVmax-B can be replaced by SUVmax-L or SUVmax-S for larger BMI subjects,while SUVmax-S can make up differences between different genders.However,correction techniques can not weaken the impact of blood glucose level on SUVmax value of liver.

Objective To investigate the optimal distance between the upper and lower targets in the subsection total body irradiation(TBI)using helical tomotherapy,and to analyze the dose distribution of abutment regions. Methods A total of 8 patients with acute leukemia with a height of about 120 cm were involved in the study. All patients were scanned from the calvarium to the toe by computerized tomography (CT,Siemens)with a thickness of 5 mm,and a lead wire was placed at a point 10 cm above the patella as a marker of the boundary between the upper and lower targets. The delineation of target volumes and organs at risk(OAR)was performed in the Varian Eclipse 10.0 doctor workstation. The different distances between the lead wires and the boundary of the two targets were delineated, and images were transferred to the HT workstation to design the radiotherapy planning,including Jaw width(5 cm),modulation factor(1.8),and pitch(0.43). The plans were superimposed together, and then the dose distribution in abutment regions with different target gaps was analyzed to find the optimal distance. Results When the target gap was 5 cm, the dose distribution in abutment regions was satisfactory. However,the dose was obviously insufficient when the gap was more than 5 cm;the doses in abutment regions significantly exceeded the prescribed doses when the gap was less than 5 cm. Conclusions In the subsection TBI using HT, different parameters were designed,including Jaw width(5 cm), modulation factor(1.8), pitch(0.43), and slice thickness(5 mm). The upper and lower borders of the targets should be 2.5 cm away from the lead wire,that is,a gap of 5 cm,thus avoiding the dose-related hot or cold spots in the target convergence and ensuring a safer and more accurate radiotherapy.

Objective To evaluate the feasibility of total marrow and lymphatic irradiation (TMLI)with helical tomotherapy as a conditioning regimen before hematopoietic stem cell transplantation (HSCT).Methods Seven children with acute lymphoblastic leukemia and aplastic anemia were recruited as study subjects.The median age was 7 years old.The prescribed dose was 12 Gy/6 fractions twice daily.The exposure dose of the target and the organs at risk between helical helical tomotherapy-based TMLI regimen and total body irradiation (TBI) regimen were statistically compared,and acute toxicity grading was performed for all patients.Results Compared with the TBI regimen,the average exposure dose reduction for organs at risk after the TMLI regimen was ranged from 4.2％ to 40.6％.The average exposure dose reduction for the kidney was the largest among all organs.The acute toxicities experienced by all patients were graded and recorded including 2 cases of nausea,5 cases of vomiting,1 case of anorexia,1 case of eryhema,3 cases of diarrhea,and 1 case of oral mucositis.Only grade 1-2 toxicities were observed,and no grade 3-4 toxicities occurred.Conclusions The findings in this study confirm the feasibility of helical helical tomotherapy-based TMLI regimen.Compared with the TBI regimen,the mean duration of treatment for the TMLI regimen with an equivalent dose is not increased.The exposure dose experienced by organs at risk is reduced and the predicted incidence rate is decreased when the TMLI regimen is employed,which provides a myeloablative pretreatment strategy.However,the long-term toxicity of TMLI regime remains to be evaluated by clinical trials.

Objective To investigate the optimal distance between upper and lower target volumes and their correlated planning parameters by analyzing the dose distribution in the abutment regions during total body irradiation ( TBI) using helical tomotherapy. Methods A total of 10 patients with acute leukemia and with a height around 120 cm were enrolled. All patients were scanned by a Siemens simulation computerized tomography (CT) at a slice thickness of 5 mm. A lead wire was placed 10. 0 cm above the patella as a marker of the separation boundary for the upper and lower target volumes. The delineations of target volumes and organs at risk ( OARs ) were performed in the Varian Eclipse 13. 5 workstation with targets shrunk beyond the separation boundary at different distances. After contours and CT images were transferred to HT workstation, treatment plans were designed with different field width (FW, 5. 0 cm/2. 5 cm/1. 0 cm) and pitch values (0. 430/0. 287) at a modulation factor of 1. 8. All the plans were optimized with a dose calculation grid of 0. 195 cm × 0. 195 cm and identical planning parameters. The correlation between treatment planning parameters and targets shrunk distances were investigated by analyzing the dose distributions in the abutment area. Results The study demonstrated that the dose distributions in the abutment area were influenced only by the field width parameters: when the gap distance between the upper and lower targets was 5. 0 cm, the optimal FW is 5. 0 cm;Similarly when the gap distances were 2. 0 cm and 1. 0 cm, and the optimal FW 2. 5 cm and 1. 0 cm, respectively. In another words, the dose distribution of the abutment region was optimal when the target gap distance was equal to FW. Pitch values did not affect the quality of dose distribution in the abutment region and the overall treatment time ratio. Overall treatment time was inversely related to the FW. Conclusions Consistent target distance and FW is helpful to improve the dose homogeneity in the abutment area during TBI with HT. Appropriate planning parameters is critical to balance the treatment efficacy and efficiency.

Objective To investigate the commissioning and testing of the Eclipse model of an Edge accelerator with high-definition muhi-leaf collimator (HD-MLC).Methods The percentage depth dose (PDD),profile,output factor measured by Razor and CC13 were statistically compared with the standard data.Penumbra,transmission factor (TF),leakage,concave-convex groove,accuracy of movement and dosimetry leaf gap (DLG) were measured with EBT3,electronic portal image device (EPID) and PTW SRS1000&SRS1500.The optimal DLG/TF was acquired when the γ pass rate of test cases was the highest.The point dose of regular fields,intensity-modulated radiation therapy (IMRT) and volume-modulated radiation therapy (VMAT) was verified with FC65-G.The planar dose of these case was verified with Octavius 4D and EBT3.Results The measured PDD data were consistent with the standard data.The measured penumbra of 3 cm and 4 cm square fields was smaller,whereas that of 6 cm square field was larger than the standard values.The left and right edge,field size,center of the field were distributed within the range of-1.0-0.4 mm、0.2-1.7 mm,-0.3-1.9 mm and-0.1-0.8 mm,respectively.The mean penumbra of the left and right MLC in different positions were (2.5±0.042) mm and (2.7±0.005) mm.The leakage of MLC was 0.009-0.016.The measured DLG/TF was 0.1861 cm/0.0116 and the optimal DLG/TF was 0.015 cm/0.014.The differences of point dose of all the test cases except the one which was in the low-dose area were within ±3％.Local and global γ pass rates of all IMRT were 79.81％-100％ and 96.3％-100％ (3％/3 mm),71.3％-98.9％ and 94.3％-99.8％ for VMAT cases.Conclusions This method can accurately test and commission the Eclipse treatment planning model of Edge Linac equipped with HD-MLC.

Objective:To evaluate the volumetric modulated arc therapy (VMAT) dose verification of cervical cancer based on γ rule and dose volume histogram (DVH) and to perform correlation analysis between the evaluation results and the dose differences.Methods:Twenty cervical cancer VMAT plans were selected and performed on TrueBeam Linac. The delivered point and surface dose was measured by FC-65 G and ArcCheck and the results were compared to those calculated by Eclipse. The dose of patients was reconstructed by 3DVH. Then, differences between the reconstructed and plan value of D mean, D 95%, D 98% and D 2% of PTV, V 20Gy of left and right femoral head, V 40Gy of rectum, D 1cm 3 of cord, D 98%, D 2% and D 50% of the 50% prescription iso-dose volume (IDV), were evaluated and 3-dimensional (3D) γ was assessed for each organ. Lastly, Pearson’s correlation coefficient was used to analyze the relationship between point dose difference, 2D γ pass-rate (γ%), γ mean and 3D γ% of each organ and the dose difference. Results:Small differences were found between the point dose measured, reconstructed and the plan value. Differences between D mean of PTV, all dose parameters of IDV and plan values were all within 3% and V 40Gy of rectum showed the largest difference. As for the 3D γ%, the maximum pass rate was found for the left and right femoral head and the maximum variance for cord D 1cm 3. There was a moderate correlation between measured and reconstructed point dose deviation and dose difference of each organ, while no significant correlation was found for 2D γ%. Strong correlation was found between 3D γ% of target and D 50% of PTV/IDV and no correlation was found for other organs. Conclusion:The performance of both γ-and DVH-based evaluation can reveal dose error for dose verification, but both of them have some limitations and should be combined in clinical practice.