Objective To evaluate the effects of the multiple factors especially image geometric accuracy of the imaging system on the segmentations of target areas and organs-at-risk.Methods The study used phantoms to test the imaging performance of the 1.5T magnetic resonance(MR)linear accelerator system,including the assessments of MR image geometric distortion and the segmentation errors caused by factors such as image geometric distortion.Model 604-GS large field MR image distortion phantom was used to explore the geometric distortion of the MR images for MR-guided radiotherapy;and CIRS Model 008z upper abdominal phantom was used to analyze the segmentation errors of target areas and organs-at-risk.Results The average geometric distortion and maximum distortion of 3D T1WI-FFE images vs 3D T2WI-TSE images were 0.54 mm vs 0.53 mm and 1.96 mm vs 1.68 mm,respectively;and the control points of the large distortions were distributed at the edges of the phantom,which was consistent with the MR imaging characteristics previously reported.Compared with CT-based segmentation contour,the MDA was 1.17 mm and DSC was 0.91 for 3D T1WI-FFE,while MDA was 0.86 mm and DSC was 0.94 for 3D T2WI-TSE.Conclusion The study quantitatively assesses the geometric accuracy of the imaging system for MR-guided radiotherapy.The phantom-based contour analysis reveals that with CT image as gold standard,the segmentation error in MRI images meets the clinical requirements,and that 3D T2WI-TSE image is advantageous over 3D T1WI-FFE image in segmentation accuracy.

Objective:To analyze the time needed for active breathing coordinator (ABC) coaching in tumor patients, and to explore the influencing factors of coaching time.Methods:A retrospective study was conducted on 93 patients who received ABC treatment led by the same staff at the Cancer Hospital of Chinese Academy of Medical Sciences from September 2019 to April 2021. The effects of education level, body mass index (BMI), age, gender and disease type on the couching time were analyzed. The coaching time was expressed as Mean ± SD. Independent sample t-test or rank sum test was used for comparison between different groups. P<0.05 was considered statistically significant. Results:Statistical significance was observed in the effect of education level, BMI and age on coaching time. The coaching time in the higher education group was (9.74±3.80) min, significantly shorter than the (13.79±6.03) min ( P=0.001) of the primary education group and the (13.03±5.14) min ( P=0.021) of the middle education group. The couching time in the BMI<24 kg/m 2 group was (10.27±3.98) min, significantly shorter compared with (12.74±5.60) min ( P<0.001) in the BMI≥24 kg/m 2 group. The coaching time in the ≥60 years old group was (14.12±5.06) min, significantly longer than the (9.86±3.76) min ( P=0.002) of the ≤40 years old group and the (11.30±5.10) min ( P=0.021) of the 40-60 years old group. No significant differences were noted in the effect of gender, disease type and tumor staging on the coaching time. The coaching time in males and females was (13.54±5.89) and (10.94±4.61) min, respectively ( P=0.071). The coaching time of patients with breast cancer, lung cancer, liver cancer, mediastinal lymphoma and pancreatic cancer was (10.75±4.72), (15.30±5.57), (11.69±4.96), (9.86±3.61) and (12.15±0.07) min, respectively ( P=0.071). The coaching time of stageⅠ,Ⅱ,Ⅲ and Ⅳ patients was (10.35±4.37), (11.88±5.30), (9.52±2.51) and (14.32±5.27) min ( P=0.060). Conclusions:Patients with higher education level and BMI<24 kg/m 2 require less ABC coaching time. Patients aged≥60 years require longer coaching time. Gender, disease type and clinical stage exert no significant effect on the duration of coaching.

Objective:To investigate the workflow, efficacy and safety of MR-Linac in liver malignancies.Methods:Clinical data of 15 patients with hepatocellular carcinomas (HCC) or liver metastases treated with MR-Linac between November 2019 and July 2021 were retrospectively analyzed. The workflow of MR-Linac was investigated and image identification rate was analyzed. Patients were followed up for response and toxicity assessment.Results:Fifteen patients (6 HCC, 8 liver metastases from colorectal cancer, 1 liver metastasis from breast cancer) were enrolled. A total of 21 lesions were treated, consisting of 10 patients with single lesion, 4 patients with double lesions and 1 patient with triple lesions. The median tumor size was 2.4 cm (0.8-9.8 cm). The identification rate for gross tumor volume (GTV) in MR-Linac was 13/15. Although GTV of two patients were unclearly displayed in MR-Linac images, the presence of adjacent blood vessel and bile duct assisted the precise registration. All the patients were treated with stereotactic body radiation therapy (SBRT). For HCC, the median fraction dose for GTV or planning gross tumor volume (PGTV) was 6 Gy (5-10 Gy) and the median number of fractions was 9(5-10). The median total dose was 52 Gy (50-54 Gy) and the median equivalent dose in 2 Gy fraction (EQD 2Gy) at α/ β= 10 was 72 Gy (62.5-83.3 Gy). For liver metastases, the median fraction dose for GTV or PGTV was 5 Gy (5-10 Gy) and the median number of fractions was 10(5-10). The median total dose was 50 Gy (40-50 Gy) and the median EQD 2Gy at α/ β=5 was 71.4 Gy (71.4-107.1 Gy). At 1 month after SBRT, the in-field objective response rate (ORR) was 8/13 and the disease control rate was 13/13. At 3-6 months after SBRT, the in-filed ORR was increased to 6/6. During the median follow-up of 4.0 months (0.3-11.6), 4-month local progression-free survival, progression-free survival and overall survival were 15/15, 11/15 and 15/15, respectively. Toxicities were mild and no grade 3 or higher toxicities were observed. Conclusions:MR-Linac provides a platform with high identification rates of liver lesions. Besides, the presence of adjacent blood vessel and bile duct also assists the precise registration. It is especially suitable for liver malignancies with promising local control and well tolerance.

Objective:To describe a prospective study of pre-operative tumor-bed boost performed at the 1.5 T MR-Linac in combination with adjuvant whole breast irradiation, and a first case, with an accentuation on clinical feasibility and safety.Methods:A phase II, single arm study recruiting early stage patients follows a paradigm that first boosts the tumor bed and then undergoes breast conservative surgery in 2 weeks, and last irradiates the whole breast in 6 weeks. The primary endpoint is ≥ grade 2 acute breast toxicity. A 43 years old patient affected by a breast carcinoma, not special type of the right-sided lateral quadrant, staged cT 2N 0M 0, was planned and treated. The dose, 8 Gy for one time, was calculated by Monaco on CT simulation images. Both the air electron stream effect (ESE) and the electron return effect (ERE) at the presence of 1.5 T magnetic field were evaluated. During the pre-treatment evaluation, we carried out adaptation-to-position adjustment. Results:The normal organ dosimetry is within toleration. The Dmax to the skin, the chin and the right upper arm was 8.44 Gy, 28.5 cGy and 17.8 cGy, respectively. There was no increased toxicity from ERE and ESE, and the treatment was well tolerated without > grade 1 acute toxicity. The patient received breast conservative surgery on day 7 without delayed wound healing.Conclusions:This is the first case successfully treated within a clinical trial by pre-operative tumor-bed boost under 1.5 T MR-Linac in our institution. More participants are needed to validate and optimize the paradigm.

With aligned MR registration, the MR-Linac provides superior soft tissue resolution for prostate cancer. No fiducial markers or electromagnetic transponders insertion is needed to guarantee high-precision radiotherapy. The highly-recommended Adapt-To-Shape (ATS) workflow can resolve all the problems encountered during prostate cancer radiotherapy, including prostate volume changes and adjacent organs motion, both inter-fractionally and intra-fractionally. With all the above advantages, MR-Linac performs outstandingly than conventional linac in prostate cancer RT delivery, and probably helps us to reduce the CTV-PTV margin safely in the near future. Nevertheless, it is difficult to implement the ATS workflow in clinical practice. In this article, the standard ATS workflow for prostate cancer was summarized based on our own experience.

Objective:To analyze the duration of each phase of Unity MR-linac in clinical application, aiming to provide reference for clinical optimization of the process time.Methods:Clinical data of 55 patients treated with Unity MR-linac were retrospectively analyzed. All patients were divided into the adapt to position (ATP) and adapt to shape (ATS) groups according to the planning method. The duration of each phase in the treatment process, the name and the time of each sequence, the number of beams, segments and total monitor units (MUs) were recorded and compared between two groups. In addition, the set-up time was counted according to different treatment sites. The time of each sequence and set-up time were expressed as the median M (Q 1, Q 3), and the number of beams, segments and total MUs of each plan were described as the mean±SD. Results:42 patients underwent ATP with a total of 305 treatment sessions: setup time was 3(2, 5) min, MR scanning time was 5(4, 7) min, registration time was 3(3, 4) min, adaptive planning time was 8(4, 12) min, beam on time was 8(6, 11) min, and the total time was 30(25, 36) min. 13 patients received ATS with a total of 65 treatment sessions: setup time was 2(2, 3) min, MR scanning time was 7(5, 8) min, registration time was 4(3, 5) min, time of delineation of target and organs at risk was 12(9, 16) min, adaptive planning time was 11(10, 14) min, beam on time was 10(9, 11) min and the total time was 55(49, 61) min. The set-up time according to treatment sites was 4(2, 4) min in the head and neck, 2(2, 4) min in the chest, and 3(2, 5) min in the abdomen. The number of fields, segments and total MUs during ATP were 8.1±1.7, 49.9±31.2, 846.75±363.44 in the head and neck, 8.0±2.0, 60.7±13.3, 790.21±279.00 in the chest, and 9.7±2.0, 81.2±22.3, 2007.32±1053.81 in the abdomen, respectively. The number of fields, segments and total MUs during ATS in head and neck of one case were 13, 39, 993.07, and 9.5±1.5, 65.5±6.3, 2763.26±835.41 in the abdomen.Conclusions:MR-guided radiotherapy yields huge potential in clinical application. However, there is still much room for the improvement of shortening the process duration.

Objective:To evaluate the application of visual feedback coaching method, which is embedded in an optical surface monitoring system, in deep inspiration breath holding during the radiotherapy in left breast cancer patients after breast-conserving surgery.Methods:Thirty patients with left breast cancer, who were scheduled to receive the whole breast radiotherapy after breast-conserving surgery, met the requirements of deep inspiration breath holding after respiratory coaching with the visual feedback coaching module in the optical surface monitoring system. Active breathing control equipment was used to control breath-holding state and CT simulation was performed. During treatment, optical surface monitoring system was used to guide radiotherapy. All patients were randomly divided into two groups. In group A ( n=15), visual feedback respiratory training method was utilized and not employed in group B ( n=15). In group A, the visual feedback coaching bar of the optical surface monitoring system was implemented, while audio interactive method was employed to guide patients to hold their breath. Real-time data of optical body surface monitoring were used to compare the interfraction reproducibility and intrafraction stability of breath holding fraction between two groups. Besides, the number of breath holding and treatment time per fraction were also compared. GraphPad prism 6.0 software was used for data processing and mapping, and SPSS 21.0 software was used for analyzing mean value and normality testing. Results:Compared with the control group, the reproducibility in the experiment group was reduced from 1.5 mm to 0.7 mm, the stability was reduced from 1.1 mm to 0.8 mm, the mean number of breath holding required per fraction was decreased from 4.6 to 2.4, the mean beam-on time per fraction from 336 s to 235 s, and the treatment time per fraction was shortened from 847 s to 602 s (all P<0.05), respectively. Conclusions:The application of visual feedback coaching method can improve the reproducibility and stability of breath holding during radiotherapy for left breast cancer, and it can also effectively reduce the number of breath holding and shorten the treatment time per fraction.

Objective:To summarize the experience of ELEKTA Unity MR-linac in clinical application in our hospital and analyze the positioning accuracy, process time and other related issues.Methods:A total of 14 patients enrolled in the Unity MR-Linac study were reviewed. All treatment time (including positioning, scanning, replanning, and beam discharge) and setup errors in 3directions were statistically analyzed. 11 patients with conventional accelerators using the multifunctional immobilization system (MIS) were randomly selected to make statistical analysis of the setup errors, and the differences between the Unity group and the conventional accelerators using the MIS were compared using t-test. Results:In the Unity group, the setup errors in X, Y and Z directions were (-0.15±0.30) cm, (0.02±0.57) cm and (-0.10±0.28) cm, respectively. The average treatment time was 36.87minutes. The average positioning time was 5.40minutes. The mean scan time was 7.48minutes, the mean adaptive plan time was 7.46minutes, and the mean beam time was 9.48minutes. In the conventional accelerator group, the setup errors were (0.05±0.25) cm, (-0.01±0.25) cm and (-0.03±0.23) cm, respectively. The results of the setup errors of patients fixed with MIS showed that there were significant differences in the left and right directions ( P<0.001), while there were no significant differences in the Y and Z directions ( P=0.061 and 0.374) between two groups. Conclusions:Except in the X direction, there is no significant difference in setup errors between the Unity and conventional accelerator groups in the condition of laser-free system. Under smooth circumstances, the treatment time by using ATP (adapt to position) workflow will also be within the range of tolerance of the patients. Magnetic-guided radiotherapy has a promising application prospect, whereas the procedure needs to be optimized.

Objective:To establish the basic procedures of the application of optical surface monitoring system (OSMS) in the deep inspiration breath hold (DIBH) radiotherapy for patients with left sided breast cancer and compare the performance of OSMS and cone-beam CT (CBCT) in the determination of the set-up errors of DIBH radiotherapy for patients with left sided breast cancer.Methods:Twenty patients with left sided breast cancer received DIBH radiotherapy. Through the registration of CBCT images with the planning CT images, and the registration of OSMS radiography images with the outer contour of the body surface, translational set-up errors and rotational errors were determined along the lateral-medial ( Rx), superior-inferior ( Ry) and anterior-posterior ( Rz) directions. Pearson correlation analysis was performed to evaluate the correlation of the set-up errors determined by two methods, and Bland- Altman plot analysis was used to assess the coincidence of these two methods. Results:Two methods were positively correlated. The Rz volume was 0.84, 0.74 and 0.84 in the x, y and z directions, and 0.65, 0.41 and 0.54 in the Rx, Ry and Rz directions, respectively (all P<0.01). The 95% CI of agreement were within preset 5 mm tolerance (-0.37-0.42cm, -0.39-0.41cm, -0.29-0.49cm ) in x, y and z directions for two methods. The 95% CI of agreement were within preset 3 ° tolerance -2.9°-1.4°, -2.6°-1.4°, -2.4°-2.5°in Rx, Ry and Rz directions for two methods. The system errors of 20 patients with left sided breast cancer receiving DIBH radiotherapy were <0.18cm and the random errors were <0.24cm. Conclusions:OSMS is equivalent to CBCT in the determination and stimulation of set-up errors for patients with left sided breast cancer receiving DIBH radiotherapy. The combination of CBCT and OSMS is a safe and reliable method.

Objective:To evaluate the incidence of early cardiac injury in patients with left-sided breast cancer receiving hypofractionated radiotherapy after breast conserving surgery, and to investigate the correlation between cardiac injury and hypofractionated radiotherapy dose.Methods:We prospectively enrolled 103 breast cancer patients who received whole breast with or without regional nodal irradiation after breast conserving surgery using either deep inspiration breath-hold (DIBH) or free breathing (FB) radiotherapy technique. Cardiac examinations that included N-terminal pro-B-type natriuretic peptide (NT-proBNP), electrocardiogram, and myocardial perfusion imaging were performed routinely before and after radiotherapy. The effects of heart dose, systemic therapy and individual factors (Framingham score) on the incidence of cardiac events were analyzed.Results:The median age was 48 years. The mean dose (Dmean) of the heart, left anterior descending coronary artery (LAD), left ventricular (LV), and right ventricular (RV) were 4.0, 16.9, 6.3, and 4.4 Gy, respectively. With a median follow-up of 13.4 months, no patient had clinical cardiac abnormalities. The incidence rates of subclinical cardiac events at 1- 6- and 12-month were 23.5%, 31.6%, and 41.3%, respectively. The DIBH group had a lower mean dose, maximum dose, and V5-V40 in the heart, LAD, LV, and RV than the FB group ( P<0.001). Univariate analysis showed an increased incidence of subclinical cardiac events with heart Dmean >4 Gy, LAD V40 > 20%, LV Dmean >6 Gy, RV Dmean >7 Gy, or cumulative doses of anthracycline or taxane > 300 mg/m 2 (All P<0.05). Anti-HER2 targeted therapy, endocrine therapy and Framingham score were not associated with the incidence of subclinical cardiac events (all P>0.05). Multivariate analysis demonstrated that Dmean of LV and RV were independently associated with the increased incidence of subclinical cardiac events. Conclusions:Early subclinical heart injury are found in patients with left-sided breast cancer after hypofractionated radiotherapy. The increased incidence of subclinical cardiac events after radiotherapy is positively associated with the cardiac radiation doses.