The effect of primary tumor volume on the prognosis of nasopharyngeal carcinoma in era of volumetric modulated arc therapy: a propensity score matched cohort study

Abstract Objective The role of Primary Tumor Volume (PTV) in Nasopharyngeal Carcinoma (NPC) treated with Volumetric Modulated Arc Therapy (VMAT) is still unclear. The aim of this study was to access the effect of PTV in prognosis prediction of nasopharyngeal carcinoma in era of VMAT. Methods Between January 20 and November 2011, 498 consecutive NPC patients with stage I-IVA disease who received VMAT at a single center were retrospectively analyzed. Receiver Operating Characteristic (ROC) was performed to access the cut-off point of PTV. Univariate Kaplan-Meier and multivariate Cox regression analyses were used to evaluate prognostic value for PTV. The Propensity Score Matching (PSM) was used to adjust baseline potential confounders. Results The 5-year Locol-Regional Failure-Free (L-FFR), Distant Failure-Free Survival (D-FFR), Disease-Free Survival (DFS) and Overall Survival (OS) were 90.6%, 83.7%, 71.5% and 79.3%, respectively. Before PSM, the 5-year L-FFR, D-FFR, DFS, OS rates for NPC patients with PTV ≤ 38 mL vs. PTV > 38 mL were 94.1% vs. 90.4% (p= 0.063), 87.9% vs. 76.3% (p< 0.001), 78.5% vs. 58.5% (p< 0.001) and 86.3% vs. 66.7% (p< 0.001) respectively. Multivariate analysis showed PTV was an independent prognostic factor for D-FFS (p= 0.034), DFS (p= 0.002) and OS (p= 0.001). PTV classified was still an independent prognostic factor for OS after PSM (HR = 2.034, p= 0.025. Conclusions PTV had a substantial impact on the prognosis of NPC patients treated with VMAT before and after PSM simultaneously. PTV > 38 mL may be considered as an indicator of the clinical stage of nasopharyngeal carcinoma. Level of evidence III.

Study on the sensitivity of a volumetric modulated arc therapy plan verification equipment on multi-leaf collimator opening and closing errors and its gamma pass rate limit / 生物医学工程学杂志

To investigate the γ pass rate limit of plan verification equipment for volumetric modulated arc therapy (VMAT) plan verification and its sensitivity on the opening and closing errors of multi-leaf collimator (MLC), 50 cases of nasopharyngeal carcinoma VMAT plan with clockwise and counterclockwise full arcs were randomly selected. Eight kinds of MLC opening and closing errors were introduced in 10 cases of them, and 80 plans with errors were generated. Firstly, the plan verification was conducted in the form of field-by-field measurement and true composite measurement. The γ analysis with the criteria of 3% dose difference, distance to agreement of 2 mm, 10% dose threshold, and absolute dose global normalized conditions were performed for these fields. Then gradient analysis was used to investigate the sensitivity of field-by-field measurement and true composite measurement on MLC opening and closing errors, and the receiver operating characteristic curve (ROC) was used to investigate the optimal threshold of γ pass rate for identifying errors. Tolerance limits and action limits for γ pass rates were calculated using statistical process control (SPC) method for another 40 cases. The error identification ability using the tolerance limit calculated by SPC method and the universal tolerance limit (95%) were compared with using the optimal threshold of ROC. The results show that for the true composite measurement, the clockwise arc and the counterclockwise arc, the descent gradients of the γ passing rate with per millimeter MLC opening error are 10.61%, 7.62% and 6.66%, respectively, and the descent gradients with per millimeter MLC closing error are 9.75%, 7.36% and 6.37%, respectively. The optimal thresholds obtained by the ROC method are 99.35%, 97.95% and 98.25%, respectively, and the tolerance limits obtained by the SPC method are 98.98%, 97.74% and 98.62%, respectively. The tolerance limit calculated by SPC method is close to the optimal threshold of ROC, both of which could identify all errors of ±2 mm, while the universal tolerance limit can only partially identify them, indicating that the universal tolerance limit is not sensitive on some large errors. Therefore, considering the factors such as ease of use and accuracy, it is suggested to use the true composite measurement in clinical practice, and to formulate tolerance limits and action limits suitable for the actual process of the institution based on the SPC method. In conclusion, it is expected that the results of this study can provide some references for institutions to optimize the radiotherapy plan verification process, set appropriate pass rate limit, and promote the standardization of plan verification.

Comprehensive comparison between Halcyon 2.0 and Truebeam VMAT plans for different treatment sites: dosimetric quality and plan complexity / 中华放射肿瘤学杂志

Objective:To analyze the differences in dosimetric quality and plan complexity of volumetric modulated arc therapy (VMAT) plans based on Halcyon 2.0 and Truebeam for different treatment sites of the patients.Methods:Halcyon 2.0 VMAT plans in head & neck, chest, abdomen, and pelvis treatment sites of 49 cases were retrospectively selected and the VMAT plans were re-designed based on Truebeam with the same optimization parameters. The differences in dosimetric metrics and plan complexity between the two types of plans were compared and analyzed. P<0.05 was considered as statistically significant. Results:In terms of PTV, Halcyon 2.0 plans showed better homogeneity index (HI), conformal index (CI) in the head & neck and chest. Besides, Halcyon 2.0 plans yielded better D 98% and CI in the abdomen and better D 2% in the pelvis. For organs at risk (OAR), the D 20% and D mean of bilateral lungs, and D meanof heart for Halcyon 2.0 plans in the chest were lower than those for Truebeam plans (all P<0.05). For the complexity metrics, the median average aperture area variability (AAV) of Halcyon 2.0 plans in the head & neck, abdomen and pelvis were 0.414, 0.425 and 0.432, which were better than 0.385, 0.368 and 0.361 of Truebeam plans in the corresponding sites, respectively. In the abdomen and pelvis, Halcyon 2.0 plans showed better median modulation complexity score (MCS) than Truebeam plans (0.320 vs. 0.268, 0.303 vs. 0.282; both P<0.05). The median small aperture score (SAS) for all plans of Halcyon 2.0 were better than that of Truebeam plans (all P<0.05), and the median plan average beam area (PA) of all plans of Halcyon 2.0 were larger than that of Truebeam plans (all P<0.05). Conclusions:Compared with conventional fractionated VMAT plans based on Halcyon 2.0 and Truebeam, Halcyon 2.0 plans have similar or even better dosimetric quality. However, Halcyon 2.0 plans have lower plan complexity, which makes it an advantage in clinical application.

Complexity score-based plan quality control of VMAT / 中华放射肿瘤学杂志

Objective:To explore the difference in the complexity of different treatment planning systems, multi-leaf collimator (MLC) types and treatment sites of volume-modulated arc therapy (VMAT), and propose a complexity score for plan quality control.Methods:Statistical analysis of 12 complexity metrics including Monaco and Eclipse, Agility, Millennium and High-definition MLC, nasopharyngeal, lung and cervical cancer was performed. Spearman correlation coefficient between complexity metrics was calculated. Principal component analysis was conducted to reduce the dimensionality of the original data set to the first two principal components and explain its physical meaning. Complexity score based on the principal components was calculated to establish warning and action thresholds for plan quality control. The correlation between complexity metrics and γ pass rate was analyzed.Results:Except cervical cancer aperture sub-regions metric, other metrics had significant differences between Monaco and Eclipse. Monaco MLC had a more regular field but higher MU, smaller leaf gap, and longer leaf travel distance. High-definition MLC with smaller leaf width significantly added MLC aperture-related metrics. The first two principal components explained over 80% of the total variance of the original dataset, complexity score was weighted average of first two principal components. The distribution of complexity score for different equipment and sites was different. The warning threshold was expressed as the average plus standard deviation, and the action threshold was expressed as the average plus 2 standard deviations. Complexity metrics and complexity scores had small correlation with γ pass rate, showing weak or irrelevant but statistically significant. Conclusions:Different planning systems, MLC types, and treatment site complexity metrics are significantly different. The complexity score is a useful tool for plan quality control.

The application of the RapidPlan module based on O-ring accelerator in volumetric modulated arc therapy for cervical cancer / 中华放射医学与防护杂志

Objective:To study the clinical feasibility and advantages of the RapidPlan module based on Halcyon 2.0 ring medical linear accelerator in the design of volumetric modulated arc therapy (VMAT) plans after cervical cancer surgery.Methods:The data of 98 clinical cervical cancer cases were selected from the database, and VMAT artificial radiotherapy plans were designed based on Halcyon 2.0. Then, the designed plans were imported into the RapidPlan module to train the module for a prediction model with high goodness of fit. Another 20 patients after cervical cancer surgery were selected as the validation set to compare the differences in dosimetry, plan consistency, and plan execution efficiency between the manual plans and RapidPlan automatic plans.Results:The RapidPlan automatic plans could obtain dose distribution of target volume and organs at risk with the same quality as the manual plans. The RapidPlan automatic plans provided slightly inferior protection of the femoral head but superior protection of the spinal cord compared to the manual plans, and the difference was statistically significant ( t = 4.71, P<0.001). The average MU of the RapidPlan automatic plans was 687.46, which was lower than that of the manual plan (815.34), and the difference was statistically significant ( t = 6.09, P < 0.05). The portal dosimetry (PD) verification revealed that the average γ passing rate (1 mm/1%) of the RapidPlan automatic plans was 89.48%and that of the manual plans was 88.22%, and the difference was statistically significant ( t = 3.35, P < 0.05). Conclusion:RapidPlan automatic plans based on the Halcyon 2.0 platform can meet the clinical needs of the VMAT program for cervical cancer and has certain advantages.

Dosimetric study of volumetric modulated arc therapy and tomo direct simultaneous integrated boost for patients receiving breast-conserving surgery for left breast cancer / 国际肿瘤学杂志

Objective:To explore the dosimetry difference between volumetric modulated arc therapy (VMAT) and tomo direct (TD) in tumor bed simultaneous push radiotherapy after left breast-conserving surgery, and to provide more dosimetry reference for clinic.Methods:A total of 22 patients with left breast cancer who underwent simultaneous quantitative radiotherapy after breast-conserving surgery were selected from the Department of Radiation Oncology, Yunnan Cancer Hospital from December 2018 to June 2020. The localized CT images and target organs at risk and other structural data were collected. Two radiotherapy plans, VMAT and TD, were designed for the same patient, and the dosimetry differences of target areas and organs at risk were compared and analyzed between the two groups.Results:In terms of target dosimetry, there were statistically significant differences in the D 2% [ (59.99±0.19) Gy vs. (59.55±0.51) Gy, t=4.09, P<0.001], D 98% [ (57.19±0.08) Gy vs. (57.46±0.22) Gy, t=-5.10, P<0.001], conformal index (CI) (0.76±0.05 vs. 0.58±0.13, t=8.19, P<0.001) and homogeneity index (HI) (0.05±0.00 vs. 0.04±0.01, t=4.89, P<0.001) of the planning gross tumor volume (PGTV) between VMAT and TD plans. However, there was no statistically significant difference in the D 50% [ (58.73±0.10) Gy vs. (58.73±0.24) Gy, t=-0.03, P=0.974]. There were statistically significant differences in the D 50% [ (52.21±0.33) Gy vs. (53.00±0.72) Gy, t=-4.81, P<0.001], D 98% [ (48.44±0.43) Gy vs. (49.09±0.21) Gy, t=-6.80, P<0.001], CI (0.83±0.06 vs. 0.67±0.06, t=10.52, P<0.001) and HI (0.20±0.01 vs. 0.19±0.01, t=8.75, P<0.001) of the planned target volume (PTV) between the two plans. However, there was no statistically significant difference in the D 2% [ (59.01±0.45) Gy vs. (59.00±0.48) Gy, t=0.22, P=0.830]. In terms of organs at risk, there were statistically significant differences in the V 20 [ (18.81±2.86) % vs. (22.03±1.91) %, t=-5.36, P<0.001] and D mean [ (11.66±1.32) Gy vs. (12.85±1.46) Gy, t=-4.10, P=0.007] of left lung, V 5 [ (5.70±2.90) % vs. (0.30±0.13) %, t=16.44, P<0.001] and D mean [ (2.45±0.29) Gy vs. (0.43±0.14) Gy, t=9.09, P<0.001] of right lung, D mean [ (3.22±0.72) Gy vs. (1.69±0.80) Gy, t=5.41, P<0.001] of right breast, D 2% [ (5.37±1.97) Gy vs. (0.46±0.09) Gy, t=11.75, P<0.001] of cord between VMAT and TD plans. There were no significant differences in the V 5 of left lung [ (53.00±5.99) % vs. (50.00±7.69) %, t=1.91, P=0.061], V 5 of right breast [ (11.51±4.60) % vs. (8.06±3.49) %, t=1.59, P=0.120], V 30 [ (1.49±0.69) % vs. (1.51±0.71) %, t=-0.06, P=0.952] and D mean [ (3.99±0.97) Gy vs. (3.90±1.03) Gy, t=0.56, P=0.581] of heart between the two plans. Conclusion:TD and VMAT can meet the clinical dosimetry requirements for patients with left breast cancer after breast-conserving surgery. However, the two techniques have their own characteristics. VMAT has better conformity and TD has better uniformity. TD is significantly better than VMAT in protecting the right lung, right breast and spinal cord of healthy organs at risk. VMAT is better in protecting the left lung. Both VMAT and TD basically achieve the same protection for heart.

Dosimetric comparison of hippocampal avoidance wholebrain radiotherapy with flattening filter and flattening filter-free modes / 中国辐射卫生

@#<b>Objective</b> To compare the dosimetric differences of volumetric modulated arc therapy (VMAT) with flattening filter(FF) and flattening filter-free(FFF) modes in hippocampal avoidance whole brain radiotherapy. <b>Methods</b> We included 15 patients with hippocampal-sparing whole brain radiotherapy, and designed two radiotherapy plans of FF-VMAT and FFF-VMAT for each patient. On the premise of meeting clinical dose requirements, the two plans’ dosimetry, total number of monitor units, and beam-on time were compared. <b>Results</b> There were no significant differences in the target coverage, conformity index, and dose gradient of the FF-VMAT and FFF-VMAT plans (<i>P</i> > 0.05). The <i>D</i>_max, <i>D</i>_100%, and <i>D</i>_meanto the hippocampal tissue were significantly lower with FFF-VMAT [(15.13 ± 0.38) Gy, (7.12 ± 0.34) Gy, and (9.76 ± 0.43) Gy, respectively)] than with FF-VMAT (16.46 ± 0.56) Gy, (7.72 ± 0.28) Gy, and (10.54 ± 0.48) Gy, respectively)] (<i>P</i> < 0.05). The <i>D</i>_maxto the left and right lenses and the <i>D</i>_meanto the left and right eyeballs with FFF-VMAT were (7.26 ± 0.43) Gy, (6.29 ± 1.13) Gy, (11.01 ± 0.94) Gy, and (9.78 ± 1.13) Gy, respectively, which were significantly lower than FF-VMAT’s corresponding doses of (8.09 ± 0.66) Gy, (7.80 ± 0.74) Gy, (11.38 ± 1.09) Gy, and (11.05 ± 0.90) Gy, respectively (<i>P</i> < 0.05). The doses to other organs at risk including the optic nerve and optic chiasm were all controlled within the safe dosage ranges, with no significant differences between the two plans (<i>P</i> > 0.05). The FFF-VMAT plan had a significantly greater number of monitor units and a significantly shorter beam-on time than the FF-VMAT plan (<i>P</i> < 0.05). <b>Conclusion</b> Both FF-VMAT and FFF-VMAT can meet the clinical requirements, with FFF-VMAT having better hippocampus and lens protection, shorter beam-on time, and higher treatment efficiency.

Dosimetric effect of CT truncated regionson radiotherapy for thoracic esophageal cancer / 中国辐射卫生

@#<b>Objective</b> To investigate the dosimetric effect of truncated regions in computed tomography (CT) images on the targets and organs at risk in volumetric modulated arc therapy (VMAT) for middle thoracic esophageal cancer. <b>Methods</b> CT images of 15 patients with middle thoracic esophageal cancer were selected. Circle masks were used to make the volume of the truncated region account for 10%, 20%, 30%, and 40% of the arm volume, and the corresponding truncated CT images were obtained. The real CT was denoted as CT0. Two radiotherapy plans were made on CT0. One plan was VMAT_1F with full arcs, and the other one was VMAT_3F with arm avoidance. The plans were transplanted to four truncated CT, respectively, and the dosimetric differences between different plans were compared using Wilcoxon signed-rank test. <b>Results</b> Compared with VMAT_1F in CT0, <i>D</i>_mean and <i>V</i>₅ of the lung decreased in VMAT_3F, but <i>D</i>_max of the spinal cord, <i>D</i>_mean of the heart, and <i>V</i>₂₀ of the lung increased. In VMAT_3F, there was no statistically significant difference between the dosimetric parameters in the four truncated CT and those in CT0 (all <i>P</i> > 0.05). In VMAT_1F, except for homogeneity index and <i>D</i>_max of the spinal cord, the dosimetric parameters in four truncated CT were significantly different from those in CT0 (<i>P</i> < 0.05). The dosimetric difference increased with the increase in truncated region-to-volume ratio. <b>Conclusion</b> Complete CT data should be collected in clinical practice, and the radiation field avoiding the truncated regionshould be set if necessary to reduce the influence of the truncated region on dosimetry.

The application and correlation study of γ rule and DVH evaluation for VMAT dose verification evaluation of cervical cancer patients / 中华放射肿瘤学杂志

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.

Application of helical tomotherapy in the treatment of synchronous bilateral breast cancer / 中华放射医学与防护杂志

Objective:To study the differences in the dosimetry and delivery time between helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) in postoperative radiotherapy of synchronous bilateral breast cancer (SBBC) and to explore the feasibility of clinical application of the HT technology.Methods:A retrospective analysis was conducted for nine SBBC patients who underwent modified radical postoperative radiotherapy in the Fourth Affiliated Hospital of Guangxi Medical University from February 2017 to May 2022. For each patient, the Precision planning system was used to formulate the HT plan, and the RayStation planning system was employed to develop the VMAT plan. All plans obtained were divided into HT group and VMAT group according to plan type. The paired sample t-test was used to compare the dosimetric parameters of the target volume and organ at risk (OAR) and delivery time between the two radiotherapy technologies. Results:The plans of both groups could meet the clinical treatment requirements. The coverage ( D95% and V100%), conformity index (CI), average dose ( Dmean), and median dose ( D50%) of the target volumes in the HT group were better than those in the VMAT group, and the differences were statistically significant ( t=-3.21, -3.39, -5.03, 3.76, 4.97, P < 0.05). The differences in the maximum dose ( D2%), minimum dose ( D98%), high dose volumes ( V107% and V110%), and homogeneity index (HI) of the target volumes between the two groups were not statistically significant ( P > 0.05). Regarding the OAR, the V20 and Dmean of both lungs in the HT group were significantly lower than those in the VMAT group, but the irradiation volume V5 of both lungs in the HT group was significantly higher than that in the VMAT group ( t=-3.01, 3.83, -2.81, P < 0.05). Moreover, V20, V30, V40, and Dmean of heart and the V20 and Dmean of liver in the HT group were significantly lower than those in the VMAT group, with statistically significant differences ( t=3.76, -2.83, -2.74, 5.93, 4.57, 4.48, P < 0.05). There was no significant difference in the radiation doses to other OARs (spinal cord, thyroid gland, and humerus head, P > 0.05). The delivery time of the HT group was significantly higher than that of the VMAT group ( t = 11.32, P < 0.05). Conclusions:Compared with VMAT, HT has greater dosimetric advantages, and can provide higher target coverage, conformability and average dose, and significantly reduce the overall radiation doses to both lungs, heart, and liver in OARs. However, the irradiation volume V5 at low-dose areas of both lungs and the delivery time in the HT group are higher than those in the VMAT group, but still meet the clinical treatment requirements. Therefore, it is feasible to apply the HT technology to the modified radical postoperative radiotherapy of SBBC.

Feasibility and safety of simultaneous integrated boost in volumetric modulated arc therapy for early breast cancer after breast-conserving surgery / 肿瘤研究与临床

Objective:To investigate the feasibility and adverse reactions of simultaneous integrated boost (SIB) in volumetric modulated arc therapy (VMAT) for early breast cancer after breast-conserving surgery.Methods:A total of 67 patients with early breast cancer after breast-conserving surgery at Zhongshan People's Hospital from September 2019 to May 2021 were enrolled. All patients received VMAT-SIB to the whole breast and tumor bed. The total breast dose and tumor bed dose were 40.5Gy/15 times every 3 weeks and 48 Gy/15 every 3 weeks respectively. The exposure dose of organs at risk and acute adverse reactions of radiotherapy were evaluated.Results:The average doses of planning target volume of the whole brease (PTV WB) and planning target volume of the boost(PTV BOOST) were (42.0±2.1) Gy and (49.9±0.8) Gy, respectively. The V 95% and V 105% of PTV WB and PTV BOOST were (98.8±1.2)% and (31.4±11.3)%, (99.8±0.6)% and (22.9±10.2)%, respectively. The V 5Gy, V 20Gy, V 30Gy and mean dose (D mean) of ipsilateral lung were (52.4±12.0)%, (15.3±4.5)%, (6.7±2.2)% and (11.0±2.4) Gy respectively. The V 18Gy, V 40Gy and D mean of heart were 3.80% (0.48%,9.60%), 0 (0,0.16%) and (6.7±2.1) Gy respectively. At the end of radiotherapy, 19 patients (29%) of all 67 patients had no acute skin toxicity, 41 patients (61%) showed radiation erythema, 5 patients (7%) had radioactive dry peeling and 2 patients (3%) had wet peeling mainly located in the nipple, areola area and breast folds. None of the patients had grade 3-4 acute skin reactions. Breast swelling and breast pain were found respectively in 9 patients (13%) and 7 patients (10%). No local recurrence or distant metastases were observed during the follow-up period. The 2-year disease-free survival rate was 100%. Conclusions:VMAT combined with SIB is feasible in the treatment of early breast cancer. The adverse reactions of radiotherapy are mild and well tolerated.

Application of independent dose verification of volumetric modulated arc therapy based on Monte Carlo / 中华放射肿瘤学杂志

Objective:To develop a verification platform based on Monte Carlo (MC) for independent dose verification of volumetric modulated arc therapy (VMAT) plans.Methods:The head model including collimator of Varian TrueBeam linear accelerator was constructed by using EGSnrc/BEAMnrc, and the independent dose verification platform for the patients’ VMAT plans was built based on the head model and an in-house code. The percent depth dose (PDD) curves and off-axis ratios for different field sizes, the dose distribution of two irregular fields and three VMAT plans of the head and neck, chest, and pelvis were simulated using the platform. The simulated results of the PDD curves and the off-axis ratios of different field sizes were compared with the blue water measurement results. The difference between the irregular fields and the actual ArcCHECK measurements was also investigated. Besides, the differences among the MC simulated dose, TPS calculated dose and the ArcCHECK measured dose were analyzed by several methods, such as γ analysis and dose-volume histogram to verify whether the platform could be independently employed for dose verification.Results:The MC simulated results of PDD curves and off-axis ratios from 4 cm×4 cm to 40 cm×40 cm were in good agreement with the measured results. And the γ passing rates between the MC simulation and the ArcCHECK measurement for the irregular fields were above 98.1% and 99.1% for 3%/2 mm and 3%/3 mm, respectively. For VMAT plans of three patients, the γ results between the MC simulated dose and ArcCHECK measured dose were better than 93.8% and 95.9% under the criteria of 3%/2 mm and 3%/3 mm respectively. At the same time, the γ passing rates of nasopharyngeal, lung, and rectal cancers were 95.2%, 98.6% and 98.9% based on 3D γ analysis using TPS calculated dose and MC simulated dose under the criteria of 3%/3 mm; the passing rates of these three were 90.3%, 95.1% and 96.7% for 3%/2 mm, respectively.Conclusions:The simulation results of the MC-based verification platform developed in this study show a good agreement with the actual measurement results, and the simulation results are closer to the real dose distribution using the patients’ data. The preliminary results demonstrate that the platform can be used for accurate independent dose verification of VMAT plans.

Meta-analysis of dosimetric comparison between volumetric-modulated arc therapy and intensity-modulated radiotherapy for breast cancer after modified radical mastectomy / 中华放射肿瘤学杂志

Objective:To compare the dosimetric differences between volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) on planning target volume (PTV) and organ-at-risk (OAR) for breast cancer after modified radical mastectomy, aiming to provide evidence-based reference for clinical practice.Methods:According to strict inclusion and exclusion criteria, literature search was performed in PubMed, Cochrane Library, FMRS, CNKI, Wanfang Data and VIP full text databases from the inception of databases up to March 2020. The controlled clinical trials of dosimetric comparison between VMAT and IMRT for breast cancer following modified radical mastectomy were selected. The meta-analysis was performed using Stata14 software.Results:The meta-analysis included 281 patients from 13 observational studies. Compared with IMRT, VMAT significantly increased the PTV dose coverage D 95%( P<0.001) and significantly improved the PTV homogeneity index (HI, P<0.001) and conformity index (CI, P=0.004). Compared with IMRT, VMAT more effectively decreased the ipsilateral lung V 20Gy (WMD=1.332, P=0.027) and contralateral lung V 10Gy ( P=0.003). There were no significant differences in theD mean, V 5Gy, V 10Gy and V 30Gy of the ipsilateral lung, D mean and V 5Gy of the contralateral lung, D mean, V 10Gy and V 30Gy of the heart between VMAT and IMRT (all P>0.05). Compared with VMAT, IMRT reduced the cardiac V 5Gy ( P=0.001). However, sensitivity analysis of included literature on cardiac V 5Gy showed that the P value was reversed, indicating that the stability of the results was poor. VMAT significantly shortened the delivery time ( P<0.001) and the number of monitor units ( P<0.001) compared to IMRT. Conclusion:Compared with IMRT, VMAT can achieves superior target dose coverage, HI and CI, better protection for the ipsilateral and contralateral lung, fewer monitor units and shorter delivery time.

Dosimetric comparison of three techniques in radiotherapy for breast cancer after modified mastectomy / 中华放射肿瘤学杂志

Objective:To analyze and compare the dosimetric differences based on volumetric-modulated arc therapy (VMAT), fixed field intensity-modulated radiotherapy (F_IMRT), and electron irradiation combined with VMAT (E&VMAT) in radiotherapy for breast cancer after modified mastectomy, aiming to provide reference for clinical selection of treatment plan.Methods:Ten patients with the left breast cancer who received radiotherapy after modified mastectomy were randomly selected. The target areas included chest wall and supraclavicular region, and the prescribed dose was 43.5 Gy in 15 fractions (2.9 Gy/F). Based on the Pinnacle 3 planning system, the VMAT, F_IMRT and E&VMAT plans (electron beam for chest wall, VMAT for supraclavicular area) were designed for each patient. The conformity and homogeneity of the target areas, the dose of organs at risk and treatment time were compared. Results:The VMAT plan could improve the dose distribution of the target areas. The conformity index and homogeneity index of the target dose were significantly better than those of the F_IMRT and E&VMAT plans (all P<0.05). The average dose, V 30Gy, V 20Gy, V 10Gy of the left lung in the VMAT plan were significantly better than those in the F_IMRT and E&VMAT plans (all P<0.05). The V 5Gy of the left lung in the VMAT plan was significantly better than that in the F_IMRT plan ( P<0.05). There was no statistical difference in the V 5Gy of the left lung between the VMAT and E&VMAT plans ( P>0.05). The heart, right breast and right lung of the VMAT plan could meet the clinical dose limit requirements. The treatment time of the VMAT, F_IMRT and E&VMAT plans was (326±27) s, (1 082±169) s, and (562±48) s, respectively. Conclusions:Compared with the F_IMRT and E&VMAT plans, the VMAT plan has better quality and shorter treatment time. VMAT plan has higher value in clinical application compared with the F_IMRT and E&VMAT plans.

Comparison between HyperArc and conventional VMAT approach for brain metastases / 中华放射肿瘤学杂志

Objective:To compare the dosimetric parameters and plan complexity between newly-delicated HyperArc (HA) and conventional volumetric-modulated arc therapy (VMAT) in the treatment of brain metastases.Methods:For 26 patients with brain metastases, HA, conventional coplanar (Cop) and non-coplanar (Non-cop) VMAT plans with a prescription dose of 9 Gy 3fx or 6 Gy 5fx were generated. The dosimetric parameters for planning target volume (PTV), RTOG conformity index (RTOG CI), Paddick CI, homogeneity index (HI), gradient index (GI), maximum dose (D max) of brainstem and dose-volume parameters of brain-PTV(V 2Gy-V 26Gy) were statisticaly compared among these three approaches. In addition, the monitor unit (MU) and the plan complexity parameters (including MCSv and AlPO) were statistically compared. Results:To prevent missed targets during treatment, all plans were established with RTOG CI of greater than 1.1. For Paddick CI, HA provided significantly higher conformity (0.89±0.019) than Non-cop (0.87±0.036, P=0.001) and Cop (0.88±0.017, P=0.003) VMAT. For GI, the fastest dose fall-off was noted in HA (3.35±0.64), followed by conventional Non-cop VMAT of (3.70±0.80), and conventional Cop VMAT of (4.90±1.85)(all P<0.05). For the brainstem sparing, HA plan performed better than Non-cop plan[(604.14±531.61) cGy vs.(682.75±558.22) cGy, P<0.05)]. For normal brain tissue sparing, HA approach showed significant reduction than conventional Cop and Non-cop VMAT (both P<0.05). For MU, HA approach (2 872.60 ± 566.93) was significantly lower than those of Non-cop VMAT (3 771.28 ± 1 022.38, P<0.05) and Cop VMAT (4 494.08 ± 1 323.09, P<0.05). In terms of plan complexity, the MCSv of Cop plan was the lowest, indicating that the complexity was the highest ( P<0.05). The AlPO of HA was significantly higher than that of Non-cop VMAT ( P<0.05), suggesting that the complexity of HA plan was lower ( P<0.05). Conclusion:For the treatment of brain metastases, HA provides better conformity, more rapid dose fall-off, better sparing of brainstem and normal brain tissues and less plan complexity compared with conventional VMAT.

First clinical application and dosimetric verification of total body irradiation with volumetric modulated arc therapy / 中华放射肿瘤学杂志

Objective:To investigate the implementation procedures and dosimetric verification of the first patient treated with total body irradiation (TBI) based on volumetric modulated arc therapy (VMAT).Methods:Two sets of CT images were acquired under the head-in first and foot-in first to contour the planning target volume (PTV) of the cranial and caudal segments to accomplish the treatment of the whole body length, on which two interrelated plans of 5 subsequent isocenters with a total of 15 VMAT fields were performed to cover all PTVs. The plans were prescribed to ensure 90% PTV dose coverage with a total dose of 12 Gy in 6 fractions. Firstly, a dose optimization was performed on the caudal CT images, then the cranial CT images were optimized based on the dose distribution of the caudal CT images. The evaluation of the final treatment plan was carried out based on a plan sum of both two sets of images. The parameters of PTV and organs at risk (OARs) were measured by dose volume histograms from the accumulated plan. The quality assurance comprised the verification of the VMAT plans for each individual isocenter via Delta4 phantom. The dose distribution in the overlapped region between two adjacent central fields was verified with EBT3 film. The absolute dose at the overlapped region between two images was measured via Pinpoint chamber. In vivo dosimetry on the patient′s skin was monitored by MOSFET dosimeters. The results of planning parameters and treatment duration were analyzed. Results:The mean doses of two segments of PTVs were 12.45 Gy and 12.37 Gy. The mean dose for the lung was 10.8 Gy. The machine unit (MU) and mean treatment delivery time were 2 883 MU and 24.3 min, and the mean total time per fraction was 121 min. The mean 3%/3 mmγ-analysis pass rate for each isocenter VMAT plan was (99.74±0.42)%, and the mean 5%/5 mmγ-analysis pass rate for the overlapped region was (90.11±2.72)%. The average deviation of absolute dose in the overlap region of the caudal and cranial images was (3.6±0.4)%. In vivo measurement of 8 points on the patient showed that the dose of each region was ranged from 1.57 Gy to 2.04 Gy. Conclusion:According to the results of dosimetric verification, TBI based on multi-isocenter VMAT can be applied in clinical practice, which remains to be improved in terms of dose distribution, measurement results and clinical efficiency.

An automatic VMAT planning method for primary liver cancer radiotherapy based on predicting the feasibility DVH / 中华放射肿瘤学杂志

Objective:To establish an automatic planning method using volumetric-modulated arc therapy (VMAT) for primary liver cancer (PLC) radiotherapy based on predicting the feasibility dose-volume histogram (DVH) and evaluate its performance.Methods:Ten patients with PLC were randomly chosen in this retrospective study. Pinnacle Auto-Planning was used to design the VMAT automatic plan, and the feasibility DVH curve was obtained through the PlanIQ dose prediction, and the initial optimization objectives of the automatic plan were set according to the displayed feasible objectives interval. The plans were accessed according to dosimetric parameters of the planning target volume and organs at risk as well as the monitor units. All patients′ automatic plans were compared with clinically accepted manual plans by using the paired t-test. Results:There was no significant difference of the planning target volume D 2%, D 98%, D mean or homogeneity index between the automatic and manual plans ((58.55±2.81) Gy vs.(57.98±4.17) Gy, (47.15±1.58) Gy vs.(47.82±1.38) Gy, (53.14±0.95) Gy vs.(53.44±1.67) Gy and 1.15±0.05 vs. 1.14±0.07, all P>0.05). The planning target volume conformity index of the manual plan was slightly higher than that of the automatic plan (0.77±0.08 vs. 0.69±0.06, P<0.05). The mean doses of normal liver, V 30Gy, V 20Gy, V 10Gy, V 5Gy and V< 5Gy of the automatic plan were significantly better than those of the manual plan ((26.68±11.13)% vs.(28.00±10.95)%, (29.96±11.50)% vs.(31.89±11.51)%, (34.88±11.51)% vs.(38.66±11.67)%, (45.38±12.40)% vs.(50.74±13.56)%, and (628.52±191.80) cm 3vs.(563.15±188.39) cm 3, all P<0.05). The mean doses of the small intestine, the duodenum, and the heart, as well as lung V 10 of the automatic plan were significantly less than those of the manual plan ((1.83±2.17) Gy vs.(2.37±2.81) Gy, (9.15±9.36) Gy vs.(11.18±10.49) Gy, and (5.44±3.10) Gy vs.(6.25±3.26) Gy, as well as (12.70±7.08)% vs.(14.47±8.11)%, all P<0.05). Monitor units did not significantly differ between two plans ((710.67±163.72) MU vs.(707.53±155.89) MU, P>0.05). Conclusions:The automatic planning method using VMAT for PLC radiotherapy based on predicting the feasibility DVH enhances the quality for PLC plans, especially in terms of normal liver sparing. Besides, it also has advantages for the protection of the intestine, whole lung and heart.

Study of feasibility of exchanging intensity-modulated radiotherapy plans after beam matching on two Linacs / 中华放射肿瘤学杂志

Objective:To explore the feasibility of the clinical implementation of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans with 6MV photon on two Elekta Linacs (Versa HD and Synergy) after beam matching.Methods:The images of 12 patients with nasopharyngeal carcinoma, central lung cancer and prostate cancer were randomly selected, and the IMRT and VMAT plans were designed. Two different dose tools of ionization chamber and three-dimensional detector ArcCheck were used to verify the individualized radiation treatment of 6MV photon beams on two Linacs and compare the differences.Results:The deviations between the doses of two Linacs (Versa HD and Synergy) measured by the ion chamber and treatment planning system were (0.32±1.32)% and (0.54±1.29)%. The differences of all plans were within the range of ±3%, and the deviations of the point dose between two Linacs were within the range of ±2% with no statistical significance (both P>0.05). The γ analysis of verification using ArcCheck showed that the passing rates of all plans under the 2mm/3% and 3mm/3% with 10% threshold conditions were over 95%, respectively. The average differences between two Linacs were 0.19%(2mm/3%) and 0.09%(3mm/3%). Conclusions:The results of performing IMRT/VMAT plans on two Linacs meet the clinical requirements and the differences between two Linacs are small. Hence, the same plans can be implemented interchangeably on different Linacs.

A new approach to spare organs at risk for breast cancer radiotherapy-half field segmented VMAT delivery technique / 中华放射医学与防护杂志

Objective:To explore a new technology that can protect the lungs and heart better by utilizing the dose distribution attributes of the half-field and the characteristics of the VMAT (volumetric modulated arc therapy) technology.Methods:A three-dimensional water tank was used to measure the dose of symmetrical field and half field edge and analyze them comparatively. A total of 50 patients with left breast cancer receiving the postoperative radiotherapy were selected. Among them, 25 patients were performed conserving surgery and 25 patients were performed radical mastectomy. After the operation, all the patients received the prescription dose of 50 Gy in 25 fractions. Based on the Eclipse system, the symmetrical field continuous arc VMAT technology and the semi-field segmented arc VMAT technology were used to design the plan. Besides, the dose suitability data and the treatment efficiency of target areas and organs at risk were compared and analyzed.Results:The radiation size of half-field did not increase with the increased depth in the water mode. The symmetric field gradually enlarged due to the angle of tensor factor, increased to about 2 cm at the depth of 30 cm, and the delivery dose in the half-field was lower than that in the symmetric field. The closer the field edge is, the more obvious it is. Compared with the symmetric field continuous arc plan, the half-field segmental arc VMAT plan significantly improved the delivery dose of the lungs and heart ( t=-4.11, -4.42, P=0.00), in which the mean values of V5, V30, and Dmean for the whole structure of the heart were reduced by 52.5%, 65.5%, and 47%, respectively. The left anterior descending coronary artery, which was closely related to the target area, had a decrease of more than 20%. The mean values of V5, V10, V20, and Dmean of the affected lung were reduced by 21.6%, 24.8%, 25.0%, and 23.2%, respectively. The mean values of the doses of other endangered healthy organs, and the execution time of half-field segment arc plan were also better than the continuous arc plan. Conclusions:For breast cancer radiotherapy, the combination of half-field and VMAT can give full play to the advantages of half-field and VMAT, and significantly reduce the irradiated dose of the heart, affected lung, and healthy side of the breast.

Dosimetric study of helical tomotherapy and volumetric modulated arc therapy simultaneous integrated boost for patients receiving breast-conserving surgery of left breast / 国际肿瘤学杂志

Objective:To compare the dosimetric characteristics of helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT) after left breast conserving surgery.Methods:Twenty-four patients with left breast cancer after breast-conserving surgery who were admitted to the Department of Radiation Oncology of Tumor Hospital of Yunnan Province from May 2016 to May 2019 were selected. The HT plan and the VMAT plan were designed for the same patient. The target dose and the dose volume parameters of organs at risk were compared and analyzed in the two radiotherapy plans.Results:There were significant differences in the D 2% [(59.68±0.46) Gy vs. (60.06±0.20) Gy, t=-4.229, P<0.001], D 98% [(57.46±0.44) Gy vs. (57.20±0.07) Gy, t=2.912, P<0.001], conformity index (CI) (0.80±0.05 vs. 0.76±0.04, t=4.079, P<0.001) and homogeneity index (HI) (0.04±0.01 vs. 0.05±0.00, t=-5.505, P<0.001) of the planning gross tumor volume (PGTV) between the HT and VMAT plans. However, there was no significant difference in the D 50% [(58.77±0.46) Gy vs. (58.75±0.11) Gy, t=0.179, P=0.859]. There were significant differences in the D 50% [(51.99±0.39) Gy vs. (52.39±0.36) Gy, t=-5.278, P<0.001], D 98% [(49.46±0.29) Gy vs. (48.35±0.46) Gy, t=9.538, P<0.001] and HI (0.19±0.01 vs. 0.21±0.01, t=-7.538, P<0.001) of the planned target volume (PTV) between the two plans. However, there were no significant differences in the D 2% [(59.13±0.64) Gy vs. (59.09±0.46) Gy, t=0.511, P=0.614] and CI (0.83±0.04 vs. 0.82±0.04, t=1.637, P=0.115). In terms of organs at risk, there were significant differences in the V 5 [(57.90±1.42)% vs. (52.40±5.74)%, t=4.812, P<0.001], V 20 [(22.40±2.17)% vs. (18.40±3.16)%, t=5.573, P<0.001] and D mean [(12.71±0.55) Gy vs. (11.46±1.26) Gy, t=4.963, P<0.001] of left lung, D mean of right lung [(3.42±0.27) Gy vs. (2.49±0.24) Gy, t=13.310, P<0.001], D mean of right breast [(4.41±0.50) Gy vs. (3.12±0.65) Gy, t=10.326, P<0.001], V 30 [(0.55±0.37)% vs. (1.24±1.11)%, t=-4.020, P=0.001] and D mean of heart [(4.68±0.62) Gy vs. (3.83±0.88) Gy, t=7.335, P<0.001], D mean of left atrium [(2.53±0.31) Gy vs. (2.16±0.28) Gy, t=5.488, P<0.001], D mean of right atrium [(2.77±0.43) Gy vs. (2.20±0.30) Gy, t=7.103, P<0.001], D mean of right ventricle [(5.10±0.72) Gy vs. (3.72±0.94) Gy, t=9.802, P<0.001] and D 2% of spinal cord [(14.79±2.73) Gy vs. (5.42±2.23) Gy, t=14.788, P<0.001] between HT and VMAT plans. There was no significant difference in the D mean of left ventricle [(5.10±1.19) Gy vs. (4.80±1.54) Gy, t=1.250, P=0.224]. Conclusion:Both the HT plan and the VMAT plan can meet the treatment requirements. The HT plan can provide better target area conformity and dose uniformity. The VMAT plan has more advantages in terms of organs at risk. The HT plan shows an advantage only in exposure to high-dose area.