AbstractObjectiveTo investigate the dosimetric impact of different collimator angle optimization methods in intensity‐modulated radiotherapy of gastric cancer.MethodsA total of 10 gastric cases were retrospectively selected in this study. Three sets of plans were generated with different collimator angle optimization: setting the collimator angle to 0° (CL0), applying Eclipse automatic collimator angle optimization (CLA), and setting the collimator angle corresponding to the minimum X‐jaw gap (CLX). Different dosimetric metrics were applied in comparison of the target volume and normal tissues. Delivery efficiency was accessed in terms of control points, split fields, monitor units, and treatment time. All plans were verified using the 2‐D array MatriXX, and the γ‐index analysis was carried out by using different criteria.ResultsThere was no significant difference in dosimetric comparison of planning target volume and organs at risk. Compared with CL0, Both CLA and CLX can significantly reduce control points, split fields, and monitor units, except that CLA increased treatment time. For dose verification, the γ passing rate showed a tendency of CLx > CLA > CL0.ConclusionFor intensity‐modulated radiotherapy for gastric cancer, CLA and CLX can obtain comparable dosimetry distribution in respect to CL0. However, CLX can significantly increase the dose delivery efficiency and verification passing rates. It was suggested that CLx was beneficial in intensity‐modulated radiotherapy for gastric cancer.

The precision and efficiency of the registration of megavolt-level electronic portal imaging devices (EPID) images with the naked eye in the orthogonal window are reduced. This study aims to develop a new registration algorithm with enhanced accuracy and efficiency. Ten setup errors with different translation and rotation were simulated with the phantom. For each error, one set of simulated computer tomography images and EPID images were acquired and registered with the traditional and the new method. The traditional method was performed by two senior physicists with the Varian Offline Review software. The new method is basing on the comparison of the precise contours of the same bone structure in the digital reconstruction radiography images and the EPID images, and the contours were fitted with an automatic edge detection algorithm based on gradient images. The average error of the new method was decreased by 44.44%, 28.33%, 49.09% in the translation of X, Y, and Z axes (The traditional vs. the new: X axes, 0.45 mm vs. 0.25 mm; Y axes, 0.75 mm vs. 0.35 mm; Z axes, 0.55 mm vs. 0.28 mm), 42.86% and 40.48% in the rotation of X and Z axes (The traditional vs. the new: X axes, 0.49° vs. 0.28°; Z axes, 0.42° vs. 0.25°), respectively. The average elapsed time in the new method was reduced by 11.14% (The traditional vs. the new: 44 s vs. 39.1 s). The new registration method has significant advantages of accuracy and efficiency compared with the traditional method.

Objective To investigate the impact of four different collimator angle optimization techniques on the planning target volume (PTV) and organ at risk (OAR) during intensity-modulated radiotherapy (IMRT) for gastric cancer.Methods Ten patients with gastric cancer undergoing IMRT in Zhongnan Hospital of Wuhan University from 2015 to 2016 years were recruited in this study.All IMRT plans were designed by conventional five fields (330°,10°,45°,90°and 180°).In the Eclipse treatment planning system,four different collimator angle optimization techniques with consistent planning optimization parameters were employed to design the IMRT plan.Collimator angle optimization techniques included the following aspects.The collimator angle was set at 0 degree (CL0),collimator angle was set at 90 degree (CL90),Eclipse automatic collimator angle optimization (CLA) was adopted and collimator angle was set as the angle when the distance between X-Jaws and PTV (CLx) was the shortest.The dosimetric parameters mainly included the conformal index (CI) of PTV,the homogeneity index (HI),the mean dose (Mean),and the dosage of OAR.The treatment time (Time),monitor unit (MU),control point (CP),split field (SF) and conformal distance (Fx) were also considered.Results Regarding CL0 as the control,the CI,HI and Mean did not significantly differ among four collimator angle optimization techniques (all P＞0.05),whereas CLx could significantly increase the average dose of PTV in the target area (P＜0.05);CLx optimization reduced the liver (V30 reduction by 1.54％),left kidney (V12 decrease by 1.46％),right kidney and other OARs,whereas it slightly increased the maximum dose of the small intestine and spinal cord (＜1％).CLgo and CLA optimization elevated the dose of OAR in gastric cancer.Among four different collimator angle optimization techniques,CLx optimization reduced the MU (25.02％),CP (26.03％),Fx (20.27％) and SF (by 1.3separate fields on average) and treatment time (10.03％).CLgo and CLA optimization could decrease the MU,CP,Fx and SF.CL90 optimization had certain advantages in shortening the treatment time,whereas CLA optimization could prolong the treatment time by 5.04％.Conclusions During IMRT for gastric cancer,CL90,CLA and CLx collimator angle optimization techniques can obtain comparable dosimetry distribution to CL0 optimization technique,which can reduce the MU,decrease the radiation leakage,shorten the treatment time and improve treatment efficiency.

Purposes The main aim of the study was to investigate the dosimetric difference between acuros XB algorithm (AXB), anisotropic analytic algorithm (AAA), and pencil beam convolution (PBC) algorithm in stereotactic body radiation therapy (SBRT) plan for non-small cell lung cancer (NSCLC). Patients and Methods Thirty-eight NSCLC patients were included. GTV, PTV, and organs at risk were delineated by the radiation oncologists. Three optimized SBRT plans for each patients were gained using three algorithms of AXB, AAA, and PBC with the identical plan parameters. Dosimetric endpoints were collected and compared among the three plans, including dosimetric criteria: V100%, V90%, PTV Dmin, Dmax, Dmean, homogeneity index (HI), and Paddick conformity index (CI). Results AXB plan resulted in decreased V100% with a mean difference 6.14% compared with PBC plan (For V100%, AXB vs AAA vs PBC=93.44% vs 95.54% vs 99.58%, P<0.05). Three plans showed no significant difference as to the parameter V90%. AXB plan leaded to reduced Dmin of PTV compared with other two algorithms (For Dmin of PTV, AXB vs AAA vs PBC=4048cGy vs 4365Gy vs 4873Gy, P<0.05). PBC induced the enhanced trend of Dmax of PTV compared with other two algorithms (Dmax among three algorithms, P>0.05); and increased the Dmean of PTV in three algorithms with significant difference (For Dmean of PTV, AXB vs AAA vs PBC=5332cGy vs 5330Gy vs 5785Gy, P<0.05). AXB algorithm achieved a similar plan conformity with other two algorithms (For CI, AXB vs AAA vs PBC=0.80 vs 0.85 vs 0.71, P>0.05). Conclusion For SBRT plan of NSCLC, AAA and PBC algorithms overestimate target coverage, AXB algorithm is recommended for the SBRT plan of NSCLC.

Objective To evaluate the clinical efficacy and prognostic factors of stereotactic body radiotherapy(SBRT)for pulmonary oligometastases,and to further explore the patients most suitable for SBRT. Methods From 2012 to 2105,51 patients with 76 oligometastatic lung tumors were treated with SBRT.In those patients,27 had primary lung tumors and the others had extrapulmonary tumors. Seven patients had squamous cell carcinoma,thirty-five had adenocarcinoma, and the rest had other types of cancer. The patients received radiotherapy at a dose of 50 Gy in five fractions or 60 Gy in three fractions. Survival analysis was made by the Kaplan-Meier method. A multivariate analysis was made by the Cox model. Results The 1-and 2-year local control rates were 86%(65/76)and 80%(61/76),respectively. The 1-and 2-year overall survival(OS)rates were 80%(41/51)and 55%(28/51),respectively. The median survival time was 30(2-57)months,while the median progression-free survival time was 8(1-32)months. Twenty-one patients had grade 1 radiation pneumonitis(RP),while one patient had grade 2 RP. The multivariate analysis revealed that no more than 2 oligometastatic lung tumors,progression-free interval(PFI), and a performance score(PS)no higher than 1 were independent factors for OS(all P<0.05). Conclusions SBRT is effective and safe for treating pulmonary oligometastases. The number of oligometastatic lung tumors,PFI,and PS are independent prognostic factors for OS. Suitable patients and the appropriate timing of treatment are key to the efficacy of SBRT.

Objective To divide computed tomography (CT) values into different ranges and investigate the influence of CT value division on dose calculation, and to propose a method to combine magnetic resonance imaging (MRI) with assigned CT values.Methods Ten CT images each were collected from patients with head and neck, chest, and pelvic tumors.Random sampling was performed for the CT values of main tissues or organs at the three parts, and then the mean CT value of each tissue or organ was calculated to divide the CT values into different ranges.A virtual phantom was built in the Varian Eclipse treatment planning system, and for the prescribed dose of 100 cGy, the machine output was recorded at different CT values.The influence of different CT value ranges on dose calculation was analyzed.The treatment plans of intensity-modulated radiotherapy were selected from 5 cervical cancer patients, and new CT values were assigned to the planning target volume (PTV) and organs at risk to obtain new CT images.The plans were transferred to the new CT images and compared with the results on the original CT images in terms of dosimetric parameters.Results After dividing the CT values into different ranges and verifying the results in dose calculation, the CT values corresponding to different human tissues or organs were-100 to 100 HU.The influence of CT value variation on dose calculation was within 3%.In the same treatment plan, there were small differences in dosimetric parameters between new CT images and original CT images.Dmax, Dmean, D98%, D95%, D5%, and D2% of PTV were all below 3%, and Dmax and Dmean of the bladder, rectum, small intestine, femoral head, and bone marrow were below 2%.Conclusions The influence of CT value division on dose calculation in the treatment planning for pelvic tumors is acceptable, so it can be used in combination with MRI.

Objective To evaluate the effect of home-made immobilization device with KV-CBCT in lung-SBRT and investigate its clinical use value.Methods Choosing 10 lung tumor patients (half centre type tumor;half peripheral type) random analysis the interfractional and intrafractional setup errors in the SBRT process by this fixed device with KV-CBCT.The concrete method is using Varian's KV-CBCT scans the patients before and after the SBRT each time,then make the registration between the reconstructed 3 d image and the planned CT image (both based on bone landmark),we then obtain the average setup errors in LR,AP and SI directions.Simultaneously,this research make contrastive analysis of setup errors among this fixed device and other fixed devices such as vacuum pad,phantom in body IMRT.All data make one-factor analysis of variance by SSPS 17.0.Results All the setup errors data was gaussian distribution,the centre type interfraction was at (0.01 ±0.32) cm (LR),(-0.08 ±0.38) cm (AP),(0.14 ±0.36) cm (SI) of the cross section,peripheral type interfraction was at (0.01 ± 0.32) cm (LR),(-0.08 ± 0.38) cm (AP),(0.14 ± 0.36) cm (SI) of the cross section (P =0.001).We found out that the average of lung tumor's setup error at all three directions have no significant difference-the largest was the AP directions (P =0.003),the second was the SI direction (P =0.003) and the smallest was the LR direction (P =0.001).The central type has no significant difference at three directions.Compare to the other fixed device,the average setup errors of our device are (0.09 ± 0.33) cm (LR),(-0.10 ± 0.44) cm (SI),(0.17 ±0.35) cm (AP) better than the report at present paper.As the interfraction setup error was small enough by using this fixed device while it has beyond the system algorithm,the registration software of system shows (0.0 ± 0.0 cm).Conclusions The range of lung tumor motion can be cut down obviously and enhance each placement accuracy,repeatability,on SBRT with home-made immobilization device.

Objective:To analyze the set-up errors in radiotherapy for nasopharyngeal carcinoma(NPC)and to determine the margins required for clinical target volume(CTVs)and organs at risk volume(OARs)respectively to plan target volume(PTVs)and organs at risk volume(PRVs).Methods:The set up errors of 14 patients in radiotherapy for NPC during May to June in 2013 were measured and analyzed in this study.Linear errors(x,y,z axis)were obtained by cone beam CT(CBCT).MPTV and MPRV were determined.Results:Fourteen patients received a total of 84CBCT scans before treatment.The systematic errors on x(left-right),y(superior-inferior),and z(anterior-posterior)directions were(-0.7±1.40)mm,(-0.39±1.66)mm,and(-0.14±1.21)mm respectively.MPTV was 2.38mm in xaxis,2.64mm in yaxis,and 3.17mm in z axis.MPRV was 1.43mm in xaxis,1.60mm in yaxis,and 1.81mm in zaxis.Conclusion:Set-up errors were unavoidable in NPC irradiation.To minimize the influence of set-up errors,we suggest a PTV margin of 2.5mm,3mm and 3.5mm on x,y,zdirections,respectively and a PRV margin of 1.5mm,2mm,2mm on x,y,zdirections,respectively for optic nerve,optic chiasm and brain stem and a PRV margin of 6mm for spinal cord.

Objective To investigate the CT number linearity of the cone-beam CT (CBCT) images at the different spatial locations in the scanning area.Methods The CatphanS04 phantom at the different locations are scanned repeatcdly using the CBCT on the Varian 23EX linear accelerator.The phantom is located the isocenter point,eccentric 3 cm,eccentric 6 cm,and different points on the z-axis successively on the accelerator.The scanned mode is the standard head mode.The reconstructive thickness is 2.5 cm.The different densities inserts of CTP404 module on the different locations are measured via Eclips treatment planning system (TPS) and computed by Matlab 7.0 and the CT linear fitting are then processed.In order to understand better the linear distribution along with the value of CT in the spatial distribution the results are compared with the fan-beam CT.Results Phantom studies show that:CBCT has good linearity performance not only under the standard header (body) of the scanning conditions,but also on such locations including the cross-sectional,the sagittal,the coronal plane and the eccentric position ( R2 ＞ 0.953 ).Bowtie filtration device does not change the CT finearity but changes the value of CT.Conclusions The linearity of X-ray CBCT on the Varian linear accelerator is favorable.CBCT will be used in the TPS dose calculation via further correction of the CT value.