Objective To evaluate the patient dose from Hi-ART MV helical CT imaging in image-guided radiotherapy.Methods Weighted CT dose index (CTDI_W) was measured with PTW TM30009 CT ion chamber in head and body phantoms,respectively,for slice thicknesses of 2,4,6 mm with scanned range of 5 cm and 15 cm.Dose length products (DLP) were subsequently calculated.The CTDI_W and DLP were compared with XVI kV CBCT and ACQSim simulator CT for routine clinical protocols.Results An inverse relationship between CTDI and the slice thickness was found.The dose distribution was inhomogeneous owing to the attenuation of the couch.CTDI and DLP had close relationship with the slice thickness and the scanned range.Patient dose from MVCT was lower than XVI CBCT for head,but larger for body scan.Results CTDI_W can be used to assess the patient dose in MV helical CT due to its simplicity for measurement and reproducibility.Regular measurement should be performed in QA & QC program.Appropriate slice thickness and scan range should be chosen to reduce the patient dose.

easurement should be performed in QA & QC program. Optimal image parameters should be chosen to reduce the scanning range and patient dose.

Objective To explore the application value of multi-ISO center planning method in intensity-modulated radiotherapy for carniospinal irradiation.Methods Ten patients treated with craniospinal irradiation with helical tomotherapy were selected.For these patients, new plans were designed with multi-ISO centers planning method on the treatment planning system (TPS) named Eclipse 11.0.Dose distribution to the tumor, OARs and normal tissue, the treatment time and the monitor units (MUs) of the two plans were compared.Results The plans designed in two groups satisfied all clinical requirements.For the tumor target (PTV) , the difference of D95％ between two groups was not statistical significant, while D9s ％ , D2 ％ and HI in HT group were superior to M-ISO group (t =2.822,2.333,4.743, P ＜0.05) , D50％ , D and CI in M-ISO group were superior to HT group (t =5.259,3.685,8.835 ,P ＜ 0.05).The dose of OARs such as cochlea, parotid, submandibular gland, thyroid gland and kidney in HT group was lower than M-ISO group (t =4.365,5.416,2.674,3.077,2.782,2.607,4.659,P ＜0.05) , and the dose of pancreas and small bowel was higher than M-ISO group (t =5.265,5.935, P ＜ 0.05).Differences were not significant for V5 of normal tissue between two groups;while V10, V20 and V36 of normal tissue in M-ISO group were lower than HT group (t =3.57,3.701,2.602, P ＜ 0.05).M-ISO group reduced 41.0％ of the treatment time by average and reduced 94.1％ MUs by average.Conclusions Intensity-modulated radiotherapy for carniospinal irradiation with multi-ISO centers planning method not only met the requirements of clinical dosimetry, but also shorten the treatment time, reduced the damage to the machine.Multi-ISO centers planning method might be promoted as a new design scheme.

Objective To evaluate the penumbra of a new multileaf collimator equipped with Elekta Synergy accelerator. Methods The penumbra were derived from beam profiles measured in air and water using PinPoint ion chamber with PTW MP3 water phantom. Variations of penumbra with X-ray beam energy, depth in water, and leaf position were investigated. Results The penumbra in air for 6 MV X-ray was 2 mm less than that at depth of maximal dose in water. The penumbra of leaf side was 1 mm less than that of the leaf end. The penumbra had close relationship with beam energy, depth in water and leaf position. Penumbra was increased with beam quality and water depth. The leaf position had great influence on the penumbra. Conclusions The penumbra of the multileaf collimator is related to its original design and radiation delivery technique. Special considerations should be taken into during treatment planning.Regular measurement should be performed to guarantee the delivery quality.

Objective To evaluate the variations of effective doges with the preset scanning parameters from linac-integrated kV cone beam CT( CBCT). Methods Weighted CT dose index(CTDIW) were measured with PTW TM30009 CT ion chamber in head phantom and body phantom, respectively, for different combinations of tube voltage, mAs, collimator and gantry rotation range. Dose length products(DLP) were derived from CTDIW and effective doses(E) were calculated by the DLP and EDLP. Results CTDIW and effective dose had the quadratical relationship with tube voltage, depending linearly on product of tube current and exposure time. Effective dose had close relationship with the collimator and the gantry rotation range. Both the DLP and ED for CBCT were lower than the reference dose level recommended for conventional CT. Conclusions Effective dose from CBCT has a close relationship with the scanning parameters. Optimal imaging parameters should be chosen according to the patient's anatomy to reduce patient dose.

Objective To evaluate the role of equivalent uniform dose (EUD) in planning optimization of intensity-modulated radiotherapy (IMRT) for prostate cancer.Methods Ten patients with prostate cancer were randomly selected who treated with IMRT.For these patients,the treatment plans were designed with dose-volume objectives.Based on these plans,new plans were designed through replacing the dose-volume objectives with maximum EUD for rectum,bladder and small bowel,while keeping the dosevolume objectives unchanged.Comparison was made between the new plans and the former cones by paired t-test.Results The conformity index of planning target volume was better with EUD optimization compared to dose-volume (1.00 ± 0.04 ∶ 0.94 ± 0.04,t =3.80,P =0.04).The D53,D30 and Dicm3 for rectum was better with EUD optimization compared to dose-volume (24.4 ± 2.7 ∶ 25.5 ± 2.6,t =-3.82,P =0.004,34.1 ±4.3∶39.1±2.1,t=-3.80,P=0.004 and51.4±1.0∶51.8±0.9,t=-2.42,P=0.039),with V10,V20 for bladder and V10,V20,V30,V40 for small bowel also better with EUD optimization (92.2 ±6.2∶99.4±1.1,t=-4.28,P=0.002;70.7±5.7∶78.7±6.3,t=-3.10,P=0.013 and 62.2±30.2∶74.7 ±30.0,t =-4.18,P =0.002;34.3 ±26.3∶46.5 ±30.9,t =-5.46,P =0.000;17.1 ±17.0∶25.1 ±22.6,t=-3.52,P=0.007;10.6± 11.5∶ 15.6± 16.1,t=-2.64,P=0.030).Conclusions The conformity index of planning target volume is better with EUD optimization compared to dose-volume.And the dose to rectum,bladder and small bowel can be reduced through optimization with EUD optimization compared to dose-volume.

Objective The aim of this study was to evaluate the role of multicriteria optimization (MCO) in planning of intensity-modulated radiotherapy (IMRT).Methods Twenty IMRT patients (ten with prostate and ten with lung cancers) were randomly selected.For these patients,the treatment plans were designed with direct machine parameter optimization (DMPO).Based on these plans,new plans were designed with MCO,while keeping the setting conditions unchanged.Comparison was made between the two plans including the dose distribution,the dose volume histogram,the time of optimization and number of monitor unit (MU),but were play by pairing-t test.Results The plan designed in both optimizations satisfied all clinical requirements.For the same or better target coverage,rectum,bladder and small bowel were better with MCO compared with DMPO,MCO reduced 58％ of the time for optimization by average while MU increased 32％ by average for prostate cancer.For lung cancer,the whole lung,heart and spinal cord were better with MCO compared with DMPO,MCO reduced 59％ of the time for optimization by average while MU increased 11％ by average.Conclusions In comparison with DMPO,MCO reduces the dose of organs at risk,shorten the time of optimization.

Objective To investigate the dose and mechanical properties of medical electron linear accelerators in grass-roots radiotherapy units in Sichuan Province,China via sampling and inspection.Methods A total of eight radiotherapy units in Sichuan Province were selected by sampling,and the tests were performed for the dose and mechanical properties of the medical electron linear accelerators in use.Among these accelerators,there were 5 imported accelerators and 3 domestic accelerators.The test items and methods were determined according to the requirements in GB15213-94.Results Among the 14 test items,the items related to the flatness,symmetry,and overlap of radiation field.The other tests of dose accuracy and mechanical precision achieved good results.Conclusions There is a need to strengthen the daily quality control work for dose and mechanical accuracy of medical electron linear accelerators in grass-roots radiotherapy units in Sichuan Province and perfect the allocation of professional equipment and personnel and training of related personnel.With the support of Sichuan Radiotherapy Quality Control Center,quality control supervision and guidance should cover the whole province.

Objective To compare dosimetric parameters between automatic three-dimensional conformal radiotherapy (a3DCRT),inverse three-dimensional conformal radiotherapy (i3DRT),inverse intensity-modulated radiotherapy (iIMRT).Methods Ten lung cancer patients with a single target and 10 intracranial tumor patients also with a single target,who were treated in our radiotherapy center from 2014 to 2015,were included in the study.Their image data were transferred to RayStation 4.5 via network,and then the treatment plans for a3DCRT,i3DCRT,and iIMRT were designed for the 20 patients.The dosimetric parameters for planning target volume (PTV) and organs at risk (OAR) were compared between the three plans using multiple dependent variables and two dependent variables.Results For lung cancer patients,iIMRT achieved better results in D98％,D50％,D2％,conformity index (CI),and homogeneity index (HI) than i3DCRT and a3DCRT (P=O.007,0.001,0.002,0.000,and 0.000),and the CI of a3DCRT was superior to that of i3DCRT (P=O.000);there were no significant differences in heart D33,spinal cord Dmax and D1 cm3,and both lungs between the three plans (P=O.702,0.237,0.163,0.739,0.908,0.832,0.886,0.722,0.429,0.840,and 0.702).For intracranial tumor patients,there were no significant differences in dosimetric parameters between the three plans,except that the CI of iIMRT and a3DCRT was superior to that of i3DCRT (P=O.648,0.783,0.256,0.931,0.002,and 0.034);there were no significant differences in whole brain irradiation dose between the three plans (P=0.446,0.755,0.772,0.0266,0.440,0.290,and 0.939).Conclusions For the single target in patients with lung cancer and intracranial tumors,a3DCRT can improve the CI of PTV compared with i3DCRT,and shows no significant dosimetric disadvantage for OARs compared with iIMRT.Considering the simplicity and low cost of 3DCRT,a3DCRT holds promise as a novel radiotherapy technique.

Objective To compare the effective dose deposited in patients between helical tomotherapy (HT) and multi-ISO radiotherapy (M-ISO) in carniospinal irradiation (CSI).Methods Nine children with craniospinal irradiation were selected .For these patients , new plans were designed with HT and M-ISO centers planning method on the treatment planning system ( TPS) .The effective dose of the nine patients from 18 treatment plans were calculated ,and the difference of the effective dose between HT and M-ISO was compared using paired t-test.Results The plans designed in two groups were both satisfied all clinical requirements .For the planning target volume ( PTV ) , no statistically significant difference was found in D95% between two groups ( P>0.05 ) , while D98%, D2% and homogeneity index (HI) in HT group were superior to M-ISO group (t=2.762, 2.413, 4.563, P<0.05), D50%, Dmean and CI in M-ISO group were superior to HT group (t=5.259, 3.685, 7.815, P<0.05).HT and M-ISO had different advantages in the protection of the OARs .The effective dose of patients in M-ISO group was superior to HT group (t=5.921, P<0.05).Conclusions HT and M-ISO have different advantages in CSI.The low dose area has greater influence on the effective dose in HT group compared to M-ISO group. The low dose area should be concerned while designing the treatment planning for CSI .