Objective To study the impact of the resolution of reference dose distribution and evaluated dose distribution to Gamma rate in the verification of IMRT. Methods Designed four fields, the resolution of dose distribution calculated in water phantom and exported from TPS are 1 ,2,3 ,4,5,6 mm. To calculate Gamma index by IBA's OmniPro-I'mRT software in different sampling resolution. Results When the resolution of evaluated dose distribution was fixed, the change of reference dose distribution's resolution has little effect on Gamma rate (5％ to IMRT field) ;When the resolution of reference dose distribution was fixed , the Gamma rate increased as the evaluated dose distribution's resolution ( ＞ 1 mm) raise ( the Gamma rate increase ( 15. 2 ±6. 2) ％ ( t = 11. 99 ,P < 0. 01 ) and ( 14. 9 ± 5. 5) ％ ( t = 13. 24 , P ＜ 0. 01 ) while the resolution of evaluated dose distribution changed from 6 mm t0 3 mm and from 3 mm to 1 mm　respectively) .Conclusions To use Camma method for verification of IMRT, the measured data can be as a reference dose distribution without　interpolation;the computed data by TPS can be as a evaluated dose distribution and it is more appropriate for the resolution of 1 mm.

Objective To investigate the dosimetric characteristics and their clinical applications of volumetric modulated Arc therapy (RapidArc) with fixed-fields intensity modulated radiotherapy for early stage nasal NK/T-cell lymphoma.Methods Ten patients with stage Ⅰ E and Ⅱ E nasal NK/T-cell lymphoma were enrolled in the study.Five field coplanar plan (5F),nine field coplanar plan (9F),five field non-coplanar plan (5F-N) and RapidArc plans were designed for each patient,in which 5F plan was set as the control group.Conformity index (CI) and homogeneity index (HI) as well as the maximum dose of organs at risks were compared.Results The target CI of 5F,9F,5F-N and RapidArc plan was 0.419±0.159,0.478 ±0.181,0.465 ±0.121 and 0.518 ±0.111,respectively.Compared with 5F (0.136±0.038),the target HI of 9F and RapidArc plan was 0.111 ±0.027 and 0.112 ±0.031 (t =3.11,3.04,P ＜ 0.05).9F plan significantly increased the Dmax of lens in the contralateral side(t =2.82,P ＜ 0.05) and in ipsilateral side (t =3.25,P ＜ 0.05),while 5F-N plan decreased the Dmax of optical nerves by up to 9％.RapidArc plan effectively reduced the radiation to organs at risk in lens (t =3.25,P ＜0.05),eyes (t =3.25,P ＜0.05),optical nerve (t =2.57,P ＜0.05) and optical chaism(t =7.62,P ＜0.05).The delivery efficiency of four plans ranked as RapidArc ＞ 5F ＞ 5F-N ＞ 9F.Conclusions RapidArc produced statistically significant improvement in the dose distributions of targets,and also reduced the Dmax of organs at risk,which would be the better choice of radiotherapy for nasal NK/T-cell lymphoma.

Objective To evaluate the dosimetry of high-energy electron beams by using GafChromic EBT film. Methods The percent depth doses of electron beams of 4 MeV,6 MeV,8 MeV,10MeV, 12 MeV and 15 MeV were measured with EBT. The results were then compared with the measurements with diode detector in RFA and parallel plate chamber in water tank. Results The percent depth dose curves using EBT film had a good agreement with those using the other two detectors. Furthermore, no differences were found between up-right and tilt setup methods. When film upper edge is higher than water surface, a sharp drop of measurement results using EBT film was observed in comparison with those from diode detector in build-up region. Conclusions EBT film can be applied to measure percent depth doses of high-energy electron beams. During the EBT film measurements, the film should be tilted at the angle of 5degrees to the central axis of the field. When choosing up-right setup method, the edge of the film should be parallel to the water surface.

Objective:To inspect the dosimetry characteristic of a 2-D ionization chamber array and its response to oblique incident electron beam.And to discuss feasibility to using it to validate the electron arc therapy plan.Materials and methods:(1)The 2-D ionization chamber array was calibrated referring to a themble chamber,comparing the response to electron beams with incidence angle ranged from-50°to 50°.(2)Phantom test plans of 6 and 10MeV electron beam arc therapy were designed,with the beam rotation arcs of 30°,60°and 90° respectively,symmetric to the Central axis of 0°gantry angle.Dose distribution of each plan was verifled with the 2-D array.Results:(1)Measurement differences between the central detector of the array and the thimble chamber were less than 2%,under the planned oblique inddent 6/10MeV electron beam.(2)For the all test plans,dose error was less than 3%at dmax in the symmetric axis of the electron beam arcs.Off-axis dose error was less than 2%within the central 70%area of the profile in non-rotating direction,and smaller than 1.5%in the rotational direction.The measured dose distribution had good agreement with the TPS calculation in isodose curves between 100%and 20%.The gammapass rates(△D=5%,△d=5cm)were 99.98%、99.89%、99.74%、98.64%、99.16%and 99.44%respectively for 6 and 10 MeV plans with electron beam arcs of 30°,60°and 90°.Conclusion:it is practicable using the tested 2-D ionization chamber array to verify and validate the electron beam arc therapy plan.

Objective To explore the clinical application of the multi-network anatomical lavage on the treatment of chronic osteomyelitis after fracture surgery. Methods A retrospective analysis of 40 patients (41 sites) with chronic osteomyelitis after fracture surgery was performed from June 2006 to December 2008. There were 35 males and 5 females with an average of 42.7 years (range, 16-68). All 40 cases were treated with debridement, closing the cavity, and placing the multi-tube drainage network anatomical catheter lavage system. At the same time, sensitive antibiotics were used for 3 to 4 weeks. Rechecks were scheduled every 3 months after operation, including wound healing, X-ray presentation, ESR and C-reactive protein.Cure criteria depends on the conditions of the inflammation when the lavage treatment was over, and whether it relapsed six months after operation, including wound healing, systemic symptoms, ESR and C-reactive protein. Results Judged by the clinical outcomes when the lavage treatment was over and six months after operation, the effects were categorized into 3 levels, including excellent in 37 cases with primary wound healing, and without relapse six months later;, good in 2 with poor wound healing, the wound healed after a period of treatment without recurrence; poor in one with recurrent sinus infection and a prolonged unhealed wound, after another operation he was healed. 36 cases were treated with bone graft and internal fixation operation, and the fractures were healed after surgery, the fractures were healed directly in 4 cases without bone graft. The patients were followed up for an average of 43.2 months (range, 30-50) after operation, and none relapsed. Conclusion The multi-tube drainage network anatomical method is feasible and effective on the treatment of chronic osteomyelitis after fracture surgery with a high cure rate.

ObjectiveTo test a three-dimensional dose verification system,which reconstructing dose to anatomy based on modeling and online measurements ( RDBMOM ),and to evaluate the accuracy and feasibility of its application in clinical intensity-modulated radiotherapy (IMRT) quality assurance.Methods Phantom plans of regular and irregular fields were selected for the testing.All test plans were implemented and the dose distributions were measured using the thimble ion-chamber and two-dimensional ion-chamber array,the accuracy of RDBMOM were then evaluated by comparing the corresponding results.Two practical treated nasopharyngeal carcinoma IMRT plans were verified with RDBMOM and the clinic significancy were valued.ResultsCompared with measurements of the thimble ion-chamber,deviations of RDBMOM were within 1％ in all tested cases except small field of 3 cm ×3 cm.The largest deviation of reconstructed dose in IMRT cases was 2.12％.The dose profile reconstructed by RDBMOM coincided with the measurement using two-dimensional ion-chamber array.The γ rates (3％/3 mm) were 94.56％ - 100％.The RDBMOM verification of IMRT cases shown that the γ rate ＞ 99％ in total and ＞ 98％ in planning target volume,deviation in D95 ＜0.4％,but the largest deviations in mean dose of the parotids and lens were 2.97％ and 59.58％ respectively.ConclusionsAccuracy of the tested system satisfies the demand of IMRT dose verification.RDBMOM is able to provide information of volumetric dosimctry and anatomical location of dose error,which is benefit for evaluating the clinical value of verification results.

ObjectiveTo compare planning quality,treatment efficiency and delivery accuracy for initial treated nasopharyngeal carcinoma (NPC) with step & shoot intensity modulated radiation therapy (ssIMRT) and volumetric modulated arc therapy (VMAT).These results will help make a clinic choice of the therapeutical technique.MethodsTwenty-six NPC cases were planned with the same dose prescription and objective constrains by means of 9-field ss-IMRT and VMAT respectively.Compare:( 1 ) plan dosimetric distribution,conformity index and homogeneity index of the targets,the average dose,maximum dose and interested dose-volume histograms of organs at risk (OAR) et al;(2) delivery times of the therapy plans ;(3) the accuracy of treatment plans dose verification.ResultsBoth therapeutical plans can achieve the clinic dosimetric demands.Compared to ss-IMRT,VMAT had less inferior target coverage.The CI and HI of the PGTV was 0.57 and 0.08 ( ss-IMRT),0.48 and 0.12 (VMAT) respectively ( t =-4.52,- 8.33,P =0.000,0.000).Except of brain stem,VMAT had higher mean dose and maximum dose of OARs than ss-IMRT (t=-9.57 - -3.71,P=0.000 -0.001).The spinal cord D1cc and parotids D50％ were increased by 11.9％ and 6.5％ averagely.The treatment times of ss-IMRT and VMAT were 803.7 s and 389.3 s respectively (t =24.12,P =0.000),while V MAT decreasing by 51.6％.The pass ratios of γ (3mm,3％ ) from the dose verification were 99.4％ (ss-IMRT) and 98.0％ (VMAT) respectively ( t =5.19,P =0.000).ConclusionsThe dose distribution of VMAT for initial treated nasopharyngeal carcinoma can achieve the clinic demands,but slightly worse than 9-field ss-IMRT.VMAT has the advantage of high efficiency and dosimetric accuracy.

Objective To study the dosimetric characteristics of flattened and flattening filter free (FFF) beams with 6 MV and 10 MV photon energy using a novel dual-energy medical linear accelerator (Elekta Versa HDTM),to identify the dosimetric characteristics and advantages of FFF beams,and to provide a basis for their clinical application.Methods The percentage depth dose (PDD),profiles/dose rate of off-axis ratio (OAR),field size,penumbral width,dose out of the fields,collimator scatter factor (Sc),and total scatter factor (Sc,p) were compared between flattened and FFF beams.Results (1) After beam energy matching,the FFF beams had the same beam energy with the flattened beams.The matching error of PDD at a depth of 10 cm was less than 1％ between fields.(2) The FFF beams had a smaller variation in dose rate of OAR with the depth than the flattened beams.(3) The FFF beams had smaller variations in field size and penumbral width than the flattened beams.Moreover,the penumbral width of the FFF beams increased with the increasing field size or depth.The FFF beams had a lower dose out of the fields than the flattened beams.(4) The FFF beams had smaller variations in Sc and Sc,p with the field size and depth than the flattened beams.Conclusions Removal of the flattening filter can substantially improve the dose rate,shorten radiotherapy time,and reduce leakage and scattering of the head.The dosimetric advantages make the FFF beams appropriate for clinical treatment.

Objective:To analyze the impacts of different registration ranges on the accuracy of multiple metastases treated with helical tomotherapy.Methods:According to the locations of target volumes, 28 patients with multiple metastases were divided into the head/chest group ( n= 15) and the chest/pelvis group ( n= 13). The CT and MVCT images acquired in first fraction were studied and compared in two groups, which were captured and matched with different registration ranges (all targets/the targets in proximity to the head/ the targets in proximity to the foot). The CTV MVCT volume coverage rate (CR) under the matched target volumes, the dice similarity coefficient (DSC) between the CTV CT and CTV MVCT, and the position deviation of the CTV geometric center were compared. Results:We observed similar results in the head/chest group and chest/pelvis group. Specifically, there was no significant difference in the CR, DSC and geometric center deviation between the two target regions when registered with all targets ( P>0.05). Regarding single target region registration, the DSC and geometric center deviation of this target were significantly superior to the other non-registered target ( P< 0.05). To a single target, the CR, DSC, and geometric center deviation obtained with registration presented the best performance, which was significantly greater than these parameters obtained with all targets registration, while the other side target area obtained the worst results ( P< 0.05). Conclusions:Registration of one target region may reduce the accuracy of other non-registered targets. We recommend that the image guidance ranges for multiple metastases treated with tomotherapy should include all target regions or independent registrations for different targets.

OBJECTIVETo study the correction of algorithm for Varian enhanced dynamic wedge(EDW) factors and compare the dose/monitor unit (MU) deviation measured at the central axis of EDW field with that obtained by manual calculation or using the treatment planning system.

METHODSEDW factors and dose were measured with Thimble ion chamber at 10 cm depth under the water for 6 MV and 10 MV photon on Varian linear accelerator. The corresponding calculations were done with the radiation treatment planning system. An analytic formula, namely the MU Fraction model, was used to calculate the EDW factor, which was corrected with a constant factor. The MU of conventional 2-D planning derived from manual calculating, treatment planning system, and actual measurements were compared.

RESULTSWith the measured results as the standard, the corrected manual calculation deviation of EDW factors was significantly reduced. For photon 6 MV, the maximum deviation reduced from 4.2% to 1.3% for 60° symmetry fields was, and from -4.7% to -1.8% for asymmetric fields. For photon 10 MV, the maximum deviation for all EDW fields was reduced from -3.0% to 1.1%. Comparison of the manual calculations with the measured results showed a MU deviation for symmetric fields within 2%, and more than 5% for some asymmetric fields. The deviation between the calculations of the treatment planning and the measured results was less than 1.5%.

CONCLUSIONConstant factor correction can effectively reduce the deviation of manual calculation. For MU calculation of EDW field in conventional 2-D dimensional treatment planning, the corrected results of symmetric fields meet clinical requirements. While the minimum distance between the field edge and the central axis was less than 4 cm in asymmetric fields, the corresponding special method, measurement or the treatment planning system should be used to calculate the dose/MU.