Objective To evaluate the absorbed doses of lower-neck and supraclaviclar subclinical target and the normal tissues of nasopharyngeal carcinoma using three different intensity-modulated radiation therapy (IMRT) techniques. Methods Three radiotherapy techniques were single tangential low neck-supraclavicular field technique (tech1), seven portal IMRT in which the gantry angles are 180°, 150°, 120°, 90°, 270°, 210°(tech2) and 240°and eight portal IMRT in which the gantry angles are 180°, 150°, 120°,90°,0°,270°,210°and 240°(tech3). The dose distribution of lower-neck and supraclaviclar subclinical target and normal tissues were analyzed through the dose-volume histograms, high dose volumes were analyzed using V60 (volume of accepted > 60 Gy/all volume × 100%). The delivery efficiencies were evaluated by means of the total number of segments and MUs. Results The V60 of PTV2 were 65%, 10% and 3% in tech1, tech2 and teeh3 respectively. The maximum doses of spinal cord were 42.0, 48.9 and 45.1 Gy in techl, tech2 and tech3 respectively. The average doses of trachea were 32.92, 52.17 and 36.56 Gy in techl, tech2 and tech3 respectively. Conclusions Tech1 is simple method, but the dose distribution is very nonuniform. Tech2 is better than the Tech1, but the spinal cord and trachea receive the highest doses in three strategies. Tech3 uses less number of segments and MUs than Tech2, and has the best dose distribution.

Objective To research the structure and principle of Helical Tomotherapy, and study the clinical application value of the equipment system. Methods As the first helical radiotherapy system in the mainland of China, its constructions, structure and principle were analyzed and discussed. Results Helical Tomotherapy is a new kind of radiotherapy equipment. The Hi-Art treatment system is a combination of a LINAC and a CT scanner capable of having the function of both systems. It was approved to achieve the best intensity modulated radiation therapy (IMRT), used for adjusting the setup position of the patient with MVCT and as the basis for dose reconstruction and other adaptive radiotherapy processes. It is the first integrated planning, delivery and verification system for IMRT. Conclusion Image-guided radiation therapy (IGRT) and IMRT have introduced a new era in radiation oncology which will better fight cancer and simultaneously improve the patients' quality of life. Having been designed from the ground up for IGRT and IMRT, the tomotherapy system is in the forefront of technical advancements for efficacy and processes to make it efficiently.

Objective To compare the dosimetric differences between helical tomotherapy (HT) and volume-modulated arc therapy (VMAT) in the treatment of upper thoracic esophageal carcinoma (UTEC).Methods A total of 10 patients with UTEC were randomly selected.HT plan and double-arc VMAT plan were designed and optimized for each patient.The prescription dose was 50 Gy/30 fractions for gross target volume (GTV), 66 Gy/30 fractions for planned target volume (PTV).The dose distribution and conformal index (CI), homogeneity index (HI) of target volume, the D1％, D5％, Dg5％, D99％, and dose of organ at risk (OAR) were analyzed by using the dose volume histogram (DVH).The monitor units and delivery time were also evaluated.Results For GTV and PTV, the D99％ of HT plans were slightly higher than those of VMAT plans (t =4.476, 3.756, P ＜ 0.05) , but no significant differences in D1％ , D5％ , D95％ , HI and CI (P ＞ 0.05) were found.The V10, V15, V20 and mean lung dose (MLD) to the total-lung of HT plans were all significantly lower than those of VMAT plans (t =-3.369,-4.824, -4.869,-3.657, P ＜ 0.05).There were no significant differences for V5, V30 and Dmax of cord (P ＞ 0.05).The monitor units and delivery time of VMAT plans were significantly lower than those of HT plans (t =13.970, 7.982, P ＜ 0.05).Conclusions Both HT and VMAT are appropriate for esophageal cancer radiotherapy.HT significantly reduces the radiation dose of the total-lung, while VMAT has obvious advantages in efficiency.

OBJECTIVETo evaluate the feasibility and accuracy of using Megavoltage CT(MVCT) for head and neck dose calculation.

METHODSThe cheese Phantom was imaged using MVCT scanner, and the MVCT value density calibration curve was established. Conventional CT and MVCT image of nasopharyngeal carcinoma was acquired respectively, and IMRT plan was designed on conventional CT image of NPC patient. The conventional CT plan was copied to MVCT image. The dose distribution was calculated for tumor and normal tissue using the MVCT value density calibration curve, and compared with that of conventional CT. Ten NPC patients were collected for dose verification of IMRT plan on MVCT images.

RESULTSThe MVCT numbers depended linearly on the electron density of the sample, and the stability of the MVCT numbers to electron density was good.The error between the measured dose and calculated dose in measured point was less than 3%.The isodose distribution was well agreement with that calculated by planning system.

CONCLUSIONSPerforming dose recalculation using MVCT of Tomotherapy in head and neck region was feasible.and the dose distributions on kVCT and MVCT were in excellent agreement.

Algorithms ; Head and Neck Neoplasms ; radiotherapy ; Humans ; Phantoms, Imaging ; Radiosurgery ; instrumentation ; methods ; Radiotherapy Dosage ; Tomography, Spiral Computed ; instrumentation

Objective To investigate the feasibility of dose verification of intensity modulated (IM) planning of helical tomotherapy (HT) using two-dimensional ion chamber array (2DICA),and develop an efficient way to validate the dose delivered under the parameters mirroring those during the treatment. Meth-ods A 2DICA,I'mRT MatriXX and MULTICube equivalent solid water phantom from IBA company were used to verify the dose distribution of 10 IM planning. The combined phantom was set up to measure the dose distributions on coronal and sagittal surface. The precise setup of phantom was guided by HTMVCT images. After the irradiation, the measured dose distributions on the coronal and sngittal plane were compared with those calculated by the IM planning system for verification. The results were evaluated and the feasibility of the different measuring methods was studied. Results The dose distribution measured by the MatriXX 2DICA was well consistent with that calculated by the treatment planning system. The errors between the measured dose and predicted dose in the selected points were within ±3%. In the comparison of the pixel-segmented ionization chamber versus treatment planning system using the 3 mm/3% γ criteria, the passing ratio of pixels with γ parameter ≤1 was 97.76% and 96.83%, respectively. Conclusions MatriXX is a-ble to measure the absolute and relative dose distributions simultaneously,which can be used for dose verifi-cation of IM planning.

Objective To compare the dosimetric characteristics of helical tomotherapy(HT)and step-and-shoot intensity modulated radiotherapy(IMRT)for post-operative cervix cancer patients. Methods Ten patients with post-operative cervix cancer were enrolled in this study.HT and IMRT plans were developed for each patient.The dose distributions of the targets,organs at risk(OARs),CI and HI were analyzed and compared.The prescribed dose was 60 Gy/25 f for CTV1,50 Gy/25 f for CTV2.The iso-dose line of 50 Gy was used.Results The homogeneity indexes(HI)(0.94±0.03),conformity index(C1)(1.28±0.02)in HT group were better than in IMRT group(0.85±0.01 and 1.36±0.03),respectively(t=5.12,-6.34,P<0.001).The Dmean of PTV in HT group(51.77 Gy)was lower than that in IMRT group(54.53 Gy)(t=-8.01,P<0.05).The Dmax ,Dmean,V30,V40 and V50 of bladder、rectum and small bowel were lower in HT group than those in IM RT group.The Dmax,Dmean,V30 and V40 of right and left femoral head were lower in HT group than those in IMRT group.Conclusion Helical tomotherapy treatment plan has a better homogeneity,steeper dose gradient,and a better protection for organs at risk.

Objective To investigate the dosimetric characteristics of helical tomotherapy(HT),intensity-modulated radiation therapy(IMRT)and three.dimensional conformal radiation therapy(3D-CRT)for the post-operative breast cancer as well as their comparison in protecting the normal tissues.Methods The CT images of 10 postoperative patients with early stage breast cancer were transferRed into HT and IMRT and 3D- CRT planning system respectively after the target region and normal tissues were drawn out with the same doctor.Each prescribed dose for three kinds of plans was 50 Gy/25 fractions.Inrradiation doses and volume at heart and double lungs as well as conformity index(CI)and homogeneity index(HI)were evaluated.Results The PTV volume of prescribed target dose of 95% and 100%in HT, IMRT and 3D-CRT groups were 99.13%and 95.87%,97.80%and 94.05%,96.37%and 87.29%.respectively.The CI and HI in HT.IMRT and 3D-CRT groups were 0.80±0.10 and 1.09 ±0.03,0.65±0.07 and 1.14±0.02,0.40±0.08 and 1.17±0.04,respectively V5,V10 and V20 of the heart were the lowest at 3D-CRT than HT and lM RT.V5 of the diseased lung was the lowest at 3D-CRT compared to HT and IMRT.V5 and V10 of the healthy lung were the lowest at 3 D-CRT compared to other groups.Conclusions Compared with IMRT and 3D-CRT.HT technique in treating breast cancer had the best conformity index and homogeneity index as well as steeper dose gradient.Irradiated doses and volume at the heart was the lowest at 3D- CRT and the highest at IMRT.Irradiated doses and volume of the heart and healthy lung as well as the diseased lung were the lowest at 3D-CRT compared to HT and IMRT groups.

Objective To evaluate the clinical feasibility of quality assurance of helical tomotherapy intensity modulated radiation therapy (IMRT) through a series of clinical case studies. Methods Tomotherapy planning system was used to provide optimized IMRT treatment plans. To verify the dose of IMRT plans,the cylindrical Virtual Water phantom,0.056cm3 AISL, ion chamber and EDR2 film were used for getting the absolute and relative doses from tomotherapy IMRT planning. The film and ion chamber were placed into the phantom. The doses of the interesting points and isodose distribution of the axial plane were measured,then the results were compared with those from the calculation in planning system for verification. Before the irradiation,kVCT images of the phantom were registered by tomotherapy MVCT images. So the setup of phantom was guided for verifying the position. Results The isedose distribution (on the axial plane) measured by the film was well consistent with that calculated by tomotherapy planning system. The error between the measured dose and predicted dose in the measured points was less than 3%. The setup error of the phantom was able to be kept within 1 mm. There was 2 mm offset along the vertical direction of couch from the virtual isocenter to beam isocenter,which should be considered during the phantom/patient setup. Conclusions The procedures for quality assurance of tomotherapy IMRT are feasible in our experience. And helical tomotherapy IMRT QA system has been constituted.

Objective To study dosimetric characteristics of helical tomotherapy (HT) by comparing its treatment plans with linear accelerator-based step-and-shoot intensity modulated radiation therapy (IMRT) for nasopharyngeal carcinoma(NPC). Methods Targets on CT images of 10 NPC patients were delineated and transferred to HT and IMRT treatment plan systems. The prescription dose was 70 Gy/33 f for pGTV and GTVnd,60 Gy/33 f for FTV1 ,and 54 Gy/33 f for PTV2. The limit dose of organ at risk was parotid V35 ＜50% ,brain-stem＜54 Gy,spinal cord ＜45 Gy and lens ＜9 Gy. Data of the two groups were compared by paired t-test. Results The dose distribution, conformality and homogeneity were good in both groups.But the homogeneity index(HI) and Dmean of PTV1 in HT group were better than IMRT group( P ＜ 0.01 ).The Dmean of PTV1 in HT group(63.84 Gy)was lower than IMRT group(70.30 Gy). The Dmean, V35 and V30 of parotids,and the Dmax of larynx-esophagus were lower in HT group than IMRT group. Conclusions Helical tomotherapy treatment plan has a better homogeneity, steeper dose gradient, and a better protection for organs at risk.

Objective To evaluate the dosimetric effect of carbon fiber tabletop on the patient doses in radiotherapy. Methods The transmission factors of couch and inserts were measured in air and solid water phantom using 0.6 cm3 ion chamber and PTW 2D ion chamber array for 6 MV ,10 MV and 18 MV X-ray,respectively. Absorbed doses at depth of maximum dose ,5 cm and 10 cm in solid water were measured with the 2D ion chamber array. Absorbed doses fluctuations with different gantry angles and air gaps between phantom and couch were also measured. Results The posterior field measurement showed that the reductions of absorbed doses at the depth maximum dose,5 cm and 10 cm were within 5%. The ratios of the absorbed doses with to without couch increased with the oblique incident angles and varied slightly with the air gap at depth of 5 cm. The transmission factors of inserts were less than those of couch owing to its thinner thickness. Conclusion The carbon-fiber tabletop affects the absorbed doses and dose distributions of the target, and this effect changes with the gantry angle and air gap. Special considerations should be taken during treatment planning.