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Objective@#To investigate the effect of simple artifacts on the calculation of radiation dose in actual clinical operations by the aid of artificially caused CT artifacts.@*Methods@#The phantom was scanned using CT before and after replacing the titanium alloy component. Then, the CT values were measured at different distances before and after replacement. After correcting the CT value of the titanium alloy region to the CT value of the water phantom, the doses to the phantom were calculated by using Varian′s AAA algorithm, AXB algorithm and Pinnacle system′s CCC algorithm. The absolute dose values at different distances were furtherly analyzed.@*Results@#Varian system was consistent with Pinnacle system in evaluating the CT values. When the CT value deviated by less than 30 HU for a uniform phantom, the dose deviations of the three different algorithms were within 6.0 %-12.0 % at a distance of 0.5 cm from the body surface, and less than 1.0% at a distance of more than 1.5 cm from the body surface. When the CT value deviated by 15 HU for the lung phantom, both Varian′s AAA algorithm and Varian′s AXB algorithm showed about 1.0% dose deviation. However, the CCC algorithm of the Pinnacle system had a significant difference (5.0%) in dose values under the same conditions.@*Conclusions@#CT artifacts have noticeable effects on the calculation of radiation dose and change tissue dose distribution which may result in insufficient or excessive exposure doses.
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Objective To test the accuracy of a three-dimensional dose verification system CompassR,which reconstructing dose distribution based on measurements and independent dose calculation,and to evaluate the feasibility of its application in clinical intensity-modulated radiotherapy (IMRT) quality assure.Methods A set of square-wave chart patterns of 2 cm,1 cm and 0.5 cm gaps was designed and 11 completed IMRT lung plans were selected for the test.EDR2 film and the ionization chamber were used for test and verifying of plane dose distribution and some special points dose of CompassR.The IMRT phantom plans were verified by CompassR with three-dimension based on anatomical information.Parameters including the volume γ pass rate and the average dose deviation were tested using dose volume histograms.Results In square-wave chart patterns test,the dose distribution reconstructed and calculated by CompassR coincided with the measurement using film.The γ pass rates (3％/3 mm,2％/2 mm) exceeded 90％.When the width of field is 0.5 cm,the γ pass rate was a little lower on account of the penumbra zone.Compared to the dose distribution profile which was measured by film,the maximum deviations of the dose distribution profile which was reconstructed and calculated by CompassR were 3.21％ and 2.70％.The absolute dose deviation of specific point in the IMRT plans was less than 3％,the maximum deviation occurred in the lung.Compared to film,the averageγpass rates on the isocenter plain in IMRT plan were (94.65 + 1.93)％ (3％/3 mm) which was reconstructed by CompassR.In three-dimensional dose verification,the volume γ pass rates of targets and risk organs were not less than 90％,and the deviation of average dose was less than 1％.Conclusions Accuracy of the tested system satisfies the demand of IMRT dose verification.CompassR could provide information of volumetric dosimetry and anatomical location of dose error,which is benefit for evaluating the clinical value of verification result.
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Objective To seek the curative effect of stereotactic radiation therapy (SRT) combined with gemcitabine for unresectable advanced pancreatic carcinoma.Methods 24 patients were treated by SRT of 6MV X-ray.Patients were fixed with the rack of stereotactic localization and heated plastics mould.The CT scanning results were put into the treatment planning system.According to the target area of tumor,sensitive organs and moving error drew GTV,CTV and PTV.The best plan was selected by the dose-volume histogram (DVH).5 to 7 beams of non-coplanar radiation ray were chosen.PTV was surrounded by ≥95 ％ isodose curves.Conventional fraction,5 fractions per week,1.8-2 Gy per fraction was used.All patients received a total dose of 50-60 Gy.Gemcitabine was performed 1000 mg/m2,once a week,iv gtt,in the 1st,2nd and 4th,5 th weeks.Results In chemo-radiotherapy,50.0 ％ (12/24) patients showed light nausea,41.7 ％ (10/24) patients showed leucopenia or thrombocytopenia of grade 1 or 2,after symptomatic treatment,all patients completed the planned treatment.In a period of one month to three months,after SRT combined with chemotherapy,appetite improvement was 83.3 ％ (20/24),jaundice disappeared in 6 of 6 patients (100.0 ％),abdominal pain was relieved in 21 of 24 patients (87.5 ％),3 patients were relieved completely among them.The complete remission (CR) rate was 16.7 ％ (4/24) and partial remission (PR) rate was 66.7 ％ (16/24),with CR+PR rate of 83.4 ％ (20/24).One-year survival rate was 70.8 ％ (17/24).As a consequence of cachexia,intestinal obstruction or bleeding,7 patients died within one year.Nobody survived more than 2 years.Conclusions SRT combined with gemcitabine for advanced pancreatic carcinoma may relieve symptoms.It is an effective approach to improve life quality and prolong survival time for advanced pancreatic carcinoma,especially lod and weak patients are more suitable to select SRT combined with gemcitabine.
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Objective To study the spatial distribution of set-up errors for cervical cancer with intensity modulated radiation therapy (IMRT) and to provide referential safety margin out of clinical tumor volume (CTV) during treatment plan design. Methods Six patients with cervical cancer were treated with IMRT in prone position, belly board and thermoplastic cast was used for immobilization. Measurement were made on a daily basis setup under five consecutive treatments with electron portal images device (EPID).Portal films from two projection (one anter-posterior and one opposite lateral)were taken. Sixty portal films were analyzed. The translational and rotational deviations were analyzed by registering and comparing the bony structures of EPID and digitally reconstructed radiographs (DRR). Results The translational deviations were (3.1 ±1.8) mm, (3.9 ±3.3) mm, (4.2 ±2.6) mm in medi-lateral, cranio-caudal and anterior-posterior directions, the rotational deviations were in coronal plane (0.8±0.9)° and sagittal plane (1.2±1)°. Conclusion For the patients with cervical cancer undergoing IMRT, the margins between the CTV and PTV should be 7.1 mm in lateral direction, 10.4 mm in cranio-caudal and 10.8 mm in anterior-posterior directions. The sign on patients body can help to reduce the setup errors.
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Objective To evaluate the short-term clinical effect of 125Ⅰ seeds interstitial braehytherapy for recurrent malignant tumor after radiotherapy. Methods 21 patients with recurrent gynecologic tumors after radiotherapy received 125Ⅰ seeds interstitial braehytherapy through TPS, ultrasound. 125Ⅰ seeds radiotherapy per grain was for 20.72-29.60 MBq. The distribution of seeds was checked by X-my after treatment. The clinical therapeutic efficacy was observed by chest CT, ultrasound. Results The overall effective rate was 100 %, CR 85.71%(18/21), PR 14.29 %(3/21). Conclusion 125Ⅰ seeds interstitial brachytherapy is minimally invasive, convenient, safe, utility and feasible in clinical practice. The radioactive protection is easy. It is a new and high technology of malignant tumor treatment. Colligation treatment method is increased by this technique. But this technology cannot replace routine method.
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Objective To eompare the dose distribution of three-dimension conformal radiation therapy(3DCRT) and common radiation therapy (CRT) of the planning target volume(PTV) and organ at risk (OAR) in recurred cervical cancer treatment planning. Methods Thirteen patients,who had cervical cancer recurred in pelvis treated with 3DCRT in Shanxi Cancer Hospital from May to August 2007, were selected. After CT simulation, the CT images were transferred into Topslane treatment system. The same physicist designed 3DCRT plan and common radiation therapy plan for every patient,total dose 50 Gy, 90 % is dose covered PTV, then compared the dose distribution of PTV and OAR.Results At the same prescribed dose of 50Gy,there were no significant differences on OAR maximum dose between 3DCRT plans and common radiation therapy plans(P >0.05), however, there was significant differences on PTV maximum dose(P <0.01). The difference of PTV uniformity were significant between 3DCRT plans and common radiation therapy plans (P <0.001). Compared the high dose region of OAR(V40), the difference was significant (P <0.001). Between 3DCRT plans and common radiation therapy plans, they showed 53.31 ml (90.69 %), 124.00 ml (79.47 %), 655.16 m1(92.22 %) median reduction in the V40 of rectum, bladder, intestine, respectively. Conclusion At the same PTV coverage of the prescribed dose, 3DCRT plans showed worse dose uniformity, however, the radiation volume to organs at risk in 3DCRT plans were smaller than common radiation therapy plans. So patients with cervical cancer recurred in pelvis received 3DCRT may be potentially diminish the Normal Tissue Complications Probability(NTCP).
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Objective To study the 3D CRT plan for hepatic tumors. Methods The 3DCRT plan of 50 cases of primary or metastasis hepatic cancer were designed according to the request of the doctors for CTV and the restricted receiving dose of the peripheral normal sensitive organs. The best plan was chosen referring the dose-volume histogram. Results By using ICRU dose reference point (the central point of tumor) as the dose 100 % and 80 % ~ 90 % dose line can be surrounded above 90 % of the PTV(planning tumor volume). The degree of 90 % dose line surrounding PTV was related to the scope of target area and its location. Conclusion The focus in different localization can be treated with different design when devise the treatment plan of the hepatic tumors. The reaction to radiotherapy was directly influenced by the volume of dosage of radiation to the normal hepatic tissues, and it also had great influence to the choice of prescription dose and the dose division style.