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Objective:To compare and analyze the differences in the setup accuracy of different immobilization method in breast cancer radiotherapy after breast-conserving surgery.Methods:A retrospective study was conducted on 60 patients who received radiotherapy after breast-conserving surgery from January to August, 2021. These patients were divided into two groups. One group consisted of 30 cases who were immobilized using a modified body thermoplastic membrane combined with a multifunction body board during the breast cancer radiotherapy and was called the modified body thermoplastic membrane group. The other group comprised 30 cases immobilized using a vacuum cushion during breast cancer radiotherapy and was referred to as the vacuum cushion group. The setup errors, 3D vector errors, the proportion of errors of > 5 mm, and the dosimetric differences in the planning target volume (PTV) and the clinical target volume (CTV) before and after simulated treatment bed moving (including the PTV_ V100, PTV_ V95, and CTV_ V95 before simulated treatment bed moving and the PTV_ V100 S, PTV_ V95 S, and CTV_ V95 S after simulated treatment bed moving) were compared between two groups. Moreover, for the modified body thermoplastic membrane group, the changes in the average setup errors at different radiotherapy stages were also analyzed. Results:A total of 369 cone-beam CT scans were conducted for 60 patients, including 195 CT scans for the modified body thermoplastic membrane group and 174 CT scans for the vacuum cushion group. The setup errors in the x, y, and z directions (right-left, anterior-posterior, and superior-inferior, respectively) of the modified body thermoplastic membrane group were (2.59±1.98) mm, (2.38±2.04) mm, and (1.45±1.16) mm, respectively, while those of the other group were (2.24±1.63) mm, (2.78±2.17) mm, and (2.70±1.88) mm, respectively. The 3D vector errors of both groups were (4.32±2.28) mm and (5.13±2.14) mm, respectively. Therefore, the setup error in direction z and the 3D vector error of the modified body thermoplastic membrane group were less than those of the vacuum cushion group ( t = -7.77, -3.41, P<0.05). Moreover, the proportion of setup errors of > 5 mm in the x direction of the vacuum cushion group was lower than that of the modified body thermoplastic membrane group ( χ2 = 7.13, P<0.05), while such proportion in the z direction of the modified body thermoplastic membrane group was lower than that of the vacuum cushion group ( χ2= 5.90, P<0.05). After the simulated treatment bed moving, the PTV_ V100 S of the modified body thermoplastic membrane group was better than that of the vacuum cushion group ( t = 2.47, P < 0.05). Furthermore, for the modified body thermoplastic membrane group, the setup errors in the x direction in the first week were higher than those in the 2-3 weeks and 4-5 weeks ( P<0.05). Conclusions:The modified body thermoplastic membrane combined with a multifunction body board yield better immobilization effects than a vacuum cushion. However, it produces high setup errors in the x direction in the first week of the radiotherapy, to which special attention should be paid.
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Objective To compare the errors of final isocenter marking method and reference point marking method for CT simulation positioning in intensity-modulated radiotherapy (IMRT).Methods From 2009 to 2012,327 patients with head and neck cancer for IMRT underwent CT simulation positioning using the Philips Brilliance CT Big Bore scanner and Philips Tumor LOC workstation and were divided into final isocenter marking group (n =208) and reference point marking group (n =119) according to positioning methods.Target volume delineation and treatment plan design were performed on the Varian Eclipse treatment planning system (TPS).Before treatment,kilovoltage cone-beam CT scans and registration were performed with the Varian EX on-board imager system to obtain beam position errors in the right-left (RL),superior-inferior (SI),and anterior-posterior (AP) directions,and then comparisons of errors between the two groups were made by independent-samples t test.Finally,the TPS was used to measure the changes in the doses to the organs at risk after moving isocenters in the RL,SI,and AP directions among 5 patients with nasopharyngeal carcinoma.Results The mean beam position errors in the three directions were less in the final isocenter marking group than in the reference point marking group (P =0.02,0.01,0.03).After moving isocenters in the three directions,the target dose was reduced and the dose to the normal tissue around the target tumor was increased significantly.The error in the AP direction had the maximum influence on the spinal cord and brainstem.Conclusions Final isocenter marking method leads to less beam position error than reference point marking method in CT simulation positioning.Small isocenter motion can cause large changes in the doses to the organs at risk.
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Objective To analyze the influence of tumor volume change on intensity modulated radiotherapy(IMRT)for nasopharyngeal carcinoma by analyzing the repeated CT simulation.Methods Twenty nasopharyngeal carcinoma patients undergoing IMRT from July 2011 to November 2012 were selected in the study.The first CT simulation was conducted prior to radiotherapy,and the repeated CT simulation was finished after radiotherapy of 30 Gy.The first and the repeated CT images were fused in treatment planning system and GTV volume shrink rate was calculated.The original plan was used to recalculate the dose distribution on repeated CT.The dose volume histogram was used to calculate the dose difference of organs at risk including the brain stem and spinal cord.Results Compared with the first CT,GTV volume shrink rate of the repeated CT simulation was 28.7％,the maximum dose,1 cm3 volume and the average dose percentage of the brain stem and spinal cord were increased(t=0.83-3.17,P＜0.05).Conclusions GTV volume shrinked significantly after radiotherapy of 30 Gy in IMRT for nasopharyngeal carcinoma.The dose of the organs at risk increased accordingly.
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Objective:To discuss application of large aperture 16 row spiral CT in radiotherapy simulation positioning. Methods: To apply CT simulation positioning with large aperture 16 row spiral CT for the breast tangential field by early breast cancer after breast conserving surgery and radical radiotherapy. Compare CT-simulation and X-ray conventional positioning technique and Compare large aperture 16 row spiral CT and single row spiral CT image. Results: The application of large aperture 16 row spiral CT avoided the error because of body limited. Large aperture 16 row spiral CT simulation position validation error is superior to X-ray positioning. Its image quality is better than that of single row spiral CT. Conclusion:The application of large aperture 16 row spiral CT make simulation positioning more accurate, planned and treatment more accurate, it can provide guarantee of accurate simulation positioning for accurate plan and treatment.
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ObjectiveTo evaluate setup errors of image guided radiation therapy (IGRT) for body tumors immbilized with vacuum cushions and localized with final isocenter marked method using kilovoltage cone beam CT (KVCBCT).MethodsA retrospective study has been carried out for 223 patients from March 2009 to April 2011.All patients were immobilized with vacuum cushions and localized with final isocenter marked method in Philips PQS CT or Philips Brilliance CT Big Bore scanner,which were equipped with LAP movable laser systems. The CT images were transferred to a Varian Eclipse workstation for contouring and treatment planning.Before irradiation,a KVCBCT scan was performed and image registration was done on a Varian iX linear accelerator via OBI system.Each set of setup errors in right-left ( RL),superior-inferior (SI),and anterior-posterior (AP) directions were gathered.An independent-samples t-test statistical analysis was conducted with the 758 sets of data using SPSS 16.0.Results The statistical analysis showed that setup errors from the 758 datasets were depicted a Gaussian distribution.The system errors ± random errors in RL,SI and AP were ( -0.5 ±2.8) mm,(0.0±3.0) mm and (0.4±3.4)mm,respectively.Referring to the formula for planning target volume margin calculation,M =2.5Σ + 0.7δ,the margins were calculated as 3.2,2.1 and 3.4 mm,respectively.ConclusionsThe margins derived from this retrospective study have confirmed the premise that the treatment plans were executed in patients with high reliability,thereby created a high sense of confidence for the clinicians.
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Objective To evaluate the setup errors of image guided radiation therapy (IGRT) for head-and-neck cancer using kilovoltage cone beam CT( kV CBCT).Methods 256 patients with head-and-neck cancer were treated with intensity modulated radiation therapy (IMRT) from March 2009 to October 2011.All patients were immobilized with head-and-neck mask and localized with final isocenter marking method using the Philips PQS CT or Philips Brilliance CT Big Bore scanners,which were equipped with LAP movable laser systems.The CT images were transferred to a Varian Eclipse V8.6 workstation for contouring and planning.A kV cone-beam CT scans was acquired,and registered before the treatment for every patient on a Varian iX linear accelerator via OBI system.The setup errors in the right-left ( RL),superior-inferior (SI),and anterior-posterior (AP) directions were recorded.Results The setup errors for the 473 datasets followed a Gaussian distribution.The systematic errors ± random errors in the RL,SI and AP were(-0.6 ± 1.3 ),(0.5 ± 1.6) and (0.9 ± 1.7 ) mm,respectively.The planning target volume (PTV) margins were calculated respectively as 2.4,2.4 and 3.4 mm according to the formula of M =2.5∑ +0.7δ The margins of 288 sets of data using the Big Bore CT scanner were calculated as 2.0,2.1 and 1.7 mm,respectively.Conclusions The setup errors using final isocenter marking method are smaller than those using reference point marking method.The result derived from this retrospective study could be used to set the margin between CTV and PTV.
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Objective To investigate the correction of manual monitor unit calculation for asymmetric fields using the Varian enhanced dynamic wedge.Methods Monitor unit (MU) was calculated when the field sizes ranged from 6 cm × 6 cm to 20 cm × 20 cm at a depth of 5 cm using Varian Eclipse and both 6 MV and 10 MV X-rays data from Varian Clinac 23EX for all seven available EDW angles,including 10°15°,20°,25°,30°,45°and 60° The field size was kept fixed,and the distance between geometry center of field and isocenter was increased in increments of 1 cm,ranging from -9 cm to 4 cm.When the field size was the same,the correction factor was defined as the ratio of MU calculated for asymmetric field to monitor unit calculated for symmetric field.To ensure the correction factors obtained above could be used in routine manual calculation for EDW fields,measurements were made at a depth of 5 cm for 30°and 45°EDW with field size of 10 cm × 10 cm using 6 MV X-rays.Results The correction factor was independent of field dimensions,so the average value was adopted to make practical calculation.Without correction,the maximum error was 18% for 30°,and 30% for 45.After the results of monitor unit calculation were corrected,the largest error was - 1.8% and - 1.7% for 30° and 45°EDW,respectively.The magnitude of errors was within the clinical tolerance limits.Conclusions For asymmetric EDW fields,there is very large difference between the prescribed dose by manual calculation using EDW factors measured for symmetric fields and that delivered during treatment in order to obtain correct dose to reference point.The errors are decreased to be acceptable after correction.The method of correction is simple and independent of machine specific beam parameters.
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Objective To compare the planning systems of the simplified manual intensity modulated (SMIM) irradiation and standard tangential (ST) irradiation,in order to explore the application of SMIM technique in clinic.Methods In 64 cases of breast cancers after breast conserving surgery,each underwent both SMIM and ST planning systems.SMIM planning was designed by copying additional fields for shielding the high dose areas from internal or lateral tangential field.The high dose areas were reduced by adjusting the size of the additional field and open tangential field.To optimize the SMIM planning,3 high dose areas (＞ 103% ,＞ 105% and ＞ 107%) were shielded and 3 protocols carried out.The wedges were also optimized in ST plan.The target coverage and dose homogeneity and dose of organ at risk were compared between SMIM and ST planning systems.Results When the dose was normalized to cover the volume of 95% CTV,85% of the shielded areas in optimal SMIM planning were that of ＞ 103% high dose area,and 94% of target area was covered.The study on the volume of breast CTV showed that,in the large breast group,SMIM could not only significantly reduce the high dose areas,and the maximum dose as well as the dose of organ at risk,but also enhance the dose homogeneity index.However,no such effect was not significant in the small breast group.Conclusions The simplified manual intensity modulated technique can improve target dose homogeneity in the large breast cases instead of the standard tangential technique.
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Objective To restrospectively investigate clinical outcomes and prognositic factors in localized prostate cancer treated with neoadjuvant endocrine therapy followed by intensity modulated radiotherapy (IMRT). Methods Between March 2003 and October 2008, 54 localized prostate cancer treated by IMRT were recruited. All patients had received endocrine therapy before IMRT. The endocrine therapy included surgical castration or medical castration in combination with antiandrogens. The target of IMRT was the prostate and seminal vesicles with or without pelvis. The biochemical failure was defined according to the phoenix definition. By using the risk grouping standard proposed by D'Amico, patients were divided into three groups: low-risk group (n = 5), intermediate-risk group (n = 12), and high-risk group (n = 37). Kaplan-Meier method was used to calculate the overall survival rate. Prognostic factors were analyzed by univariate and multiple Cox regression analysis. Results The follow-up rate was 98%. The number of patients under follow-up was 39 at 3 years and 25 at 5 years. Potential prognostic factors, including risk groups, mode of endocrine therapy, time of endocrine therapy, phoenix grouping before IMRT, the prostate specific antigen doubling time (PSADT) before radiotherapy, PSA value before IMRT, interval of endocrine therapy and IMRT, irradiation region, and irradiation dose were analyzed by survival analysis. In univariate analysis, time of endocrine therapy (75 % vs 95 %, χ~2= 6. 45, P = 0. 011), phoenix grouping before IMRT (87% vs 96%, χ~2 = 4. 36, P = 0. 037), interval of endocrine therapy and IMRT (80% vs 95% ,χ~2= 11.60,P= 0. 001) ,irradiationdose(75% vs 91% ,χ~2=5.92,P= 0. 015) were statisticallysignificant prognostic factors for3 - year overall survival , and risk groups (85 vs 53 vs 29 , χ~2= 6. 40,P =0. 041) and PSADT before IMRT (62 vs 120, U =24. 50,P =0. 003) were significant factors for the median survival time. In the multiple Cox regression model, only time of endocrine therapy and phoenix grouping before IMRT were significantly related to the overall survival. The 3-year overall survival rates in patients with endocrine therapy less than 3 months versus more than 3 months were 75% versus 95% (χ~2= 5.45, P= 0.020). The 5-year overall survival rates in patients with biochemical failure versus nobiochemieal failure was 71% versus 92% (χ~2= 8.83 , P= 0.003) Conclusions Neoadjuvant endocrine therapy should last at least three months. Intensity modulate radiotherapy should start before biochemical failure after the endocrine therapy.
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Objective To evaluate the effect of dose-rate and leaf position tolerance on the point dose in step-and-shoot intensity-modulated radiotherapy(IMRT). Methods IMRT plans of 2 prostate cancer patients were selected and recalculated for a water phantom.An ionization chamber was used to measure the dose of some points in the phantom at five nominal dose-rates:100 MU/min,200 MU/min,300 MU/min,400 MU/min and 500 MU/min.It was necessary to adiust the position of the water phantom to locate the ionization chamber in region where the dose gradient was very low in order to minimize the effect of dose gradient on the measured results.When measuring the effect of leaf position tolerance on point dose,the dose-rate was kept constant and the values of tolerance were 1 mm,2 mm,3 mm and 4 mm.This work was conducted on a Varian 23EX equipped with a Millennium 120-leaf multi-leat collimator(MLC).The treatment planning system was Varian Eclipse. Results As the dose-rate increased,the error between the measured dose and the calculated dose also enlarged.The difference between the maximum and the minimum was 1.2%.When MLC control system was working normally,tlle effect of leaf position tolerance on the measured point dose was very little and negligible. Conclusions The dose-rate must be selected suitably to ensure that the delivery can be finished in a short time with the radiobiological effect taking into account.It should be noted that the error between the measured dose and the calculated dose increases with the trend of inereasing more rapidly at higher dose rates.The value of leaf position tolerance should not be set too large,in order to minimize the difference between the measured dose and the planned dose in the region of steep gradient and find as early as possible when the multi-leaf collimator control system performs improperly.