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Objective:To investigate the impacts of the composition and physical density of tissue on the dose distribution of implanted 125I seeds, in order to provide references for the clinical dose calculation and assessment of implanted radioactive particles. Methods:The OncoSeed 6711 physical model of 125I seeds was established using thes of twareegs_brachy and was validated through the calculation of dose rate constant and the radial dose function [ g( r)] in water. Then, based on the element composition and physical density of different types of tissue, the g( r) and absorbed dose ratein water, prostate, breast, muscle, and bone were calculated. Results:The calculated dose rate constant (0.950 cGy·h -1·U -1) and g( r)in water approached the values in related literature. The absorbed dose in bone was 6.042 times than that in water at a distance of 0.05 cm from the implanted source. The difference between the absorbed doses in breast and water was more than 10% at a distance of less than 1.7 cm from the implanted source. The difference between the absorbed doses in prostate/muscle and water was less than 5% at the same radial location. Conclusions:The dose distribution of 125I seeds in some types of human tissue is significantly different from that in water, which should be carefully considered in clinical dose calculation.
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Objective:To evaluate the impacts of tissue heterogeneity on dose calculation of cervical brachytherapy by comparing the doses calculated by two clinically used dose calculation method and the CT image-based Monte Carlo (MC) method.Methods:This study retrospectively selected 11 patients with cervical cancer treated with 3D brachytherapy in Anhui Provincial Cancer Hospital from January 2018 to June 2020. The dose distribution of each plan was calculated via three methods, dose calculation method described in American Association of Physicist in Medicine(AAPM) Task Group No. 43 Report (TG43-BT), Acuros BV(BV-BT) used to perform accurate dose calculations in high-dose-rate (HDR) brachytherapy with phantom heterogeneity, and CT image-based EGSnrc tool kit used to perform Monte Carlosimulation (MC-BT). The dose volumes( V3 Gy, V6 Gy, V9 Gy, and V12 Gy), target volume doses( D98, D90, D50), D2 cm 3 of organs at risk (OARs) calculated by the three methods were compared. Results:The HRCTV D90obtained by TG43-BT was 6.274 Gy, which was even overestimated by around 5% compared to the result calculated by MC-BT. Meanwhile, TG43-BT overestimated the dose volumesand the target volume doses compared to MC-BT.Except for D50 and V12 Gy, the differences between the doses to tumor calculated by BV-BT and MC-BT were not statistically significant( P>0.05). There was also no significant statistical difference between the D2 cm 3 of rectum, small intestine, and sigmoid calculated by BV-BT and MC-BT ( P>0.05). In contrast, the dose to D2 cm 3 of bladder determined by MC-BT was 4.609 Gy, which was notably higher than those deter mined by TG43-BT and BV-BT. Conclusions:TG43-BT overestimated the doses to tumor targets and most OARs since the effects of tissue heterogeneity were not taken into consideration. BV-BT performed efficient calculation and most of the dose distributionin target volume and OARs obtained by BV-BT were consistent with that calculated by MC-BT. Nevertheless, low accuracy occurred for the regions near the sources and full bladder, which warrants further caution in clinical evaluation.
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Objective:To develope a self-adjustable automatic planning method of intensity modulated radiotherapy based on predicted dose, in order to enhance the robustness of automatic planning.Methods:After the patients′ dose by 3D U-Res-Net_B network was predicted, the current dose was calculated based on the last iteration result, then the predicted dose was combined to calculate the target dose and optimized. With all iterations completed or exit conditions satisfied, final treatment plannings would be acquired. A total of 30 cases of rectal cancer were tested to verify the effectiveness of the algorithm.Results:The mean value of planning target volumes′ V100% was (95.03±0.91)% for clinical plans, close to (94.67±1.96)% for automatical plans( P>0.05), and better than (92.90±2.13)% for predicted dose with the statisically significant difference ( t=29.0, P<0.05). Automatic planning′s indexes such as V35 of small intestines, V40 of bladders and V20 - V40 of femoral heads were lower than predicted and clinical ones, with the statisically significant difference( t=4.5-118.0, P<0.05). Discrepancy in other indexes of organs at risk was not statistically significantly different( P>0.05). Conclusions:This method made automatic planning processes more robust and more adaptive to difficult clinical situations.
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Objective:To develop a deep learning model for predicting three-dimensional (3D) voxel-wise dose distributions for intensity-modulated radiotherapy (IMRT).Methods:A total of 110 postoperative rectal cancer cases treated by IMRT were considered in the study, of which 90 cases were randomly selected as the training-validating set and the remaining as the testing set. A 3D deep learning model named 3D U-Res-Net was constructed to predict 3D dose distributions. Three types of 3D matrices from CT images, structure sets and beam configurations were fed into the independent input channel, respectively, and the 3D matrix of IMRT dose distributions was taken as the output to train the 3D model. The obtained 3D model was used to predict new 3D dose distributions. The predicted accuracy was evaluated in two aspects: the average dose prediction bias and mean absolute errors (MAEs)of all voxels within the body, the dice similarity coefficients (DSCs), Hausdorff distance(HD 95) and mean surface distance (MSD) of different isodose surfaces were used to address the spatial correspondence between predicted and clinical delivered 3D dose distributions; the dosimetric index (DI) including homogeneity index, conformity index, V50, V45 for PTV and OARs between predicted and clinical truth were statistically analyzed with the paired-samples t test. Results:For the 20 testing cases, the average prediction bias ranged from -2.12% to 2.88%, and the MAEs varied from 2.55% to 5.75%. The DSCs value was above 0.9 for all isodose surfaces, the average MSD ranged from 0.21 cm to 0.45 cm, and the average HD 95 varied from 0.61 cm to 1.54 cm. There was no statistically significant difference for all DIs, except for bladder Dmean. Conclusions:This study developed a deep learning model based on 3D U-Res-Net by considering beam configurations input and achieved an accurate 3D voxel-wise dose prediction for rectal cancer treated by IMRT.
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Objective:To investigate the dosimetry differences in the treatment of locally advanced cervical cancer with intracavitary/interstitial brachytherapy (IC/IS BT), intracavity brachytherapy combined with intensity modulated radiotherapy (ICBT+ IMRT) and simple IMRT.Methods:Totally 16 patients with local advanced cervical cancer were retrospectively selected, which were treated by three-dimensional brachytherapy. On the basis of the original three-dimensional intracavitary/interstitial brachytherapy plan, ICBT+ IMRT and IMRT plans were designed respectively to study the dosimetry differences of target and different organs at risk for the three kinds of plans.Results:A total of 75 brachytherapy treatment plans were designed, including 25 IC/IS BT, 25 ICBT+ IMRT and 25 IMRT. There was not statistically significant difference of target dose parameters between ICBT+ IMRT and IC/IS BT plan ( P>0.05). ICBT+ IMRT plans had better OAR sparing than IC/IS BT. The doses of OARs in the IMRT plans were relatively large and the volume irradiated to more than 60 Gy ( V60) was significantly higher( t=6.77, 10.37, 4.61, 2.83, P<0.05). Conclusions:The ICBT+ IMRT technique not only provides better target coverage, but also maintains low doses to the OARS, which can be used as an alternative treatment to IC/IS BT. Although the target coverage of IMRT is better, the protection of OARs is not satisfied, so it is not suitable for local boost therapy of advanced cervical cancer.
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Objective To evaluate the feasibility of utilizing dose-volume histogram (DVH) prediction models of organs at risk (OARs) to deliver automatic treatment planning of prostate cancer.Methods The training set included 30 cases randomly selected from a database of 42 cases of prostate cancer receiving treatment planning.The bladder and rectum were divided into sub-volumes (Ai) of 3 mm in layer thickness according to the spatial distance from the boundary of planning target volume (PTV).A skewed normal Gaussian function was adopted to fit the differential DVH of Ai,and a precise mathematical model was built after optimization.Using the embedded C++ subroutine of Pinnacle scripa,ahe volume of each Ai of the remaining validation set for 12 patients was obtained to predict the DVH parameters of these OARa,ahich were used as the objective functions to create personalized Pinnacle script.Finalla,automatic plans were generated using the script.The dosimetric differences among the original clinical plannina,aredicted value and the automatic treatment planning were statistically compared with paired t-test.Results DVH residual analysis demonstrated that predictive volume fraction of the bladder and rectum above 6 000 cGy were lower than those of the original clinical planning.The automatic treatment planning significantly reduced the V70,V60,V50 of the bladder and the V70 and V60 of the rectum than the original clinical planning (all P＜0.05),the coverage and conformal index (CI) of PTV remained unchangea,and the homogeneity index (HI) was slightly decreased with no statistical significance (P＞ 0.05).Conclusion The automatic treatment planning of the prostate cancer based on the DVH prediction models can reduce the irradiation dose of OARs and improve the treatment planning efficiency.
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Objective To compare the sensitivity of Deha4 and ArcCHECK 3D detectors to detect the multi-leaf collimator (MLC) positioning errors in the dose verification of volumetric modulated arc therapy (VMAT) plans for nasopharyngeal carcinoma (NPC).Methods Ten NPC patients receiving VMAT plans were selected.The positioning error of 0.5-4.0 mm was introduced into the leaves of each MLC segment in the original file to expand,contract or shift the whole segments.The possible positioning errors of MLC in the treatment of VMAT were simulated.The Delta4 and ArcCHECK were utilized to verify the measurements.The absolute gamma passing rate was compared between the calculated dose and the measured dose of the VMAT plan by using the paired t-test.Results When the evaluation criterion was taken as 3 mm/3％,the absolute passing rate verified by the original plans of two detectors was greater than 95％.The positioning errors of MLC expansion,contraction and shifting detected by Delta4 and ArcCHECK were 1.5 mm,1.0 mm,2.0 mm and 3.0 mm,1.0 mm,and 3.0 mm,respectively.When taking 2 mm/2％ as the evaluation criterion,the absolute passing rate verified by the original plan was decreased significantly.Delta4 and ArcCHECK detected that the positioning errors of MLC expansion,contraction and shifting were 1.0 mm,1.0 mm,2.0 mm and 1.5 mm,0.5 mm,and 2.0 mm,respectively.Conclusions The dose verification of the VMAT plan for NPC by Delta4 and ArcCHECK can detect different types and sizes of MLC positioning errors,whereas the detection sensitivity slightly differs between Delta4 and ArcCHECK.Both of them are not sensitive to detect the MLC positioning errors less than 1.0 mm.It is fairly necessary to strengthen the quality assurance of MLC in the daily work.
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Objective To explore the feasibility of application of the Monte Carlo method to simulate the whole body dose distribution in patients with total body X (γ) ray irradiation by comparing the actual measurement results.Methods A Monte Carlo model of a 6 MV Elekta Synergy Clinical linear accelerator was established by MCNPX.According to the relationship between the CT value and the density of the material,the CT of the ATOM physical phantom was converted into a voxel phantom for MCNPX calculation.The dose distribution of the whole body was simulated in the total body X (γ) ray irradiation.The simulated results were compared with the measurement values of the thermoluminescence dosimetry at different positions in the ATOM physical phantom to analyze the differences.Results The difference between the depth dose curve and the off-axis dose curve and the actual measurement values calculated by the 6 MV accelerator treatment head model in the water tank was less than 2％,with the maximum dose depth of approximately 1.5 cm and field size of 10 cm× 10 cm,which were consistent with the actual measurement values.The maximum difference between the simulated results at different locations in the body and the thermoluminescence dosimeter was approximately 4％,and the simulated results of MCNPX were almost in good agreement with the results of thermoluminescence.Conclusions The whole body dose distribution in patient with total body X (γ) ray irradiation can be accurately simulated by MCNPX.Monte Carlo simulation makes it possible to optimize the uniformity of the total body dose during the total body irradiation process.
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Objective To study the dosimetric parameters of Varian GammaMed Plus HDR 192 Ir source via Monte Carlo ( MC ) method based on the recommendation of the American Association of Physicist in Medicine ( AAPM) and European Society for Radiotherapy and Oncology ( ESTRO) . Methods Using the Monte Carlo program EGSnrc, an accurate model of 192 Ir source for MC calculations was establish firstly. Through formula derivation, bilinear interpolation and unit conversion, the air kerma strength per unit source activity, the dose rate constant, radial dose function and anisotropy function was obtained then , and compare the result with those in other published studies. Results The air kerma strength per unit source activity was 9. 781 × 10-8 U/Bq. The dose rate constant was 1. 113 cGy · h-1 · U-1 , with a discrepancy of less than 0. 4％ compared with result published in other works. Furthermore, the curves of radial dose function and anisotropy function overall agree with the data shown in the literature. Conclusions The feasibility of performing dosimetric studies of 192 Ir source using the MC software EGSnrc was demonstrated. This work provides a theoretical guidance on analysis of the dose distribution of brachytherapy and on evaluation of the dose accuracy of clinical radiotherapy.
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Objective To measure the setup errors in thoracic esophageal carcinoma treated with intensity modulated radiotherapy (IMRT) using kilo-voltage cone-beam CT (kV-CBCT),and to evaluate the impact of the setup errors on the dose distributions in tumor target volume and the peripheral normal tissues.Methods Twenty-one patients with thoracic esophageal carcinoma undergoing image guided IMRT (IG-IMRT) were included in this study. Using kV-CBCT,173 setup errors of these patients were acquired before treatment.By shifting the isocenters,these setup errors were simulated in the 3-dimentional treatment planning system and the corresponding impact of the dose distribution in tumor target volume and peripheral organs were evaluated.Results The translational deviations of lateral,longitudinal and vertical directions were ( 2.73 ± 1.85 ),( 3.19 ± 2.71 ),and ( 2.35 ± 1.71 ) mm,respectively.The dose of gross tumor volume (GTV) was not impacted significantly by the setup errors. However,comparing with the standard plan without setup errors,the setup errors in the simulated plan reduced the dose of 95％ planning target volume (PTV) by 3.38 Gy.The dose to PTV Dmin and PTV Dmean were also reduced by 9.83 Gy and 0.65 Gy respectively. The correction of setup errors improved the conformity index (CI) and the homogeneity index (HI) for PTV.The C1 and HI for the standard plan were 0.74 ± 0.10 and 1.07 ±0.02, respectively. The C1 and H1 for the simulated plan were 0.69 ± 0.08 and 1.13 ± 0.07,respectively.Statistically significance was observed in these differences ( t =3.43 and -3.91 respectively,P ＜ 0.05 ). No statistical significance was observed in the dose differences in lungs,spinal cord and heart between the two plans ( P ＞ 0.05).The mean maximum dose of the spinal cord was (42.20 ± 4.97 ) Gy in the simulation plan,which was (41.37 ± 2.75 ) Gy in the standard plan.For some patients,the maximum dose of the spinal cord exceeded the tolerance level of 45 Gy in the simulation plan,and one case even reached 52.8 Gy.Conclusions Using the image guidance of kV-CBCT,the setup errors can be reduced significantly for patients with esophageal carcinoma receiving IG-IMRT.The correction of setup errors can increase the treatment precision and enhance the dose in PTV.No significant dose changes were observed in the lung,spinal cord and heart as a result of setup error correctio.
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Objective To investigate the safety and clinical outcome of total body irradiation (TBI) and the real-time in vivo dosimetry with semiconductor dosimeter in hematogenous stem cell transplantation (HSCT). Methods Fifty-seven patients requiring HSCT were treated with TBI. The TBI was given with the semi-sitting or standing position or lateralcumbent posture, using 6 MV X-ray beams and opposed parallel fields technique (two or four fields, AP/PA fields) in a single fraction or multiple fractions. The real-time in vivo dosimetry was performed with six diodes positioned on the surface of patients to adjust the dose homo-geneity of the midplane using the different thickness lead sheets. Results Mild to moderate nausea, vomi-ting and swollen parotid occurred in 41 patients after TBI, which were relieved after allopathy therapy. No radiation-induced interstitial pneumonia was observed. All patients fulfilled the HSCT. The homogeneity of relative dose (normalize to umbilicus dose) in the different positions accorded with the requirement of the prescription dose. Conclusions The opposed parallel radiation, with the semi-sitting or standing positions or lateralcumbent posture, combined with the real-time in vivo dosimetry with semiconductor dosimeter is an effective and safe technique for TBI.
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Objective To observe effect of Dermlin and silver zinc emulsion in treatment of phase Ⅱ and Ⅲ pressure ulcer, and explore a new method which is easy to operate, safe and easily accepted by elderly patients. Methods 38 elderly patients with pressure ulcer from July, 2007 to June,2010 were selected and divided into the treatment group and the control group with 19 patients in each group. The treatment group adopted Dermlin and silver zinc emulsion, while the control group used Comfeel dressing. The treatment effect and cure time of the two groups were compared. Results The treatment effect of the treatment group was better than that of the control group, time used to achieve significant effect was also less in the treatment group. Conclusions Application of Dermlin and silver zinc emulsion in treatment of phase Ⅱ and Ⅲ pressure ulcer can achieve better effect than comfeel dressing, besides it is easy to operate and worthy of clinical practice.