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@#<b>Objective</b> To investigate the dosimetric effect of truncated regions in computed tomography (CT) images on the targets and organs at risk in volumetric modulated arc therapy (VMAT) for middle thoracic esophageal cancer. <b>Methods</b> CT images of 15 patients with middle thoracic esophageal cancer were selected. Circle masks were used to make the volume of the truncated region account for 10%, 20%, 30%, and 40% of the arm volume, and the corresponding truncated CT images were obtained. The real CT was denoted as CT0. Two radiotherapy plans were made on CT0. One plan was VMAT_1F with full arcs, and the other one was VMAT_3F with arm avoidance. The plans were transplanted to four truncated CT, respectively, and the dosimetric differences between different plans were compared using Wilcoxon signed-rank test. <b>Results</b> Compared with VMAT_1F in CT0, <i>D</i><sub>mean</sub> and <i>V</i><sub>5</sub> of the lung decreased in VMAT_3F, but <i>D</i><sub>max</sub> of the spinal cord, <i>D</i><sub>mean</sub> of the heart, and <i>V</i><sub>20</sub> of the lung increased. In VMAT_3F, there was no statistically significant difference between the dosimetric parameters in the four truncated CT and those in CT0 (all <i>P</i> > 0.05). In VMAT_1F, except for homogeneity index and <i>D</i><sub>max</sub> of the spinal cord, the dosimetric parameters in four truncated CT were significantly different from those in CT0 (<i>P</i> < 0.05). The dosimetric difference increased with the increase in truncated region-to-volume ratio. <b>Conclusion</b> Complete CT data should be collected in clinical practice, and the radiation field avoiding the truncated regionshould be set if necessary to reduce the influence of the truncated region on dosimetry.
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Background:Palliative radiotherapy offers significant relief in the huge physical distress of patients with bony metastasis. The enormous potential of conformal techniques has not been tested in palliative settings. However,the increasing life span of patients with metastatic disease demands to optimize the radiotherapy techniques to provide maximal durable symptomatic relief. Despitean increase in the utilization of the 3DCRT technique for palliative bony metastasis, the optimal beam arrangement remains unknown. Materials and Methods:Ten patients of vertebral bony metastasis were retrospectively selected and four virtual 3DCRT plans were generated for each patient. The field approaches were a single field, two fields, three fields and five field approaches. For PTV, D90, D50, Dmean, Conformity index (CI) were evaluated.Dmean was evaluated for the esophagus, bowel, kidneys, and combined lungs. Dose-volume histograms were computed for the various treatment plans and compared. Statistical analysis was done by ANOVA test. Results:A total of forty radiotherapy plans were generated. PTV parameters were significantly better with two field plans over one field plans in terms of D90 (p= 0.002), D50 (p= 0.02), Dmean(p=0.0009). Dmeanwassignificantly better with three field approach compared to two field approach (p=0.0006). The Dmeanwas significantly increased for organs at risk in two fields and three field plans.Five field approach did not showan advantage in terms of dosimetry of PTV but there was a significant rise in the dose to Organs at risk (OAR’s). Conclusion:The three field plans showed better dose distribution to the PTV with an acceptable increase in the dose to OAR’s.
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Objective To analyze the dosimetric effect of inconsistent bladder filling states between the CT simulation and treatment for prostate cancer patients undergoing intensity-modulated radiotherapy (IMRT).Methods A total of 42 prostate cancer patients treated with IMRT were selected.After vacuum pad immobilization and simulation CT scan,the delineation of targets and organs-at-risk (OARs),treatment planning and dose calculation were performed on treatment planning system (TPS).The cone-beam-CT (CBCT) acquired before the first treatment was registered to planning CT,on which the target contours were duplicated and OARs were delineated.After dose recalculation on the CBCT using the same plan,the dosimetric differences on the CT and CBCT were compared,including mean dose of the planning target volume (PTV),homogeneity index (HI),conformity index (CI);the mean dose,V30,V40,V50,V60,and V65 of bladder and rectum respectively.Results Relative to the bladder volumes at simulation,the patients were divided into two groups with larger (15 cases) or smaller (27 cases) bladders at the first treatment.Comparing the parameters obtained from simulation CT with that from CBCT,the differences of the following parameters were of statistical significance:the bladder volume,PTV HI,PTV CI in both groups (t =6.838,-4.372,-3.553,-3.462,6.380,5.037,P＜ 0.05),the bladder V30,V40,V50,V60,V65(t=-5.004,-4.092,-3.124,-2.707,-2.489,P ＜0.05) and rectal V40,V50,V60,V65,mean dose in the group with smaller bladders (t=-2.946,-2.643,-2.426,-3.127,-2.530,P ＜ 0.05),and the bladder V30,V40,V50 and mean dose in group with larger bladders (t =5.107,4.204,3.777,4.155,P＜0.05).Conclusions For prostate cancer patients undergoing IMRT,the inconsistent bladder filling states between the planning and treatment will cause disimetric differences of targets and OARs.
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Concurrent chemoradiotherapy can improve the survival rate in patients with advanced pelvic tumors.However,it also increases the incidence of hematologic toxicity and other adverse events.Patients cannot tolerate these adverse events and discontinue the therapy.Pelvic bone marrow-sparing intensity-modulated radiotherapy (PBMS-IMRT) possesses obvious advantages in reducing the radiation dose and volume of the pelvic bone marrow.In this article,comparison between PBMS-IMRT and other irradiation therapies,correlation between dosimetric parameters and hematologic toxicity and imaging methods with precise delineation of the active bone marrow were reviewed.
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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 compare the pre-and post-operative tumor target volume and to examine the consistency in physical dosimetric parameters of organs at risk (OAR) following 3D-printed coplanar template (3D-PCT)-assisted and CT-guided radioactive seed implantation.Methods The 3D-printed coplanar template was designed using a computer software, and the coordinate system was established where the center was used as the basis for setting the x axis and y axis.Crosses defining the center of treatment were drawn on the patient''s body and matched with the corresponding central point, x axis, and y axis of the coplanar template.3D-PCT-assisted and CT-guided radioactive seed implantation was performed based on the pre-operative plan, and the pre-operative, operative, and post-operative plans were designed to evaluate the target tumor volume and the normal dose received by the tissues.In addition, dosimetric parameters, including D90(minimum dose received by 90% of the gross target volume), V100, V150, V200(percentage of GTV that received 100%, 150%, and 200% of the prescribed dose, respectively), minimum peripheral dose (MPD), conformal index (CI), external index (EI), and homogeneity index (HI) in the pre-operative and post-operative plans were also assessed and compared using the Wilcoxon test. Results Fourteen patients treated in our institution from August to October, 2016 were included in this study. The median age of the patients was 61.5 years, and the median Karnofsky Performance Scale score was 80. A total of 14 lesions from the 14 patients were treated by seed implantation in the neck (n=4), chest (n=3), abdomen (n=5), and pelvis (n=2). Of the 14 patients that underwent implantation, 8 had previously received radiation therapy, and 6 had not received radiation therapy. Dosage optimization was performed for all patients during the operation. The median activity of the implanted seeds was 0.625 mCi (0.55-0.75 mCi,1 Ci=3.7×1010 Bq), and the preoperatively planned median number of needling and implanted seeds were 9(4-34) and 45.5(10-162), respectively. However, the actual median number of needling and implanted seeds were 9.5(4-34) and 45.5(10-162), respectively. Dosimetric analysis showed that there were no significant changes in tumor volume (P=0.135), D90(P=0.208), MPD (P=0.104), V100(P=0.542), V150(P=0.754), V200(P=0.583), CI (P=0.426), EI (P=0.326), and HI (P=0.952) after implantation. Conclusions 3D-PCT guidance and dosage optimization can result in good consistency between pre-and post-operative plans for radioactive seed implantation. 3D-PCT is a convenient and cheap technique suitable for large-scale clinical application.