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Objective To explore the dosimetric characteristics of single photon emission computed tomography(SPECT)combined with bone marrow sparing intensity modulated radiotherapy in patients with cervical cancer.Methods Twenty patients with cervical cancer after hysterectomy were performed on 99Tc thiocolloid SPECT bone marrow imaging to determine the active bone marrow in the pelvis.SPECT image combined with the simulation CT was used as the primary planning data set.Two plans for bone marrow sparing modulated radiotherapy were generated according to the bone marrow volume defined by SPECT and outline of the pelvis(SPECT-IMRT planning and BMS-IMRT planning).Furthermore,the target section and the dosimetric distribution in organs at risk(bone marrow,small intestine,rectum and bladder)in the two plannings were compared.The prescribed dose to the PTV was 45 Gy.Results The volume of the bone marrow in SPECT-IMRT planning and BMS-IMRT planning was(238.15 ±36.82)and(1 100.61 ±109.92)cm3,respectively(t＝33.273,P＜0.05).The average bone marrow volume of SPECT-IMRT planning in high-dose radiation region(V30,V40and V45)was decreased by 6.9％,5.7％and 2.6％respectively compared with BMS-IMRT planning(t ＝3.540,3.4261,3.448,P＜0.05),but there was no statistical significant difference between the two plannings in the dose volume of low-dose radiation(V10and V20,P＞0.05).The PTV coverage rate and exposure dose of other organs at risk(small intestine,rectum and bladder)in the two plannings were not significantly different(P＞0.05).Conclusions SPECT bone marrow imaging could clearly show the range of active bone marrow on CT scan images.Compared with BMS-IMRT,SPECT-IMRT could further reduce the dose volume of high-dose radiation(V30,V40and V45).Yet the clinical significance of this advantage also needs to be confirmed by large-scale clinical studies.
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ObjectiveThis study was to explore the feasibility of using the orthogonal plane dose formed by the coronal and sagittal plane to verify the volumetric modulated arc therapy (VMAT) plan.MethodsThe VMAT plans of 12 patients were included in this study.The orthogonal plane dose formed by the coronal and sagittal plane were measured based on the combination of 2D ionization chamber array and multicube phantom,and the point dose were measured based on a multiple hole cylindrical phantom attached with two 0.125 cm3 ionization chamber probes.ResultsIn the measurement of the point dose,the average error was 1.5％ in high dose area ( more than 80％ of maximum),and 1.7％ in low dose area ( less than 80％ of maximum),respectively.The discrepancy of point dose measurement was 1.3％ between the 2D ionization chamber array and the VMAT planning system.In the measurement of the orthogonal plane dose,the pass rate of γ were 93.7％ for 2％/2 mm and 97.2％ for 3％/3 mm.ConclusionIt is reliable for using the orthogonal plane dose formed by the coronal and sagittal plane to verify the VMAT plan.
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Objective To explorer the application in detection the position accuracy of the multileaf collimator of Varian accelerator with dynamic therapy log files. Methods A pre-designed MLC format files named PMLC for two Varian accelerators, the dynamic treatment log files were recorded 10 times on a different date, and be converted into the MLC format files named DMLC, compared with the original plan PMLC, so we can analysis two files for each leaf position deviation. In addition, we analysis the repeatability of MLC leaves position accuracy between 10 dynalog files of two accelerators. Results No statistically significant difference between the average position of the 10 times leaf position of the two accelerators,their were 0. 29 -0. 29 and 0. 29 -0. 30(z = -0. 77, P=0. 442). About 40% ,30% ,20% and 10% of the leaf position deviation was at ≤0. 2 mm, 0. 3 mm,0. 5 mm and 0. 4 mm,respectively. the maximum value was 0. 5 mm. More than 86% of the leaf position are completely coincident between 10 dynamic treatment files of two accelerators,The rate of position deviation no more 0. 05 mm was 96. 6% and 97.3%, respectively.And the maximum value was 0. 09 mm. Conclusions Dynamic treatment log file is a splendid tool in testing the actual position of multi-leaf collimator. The multi-leaf collimator of two accelerators be detected are precise and stabilized.