ABSTRACT
Objective To analyze the differences between calculated and actual volumes of regions of interest ( ROIs) in three treatment planning systems ( TPSs):PrecisePlan, Xio, and Oncentra, to transfer different ROIs and compare their calculated volume between the three TPSs, and to provide a basis for clinical application. Methods Different sizes of ROIs were delineated on 5 sets of computed tomography ( CT) images with different slice thickness. Square and round regions with different slice numbers were contoured in a homogeneous phantom. Three groups of patients ( n=5) with head and neck tumor, chest and abdomen tumor, and pelvic tumor, respectively, were enrolled as subjects. All the ROIs were independently transferred back and forth between three TPSs and different workstations with the same system in DICOM RT format. The changes in actual and calculated ROI volumes were evaluated after back and forth transfer. Results There was a significant positive linear correlation between the calculated volume, slice thickness, slice number, and actual volume of ROI in each TPS ( PrecisePlan:R2=0. 994, P<0. 01;Xio:R2=0. 997, P<0. 01;Oncentra:R2=0. 995, P<0. 01) . There were significant differences in all calculated ROI volumes of the head, chest and abdomen between the three TPS ( P<0. 05) except for the calculated ROI volumes of the chest and abdomen between Oncentra and Xio ( P=0. 114 ) . Conclusions The variations in volume calculation algorithm and slice thickness are the main causes of differences in calculated ROI volume. Particularly, small?volume ROIs have the greatest variation in calculated volume. To avoid a secondary reconstruction of ROI volume, it is recommended to transfer ROI back and forth between dose calculation workstations with the same TPS.
ABSTRACT
Objective To explore the treatment procedure of pediatric vaginal rhabdomyosarcoma ( RMS) using 60 Co high?dose?rate three?dimensional ( 3D ) brachytherapy, and to analyze its dosimetric feasibility. Methods Computed tomography ( CT ) images were collected from five children undergoing radiotherapy for vaginal RMS. Three treatment plans were designed:plan A using 3D conformal radiotherapy with external beam irradiation, plan B using brachytherapy, and plan C using brachytherapy combined with external beam irradiation. Dosimetric parameters for clinical target volume ( CTV ) and organs at risk ( OARs ) were evaluated based on EQD 2 and analyzed using one ? way analysis of variance . Results Compared with plan A, plan C had significantly larger D90, D50, and Dmean for CTV ( all P=0?00), significantly lower doses to the rectum, bladder, and femoral head, and a significantly higher dose to the ovary ( all P=0?00) . Compared with plan B, plan C had a larger D90 for CTV, smaller D50 and Dmean for CTV, a lower dose to the ovary, and higher doses to the rectum, bladder, and femoral head. Among the three plans, plan B had the smallest D2 cm3 for the rectum and bladder. Conclusions The optimal radiotherapy plan for pediatric vaginal RMS should be based on the primary tumor location and residual tumor after surgery. CT image?guided 60 Co high?dose?rate 3D brachytherapy is convenient, effective, and well tolerated by children. It also achieves a high dose to CTV as well as good protection of normal tissue.
ABSTRACT
Objective To study the scattering effect of Co-Cr-Mo hip prosthesis which was high Z material for patients undergoing pelvic irradiation.Methods The hip prosthesis was set in water phantom (30 cm×30 cm×30 cm), determing points were chosen on the entrance side of both 6 MV and 10 MV beams at the distance of 0.5 cm, 1.0 cm, 2.0 cm to the hip prosthesis, and also on the exit side of both 6 MV and 10 MV beams at the distance of 3.0 cm, 5.0 cm, 7.0 cm to the hip prostheses.Dose behind the hip prosthesis at depths of 5.0 cm and 10.0 cm for 6 MV and 10 MV beams are also measured.ResultsThe dose deviation on the beams′ entrance side is between 0 to 5.0%, the backscatter effect was more obviously with the higher energy beam.The dose deviation on the beams′ exit side was between 21.6%-30.8%.With the same field size and depth, dose deviation becomes smaller when the beam energy was higher;while with the same energy and depth, dose deviation becomes smaller when the field size was bigger.Dose profiles behind the head of the hip prosthesis indicate obvious attenuation of the beam.Conclusions Beam arrangements that avoid the prosthesis should be considered first or we should at least reduce the weight of the beam that pass through the prosthesis.