| Purpose The aim of this study is to compare treatment plannings in dosimetric study among conventional radiotherapy, three-dimensional conformal radiotherapy and intensity modulated radiation therapy.Parameters such as the number of beams, different ray energy have been investigated.Methods 10 posthysterectomy Cervical Cancer Patients were recruited. a customized immobilization device was fabricated to minimize variability in the daily setup and the positioning markers were set on the model. An hour before scanning the patient was told to empty bladder and rectum,then drink 1200 ml methylglucamine .A vaginal marker was placed in vaginal cuff before CT scanning.The CT enhanced scan images of patients were transmitted to ADAC Pinnacle 8.0 planning system. The clinical target volume (CTV) and organ at risk were contoured on the individual axial CT slices of each patient according to the guideline of RTOG. The CTV include the presacral lymph node-region,the common, external, and internal iliac lymph node regions and the upper 3.0 cm of vagina and paravaginal soft tissue lateral to the vagina .The CTV was expanded by 10 mm to create the PTV (Planning Target Volume). 5,7, 9 field intensity modulated radiation therapy plan using 6MV-X ray were created and 5 field IMRT plan using 10MV-X ray, 15MV-X ray were created. Another two field(AP-PA) plan(2FC) and 4 field conformal radiation therapy plan(4FC) were designed conform to the same PTV.All plans were normalized to deliver 45 Gy to the PTV. Isodose distributions and dose–volume histograms (DVH) of target and organ at risk were compared from three aspects:1.dose comparison of IMRT,3DCRT and 2FC,2.does comparison of IMRT with 5 fields,7fields,9 fields, 3. does comparison of IMRT with 6MV,10MV,15MV X ray.Results Isodose distributions and dose–volume histograms (DVH) of 10 Posthysterectomy Cervical Cancer Patients were compared. 1. dose comparison of IMRT,3DCRT and 2FC :IMRT had advantages over 3DCRT and 2FC in terms of CI and SI.The SI of 3DCRT,IMRT,2FC were 1.14±1.03 , 1.06士0.12 , 1.67±0.52 respectively(P=0.000);The CI of 3DCRT,IMRT,2FC were 0.48士0.28,0.83士0.04,0.15士0.14 respectively(P=0.000).IMRT was superior to 3DCRT and 2FC in reducing the irradiated volume of small bowel ,bladder ,rectum, femoral head ,healthy tissue and bone marrow at high does level, especially at prescribed dose(45Gy)level. The reduction volume of small intestine ,rectum,bladder,bone marrow,left femoral head ,right femoral head ,healthy tissue were 13.72%,51.88%;45.23%,91.64%;41.85%,96.13%;33.67%,43.65%;10.44%,11.63%;20.08%,23.13%;27.36%,31.28% respectively. The NTCP of small intestine with 2FC,3DCRT,IMRT were 6.43±3.31,1.29±1.25,0.91±0.28(P=0.000)respectively(P=0.000).2. In IMRT plans with different numbers ,9F- IMRT had advantages over 5F-IMRTand 7F-IMRT in terms of SI, but have no differences in CI.The SI of 5 field,7 field,9field were 1.13±0.14,1.10±0.09,0.90±0.08 respectively ( P=0.002 ) . The CI of 5 field,7 field,9field were 0.82±0.41,0.83±0.04,0.86±0.03(P=0.112).At low dose level the irradiation volume of small bowel, rectum ,bladder have no difference; 5 field IMRT was superior to 7field and 9 field in reducing the irradiated volume of femoral head and bone marrow(P﹤0.05). At prescribed dose levels, At prescribed dose level 9F-IMRT decreased the irradiated volume of OARS,but only the difference of small intestine and rectum were significant. The P value were 0.029,0.005 respectively. The irradiation volume of small intestine and rectum in 5 fields,7fields,9fields were 2.69±0.70,6.47±2.12;2.46±0.68,3.61±1.91;1.73±0.54,2.83±1.65 respectively.3. The difference in IMRT plans with different ray energy have no significance.Conclusion 1.Our results suggest that IMRT is an effective means of reducing the volume of OAR at high dose level especially prescribed dose irradiated and achieving better dose distribution in posthysterectomy Cervical Cancer Patients receiving RT. It was proposed to a conventional means in treatment of posthysterectomy Cervical Cancer Patients; 2.In IMRT plans with different numbers of portal,9F-IMRT had advantages over 5F-IMRT and 7F-IMRT in terms of HI ,but have no differences in CI. 9F-IMRT reduced the volume of small bowel, rectum at prescribed dose levels,but increased irradiated volume of femoral head and bone marrow at low dose levels and prolonged treatment time and increased the does of irrational leakage. Five fields was proposed in IMRT of posthysterectomy Cervical Cancer Patients. 3.The difference of target dose distribution and irradiated volume of OARS in IMRT plans with different ray energy have no significance,but 15MV,10MV X ray generated neutron. 6MV-X ray was proposed in IMRT of posthysterectomy Cervical Cancer Patients.4.SI has advantages in evaluating the homogeneity of PTV over HI. |
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