Target Center Bias And Dosimetry Study In The Course Of Three Dimensional Conformal Radiotherapy With Esophageal Carcinoma

Objective: To observe the target center bias and the changes of the tumor in the course of three dimensional conformal radiotherapy with esophageal carcinoma by three dimensional conformal treatment planning system (TPS) and image fusion, and analyse the influence to the dose distribution of tumor target and the normal tissue around esophageal carcinoma,exploring the necessity and possibility of re-localiza- tion in the course of three dimensional conformal radiotherapy with esophageal carcinoma.Methods: 40 patients of untreated esophageal carcinoma were treated with three dimensional conformal radiotherapy in the Forth Hospital of Hebei Medical University from July 2005 to November 2006.After scanned by CT simulator, the CT images were transferred through local network to the treatment planning system (ADAC Pinnacle 6.2b or ADAC Pinnacle 7.6b) and reconstructed by TPS.Then outlined the gross tumor volume (GTV₁),clinical target volume (CTV₁), planning target volume (PTV₁) and organs at risk(OARs). Physists made three dimensional conformal treatment planning for every patients, prescription dose:3000cGy, 200cGy/per fraction, 1 fraction/ per day, 5 fractions/per week, made PTVD₉₅≥3000 cGy,and assessed the treatment planning by DVH(Dose Volume Histagram-DVH). After the patients had followed the dose of 3000cGy/15 fractions,the second CT conformal simulation was executed, then made the latter phase treatment planning.The criteria of the latter one was identical to the former,and take the new GTV geometrial center as the center of field.Besides, made PTV₂D₉₅≥3000cGy.Patients were treated by the latter phase treatment planning.After scanned by CT simulator,the new images were transferred to the former phase treatment planning and fused.Named the first tumor targets GTV₁,CTV₁,PTV₁,and named the re-localized tumor targets GTV₂,CTV₂,PTV₂.Let physists make two plannings once more. Planning1: prescription dose was 6000cGy, 200cGy/per fraction, 1 fraction/ per day, 5 fractions/per week,take GTV₁ geometrial center as the center of field, PTV₁D₉₅≥6000 cGy, the maximum dose of spinal cord was no more than 4500 cGy, and assessed the planning by DVH; Planning2 was devided into two phases, the prescription dose of the former phase was 3000 cGy, 200cGy/per fraction, 1 fraction/ per day, 5 fractions/per week, take GTV₁ geometrial center as the center of field, PTV₁D₉₅≥3000 cGy,and made the best to reduce the dose of lungs and spinal cord.Moreover,fused the two phases plannings.Observed and analysed the dose distribution of GTV₁,CTV₁,PTV₁,GTV₂,CTV₂,PTV₂ and OAR respectively.Results: (1) The mean values of GTV₁ length,maximum width,maximum anteroposterior,volume were 7.52cm, 4.73cm,3.38cm,55.26cm³ respectively;and the ones of GTV₂ were 7.30cm,4.13cm,2.85cm,40.59cm³ respectively.Of that, the maximum width,maximum anteroposterior and volume were diminuted.and there were significant differences,P<0.001. (2) The geometrial center of GTV had deviated 0.29cm,0.68 cm,0.29 cm on average along X,Y,Z axis. (3) The D₁₀₀ and D₉₅ of GTV₁,CTV₁,PTV₁ in planning1 were 6053.45±110.36 cGy,5598.90±399.38 cGy,4796.18±496.04 cGy and 6172.40±79.82 cGy,6111.03±80.02cGy,5983.55±57.42cGy respectively; The D₁₀₀ and D₉₅ of GTV₂,CTV₂,PTV₂ were 5933.40±503.22 cGy,4846.75±1678.35 cGy,3186.10±1781.49 cGy and 6167.93±82.81cGy,5821.93±1053.93cGy,5482.13±1221.65cGy respectively.Of that,the average dose of PTV₂D₉₅ was 5482.13 cGy,lower than PTV₁D₉₅. There was a significant difference,P=0.000.(4) The D₁₀₀ and D₉₅ of GTV₁,CTV₁,PTV₁ in planning2 were 5866.43±561.83 cGy,5104.68±889.69cGy,4099.80±1207.59cGy and 6119.90±451.53cGy,5972.73±481.23cGy,5546.70±620.10cGy respectively; the D₁₀₀ and D₉₅ of GTV₂,CTV₂,PTV₂ in planning2 were 6037.25±263.99cGy,5342.48±840.61 cGy,4308.50±884.97cGy and 6196.50±97.46cGy,6002.73±507.38cGy,5700.58±700.45cGy respectively. Of that,the average dose of PTV₂D₉₅ was 5700.58cGy,higher than PTV₁D₉₅. There was a significant difference,P=0.035.(5) The lung mean dose,the lung dose of received 5Gy,10Gy,15Gy,20Gy,25Gy,30Gy,35Gy (V₅,V₁₀,V₁₅,V₂₀,V₂₅,V₃₀, V₃₅)and normal tissue complication probability(NTCP) of lungs in planning1 and planning2 were 1244.00±407.44cGy,47.18±18.22%,37.81±14.30%,30.50±10.23%,22.99±7.60%,18.17±7.18%,14.27±7.01%,10.80±5.65%,2.38±2.99% and 1211.79±381.95cGy,46.20±19.92%,36.31±15.91%,30.06±9.99%,22.33±7.29%,17.47±6.59%,13.62±6.40%,10.04±5.12%,1.63±2.25% respectively. There were no obvious significant differences,P=0.686,0.973,0.878,0.971,0.892,0.544,0.475,0.348,0.356. The mean dose,V40,V45,NTCP of heart in planning1 and planning2 were 2127.96±1327.38cGy,27.96±19.93%,20.94±11.00%,15.23±21.99% and 2060.64±1275.38 cGy,26.33±19.34%,19.16±15.48%,10.62±18.25% respectively. There were no obvious significant differences,P>0.05.Conclusions: After patients with esophageal carcinoma had received the dose of 3000cGy,GTV geometrical center had some deviations along X,Y,Z axis.And the maximum width,the maximum anteroposterior and the volume of tumor had diminuted,but the length of tumor hadn't shortened.The changes of tumor location and shape made the original isodose curves not cover with the tumor fully,so made some tumors had not received the sufficiency doses.Re-localization in the middle of conformal radiotherapy can make the tumor receive enough dose,so we think it is necessary for patients with esophageal carcinoma to re-localize in the middle of conformal radiotherapy. But after verifications of treatment planning repeatly,the 95% PTV volume had received 5480cGy dose at least. Besides, re-localization can not reduce the doses of lung,heart,spinal cord.So we think it can be accepted not to re-localize in the middle of conformal radiotherapy.