| Objective: Measuring the setup errors of patients with esophagus carcinoma and lung carcinoma during the radiotherapy, evaluating the effect of setup errors against the physical dosimeter at target and normal tissues by a simulation of three dimensional (3D) treatment planning, finding a reasonable margin from the Clinic Target Volume (CTV) to the Planning Target Volume (PTV).Methods: 42 cases of untreated esophageal cancer and 31 cases of untreated lung cancer were enrolled into this study from January. 2007 to January. 2008, fastening all patients with a subpressure vacuum pad, processing the CT simulation with the same posture, scanning the CT image to the treatment planning system(ADAC Pinnacle 7.6c), the doctor contoured the GTV, CTV, PTV and the organs at risk(OAR). The Physicist firstly made the planing according to the doctor requests and ensure the best distribution at the target. Thereafter, the 0o and 90o Digital Reconstructed Radiograph(DRR)were transmitted to the iView GT workshop. Meanwhile, 2 copies of cross-cut Electronic Portal Image (EPI), were required before radiotherapy. Two doctors confirm the variance of the osteal mark from the EPI and DRR, and output a 3 D direction (left to right, superior to inferior, anterior to posterior) of the setup errors through the iView GT software. The effects of setup errors were simulated in the treatment planning system by moving the isocenter and then recalculating the dose distribution without changing the field angle, shape and weighing, we would have the new plan (PLAN2) after calculation, retract the PTV from the original plan (PLAN1) to get CTVx1, CTVx2, CTVx3, CTVx4, CTVx5, CTVx6, select all the identical values as CTVx from the PLAN1 and PLAN2, confirm the distance between CTVx and PTV, minimum value was the margin from CTV to PTV.Result: (1)The systematic setup errors for esophageal cancer were -2.31mm, -0.55mm and -0.16mm, the random errors were 4.42mm, 4.35mm and 4.48mm at the direction of left to right(LR), anterior to posterior(AP), superior to inferior (SI)respectively, for lung cancer, the systematic errors were -2.18mm, -2.67mm and 1.33mm, the random errors were 5.20mm, 3.80mm and 4.01mm at the direction of LR, AP and SI. (2)Defining the maximum value of the retraction area, including the 95% setup errors. In this paper, it was achieved 10mm left to right, 10mm anterior to posterior, 9mm superior to inferior for esophageal cancer, 12mm left to right, 10mm anterior to posterior, 10mm superior to inferior as maximum value for lung cancer. (3)The average values of D100, D95, D90, V100, V95 in GTVPLAN1 for esophageal cancer were higher than that of GTVPLAN2, however, V105 was lower. Furthermore, there were significant difference between D100, D95, D90, V100 in GTVPLAN1 and that of GTVPLAN2, P<0.05, there were not significant difference between V105, V95, V90 in GTVPLAN1 and that of GTVPLAN2, P>0.05. The dose indexes of CTVPLAN2 was lower than that of CTVPLAN1, P<0.01. The dose indexes of PTVPLAN2 was lower than that of PTVPLAN1, P <0.05. The average doses of lung for PLAN1 and PLAN2 were 1220.64±302.21cGy and 1191.61±309.10cGy respectively, V20 were 22.49±5.20% and 22.02±5.47%, V30 were 12.57±4.80% and 12.10±4.80%. The average doses of heart for PLAN1 and PLAN2 were 2077.62±1292.75cGy and 2036.23±1295.86cGy, V40 were 24.59±19.89% and 23.77±19.85% respectively, V50 were 12.46±11.65% and 11.78±11.82%. In the original plan, none of patients doses of the spinal cord exceeded 4500cGy, while 18 cases (42.86%) of PLAN2 were more than 4500cGy, with maximum 5503.90cGy. (4)Medium setup errors of LR, SI, AP in cervical esophageal carcinoma were 2.52±1.96mm, 3.56±2.34mm, 2.37±2.56mm, respectively. That of upper segment esophageal carcinoma were 3.97±2.97mm, 3.50±3.23 mm, 3.18±2.23mm, respectively. That of middle segment were 4.34±3.23mm, 3.46±2.99mm, 3.55±3.11mm. That of lower segment were 2.46±1.78mm, 2.58±1.88mm, 3.06±2.54mm. The CTVD95 of PLAN1 and PLAN2 in cervical esophageal carcinoma were 6115.33±63.57cGy and 5832.67±221.09cGy respectively. That of upper segment esophageal carcinoma were 5960.09±298.98cGy, 5889.09±327.52cGy, respectively. That of middle segment were 6211.20±135.05cGy, 6143.08±132.75cGy. That of lower segment were 6167.67±27.47cGy, 6075.00±126.65cGy. Medium setup errors of LR, SI, AP in center lung cancer were 4.62±3.36mm, 3.41±2.66mm, 3.47±2.90mm, respectively. Medium setup errors of LR, SI, AP in peripheral lung cancer were 4.21±3.02mm, 2.76±2.37mm, 4.53±2.73mm. The CTVD95 of PLAN1 and PLAN2 in center lung cancer were 6109.60±271.69cGy, 6002.96±288.73cGy. That of peripheral lung cancer were 5972.00±546.53cGy, 6030.50±569.12cGy. (5)The dose indexes of CTVx1, CTVx2, CTVx3, CTVx4, CTVx5, CTVx6 for PLAN1 were higher than that of PLAN2 in esophageal carcinoma. The dose indexes of CTVx1 were no significant difference between PLAN1 and PLAN2, P>0.05. (6)The D100, V100, V95 of GTVPLAN2 for lung cancer were lower than that of GTVPLAN1, P<0.05. The dose indexes of CTV PLAN2 were lower than that of CTVPLAN1, all the indexes had significant difference between CTVPLAN1 and CTV PLAN2, except V105, P<0.05. The dose indexes of PTV PLAN2 were lower than that of PTVPLAN1, P<0.05. The average doses of lung for PLAN1 and PLAN2 were 1382.04±299.17cGy and 1352.02±314.07cGy, V20 were 24.31±5.24% and 23.74±5.45% respectively, V30 were 16.81±4.15% and 16.28±4.23%. The average doses of heart for PLAN1 and PLAN2 were 1800.82±1186.99cGy and 1758.07±1170.38cGy, V40 were 19.29±16.24% and 18.57±15.78% respectively, V50 were 13.99±13.36%和13.14±12.76%. In the original plan, none of patients exceeded 4500cGy with the doses of the spinal cord, while 9 cases (29.03%) in PLAN2 were more than 4500cGy, with maximum 5566.20cGy. The doses of PLAN1 for esophagus were higher than that of the PLAN2, Dmax was significant difference between in PLAN1 and in PLAN2, others (including Dmean, V40, V50, V60, NTCP) with no significant difference, P>0.05. (7)The dose indexes of CTVx1, CTVx2, CTVx3, CTVx4, CTVx5, CTVx6 for PLAN1 were higher than that of PLAN2 in lung cancer. The dose indexes of CTVx1 and CTVx2 were no significant difference between PLAN1 and PLAN2, P>0.05.Conclusion: The setup errors would affect dose distribution which reduced the target input. It may not increase NTCP of lungs, heart and esophageal, however, the doses of spinal cord were far more than the limitation. Furthermore, it was more sensitive of setup errors with esophageal cancer in cervical segment than that of upper, middle or lower segment esophageal cancer. The CTV to PTV margin by the PTV retraction method based on our setup errors for esophageal cancer were 10mm left to right, 10mm anterior to posterior and 9mm superior to inferior, for lung cancer were 11mm left to right, 9mm anterior to posterior and 9mm superior to inferior. |
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