ABSTRACT
Objective To measure the setup errors in thoracic esophageal carcinoma treated with intensity modulated radiotherapy (IMRT) using kilo-voltage cone-beam CT (kV-CBCT),and to evaluate the impact of the setup errors on the dose distributions in tumor target volume and the peripheral normal tissues.Methods Twenty-one patients with thoracic esophageal carcinoma undergoing image guided IMRT (IG-IMRT) were included in this study. Using kV-CBCT,173 setup errors of these patients were acquired before treatment.By shifting the isocenters,these setup errors were simulated in the 3-dimentional treatment planning system and the corresponding impact of the dose distribution in tumor target volume and peripheral organs were evaluated.Results The translational deviations of lateral,longitudinal and vertical directions were ( 2.73 ± 1.85 ),( 3.19 ± 2.71 ),and ( 2.35 ± 1.71 ) mm,respectively.The dose of gross tumor volume (GTV) was not impacted significantly by the setup errors. However,comparing with the standard plan without setup errors,the setup errors in the simulated plan reduced the dose of 95％ planning target volume (PTV) by 3.38 Gy.The dose to PTV Dmin and PTV Dmean were also reduced by 9.83 Gy and 0.65 Gy respectively. The correction of setup errors improved the conformity index (CI) and the homogeneity index (HI) for PTV.The C1 and HI for the standard plan were 0.74 ± 0.10 and 1.07 ±0.02, respectively. The C1 and H1 for the simulated plan were 0.69 ± 0.08 and 1.13 ± 0.07,respectively.Statistically significance was observed in these differences ( t =3.43 and -3.91 respectively,P ＜ 0.05 ). No statistical significance was observed in the dose differences in lungs,spinal cord and heart between the two plans ( P ＞ 0.05).The mean maximum dose of the spinal cord was (42.20 ± 4.97 ) Gy in the simulation plan,which was (41.37 ± 2.75 ) Gy in the standard plan.For some patients,the maximum dose of the spinal cord exceeded the tolerance level of 45 Gy in the simulation plan,and one case even reached 52.8 Gy.Conclusions Using the image guidance of kV-CBCT,the setup errors can be reduced significantly for patients with esophageal carcinoma receiving IG-IMRT.The correction of setup errors can increase the treatment precision and enhance the dose in PTV.No significant dose changes were observed in the lung,spinal cord and heart as a result of setup error correctio.
ABSTRACT
Objective To investigate the safety and clinical outcome of total body irradiation (TBI) and the real-time in vivo dosimetry with semiconductor dosimeter in hematogenous stem cell transplantation (HSCT). Methods Fifty-seven patients requiring HSCT were treated with TBI. The TBI was given with the semi-sitting or standing position or lateralcumbent posture, using 6 MV X-ray beams and opposed parallel fields technique (two or four fields, AP/PA fields) in a single fraction or multiple fractions. The real-time in vivo dosimetry was performed with six diodes positioned on the surface of patients to adjust the dose homo-geneity of the midplane using the different thickness lead sheets. Results Mild to moderate nausea, vomi-ting and swollen parotid occurred in 41 patients after TBI, which were relieved after allopathy therapy. No radiation-induced interstitial pneumonia was observed. All patients fulfilled the HSCT. The homogeneity of relative dose (normalize to umbilicus dose) in the different positions accorded with the requirement of the prescription dose. Conclusions The opposed parallel radiation, with the semi-sitting or standing positions or lateralcumbent posture, combined with the real-time in vivo dosimetry with semiconductor dosimeter is an effective and safe technique for TBI.