Objective:To introduce estimate a technique ofregulative aperture methodin locating lung block in TBI.Methods:We excavated a square aperture in the foam template which is used to fasten the lung block,and the projection formed by the field light through the aperture is used as the reference for adjusting the location of the lung block.Measure the windage of lung shades and block shades by X-ray,in 8 patients.Results:windage values of head-feet and left-right orientations are smaller inregulative aperture modethan in conventional method respectively.Conclusions:Regulative aperture methodis an easy and effective technique to improve lung shielding precision in TBI.

Objective To compare the dosimetric differences between pencil beam convolution (PBC) and anisotropic analytical algorithm (AAA) in Eclipse treatment planning system for intensitymodulated radiotherapy (IMRT) planning of lung cancer patients and dosimetric verification.Methods 10 IMRT plans of lung cancer patients were calculated using the PBC and AAA and the differences of dosimetric parameter were analyzed according to dose-volume histogram of planning target volume (PTV),lung and spinal cord.The verification measurements were performed on an inhomogeneous thorax phantom using a pinpoint ionization chamber.The agreement between calculated and measured doses was determined.The paired t test was used to compare the results.Results Compared with PBC,the AAA predicted higher maximum PTV dose (t =-4.03,P =0.010),lower minimum PTV dose (t =5.09,P =0.040),and a reduction of the volume of PTV covered by the prescribed dose.The AAA also predicted slightly increases than the PBC algorithm in the mean dose to the lung and the V20 as well as the maximum dose to the spinal cord,and the differences were statistically significant (t =-3.99,-2.79,-5.46,P =0.010,0.038,0.003).In the verification measurements,the agreement between the AAA and measurement was within 2％and superior to the PBC algorithm on isocenter (t =-3.82,P =0.012).Conclusions For IMRT treatment planning of lung cancer,the PBC algorithm overestimates the dose to the PTV and underestimates the dose to the lung and the spinal cord,so the AAA for treating planning in which the tissue inhomogeneous such as lung is present is recommended.

Objective To evaluate the therapeutic effects of stereotactic conformal radiotherapy (SCRT) on 30 cases of thalamic and brainstem tumors. Methods During the period from October 1997 to April 2002, 30 patients, 19 male and 11 female, with an age range from 13 to 68 years (an average of 37 years) suffering from thalamic and brainstem tumors, were treated in our institute. The size of the tumors ranged from 3.5 cm 3 to 73.0 cm 3 with an average of 16.5 cm 3. Eight cases were treated with SCRT after regular radiotherapy, 7 cases were treated with SCRT after surgical resection of the tumor and 15 cases were treated with SCRT only. Results The clinical symptoms of all the patients disappeared thoroughly. Their KPS was significantly improved (P

OBJECTIVETo measure the imaging dose in the head phantom by different image-guided methods.

METHODSThe imaging dose was measured in a cylindrical phantom on a Varian Clinac iX linear accelerator equipped with EPID, OBI, CBCT using a PTW 0.6 cc ion chamber with UNIDOS E dosimeter. 2D images were acquired by two perpendicular fields (0 degrees & 270 degrees), and the 3D images by CBCT.

RESULTSThe 2D imaging average dose for OBI (KV X-ray) was 0.74 mGy in the head phantom. It was significantly lower than 90.93 mGy for EPID (MV X-ray) and the image quality was better. For a standard CBCT (KV X-ray), the imaging average dose was 4.77 mGy. For a low dose mode, the imaging dose was 50% of the standard mode. Moreover, 3D images could match accurately.

CONCLUSIONFor the OBI system, the imaging dose is lower and image quality is better than EPID. The 3D image-guided method for CBCT is better than 2D and is also safe for daily position verification. Therefore, during treatment positioning, the appropriate image-guide methods and scanning parameters can effectively reduce the additional dose to the patients.

Head and Neck Neoplasms ; radiotherapy ; Humans ; Radiotherapy Dosage ; Radiotherapy Planning, Computer-Assisted ; methods

Objective:To compare the dosimetric differences of the planning target volume(PTV)and the organs at risk(OAR)for postoperative patients with cervical cancer on intensity-modulated radiotherapy(IMRT)and conventional 4 fields(4F)or 2 fields(2F)radiotherapy.Methods:Six postoperative patients with cervical cancer were chosen randomly.The next steps were CT scan,PTV and OAR contouring.The treatment protocols were designed into conventional 4F,2F and IMRT by TPS.Finally,the doso distribution and DVH were compared.Results:About the conformability of PTV,IMRT showed a significantly superior dose distribution over conventional 4F(P=0.015),and conventional 4F was superior to 2F(P=0.043).IMRT as compared with conventional 4F or 2F protocols,the received dose of the 50%volume of bladder was reduced by 25.8%and 27.5%,the rectum was reduced by 12%and 14.3%,the small intestine was reduced by 36.5%and 50%.But the differences of the femoral head(left & right)and the ilium have no statistical significance.Conclusion:in postoperative radiotherapy for cervical cancer,IMRT have Inore dosimetric advantages than conventional radiotherapy.