Objective To measure the displacement of the silver clips guided by kV-plain film at state of moderate deep inspiration hold(mDIBH) assisted by active breathing control(ABC) and to explore the margin of clinical target volume(CTV) to planning target volume(PTV) for breast cancer patients treated with three-dimensional conformal external-beam partial breast irradiation (EB-PBI) assisted by ABC. Methods The patients undertook CT simulation assisted by ABC to get the CT images on the respiratory condition of mDIBH. Four selected silver clips in breast cavity were delineated and the cavity based on all of the clips were delineated as gross tumor volume (GTV). Before each irradiation, two orthogonal kV-plain films were taken for the patients in the respiratory condition of mDIBH assisted by ABC device. 2D-2D auto-matie registration was performed based on pixel between the kV-plain films and the digital reconstructed radi-ographs(DRR). Then manual registration was undertook to get the shifts of the four clips separately at LAT, LNG,and VRT directions. Based on the shift data,the margins of CTV to PTV at LAT,LNG and VRT direc-tions were calculated. Results The margins from CTV to PTV were 5.00 mm,7.78 mm and 9.30 mm at LAT,LNG and VRT directions based on the clip at cephal border of the cavity. The corresponding margins were 4.40 mm,6.43 mm and 6.73 mm based on the clip at bottom of the cavity;5.04 mm,8.63 mm and 10.54 mm based on the clip at lateral border of the cavity;5.40 mm,8.59 ram and 10.81 mm based on the clip at pedal border of the cavity. Conclusions The silver clips in breast cavity can be clearly showed on the kV-plain film. The displacement of the clips can be exactly measured by registration of kV-plain film and planning DRR in condition of mDIBH assisted by ABC. The margins from CTV to PTV for EB-PBI can be calculated based on the displacement of the clips.

Objective To estimate the appropriate margins for the clinical target volume (CTV) with or without online correction using cone-beam CT(CBCT) during the processs of radiation for non-small cell lung cancer(NSCLC) patients. Methods Eight patients with NSCLC treated with three-dimensional conformal ra-diotherapy(3D-CRT) were investigated, kV CBCT scans were performed before and immediately after radio-therapy. Then analysis of these images was performed using automatic and manual registration of the CBCT and planning computed tomography images. The patient positioning and organ motion were corrected by moving the couch in the left- right (X), cranio- caudal (Y), and anterior- posterior (Z) directions accordingly, and CBCTonline-guided correction data were recorded. The clinical study performed 2-3 times per week. CBCT data ac-quired before treatment delivery were used to evaluate the positioning error and organ motion, and that acquired after treatment were used to assess intrafraction tumor displacement and organ motion. These data were used in a standard formula to calculate CTV-to-PTV(planning target volume) margin of online-guided correction and non-online-guided correction. Results Total of 143 sets of CBCT images were analyzed. On the condition of non- correction, the margins required to account for total errors were 8 mm, 9 nun, 11 mm in X, Y and Z direc-tions respectively. When the tumor was corrected every fraction, margins required to account for intrafraction errors were 2 mm in each directions. Conclusion There are some extent of errors from positioning and organ motion in 3D-CRT for NSCLC. Online correction approach based on CBCT images analysis can be used to re-duce the impact obviously and to estimate the appropriate margins for the CTV.

Objective To investigate how much the patient setup accuracy for irradiation of head and neck cancer can be improved by online setup verification and offline setup verification using cone-beam computed tomography(CBCT), and the feasibility of image-guided adaptive correction procedure to reduce the PIN margin.Methods 16 patients of head-and-neck cancer treated with three-dimensional conformal radiotherapy (3D-CRT)or intensity modulated radiotherapy(IMRT)were investigated. The first online kV CBCT scan, rigid image registration, setup correction were performed before radiotherapy. The second kV CBCT scan were acquired immediately after treatment and analysis was performed as above. CBCT scans were acquired at two or three fractions weekly during the entire course of radiotherapy and CBCT online-guided correction data were recorded. The data was used to calculate the population-based CTV-PTV margins under the condition of non-correction, correction every fraction and compensation of the systematic setup error respectively. The number of initial images required to predict systematic setup error was evaluated with the permission of 0.5 mm residue error. Results Total of 320 sets of CBCT images were analyzed for 16 patients. Under the condition of non-correction, the margins required to account for total error are 5.7 mm,5.6 mm,and 7.3 mm in the left-right(X axis),cranio-eaudal(Y axis), and anterior-posterior (Z axis)directions respectively, when the tumor was corrected every fraction, the margins required to account for intrafraetion error are 1.7 mm,1.7 mm,and 2.3 mm in X, Y,and Z axis.To correct the systematic setup error,8 sets of CBCT images are adequate. After compensation for the effect of the systematic setup error, 2.7 mm,2.5 mm, and 3.6 mm PTV margins are necessary in X, Y, and Z axis respectively. Conclusions There exists some extent of setup error in head and neck 3D-CRT or IMRT.The on-line CBCT correction and the approach based on off-line adaptive correction both can be used to reduce the impact of setup error obviously, the required margins for the PTV was reduced accordingly.

Objective To investigate the feasibility of online and offline cone-beam CT (CBCT) guided radiotherapy for lung cancer. Methods Fourteen patients with lung tumor treated by three-dimen-sional conformal radiotherapy were investigated. Online kV CBCT scan,image registration and setup correc-tion were performed before and immediately after radiotherapy. CBCT online-guided correction data were used to calculate the population-based CTV-PTV margins under the condition of non-correction and correction in every fraction respectively. The numbers of initial images and the population-based CTV-PTV margins af-ter the offline compensation of the system setup error were evaluated with the permission of 0.5 mm and 1.5 mm maximal residue error,respectively. Results Under the condition of non-correction,the required mar-gins for total error were 5.7 mm,8.0 mm and 7.8 mm in the left-right(x axis) ,cranio-caudal(y axis) and anterior-posterior(z axis) directions, respectively. When the tumor was corrected in every fraction, the re-quired margins for intra-fraction error were 2.4 mm,2.4 mm and 2.3 mm in x,y and z axes, respectively. To correct the systematic setup error,9 sets of CBCT images for 3.3 mm,3.7 mm and 3.6 mm PTV margins, and 7 sets of CBCT images for 3.9 mm,4.3 mm and 4.3 mm PTV margins in x,y and z axes were necessary when 0. 5 mm and 1.5 mm maximal residue errosr were permited respectively. Conclusions Both of the online CBCT correction and the offline adaptive correction can markedly reduce the impact of setup error and reduce the required PTV margins accordingly. It is feasible to deliver the online and offline image guided ra-diation for patients with lung tumor.

Objective To optimize the registration template of kilovohage cone-beam CT (CBCT) guided radiotherapy in whole breast irradiation(WBI)after lumpectomy of breast cancer.Methods From April 2006 to July 2009,twelve patients undergoing WBI with intensity-modulated radiotherapy (IMRT)were recruited in this study.All patients were performed with both conventional planning CT and CBCT integrated on Varian 23 EX.Six distinguishable referenee points(the diameter 1 mm)around the lumpectomy cavity and the surrounding gland on the planning CT image were marked.The images were manually registered offline based on the breast surface,surgical clips,breast gland,contiguous rib,ipsilaterai lung and its external contours,respectively.The same six reference points were then marked on the CBCT image.The performance of the five registration templates was compared using the concept of registration error,while the registration time was taken into account.The registration error was calculated based on the six reference points'translations between the planning CT image and CBCT image,and analyzed with SPSS 13.0 software using one-way ANOVA.Results The values of the registration error for the breast surface,surgical clips,breast gland, contiguous rib,ipsilateral lung and its external contours were(0.60±0.20),(0.43±0.15),(0.49±0.19),(0.69±0.36)and(0.94±0.49)cm,respectively,and the registration time were(3.8±1.1),(3.0±0.9),(4.7±1.7),(4.3±1.3)and(4.5±1.3)min,respectively.There was no statistical difforence between the breast surface,surgical clips and breast gland registration template(t=0.48-1.36,P>0.05),the same result trend to contiguous rib compared with ipsilateral lung(t=2.00,P=0.055),however,there was significant difference between surgical clips and the last two registration methods(t=2.08-4.08,P<0.05).Conclusion In this initial study with a modest number of patients,surgical clips show a best registration template from the standpoint of accuracy and efficiency,whereas contiguous rib and ipsilateral lung are not an ideal method.

Objective To enlarge the scan width of cone-beam computed tomograpby(CBCT) and offer the integrity of structures( including tumor targets and organs at risk) on CBCT images by pasting the CBCT images together without gap or data lost. Methods Patients received CBCT scan twice at different longitude position. The two CBCT image series were then imported to TPS and fused with the planning CT. The same layer of two CBCT series was found by analyzing the two fusion results and recording their sequence numbers. The CBCT image series and the sequence numbers were sent to" CBCT Pasting", a special software we developed for this investigation. Then the software merged the CBCT series into the same reference flame. To validate the feasibility of CBCT Pasting,we observed its geometric characteristics by patients and phantoms. Results On the images of phantom, the difference was 0.26% (28.34 cm3) of the total body volume,and 1.87% (12.82cm3) and 1.47%(10.07cm3) of the two lungs between CT and CBCT images. On the images of patients, the difference was 1.97% (64.53cm3) ,2.30%(33.32cm3) and 1.75%(31.21cm3) for the total-lung,the left lung and the right lung. Conclusions The CBCT scan and pasting can enlarge the scan width without image data lost. This technique can provide a chance to observe the whole target and OAR and help physicists to evaluate the treatment plan.