| IEstablishment of the optimal image alignment method for kilovoltage cone-beam CT (kVCBCT) and simulation CT in bladder cancerObjective:To compare the repeatability, accuracy and time cost in three different alignment methods used kilovoltage cone beam CT (kVCBCT) and simulation CT of bladder cancer in MIM software.Materials and Methods:From October 2008 to December 2010,12 patients with bladder cancer who received radiotherapy in our hospital were included in this study. Images of simulation CT before radiotherapy and those of kVCBCT before the first irradiation were aligned with the automatic registration method, respectively, including Rigid Assisted Alignment, Box-based Alignment and Contour-based Alignment in MIM software. All the images were aligned by the same physician at three different moments. The distances which the center coordinates of the two series CT images moved in the alignments in the LR, SI, and AP directions, and the time spent in each method were recorded. All the results were evaluated with a single-blind approach by another physician and a physicist independently.Results:108 data of the 12 patients were obtained in three different alignment methods at three different moments. The results showed the maximum motion distances were less than lmm with both the Contour-based Alignment and the Box-based Alignment, while the motion ranges were larger in the Rigid Assisted alignment. The Contour-based Alignment used the longest time,44.81 seconds on average. It’s indicated the Contour based alignment might be the optimal method for alignment in our study.Conclusion:In the MIM software, the Contour-based Alignment is the precise method, and the time cost is within an acceptable range. IIQuantitative determination of Internal target volume (ITV) of bladder during the irradiation of bladder cancerObjective:To observe the differences on the volume of bladder between the simulation CT and the kVCBCT scans, as well as each kVCBCT image, for the interfraction and intrafraction differences in bladder during irradiation of bladder cancer.Materials and Methods:From October 2008 to December 2010,12 patients of bladder cancer in our hospital with radical radiotherapy were selected. All the patients received simulation CT scan before radiotherapy. During the radiotherapy, each patient took a kVCBCT scan before and after irradiation every day at the first week, and repeated kVCBCT scans before and after irradiation only once a week at any day since the second week, without on-line kVCBCT position correction. All image data were sent to the MIM software, and the outline of the bladder was sketched. After alignment of the compared images, the bladder volumes were compared between simulation CT and each kVCBCT before irradiation,, and between the before and after treatment kVCBCT. In the meanwhile, the changes of overlapped bladder volume in the kVCBCT images scanned before and after the first and subsequent irradiation were observed.Results:With a total of 12 simulation CT images and 232 kVCBCT images, the average bladder volume in 12 simulation CT scans was 104.68±41.32ml,the change of bladder volume of 12 patients was 108.82±48.73ml(41.96-292.60ml)by kVCBCT images. In 7 patients the change range of bladder volumes before each irradiation waswithin 20% relative to its mean value (coefficient of variation), but 5 patients had a variance more than 20%. Average bladder volume before each irradiation changed significantly in comparison (P<0.05) with the volume of the simulation CT in 10 patients. Volumes of intrafraction treatment significantly different (P<0.05) in 6 patients, while volumes of interfraction treatment altered significantly (P<0.05)in 8 patients.Conclusion:bladder volume changes obviously during treatment, contouring an ITV according to the outline of the bladder is necessary. The accurate determination of the bladder ITV for bladder cancerObjective:Using the total volume of the bladder by superimposed contours of all kVCBCT as a combined index, to assess the the feasibility of contouring ITV outlines according to the volumes of bladder of the first five treatments as a adaptive individual bladder cancer therapy; To evaluate two methods of generating ITV the external isotropic expansion of bladder CTV contoured based a simulation CT, as well as anisotropy margin expansion.Materials and Methods:From October 2008 to December 2010,12 patients of bladder cancer received radiotherapy in our hospital were selected. All the patients received simulation CT scan before radiotherapy. During the radiotherapy, each patient took a kVCBCT scan before and after irradiation every day at the first week, and repeated kVCBCT scans before and after irradiation only once a week at any day since the second week, without on-line kVCBCT position correction. Overall volume of the bladder (VCBCT-Total) under the outline image of each kVCBCT of each patient was obtained. Overlap two new-received bladder volumes of kVCBCT at each kVCBCT treatment day, and accumulate the volume (VCBCT-Total-#) and calculate its percentage of VCBCT-Total followed by subsequent kVCBCT treatment day. Outlining all the bladders in the simulator CT scans as CTV, and expanding uniform a 10 mm margin as ITVB. VCBCT-Total, VITVB, conformal index (CI), VCBCT-ITVB-EX (the exceed part of CBCT’s ITV beyond contour of ITVB), VITVB-CBCT-SF (the superfluous part of VITVB within the contour of ITVB beyond the VCBCT-Total coverage area) of each patient were recorded,. Sketching the margin of bladders in the simulator CT scans as the CTV, CTV-to-ITV margins of 10 mm inferior,20 mm superior,11 mm left,8 mm right,20 mm anterior and 14 mm posterior were required to contour VITVC.VCBCT-Total and VITVC, CI, VCBCT-ITVC-EX and VITVC-CBCT-SF wereResults:The total volume of superimposed bladder of 12 patients was 191.49±75.80.24ml (108.63～350.60ml). The average of V% of its CBCT-Total’s volume in D4, D5 of the first week were more than 90%, the lower confidence interval of the percentage of D5 is close to 90%, and only 1 patient results far away from 90%. Homogeneous volume expansion ITV after 10mm ranged from 300.14±79.23ml (197.80～437.57ml), CI range:0.52±0.06 (0.38～0.06), VCBCT-ITVB-EX was ranged from 126.63±36.77ml (72.31～194.96ml). The volume of non-uniform outside expanded ITV was 412.30±102.82ml (272.77～566.36ml) between the CI ranges from:0.44±0.08 (0.29～0.57), and VCBCT-ITVC-EX:225.14±53.51ml (148.46 326.34ml). Compared with 10mm external uniform expansion (plan B), the non-uniform expansion of the bladder (plan C) had a percentage of VEX significantly reduced, and the results were significantly different (P= 0.00); the percentage of VSP accounts for PTV significantly increased, resulting in significant differences (P= 0.00).Conclusion:From the variation of bladder volume and spatial position in kVCBCT, it is feasible to establish the ITV of individual bladder cancer treatment with the total volume of the bladder by superimposed contours of the first five kVCBCT scans. Only using 10 mm expansion of the simulator CT to contour ITV may cause a bladder leakage area during the treatment period, and a big range of normal tissue irradiated volume. External non-uniform expansion of the ITV can cover the bladder area better, but a large range of normal tissue irradiated volume is also existed. The study about radiation dosimetry affected by individual identified bladder ITV in bladder cancerObjective:The radiation treatment plans, Plan A, Plan B and Plan C were designed separately by an adaptive individual bladder ITV, an uniform or non-uniform expansion bladder ITV. Radiation dose received by the bladder ITV and surrounding normal tissues in these three different plans were compared.Materials and Methods:From October 2008 to December 2010,12 patients with bladder cancer who received radiotherapy in our hospital were included in this study. 0.8mm outside expansion of three different ITV obtained from partⅢ, corresponding PTVA, PTVB and PTVC was established. All the plans were designed with reverse beam IMRT technique. PTV2 was defined from a tumor boost irradiation volume. Make sure all treatment plans were generated to prescription dose on PTVs and limiting doses on organs at risk according to standard, then copy PTVA to Plan B and C to observe the dose of 95% PTVA and 99% PTVA on the three plans. Dosage of 99% PTVA lower than 95% of prescription dose was considered as an existing of unacceptable radiation leakage. The lowest dose received on 95% and 99% PTVA volume was registered, the volume beyond PTVA but within the 41.8Gy isodose(95% isodose) was defined as VA(4180-PTVA),VB(4180-PTVA)and VC(4180-PTVA), and their average dosage reflected the extra irradiation volume and dose of normal tissues was recorded.Results:All the three plans were designed achieving the planned requirements. In Plan A, lowest dosage on 95% and 99% of PTVA were 44.17Gy±0.21Gy and 43.42Gy±0.58Gy, both were in line with required dose. Copy PTVA to Plan B,95% and 99% of PTVA received 42.66Gy±4.33Gy and 35.72Gy±9.93Gy, unacceptable irradiation leakage occurred in 7 patients (Dosage on 99% of PTVA was less than 41.8Gy). Copy PTVA to Plan C,95% and 99% of PTVA got a dosage of 44.21Gy±1.17Gy,41.06Gy±6.16Gy on average. There were 4 unacceptable irradiation leakages in plan C. The number of irradiation leakage had a significant difference between Plan A and Plan B (P=0.005), but was not statistically different between Plan A and Plan C (P=0.093). The volume of VA(4180-PTVA),、VB(4180-PTVA) and VC(4180-PTVA) was 97.47±39.18ml,390.98±119.67ml and 471.57±124.93ml (Plan A vs. Plan B, P=0.000; Plan A vs. Plan C,P=0.000), the average dosage of them was 42.99±0.32Gy, 44.41±0.29Gy and 44.56±0.22Gy (Plan A vs. Plan B, P=0.000; Plan A vs. Plan C, P=0.000). Conclusion:A radiation treatment plan based on an isotropic or an anisotropic expansion ITV exists unacceptable irradiation leakage and excessive irradiation of normal tissues surrounding the bladder, so determination of an individual bladder ITV in bladder cancer treatment planning is valuable. |
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