利用四维锥形束CT指导肺癌内靶区的勾画

目的 研究四维锥形束CT(4D-CBCT)指导肺癌内靶区勾画的可行性。方法 简单随机法选取本院24例肺癌患者。平静呼吸下CT模拟定位获得CT图像,首次治疗前4D-CBCT扫描获得4D-CBCT中位图像,将4D图像重建算法更改为3D,获得3D-CBCT图像。图像融合算法取骨配准,分别在定位CT、4D-CBCT中位图像、3D-CBCT图像上勾画大体肿瘤靶区(GTV),定义GTV到临床靶区(CTV)的外扩边界为7 mm,获得CTV_CT、ITV_4D和ITV_3D,基于CTV_CT在三维方向上外扩5 mm得到ITV_CT。比较靶区间中心点位置、体积、相似度和相互包含关系的差异。结果 ITV_CT与ITV_3D在中下叶组的头脚方向上,靶区中心点位置差异有统计学意义(Z=-2.027,P<0.05)。在靶区体积方面,ITV_CT最大,与ITV_3D相比差异有统计学意义(Z=-2.941,P<0.05),ITV_4D最小,但与ITV_3D相比差异无统计学意义(P>0.05)。ITV_CT与ITV_3D相似度均数<75%,ITV_4D与ITV_3D相似度均数>90%(Z=-2.940、-2.975,P<0.05)。ITV_CT、ITV_4D未被ITV_3D包含的比例均数为40%和5%(Z=-2.952、-3.185,P<0.05)。结论 4D-CBCT的中位图像可以缩小内靶区的勾画范围,为肺癌的自适应放疗提供选择。     

基于3D-CT、4D-CT和锥形束CT定义的非小细胞肺癌内靶区比较

目的 比较基于三维CT（3D-CT）、四维CT（4D-CT）和锥形束CT（CBCT）图像定义的非小细胞肺癌（NSCLC）内靶区（ITV）位置和体积差异。方法 31例周围型NSCLC患者,完成胸部3D-CT和4D-CT定位扫描,放疗首次拍摄CBCT。在3D-CT、4D-CT最大密度投影（MIP）、CBCT图像上勾画大体肿瘤靶区（GTV）,定义GTV到临床靶区（CTV）的外扩边界为7 mm,获得CTV_3D、ITV_MIP 和ITV_CBCT。基于CTV_3D在左右、前后方向外扩5 mm,头脚方向外扩5 mm得到ITV_{5 mm}、外扩10 mm得到ITV_{10 mm}。比较靶区间位置、体积、相似度和相互包含关系差异。结果 肺上叶组中,ITV_{10 mm}、ITV_{5 mm}、ITV_MIP 和ITV_CBCT的中位比值分别为2.33、1.88和1.03,中下叶组的分别为2.13、1.76和1.10,两组间差异均无统计学意义。全组ITV_MIP 与ITV_CBCT间相似度的中位数为0.83,大于ITV_{10 mm} 与ITV_CBCT间（0.60）和ITV_5mm 与ITV_CBCT间的相似度（0.66）（Z=-4.86、-4.86,P<0.05）。全组ITV_CBCT未被ITV_{10 mm}、ITV_{5 mm}、ITV_MIP 包含比例的中位数分别为0.10%、1.63%和15.21%,而ITV_{10 mm}、ITV_{5 mm}、ITV_MIP未被ITV_CBCT包含的比例分别为57.08%、48.89%和20.04%。肺上叶组和中下叶组ITV_CBCT未被ITV_{5 mm}包含比例的中位数为1.24%和5.8%,两组差异无统计学意义。结论 基于4D-CT定义的个体化ITV不能有效地包含基于CBCT定义的在线ITV,利用源于4D-CT的ITV制定放疗计划,可能导致脱靶。基于常规3D-CT均匀外扩定义的ITV能够较好包含源于CBCT的ITV,但体积远远大于后者。     

诊断PET-CT用于食管癌原发肿瘤大体肿瘤体积勾画的比较研究

目的 比较单纯参考诊断¹⁸F-FDG PET-CT（PET-CT）在3D-CT上勾画的食管原发肿瘤大体肿瘤体积（GTV）与利用3D-CT和诊断PET-CT形变配准后勾画的GTV体积和位置差异。方法 选择在本院行同步放化疗的胸段食管癌患者72例,所有患者放疗前均行诊断PET-CT扫描和常规3D-CT模拟定位扫描。单纯基于常规3D-CT勾画GTV定义为GTV_3D,参考诊断PET-CT在3D-CT上勾画的GTV定义为GTV_PET-ref,基于3D-CT和诊断PET-CT形变配准图像上勾画的GTV定义为GTV_PET-reg。比较3种GTV剂量指标间的差异。结果 全组患者GTV_3D、GTV_PET-ref、GTV_PET-reg靶区中位体积分别为44.90、40.36、41.15 cm³,各靶区间体积大小差异无统计学意义（P>0.05）。三者靶区平均长度分别为8.54、9.29、8.38 cm,GTV_PET-ref>GTV_3D（t=2.134,P<0.05）。GTV_PET-ref对GTV_3D、GTV_PET-reg对GTV_3D的中位包含度（DI）值分别为0.86、0.82,两者间差异有统计学意义（Z=-2.741,P<0.05）;GTV_3D对 GTV_PET-ref、GTV_3D对GTV_PET-reg的中位DI值分别为0.87、0.84,两者间差异有统计学意义（Z=-1.429,P<0.05）。GTV_3D与GTV_PET-ref、GTV_3D与GTV_PET-reg的中位适形指数（CI）值分别为0.72、0.68,两者间差异有统计学意义（Z=2.756,P<0.05）。GTV_3D与GTV_PET-ref、GTV_3D与GTV_PET-reg、GTV_PET-ref与GTV_PET-reg的CI与靶区中心间距均呈显著负相关（P<0.05）。结论 参考诊断PET-CT在靶区体积大小及靶区空间位置与基于诊断PET-CT形变配准所勾画食管癌原发肿瘤GTV差异均无统计学意义,因此,建议放疗医生可以参照治疗前近期的诊断PET-CT勾画食管癌原发肿瘤GTV。     

基于锥形束CT的头颈部肿瘤在线与离线结合图像引导放疗的研究

目的 分析锥形束CT(CBCT)在线摆位校正与离线自适应校正在减小头颈部肿瘤临床靶区(CTV)外放,从而减轻正常组织并发症中的作用。方法 16例行三维适形放疗的头颈部癌症患者入组。分次放疗前后均行在线CBCT扫描1次,并与计划CT图像配准,记录各个方向的配准差值。放疗前后的配准差值分别作为放疗分次间误差和分次内误差,用于计算每例患者的系统误差和随机误差。利用CTV外放计算公式,计算在线校正前后CTV外放;以0.5 mm为允许的最大残余系统误差,计算离线校正系统摆位误差后CTV外放。结果 未经在线校正,左右、头脚和前后方向上群体化CTV外放分别为5.7 mm、5.6 mm和7.3 mm;每分次放疗均行在线校正,3个方向上群体化CTV外放分别为1.7 mm、1.7 mm和2.3 mm;对系统摆位误差进行离线自适应校正,3个方向上群体化CTV外放分别为2.7 mm、2.5 mm和3.6 mm。结论 基于CBCT图像分析的在线校正和离线自适应校正均能明显减小摆位误差,有助于缩小CTV外放,并有望减轻正常组织并发症。     

基于锥形束CT的头颈部肿瘤在线与离线结合图像引导放疗的研究

目的 分析锥形束CT(CBCT)在线摆位校正与离线自适应校正在减小头颈部肿瘤临床靶区(CTV)外放,从而减轻正常组织并发症中的作用.方法 16例行三维适形放疗的头颈部癌症患者入组.分次放疗前后均行在线CBCT扫描1次,并与计划CT图像配准,记录各个方向的配准差值.放疗前后的配准差值分别作为放疗分次间误差和分次内误差,用于计算每例患者的系统误差和随机误差.利用CTV外放计算公式,计算在线校正前后CTV外放;以0.5 mm为允许的最大残余系统误差,计算离线校正系统摆位误差后CTV外放.结果 未经在线校正,左右、头脚和前后方向上群体化CTV外放分别为5.7mm、5.6 mm和7.3 mm;每分次放疗均行在线校正,3个方向上群体化CTV外放分别为1.7 mm、1.7 mm和2.3 mm;对系统摆位误差进行离线自适应校正,3个方向上群体化CTV外放分别为2.7 mm、2.5mm和3.6 mm.结论 基于CBCT图像分析的在线校正和离线自适应校正均能明显减小摆位误差,有助于缩小CTV外放,并有望减轻正常组织并发症.     

基于锥形束CT的头颈部肿瘤在线与离线结合图像引导放疗的研究

目的 分析锥形束CT(CBCT)在线摆位校正与离线自适应校正在减小头颈部肿瘤临床靶区(CTV)外放,从而减轻正常组织并发症中的作用.方法 16例行三维适形放疗的头颈部癌症患者入组.分次放疗前后均行在线CBCT扫描1次,并与计划CT图像配准,记录各个方向的配准差值.放疗前后的配准差值分别作为放疗分次间误差和分次内误差,用于计算每例患者的系统误差和随机误差.利用CTV外放计算公式,计算在线校正前后CTV外放;以0.5 mm为允许的最大残余系统误差,计算离线校正系统摆位误差后CTV外放.结果 未经在线校正,左右、头脚和前后方向上群体化CTV外放分别为5.7mm、5.6 mm和7.3 mm;每分次放疗均行在线校正,3个方向上群体化CTV外放分别为1.7 mm、1.7 mm和2.3 mm;对系统摆位误差进行离线自适应校正,3个方向上群体化CTV外放分别为2.7 mm、2.5mm和3.6 mm.结论 基于CBCT图像分析的在线校正和离线自适应校正均能明显减小摆位误差,有助于缩小CTV外放,并有望减轻正常组织并发症.     

基于锥形束CT的头颈部肿瘤在线与离线结合图像引导放疗的研究

目的 分析锥形束CT(CBCT)在线摆位校正与离线自适应校正在减小头颈部肿瘤临床靶区(CTV)外放,从而减轻正常组织并发症中的作用.方法 16例行三维适形放疗的头颈部癌症患者入组.分次放疗前后均行在线CBCT扫描1次,并与计划CT图像配准,记录各个方向的配准差值.放疗前后的配准差值分别作为放疗分次间误差和分次内误差,用于计算每例患者的系统误差和随机误差.利用CTV外放计算公式,计算在线校正前后CTV外放;以0.5 mm为允许的最大残余系统误差,计算离线校正系统摆位误差后CTV外放.结果 未经在线校正,左右、头脚和前后方向上群体化CTV外放分别为5.7mm、5.6 mm和7.3 mm;每分次放疗均行在线校正,3个方向上群体化CTV外放分别为1.7 mm、1.7 mm和2.3 mm;对系统摆位误差进行离线自适应校正,3个方向上群体化CTV外放分别为2.7 mm、2.5mm和3.6 mm.结论 基于CBCT图像分析的在线校正和离线自适应校正均能明显减小摆位误差,有助于缩小CTV外放,并有望减轻正常组织并发症.     

基于锥形束CT的头颈部肿瘤在线与离线结合图像引导放疗的研究

目的 分析锥形束CT(CBCT)在线摆位校正与离线自适应校正在减小头颈部肿瘤临床靶区(CTV)外放,从而减轻正常组织并发症中的作用.方法 16例行三维适形放疗的头颈部癌症患者入组.分次放疗前后均行在线CBCT扫描1次,并与计划CT图像配准,记录各个方向的配准差值.放疗前后的配准差值分别作为放疗分次间误差和分次内误差,用于计算每例患者的系统误差和随机误差.利用CTV外放计算公式,计算在线校正前后CTV外放;以0.5 mm为允许的最大残余系统误差,计算离线校正系统摆位误差后CTV外放.结果 未经在线校正,左右、头脚和前后方向上群体化CTV外放分别为5.7mm、5.6 mm和7.3 mm;每分次放疗均行在线校正,3个方向上群体化CTV外放分别为1.7 mm、1.7 mm和2.3 mm;对系统摆位误差进行离线自适应校正,3个方向上群体化CTV外放分别为2.7 mm、2.5mm和3.6 mm.结论 基于CBCT图像分析的在线校正和离线自适应校正均能明显减小摆位误差,有助于缩小CTV外放,并有望减轻正常组织并发症.     

基于锥形束CT的头颈部肿瘤在线与离线结合图像引导放疗的研究

目的 分析锥形束CT(CBCT)在线摆位校正与离线自适应校正在减小头颈部肿瘤临床靶区(CTV)外放,从而减轻正常组织并发症中的作用.方法 16例行三维适形放疗的头颈部癌症患者入组.分次放疗前后均行在线CBCT扫描1次,并与计划CT图像配准,记录各个方向的配准差值.放疗前后的配准差值分别作为放疗分次间误差和分次内误差,用于计算每例患者的系统误差和随机误差.利用CTV外放计算公式,计算在线校正前后CTV外放;以0.5 mm为允许的最大残余系统误差,计算离线校正系统摆位误差后CTV外放.结果 未经在线校正,左右、头脚和前后方向上群体化CTV外放分别为5.7mm、5.6 mm和7.3 mm;每分次放疗均行在线校正,3个方向上群体化CTV外放分别为1.7 mm、1.7 mm和2.3 mm;对系统摆位误差进行离线自适应校正,3个方向上群体化CTV外放分别为2.7 mm、2.5mm和3.6 mm.结论 基于CBCT图像分析的在线校正和离线自适应校正均能明显减小摆位误差,有助于缩小CTV外放,并有望减轻正常组织并发症.     

基于锥形束CT的头颈部肿瘤在线与离线结合图像引导放疗的研究

目的 分析锥形束CT(CBCT)在线摆位校正与离线自适应校正在减小头颈部肿瘤临床靶区(CTV)外放,从而减轻正常组织并发症中的作用.方法 16例行三维适形放疗的头颈部癌症患者入组.分次放疗前后均行在线CBCT扫描1次,并与计划CT图像配准,记录各个方向的配准差值.放疗前后的配准差值分别作为放疗分次间误差和分次内误差,用于计算每例患者的系统误差和随机误差.利用CTV外放计算公式,计算在线校正前后CTV外放;以0.5 mm为允许的最大残余系统误差,计算离线校正系统摆位误差后CTV外放.结果 未经在线校正,左右、头脚和前后方向上群体化CTV外放分别为5.7mm、5.6 mm和7.3 mm;每分次放疗均行在线校正,3个方向上群体化CTV外放分别为1.7 mm、1.7 mm和2.3 mm;对系统摆位误差进行离线自适应校正,3个方向上群体化CTV外放分别为2.7 mm、2.5mm和3.6 mm.结论 基于CBCT图像分析的在线校正和离线自适应校正均能明显减小摆位误差,有助于缩小CTV外放,并有望减轻正常组织并发症.     

Segmentation process significantly influences the accuracy of 3D surface models derived from cone beam computed tomography

Aims

To assess the accuracy of surface models derived from 3D cone beam computed tomography (CBCT) with two different segmentation protocols.

Materials and methods

Seven fresh-frozen cadaver heads were used. There was no conflict of interests in this study. CBCT scans were made of the heads and 3D surface models were created of the mandible using two different segmentation protocols. The one series of 3D models was segmented by a commercial software company, while the other series was done by an experienced 3D clinician. The heads were then macerated following a standard process. A high resolution laser surface scanner was used to make a 3D model of the macerated mandibles, which acted as the reference 3D model or “gold standard”. The 3D models generated from the two rendering protocols were compared with the “gold standard” using a point-based rigid registration algorithm to superimpose the three 3D models. The linear difference at 25 anatomic and cephalometric landmarks between the laser surface scan and the 3D models generate from the two rendering protocols was measured repeatedly in two sessions with one week interval.

Results

The agreement between the repeated measurement was excellent (ICC = 0.923–1.000). The mean deviation from the gold standard by the 3D models generated from the CS group was 0.330 mm ± 0.427, while the mean deviation from the Clinician's rendering was 0.763 mm ± 0.392. The surface models segmented by both CS and DS protocols tend to be larger than those of the reference models. In the DS group, the biggest mean differences with the LSS models were found at the points ConLatR (CI: 0.83–1.23), ConMedR (CI: −3.16 to 2.25), CoLatL (CI: −0.68 to 2.23), Spine (CI: 1.19–2.28), ConAntL (CI: 0.84–1.69), ConSupR (CI: −1.12 to 1.47) and RetMolR (CI: 0.84–1.80).

Conclusion

The Commercially segmented models resembled the reality more closely than the Doctor's segmented models. If 3D models are needed for surgical drilling guides or surgical planning which requires high precision, the additional cost of the commercial segmentation services seem to be justified to produce a more accurate surface models.     

Use of cone beam computed tomography in periodontology

Diagnosis of periodontal disease mainly depends on clinical signs and symptoms. However, in the case of bone destruction, radiographs are valuable diagnostic tools as an adjunct to the clinical examination. Two dimensional periapical and panoramic radiographs are routinely used for diagnosing periodontal bone levels. In two dimensional imaging, evaluation of bone craters, lamina dura and periodontal bone level is limited by projection geometry and superpositions of adjacent anatomical structures. Those limitations of 2D radiographs can be eliminated by three-dimensional imaging techniques such as computed tomography. Cone beam computed tomography (CBCT) generates 3D volumetric images and is also commonly used in dentistry. All CBCT units provide axial, coronal and sagittal multi-planar reconstructed images without magnification. Also, panoramic images without distortion and magnification can be generated with curved planar reformation. CBCT displays 3D images that are necessary for the diagnosis of intra bony defects, furcation involvements and buccal/lingual bone destructions. CBCT applications provide obvious benefits in periodontics, however; it should be used only in correct indications considering the necessity and the potential hazards of the examination.     

An audit of image quality of three dental cone beam computed tomography units

Critical analysis of cone beam computed tomography (CBCT) image quality is recommended as part of a quality assurance program.^1,2 There are few papers³ in the literature concerning subjective image quality on CBCT imaging.This study, performed as part of an audit, reviewed all images of the jaws performed on three different CBCT units over a twelve month period. Images were graded according to an agreed standard¹ and reasons for image rejection recorded.The results demonstrated that the main reasons for image rejection were motion artefact and problems with field of view size and positioning.The need for reducing the number of rejected images in order to optimize patient dose, and ways to achieve this, are discussed     

Implagraphy牙颌面锥形束CT不同扫描体位的辐射剂量对比研究

目的 测算Implagraphy牙颌面锥形束CT(CBCT)体模不同扫描体位的组织器官吸收剂量、当量剂量及有效剂量,为相应的防护措施提供客观依据。方法 使用仿真成年男性头颈部体模及热释光剂量计,分别测量Implagraphy CBCT下颌、上颌及颞下颌关节(TMJ)扫描时脑垂体、眼晶状体、腮腺、颌下腺、舌下腺、颅骨板障、下颌松质骨、颈椎松质骨、颊部皮肤、颈部皮肤、甲状腺、食管及口腔黏膜等组织器官的吸收剂量,计算眼晶状体、皮肤的当量剂量,及Implagraphy CBCT不同扫描体位的有效剂量E₁₉₉₀及E₂₀₀₇。结果 Implagraphy CBCT各扫描体位的吸收剂量分别为:下颌扫描(0.99±0.09)~(12.85±0.09)mGy,上颌扫描(0.93±0.01)~(13.07±0.02)mGy,TMJ扫描(0.68±0.01)~(10.18±0.04)mGy,相同组织器官在不同扫描体位的吸收剂量的差异具有统计学意义(F=19.61~30992.27,P<0.05)。在不同扫描体位,眼晶状体及皮肤的当量剂量分别为(1.11±0.07)~(5.76±0.06)mSv和(6.96±0.06)~(10.64±0.07)mSv,差异具有统计学意义(F=4473.02、9385.50,P<0.05)。有效剂量E₁₉₉₀及E₂₀₀₇分别为:下颌扫描(191.35±1.53)和(325.17±2.58)μSv,上颌扫描(106.62±2.17)和(226.28±2.81)μSv,TMJ扫描(104.21±1.02)和(142.36±1.90)μSv。结论 在牙颌面CBCT检查过程中,采用尽可能小的扫描视野、准确地扫描体位,正确使用铅胶帽、围领及防护镜等屏蔽措施,使X射线辐射照射保持在可以合理达到的尽可能低的水平。     

The usage of digital radiography and cone beam computed tomography among Turkish dentists

Objectives

The aim of this study was to determine the prevalence of the use of digital radiography and report how it was used by Turkish dentists.

Methods

The survey was based on 383 dentists who were present at the sixteenth International Congress organized by the Turkish Dental Association. A questionnaire which consisted of 19 questions was given to the dentists who participated in the study. Data were assessed according to frequency distribution and the χ² test was used to determine the significance of differences between two independent groups.

Results

376 questionnaires were analysed. The mean age of the dentists who participated in the study was 37.14 ± 9.6 years (range: 20–63 years). The distribution of the dentists according to the 7 regions of Turkey were: Marmara 58%, Aegean 13% and Mediterranean 10%, Central Anatolia 8%, Black Sea 7%, Southeastern Anatolia 3%, Eastern Anatolia 1%. 124 dentists (33%) said they did not work with digital radiography. 95 dentists indicated that they did not use digital radiography owing to cost (60%). 252 dentists (67%) said they used digital radiography. 40% of the participants noted that the repetition of periapical radiographs was due to digital radiography. 166 dentists (55.9%) and 79.1% academicians had knowledge about cone beam CT (CBCT).

Conclusion

Digital radiography users are increasing in Turkey and levels of knowledge of CBCT and awareness of radiation safety has also increased.     

Dimensional stability in composite cone beam computed tomography

An automated increase in the field of view (FOV) for multipurpose cone beam CT (CBCT) by "stitching" (joining) up to three component volumes to yield a larger composite volume must still ensure dimensional stability, especially if the image is to form the basis for a surgical splint. Dimensional stability, image discrepancies and the influence of movement artefacts between exposures were evaluated. The first consumer installation of the Kodak 9000 three-dimensional (3D) extraoral imaging system with stitching software was used for the evaluation of a human mandible with three endodontic instruments as markers. The distances between several reproducible points were measured directly and the results compared with the values measured on screen. Displacements of the mandible along all axes between exposures as well as angular displacements were conducted to test the capability of the system. The standard deviations (SD) of the results for the vertical distances varied between 0.212 mm and 0.409 mm (approximately 1-2 voxels; range, 0.6-1.3 mm) and may be considered the systematic error. The SD of the results for the horizontal and diagonal distances varied between 0.195 mm and 0.571 mm (approximately 1-3 voxels; range, 0.6-1.7 mm) if the group with overall horizontal angulations of 10° and a central rotation of 20° was omitted. In conclusion, the evaluated stitching software is a useful tool to expand the options of combined CBCT with an initial small FOV by allowing a merger of up to three component volumes to yield a larger FOV of about 80 × 80 × 37 mm. The dimensional stability was acceptable when seen in relation to the induced disturbance. Further evaluation of this composite CBCT/digital imaging and communications in medicine system for subsequent splint fabrication may yield promising results.     

Optimization of exposure parameters for cone beam computed tomography sialography

Objectives

The assessment of image quality is a crucial step in the development of a new imaging protocol. Having proposed and reported on a preliminary protocol for sialography using cone beam CT (CBCT), the purpose of this study was to further optimize this protocol by maximizing the image signal difference-to-noise ratio (SDNR) and to relate these new data to previously published dosimetric data for CBCT sialography.

Methods

An imaging phantom was constructed using samples with different concentrations of iodine and a water-immersed mandible. The CB MercuRay (Hitachi Medical Systems, Tokyo, Japan) was used to image the phantom using different peak kilovoltage (kVp) and milliamperage (mA) settings. SDNR was then calculated using the raw images based on mean pixel values (MPV) measured in selected regions of interest (ROI). Finally, a figure of merit (FOM) was calculated to examine the trade-off between image SDNR and effective radiation dose.

Results

The SDNR demonstrated an expected increase as the kVp increased from 60 to 120. Also, images made with the higher mA setting (15) had greater SDNR. The iodine concentration also influenced the image quality such that SDNR increased with increased amounts of iodine. The calculated FOM was greatest for the technique using 80 kVp, with equivalent results for 10 mA and 15 mA.

Conclusion

An optimized protocol for CBCT sialography using CB MercuRay entails a 6 inch field of view with 80 kVp and 10 mA.     

勾画者及勾画标准对基于4D-CT周围型肺癌靶区勾画的影响

目的 探讨勾画者及勾画标准对基于4D-CT周围型肺癌原发肿瘤靶区勾画的影响。方法 选择12例行4D-CT模拟定位扫描的周围型肺癌患者,在勾画标准制定前后,6名放疗医生分别在4D-CT的吸气末时相(0%)、呼气末时相(50%)和3D-CT图像上勾画大体肿瘤体积GTV₀、GTV₅₀和GTV_3D,GTV₀和GTV₅₀分别融合得到勾画标准制定前后的内大体肿瘤体积IGTV_IN+EX,在4D-CT的最大密度投影(MIP)图像上勾画内大体肿瘤体积IGTV_MIP。对勾画标准制定前后同一勾画者及勾画者之间靶区勾画进行比较。结果 勾画标准制定前后,6位勾画者所勾画的GTV₀、GTV₅₀、GTV_3D、IGTV_MIP及融合靶区IGTV_IN+EX的平均变异系数为0.50±0.25和0.24±0.10,0.52±0.38和0.26±0.12,0.45±0.19和0.20±0.07, 0.54±0.27和0.23±0.09,0.44±0.23和0.26±0.09,两两间差异有统计学意义(t=3.38、2.44、3.60、4.20、3.11,P<0.05);勾画标准制定前及后6位不同勾画者所勾画GTV₀、GTV₅₀、GTV_3D、IGTV_MIP中同一靶区体积间差异无统计学意义;勾画者3、6在标准制定前后所勾画GTV₀、GTV₅₀及IGTV_IN+EX差异有统计学意义(t=2.46、2.91、3.28,P<0.05;t=2.40、2.79、3.22,P<0.05),勾画者4所勾画GTV₀、GTV₅₀、IGTV_IN+EX、IGTV_MIP、GTV_3D前后差异有统计学意义(t=2.70、3.21、3.04、3.99、3.00,P<0.05)。结论 无论基于3D-CT还是4D-CT图像勾画周围型肺癌GTV或基于4D-CT勾画其IGTV_MIP,就勾画者群体而言,统一的勾画标准指导可减少勾画者间的差异,但对勾画者个体而言,统一的勾画标准对其勾画某一特定靶区的影响不一。     

A study on planning organ at risk volume for the rectum using cone beam computed tomography in the treatment of prostate cancer

In this study, we analyzed planning organ at risk volume (PRV) for the rectum using a series of cone beam computed tomographies (CBCTs) acquired during the treatment of prostate cancer and evaluated the dosimetric effect of different PRV definitions. Overall, 21 patients with prostate cancer were treated radically with 78 Gy in 39 fractions had in total 418 CBCTs, each acquired at the end of the first 5 fractions and then every alternate fraction. The PRV was generated from the Boolean sum volume of the rectum obtained from first 5 fractions (PRV-CBCT-5) and from all CBCTs (PRV-CBCT-All). The PRV margin was compared at the superior, middle, and inferior slices of the contoured rectum to compare PRV-CBCT-5 and PRV-CBCT-All. We also compared the dose received by the planned rectum (Rectum-computed tomography [CT]), PRV-CBCT-5, PRV-CBCT-All, and average rectum (CBCT-AV-dose-volume histogram [DVH]) at critical dose levels. The average measured rectal volume for all 21 patients for Rectum-CT, PRV-CBCT-5, and PRV-CBCT-All was 44.3 ± 15.0, 92.8 ± 40.40, and 121.5 ± 36.7 cm³, respectively. For PRV-CBCT-All, the mean ± standard deviation displacement in the anterior, posterior, right, and left lateral directions in centimeters was 2.1 ± 1.1, 0.9 ± 0.5, 0.9 ± 0.8, and 1.1 ± 0.7 for the superior rectum; 0.8 ± 0.5, 1.1 ± 0.5, 1.0 ± 0.5, and 1.0 ± 0.5 for the middle rectum; and 0.3 ± 0.3; 0.9 ± 0.5; 0.4 ± 0.2, and 0.5 ± 0.3 for the inferior rectum, respectively. The first 5 CBCTs did not predict the PRV for individual patients. Our study shows that the PRV margin is different for superior, middle, and the inferior parts of the rectum, it is wider superiorly and narrower inferiorly. A uniform PRV margin does not represent the actual rectal variations during treatment for all treatment fractions. The large variation in interpatient rectal size implies a potential role for adaptive radiotherapy for prostate cancer.