Differences in abdominal organ movement between supine and prone positions measured using four-dimensional computed tomography.

BACKGROUND AND PURPOSE: To analyze the differences in intrafractional organ movement throughout the breathing cycles between the supine and prone positions using four-dimensional computed tomography (4D CT). MATERIALS AND METHODS: We performed 4D CT on nine volunteers in the supine and prone positions, with each examinee asked to breathe normally during scanning. The movement of abdominal organs in the cranio-caudal (CC), anterior-posterior (AP) and right-left (RL) directions was quantified by contouring on each phase between inspiration and expiration. RESULTS: The mean intrafractional motions of the hepatic dome, lower tip, pancreatic head and tail, both kidneys, spleen, and celiac axis in the supine/prone position were 17.3/13.0, 14.4/11.0, 12.8/8.9, 13.0/10.0, 14.3/12.1, 12.3/12.6, 11.7/12.6 and 2.2/1.8mm, respectively. Intrafractional movements of the liver dome and pancreatic head were reduced significantly in the prone position. The CC directional excursions were major determinants of the 3D displacements of the abdominal organs. Alteration from the supine to the prone position did not change the amount of intrafractional movements of kidneys, spleen, and celiac axis. CONCLUSION: There was a significant reduction in the movements of the liver and pancreas during the prone position, especially in the CC direction, suggesting possible advantage of radiotherapy to these organs in this position.     

基于4DCT的腹部器官呼吸运动分析

背景与目的：个体化准确测量器官的呼吸移动度是确定腹部肿瘤体内边界（internal margin，IM）的前提。本研究应用4DCT（four-dimensional computed tomograpy）测量腹部器官在三维方向的呼吸移动度，并进一步分析膈肌与各器官移动度的关系。方法：选择13例肝癌患者行4DCT扫描，其中5例患者合并腹主动脉旁淋巴结转移。在10个呼吸时相的CT图像中分别勾画不同的器官，包括肝脏、双肾、胰腺、脾及腹主动脉旁淋巴结。在4DCT中测量膈肌及腹部各器官在三维方向的呼吸移动度，并分析膈肌移动度与各器官移动度是否相关。结果：膈肌在头尾方向的移动度为（10.3±4．0）mm，个体差异明显。肝、左右肾脏、胰腺、脾、腹主动脉旁淋巴结在头尾方向的移动度分别为（10．1±3．9）mm、（9．3±2．9）mm、（9．6±4．1）mm、（7．6±3．0）mm、（10．6±3．3）mm、（5．7±1．8）mm。肝脏、右肾的移动度与膈肌移动度无明显差异，且呈高度线性正相关关系；左肾、胰腺、脾的移动度与膈肌动度无明显相关；双侧肾脏的移动度相仿，但一侧肾脏的运动度并不能预测对侧肾脏的运动度。结论：应用4DCT可准确测量腹部器官在三维各方向的呼吸运动度。膈肌移动度可以代表肝脏和右肾头尾方向的运动度。而腹主动脉旁淋巴结的移动度相对较小。     

Extracranial stereotactic radiation therapy: set-up accuracy of patients treated for liver metastases

PURPOSE: Patients with liver metastases might benefit from high-dose conformal radiation therapy. A high accuracy of repositioning and a reduction of target movement are necessary for such an approach. The set-up accuracy of patients with liver metastases treated with stereotactic single dose radiation was evaluated. METHODS AND MATERIALS: Twenty-four patients with liver metastases were treated with single dose radiation therapy on 26 occasions using a self-developed stereotactic frame. Liver movement was reduced by abdominal pressure. The effectiveness was evaluated under fluoroscopy. CT scans were performed on the planning day and directly before treatment. Representative reference marks were chosen and the coordinates were calculated. In addition, the target displacement was quantitatively evaluated after treatment. RESULTS: Diaphragmal movement was reduced to median 7 mm (range: 3-13 mm). The final set-up accuracy of the body was limited to all of median 1.8 mm in latero-lateral direction (range: 0.3-5.0 mm) and 2.0 mm in anterior-posterior direction (0.8-3.8 mm). Deviations of the body in cranio-caudal direction were always less than the thickness of one CT slice (<5 mm). However, a repositioning was necessary in 16 occasions. The final target shift was median 1.6 mm (0.2-7.0 mm) in latero-lateral and 2.3 mm in anterior-posterior direction (0.0-6.3 mm). The median shift in cranio-caudal direction was 4.4 mm (0.0-10.0 mm). CONCLUSIONS: In patients with liver metastases, a high set-up accuracy of the body and the target can be achieved. This allows a high-dose focal radiotherapy of these lesions. However, a control CT scan should be performed directly before therapy to confirm set-up accuracy and possibly prompt necessary corrections.     

Differences in abdominal organ movement between supine and prone positions measured using four-dimensional computed tomography

Background and purposeTo analyze the differences in intrafractional organ movement throughout the breathing cycles between the supine and prone positions using four-dimensional computed tomography (4D CT).Materials and methodsWe performed 4D CT on nine volunteers in the supine and prone positions, with each examinee asked to breathe normally during scanning. The movement of abdominal organs in the cranio–caudal (CC), anterior–posterior (AP) and right–left (RL) directions was quantified by contouring on each phase between inspiration and expiration.ResultsThe mean intrafractional motions of the hepatic dome, lower tip, pancreatic head and tail, both kidneys, spleen, and celiac axis in the supine/prone position were 17.3/13.0, 14.4/11.0, 12.8/8.9, 13.0/10.0, 14.3/12.1, 12.3/12.6, 11.7/12.6 and 2.2/1.8 mm, respectively. Intrafractional movements of the liver dome and pancreatic head were reduced significantly in the prone position. The CC directional excursions were major determinants of the 3D displacements of the abdominal organs. Alteration from the supine to the prone position did not change the amount of intrafractional movements of kidneys, spleen, and celiac axis.ConclusionThere was a significant reduction in the movements of the liver and pancreas during the prone position, especially in the CC direction, suggesting possible advantage of radiotherapy to these organs in this position.     

子宫颈癌俯卧位调强放射治疗摆位误差分析

目的研究子宫颈癌俯卧位调强放射治疗的摆位误差大小,为子宫颈癌调强放疗计划设计临床靶区体积（CTV）外放计划靶区体积（PTV）时提供参考数据。方法选取行俯卧位调强放射治疗的子宫颈癌患者6例,所有病例治疗时身下垫有孔泡沫板,热塑成形固定膜固定。连续5d治疗时用电子射野影像装置（EPID）拍射正侧位验证片各1张,共60张验证片,通过配准数字化重建图像（DRR）和EPID拍摄的验证片的骨性解剖结构,计算平移和旋转误差。结果平移误差：左右方向为（3．1±1．8）mm、头脚方向为（3．9±3．3）mm、腹背方向为（4．2±2．6）mm;旋转误差冠状面为（0．8±0．9）°、矢状面为（1．2±1）°。结论对于子宫颈癌俯卧位调强放射治疗,CTV到PTV的外放应为左右7．1mm、腹背10．8mm、头脚10.4mm,在患者身体上做摆位的标记线有助于减少摆位误差。     

Exhale fluctuation in respiratory-gated radiotherapy of the lung: a pitfall of respiratory gating shown in a synchronized internal/external marker recording study.

PURPOSE: For optimal respiratory-gated radiotherapy, exhale fluctuation was assessed by monitoring internal fiducials in a synchronized internal/external marker detection system. METHODS: Synchronized internal/external position data were collected during the entire course of treatments for 12 lung patients with 24 fiducials. Baseline was determined in the exhale phase during pre-treatment observation time, and a gating level of external waves was set in each treatment session in a simulation of respiratory-gated radiotherapy. Patients were treated under a real-time tumor-tracking (RTRT) system with an external (abdominal) respiratory motion detector. In the simulation, external gating windows were defined as those below the 30% amplitude level (i.e., imaginary beams would be triggered when part of the respiratory wave falls into this window). Exhale fluctuation (EF) was defined as the phenomenon in which the lowest point of the external wave crossed downward past the pre-determined baseline. Gating efficiency (GE) was defined as the ratio between the amount of gate-ON time and the total treatment time. RESULTS: EF occurred in 18.4% of total measurements. EF varied depending on the patient, fiducial sites, and treatment session. The mean incidence of EF for each patient varied from 2.9% to 37.5% (18.4+/-9.9). The EF magnitude was 0.2-12.2 mm in the left-right direction, 0.7-12.7 mm in the cranio-caudal direction, and 0.4-9.7 mm in the anterior-posterior direction. Total fiducial movement was 0.5-28.7 mm. GE was 36.1-69.2% (55.4+/-11.0). EF magnitude correlated with total fiducial movement. CONCLUSION: This study showed that EF is not a rare phenomenon and needs to be taken into consideration for individualized precise 4D radiotherapy.     

鼻咽癌放疗中个体化口腔支架的位置重复性

背景与目的：鼻咽癌放疗中佩戴个体化口腔支架可以保护口腔黏膜和舌．具有临床应用价值,本研究旨在探讨鼻咽癌放疗中个体化口腔支架在口腔中的位置重复性．明确其在放疗中应用的可行性。方法：选择17例初治鼻咽癌患者制作个体化口腔支架,并在口腔支架内埋入3个直径为2mm的铅点,患者戴口腔支架作面罩固定和CT扫描,放疗前及放疗中每周在常规模拟机下拍摄正侧位X线片,根据X线片计算和比较铅点在左右、前后和头脚方向的位移。在放疗40Gy时,戴原面罩并按照原来的位置标记点复查CT扫描．计算并比较两套CT图像问3个铅点和3个选择的骨性结构几何中心的位移有无差异。结果：得到240张X线片,铅点在左右、前后、头脚方向上的位移分别为（0．69±0．54）mm、（0．49±0．62）mm、（0．56±0．57）mm,三维矢量位移为（1．20＋0．77）mm（0-4．98mm）。三维方法显示3个铅点几何中心在左右、前后、头脚方向的位移分别为（0．75＋0．68）mm、（1．25±1．12）mm、（1．06±0．77）mm,三维矢量位移为（2．15±0．90）mm（1～4．24mm）。用ANOVA方法比较3个铅点和3个骨性结构几何中心在左右、前后、头脚方向上的位移及三维矢量位移,结果差异均无统计学意义（P〉0．05）。结论：鼻咽癌放疗中口腔支架在口腔中的位置重复性较好,可以和骨性结构之间形成一种固定的关系．其在鼻咽癌放疗中应用是可行的。     

Application of active breathing control in 3-dimensional conformal radiation therapy for hepatocellular carcinoma: the feasibility and benefit

BACKGROUND AND PURPOSE: To investigate the feasibility and effectiveness of utilizing active breathing coordinator (ABC) in 3DCRT for HCC. MATERIALS AND METHODS: A dosimetric comparison between the free-breathing (FB) plan and ABC plan in HCC 3DCRT was performed. Set-up errors and reproducibility of diaphragm position using ABC were measured, and patients' acceptance was also recorded. RESULTS: From April 2005 to February 2007, 28 HCC were irradiated with ABC and they tolerated ABC well. The mean dose to normal liver was reduced from 16.9Gy in FB plan to 14.3Gy in ABC plan. PTV for ABC and FB plans were 529cm(3) and 781cm(3), respectively, and V(23) were reduced from 45% to 30%. The predicted incidences of radiation-induced liver disease by Lyman model were 1% and 2.5%, respectively, in favor of ABC plan. The systematic and random errors for the ABC and FB plans were 1.2mm vs. 4.7mm, 1.6mm vs. 3.5mm, and 1.8mm vs. 2.7mm, respectively, in cranio-caudal, anterior-posterior, and left-right directions. The average intrafraction reproducibility of diaphragm position in cranio-caudal direction was 1.6mm, and the interfraction, 6.7mm. CONCLUSIONS: The utilization of ABC in HCC 3DCRT is feasible, and can reduce liver irradiation.     

Assessment of intrafractional movement and internal motion in radiotherapy of rectal cancer using megavoltage computed tomography

PURPOSE: The aim of this study was to provide estimates of setup and internal margins of patients treated for rectal carcinoma using helical tomotherapy and to assess possible margin adaptations. Using helical tomotherapy, highly conformal dose distributions can be created, and the integrated megavoltage computed tomography (MVCT) modality allows very precise daily patient positioning. In clinical protocols, however, margins originating from traditional setup procedures are still being applied. This work investigates whether this modality can aid in redefining treatment margins. METHODS AND MATERIALS: Ten patients who were treated with tomotherapy underwent MVCT scanning before and after 10 treatments. Using automatic registration the necessary setup margin was investigated by means of bony landmarks. Internal margins were assessed by delineating and describing the mesorectal movement. RESULTS: Based on bony landmarks, movement of patients during treatments was limited to 2.45 mm, 1.99 mm, and 1.09 mm in the lateral, longitudinal, and vertical direction, respectively. Systematic errors were limited to <1 mm. Measured movement of the mesorectal space was -1.6 mm (+/- 4.2 mm) and 0.1 mm (+/- 4.0 mm) for left and right lateral direction. In the antero-posterior direction, mean shifts were -2 mm (+/- 6.8 mm) and -0.4 mm (+/- 3.8 mm). Mean shifts in the cranio-caudal direction were respectively -3.2 mm (+/- 5.6 mm) and -3.2 mm (+/- 6.8 mm). CONCLUSIONS: The use of the integrated MVCT on the tomotherapy system can minimize the setup margin for rectal cancer, and can also be used to adequately describe the internal margin allowing for direct treatment margin adaptation.     

基于四维CT的平静呼吸状态下肾脏各方向运动幅度及影响因素分析

目的:探索平静呼吸状态下正常肾脏在三维方向的运动幅度及其相关的影响因素。方法:收集2018—2019年间行四维CT且能够平静呼吸的28例患者数据,肿瘤类别包括肝肿瘤、胰腺肿瘤或肺肿瘤。腹窗条件下逐层、逐呼吸时相勾画肾脏外轮廓并找到几何中心及三维方向坐标数值;计算左、右肾各个方向及三维方向位移。记录周围脏器体积及患者年龄...     

The use of magnetic sensors to monitor moderate deep inspiration breath hold during breast irradiation with dynamic MLC compensators.

BACKGROUND AND PURPOSE: To reduce the dose to the heart during left breast irradiation, a moderate deep breath hold technique (MDIBH) was introduced. Originally, verification of the MDIBH was performed with portal images acquired in movie loop during the treatment delivery. However, this verification method is not compatible with the use of dynamic MLC compensation, recently introduced because of its often superior dose distribution. Magnetic sensors were evaluated as an additional/alternative method to monitor the breath hold. MATERIAL AND METHODS: In a first phase, the reproducibility of MDIBH for breast patients was evaluated by investigating for 19 patients the set-up errors derived from portal images in cine loop acquisition during MDIBH. In a second phase, for 10 patients, the breathing curves recorded by magnetic sensors were used to monitor beam-on and beam-off while portal images were simultaneously recorded in movie loop. In a third phase, breast patients treated with dynamic MLC compensation were trained for MDIBH and monitored with magnetic sensors. RESULTS: The interfraction reproducibility of MDIBH for the initial 19 patients was recorded: the mean set-up error, the systematic and the random deviations are all smaller than 4mm in the anterior-posterior direction and in the cranio-caudal direction and smaller than 2 degrees along the rotation axis. Magnetic sensors provided a reproducible breathing curve: while the mean amplitude recorded for 10 patients varied substantially between patients, the individual standard deviation of the amplitude for each session was smaller than 3mm. For these 10 patients, the intrafraction set-up variation between the first portal image of two consecutive breath holds and the intra-breath hold set-up variation between the first and last portal image of each breath hold is smaller than 2mm in the anterior-posterior direction, smaller than 3mm in the cranio-caudal direction and smaller than 1.5 degrees along the rotation axis. CONCLUSION: Using magnetic sensors to record the breathing curve of left breast patients in MDIBH, a verification method was developed, suitable for combining MDIBH with dynamic MLC compensation.     

Semiautomated thoracic and abdominal computed tomography segmentation using the belief functions theory: application to 3D internal dosimetry

AIM: Segmentation of computed tomography (CT) images is an important step in three-dimensional (3D) internal dosimetry. To this end, a semiautomated method was developed to delineate organs, using the belief functions theory. MATERIALS AND METHODS: The membership degree of each voxel to each volume of interest is estimated by computing a basic belief assignment (bba). For each voxel V, bbas corresponding to each neighbor are aggregated to obtain a unique bba, using a merging procedure. Before aggregating information, a 3D filter is applied, in order to take into account the fact that the more the voxel V(i) is close to V, the more the information coming from V(i) is reliable. The aim is to weaken the contribution of voxels according to their distance with respect to the voxel to be classified. The algorithm was applied on 10 CT scans (pixel size, 0.98 x 0.98 mm2, slice thickness 3 mm, 120 kV). For each organ (i.e., the lung, liver, kidney, and spleen), the algorithm was applied on a part of the CT volume. First, the lung was segmented using two classes with characteristic values, C, defined by the K-means clustering algorithm. Second, the liver and kidneys were segmented using three classes with C-values defined by local mean Hounsfield Unit (HU) measurements, corresponding to fat, liver, and kidney. Third, the spleen was segmented using three classes corresponding to fat, kidney, and spleen, using local mean HU measurements. The semiautomated segmentation was compared with manual segmentation using the volume difference and the agreement (overlap) index. RESULTS: For organ segmentation, the computation duration was between 5 and 20 minutes (2.5 GHz, RAM of 1 GByte), depending on the number of classes and the volume size to classify. On the 10 patients, manual correction was needed for none on the lung, 1 on the spleen, 2 on the kidneys, and 7 on the liver, mostly owing to intercostal structures. The mean relative volume difference (+/-1 standard deviation [SD]) between manual and automated segmentation was 5.0% +/- 3.7%, 5.7% +/- 3.6%, 6.2% +/- 3.3%, and 7.5% +/- 6.5% for the lung, liver, kidney, and spleen, respectively. The corresponding mean agreement index (+/-1 SD) was 0.94 +/- 0.03, 0.90 +/- 0.01, 0.88 +/- 0.03, and 0.84 +/- 0.04. CONCLUSIONS: The algorithm allows for the delineating of organs on thoracic and abdominal CT images, and will be integrated in a 3D internal dosimetry dedicated software.     

Analysis of the motion of oropharyngeal tumors and consequences in planning target volume determination

PURPOSE: To determine adequate three-dimensional (3D) margins around the clinical target volume (CTV) of oropharyngeal cancers. METHODS AND MATERIALS: The CTV, bounded by implanted markers, was recorded under fluoroscopy in antero-posterior (AP) and lateral view. The peak-to-peak motion was measured in lateral, AP and cranio-caudal (CC) directions. RESULTS: During swallowing, the mean amplitude of motion measured was 9.4mm (0.9-18.5) and 4.1mm (0.6-11.4) in AP view in the CC and lateral direction, respectively; and 8.6mm (0.5-16.5) and 7.6mm (0.9-14.5) in lateral view in the CC and AP direction, respectively. In the non-swallowing period the motion was 1.5mm (0.3-3.2) and 1mm (0.4-3.6) in AP view in the CC and lateral direction, respectively; and 1.3mm (0.4-3.1) and 1.3mm (0.4-3.4) in lateral view in the CC and AP direction, respectively. This motion was believed to be due to breathing. CONCLUSION: If swallowing can be suppressed during CT acquisition, the contribution to the internal margin for this motion is negligible. Breathing related motion is also believed to be of limited clinical relevance in current practice. However, it might become of importance in future, with further reduction of margins.     

Tumor location,cirrhosis, and surgical history contribute to tumor movement in the liver,as measured during stereotactic irradiation using a real-time tumor-tracking radiotherapy system

PURPOSE: To investigate the three-dimensional (3D) intrafractional motion of liver tumors during real-time tumor-tracking radiotherapy (RTRT). MATERIALS AND METHODS: The data of 20 patients with liver tumors were analyzed. Before treatment, a 2-mm gold marker was implanted near the tumor. The RTRT system used fluoroscopy image processor units to determine the 3D position of the implanted marker. A linear accelerator was triggered to irradiate the tumor only when the marker was located within a permitted region. The automatically recorded tumor-motion data were analyzed to determine the amplitude of the tumor motion, curve shape of the tumor motion, treatment efficiency, frequency of movement, and hysteresis. Each of the following clinical factors was evaluated to determine its contribution to the amplitude of movement: tumor position, existence of cirrhosis, surgical history, tumor volume, and distance between the isocenter and the marker. RESULTS: The average amplitude of tumor motion in the 20 patients was 4 +/- 4 mm (range 1-12), 9 +/- 5 mm (range 2-19), and 5 +/- 3 mm (range 2-12) in the left-right, craniocaudal, and anterior-posterior (AP) direction, respectively. The tumor motion of the right lobe was significantly larger than that of the left lobe in the left-right and AP directions (p = 0.01). The tumor motion of the patients with liver cirrhosis was significantly larger than that of the patients without liver cirrhosis in the left-right and AP directions (p < 0.004). The tumor motion of the patients who had received partial hepatectomy was significantly smaller than that of the patients who had no history of any operation on the liver in the left-right and AP directions (p < 0.03). Thus, three of the five clinical factors examined (i.e., tumor position in the liver, cirrhosis, and history of surgery on the liver) significantly affected the tumor motion of the liver in the transaxial direction during stereotactic irradiation. Frequency analysis revealed that for 9 (45%) of the 20 tumors, the cardiac beat caused measurable motion. The 3D trajectory of the tumor showed hysteresis for 4 (20%) of the 20 tumors. The average treatment efficiency of RTRT was 40%. CONCLUSIONS: Tumor location, cirrhosis, and history of surgery on the liver all had an impact on the intrafractional tumor motion of the liver in the transaxial direction. This finding should be helpful in determining the smallest possible margin in individual cases of radiotherapy for liver malignancy.     

肝脏占位性病变的运动规律及其影响因素的初步临床研究

目的 探讨肝脏占位性病变的运动规律及其影响因素,为其在精确放疗时确定内靶区提供参考价值.方法 42例原发或转移肝脏肿瘤患者采用B超或CT引导下穿刺的方法将1～2个纯金标记置入肝脏肿瘤体内或邻近位置,并在X线模拟定位机下对标记的运动幅度进行测量.得出其在患者身体左右、前后、头脚方向移动数据,同时采用双变量相关分析影响其运动的因素.结果 42例患者体内标记在头脚方向的移动距离为(1.19±0.27)cm(0.5～1.9 cm),左右方向的为(0.27±0.11)cm(0.1～0.5 cm),前后方向的为(0.38±0.19)cm(0.1～0.8 cm).统计结果显示其移动距离与患者年龄、身高、体重、肿瘤位置和大小无关.结论 肝脏占位性病变的移动主要受呼吸运动影响,且在头脚方向的移动距离最大,在确定内靶区时应主要考虑其在头脚方向的移动.

Abstract：

Objective To investigate the movement,and the factors that influence such movement of liver lesions and to provide a reference for determination of internal target volume (ITV) during stereotactic radiotherapy. Methods We implanted 1 -2 gold markers into or near the liver tumors of 42 liver primary or metastasis cases percutaneously under B-ultrasound or computer tomography (CT) guidance. The marked motion of liver lesions in x ( right-left), y (superior-inferior) and z (anterior-posterior) directions was measured via X-ray simulator system. Based on the statistical analysis of the detected movements, we investigated the relevant influencing factors of liver lesions with bivariate correlation analysis. Results Data showed that mean motion amplitudes of liver lesions were 0.27 ± 0. 11 cm (0. 1 -0. 5cm) in x direction,0.38 ±0. 19 cm (0. 1 -0. 8cm) in y direction and 1.19 ±0. 27 cm (0. 5 - 1.9cm) in z direction. Motion amplitude was not correlated with the height, weight or age of the patients nor with the location or size of the tumor. Conclusions Motion of liver lesions was mainly influenced by the respiratory and has maximal amplitude in the z direction. Therefore,the motion in the z direction should be given a priority consideration while determining the ITV.     

An assessment of interfractional uterine and cervical motion: Implications for radiotherapy target volume definition in gynaecological cancer

PURPOSE: To assess interfractional movement of the uterus and cervix in patients with gynaecological cancer to aid selection of the internal margin for radiotherapy target volumes. METHODS AND MATERIALS: Thirty-three patients with gynaecological cancer had an MRI scan performed on two consecutive days. The two sets of T2-weighted axial images were co-registered, and the uterus and cervix outlined on each scan. Points were identified on the anterior uterine body (Point U), posterior cervix (Point C) and upper vagina (Point V). The displacement of each point in the antero-posterior (AP), supero-inferior (SI) and lateral directions between the two scans was measured. The changes in point position and uterine body angle were correlated with bladder volume and rectal diameter. RESULTS: The mean difference (+/-1SD) in Point U position was 7mm (+/-9.0) in the AP direction, 7.1mm (+/-6.8) SI and 0.8mm (+/-1.3) laterally. Mean Point C displacement was 4.1mm (+/-4.4) SI, 2.7mm (+/-2.8) AP, 0.3 (+/-0.8) laterally, and Point V was 2.6mm (+/-3.0) AP and 0.3mm (+/-1.0) laterally. There was correlation for uterine SI movement in relation to bladder filling, and for cervical and vaginal AP movement in relation to rectal filling. CONCLUSION: Large movements of the uterus can occur, particularly in the superior-inferior and anterior-posterior directions, but cervical displacement is less marked. Rectal filling may affect cervical position, while bladder filling has more impact on uterine body position, highlighting the need for specific instructions on bladder and rectal filling for treatment. We propose an asymmetrical margin with CTV-PTV expansion of the uterus, cervix and upper vagina of 15mm AP, 15mm SI and 7mm laterally and expansion of the nodal regions and parametria by 7mm in all directions.     

Internal movement, set-up accuracy and margins for stereotactic body radiotherapy using a stereotactic body frame

The aim of this study was to evaluate the uncertainty of patient immobilization within the Elekta body frame (SBF) used for stereotactic body radiotherapy (SBRT) and to suggest margins sufficient to ensure dose coverage to the gross target volume (GTV). The study was based on the evaluation of repeated CT-scans of 30 patients treated by SBRT. The overall uncertainty was divided between uncertainty related to internal movement of the tumor and uncertainty in the patient set-up. Standard deviations of the overall tumor displacement were 2 mm, 3 mm and 4 mm in medial-lateral (m-l), anterior-posterior (a-p), and cranio-caudal (c-c) directions, respectively. In a model based on the data, an ellipsoid planned target volume (PTV) corresponding to the standard deviations in the orthogonal directions and a scaling factor, K defined a 3-dimentional (3-D) probability density. According to the model, a 90% probability of full dose coverage of the GTV was secured using margins of 9 mm (m-l), 9 mm (a-p) and 13 mm (c-c), respectively. The overall uncertainty was dominated by internal tumor movements whereas the set-up uncertainty of the patient in the SBF was less pronounced. It was concluded that the Elekta SBF is useful for immobilisation of patients for SBRT. However, due to internal movement conventional margins of 5 mm in m-l and a-p and 10 mm in the c-c directions may be insufficient for full dose coverage.     

High-speed magnetic resonance imaging for four-dimensional treatment planning of conformal radiotherapy of moving body tumors

PURPOSE: High-speed magnetic resonance imaging (MRI) was applied to the determination of the planning target volume (PTV) of moving hepatobiliary tumors. METHODS AND MATERIALS: Three moving tumors, including two metastatic hepatic tumors and one bile duct tumor, were examined using high-speed MRI and reference fiducial markers before external radiotherapy. Patients were examined for 30 seconds under conditions of normal breathing during the examination. The coordinates of the center of the tumor contours were shown on sagittal and coronal images displayed on the monitor. RESULTS: The maximum length of movement was 10.6 +/- 7.0 mm in a craniocaudal direction; 5.2 +/- 1.8 mm in a lateral direction; and 4.6 +/- 1.6 mm in a ventrodorsal direction. When the PTV was determined using MRI at exhalation phase with a 10-mm safety margin, clinical target volume (CTV) was not covered in 19% of all images in the 3 patients. With MRI at inhalation phase with a 10-mm safety margin, CTV was not covered in 36% of all images. CONCLUSION: Four-dimensional treatment planning using high speed MRI, and integrating time and spatial information, has the potential to determine the planning target volume of moving body tumors more precisely than does conventional CT planning.     

Residual set-up errors and margins in on-line image-guided prostate localization in radiotherapy.

BACKGROUND AND PURPOSE: Image-guided on-line correction of the target position allows radiotherapy of prostate cancer with narrow set-up margins. The present study investigated the residual set-up error after on-line prostate localization and its impact on margins. MATERIALS AND METHODS: Prostate localization based on two orthogonal X-ray images of gold markers implanted in the prostate was performed with an on-board imager at four treatment sessions for 90 patients. The set-up error in the sagittal plane residual after couch adjustment was evaluated on lateral verification portal images. RESULTS: The set-up error was less than 3.0mm in 92% of the cases in the anterior-posterior (AP) direction and in 95% of the cases in the cranio-caudal (CC) direction. The set-up error was dominated by internal prostate motion taking place during the set-up procedure. Set-up margins were calculated using two formalisms: margins designed to ensure a minimum CTV dose of 95% for 90% of the patient population were 3.6mm (AP) and 3.5mm (CC). Patient-independent normal distributed set-up errors would result in margins of 4.3mm (AP) and 4.0mm (CC) to ensure complete CTV inclusion in the PTV with 90% probability. CONCLUSION: Internal prostate motion during the set-up procedure was the main contributor to residual set-up errors.