Tim J. Cullip

Direct visualization of volume data

A combination of segmentation tools and fast volume renderers that provides an interactive exploration environment for volume visualization is discussed. The tools and renderers include mechanisms that distribute volume data across multiple processors, as well as image compositing techniques and solutions to representation problems in the selection and display of subregions within bounding volumes. A volume visualization technique using the interactive control of images rendered directly from volume data coupled with a user-controlled semantic classification tool is described. The variations of parallel volume rendering being explored on the Pixel-Planes 5 system and the region-of-interest selection methods and the interactive tools used by the system are presented. The flexibility and power of combining volume rendering with region-of-interest selection techniques are demonstrated using examples of medical imaging applications.<<ETX>>

Image Registration: An Essential Part of Radiation Therapy Treatment Planning

PURPOSEnWe believe that a three-dimensional (3D) registration of nonplanning (diagnostic) imaging data with the planning computed tomography (CT) offers a substantial improvement in tumor target identification for many radiation therapy patients. The purpose of this article is to review and discuss our experience to date.nnnMETHODS AND MATERIALSnWe reviewed the charts and treatment planning records of all patients that underwent 3D radiation treatment planning in our department from June 1994 to December 1995, to learn which patients had image registration performed and why it was thought they would benefit from this approach. We also measured how much error would have been introduced into the target definition if the nonplanning imaging data had not been available and only the planning CT had been used.nnnRESULTSnBetween June 1994 and December 1995, 106 of 246 (43%) of patients undergoing 3D treatment planning had image registration. Four reasons for performing registration were identified. First, some tumor volumes have better definition on magnetic resonance imaging (MRI) than on CT. Second, a properly contrasted diagnostic CT sometimes can show the tumor target better than can the planning CT. Third, the diagnostic CT or MR may have been preoperative, with the postoperative planning CT no longer showing the tumor. Fourth, the patient may have undergone cytoreductive chemotherapy so that the postchemotherapy planning CT no longer showed the original tumor volume. In patients in whom the planning CT did not show the tumor volume well an analysis was done to determine how the treatment plan was changed with the addition of a better tumor-defining nonplanning CT or MR. We have found that the use of this additional imaging modality changed the tumor location in the treatment plan at least 1.5 cm for half of the patients, and up to 3.0 cm for 1/4 of the patients.nnnCONCLUSIONSnMultimodality and/or sequential imaging can substantially aid in better tumor definition in many patients undergoing 3D treatment planning. In some patients the appropriate nonplanning imaging source can change the perceived tumor location by several centimeters and is thus essential for proper treatment planning.

Improving treatment planning accuracy through multimodality imaging

PURPOSEnIn clinical practice, physicians are constantly comparing multiple images taken at various times during the patients treatment course. One goal of such a comparison is to accurately define the gross tumor volume (GTV). The introduction of three-dimensional treatment planning has greatly enhanced the ability to define the GTV, but there are times when the GTV is not visible on the treatment-planning computed tomography (CT) scan. We have modified our treatment-planning software to allow for interactive display of multiple, registered images that enhance the physicians ability to accurately determine the GTV.nnnMETHODS AND MATERIALSnImages are registered using interactive tools developed at the University of North Carolina at Chapel Hill (UNC). Automated methods are also available. Images registered with the treatment-planning CT scan are digitized from film. After a physician has approved the registration, the registered images are made available to the treatment-planning software. Structures and volumes of interest are contoured on all images. In the beams eye view, wire loop representations of these structures can be visualized from all image types simultaneously. Each registered image can be seamlessly viewed during the treatment-planning process, and all contours from all image types can be seen on any registered image. A beam may, therefore, be designed based on any contour.nnnRESULTSnNineteen patients have been planned and treated using multimodality imaging from November 1993 through August 1994. All registered images were digitized from film, and many were from outside institutions. Brain has been the most common site (12), but the techniques of registration and image display have also been used for the thorax (4), abdomen (2), and extremity (1). The registered image has been an magnetic resonance (MR) scan in 15 cases and a diagnostic CT scan in 5 cases. In one case, sequential MRs, one before treatment and another after 30 Gy, were used to plan patients initial fields and boost, respectively. Case illustrations are shown.nnnCONCLUSIONSnWe have successfully integrated multimodality imaging into our treatment-planning system, and its routine use is increasing. Multimodality imaging holds out the promise of improving treatment planning accuracy and, thus, takes maximum advantage of three dimensional treatment planning systems.

Three-dimensional reconstruction of a bullet path: validation by computed radiography.

Three-dimensional visualization is an important tool in the evaluation and demonstration of injury. Creating convincing graphics, however, requires strict distinction between illustrative and reconstructive visualizations and a method of validation. We present a case in which we used a radiation-planning tool to provide a 3-dimensional illustrative visualization of a contact gunshot wound to the head, and validated the result by comparing computed radiographs with radiographs taken at autopsy. We discuss the use of visualization tools for data exploration in forensic pathology.

VISTAnet: interactive real-time calculation and display of 3-dimensional radiation dose: An application of gigabit networking

Three-dimensional treatment planning can allow the clinician to create plans that are highly individualized for each patient. However, in lifting the constraints traditionally imposed by 2-dimensional planning, the clinician is faced with the need to compare a much larger number of plans. Although methods to automate that process are being developed, it is not yet clear how well they will perform. VISTAnet is a 3 year collaborative effort between the Departments of Radiation Oncology and Computer Science at the University of North Carolina, the North Carolina Supercomputing Center, BellSouth, and GTE with the medical goal of providing real-time 3-dimensional radiation dose calculation and display. With VISTAnet technology and resources, the user can inspect 3-dimensional treatment plans in real-time along with the associated dose volume histograms and can fine tune these plans in real-time with regard to beam position, weighting, wedging, and shape. Thus VISTAnet provides an alternate and, possibly, complementary approach to computerized searches for optimal radiation treatment plans. Building this system has required the development of very fast radiation dose code, methods for simultaneously manipulating and modifying multiple radiation beams, and new visualizations of 3-dimensional dose distributions.

Achieving direct volume visualization with interactive semantic region selection

The authors have achieved rates as high as 15 frames per second for interactive direct visualization of 3D data by trading some function for speed, while volume rendering with a full complement of ramp classification capabilities is performed at 1.4 frames per second. These speeds have made the combination of region selection with volume rendering practical for the first time. Semantic-driven selection, rather than geometric clipping, has proved to be a natural means of interacting with 3D data. Internal organs in medical data or other regions of interest can be built from preprocessed region primitives. The resulting combined system has been applied to real 3D medical data with encouraging results.<<ETX>>

Interactive volume visualization on a heterogeneous message-passing multicomputer

This paper describes VOL2, an interactive general-purpose volume renderer based on ray casting and implemented on Pixel-Planes 5, a distributed-memory, message-passing multicomputer. VOL2 is a pipelined renderer using image-space task parallelism and object-space data partitioning. We describe the parallelization and load balancing techniques used in order to achieve interactive response and near-real-time frame rates. We also present a number of applications for our system and derive some general conclusions about operation of image-order rendering algorithms on message-passing multicomputers.

Dosimetric effect due to the motion during deep inspiration breath hold for left-sided breast cancer radiotherapy.

Deep inspiration breath-hold (DIBH) radiotherapy for left-sided breast cancer can reduce cardiac exposure and internal motion. We modified our in-house treatment planning system (TPS) to retrospectively analyze breath-hold motion log files to calculate the dosimetric effect of the motion during breath hold. Thirty left-sided supine DIBH breast patients treated using AlignRT were studied. Breath-hold motion was recorded - three translational and three rotational displacements of the treatment surface - the Real Time Deltas (RTD). The corresponding delivered dose was estimated using the beam-on portions of the RTDs. Each motion was used to calculate dose, and the final estimated dose was the equally weighted average of the multiple resultant doses. Ten of thirty patients had internal mammary nodes (IMN) purposefully included in the tangential fields, and we evaluated the percentage of IMN covered by 40 Gy. The planned and delivered heart mean dose, lungs V20 (volume of the lungs receiving >20xa0Gy), percentage of IMN covered by 40 Gy, and IMN mean dose were compared. The averaged mean and standard deviation of the beam-on portions of the absolute RTDs were 0.81±1.29xa0mm, 0.68±0.85xa0mm, 0.76±0.85xa0mm, 0.96°±0.49°,0.93°±0.43°, and 1.03°±0.50°, for vertical, longitudinal, lateral, yaw, roll, and pitch, respectively. The averaged planned and delivered mean heart dose were 99 and 101 cGy. Lungs V20 were 6.59% and 6.74%. IMN 40 Gy coverage was 83% and 77%, and mean IMN dose was 4642 and 4518 cGy. The averaged mean motion during DIBH was smaller than 1 mm and 1°, which reflects the relative reproducibility of the patient breath hold. On average, the mean heart dose and lungs V20 were reasonably close to what have been planned. IMN 40 Gy coverage might be modestly reduced for certain cases. PACS number: 87.55.km, 87.55.N.Deep inspiration breath‐hold (DIBH) radiotherapy for left‐sided breast cancer can reduce cardiac exposure and internal motion. We modified our in‐house treatment planning system (TPS) to retrospectively analyze breath‐hold motion log files to calculate the dosimetric effect of the motion during breath hold. Thirty left‐sided supine DIBH breast patients treated using AlignRT were studied. Breath‐hold motion was recorded — three translational and three rotational displacements of the treatment surface — the Real Time Deltas (RTD). The corresponding delivered dose was estimated using the beam‐on portions of the RTDs. Each motion was used to calculate dose, and the final estimated dose was the equally weighted average of the multiple resultant doses. Ten of thirty patients had internal mammary nodes (IMN) purposefully included in the tangential fields, and we evaluated the percentage of IMN covered by 40 Gy. The planned and delivered heart mean dose, lungs V20 (volume of the lungs receiving >20 Gy), percentage of IMN covered by 40 Gy, and IMN mean dose were compared. The averaged mean and standard deviation of the beam‐on portions of the absolute RTDs were 0.81±1.29 mm, 0.68±0.85 mm, 0.76±0.85 mm, 0.96°±0.49°,0.93°±0.43°, and 1.03°±0.50°, for vertical, longitudinal, lateral, yaw, roll, and pitch, respectively. The averaged planned and delivered mean heart dose were 99 and 101 cGy. Lungs V20 were 6.59% and 6.74%. IMN 40 Gy coverage was 83% and 77%, and mean IMN dose was 4642 and 4518 cGy. The averaged mean motion during DIBH was smaller than 1 mm and 1°, which reflects the relative reproducibility of the patient breath hold. On average, the mean heart dose and lungs V20 were reasonably close to what have been planned. IMN 40 Gy coverage might be modestly reduced for certain cases. PACS number: 87.55.km, 87.55.N

VISTAnet: radiation therapy treatment planning through rapid dose calculation and interactive 3D volume visualization

VISTAnet, an experimental gigabit network test bed, ties together a CRAY Y-MP, the Pixel-Planes 5 graphics engine, and an SGI host machine to create a metacomputer capable of real-time radiation therapy dose calculation and display. We report on the methods used to manipulate and examine the 3D radiation dose distribution, with emphasis on the visualization, which uses a parallel, interactive, multimodal renderer implemented on Pixel- Places 5. The real-time display is designed to facilitate comprehension of spatial relationships among the geometrically complex anatomy and radiation dose structures that characterize a 3D radiation treatment scenario. The currently ongoing clinical evaluation of VISTAnet has already yielded encouraging results.

Is image registration of fluorodeoxyglucose-positron emission tomography/computed tomography for head-and-neck cancer treatment planning necessary?

PURPOSEnTo evaluate dosimetry and patterns of failure related to fluorodeoxyglucose-positron emission tomography (FDG-PET)-defined biological tumor volumes (BTVs) for head-and-neck squamous cell carcinoma (HNSCC) treated with definitive radiotherapy (RT).nnnMETHODS AND MATERIALSnWe conducted a retrospective study of 91 HNSCC patients who received pretreatment PET/CT scans that were not formally used for target delineation. The median follow-up was 34.5 months. Image registration was performed for PET, planning CT, and post-RT failure CT scans. Previously defined primary (CT(PRIMARY)) and nodal (CT(NODE)) gross tumor volumes (GTV) were used. The primary BTV (BTV(PRIMARY)) and nodal BTV (BTV(NODE)) were defined visually (PET(vis)). The BTV(PRIMARY) was also contoured using 40% and 50% peak PET activity (PET(40,) PET(50)). The recurrent GTVs were contoured on post-RT CT scans. Dosimetry was evaluated on the planning-CT and pretreatment PET scan. PET and CT dosimetric/volumetric data was compared for those with and without local-regional failure (LRF).nnnRESULTSnIn all, 29 of 91 (32%) patients experienced LRF: 10 local alone, 7 regional alone, and 12 local and regional. BTVs and CT volumes had less than complete overlap. BTVs were smaller than CT-defined targets. Dosimetric coverage was similar between failed and controlled groups as well as between BTVs and CT-defined volumes.nnnCONCLUSIONSnPET and CT-defined tumor volumes received similar RT doses despite having less than complete overlap and the inaccuracies of image registration. LRF correlated with both CT and PET-defined volumes. The dosimetry for PET- and/or CT-based tumor volumes was not significantly inferior in patients with LRF. CT-based delineation alone may be sufficient forxa0treatment planning in patients with HNSCC. Image registration of FDG-PET may not be necessary.