Design of a fully integrated three-dimensional computed tomography simulator and preliminary clinical evaluation

Analysis of Irradiated Lung and Heart Volumes using Virtual Simulation in Postoperative Treatment of Stage I Breast Carcinoma

Aims and Background

The aim of the study was to assess the usefulness of virtual simulation in postoperative radiotherapy treatment planning of early-stage breast cancer and to evaluate its potential to reduce the volume of critical structures exposed compared to treatment plans produced by a conventional 2D system.

Methods and Study Design

Eighteen patients undergoing breast radiotherapy following conservative surgery for small breast carcinomas were studied. Scans from spiral CT equipment (with the patient in the treatment position) were transferred to a virtual simulator. From the screen images the operator contoured breast, lung and heart. Calculations were made of the extent to which the heart and lung were included in the irradiation fields (50% isodose line of tangential fields).

Results

Manual contouring was time-consuming, but when virtual simulation was used, the mean volume of the lung included in the radiation fields was significantly reduced compared to the 2D treatment plan (4.5% vs 5.4%, P = 0.034); in addition, a slight reduction was observed for the heart (0.5% to 1.2%), but this was not statistically significant.

Conclusions

With a 3D system we obtained optimal target coverage and a reduction of the dose to critical structures (statistically significant only for the lung). From a clinical point of view, this 0.9% reduction in the mean irradiated lung volume is probably not significant, as the percentage irradiated with a 2D system is considerably below the recommended value. Furthermore, our analysis was performed in a relatively small group of patients; for a reliable estimate larger series would be required. Consequently, the 3D system should not be considered in routine treatment after breast conserving surgery for early stage carcinomas; for the time being it should be reserved for selected cases.

A realistic computed tomography simulator for small motion analysis of cerebral aneurysms

This paper describes a realistic simulator for the Computed Tomography (CT) scan process for motion analysis. In fact, we are currently developing a new framework to find small motion from the CT scan. In order to prove the fidelity of this framework, or potentially any other algorithm, we present in this paper a simulator to simulate the whole CT acquisition process with a priori known parameters. In other words, it is a digital phantom for the motion analysis that can be used to compare the results of any related algorithm with the ground-truth realistic analytical model. Such a simulator can be used by the community to test different algorithms in the biomedical imaging domain. The most important features of this simulator are its different considerations to simulate the best the real acquisition process and its generality.

Interactive tele-radiological segmentation systems for treatment and diagnosis

Telehealth is the exchange of health information and the provision of health care services through electronic information and communications technology, where participants are separated by geographic, time, social and cultural barriers. The shift of telemedicine from desktop platforms to wireless and mobile technologies is likely to have a significant impact on healthcare in the future. It is therefore crucial to develop a general information exchange e-medical system to enables its users to perform online and offline medical consultations through diagnosis. During the medical diagnosis, image analysis techniques combined with doctor's opinions could be useful for final medical decisions. Quantitative analysis of digital images requires detection and segmentation of the borders of the object of interest. In medical images, segmentation has traditionally been done by human experts. Even with the aid of image processing software (computer-assisted segmentation tools), manual segmentation of 2D and 3D CT images is tedious, time-consuming, and thus impractical, especially in cases where a large number of objects must be specified. Substantial computational and storage requirements become especially acute when object orientation and scale have to be considered. Therefore automated or semi-automated segmentation techniques are essential if these software applications are ever to gain widespread clinical use. The main purpose of this work is to analyze segmentation techniques for the definition of anatomical structures under telemedical systems.

Optimising the use of virtual and conventional simulation: a clinical and economic analysis

Background and purpose: Currently, optimal use of virtual simulation for all treatment sites is not entirely clear. This study presents data to identify specific patient groups for whom conventional simulation may be completely eliminated and replaced by virtual simulation.

Sampling and method: Two hundred and sixty patients were recruited from four treatment sites (head and neck, breast, pelvis, and thorax). Patients were randomly assigned to be treated using the usual treatment process involving conventional simulation, or a treatment process differing only in the replacement of conventional plan verification with virtual verification. Data were collected on set-up accuracy at verification, and the number of unsatisfactory verifications requiring a return to the conventional simulator. A micro-economic costing analysis was also undertaken, whereby data for each treatment process episode were also collected: number and grade of staff present, and the time for each treatment episode.

Results: The study shows no statistically significant difference in the number of returns to the conventional simulator for each site and study arm. Image registration data show similar quality of verification for each study arm. The micro-costing data show no statistical difference between the virtual and conventional simulation processes.

Conclusions: At our institution, virtual simulation including virtual verification for the sites investigated presents no disadvantage compared to conventional simulation.

Localization: conventional and CT simulation

Recent developments in imaging and computer power have led to the ability to acquire large three dimensional data sets for target localization and complex treatment planning for radiation therapy. Conventional simulation implies the use of a machine capable of the same mechanical movements as treatment units. Images obtained from these machines are essentially two dimensional with the facility to acquire a limited number of axial slices to provide patient contours and tissue density information. The recent implementation of cone beam imaging on simulators has transformed them into three dimensional imaging devices able to produce the data required for complex treatment planning. The introduction of computed axial tomography (CT) in the 1970s was a step-change in imaging and its potential use in radiotherapy was quickly realised. However, it remained a predominantly diagnostic tool until modifications were introduced to meet the needs of radiotherapy and software was developed to perform the simulation function. The comparability of conventional and virtual simulation has been the subject of a number of studies at different disease sites. The development of different cross sectional imaging modalities such as MRI and positron emission tomography has provided additional information that can be incorporated into the simulation software by image fusion and has been shown to aid in the delineation of tumours. Challenges still remain, particularly in localizing moving structures. Fast multislice scanning protocols freeze patient and organ motion in time and space, which may lead to inaccuracy in both target delineation and the choice of margins in three dimensions. Breath holding and gated respiration techniques have been demonstrated to produce four-dimensional data sets that can be used to reduce margins or to minimize dose to normal tissue or organs at risk. Image guided radiotherapy is being developed to address the interfraction movement of both target volumes and critical normal structures. Whichever method of localization and simulation is adopted, the role of quality control is important for the overall accuracy of the patient's treatment and must be adapted to reflect the networked nature of the process.

Quality assurance for computed-tomography simulators and the computed-tomography-simulation process: report of the AAPM Radiation Therapy Committee Task Group No. 66

This document presents recommendations of the American Association of Physicists in Medicine (AAPM) for quality assurance of computed-tomography- (CT) simulators and CT-simulation process. This report was prepared by Task Group No. 66 of the AAPM Radiation Therapy Committee. It was approved by the Radiation Therapy Committee and by the AAPM Science Council.

Multimodality image registration quality assurance for conformal three-dimensional treatment planning

PURPOSE

We present a quality assurance methodology to determine the accuracy of multimodality image registration and fusion for the purpose of conformal three-dimensional and intensity-modulated radiation therapy treatment planning. Registration and fusion accuracy between any combination of computed tomography (CT), magnetic resonance (MR), and positron emission computed tomography (PET) imaging studies can be evaluated.

METHODS AND MATERIALS

A commercial anthropomorphic head phantom filled with water and containing CT, MR, and PET visible targets was modified to evaluate the accuracy of multimodality image registration and fusion software. For MR and PET imaging, the water inside the phantom was doped with CuNO(3) and 18F-fluorodeoxyglucose (18F-FDG), respectively. Targets consisting of plastic spheres and pins were distributed throughout the cranium section of the phantom. Each target sphere had a conical-shaped bore with its apex at the center of the sphere. The pins had a conical extension or indentation at the free end. The contours of the spheres, sphere centers, and pin tips were used as anatomic landmark models for image registration, which was performed using affine coordinate-transformation tools provided in a commercial multimodality image registration/fusion software package. Four sets of phantom image studies were obtained: primary CT, secondary CT with different phantom immobilization, MR, and PET study. A novel CT, MR, and PET external fiducial marking system was also tested.

RESULTS

The registration of CT/CT, CT/MR, and CT/PET images allowed correlation of anatomic landmarks to within 2 mm, verifying the accuracy of the registration software and spatial fidelity of the four multimodality image sets.

CONCLUSIONS

This straightforward phantom-based quality assurance of the image registration and fusion process can be used in a routine clinical setting or for providing a working image set for development of the image registration and fusion process and new software.

Virtual simulation in patients with breast cancer

BACKGROUND

Investigation of the feasibility and effectiveness of virtual simulation in patients receiving radiotherapy of the breast.

METHODS

Twenty-three patients were included in the study. All of them underwent a course of postoperative tangential breast irradiation. The patients were prospectively randomised into two groups. Group A patients (n=11) received a conventional computed tomography -based treatment planning, group B patients (n=12) a virtual simulation. The results of both treatment planning procedures were compared.

RESULTS

The treatment planning was feasible in all patients. The time expenditure could be reduced from a median of 45.0 to 16.5 min and from 55.0 to 32.0 min for the technician and physician, respectively, using virtual simulation. Furthermore the treatment planning for the patient could be reduced from a median of 45.0 min in two sessions to 16.5 min in one session. The image quality of the digital reconstructed radiographs was satisfying compared to the simulation films. The incidence and extension of set-up corrections for the patients at the first treatment were comparable in both groups. The time interval between the planning CT and the first treatment could be reduced by 31% using virtual simulation due to the omission of the conventional simulation.

CONCLUSION

The virtual simulation is a feasible tool for the treatment planning of patients undergoing tangential irradiation of the breast. Compared with the conventional simulation procedure virtual simulation is superior regarding to the precision of patients marking, the quality of the reference images and, the time expenditure for the patients and medical staff.

Warping CT scans from nontreatment to treatment position

This paper describes a cost-effective technique that optimally utilizes all available diagnostic studies for three-dimensional treatment planning. A simulator unit modified to produce cross-sectional images (simulator-CT unit) is used to create a reference data set with the patient in the treatment position. Registration software (qsh) brings other diagnostic studies into agreement with this reference data set. Two cases are presented as examples of the use of this technique. Registration of abdominal scans from the same patient demonstrates the warping of a nontreatment position study to the treatment position. The second case is based on paired data sets through the head, in which the diagnostic study was obtained by using a gantry tilt to follow the base of the skull and to avoid sections passing through the teeth. The registration software provides a method for combining diagnostic studies into a single "master" data set. The success of the transformation depends on the operator's ability to identify corresponding anatomic landmarks for different data sets and on the magnitude of the variation in the patient's position from one procedure to the next. Limitations in image quality and the number of cross-sections obtainable from a simulator-CT unit can be partially overcome by using the described technique. Thus, the information contained in nontreatment position diagnostic tests can be used accurately for treatment planning at limited cost.

Time requirements in conformal radiotherapy treatment planning

To investigate the influence of implementing three-dimensional treatment planning on staffing needs, valid questionnaire responses from 22 radiotherapy institutions have been evaluated. Average time requirements per plan rise from 213 to 439 min upon implementation, but with experience decrease to 317 min. No institution reports additional staff positions according to estimated requirements.

Differences in target outline delineation from CT scans of brain tumours using different methods and different observers

PURPOSE

To assess errors resulting from manual transfer of contour information for three-dimensional (3-D) target reconstruction, and to determine variations in target volume delineation of brain tumours by different radiation oncologists.

MATERIALS AND METHODS

Images of 18 patients with intracranial astrocytomas were used for retrospective treatment planning by five radiation oncologists. In this study, the target outline was delineated on sequential CT slices by an experienced radiation oncologist. Thereafter, the target outline was manually reconstructed by five radiation oncologists onto an A-P or lateral scout film. The same target outline was also reconstructed as a projection using the Beam's-eye view capability on a CT simulator unit. The two target outlines were compared by encompassing each shape with the smallest rectangle. The manually-reconstructed radiation field was termed 'Field manually established on X-ray film (F-X)', and the automatically-established field was termed 'Field established by CT simulator (F-CT)'. In a second part of this study, four radiation oncologists defined contours from contrast enhanced CT images of nine patients with intracranial astrocytomas. The CT images of these nine cases included five pre-operative cases and four post-operative cases. Both gross tumour volume (GTV) and clinical target volume (CTV) were outlined on sequential CT slices. The target outlines for the four radiation oncologists were compared by identifying the smallest rectangular field surrounding the projection of these contours. The field established by each radiation oncologist was termed 'Field of target volume (F-TV)', and the overlapping portion of the four F-TVs for each case was termed 'Overlapped field of the target volume (Fo-TV)'.

RESULTS

The average distance between the isocentres of F-X and F-CT was 0.6 +/- 0.4 cm (mean +/- SD). The average ratio of the area of F-X divided by the area of F-CT was 1.04 +/- 0.12. The area of F-X was wider than the area of F-CT for four of the five oncologists. The ratio of the area of F-TV divided by the area of Fo-TV was calculated. The average ratio was relatively greater for CTV (2.07 in pre-operative cases and 2.11 in post-operative cases) than for GTV (1.12 in pre-operative cases and 1.41 in post-operative cases). Among radiation oncologists, variations in the delineation of GTV were smaller than those of CTV.

CONCLUSIONS

When using an X-ray simulator in treatment planning, errors resulting from the manual transfer of CT contour information to planar radiographs must be considered. When computer techniques are used to project contours onto radiographs errors resulting from individual variations when performing the contouring must be considered.

[Could the evaluation of the cost of complications be a worthwhile means to improve radiotherapy?]

At the present time, the current improvement of technical and dosimetric aspects of radiation oncology has to be evaluated in terms of potential benefit for the patient and the society. For this last point of view, specially designed economic analyses must be performed in order to justify the number of resources involved by these technical improvements. If the question is how the current technical procedures could reduce the risk of undesirable side-effects, the response cannot be immediately drawn from the literature. This paper emphasizes the possibility to evaluate the role of side-effects as endpoints of economic analyses when using special models in medical decision making such as Markov's. Only few oncologic situations are reliable to properly analyze the relationship between sophisticated radiation techniques and the incidence of post-radiation complications. These situations should be selected when prospective economic analyses are planned in the field of radiation therapy.

Defining the superior border of posterior fossa radiation treatment fields

PURPOSE

Lateral posterior fossa treatment fields are usually defined on traditional simulation films based on bony landmarks. The superior field border, intended to include the apex of the tentorium cerebelli, is frequently difficult to define. While sagittal magnetic resonance imaging (MRI) images or three-dimensional treatment planning tools are good means to locate the tentorial apex, these are not always available. We herein describe a method for locating the tentorial apex based on bony landmarks.

METHODS AND MATERIALS

Midsagittal magnetic resonance images of 53 patients were reviewed. Using a Cartesian grid, the geometric relationship between the tentorial apex and several bony landmarks was assessed. Two lines were defined: the first connected the posterior clinoid and the internal occipital protuberance (AB). The second was perpendicular to the first, included the tentorial apex, and extended from the base of the skull inferiorly to the "crown" of the skull superiorly (DE). Relationships between measurements were made using linear regression and least square fits.

RESULTS

Line DE was within 5 mm of the perpendicular bisector of line AB in 83% (44/53) of patients. The tentorial apex was located within 10 mm of the midpoint of DE in 91% (48/53) of patients.

CONCLUSION

In the majority of patients, the location of the tentorial apex can be estimated based on bony landmarks, to within approximately 10 mm. The technique described is a useful means of estimating the location of the tentorial apex in patients where sagittal MRI imaging or three-dimensional treatment planning tools are not available.

[Virtual simulation. First clinical results in patients with prostate cancer]

AIM

Investigation of options of virtual simulation in patients with localized prostate cancer.

PATIENTS AND METHODS

Twenty-four patients suffering from prostate cancer were virtual simulated. The clinical target volume was contoured and the planning target volume was defined after CT scan. The isocenter of the planning target volume was determined and marked at patient's skin. The precision of patients marking was controlled with conventional simulation after physical radiation treatment planning.

RESULTS

Mean differences of the patient's mark revealed between the 2 simulations in all room axes around 1 mm. The organs at risk were visualized in the digital reconstructed radiographs.

CONCLUSIONS

The precise patient's mark of the isocentre by virtual simulation allows to skip the conventional simulation. The visualisation of organs at risk leeds to an unnecessarily of an application of contrast medium and to a further relieve of the patient. The personal requirement is not higher in virtual simulation than in conventional CT based radiation treatment planning.

A prospective, randomized study addressing the need for physical simulation following virtual simulation

PURPOSE

To accurately implement a treatment plan obtained by virtual or CT simulation, conventional or physical simulation is still widely used. To evaluate the need for physical simulation, we prospectively randomized patients to undergo physical simulation or no additional simulation after virtual simulation.

METHODS AND MATERIALS

From July 1995 to September 1996, 75 patients underwent conformal four-field radiation therapy planning for prostate cancer with a commercial grade CT simulator. The patients were randomized to undergo either port filming immediately following physical simulation or port filming alone. The precision of implementing the devised plan was evaluated by comparing simulator radiographs and/or port films against the digitally reconstructed radiographs (DRRs) for x, y, and z displacements of the isocenter. Changes in beam aperture were also prospectively evaluated.

RESULTS

Thirty-seven patients were randomized to undergo physical simulation and first day port filming, and 38 had first day treatment verification films only without a physical simulation. Seventy-eight simulator radiographs and 195 first day treatment port films were reviewed. There was no statistically significant reduction in treatment setup error (>5 mm) if patients underwent physical simulation following virtual simulation. No patient required a resimulation, and there was no significant difference in changes of beam aperture.

CONCLUSIONS

Following virtual simulation, physical simulation may not be necessary to accurately implement the conformal four-field technique. Because port filming appears to be sufficient to assure precise and reliable execution of a devised treatment plan, physical simulation may be eliminated from the process of CT based planning when virtual simulation is available.

Using an artificial neural network to define the planning target volume in radiotherapy

A neural network for predicting the planning target volume in radiotherapy from the shape of the detected tumor is designed and tested in this research project. The proposed neural network is able to generalize expert medical knowledge and predict the planning target volume from a three-dimensional image of the detected tumor. Initial results for simple shaped brain tumors are presented in this paper.

Cost benefit of emerging technology in localized carcinoma of the prostate

PURPOSE

In a health care environment strongly concerned with cost containment, cost-benefit studies of new technology must include analyses of loco-regional tumor control, morbidity, impact on quality of life, and financial considerations.

METHODS AND MATERIALS

This nonrandomized study analyzes 124 patients treated with three-dimensional conformal radiation therapy (3D CRT) and 153 with standard irradiation (SRT) between January 1992 and December 1995, for histologically proven adenocarcinoma of prostate, clinical Stage T1 or T2. Mean follow-up is 1.4 years. Three-dimensional CRT consisted of six or seven coplanar oblique and lateral and, in some patients, AP fields designed to treat the prostate with a 1 to 1.7 cm margin. SRT consisted of 120 degrees bilateral arc rotation. Total doses to prostate were 67 to 70 Gy when pelvic lymph nodes were irradiated or 68.4 to 73.8 Gy when prostatic volume only was treated; dose per fraction was 1.8 Gy. Patients were interviewed weekly for severity of 12 acute intestinal and urinary pelvic irradiation side effects (0 to 4+ grading). Time and effort for 3D RTP and daily treatment with 3D CRT and SRT were recorded. Dose-volume histograms (DVHs) were calculated for gross tumor volume, planning target volume, bladder, and rectum. Actual reimbursement to the hospital and university was determined for 41 3D CRT, 43 SRT, and 40 radical prostatectomy patients treated during the same period.

RESULTS

Average treatment planning times (in minutes) were: 101 for 3D conformal therapy simulation, 66 for contouring of target volume and sensitive structures, 55 for virtual simulation, 39 for plan preparation and documentation, 65 for physical simulation, and 20 for approval of treatment plan. Daily mean treatment times were 19 min for 3D CRT with Cerrobend blocking, 16 with multileaf collimation, and 10 with bilateral arc rotation. Dosimetric analysis (DVHs) showed a reduction of 50% in volume of bladder or rectum receiving doses higher than 65 Gy. Acute side effects included dysuria, moderate difficulty in urinating, and nocturia in 25-39% of both SRT and CRT patients; loose stools or diarrhea in 5-12% of 3D CRT and 16-22% of SRT patients; moderate proctitis in 3% of 3D CRT and 12% of SRT patients (p = 0.01). Chemical disease-free survival (prostate-specific antigen < or =2 ng/ml) at 3 years was 90% with 3D CRT and 80% with SRT (p = 0.01). Average initial treatment reimbursements were $13,823 (3D CRT), $10,864 (SRT), and $12,250 (radical prostatectomy). Average total treatment reimbursement and projected cost of management of initial therapy failures per patients were $15,173, $16,264, and $16,405, respectively.

CONCLUSIONS

Three-dimensional CRT irradiated less bladder and rectum volume than SRT; CRT initial reimbursement was 28% higher than SRT and 12% higher than radical prostatectomy. Because of projected better local tumor control, average total cost of treating a patient with 3D CRT or radical prostatectomy is equivalent to cost of SRT. Treatment morbidity was lower with 3D CRT. Our findings reflect an overall benefit with 3D CRT as a new promising technology in treatment of localized prostate cancer. Dose-escalation studies may enhance its efficacy and cost benefit.

CT virtual simulation

Advances in computer technology and software design have enabled the concept of virtual simulation, first suggested by George Sherouse, to be realized. This article reviews the hardware and software requirements that provide a system that feels like a simulator and can facilitate the 3D planning process. Fast digital reconstruction of a radiograph from a CT data set provides true verification of treatment field design within the constraints of the virtual method. The clinical application of this technique is discussed in detail in relation to particular treatment sites.

Efficient CT simulation of the four-field technique for conformal radiotherapy of prostate carcinoma

PURPOSE

Conformal radiotherapy of prostate carcinoma relies on contouring of individual CT slices for target and normal tissue localization. This process can be very time consuming. In the present report, we describe a method to more efficiently localize pelvic anatomy directly from digital reconstructed radiographs (DRRs).

MATERIALS AND METHODS

Ten patients with prostate carcinoma underwent CT simulation (the spiral mode at 3 mm separation) for conformal four-field "box" radiotherapy. The bulbous urethra and bladder were opacified with iodinated contrast media. On lateral and anteroposterior DRRs, the volume of interest (VOI) was restricted to 1.0-1.5 cm tissue thickness to optimize digital radiograph reconstruction of the prostate and seminal vesicles. By removing unessential voxel elements, this method provided direct visualization of those structures. For comparison, the targets of each patient were also obtained by contouring CT axial slices.

RESULTS

The method was successfully performed if the target structures were readily visualized and geometrically corresponded to those generated by contouring axial images. The targets in 9 of 10 patients were reliable representations of the CT-contoured volumes. One patient had 18 mm variation due to the lack of bladder opacification. Using VOIs to generate thin tissue DRRs, the time required for target and normal tissue localization was on the average less than 5 min.

CONCLUSION

In CT simulation of the four-field irradiation technique for prostate carcinoma, thin-tissue DRRs allowed for efficient and accurate target localization without requiring individual axial image contouring. This method may facilitate positioning of the beam isocenter and provide reliable conformal radiotherapy.

Development of an integrated radiotherapy network system

PURPOSE

To introduce the process of developing an integrated radiotherapy network.

METHODS AND MATERIALS

We developed a new radiotherapy treatment-planning system in 1987 that we named the Computer Tomography (CT) simulator. CT images were immediately transported to multiimage monitors and to a planning computer, and treatment planning could be performed with the patient lying on the CT couch. The results of planning were used to guide a laser projector, and radiation fields were projected onto the skin of the patient. Since 1991, an integrated radiotherapy network system has been developed, which consists of a picture archiving and communicating system (PACS), a radiotherapy information database, a CT simulator, and a linear accelerator with a multileaf collimator.

RESULTS

Clinical experience has been accumulated in more than 1,000 patients. Based on our 7 years of experience, we have modified several components of our original CT simulator and have developed a second generation CT simulator. A standard protocol has been developed for communication between the CT scanner, treatment planning computer, and radiotherapy apparatus using the Ethernet network. As a result, treatment planning data can be transported to the linear accelerator within 1 min after completion of treatment planning.

CONCLUSION

This system enables us to make optimal use of CT information and to devise accurate three-dimensional (3D) treatment-planning programs. Our network also allows for the performance of fully computer-controlled dynamic arc conformal therapy.

Cone-beam CT for radiotherapy applications

Clinical implementation of cone-beam tomography has been hampered by the lack of two-dimensional electronic x-ray detectors that can encompass the full width of the body. We encountered the undersized detector problem in our development of a cone-beam CT system for radiotherapy applications. In order to mitigate the problem, we developed an algorithm which permits an increased reconstruction volume to be imaged using a detector of a given size. We describe the algorithm and report on its implementation using a radiotherapy simulator configured with a digital fluorography unit.

Three-dimensional treatment planning and conformal radiation therapy: preliminary evaluation

Preliminary clinical results are presented for 209 patients with cancer who had treatment planned on our three-dimensional radiation treatment planning (3-D RTP) system and were treated with external beam conformal radiation therapy. Average times (min) for CT volumetric simulation were: 74 without or 84 with contrast material; 36 for contouring of tumor/target volume and 44 for normal anatomy; 78 for treatment planning; 53 for plan evaluation/optimization; and 58 for verification simulation. Average time of daily treatment sessions with 3-D conformal therapy or standard techniques was comparable for brain, head and neck, thoracic, and hepatobiliary tumors (11.8-14 min and 11.5-12.1, respectively). For prostate cancer patients treated with 3-D conformal technique and Cerrobend blocks, mean treatment time was 19 min; with multileaf collimation it was 14 min and with bilateral arc rotation, 9.8 min. Acute toxicity was comparable to or lower than with standard techniques. Sophisticated 3-D RTP and conformal irradiation can be performed in a significant number of patients at a reasonable cost. Further efforts, including dose-escalation studies, are necessary to develop more versatile and efficient 3-D RTP systems and to enhance the cost benefit of this technology in treatment of patients with cancer.