Inverse plan optimization accounting for random geometric uncertainties with a multiple instance geometry approximation (MIGA).

Radiotherapy treatment plans that are optimized to be highly conformal based on a static patient geometry can be degraded by setup errors and/or intratreatment motion, particularly for IMRT plans. To achieve improved plans in the face of geometrical uncertainties, direct simulation of multiple instances of the patient anatomy (to account for setup and/or motion uncertainties) is used within the inverse planning process. This multiple instance geometry approximation (MIGA) method uses two or more instances of the patient anatomy and optimizes a single beam arrangement for all instances concurrently. Each anatomical instance can represent expected extremes or a weighted distribution of geometries. The current implementation supports mapping between instances that include distortions, but this report is limited to the use of rigid body translations/ rotations. For inverse planning, the method uses beamlet dose calculations for each instance, with the resulting doses combined using a weighted sum of the results for the multiple instances. Beamlet intensities are then optimized using the inverse planning system based on the cost for the composite dose distribution. MIGA can simulate various types of geometrical uncertainties, including random setup error and intratreatment motion. A limited number of instances are necessary to simulate Gaussian-distributed errors. IMRT plans optimized using MIGA show significantly less degradation in the face of geometrical errors, and are robust to the expected (simulated) motions. Results for a complex head/neck plan involving multiple target volumes and numerous normal structures are significantly improved when the MIGA method of inverse planning is used. Inverse planning using MIGA can lead to significant improvements over the use of simple PTV volume expansions for inclusion of geometrical uncertainties into inverse planning, since it can account for the correlated motions of the entire anatomical representation. The optimized plan results reflect the differing patient geometry situations which can be important near the surface or heterogeneities. For certain clinical situations, the MIGA optimization approach can correct for a significant part of the degradation of the plan caused by the setup uncertainties.

Optimization and clinical use of multisegment intensity-modulated radiation therapy for high-dose conformal therapy.

Intensity-modulated radiation therapy (IMRT) may be performed with many different treatment delivery techniques. This article summarizes the clinical use and optimization of multisegment IMRT plans that have been used to treat more than 350 patients with IMRT over the last 4.5 years. More than 475 separate clinical IMRT plans are reviewed, including treatments of brain, head and neck, thorax, breast and chest wall, abdomen, pelvis, prostate, and other sites. Clinical planning, plan optimization, and treatment delivery are summarized, including efforts to minimize the number of additional intensity-modulated segments needed for particular planning protocols. Interactive and automated optimization of segmental and full IMRT approaches are illustrated, and automation of the segmental IMRT planning process is discussed.

Potential improvement in the results of irradiation for prostate carcinoma using improved dose distribution.

Results for radiation treatment of prostate carcinoma indicate that nearly one-third of Stage C patients fail locally. This number will likely increase as occult failures are discovered by monitoring serum prostate specific antigen levels. Thus, there is need for techniques that would increase the local control of prostatic carcinoma. Using cross-sectional imaging and 3-dimensional treatment planning, dose distributions for photon irradiation can be created that conform more closely to the shape of the prostate and seminal vesicles, sparing additional dose to portions of bladder and rectum. A dose escalation trial is underway to investigate whether these techniques will lead to increased local control without unacceptable increases in bladder and rectal complications. While zero local failures is probably an unattainable goal, reduction in local failure in prostate cancer would likely increase the overall cure rate in this disease.

Advanced interactive planning techniques for conformal therapy: high level beam descriptions and volumetric mapping techniques.

PURPOSE: To aid in design of conformal radiation therapy treatment plans involving many conformally shaped fields, this work investigates the use of two methodologies to enhance the ease of interactive treatment planning: high-level beam constructs and beam's-eye view volumetric mapping. METHODS AND MATERIALS: High-performance computer graphics running on various workstations using a graphical visualization system (AVS) have been used in this work. Software specific to this application has been written in standard FORTRAN and C languages. A new methodology is introduced by defining radiation therapy "fields" to be composed of multiple beam "segments." Fields can then be defined as higher-level entities such as arcs, cones, and other shapes. A "segmental cone" field, for example, is defined by a symmetry axis and a cone angle, and can be used to rapidly place a series of beam segments that converge at the target volume, while reducing the degree of overlap elsewhere. A new beam's-eye view (BEV) volumetric mapping technique is presented to aid in selecting the placement of conformal radiation fields. With this technique, the relative average dose within an organ of interest is calculated for a sampling of isocentric, conformally shaped beams and displayed either as a "globe," which can be combined with the display of anatomical surfaces, or as a two-dimensionally mapped projection. The dose maps from multiple organs can be generated, stacked, or composited with relative weightings to aid in the placement of fields that minimize overlap with critical structures. RESULTS: The use of these new methodologies is demonstrated for prostate and lung treatment sites and compared to conventional planning techniques. DISCUSSION: The use of many beams for conformal treatment delivery is difficult with current interactive planning. The use of high-level beam constructs provides a means to quickly specify, place, and configure multiple beam arrangements. The BEV volumetrics aids in the placing of fields, which minimize involvement with critical normal tissues. CONCLUSIONS: Early experience with the new methodologies suggest that the new methods help to enhance (or at least speed up) the ability of a treatment planner to create optimal radiation treatment field arrangements.

A computer-controlled conformal radiotherapy system. III: Graphical simulation and monitoring of treatment delivery.

PURPOSE: Safe and efficient delivery of radiotherapy using computer-controlled machines requires new procedures to design and verify the actual delivery of these treatments. Graphical simulation and monitoring techniques for treatment delivery have been developed for this purpose. METHODS AND MATERIALS: A graphics-based simulator of the treatment machine and a set of procedures for creating and manipulating treatment delivery scripts are used to simulate machine motions, detect collisions, and monitor machine positions during treatment. The treatment delivery simulator is composed of four components: a three-dimensional dynamic model of the treatment machine; a motion simulation and collision detection algorithm, user-interface widgets that mimic the treatment machine's control and readout devices; and an icon-based interface for creating and manipulating treatment delivery scripts. These components are used in a stand-alone fashion for interactive treatment delivery planning and integrated with a machine control system for treatment implementation and monitoring. RESULTS: A graphics-based treatment delivery simulator and a set of procedures for planning and monitoring computer-controlled treatment delivery have been developed and implemented as part of a comprehensive computer-controlled conformal radiotherapy system. To date, these techniques have been used to design and help monitor computer-controlled treatments on a radiotherapy machine for more than 200 patients. Examples using these techniques for treatment delivery planning and on-line monitoring of machine motions during therapy are described. CONCLUSION: A system that provides interactive graphics-based tools for defining the sequence of machine motions, simulating treatment delivery including collision detection, and presenting the therapists with continual visual feedback from the treatment machine has been successfully implemented for routine clinical use as part of an overall system for computer-controlled conformal radiotherapy treatment, and is considered a necessary part of the routine treatment methodology.

Full integration of the beam's eye view concept into computerized treatment planning.

A complete set of beam's eye view (BEV) and beam portal design features have been integrated into a computerized 3-dimensional radiotherapy treatment planning system. Among the features implemented is the ability to mix BEV graphics with gray-scale images such as simulator and verification radiographs, and digital reconstructed radiographs. Image processing techniques have been developed to both enhance verification images and to detect radiation field boundaries. These portal simulation and presentation techniques are being used clinically to design and verify radiation fields with manual or automatically-designed field shaping blocks. The ability to perform computer dose calculations for planes which are parallel or perpendicular to a specified beam's central axis is available and this feature has also proven useful for treatment plan evaluation and optimization. Finally, direct comparison of computer-generated portal images with actual simulation and verification radiographs is also possible. These techniques allow the direct integration of "CT-directed treatment planning" with block design, simulator films and port films, and other Beam's Eye View-type displays.

A large screen digitizer system for radiation therapy treatment planning.

PURPOSE: This paper describes a new technique for manually drawing contours of anatomy over image data for the purposes of radiation therapy treatment planning. METHODS AND MATERIALS: A large area rear-projectible digitizer tablet is used together with a projection TV system to display computer graphics and image data. Large images of computed tomography or magnetic resonance cross-sections are displayed and the digitizer is used to directly trace outlines of important organs. Digitizer menus allow multiple functions for selecting images and structures, for changing the grayscale level and window, and for zooming and roaming the image. RESULTS: This device has been in clinical operation for many years and has proven to greatly increase the speed of entering cross-sectional outlines defined for serial computed tomography images sets. A small timing study of clinical usage demonstrates up to a factor of ten improvement in the speed of contour entry. CONCLUSION: For 3-dimensional radiation therapy, tumor, and target volumes, as well as important critical organs, must be delineated from serial sets of computed tomography or magnetic resonance images. Often 30 or more slices must be considered and the process of outlining structures on this number of slices can represent a significant fraction of the total treatment planning time. The device described in this paper greatly improve the ease and speed of manual contour entry for 3-dimensional radiation therapy planning.

Expanding the use and effectiveness of dose-volume histograms for 3-D treatment planning. I: Integration of 3-D dose-display.

PURPOSE: A technique is presented for overcoming a major deficiency of histogram analysis in three-dimensional (3-D) radiotherapy treatment planning; the lack of spatial information. METHODS AND MATERIALS: In this technique, histogram data and anatomic images are displayed in a side-by-side fashion. The histogram curve is used as a guide to interactively probe the nature of the corresponding 3-D dose distribution. Regions of dose that contribute to a specific dose bin or range of bins are interactively highlighted on the anatomic display as a window-style cursor is positioned along the dose-axis of the histogram display. This dose range highlighting can be applied to two-dimensional (2-D) images and to 3-D views which contain anatomic surfaces, multimodality image data, and representations of radiation beams and beam modifiers. Additionally, as a range of histogram bins is specified, dose and volume statistics for the range are continually updated and displayed. RESULTS: The implementation of these techniques is presented and their use illustrated for a nonaxial three field treatment of a hepatic tumor. CONCLUSION: By integrating displays of 3-D doses and the corresponding histogram data, it is possible to recover the positional information inherently lost in the calculation of a histogram. Important questions such as the size and location of hot spots in normal tissues and cold spots within target volumes can be more easily uncovered, making the iterative improvement of treatment plans more efficient.

Integration of magnetic resonance imaging into radiation therapy treatment planning: I. Technical considerations.

This paper presents the results of a feasibility study specifically addressing the technical and operational difficulties in making quantitative use of Magnetic Resonance Imaging (MRI) in radiation therapy treatment planning (RTTP). Selected radiotherapy patients have been studied with both CT and MRI as part of the treatment planning process. Both sets of images, along with mechanically-obtained external contour and simulator film data, are entered into the treatment planning system. All of the capabilities of the fully three dimensional planning system U-MPlan are available to both the CT and MRI images, in which any image can be used as the backdrop for interactive beam positioning, beam portal simulation, and dose distribution displays for external beam and brachytherapy applications in both 2- and 3-dimensionally-oriented displays. The study has shown that to use MRI data for RTTP, one must (a) use careful patient positioning and marking, (b) transfer information from CT to MRI and vice versa, (c) determine the geometrical consistency between the CT and MR data sets, (d) investigate the unwarping of distorted MR images, and (e) have the ability to use non-axial images for determination of beam treatment technique, dose calculations, and plan evaluation.

From manual to 3-D computerized treatment planning for 125-I stereotactic brain implants.

Aspects of planning for the treatment of high grade primary or recurrent brain tumors with stereotactically placed catheters afterloaded with high activity 125-I seeds are discussed. At our institution, planning has evolved from a simple manual process, which assumed geometric symmetry, through a more advanced manual process, that took advantage of certain mechanical properties of the stereotactic frame used, into a sophisticated, computerized planning approach that includes optimization of the source distribution and 3-D displays. Use of the simple manual method is limited to the rare situations where target volumes are quite regular in shape. The advanced manual method provides some customization for irregularly shaped volumes, but is slow and tedious to implement. The interactive, computerized approach permits identification of target volumes directly on CT slices, reconstructions in arbitrary planes, and optimization of catheter placement, source separation along each catheter, and selection of source strengths from an available inventory. A multi-format display feature which includes a probe's eye view perspective is provided to aid in planning. Integral dose-volume histograms for the target volume point out the advantages in using sophisticated, 3-D, computerized planning systems for these implants.

Boost treatment of the prostate using shaped, fixed fields.

Using a CT-based, 3-D treatment planning system and Beam's Eye-View (BEV) displays, shaped fixed-field techniques have been developed for external beam boost treatment of Stage C carcinoma of the prostate. The basic technique comprises three sets of opposing beams (laterals and +/- 45 degrees with respect to the lateral) into a 6-field arrangement. Target volumes together with bladder and rectal wall volumes are outlined on axial CT slices and combined to form 3-D volumes. For each field, an interactive BEV display is produced showing the target volume in its correct 3-D geometrical perspective and an auto-block routine is used to design focused blocks which conform to that volume. Full 3-D volume calculations computed for those plans on 17 patients were analyzed along with similar calculations for more traditional unblocked 4-field box and bilateral arc techniques. Compared to the 95% isodose volume for the 6-field conformational technique, traditional open beam full target coverage techniques typically produce high dose volumes which cover up to five times as much uninvolved tissue. Dose volume histograms illustrate that typically half as much bladder and rectal tissue is treated to high dose using the conformational boost techniques. From the dosimetric perspective of sparing normal tissues, shaped fixed-field boost techniques are shown to be clearly superior to traditional full coverage bilateral arc techniques. Smaller 8 cm X 8 cm arc techniques are shown to be quantitatively unacceptable for treatment of this advanced stage disease, as they typically misses 20-35% of the target volume.

The influence of lung density corrections on treatment planning for primary breast cancer.

Primary breast cancer is generally treated with opposed radiation beams oriented tangentially with respect to the breast. This technique attempts to minimize the dose to the lung and other normal tissues, while at the same time producing a uniform dose distribution throughout the irradiated breast. Although a part of the lung is always included in the tangential breast fields, the effect of this low density tissue on the dose distribution is rarely taken into account. In the present work, the effect of lung density correction on the dose distribution resulting from tangential breast fields is analyzed. Treatment plans for a series of 34 patients treated for breast cancer have been performed using CT data. To study the effect of density corrections on the tangential field treatment plans for these patients, eight separate treatment plans for each patient have been optimized. For each of four photon energies (60Co, and 4, 6, and 10 MV X rays), treatment plans have been optimized for each patient when density correction is employed, and when unit density is assumed. Four additional dose calculations have been obtained for each patient corresponding to use of the unit density plan, but with density corrections employed in the calculation. The effects that density correction has on the wedge angles used, on the maximum dose ("hot spot") for each of several cross-sectional cuts, on the prescription isodose level which is chosen for each plan, and on homogeneity of the dose distribution over the target volume are all analyzed for the above described plans.

The clinical utility of magnetic resonance imaging in 3-dimensional treatment planning of brain neoplasms.

Results of the clinical experience gained since 1986 in the treatment planning of patients with brain neoplasms through integration of magnetic resonance imaging (MRI) into computerized tomography (CT)-based, three-dimensional treatment planning are presented. Data from MRI can now be fully registered with CT data using appropriate three-dimensional coordinate transformations allowing: (a) display of MRI defined structures on CT images; (b) treatment planning of composite CT-MRI volumes; (c) dose display on either CT or MRI images. Treatment planning with non-coplanar beam arrangements is also facilitated by MRI because of direct acquisition of information in multiple, orthogonal planes. The advantages of this integration of information are especially evident in certain situations, for example, low grade astrocytomas with indistinct CT margins, tumors with margins obscured by bone artifact on CT scan. Target definitions have repeatedly been altered based on MRI detected abnormalities not visualized on CT scans. Regions of gadolinium enhancement on MRI T1-weighted scans can be compared to the contrast-enhancing CT tumor volumes, while abnormalities detected on MRI T2-weighted scans are the counterpart of CT-defined edema. Generally, MRI markedly increased the apparent macroscopic tumor volume from that seen on contrast-CT alone. However, CT tumor information was also necessary as it defined abnormalities not always perceptible with MRI (on average, 19% of composite CT-MRI volume seen on CT only). In all, the integration of MRI data with CT information has been found to be practical, and often necessary, for the three-dimensional treatment of brain neoplasms.

A computer-controlled conformal radiotherapy system. I: Overview.

PURPOSE: Equipment developed for use with computer-controlled conformal radiotherapy (CCRT) treatment techniques, including multileaf collimators and/or computer-control systems for treatment machines, are now available. The purpose of this work is to develop a system that will allow the safe, efficient, and accurate delivery of CCRT treatments as routine clinical treatments, and permit modifications of the system so that the delivery process can be optimized. METHODS AND MATERIALS: The needs and requirements for a system that can fully support modern computer-controlled treatment machines equipped with multileaf collimators and segmental or dynamic conformal therapy capabilities have been analyzed and evaluated. This analysis has been used to design and then implement a complete approach to the delivery of CCRT treatments. RESULTS: The computer-controlled conformal radiotherapy system (CCRS) described here consists of a process for the delivery of CCRT treatments, and a complex software system that implements the treatment process. The CCRS system described here includes systems for plan transfer, treatment delivery planning, sequencing of the actual treatment delivery process, graphical simulation and verification tools, as well as an electronic chart that is an integral part of the system. The CCRS system has been implemented for use with a number of different treatment machines. The system has been used clinically for more than 2 years to perform CCRT treatments for more than 200 patients. CONCLUSIONS: A comprehensive system for the implementation and delivery of computer-controlled conformal radiation therapy (CCRT) plans has been designed and implemented for routine clinical use with multisegment, computer-controlled, multileaf-collimated conformal therapy. The CCRS system has been successfully implemented to perform these complex treatments, and is considered quite important to the clinical use of modern computer-controlled treatment techniques.

A computer-controlled conformal radiotherapy system. II: Sequence processor.

PURPOSE: A sequence processor (SP) is described as part of a larger computer-controlled conformal radiotherapy system (CCRS). The SP provides the means to accept and then translate highly sophisticated radiation therapy treatment plans into vendor specific instructions to control treatment delivery on a computer-controlled treatment machine. METHODS AND MATERIALS: The sequence processor (SP) is a small workstation computer that interfaces to the control computer of computer-controlled treatment machines, and to other parts of the larger CCRS system. The system reported here has been interfaced to a computer-controlled racetrack microtron with two treatment gantries, and also to other linear accelerator treatment machines equipped with multileaf collimators. An extensive design process has been used in defining the role of the SP within the context of the larger CCRS project. Flexibility and integration with various components of the project, including databases, treatment planning system, graphical simulator, were key factors in the development. In conjunction with the planned set of treatment fields, a procedural scripting language is used to define the sequence of treatment events that are performed, including operator interactions, communications to other systems such as dosimetry and portal imaging devices, and database management. RESULTS: A flexible system has been developed to allow investigation into procedural steps required for simulating and delivering complex radiation treatments. The system has been used to automate portions of the acceptance testing for the control system of the microtron, and is used for routine daily quality assurance testing. The sequence processor system described here has been used to deliver all clinical treatments performed on the microtron system in 2 years of clinical treatment (more than 200 patients treated to a variety of treatment sites). CONCLUSIONS: The sequence processor system has enabled the delivery of complex treatment using computer-controlled treatment machines. The flexibility of the system allows integration with secondary devices and modification of procedural steps, making it possible to develop effective techniques for insuring safe and efficient computer-controlled conformal radiation therapy treatments.

A computer-controlled conformal radiotherapy system. IV: Electronic chart.

PURPOSE: The design and implementation of a system for electronically tracking relevant plan, prescription, and treatment data for computer-controlled conformal radiation therapy is described. METHODS AND MATERIALS: The electronic charting system is implemented on a computer cluster coupled by high-speed networks to computer-controlled therapy machines. A methodical approach to the specification and design of an integrated solution has been used in developing the system. The electronic chart system is designed to allow identification and access of patient-specific data including treatment-planning data, treatment prescription information, and charting of doses. An in-house developed database system is used to provide an integrated approach to the database requirements of the design. A hierarchy of databases is used for both centralization and distribution of the treatment data for specific treatment machines. RESULTS: The basic electronic database system has been implemented and has been in use since July 1993. The system has been used to download and manage treatment data on all patients treated on our first fully computer-controlled treatment machine. To date, electronic dose charting functions have not been fully implemented clinically, requiring the continued use of paper charting for dose tracking. CONCLUSIONS: The routine clinical application of complex computer-controlled conformal treatment procedures requires the management of large quantities of information for describing and tracking treatments. An integrated and comprehensive approach to this problem has led to a full electronic chart for conformal radiation therapy treatments.

Three-dimensional treatment planning of intracavitary gynecologic implants: analysis of ten cases and implications for dose specification.

PURPOSE: Results of 3-dimensional treatment planning for ten intracavitary gynecologic implants and implications for dose specification are presented. METHODS AND MATERIALS: Using a computed tomographic (CT) compatible intracavitary applicator we have performed CT scans during gynecologic brachytherapy in 10 cases. A CT-based treatment planning system with 3-dimensional capabilities was used to calculate and display dose in three dimensions. Conventional point doses including the estimated bladder and rectal maximum doses and dose to Point A were acquired from orthogonal simulation films. CT maximum bladder and rectal doses and minimum cervix doses were ascertained from isodose lines displayed on individual CT images. Dose volume histograms for the bladder, rectum and cervix were generated and used to obtain volume of the cervix target volume receiving less than the prescribed dose and the volume of bladder and rectum receiving more than the orthogonal maximum doses. The 5 cc volume of bladder and rectum receiving the highest dose were also calculated. RESULTS: Average values of CT point doses and volumes are compared with the traditionally obtained doses. As demonstrated by others, much higher bladder and rectal doses are found using the CT information. The minimum dose to the cervix target volume is lower than the dose to Point A in each case. CT maximum bladder and rectum and minimum cervix target doses may not be the best index doses to correlate with outcome because of the small volumes receiving the dose. CONCLUSION: We hypothesize that clinically useful bladder, rectal and cervix target volume doses will include volume information which is obtainable with dose volume histogram analysis.

Three-dimensional treatment planning of astrocytomas: a dosimetric study of cerebral irradiation.

To demonstrate that 3-dimensional planning is both practical and applicable to the treatment of high-grade astrocytomas, 50 patients over a 2-year period have received cerebral irradiation delivered in focussed, non-axial techniques employing from 2 to 5 beams. Astrocytomas have been planned using rapid, practical incorporation of CT data to define appropriate tumor volumes. Tumor + 3.0 cm and tumor + 1.5 cm volumes have been treated to conventional doses of 4500 cGy and 5940 cGy, respectively, using beam orientations that maximally spared normal remaining parenchyma. Analyses of 3-dimensionally calculated plans have been performed using integral dose-volume histograms (DVH) to help select treatment techniques. Using identical CT-based volumetric data as input for generation of Beam's Eye View (BEV) designed blocks, DVH curves demonstrate dosimetric advantages of non-axial techniques over conventional parallel-opposed orientations. Assessment of the non-axial techniques in selected cases indicates that uniform target volume coverage could be maintained with a typical reduction of 30% in the total amount of brain tissue treated to high dose (95% isodose line).

Treatment planning issues related to prostate movement in response to differential filling of the rectum and bladder.

Conventional stimulation for patients with localized prostatic carcinoma often includes opacification of the dose limiting adjacent normal tissues. However, CT-based treatment planning is performed with the bladder and the rectum naturally filled or emptied. These latter conditions more closely approximate those in place at treatment Comparison of these CT-based treatment plans to simulator films taken with the rectum and bladder opacified yielded indirect evidence of movement of the prostate gland by 0.5 cm or more in 31 of 50 consecutive patients. The range of motion was 0 to 2 cm with an average of 0.5 cm (1.0 cm in the 31 patients). Six additional patients (five with local recurrence following I-125 seed implantation) were analyzed separately using CT scans. Registered CT images (3 mm slices) taken with the rectum and bladder full and/or empty provided direct evidence of prostate movement in 3 of the 6 patients. The dosimetric consequences of this movement are demonstrated using 3-dimensional dose distributions.

The impact of treatment complexity and computer-control delivery technology on treatment delivery errors.

PURPOSE: To analyze treatment delivery errors for three-dimensional (3D) conformal therapy performed at various levels of treatment delivery automation and complexity, ranging from manual field setup to virtually complete computer-controlled treatment delivery using a computer-controlled conformal radiotherapy system (CCRS). METHODS AND MATERIALS: All treatment delivery errors which occurred in our department during a 15-month period were analyzed. Approximately 34,000 treatment sessions (114,000 individual treatment segments [ports]) on four treatment machines were studied. All treatment delivery errors logged by treatment therapists or quality assurance reviews (152 in all) were analyzed. Machines "M1" and "M2" were operated in a standard manual setup mode, with no record and verify system (R/V). MLC machines "M3" and "M4" treated patients under the control of the CCRS system, which (1) downloads the treatment delivery plan from the planning system; (2) performs some (or all) of the machine set up and treatment delivery for each field; (3) monitors treatment delivery; (4) records all treatment parameters; and (5) notes exceptions to the electronically-prescribed plan. Complete external computer control is not available on M3; therefore, it uses as many CCRS features as possible, while M4 operates completely under CCRS control and performs semi-automated and automated multi-segment intensity modulated treatments. Analysis of treatment complexity was based on numbers of fields, individual segments, nonaxial and noncoplanar plans, multisegment intensity modulation, and pseudoisocentric treatments studied for a 6-month period (505 patients) concurrent with the period in which the delivery errors were obtained. Treatment delivery time was obtained from the computerized scheduling system (for manual treatments) or from CCRS system logs. Treatment therapists rotate among the machines; therefore, this analysis does not depend on fixed therapist staff on particular machines. RESULTS: The overall reported error rate (all treatments, machines) was 0.13% per segment, or 0.44% per treatment session. The rate (per machine) depended on automation and plan complexity. The error rates per segment for machines M1 through M4 were 0.16%, 0.27%, 0.12%, 0.05%, respectively, while plan complexity increased from M1 up to machine M4. Machine M4 (the most complex plans and automation) had the lowest error rate. The error rate decreased with increasing automation in spite of increasing plan complexity, while for the manual machines, the error rate increased with complexity. Note that the real error rates on the two manual machines are likely to be higher than shown here (due to unnoticed and/or unreported errors), while (particularly on M4) virtually all random treatment delivery errors were noted by the CCRS system and related QA checks (including routine checks of machine and table readouts for each treatment). Treatment delivery times averaged from 14 min to 23 min per plan, and depended on the number of segments/plan, although this analysis is complicated by other factors. CONCLUSION: Use of a sophisticated computer-controlled delivery system for routine patient treatments with complex 3D conformal plans has led to a decrease in treatment delivery errors, while at the same time allowing delivery of increasingly complex and sophisticated conformal plans with little increase in treatment time. With renewed vigilance for the possibility of systematic problems, it is clear that use of complete and integrated computer-controlled delivery systems can provide improvements in treatment delivery, since more complex plans can be delivered with fewer errors, and without increasing treatment time.