[en] Purpose: Both human and computer optimization of treatment plans have advantages; humans are much better at global pattern recognition, and computers are much better at detailed calculations. A major impediment to human optimization of treatment plans by manipulation of beam parameters is the long time required for feedback to the operator on the effectiveness of a change in beam parameters. Our goal was to create a real-time dose calculation and display system that provides the planner with immediate (fraction of a second) feedback with displays of three-dimensional (3D) isodose surfaces, digitally reconstructed radiographs (DRRs), dose-volume histograms, and/or a figure of merit (FOM) (i.e., a single value plan score function). This will allow the experienced treatment planner to optimize a plan by adjusting beam parameters based on a direct indication of plan effectiveness, the FOM value, and to use 3D display of target, critical organs, DRRs, and isodose contours to guide changes aimed at improving the FOM value. Methods and Materials: We use computer platforms that contain easily utilized parallel processors and very tight coupling between calculation and display. We ported code running on a network of two workstations and an array of transputers to a single multiprocessor workstation. Our current high-performance graphics workstation contains four 150-MHz processors that can be readily used in a shared-memory multithreaded calculation. Results: When a 10 x 10-cm beam is moved, using an 8-mm dose grid, the full 3D dose matrix is recalculated using a Bentley-Milan-type dose calculation algorithm, and the 3D dose surface display is then updated, all in < 0.1 s. A 64 x 64-pixel DRR calculation can be performed in < 0.1 s. Other features, such as automated aperture calculation, are still required to make real-time feedback practical for clinical use. Conclusion: We demonstrate that real-time plan optimization using general purpose multiprocessor workstations is a practical goal. Parallel processing technology provides this capability for 3D planning systems, and when combined with objective plan ranking algorithms should prove effective for optimizing 3D conformal radiation therapy. Compared to our earlier transputer work, multiprocessor workstations are more easily programmed, making software development costs more reasonable compared with uni processor development costs. How the dose calculation is partitioned into parallel tasks on a multiprocessor work station can make a significant difference in performance. Shared-memory multiprocessor workstations are our first choice for future work, because they require minimum programming effort and continue to be driven to higher performance by competition in the workstation arena

[en] Purpose: To evaluate the relative frequency and magnitude of intratreatment and intertreatment displacements in the patient positioning for pelvic radiotherapy using electronic portal imaging. Methods and Materials: Five hundred ninety-four electronic portal images of seven patients treated with a four-field pelvic technique were evaluated. All patients were treated prone without an immobilization device. Two fields were treated per day, from which an average of two electronic portal images were obtained for each field. No treatment was interrupted or adjusted on the basis of these images. Each image was aligned to the corresponding simulation film to measure the displacements in the mediolateral, craniocaudal, and anteroposterior directions relative to the simulated center. The intertreatment displacement was the displacement measured from the initial image for each daily treated field. For each daily treated field the intratreatment displacement was calculated by subtracting the displacement measured on the initial image from the displacement measured on the final image. Results: The frequency of intertreatment displacements exceeding 10 mm was 3%, 16%, and 23% for the mediolateral, craniocaudal, and anteroposterior translations, respectively. There were no intratreatment displacements exceeding 10 mm (p < 0.001). The frequency of intertreatment displacements exceeding 5 mm was 40, 52, and 51% for the mediolateral, craniocaudal, and anteroposterior translations, respectively; whereas, the frequency of intratreatment displacements exceeding 5 mm was 1, 5, and 7% for the same translations, respectively (p < 0.001). The standard deviation of the intertreatment displacements was at least three times as great as the standard deviation of the intratreatment displacements for all translations. These deviations were greater than the precision limit of the measurement technique, which is approximately 1 mm. Each patient had one direction where systematic error predominated in intertreatment positioning. Random error predominated for intratreatment positioning and for the other two directions in intertreatment positioning. Conclusions: During a course of pelvic radiotherapy, the frequency of intertreatment displacements exceeding 5 and 10 mm is significantly greater than the frequency of intratreatment displacements of these magnitudes. Errors in intertreatment positioning are predominantly systematic in one direction for each patient, whereas intratreatment error is predominantly random. Because patients do not move considerably during the daily treatment of a pelvic field, a single electronic portal image per daily field may be considered representative of the treated position

[en] PURPOSE: 3-D conformal radiation therapy (3DCRT) holds promise in allowing safe escalation of radiation dose to increase the local control of prostate cancer. Prospective evaluation of this new modality requires strict quality assurance (QA). We report the results of QA review on patients receiving 3DCRT for prostate cancer on a cooperative group trial. MATERIALS and METHODS: In 1993 the NCI awarded the ACR/RTOG and nine institutions an RFA grant to study the use of 3DCRT in the treatment of prostate cancer. A phase I/II trial was developed to: a) test the feasibility of conducting 3DCRT radiation dose escalation in a cooperative group setting; b) establish the maximum tolerated radiation dose that can be delivered to the prostate; and c) quantify the normal tissue toxicity rate when using 3DCRT. In order to assure protocol compliance each participating institution was required to implement data exchange capabilities with the RTOG 3D QA center. The QA center reviews at a minimum the first five case from each participating center and spot checks subsequent submissions. For each case review the following parameters are evaluated: 1) target volume delineation, 2) normal structure delineation, 3) CT data quality, 4) field placement, 5) field shaping, and 6) dose distribution. RESULTS: Since the first patient was registered on August 23, 1994, an additional 170 patients have been accrued. Each of the nine original approved institutions has participated and three other centers have recently passed quality assurance bench marks for study participation. Eighty patients have been treated at the first dose level (68.4 Gy minimum PTV dose) and accrual is currently ongoing at the second dose level (73.8 Gy minimum PTV dose). Of the 124 cases that have undergone complete or partial QA review, 30 cases (24%) have had some problems with data exchange. Five of 67 CT scans were not acquired by protocol standards. Target volume delineation required the submitting institution's correction and resubmission in 7 of 67 (10.4%) reviewed cases. Normal tissues required correction in 6 of 67 (8.9%) of cases. Initial field shaping differed from the submitted treatment plan by more than 5 mm in significant regions of the field in only 2% of the cases. Isocenter shifts of more than 5 mm on at least one of the treated fields was identified in 7% of initial port films examined. Dosimetry review has demonstrated that 14 of 86 cases (16.3%) had minor variations in target volume coverage (<100% of the target volume coverage by the prescription isodose) and 3.4% had major variation in dose coverage (<95% coverage of target volume by prescription isodose). Nineteen of 93 cases (20%) had more than 7% heterogeneity of dose within the planning target volume. CONCLUSION: 3DCRT can be studied and implemented in a cooperative group setting. Although data exchange problems in this study have been frequent, most of these problems occurred early in the trial and have been resolved in most circumstances. A significant amount of variation has been identified in the definition of target volumes and organs at risk. Similarly, field shaping and port film evaluation showed occasional errors. It is our impression that quality assurance is a critical component of 3DCRT in the cooperative group setting. As experience in the planning of patients with 3DCRT increases, it is expected that the frequency of planning variations will diminish

[en] The Advanced Technology QA Consortium (ATC) has identified a problem in the encoding of DICOM RT Dose objects when these objects are converted from Implicit-VR (Little-Endian) transfer syntax to an Explicit-VR transfer syntax. There exist data elements, which can be represented in Implicit-VR Little-Endian transfer syntax but that cannot be represented in Explicit-VR Little-Endian transfer syntax. (letter to the editor)

[en] Purpose: We recently replaced our university developed CT simulator prototype with a commercial grade spiral CT simulator (Picker AcQsim) that is networked with three independent virtual simulation workstations and our 3D radiation therapy planning (3D-RTP) system multiple workstations. This presentation will report our initial experience with this CT simulation device and define criteria for optimum clinical use as well as describe some potential drawbacks of the current system. Methods and Materials: Over a 10 month period, 210 patients underwent CT simulation using the AcQsim. An additional 127 patients had a volumetric CT scan done on the device with their CT data and target and normal tissue contours ultimately transferred to our 3D-RTP system. We currently perform the initial patient localization and immobilization in the CT simulation suite by using CT topograms and a fiducial laser marking system. Immobilization devices, required for all patients undergoing CT simulation, are constructed and registered to a device that defines the treatment table coordinates. Orthogonal anterior and lateral CT topograms document patient alignment and the position of a reference coordinate center. The volumetric CT scan with appropriate CT contrast materials administered is obtained while the patient is in the immobilization device. On average, more than 100 CT slices are obtained per study. Contours defining tumor, target, and normal tissues are drawn on a slice by slice basis. Isocenter definition can be automatically defined within the target volume and marked on the patient and immobilization device before leaving the initial CT simulation session. Virtual simulation is then performed on the patient data set with the assistance of predefined target volumes and normal tissue contours displayed on rapidly computed digital reconstructed radiographs (DRRs) in a manner similar to a conventional fluoroscopic radiotherapy simulator. Lastly, a verification simulation is performed with the patient on a conventional simulator in which portal radiographs are compared against DRRs. Results: Several important issues have been identified that impact on clinical utilization of the CT simulator. Thin, finely spaced CT slices improve the DRR quality but potentially degrade the quality of cross sectional images used for image segmentation. Large data sets also increase the workload for anatomic image segmentation (contouring) and raise concerns regarding data storage and easy network access. Software for image segmentation has been significantly improved allowing rapid drawing of contours around tumor/target volumes and normal tissues and improved edit functions that allow interpolation, copying, and correction of contours. These tools have reduced the time for defining all the normal tissues and target volumes for some sites (e.g. prostate) to less than 30 minutes. Acquisition of this large volume CT data currently takes less than 30 minutes potentially reducing patient time in the simulation/planning process. Difficult simulations, such as mantle/periaortic and craniospinal fields that typically require multiple 2-3 hour simulation sessions, now take half as much time with the spiral CT scanner. Subsequent field reductions or secondary fields can be planned without the physical presence of the patient. A comparison of predicted isocenter shift coordinates and actual coordinates used for verification simulation showed that the average change in isocenter position was less than a few mm indicating that the verification process can likely be eliminated. Disadvantages of current device include limited CT ring size (70 cm) and reconstruction window (48 cm) which prevent universal application of technique to all patients. Conclusion: The AcQsim offers significant advantages over a conventional simulator in terms of patient compliance and fatigue, as well as departmental throughput. In virtual simulation, after the initial acquisition of CT data, the CT scanner portion of the CT simulator can be used to acquire other patient data sets. Furthermore, as the plan and treatment course evolve the patient need not necessarily return to the scanner. A major advantage of the CT simulation process is the display of defined target volumes and critical structures on a high quality DRR that allows the choice of optimal beam projection to maximize target volume coverage and minimize treatment of adjacent tissues. The optimum choice of CT scan spacing and thickness is a function of desired DRR quality and the available space or image storage. The verification simulation process is likely to be eliminated as confidence in the software mounts and other security systems, such as record and verify, are added to our treatment units

[en] Purpose: The goal was to determine an adequate planning target volume (PTV) margin for three-dimensional conformal radiotherapy (3D CRT) of prostate cancer. The uncertainty in the internal positions of the prostate and seminal vesicles and the uncertainty in the treatment set-ups for a single group of patients was measured. Methods: Weekly computed tomography (CT) scans of the pelvis (n=38) and daily electronic portal images (n=1225) were reviewed for six patients who received seven-field 3D CRT for prostate cancer. The weekly CT scans were registered in three dimensions to the original treatment planning CT scan using commercially available software. This registration permitted measurement of the motion in the center-of-volume (COV) of the prostate and seminal vesicles throughout the course of therapy. The daily portal images (PI) were registered to the corresponding simulation films to measure the set-up displacement for each of the seven fields. The field displacements were then entered into a matrix program which calculated the isocenter displacement by a least squares method. The uncertainty in the internal positions of the prostate and seminal vesicles (standard deviation of the motions) was added to the uncertainty in the set-up (standard deviation of the isocenter displacements) in quadrature to arrive at a total uncertainty. Positive directions were defined in the left, anterior, and superior directions. A discussion of an adequate PTV was based on these results. Results: The mean magnitude of motion for the COV of the prostate ± the standard deviation was 0 ± 1 mm in the left-right (LR) direction, 0.5 ± 2.8 mm in the anterior-posterior (AP) direction, and 0.5 ± 3.5 mm in the superior-inferior (SI) direction. The mean magnitude of motion for the COV of the seminal vesicles ± the standard deviation was -0.3 ± 1.5 mm in the LR, 0.6 ± 4.1 mm in the AP, and 0.7 ± 2.3 mm in the SI directions, respectively. For all patients the mean isocenter displacement ± the standard deviation was 0.5 ± 3.4 mm in the LR, 1.7 ± 3.3 mm in the AP, and -0.4 ± 2.4 mm in the SI directions, respectively. The total uncertainty, which includes organ position and set-up uncertainty, for the prostate was 3.5 mm, 4.3 mm, and 4.2 mm in the LR, AP, and SI directions, respectively. For the seminal vesicles, the total uncertainty was 3.7 mm, 5.3 mm, and 3.3 mm in the LR, AP, and SI directions, respectively. The percent change in rectal volume correlated with motion of the prostate in the AP direction and with motion of the seminal vesicles in the SI direction. To account for the uncertainties with a 95% or 99% probability, PTV margins equal to two times or three times the total uncertainties are required (10 - 16 mm), respectively. Conclusions: PTV margins of 10 - 16 mm are required to encompass all (99%) possible positions of the prostate or seminal vesicles during 3D CRT. PTV margins of 7 - 11 mm will encompass the measured uncertainties with a 95% probability. PTV margins as small as 5 mm may not adequately cover the target volume. Clinicians and investigators are using 5 - 10 mm as a range for PTV margins in a current 3D CRT dose escalation protocol for prostate cancer (RTOG 94-06). Results from this trial will determine whether toxicity and local tumor control are acceptable

[en] Purpose: Guidelines to conduct multi-institutional three-dimensional conformal radiation therapy (3-D CRT) clinical trials are needed as the modality emerges from a single institution procedure to a research tool in multi-institution clinical group trials. The guidelines are used (1) to ensure that participating institutions have the proper equipment and appropriate techniques to administer 3D CRT; (2) to define a standard data set to be submitted to a review center for each treated patient to assess protocol compliance; and (3) to establish a quality assurance (QA) review process of the submitted data. Materials and Methods: Computer hardware and software components have been implemented which allow the digital data transfer (via either the Internet or magnetic tape), display, manipulation, and storage of a 3D CRT protocol patient treatment planning and image data set for QA review. Each participating institution is required to complete a 3D CRT Facility Questionnaire and submit it to the RTOG 3-D QA Center prior to enrolling patients on a 3-D CRT protocol. In addition, a protocol 'dry run' test has been designed to demonstrate each participating institutions' ability to submit a protocol compliant data set prior to placing patients on a 3D CRT study. This dry run test involves the digital transfer of all protocol required data and the supporting hard copy documentation excepting simulation or portal films/images. Results: The 3D CRT Facility Questionnaire includes descriptions of: (1) linac model, collimation system and energies to be used; (2) isocenter accuracy for gantry, collimator, and couch rotations; (3) type of immobilization repositioning system and patient motion studies if required by protocol (set-up uncertainty, organ movement); and (4) treatment verification system(s). The 3-D RTP system must have the following capabilities: (1) ability to handle at least 40 axial CT slices; (2) beam's-eye-view (BEV) display; (3) calculate 3-D dose matrices; (4) display/hard copy of superimposed isodose distributions on 2-D CT axial, saggital, and coronal image planes (optionally, multiple axial plots with adequate internal structure detail without CT images); (5) calculate/display/hard copy dose-volume histograms (DVH); (6) non-coplanar beams capability for both beam geometry definition and dose computation (optional depending on site specific protocol); and (7) calculate and display digital reconstructed radiographs (DRRs) with superimposed target volume, critical structure contours and treatment aperture (optional depending on site specific protocol). The results of the dry run test have demonstrated some difficulty in compliance with the QA guidelines, primarily pertaining to digital data transfer, and which, as the process is better defined through usage, have influenced rational modification of these guidelines. See for example 3-D RTP system requirement No.4 above (display/hard copy of superimposed isodose curves). Digital data submitted for each protocol patient include: (1) volumetric patient CT image data; (2) patient contours including target volume(s) and critical normal tissues; (3) volumetric 3-D dose distribution data including fractionation; (4) beam modality/geometry specification; (5) DVHs; and (6) digital simulator, DRRs, and portal images (optional). A 3-D QA Center staff radiation oncologist and physicist review all target volumes and designated critical structures contours superimposed on CT display, first day portal films on all patients, and the 3D dose distribution. The case is classified as per protocol if the prescription dose covers 100% of the planning target volume; as a minor variation (marginal coverage) if the prescription dose covers between ≥95% to <100% of the planning target volume; or as a major variation (miss) if the prescription dose covers less than 95% of the planning target volume. Conclusion: The technology and methodology to conduct multi-institutional 3-D CRT clinical trials is now in place. Quality assurance guidelines which address technical capability requirement s, data reporting, and treatment compliance issues are being implemented into active and developing 3D CRT protocols

[en] Purpose: To determine an adequate planning target volume (PTV) margin for three-dimensional conformal radiotherapy (3D CRT) of prostate cancer, the uncertainties in the internal positions of the prostate and seminal vesicles (SV) and in the treatment setups were measured. Methods and Materials: Weekly computed tomography (CT) scans of the pelvis (n = 51) and daily electronic portal images (n = 1630) were reviewed for eight patients who received seven-field 3D CRT for prostate cancer. The CT scans were registered in three dimensions to the original planning CT scan using commercially available software to measure the center-of volume (COV) motion of the prostate and SV. The daily portal images were registered to the corresponding simulation films to measure the setup displacements. The standard deviation (SD) of the internal organ motions was added to the SD of the setups in quadrature to determine the total uncertainty. Positive directions were left, anterior, and superior. Rotations necessary to register the CT scans and portal images were minimal and not further analyzed. Results: The mean motion for the COV of the prostate ± the SD was 0 ± 0.9 mm in the left-right (LR), 0.5 ± 2.6 mm in the anterior-posterior (AP), and 1.5 ± 3.9 mm in the superior-inferior (SI) directions. The mean motion for the COV of the SV ± the SD was 0.3 ± 1.7 mm in the LR, 0.7 ± 3.8 mm in the AP, and 0.9 ± 3.5 mm in the SI directions. For all patients the mean isocenter displacement ± the SD was 0 ± 3.1 mm in the LR, 1.4 ± 3.0 mm in the AP, and -0.4 ± 2.1 mm in the SI directions. The total uncertainty for the prostate was 3.2 mm, 4.0 mm, and 4.4 mm in the LR, AP, and SI directions, respectively. For the SV, the total uncertainty was 3.5, 4.8, and 4.1 mm in the LR, AP, and SI directions, respectively. Conclusions: PTV margins of 10 to 16 mm are required to encompass all (99%) possible positions of the prostate or SV during 3D CRT. PTV margins of 7 to 11 mm will encompass the measured uncertainties with a 95% probability. PTV margins of 5 mm may not adequately cover the intended volume

[en] Purpose: To determine whether the clinical implementation of an electronic portal imaging device can improve the precision of daily external beam radiotherapy. Methods and Materials: In 1991, an electronic portal imaging device was installed on a dual energy linear accelerator in our clinic. After training the radiotherapy technologists in the acquisition and evaluation of portal images, we performed a randomized study to determine whether online observation, interruption, and intervention would result in more precise daily setup. The patients were randomized to one of two groups: those whose treatments were actively monitored by the radiotherapy technologists and those that were imaged but not monitored. The treating technologists were instructed to correct the following treatment errors: (a) field placement error (FPE) > 1 cm; (b) incorrect block; (c) incorrect collimator setting; (d) absent customized block. Time of treatment delivery was recorded by our patient tracking and billing computers and compared to a matched set of patients not participating in the study. After the patients radiation therapy course was completed, an offline analysis of the patient setup error was planned. Results: Thirty-two patients were treated to 34 anatomical sites in this study. In 893 treatment sessions, 1,873 fields were treated (1,089 fields monitored and 794 fields unmonitored). Ninety percent of the treated fields had at least one image stored for offline analysis. Eighty-seven percent of these images were analyzed offline. Of the 1,011 fields imaged in the monitored arm, only 14 (1.4%) had an intervention recorded by the technologist. Despite infrequent online intervention, offline analysis demonstrated that the incidence of FPE > 10 mm in the monitored and unmonitored groups was 56 out of 881 (6.1%) and 95 out of 595 (11.2%), respectively; p < 0.01. A significant reduction in the incidence of FPE > 10 mm was confined to the pelvic fields. The time to treat patients in this study was 10.78 min (monitored) and 10.10 min (unmonitored). Features that were identified that prevented the technologists from recognizing more errors online include poor image quality inherent to the portal imaging device used in this study, artifacts on the portal images related to table supports, and small field size lacking sufficient anatomical detail to detect FPEs. Furthermore, tools to objectively evaluate a portal image for the presence of field placement error were lacking. These include magnification factor corrections between the simulation of portal image, online measurement tools, image enhancement tools, and image registration algorithms. Conclusion: The use of an electronic portal imaging device in our clinic has been implemented without a significant increase in patient treatment time. Online intervention and correction of patient positioning occurred rarely, despite FPEs of > 10 mm being present in more than 10% of the treated fields. A significant reduction in FPEs exceeding 10 mm was made in the group of patients receiving pelvic radiotherapy. It is likely that this improvement was made secondarily to a decrease in systematic error and not because of online interventions. More significant improvements in portal image quality and the availability of online image registration tools are required before substantial improvements can be made in patient positioning with online portal imaging

[en] Purpose: We have developed a software tool for interactively verifying treatment plan implementation. The Electronic View Box (EVB) tool copies the paradigm of current practice but does so electronically. A portal image (online portal image or digitized port film) is displayed side by side with a prescription image (digitized simulator film or digitally reconstructed radiograph). The user can measure distances between features in prescription and portal images and 'write' on the display, either to approve the image or to indicate required corrective actions. The EVB tool also provides several features not available in conventional verification practice using a light box. Methods and Materials: The EVB tool has been written in ANSI C using the X window system. The tool makes use of the Virtual Machine Platform and Foundation Library specifications of the NCI-sponsored Radiation Therapy Planning Tools Collaborative Working Group for portability into an arbitrary treatment planning system that conforms to these specifications. The present EVB tool is based on an earlier Verification Image Review tool, but with a substantial redesign of the user interface. A graphical user interface prototyping system was used in iteratively refining the tool layout to allow rapid modifications of the interface in response to user comments. Results: Features of the EVB tool include 1) hierarchical selection of digital portal images based on physician name, patient name, and field identifier; 2) side-by-side presentation of prescription and portal images at equal magnification and orientation, and with independent grayscale controls; 3) 'trace' facility for outlining anatomical structures; 4) 'ruler' facility for measuring distances; 5) zoomed display of corresponding regions in both images; 6) image contrast enhancement; and 7) communication of portal image evaluation results (approval, block modification, repeat image acquisition, etc.). Conclusion: The EVB tool facilitates the rapid comparison of prescription and portal images and permits electronic communication of corrections in port shape and positioning