92 The use of adaptive radiation therapy to reduce setup error: A prospective clinical study
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204 I. J. Radiation Oncology 0 Biology 0 Physics Volume 36, Number I, Supplement, 1996 91 INITIAL CLINICAL EXPERIENCE WITH AN INTERACTIVE, VIDEO-BASED PATIENT-POSITIONING SYSTEM FOR HEAD AND NECK TREATMENT Johnson,L. Scott, Hadley, Scott W., Milliken*, Barrett D., Pelizzari, Charles A., Haraf, Daniel J., Nguyen, Ai and Chen, George T.Y Department of Radiation and Cellular Oncology, The University of Chicago and *Department of Radiology, University of Illinois at Chicago, Chicago, Illinois Objective: To evaluate an interactive, video-baaed system for positioning head and neck patients. Materials and Methods: System hardware includes two B&W CCD cameras (mounted to provide left-lateral and AP-inferior views), zoom lenses, and a PC equipped with a frame grabber. Custom software is used to acquire and archive video images, as well as to display real-time subtraction images revealing patient misalignment in multiple views. Live subtraction images are obtained by subtracting a reference image (i.e., an image of the patient in the correct position) from real-time video. As seen in the figure, darker regions of the subtraction image indicate where the patient is currently, while lighter regions indicate where the patient should be. Adjustments in the patient’s position am updated and displayed in less than 0.07s, allowing the therapist to interactively detect and correct setup discrepancies. Patients selected for study are treated BID and immobilized with conventional litecast straps attached to a baseframe which is registered to the treatment couch. Morning setups are performed by aligning litecast marks and patient anatomy to treatment room lasers. Afternoon setups begin with the same procedure, and then live subtraction images are used to fine-tune the setup. At morning and afternoon setups, video images and verification films am taken after positioning is complete. These are visually registered offline to determine the distribution of setup errors per patient, with and without video assistance. Results: Without video assistance, the standard deviation of setup errors typically ranged from 5 to 7mm and was patient-dependent. With video assistance, standard deviations are reduced to 1 to 4mm, with the result depending on patient coopertiveness and the length of time spent fine-tuning the setups. At current levels of experience, 3 to 4mm accuracy is easily achieved in about 30s while 1 to 3mm accuracy is achieved in about 1 to 2 minutes. Studies with healthy, cooperative volunteers show that standard deviations of less than lmm am achievable, if adequate time is spent in careful alignment. Conclusion: Interactive, video-assisted patient positioning is shown to reduce random setup errors to within 1 to 4mm in head and neck patients, without a significant increase in overall treatment time or labor-intensive procedures. The real-time subtraction images were found to be intuitively easy to understand and use, and the overall system was readily accepted by the therapists as a new tool to quickly and accurately reproduce patient position. Unlike retrospective portal film analysis, the use of two live images allows for true 3D positioning and the correction of out-of-plane rotation before treatment. Although the system is limited to registration of external anatomy, external and bony anatomy in the head and neck are well correlated, and setup errors measured in both video and portal images are in good agreement. With significant improvement in head and neck alignment and the elimination of setup discrepancies greater than 5mm, margins associated with aperture design can potentially be reduced, thereby decreasing normal tissue irradiation. 92 THE USE OF ADAPTIVE RADIATION THERAPY TO REDUCE SETUP ERROR A PROSPECTIVE CLINICAL STUDY Di Yan, D-SC., John Wong, Ph.D., Frank Vicini, M.D., John Robertson, M.D., Eric Honvitz, M.D., Donald Bmbbins, M.D., Carla Cook, M.D., Gary Gustafson, M.D., Jannifer Stromberg, M.D., and Alvaro Martinez, M.D., FACR Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI. Purpose: Adaptive Radiation Therapy (ART) is a closed-loop feedback process where each patients treatment is adaptively optimized according to the individual variation information measured during the course of treatment. The process aims to maximize the benefits of treatment for the individual patient. A prospective study is currently being conducted to test the feasibility and effectiveness of ART for clinical use. The present study is limited to compensating the effects of systematic setup error. Methods and Materials: The study includes 20 patients treated on a linear accelerator equipped with a computer controlled multileaf collimator (MLC) and a electronic portal imaging device (EPID). Alpha cradles are used to immobilize those patients treated for disease in the thoracic and abdominal regions, and thermal plastic masks for the head and neck. Portal images are acquired daily. Setup error of each treatment field is quantified off-line every day. As determined from an earlier retrospective study of different clinical sites, the measured setup variation from the first 4 to 9 days, are used to estimate systematic setup error and the standard deviation of random setup error for each field. Setup adjustment is made if estimated systematic setup error of the treatment field was larger than or equal to 2 mm. Instead of the conventional approach of repositioning the patient, setup correction is implemented by reshaping MLC to compensate for the estimated systematic error. The entire process from analysis of portal images to the implementation of the modified MLC field is performed via computer network. Systematic and random setup errors of the treatment after adjustment are compared with those prior to adjustment. Finally, the frequency distributions of block overlap cumulated throughout the treatment course are evaluated. Results: Sixty-seven percent of all treatment fields were reshaped to compensate for the estimated systematic errors. At the time of this writing, eight patients had completed the study. Their mean systematic setup error was 4 mm with a range of 2 mm to 6 mm before adjustment; and was reduced to 0.8 mm with a range of 0.2 mm to 1.8 mm after adjustments, There was no significant difference in their random setup errors before and after adjustment. Analysis of the block overlap distributions shows that the fractions of the prescribed field areas covered by the daily treatment increased after setup adjustment. The block overlap distributions also show that the magnitude of random setup errors at different field edges were different; 50% of which were small enough to allow the treatment margin to be reduced to 4 mm or less. Results from the on-going treatments of the remaining 12 patients show similar trends and magnitudes, and are not expected to be different. Conclusion: Our prospective study demonstrates that the ART process provides an effective and reliable approach to compensate for the systematic setup error of the individual patient. Adjusting the MLC field allows accurate setup adjustment as small as 2 mm, minimizes the possibility of “unsettling” the patient and reduces the work load of the therapists, The ART process can be extended to correct for random setup errors by further modification of the MLC field shape and prescribed dose. Most importantly, ART integrates the use of advanced technologies to maximize treatment benefits, and can be important in the implementation of dose escalated conformal therapy.
Transcript of 92 The use of adaptive radiation therapy to reduce setup error: A prospective clinical study
204 I. J. Radiation Oncology 0 Biology 0 Physics Volume 36, Number I, Supplement, 1996
91 INITIAL CLINICAL EXPERIENCE WITH AN INTERACTIVE, VIDEO-BASED PATIENT-POSITIONING SYSTEM FOR HEAD AND NECK TREATMENT
Johnson,L. Scott, Hadley, Scott W., Milliken*, Barrett D., Pelizzari, Charles A., Haraf, Daniel J., Nguyen, Ai and Chen, George T.Y
Department of Radiation and Cellular Oncology, The University of Chicago and *Department of Radiology, University of Illinois at Chicago, Chicago, Illinois
Objective: To evaluate an interactive, video-baaed system for positioning head and neck patients. Materials and Methods: System hardware includes two B&W CCD cameras (mounted to provide left-lateral and AP-inferior views), zoom lenses, and a PC equipped with a frame grabber. Custom software is used to acquire and archive video images, as well as to display real-time subtraction images revealing patient misalignment in multiple views. Live subtraction images are obtained by subtracting a reference image (i.e., an image of the patient in the correct position) from real-time video. As seen in the figure, darker regions of the subtraction image indicate where the patient is currently, while lighter regions indicate where the patient should be. Adjustments in the patient’s position am updated and displayed in less than 0.07s, allowing the therapist to interactively detect and correct setup discrepancies. Patients selected for study are treated BID and immobilized with conventional litecast straps attached to a baseframe which is registered to the treatment couch. Morning setups are performed by aligning litecast marks and patient anatomy to treatment room lasers. Afternoon setups begin with the same procedure, and then live subtraction images are used to fine-tune the setup. At morning and afternoon setups, video images and verification films am taken after positioning is complete. These are visually registered offline to determine the distribution of setup errors per patient, with and without video assistance. Results: Without video assistance, the standard deviation of setup errors typically ranged from 5 to 7mm and was patient-dependent. With video assistance, standard deviations are reduced to 1 to 4mm, with the result depending on patient coopertiveness and the length of time spent fine-tuning the setups. At current levels of experience, 3 to 4mm accuracy is easily achieved in about 30s while 1 to 3mm accuracy is achieved in about 1 to 2 minutes. Studies with healthy, cooperative volunteers show that standard deviations of less than lmm am achievable, if adequate time is spent in careful alignment. Conclusion: Interactive, video-assisted patient positioning is shown to reduce random setup errors to within 1 to 4mm in head and neck patients, without a significant increase in overall treatment time or labor-intensive procedures. The real-time subtraction images were found to be intuitively easy to understand and use, and the overall system was readily accepted by the therapists as a new tool to quickly and accurately reproduce patient position. Unlike retrospective portal film analysis, the use of two live images allows for true 3D positioning and the correction of out-of-plane rotation before treatment. Although the system is limited to registration of external anatomy, external and bony anatomy in the head and neck are well correlated, and setup errors measured in both video and portal images are in good agreement. With significant improvement in head and neck alignment and the elimination of setup discrepancies greater than 5mm, margins associated with aperture design can potentially be reduced, thereby decreasing normal tissue irradiation.
92 THE USE OF ADAPTIVE RADIATION THERAPY TO REDUCE SETUP ERROR A PROSPECTIVE CLINICAL STUDY
Di Yan, D-SC., John Wong, Ph.D., Frank Vicini, M.D., John Robertson, M.D., Eric Honvitz, M.D., Donald Bmbbins, M.D., Carla Cook, M.D., Gary Gustafson, M.D., Jannifer Stromberg, M.D., and Alvaro Martinez, M.D., FACR
Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI.
Purpose: Adaptive Radiation Therapy (ART) is a closed-loop feedback process where each patients treatment is adaptively optimized according to the individual variation information measured during the course of treatment. The process aims to maximize the benefits of treatment for the individual patient. A prospective study is currently being conducted to test the feasibility and effectiveness of ART for clinical use. The present study is limited to compensating the effects of systematic setup error. Methods and Materials: The study includes 20 patients treated on a linear accelerator equipped with a computer controlled multileaf collimator (MLC) and a electronic portal imaging device (EPID). Alpha cradles are used to immobilize those patients treated for disease in the thoracic and abdominal regions, and thermal plastic masks for the head and neck. Portal images are acquired daily. Setup error of each treatment field is quantified off-line every day. As determined from an earlier retrospective study of different clinical sites, the measured setup variation from the first 4 to 9 days, are used to estimate systematic setup error and the standard deviation of random setup error for each field. Setup adjustment is made if estimated systematic setup error of the treatment field was larger than or equal to 2 mm. Instead of the conventional approach of repositioning the patient, setup correction is implemented by reshaping MLC to compensate for the estimated systematic error. The entire process from analysis of portal images to the implementation of the modified MLC field is performed via computer network. Systematic and random setup errors of the treatment after adjustment are compared with those prior to adjustment. Finally, the frequency distributions of block overlap cumulated throughout the treatment course are evaluated. Results: Sixty-seven percent of all treatment fields were reshaped to compensate for the estimated systematic errors. At the time of this writing, eight patients had completed the study. Their mean systematic setup error was 4 mm with a range of 2 mm to 6 mm before adjustment; and was reduced to 0.8 mm with a range of 0.2 mm to 1.8 mm after adjustments, There was no significant difference in their random setup errors before and after adjustment. Analysis of the block overlap distributions shows that the fractions of the prescribed field areas covered by the daily treatment increased after setup adjustment. The block overlap distributions also show that the magnitude of random setup errors at different field edges were different; 50% of which were small enough to allow the treatment margin to be reduced to 4 mm or less. Results from the on-going treatments of the remaining 12 patients show similar trends and magnitudes, and are not expected to be different. Conclusion: Our prospective study demonstrates that the ART process provides an effective and reliable approach to compensate for the systematic setup error of the individual patient. Adjusting the MLC field allows accurate setup adjustment as small as 2 mm, minimizes the possibility of “unsettling” the patient and reduces the work load of the therapists, The ART process can be extended to correct for random setup errors by further modification of the MLC field shape and prescribed dose. Most importantly, ART integrates the use of advanced technologies to maximize treatment benefits, and can be important in the implementation of dose escalated conformal therapy.
