AD_________________ Award Number: W81XWH-07-1-0058 TITLE: Cone-Beam Computed Tomography for Image-Guided Radiation Therapy of Prostate Cancer PRINCIPAL INVESTIGATOR: Seungryong Cho CONTRACTING ORGANIZATION: University of Chicago Chicago, IL 60637 REPORT DATE: January 2008 TYPE OF REPORT: Annual Summary PREPARED FOR: U.S. Army Medical Research and Materiel Command Fort Detrick, Maryland 21702-5012 DISTRIBUTION STATEMENT: Approved for Public Release; Distribution Unlimited The views, opinions and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy or decision unless so designated by other documentation. 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REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To) 01-01-2008 Annual Summary 11 DEC 2006 - 11 DEC 2007 4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER Cone-Beam Computed Tomography for Image-Guided Radiation Therapy of 5b. GRANT NUMBER Prostate Cancer W81XWH-07-1-0058 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Seungryong Cho 5e. TASK NUMBER E-Mail: [email protected] 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER University of Chicago Chicago, IL 60637 9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) U.S. Army Medical Research and Materiel Command Fort Detrick, Maryland 21702-5012 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION / AVAILABILITY STATEMENT Approved for Public Release; Distribution Unlimited 13. SUPPLEMENTARY NOTES 14. ABSTRACT The success of intensity-modulated radiation therapy (IMRT) or 4-D conformal radiation therapy (CRT) is heavily reliant on accurate image- guidance in prostate cancer treatment. Cone-beam computed tomography (CBCT) is becoming one of the dominant imaging modalities for image-guidance, but current technology based on Feldkamp algorithm for image reconstruction from a circular scanning trajectory does not yield sufficient quality of images. In addition, imaging-radiation dose is one of the key issues, which has to be minimized or optimized. We report innovative CBCT scanning methods and corresponding image reconstruction algorithms that can increase the accuracy of the images and/or reduce patient dose from CBCT. Reverse helical CBCT has been developed, region-of-interest image reconstruction methods have been explored, and a few-view CBCT approach has been proposed. 15. SUBJECT TERMS Cone-beam computed tomography, image-guided radiation therapy, region-of-interest, few-view 16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE PERSON OF ABSTRACT OF PAGES USAMRMC a. REPORT b. ABSTRACT c. THIS PAGE 19b. TELEPHONE NUMBER (include area U U U UU 55 code) Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18 Table of Contents Page Introduction…………………………………………………………….………..….. 4 Body………………………………………………………………………………….. 5 Key Research Accomplishments………………………………………….…….. 8 Reportable Outcomes……………………………………………………………… 9 Conclusion…………………………………………………………………………… 10 References……………………………………………………………………………. 11 Appendices…………………………………………………………………………… 12 3 INTRODUCTION The su ess of intensity-modulated radiation therapy (IMRT) or 4-D onformal radiation therapy (CRT) is heavily reliant on a urate image-guidan e in prostate an er treatment. Cone-beam CT (CBCT) image a quisition is be oming one of the dominant imaging modal- ities, and the a ura y of the images by CBCT and the radiation dose due to CBCT are onsidered as very important issues [1,2℄. Most s anning geometries of the CBCT used in prostate an er treatment are ir ular traje tories, whi h often yield insu(cid:30) ient data for exa t volumetri image re onstru tion. As a onsequense, images re onstru ted by approx- imate algorithms, mostly based on the Feldkamp algorithm, would ontain image artifa ts su h as streaks, intensity drop, and image deformation in regions away from the traje tory plane [3℄. Radiation dose to the prostate an er patient due to CBCT must be arefully studied and imaging s hemes that an lead to minimum (or optimum if interplay between imaging and therapeuti dose onformity is onsidered) dose should be devised. This is of paramount importan e espe ially in repeated s ans during the treatment pro ess to adapt treatment plans to hanges in prostate over time. The overall obje tive of this proje t is to investigate and develop innovative CBCT s anning methods and orresponding imagere on- stru tion algorithms that an in rease the a ura y of the images of the patient's prostate and/or redu e patient dose from CBCT. Reverse heli al CBCT has been developed for exa t re onstru tion of volumetri images, region-of-interest (ROI) re onstru tion methods have been explored to redu e patient dose, and a few-view CBCT approa h has been proposed for enormous redu tion of patient dose. This report summarizes the progress of this Predo toral Traineeship Award proje t made by the re ipient during the past one year. 4 1 BODY 1 Training A omplishments At the time of this report, the re ipient, Seungryong Cho, of the Predo toral Traineeship Award has taken 22 out of 22 required ourses towards his Ph.D. degree in medi al physi s. The oursesin ludephysi sofmedi alimaging,physi sofradiationtherapy, mathemati sfor medi alphysi ists, imageguidedradiationtherapy, statisti s, anatomyofthebody, radiation biology and tea hing assistantship. 2 Resear h A omplishments 2.1 Investigation of re onstru tion algorithms for reverse heli al CBCT Heli al s anning on(cid:28)guration has been used widely in diagnosti CBCT for a quiring data su(cid:30) ient for exa t image re onstru tion over an extended volume. In image-guided radia- tion therapy (IGRT) and other appli ations of CBCT, it is di(cid:30) ult, if not impossible, to implement me hani ally a multiple-turn heli al traje tory on the imaging systems due to hardware onstraints. However, imaging systems in these appli ations often allow for the implementation of a reverse heli al traje tory in whi h the rotation dire tion hanges be- tween two turns. Be ause the reverse heli al traje tory satis(cid:28)es Tuy's ondition, it yields data su(cid:30) ient for exa t image re onstru tion within the reverse helix volume. The re ently developed hord-based algorithmssu h as the ba kproje tion (cid:28)ltration (BPF) algorithm an readily be applied to re onstru ting images on hords of a reverse heli al traje tory, and they an thus re onstru t an image within a volume overed by the hords. Conversely, the hord-based algorithms annot re onstru t images within regions that are not interse ted by hords. In a reverse helix volume, we have shown that hordless regions exist in whi h no im- ages an thus be re onstru ted by use of the hord-based algorithms. Therefore, we have re ently developed a shift-invariant (cid:28)ltered ba kproje tion (FBP) algorithm for exa t image re onstru tion within the reverse helix volume, in luding the hordless region. Results of the numeri al studies on(cid:28)rm that the proposed FBP algorithm an exa tly re onstru t an image within the entire reverse helix volume, in luding the hordless region. It is relatively straightforward to extend the proposed FBP algorithm to re onstru t images for general traje tories, in luding reverse heli al traje tories with variable pit h, titled axis, and/or ad- ditional line segments between turns. The developed algorithm needs further investigation to handle a long obje t problem and thus to be applied to a urate image re onstru tion of prostate, whi h is left as our future work. A full des ription of the algorithm is in referen e [4℄ whi h is atta hed as Appendix A. 2.2 Investigation of ROI image re onstru tion in ir ular CBCT As an attempt to redu e patient dose, s anning time, and s atter to the dete tor , and also to in rease the spatial resolution of the images from ir ular one-beam data, we have investigated algorithms for ROI image re onstru tion. A ba kproje tion-(cid:28)ltration (BPF) algorithm based on PI-line on ept has been developed to re onstru t ROI images from 5 2 trun ated data set whi h ontains only the proje tions of the ROI. Sin e a mi roCT system with a (cid:29)at-panel dete tor shares the physi s and s anning geometry of image a quisition with a CBCT system used in IGRT, we have built a prototype mi roCT that provides a hands-on experiment for validating new algorithms. Using the mi roCT system, we have validated that the proposed BPF algorithm an re onstru t ROI images without any trun ation artifa ts whi h, in ontrast, would exist in theimagesre onstru tedby onventionalalgorithms. Inmi roCTandalsoinCBCTofIGRT systems, be ause the dete tor size is limited, the use of a large geometri magni(cid:28) ation an lead to trun ated one-beam data. Motivated by our results of ROI imaging,we proposed to exploit the unique apability of the BPF algorithm for a urate ROI image re onstru tion from trun ated data to improve spatial resolution of the ROI images of a mouse leg bearing osteosar oma. The in reased spatial resolution of the ROI images has been su essfully demonstrated. Detailedwork anbefoundinreferen e[5℄whi hisalsoatta hedasAppendix B. In most IGRT pro edures, it is desirable to have a urate image of the target while spar- ingpatient dose spe i(cid:28) allyto the normaltissue outside the target. This issue be omes more important in prostate an er where there are radiation sensitive tissues near the treatment targetsu h asre tum. Unfortunately,theROIre onstru tiblebythe hord-based algorithms annot be ex lusively the target in general. The ROI usually ontains more than the target in luding those organs sensitive to the radiation. In this regard, we proposed an innova- tive, intensity-weighted ROI imaging te hnique to lower patient dose to the normal tissue surrounding the target and at the same time to preserve the image quality of the target in the ROI. The ROI in this task is divided into two subROI's. Higher dose is delivered to the inner ROI ontaining the target, and lower dose is to the outer ROI. Ea h proje tion image, therefore, will have di(cid:27)erent noise levels in two regions: inner ROI proje tion and outer ROI proje tion. This work is based on the observation that the noise from the outer ROI does not signi(cid:28) antly propagate into the inner ROI due to noise transfer property of the Hilbert transform. The preliminarystudy has been submitted to SPIE Medi al ImagingConferen e, 2008 [6℄. The abstra t is atta hed as Appendix C. 2.3 Investigation of few-view CBCT for IGRT The re ently available kV one-beam imaging apability of a linear a elerator system pro- vides ex ellent soft-tissue ontrast, whi h isanimportantbene(cid:28)t inIGRTofsu h as prostate an er. Redu tion of the treatment margins owing to improved image quality of the target would in rease the onformality of dose distribution in a fra tionated treatment where day- to-day, interfra tion organ motion is present. However, radiation dose a umulated to the patient due to daily CBCT before ea h fra tionated treatment may pose a hallenge in the patient's radiation safety. This motivated our work to develop a few3-6v0i◦ew CBCT for IGRT, where few-view means a limited number of proje tion views out of in a ir ular s an. Re ently, we have developed an iterative image re onstru tion algorithm based on total- variation (TV) minimization from in omplete one-beam proje tion data [7℄. In numeri al studies with a variety of in omplete one-beam data sets in luding trun ated data, redu ed s an range, and sparse sampling, the developed algorithm, whi h is referred to as TV algo- rithm hereafter, showed an ex ellent performan e ompared with existing algorithms su h as algebrai re onstru tion te hnique (ART) and expe tation maximization (EM). The TV 6 3 algorithm begins in general with a uniform image as an initial guess, and goes through it- eration steps to minimize the image TV. In an IGRT of prostate an er, a patient usually undergoes a CT s anning for treatment planning, whi h an provide the referen e image for image-guidan e pro edure. Therefore, we proposed a TV algorithm with a priori informa- tion in few-view CBCT for IGRT. We expe t the proposed algorithm an redu e the number of proje tions needed for volumetri image re onstru tion even further than a TV algorithm withouta priori informationdoes. The number ofproje tionsneeded inthisapproa h would be less than that of onventional CBCT by fa tor of tens. The preliminary study has been submitted to SPIE Medi al Imaging Conferen e, 2008 [8℄. The abstra t is also atta hed as Appendix D. 7 4 KEY RESEARCH ACCOMPLISHMENTS • Wehave proposedanovelimagea quisitiongeometryofreverse helixforCBCTimagers mounted on LINAC treatment systems used for prostate an er IGRT, and developed an exa t re onstru tion algorithm of the volumetri images within the reverse helix. • We have developed a prototype mi roCT with a (cid:29)at-panel dete tor, whi h has ommon physi sofimagea quisitionwithCBCTimagersmountedonLINACtreatmentsystems, to experimentally validate newly developed algorithms for prostate an er IGRT. • We have ondu ted an ROI image re onstru tion of a mouse having osteosar oma on oneleg. Alargergeometri magni(cid:28) ationhasbeenattemptedtoin reasethespatialres- olution of the ROI image, and the developed BPF algorithm su essfully re onstru ted the ROI image without trun ation artifa ts. This strategy an be applied to prostate an er IGRT with redu ed imaging dose. • We have proposed and ondu ted a preliminary investigation of the intensity-weighted ROI imaging for CBCT in prostate an er IGRT. The proposed method an bring in useful out omes in terms of dose management and image-guidan e. • We have performed a preliminary, numeri al study of few-view CBCT for prostate an er IGRT based on TV algorithm with a priori information. The su ess of the proposed method would redu e the patient dose due to prostate an er imaging by fa tor of tens. 8 5 REPORTABLE OUTCOMES Peer-reviewed Journal Arti les 1. S. Cho, J. Bian, C. A. Pelizzari, C. -T. Chen, T. -C. He, and X. Pan: Regionofinterest image re onstru tion in ir ular one-beam mi roCT, Med. Phys., 34, pp.4923-4933, 2007. 2. S. Cho, D. Xia, C. A. Pelizzari, and X. Pan: Exa t re onstru tion of volumetri images in reverse heli al one-beam CT, Med. Phys., (submitted), 2007. 3. S. Cho, E. Y. Sidky, J. Bian, and X. Pan: Dual-energy omputed radiography based on estimated spe tral properties of a spe imen radiographi system, Nu l. Inst. Meth. A,(submitted), 2007. 4. D. Xia, S. Cho, and X. Pan: Image re onstru tion for a redu ed s an in ir ular sinusoidal one-beam CT, IEEE Trans. Med. Imag., (submitted), 2007. Conferen e Pro eeding Arti les 1. S. Cho, D. Xia, C. A. Pelizzari, and X. Pan: Cone-beam CT with a modi(cid:28)ed reverse heli al traje tory for long obje t problem , Pro . MIC, M18-282, 2007. 2. D. Xia, S. Cho, and X. Pan: Re onstru tibel volume for one-beam CT with a redu ed saddle traje tory , Pro . MIC, M04-5, 2007. 3. D. Xia, S. Cho, and X. Pan: Image noise properties in ir ular sinusoidal one-beam CT , Pro . MIC, M13-285, 2007. 4. S. Cho, D. Xia, C. A. Pelizzari, and X. Pan: Exa t image re onstru tion in reverse heli al one-beam CT , Pro . Fully 3D Meeting, pp. 84-87, 2007. Conferen e Presentations and Abstra ts 1. S. Cho, D. Xia, C. A. Pelizzari, and X. Pan: Reverse heli al one-beam CT and its appli ations to image-guided radiation therapy , presented at RSNA Annual Meeting, 2007. 2. S. Cho, D. Xia, C. A. Pelizzari, and X. Pan: Exa t image re onstru tion in reverse heli al one-beam CT for radiation therapy , presented at AAPM Annual Meeting and at AAPM Midwest Chapter Meeting, 2007. 3. S. Cho, E. Pearson, D. Xia, C. A. Pelizzari, and X. Pan: Intensity-weighted region- of-interest imaging in one-beam CT , a epted to SPIE Medi al Imaging Conferen e, 2008. 4. S. Cho, E. Y. Sidky, C. A. Pelizzari, and X. Pan: Few-view one-beam omputed tomography for image-guided radiation therapy , a epted to SPIE Medi al Imaging Conferen e, 2008. Honors and Awards • Student Trainee Award, IEEE Medi al Imaging Conferen e, 2007 • Young Investigator Award (2nd pla e), AAPM Midwest Chapter Meeting, 2007 9 6 CONCLUSIONS The re ipient of the Predo toral Traineeship Award has (cid:28)nished the required ourses towards his Ph.D. degree. These trainings have proven useful for the re ipient to a hieve the proposed resear h goals. During the (cid:28)rst year, we have investigated innovative approa hes in one-beam CT for IGRT that an in rease the a ura y of the re onstru ted images and/or redu e radiation dose to the patient having prostate an er. Reverse heli al one-beam CT has been fully explored in the ontext of prostate an er IGRT and exa t image re onstru tion algorithms have been proposed. ROI imaging methods have been proposed and orresponding image re onstru tion algorithms have been developed. The te hnique has been exploited further to provide intensity-weighted ROI images that an redu e patient dose even further. Few-view one-beam CT with a priori information has been investigated and preliminary results have shown that the proposed method an potentially de rease the radiation dose by fa tor of tens. Overall, we have a hieved the goals for the (cid:28)rst year and laid down a solid foundation for the resear h inthenext two years. Our goalsinthe next two years in ludeimplementationof reverse heli alCBCT to the realsystem, applyingdi(cid:27)erent s anning geometriesin CBCT for exa t image a quisition, development of intensity-weighted ROI imagingfor the real system, and investigation of few-view one-beam CT with a priori information in depth; all of these will be studied in the ontext of appli ations to prostate an er IGRT. 10 7