Author Disclosure: L. Burgess, None; T. Zhang, None; J. Liang, None; Q. Wu, None; J. Robertson, None; D. Yan, None.

2752 The Importance of Daily Electronic Portal Imaging (EPI) in Radiotherapy

L. J. Bell1, T. P. Shakespeare1,2, A. Willis1

1Northern Sydney Cancer Centre-Royal North Shore Hospital, St Leonards, NSW, Australia, 2North Coast Cancer Institute,Coffs Harbour, NSW, Australia

Purpose/Objective(s): Studies demonstrate clinically significant localisation errors occur frequently (10%-36% of the time),and error frequency decreases with more frequent portal imaging. However prior studies have not investigated error frequencydetected by daily EPI. Our aim was to determine the frequency of clinically relevant localisation error identified by daily EPI.Secondary goals were to evaluate whether errors could be predicted based on clinical data, and the concordance betweenradiation therapists and oncologists for identification of error.

Materials/Methods: Twenty randomly selected patients’ EPI images were audited after completing their course of radiother-apy. Four areas (spine, chest, breast & prostate) were compared, with 5 patients per area selected. Clinically significant errorswere identified with reference to departmental EPI protocols. Images that were out of tolerance or where actions or movesoccurred were identified and compared between patient groups. Factors potentially predicting error that were assessed includedarea being treated, treatment intent (radical vs palliative), and perceived patient stability.

Results: A total of 475 factions (Fx) had EPI images taken (median 25, range 6 - 41). Of these, 159 were out of tolerance(33.5%). In all, 95% of patients needed an action during their course of treatment; 95% in the 1st half, 80% in the 2nd half,and 60% in last 5 treatments. Forty-one moves were made, the size ranging from 0.2 - 1cm (median 0.5cm, average 0.63cm).A total of 80% of patients needed a move during the course of their treatment; 65% in the 1st half, 50% in the 2nd half, and35% in the last 5 treatments. In addition, 181 repeat EPIs were requested.No factors predicted for frequency of errors. Of the 65% of patients requiring a move in the first half of treatment 54% requireda move in the second half. Of the 35% who had no move in the first half of therapy, 43% required a move in the second half.

There was a difference in interpretation in 9.9% of EPIs reviewed.

Conclusions: Daily EPIs identified 33.5% of images as being out of tolerance, with 80% of patients requiring at least one moveduring radiotherapy. It was not possible to predict which patients might be imaged less than once daily, and nearly half ofpatients not requiring moves in the first half of therapy required a move during the second half.Despite the use of familiar EPI protocols, image reviewers (therapists and doctors) disagreed in interpretation 10% of the time.This was not surprising as some issues relating to individual patient care will only be obvious to treating ROs. This demonstratesthe need for a team approach, with all images reviewed by both treating therapists and radiation oncologists.Given the frequency of clinically significant localization errors, we recommend daily EPIs for all patients, with all imagesideally reviewed by both treating RTs and ROs. In view of the extra time and resources required for this optimal approach,billing models may need to be reviewed.

Author Disclosure: L.J. Bell, None; T.P. Shakespeare, None; A. Willis, None.

2753 Feasibility of Image-Guided Helical Tomotherapy for Frame-Based Stereotactic Radiosurgery

T. H. Wagner1, S. L. Meeks1, K. M. Langen1, T. R. Willoughby1, P. A. Kupelian1, O. A. Zeidan1, A. P. Shah1, R. R.Manon1, K. Ruchala2, G. Olivera3

1M. D. Anderson Cancer Center Orlando, Orlando, FL, 2Tomotherapy, Inc., Madison, WI, 3Tomotherapy Inc., Madison, WI

Purpose/Objective(s): To determine the feasibility of using a commercially available helical tomotherapy unit (TomotherapyHiArt, Tomotherapy Inc., Madison, WI) for frame-based intracranial stereotactic radiosurgery.

Table 1: The percent of difference between the accumulated EUD to the reference EUD

ROI Prostate Seminal Vesicle Bladder Rectum

Simulation A B C A B C A B C A B C

Pat #1 10.1% 1.2% 2.1% 7.6% 0.6% 0.3% 8.7% 9.4% 0.3% 3.3% 11.0% 1.6%Pat #2 1.2% 0.2% 1.0% 3.9% 0.8% 1.3% 22.7% 37.1% 6.9% 3.9% 4.6% 1.2%Pat #3 4.0% 2.1% 0.7% 6.6% 4.3% 0.8% N/A N/A N/A 17.7% 14.5% 5.4%Pat #4 5.6% 0.7% 0.8% 23.1% 10.3% 0.7% 7.8% 26.2% 0.2% 27.7% 5.0% 5.5%Pat #5 0.5% 1.3% 1.4% 1.2% 0.5% 0.9% 8.1% 27.9% 0.5% 2.3% 7.2% 0.7%

S630 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006

Materials/Methods: Tomotherapy radiosurgery treatment plans using 2.5cm and 1.0 cm long tomotherapy fan beams weregenerated using image sets from patients receiving conventional linear accelerator radiosurgery. Plans were generated using avariety of tomotherapy beam widths, pitches, and modulation factors. Planned radiosurgery dose distributions were evaluatedon the basis of conformity, dose gradient, and homogeneity. Phantoms were used to evaluate the accuracy of localizing targetsin MVCT images, and of the spatial accuracy of the HiArt system’s MVCT image guidance capability. The only hardwaremodifications necessary (for frame-based radiosurgery) are to add docking hardware for a stereotactic headring to attach to thetreatment couch.

Results: The HiArt system was capable of producing radiosurgery plans meeting the RTOG acceptability criteria for doseconformity and homogeneity. The HiArt system image guidance consistency (multiple phantom alignments based on MVCTimaging) was 0.35mm. MVCT 3D target localization accuracy was 0.63 mm, or approximately the size of one MVCT imagepixel. Tomotherapy beam on times increased with target prescription dose. Beam on times were shortened with largertomotherapy fan beam lengths and for larger helical pitches. For simulated solitary metastasis targets, beam on times were onthe order of 60–70 minutes to deliver 24 Gy to the periphery of the target volume using pitches of 0.1–0.3. Narrow (small)pitches were necessary to successfully treat small target volumes. Due to limitations on minimum gantry rotational speed, it isnecessary to deliver a tomotherapy radiosurgery treatment in several passes, if a typical radiosurgery dose of 12–20� Gy is tobe delivered.

Conclusions: The tests described here demonstrate the ability of the HiArt system to plan and deliver a radiosurgical dosedistribution to a rigid body in phantom. The same process could be used to treat an intracranial radiosurgery patient using aminimally-invasive headframe for immobilization. Frame based intracranial radiosurgery can be feasibly accomplished with aHiArt treatment unit with minimal hardware modification. However, tomotherapy treatment planning and delivery proceduresmust be modified from typical fractionated radiotherapy practice to accommodate the unique requirements of stereotacticradiosurgery.

Author Disclosure: T.H. Wagner, Tomotherapy Inc., C. Other Research Support; S.L. Meeks, Tomotherapy Inc., C. OtherResearch Support; K.M. Langen, Tomotherapy Inc., C. Other Research Support; T.R. Willoughby, None; P.A. Kupelian,Tomotherapy Inc., C. Other Research Support; O.A. Zeidan, None; A.P. Shah, None; R.R. Manon, None; K. Ruchala,Tomotherapy Inc., A. Employment; G. Olivera, Tomotherapy Inc., A. Employment.

2754 A Preliminary Study for a Cone-Beam Computed Tomography (CBCT) Setup Using a Newly DevelopedImage-Guided Radiotherapy System

K. Takayama1,2, N. Kawada2, K. Nagano3, Y. Sato2, Y. Matsuo1, T. Mizowaki1, M. Kokubo3, H. Nakayama2,4, Y. Narita1,M. Hiraoka1

1Kyoto University, Kyoto, Japan, 2Mitsubishi Heavy Industries, Hiroshima, Japan, 3Institute of Biomedical Research andInnovation, Kobe, Japan, 4Kyoto Universityeristy, Kyoto, Japan

Purpose/Objective(s): We are developing an image-guided radiotherapy (IGRT) system with an imaging subsystem which isconsisted of two sets of a kilovoltage (kV) X-ray tube and a flat panel detector (FPD). The imaging subsystem providescone-beam computed tomography (CBCT) capability. The purpose of this study was to evaluate the accuracy of CBCT setupby based on a phantom study.

Materials/Methods: The IGRT system has an O-ring shaped gantry with a rigid Rahmen structure. The imaging subsystembeing mounted on the rigid gantry, distortion can be small when the gantry rotates, which contributes to constantly obtaininghigh quality of CBCT images. The FPD has an aperture of 40 cm � 30 cm. The spatial resolution is 1024�768 pixels and thedensity resolution is 14 bits. The distance between the kV X-ray source and the isocenter of the IGRT system is 100 cm andthe distance between the source and the FPD is 188 cm. The resultant field of view of the CBCT at the isocenter is 21 cm �16 cm. The angular range of projection views is 200°, and the gantry rotational speed is 7 degrees per seconds, therefore it takes29 seconds to acquire the CBCT data. An automatic image registration tool is installed to detect a displacement of the patientposition in CBCT from that in reference CT.

In this study, a pelvic phantom with artificial pelvic bones was used to evaluate the accuracy in positioning using CBCT. Firstof all, reference CT images of the phantom were scanned beforehand using a conventional CT simulator. Secondly, CBCTimages of the phantom were acquired in the treatment room, and the home position was initially calibrated to be the same asthe position in the reference CT images. Then the phantom position was shifted three dimensionally by a couch movement fromthe home position; the lateral axis, the anterior-posterior axis, the cranial-caudal axis. The movements were by �5mm in eachaxis, or in any two axes, or in all axes. After CBCT images were acquired in each shifted position, the image registration tooldetected the displacement of the phantom position in CBCT from that of in the reference CT images. The overall geometricalerrors were evaluated with the difference between the phantom shift moved by the couch and the shift detected by theregistration tool. The tube potential, the tube current and the exposure time was 120 kVp, 100 mA, 10ms, respectively. Thereconstruction voxel dimensions were 0.4 x 0.4 x 3.0 mm3 in the CBCT images, and 0.5 x 0.5 x 3.0 mm3 in the reference CTimages.

Results: The mean (�standard deviation) geometric error was 0.1 (�0.1) mm in lateral axis, 0.2 (�0.1) mm in anterior-posterior axis, 0.1 (�0.2) mm in cranial-caudal axis, respectively. The maximum geometric error was 0.2 mm in lateral axisand 0.4 mm in other axes, respectively.

Conclusions: The quality of CBCT images was acceptable for setup correction. The preliminary study for overall accuracyindicated CBCT setup was feasible with our IGRT system.

Author Disclosure: K. Takayama, Mitsubishi Heavy Industries, A. Employment; New Energy and Industrial TechnologyDevelopment Organization (NEDO), B. Research Grant; N. Kawada, New Energy and Industrial Technology DevelopmentOrganization (NEDO), B. Research Grant; K. Nagano, Mitsubishi Heavy Industries, A. Employment; Y. Sato, None; Y.Matsuo, None; T. Mizowaki, New Energy and Industrial Technology Development Organization (NEDO), B. Research Grant;M. Kokubo, None; H. Nakayama, None; Y. Narita, None; M. Hiraoka, New Energy and Industrial Technology DevelopmentOrganization (NEDO), B. Research Grant.

S631Proceedings of the 48th Annual ASTRO Meeting