Proceedings of the 52nd Annual ASTRO Meeting S747

implemented an online adaptive replanning technique to effectively address these interfraction variations in prostate cancerRT.

Materials/Methods: The online replanning process includes: (i) acquiring daily CT right before the treatment, (ii) generating con-tours of target and OARs based on the daily CT by auto-segmentation with manual editing if necessary, (iii) morphing segmentapertures based on new contours, (iv) optimizing weights of the new apertures, (v) computing and comparing dose distributionsand DVHs between the adaptive plan and the original plan with patient repositioning, (vi) transferring adaptive plan to deliverymachine, (vii) verifying the adaptive plan with an independent MU calculation, and (viii) verifying beam data transferring usinga software tool. The replanning process (ii-v) was implemented into a planning system (RealArt, Prowess) and was validated withphantom measurements and with retrospective dosimetric analyses for selected cases. This adaptive process has been recently ap-plied prospectively for selected prostate cancer patients in our clinic using a CT-on-Rails (CTVision, Siemens). At the time whenthis abstract was written, the online adaptive process had been performed for eight patients at selected fractions.

Results: Adaptive plans based on the anatomy of the day for prostate RT can be generated within 7-10 min and can be ready for de-livery within 12 min after the image acquisition. The plan quality (target coverage and/or OAR sparing) of an adaptive plan was gen-erally better than or equal to that of the repositioning plan. The adaptive plan provides the planned target coverage with reduced dosesto rectum and/or bladder (e.g., up to 40% or 75% reductions in rectal V38.2 (volume covered by 38.2 Gy) or V70, respectively), ascompared to the repositioning plan. The online replanning process, eliminating the need to shift the patient, can be performed withinthe similar or slightly longer time frame required for the current IGRT repositioning, fits into the routine clinical workflow.

Conclusions: The newly developed online adaptive replanning technique can effectively account for interfraction variations in-cluding setup errors, organ motion and deformation within a practical timeframe, and has been successfully implemented in ourclinic for online adaptive RT of prostate cancer. This online scheme enables ‘‘image-plan-treat’’, a new paradigm for IGRT thatpermits shrinking PTV margins and can facilitate accurate RT delivery particularly important for hypofractionations (e.g.,SBRT) and/or dose escalations.

Author Disclosure: C. Peng, None; E. Ahunbay, None; S. Holmes, None; D. Wang, None; C. Lawton, None; X. Li, Siemens OCS,B. Research Grant; Siemens OCS Customer Advisory Board, F. Consultant/Advisory Board.

3212 Forward Intensity Modulated Radiation Therapy for Partial Breast Irradiation Confers High Dose

Homogeneity and Conformation to the Target Volume

M. Trovo1, G. Sartor1, P. Chiovati1, M. Roncadin1, M. Arcicasa1, S. Massarut1, M. Mileto1, E. Micheli2, E. Capra1, M. G. Trovo1

1CRO-AVIANO, Aviano, Italy, 2Ospedale Civile Pordenone, Pordenone, Italy

Purpose/Objective(s): Three-dimensional conformal external beam radiotherapy has been widely used to treat patients with PBI.Typically, 4 or 5 non-coplanar high energy photon beams are employed, utilizing physical or dynamic wedges (1). To treat patientswith PBI, we used a forward-IMRT (F-IMRT) technique, employing multiple planar and non-coplanar beams. We report dosimet-ric data in terms of dose homogeneity and conformation to the target volumes, and dose distribution to the organ at risk (OAR).

Materials/Methods: Twenty-one patients underwent to PBI, consisting in 40 Gy in 10 fractions. Seven patients were treated fora left breast cancer and 14 for a right breast cancer, respectively. The CTV consisted of the lumpectomy cavity, expanded by 15mm, limited to 5 mm from the skin surface and 5 mm from the lung-chest wall interface. The PTV consisted of the CTV expansionof 1 cm. The PTV-EVAL is the structure used for dose-volume histogram constraints and analysis, as defined in the RTOG 0413protocol (2) The irradiation technique consisted in F-IMRT (field-within-field technique). The mean number of beams was 6 (4-11)and the mean number of field-within-field was 2 (0-11).

Results: The mean PTV dimension was 279 mL, the mean PTV-EVAL dimension was 195 mL, the mean CTV dimension was 103mL, and the mean lumpectomy cavity dimension was 29 mL. No difference in all these volumes was noted if the lumpectomycavity was represented by the clips or by the post-surgery seroma. The mean dose covering the 95% of the PTV-EVAL was98%; the mean average-PTV-EVAL dose was 100.8%. The mean homogeneity index (HI), defined as (D2-D98)/mean dose atthe PTV-EVAL, was 0.098. The mean conformity index 95 (CI95), defined as the ratio between the PTV-EVAL and the irradiatedvolume by the 95% isodose, was 1.4. The mean CI50 was 3.7. The mean heart V5% was 2.4%; the mean V15%, V30%, V60%ipsilateral lung were 17.2%, 6.4%, 2.5%, respectively. The mean V100% and V50% ipsilateral breast were 16.9% and 57.4%, re-spectively. The V3% controlateral lung was 1.7%. The V3% controlateral breast and thyroid were 0% in all cases except in 2 and 1patients, respectively. No difference were noted in the HI, CI95, CI50 and dose delivered to the OAR for left vs. right, for #5 vs.$6 portals, or for #7 vs. $8 fields (including fields-within-fields).

Conclusions: High dose homogeneity (HI = 0.098) and dose conformation (CI95 = 1.4) can be achieved by using a simplifiedF-IMRT technique. The doses delivered to the OAR seem to be lower than those imposed by the dose-volume constraints usuallyemployed. In particular, we were able to widely spare the ipsilateral lung from low-dose irradiation (V15% \ 17%).1. Int J Radiat Oncol Biol Phys 2005;63:1531-7.2. http://www.rtog.org/members/protocols/0413/0413.pdf.

Author Disclosure: M. Trovo, None; G. Sartor, None; P. Chiovati, None; M. Roncadin, None; M. Arcicasa , None; S. Massarut,None; M. Mileto, None; E. Micheli, None; E. Capra, None; M.G. Trovo, None.

3213 A Comparison of Heart and Coronary Artery Doses Associated with Intensity Modulated Radiotherapy

(IMRT) vs. 3-dimensional Conformal Radiotherapy (3DCRT) for Distal Esophageal Cancer

T. P. Kole1, O. Aghayere2, J. Kwah3, E. Yorke4, K. A. Goodman4

1UMDNJ-NJMS, Newark, NJ, 2University at Buffalo School of Medicine and Biomedical Sciences, Buffalo, NY, 3DrexelUniversity College of Medicine, Philadelphia, PA, 4Memorial Sloan-Kettering Cancer Center, New York, NY

Purpose/Objective(s): The purpose of this study was to compare heart and coronary artery radiation exposure using IMRT vs.4-field 3DCRT treatment plans for patients with distal esophageal cancer undergoing chemoradiation.

S748 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010

Materials/Methods: Nineteen patients with distal esophagus/gastroesophageal junction cancers treated with IMRT from 3/07 to5/08 at MSKCC were identified. All patients were treated to 50.4 Gy with 5-field IMRT plans (6 MV) normalized so at least 95% ofthe PTV received prescription dose (PD) or more. Dose and dose-volume constraints were applied to lungs, heart, liver, kidneys,stomach, and spinal cord. 3DCRT plans with 4-field beam arrangements (unequally weighted, 15 MV) were generated. Beamswere conformed to a volume expanded 6 mm radially and 10 mm superior/inferiorly around the PTV. The maximum cord dosemet the same constraint (45 Gy) as for IMRT when 3DCRT plans were normalized to give 95% of the PTV at least PD of 50.4Gy. DVHs of the PTV, heart, right coronary artery (RCA), left coronary artery (LCA) and other critical normal tissues (lungs, stom-ach, liver, spinal cord, left kidney, and right kidney) were compared between the IMRT and 3DCRT plans for each patient andselected parameters were statistically evaluated using the Wilcoxon rank-sum test.

Results: IMRT treatment planning showed significant reduction(p\0.05) in heart dose over 3DCRT as assessed by average meandose (22.9 vs. 28.2Gy) and V30 (24.8% vs. 61.0%). There was also significant sparing of the RCA with an average mean dose of23.8Gy vs. 35.5Gy, while the LCA showed no significant improvement with a mean dose of 11.2 Gy vs. 9.2 Gy, p = 0.11. Therewas no significant difference in percent of total lung volume receiving at least 10 Gy (V10; 41.5 vs. 35.1, p = 0.15), 15 Gy (V15;29.1 vs. 31.3, p = 0.9), or 20 Gy (V20; 18.2 vs. 15.9, p = 0.07), or mean lung dose (11.18 vs. 10.17 Gy, p = 0.21) between the 2planning methods. There were also no significant differences observed for the kidneys, liver, stomach, or spinal cord. IMRTachieved a significant improvement in target conformity as measured by the conformality index (CI) (ratio of total volume receiving95% of PD to PTV receiving 95% of PD), with the mean CI reduced from 1.56 to 1.30 using IMRT.

Conclusions: Treatment of patients with locally-advanced distal esophageal cancer using IMRT significantly decreases the expo-sure of the heart and RCA when compared to 3DCRT. Long-term studies are necessary to determine what implications this benefitmay have on development of coronary artery disease and other cardiac complications.

Author Disclosure: T.P. Kole, None; O. Aghayere, None; J. Kwah, None; E. Yorke, None; K.A. Goodman, None.

3214 Development of 3D Dosimetry System using Polymer Gel (TENOMAG) and Optical-CT Scanner in

Prostate IMRT

S. Lee1, J. Yi2, J. Park2, S. Cho3, J. Shim1, K. Chang1, Y. Cao1, S. Lee4, H. Huh5, C. Kim1

1Department of radiation Oncology, College of Medicine, Korea University, Seoul, Republic of Korea, 2INFINITT Healthcare,Seoul, Republic of Korea, 3Department of Radiation Oncology, Eulji University, Seoul, Republic of Korea, 4Cheil GeneralHospital and Woman’s Healthcare Center, Department of Radiation Oncology, Kwandong University College of Medicine,Seoul, Republic of Korea, 5Department of Radiation Oncology, Inha University, Incheon, Republic of Korea

Purpose/Objective(s): Modern radiation treatment techniques like IMRT involve a highly sophisticated treatment process. a majorconcern is that the pace of innovation in treatment delivery has not been matched by corresponding technological advances capableof verifying these distributions. Therefore, a 3D verification system can be the best solution. In this study, we use a home-made geldosimeter and optical-CT scanner (VSTA, MODUS, Canada) to evaluate 3D dose distribution and the accuracy of 3D QA software.

Materials/Methods: The gel dosimeter used in this study is tetrakis hydroxymethyl phosphonium chloridenormoxic methacrylicacidgelatin (TENOMAG) which is developed in KUMC laboratory. The gel dosimeter is taken through an entire IMRT treatmentprocedure and irradiated by an external beam which is delivered by iX treatment system. Optical-CT scanner was used to readoutthe dose distribution in gel dosimeter. The Xelis Flatform which is developed by INFINITT corporation is used to display the 3Ddose distribution by loading the Dicom RT Data which is exported from RTP and optical-CT reconstructed VFF file. Independentpatient specific quality assurance (PSQA) using ionizing chamber and EBT film is performed to compare the dose distribution ofRTP with gel dosimeter. After calibration, the Data analysis is achieved by comparing the RTP data with the VFF data using pro-filing, Gamma map, and DTA.

Results: The agreement between the normalized EBT, gel dosimeter and RTP data was evaluated using both qualitative and quan-titative methods like profiling, Gamma map and DTA. The profiles showed good agreement between RTP data, gel dosimeter, andGamma distribution and the precision of the dose distribution is within ± 5%.

Conclusions: The 3D dose verification tool which is developed in this study evaluates the accuracy of the three dimensional dosedistributions and PSQA of each patient. And more comfortable clinical implications could be expected in further study.

Author Disclosure: S. Lee, The support of Korea University Grant, B. Research Grant; J. Yi, None; J. Park, None; S. Cho, None;J. Shim, None; K. Chang, None; Y. Cao, None; S. Lee, None; H. Huh, None; C. Kim, None.

3215 Evaluating Inter-fraction Variations in Tumor Volumes with Repeated 4D-CT

W. Lu1, G. Neuner1, Z. Wang1, R. George1, J. Wu2, S. Sassor1, W. Regine1, S. Feigenberg1, W. D’Souza1

1University of Maryland School of Medicine, Baltimore, MD, 2Swedish Medical Center, Seattle, WA

Purpose/Objective(s): To quantitatively evaluate the inter-fraction variation in tumor volumes with repeated 4D-CT underuncoached free-breathing conditions. A secondary objective is to examine the inter-fraction variation in the correlation betweentwo moving tumor volume measurements ITV10 and ITVMIP.

Materials/Methods: Six patients with thoracic tumors and five patients with abdominal tumors underwent 4D-CT simulations on 3separate days using a Philips Brilliance CT scanner. At each session, patients underwent 4D-CT scans under uncoached free-breath-ing conditions. Tumor volumes incorporating motion were generated: ITV10 was defined as the union of GTvs. contoured on the CTof all 10 phases; and ITVMIP which was the GTV contoured on the CT generated via Maximum Intensity Projection reconstruction.All contours were drawn by a single physician (GAN). The correlation between ITV10 and ITVMIP was evaluated by calculating theirdifference, ratio, centroid distance, root mean squared (RMS) distance, Hausdorff distance (maximum distance of closest points), andthe overlap index. We examined the inter-fraction variation in ITV10, ITVMIP, and their correlation, using ANOVA.

Results: For thoracic tumors, the mean ITV10 was 34.5 cc, the mean ITVMIP was 31.7 cc, the mean ratio of ITVMIP to ITV10 was0.90, the mean centroid distance was 1.1 mm, the mean Hausdorff distance was 7.0 mm, the mean RMS distance was 1.7 mm, and