Comparison of 3D and 4D Plans in the Radiation Therapy for Lung Cancer Using Real Time Tumor Tracking System

Volume 90  Number 1S  Supplement 2014

3729 Automatically Gated CBCT-Controlled Fast Breath-Hold SBRT Is Dosimetrically Robust and Facilitates Precision Treatments for Patients With Lung Cancer A.O. Simeonova, A. Jahnke, L. Jahnke, K. Siebenlist, F. Stieler, S. Mai, J. Boda-Heggemann, F. Wenz, and F. Lohr; UMM Mannheim, Mannheim, Germany Purpose/Objective(s): Accurate target localization and reliable prediction of respiratory motion is a challenge when treating tumors that move with respiration. Computer-controlled deep inspiration breath hold (DIBH) provides the opportunity to further reduce treatment margins over 4D-approaches and its use has been further facilitated with the advent of flattening filter free (FFF) delivery. The aim of this study was to analyze if automatically gated cone-beam-CT (CBCT)-controlled fast DIBH SBRT (Stereotactic Body Radiation Therapy) can be applied within a clinically feasible time slot and with sufficient dosimetric accuracy for both normofractionated lung IMRT treatments delivered with flattening filter and lung SBRT delivered in FFF-technique. Materials/Methods: Plans of 20 patients with primary lung cancer were reviewed. 10 patients were treated with computer-controlled fast DIBH SBRT with a dose of 60Gy (5x12Gy) in FFF-IMRT-technique (FFF-SBRT). 10 patients received conventional treatment with IMRT (conv. IMRT) with 2Gy fractional dose (cumulative dose 50-70Gy). Patient positioning was performed with CBCT. All plans were optimized with heterogeneity correction on treatment planning system with a Monte-Carlo dose calculation. The dosimetric accuracy of the plans was assessed using a global gamma index (3% dose difference, 3 mm DTA (distance to agreement), 20% threshold), and measured with a 2D array detector attached to the gantry. The treatment and the measurements were performed on a 10MV photon linear accelerator. Number of breathhold cycles and total delivery time with breathhold phases of 15/20s and recovery phases of 25s were recorded during QA procedures. Results: SBRT plans required more monitor units (MU) compared to conv. IMRT Plans (mean 2569.5757.6 vs 715.9263.6), although not in proportion to the delivered dose due to their lower complexity. The treatment time was shorter for the FFF-SBRT plans (first beam on to last beam off: mean 298.760.0s vs 391.0100.7s), whereby the beam on time (actual treatment time) was shorter for the stereotactic treatments (mean 80.4s27.3s vs 138.0s32.4s). FFF-SBRT and conv. IMRT plans were delivered with 4.51.1 and 8.12.5 breathing cycles/fraction, respectively. All modalities could be delivered accurately despite undergoing multiple beam-on/off-cycles, with mean QA pass rates over 95% (FFF-SBRT vs conv. IMRT mean 98.2 1.6% vs 98.21.9%). Conclusions: For both lung FFF-SBRT and normofractionated IMRT with conventional beam delivery treatments, automatically gated DIBH is possible with acceptable treatment times and is dosimetrically robust. This approach has therefore been introduced into the clinical routine to optimally reduce the amount of irradiated lung tissue with maximal delivery precision for lung cancer treatments. Author Disclosure: A.O. Simeonova: A. Employee; University Medical Center Mannheim, University of Heidelberg. F. Honoraria; Elekta. A. Jahnke: A. Employee; University Medical Center Mannheim, University of Heidelberg. C. Partner; Husband, University Medical Center Mannheim, University of Heidelberg. L. Jahnke: A. Employee; University Medical Center Mannheim, University of Heidelberg. F. Honoraria; Elekta. G. Consultant; Elekta. K. Siebenlist: A. Employee; University Medical Center Mannheim, University of Heidelberg. F. Stieler: A. Employee; University Medical Center Mannheim, University of Heidelberg. F. Honoraria; Elekta. S. Mai: A. Employee; University Medical Center Mannheim, University of Heidelberg. J. Boda-Heggemann: A. Employee; University Medical Center Mannheim, University of Heidelberg. H. Speakers Bureau; Elekta. F. Wenz: A. Employee; University Medical Center Mannheim, University of Heidelberg. E. Research Grant; Elekta, Zeiss. F. Honoraria; Elekta, Zeiss, Celgene, Roche, Lilly, Ipsen. I. Travel Expenses; Elekta, Zeiss, Celgene, Roche, Lilly, Ipsen. K. Advisory Board; Elekta, Celgene. Q. Patent/License Fee/Copyright; Zeiss. F. Lohr: A. Employee; University Medical Center Mannheim, University of Heidelberg. E. Research Grant; Elekta, IBA. F. Honoraria; Elekta, IBA, Board Honoraria C-

Poster Viewing Abstracts S891 Rad. I. Travel Expenses; Elekta, C-Rad, IBA. M. Stock; IMUC, ACTI, ONCY, MRKd, SAZd. S. Leadership; Board Member C-Rad.

3730 Multistage Stereotactic Radiosurgery for Large Intracranial Arteriovenous Malformations: Focused Cobalt-60 Radiosurgery Versus Robotic Radiosurgery C. Ding,1 B. Hrycushko,1 S.B. Jiang,1 L. Whitworth,1 X. Li,2 R. Abdulrahman,1 L. Nedzi,1 K. Choe,1 L. Xing,3 T.D. Solberg,4 and R.D. Timmerman1; 1University of Texas Southwestern Medical Center, Dallas, TX, 2University of Pittsburgh Medical Center, Pittsburgh, PA, 3 Stanford University, Stanford, CA, 4University of Pennsylvania, Philadelphia, PA Purpose/Objective(s): Stereotactic radiosurgery (SRS) of large intracranial arteriovenous malformations (AVMs) is challenged by a need to deliver an ablative dose while minimizing normal tissue toxicity. Spatially fractionated SRS aims to circumvent large volume brain toxicity by allowing for sublethal repair between stages. This work compares multistaged SRS treatment plans from robotic radiosurgery and focused cobalt60 radiosurgery systems for large intracranial AVMs. Materials/Methods: Eleven patients with localized intracranial arteriovenous malformations (AVM) were contoured on MRI and two orthogonal angiograms. Target volumes ranged from 15.3cm3 to 67.0cm3 (avg 30.719.2cm3). Depending on the target size and shape, each AVM was divided into 3 to 8 sub-targets (avg volume 6.93.2cm3). Each sub-target was treated in a staged approach at one to four week intervals. The prescription dose was 16-20 Gy depending on the total AVM volume. Robotic radiosurgery plans were created with cone sizes ranging from 60-80% of the sub-target size based on a previously described multi-staged inverse planning technique. Focused cobalt-60 radiosurgery plans were retrospectively generated on the same image sets with a simulated Extend frame system which can localize patients with a 1 mm re-positioning accuracy. A novel sub-target treatment planning technique was developed based on the position of individual shots from an initial plan developed for the total AVM target. Conformality and dose-volume analysis was performed to evaluate the PITV (ratio of prescription isodose volume to target volume), R50 (ratio of 50% isodose volume to target volume), and V12 Gy (volume of brain receiving 12Gy or greater). Results: The inversely optimized robotic radiosurgery plans achieved an average of 96.0%0.6 PTV coverage with a PITV of 1.230.16. The focused cobalt-60 radiosurgery plans resulted in an average of 95.8%0.6 PTV coverage with a PITV of 1.060.07. The resulting V12 Gy and R50 dose spillage values were 4.21.8 and 3.20.7, respectively, for the robotic radiosurgery plans and 4.22.0 and 3.20.4, respectively, for the focused cobalt-60 radiosurgery plans. Conclusions: The robotic radiosurgery and focused cobalt-60 radiosurgery systems can deliver a multi-staged conformal dose to treat large AVMs. Target coverage and prescription dose conformality were shown to be similar for both systems. Normal brain toxicity index values were equivalent between both systems. Author Disclosure: C. Ding: None. B. Hrycushko: None. S.B. Jiang: None. L. Whitworth: None. X. Li: None. R. Abdulrahman: None. L. Nedzi: None. K. Choe: None. L. Xing: None. T.D. Solberg: None. R.D. Timmerman: None.

3731 Comparison of 3D and 4D Plans in the Radiation Therapy for Lung Cancer Using Real Time Tumor Tracking System K. Okawa,1 M. Inoue,2 M. Taro,3 T. Koshi,1 and S. Ota1; 1Yokohama CyberKnife Center, Yokohama, Japan, 2Yokohama City University, Yokohama, Japan, 3Nagoya City University, Nagoya, Japan Purpose/Objective(s): Real time tumor tracking system is usually used for the planning of radiation therapy for lung cancer. Deformations of the

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International Journal of Radiation Oncology  Biology  Physics

target and organs at risk (OARs) during breathing are not considered in this three-dimensional (3-D) planning system, because doses are calculated at the end-exhale computed tomography (CT) images. On the other hand, the four-dimensional (4-D) plans using CT images from all respiratory phases seem to be similar to the actual doses. To know the difference between the calculated doses and actual doses delivered to the target and OARs, doses were calculated using 4-D plans and compared with those of the 3-D plans. Materials/Methods: Fourteen patients with lung cancer were treated at our institution from December 2012 to June 2013. 4-D CT scans were performed using multi slice CT and respiratory gating system. 4-D CT images were categorized into 10 respiratory phases. CT images were imported to the treatment planning system and structures were delineated on the endexhale phase CT images. Monte-Carlo algorithm was used for the dose calculation. 48 Gy in four fractions were prescribed at D95 of the PTV. Doses were calculated by both 3-D and 4-D plans in each patient. Maximum doses of the GTV (D-Max), GTV-D99, PTV-D95, Lung-V20, Conformity Index (CI) and Homogeneity index (HI) were compared in each patient. Furthermore, maximum doses of the liver, stomach, esophagus, trachea and spinal cord were also evaluated. Results: The actual doses of 4708.09 cGy  91.62 in PTV-D95 calculated by 4-D plans were significantly decreased in comparison with the prescribed doses of 4800 cGy by 3-D plans (p Z 0.02). The maximum differences of the calculated doses between 3-D and 4-D plans in GTV-D99 and PTV-D95 were 400.0 cGy and 266.7 cGy, respectively. In 3-D plans, doses were overestimated at the average of 2% (max 7.5%). The differences of maximum doses between 3-D and 4-D plans were not statistically significant in each OAR. However, the differences of calculated doses between 3-D and 4-D plans were relatively high in liver (-110.82 cGy 454.28 cGy), esophagus (-86.31 cGy - 344.27 cGy) and trachea (-972.89 cGy - 536.14 cGy), respectively. Conclusions: Although Monte-Carlo calculation has 2% uncertainty, and deformations of both target and OARs during respiration are inevitable, it was conceivable that the difference of the calculated doses between 3-D plan and 4-D plan to the target tumor were negligible. In contrast, the maximum doses of the OARs varied widely in each case. The accurate margins of OARs were affected by respiratory motions especially in organs such as liver, esophagus, and trachea. 4-D planning should be employed in the treatment planning of the cases with tumor located near the liver, esophagus and trachea to avoid the unexpected overdose-radiation to OARs. Author Disclosure: K. Okawa: None. M. Inoue: None. M. Taro: None. T. Koshi: None. S. Ota: None.

and CT for the BT. Treatment was done according to EMBRACE study protocol. A high risk clinical tumor volume (HR-CTV) and OARs (rectum, sigmoid, bowel, bladder and vagina) were defined from MR. Dose prescription was 4 x 7 Gy for HR-CTV. Biological total dose D90 to the HRCTV was kept over 85 Gy (EQD2, a/b Z 10) including EBRT. For the RSR plans the CT images and contours were copied from BT plans and prescription dose was same as in BT. Results: The average D90 to HR-CTV for RSR was 8.0  0.2 and 8.5  0.7 for BT (p Z 0.06). Difference in target coverage (V100%) was 96.6  2.0 % with RSR and 98.3  3.3 % with BT which was non-significant. Conformity index (nCI) was 1.2  0.04 with RSR and 2.2  0.2 with BT (p < 0.001). Average doses (D2cc) were not significant between techniques for bladder, rectum, sigmoid or bowel (D20%). For vaginal wall D10cc 2.5 Gy  1.1 was markedly smaller with RSR than 9.2 Gy  2.6 with BT (p < 0.001). Conclusions: Target coverage of RSR and BT plans was comparable. Dose conformity was significantly higher in RSR plans. For critical organs there was no difference in doses. For vaginal wall dose was significantly lower in RSR plans. This is due to the loading of the ring applicator in BT, increasing dose to the vaginal wall laterally and caudally. These results indicate that the RSR treatment offers a valid alternative to patients not able to undergo brachytherapy treatment. It may offer a good choice for the sexually active patients because of the low dose of the vaginal wall. The RSR treatment will require fiducial marker implantation to track the target. Author Disclosure: J. Palmgren: None. M. Anttila: None. T. Lahtinen: None.

3732 Robotic Stereotactic Radiation Therapy Compared to 3D MR Image Guided HDR Brachytherapy in the Treatment of Cervical Cancer J. Palmgren,1 M. Anttila,2 and T. Lahtinen3; 1Kuopio University Hospital, Cancer Center, Kuopio, Finland, 2Kuopio University Hospital, Department of Obstetrics and Gynecology, Kuopio, Finland, 3Kuopio University Hospital, Cancer Centre, Kuopio, Finland Purpose/Objective(s): According to a local experience on HDR brachytherapy (BT) with cervical cancer more than 50% of patients require interstitial/intracavitary treatment for adequate dose coverage. BT can be a stressful procedure for patients because of invasive nature and anesthesia. A feasibility study was made in order to explore the possibility to replace BT with Robotic Stereotactic Radiation therapy (RSR). Primary endpoint was to check if it is possible to create acceptable treatment plan with RSR, following the BT guidelines to the target and critical organs. Secondary endpoint was to find out where RSR might offer advantages over BT. Materials/Methods: We compared BT plans with RSR treatment plans in 12 cervical cancer patients. All patients were treated with BT. Before BT boost, patients received 45 Gy chemoradiation therapy. BT treatment applicators were inserted under anaesthesia. An average of four interstitial needles was used with ring-type applicator. Patients were imaged with MR

3733 Verification Real-Time Image Acquisition System (VERITAS) J. Rottmann,1,2 D. Kozono,1,2 R. Mak,1,2 A. Chen,1,2 F.L. Hacker,1,2 and R.I. Berbeco1,2; 1Brigham and Women’s Hospital / Dana-Farber Cancer Institute, Boston, MA, 2Harvard Medical School, Boston, MA Purpose/Objective(s): To create a novel clinical software tool for realtime in-treatment quantification and visualization of tumor location with respect to the planned position and the therapy beam aperture. Currently, image-guided radiation therapy relies on immobilization and reproducible motion after initial patient setup. We seek a comprehensive tool for capturing tumor location during radiation therapy and facilitating advanced applications. Materials/Methods: We combine a real-time soft tissue motion estimation algorithm based on 2D projection images with a fast 2D/3D registration for absolute tumor tracking in the treatment planning CT frame of reference. A frame grabber is used to obtain images from an electronic portal imaging device (EPID) operating in cine mode at a frequency of 12.9 Hz. These images are directed to a Verification Real-Time image Acquisition System (VERITAS) for processing before display. The real-time images are processed to optimize display contrast and estimate tumor motion. Treatment planning information, including physician-drawn contours is exported to the VERITAS prior to treatment. We test the proposed tool with images collected during lung SBRT treatments carried out at our institution. Radiation therapy was delivered with a 6 MV beam in 3 fractions to 54 Gy or in 5 fractions to 60 Gy, using 9-11 beams, including non-coplanar geometries. Results: Electronic portal images at a frame rate of 12.9 Hz and with a pixel size of (0.43 x 0.43) mm2 at iso-center were acquired for patients treated with SBRT for non-small cell lung cancer. The tool was successfully tested and display latency was measured to be w250ms. The treatment aperture can be visualized with overlaid target contours during treatment delivery in real-time. ITV, PTV (and GTV) contour positions are adjusted with organ motion in real-time allowing the clinician to visually inspect target coverage throughout the treatment delivery. In cases where image contrast becomes too low to extract reliable tumor motion estimates (uncertainty > 3mm) only the planned contour position is overlaid and a