A Free Form Deformation-based 3D Registration Algorithm for Image Guided Breast Radiotherapy

Proceedings of the 51st Annual ASTRO Meeting

3181

Integral Dose Variation in Three-dimensional Conformal Radiotherapy, Intensity-modulated Radiotherapy, and Helical Tomotherapy

R. Yang1, S. Xu2, W. Jiang1, G. Zhou2, J. Wang1 1

Peking University Third Hospital, Beijing, China, 2The General Hospital of the People’s Liberation Army, Beijing, China

Purpose/Objective(s): To evaluate the integral doses (IDs) to organs at risk (OARs), normal tissue (NT) and the whole body in three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) and helical tomotherapy (HT) for whole pelvic radiotherapy (WPRT) in postoperative endometrial cancer patients. Materials/Methods: We selected ten patients with endometrial cancer undergoing postoperative WPRT. Plans of 3DCRT using both 6-MV (6MV-3DCRT) and 18-MV (18MV-3DCRT), static IMRT using a conventional linac with 6-MV (6MV-IMRT) and 18-MV (18MV-IMRT), and HT using 6-MV were developed for each patient. The IDs to OARs, NT and the whole body were compared. Results: Compared with 3DCRT, both IMRT and HT significantly improved dose conformity and the IDs to OARs (8.8% - 29.9%, p \ 0.05). Compared with 6MV-3DCRT, IMRT resulted in 13.2% and 11.0% lower IDs to NT and the whole body (p = 0.00), whereas no significant difference was found in HT plans. Compared directly with IMRT, HT reduced the IDs to rectum and bladder (p \ 0.05), whereas the IDs to NT were 13.9% higher than with 6MV-IMRT (p = 0.00), the IDs to pelvic bones also slightly increased with HT (p \ 0.05). The use of 18MV reduced the IDs to NT 5.8% and 2.7%, to the whole body 4.8% and 2.1% in the 3DCRT and IMRT plans (p = 0.00). Conclusions: In postoperative WPRT of endometrial cancer, IMRT and HT result in better conformity and lower IDs to OARs compared with 3DCRT. The IDs to NT and the whole body were significantly lower with IMRT, whereas no significant difference was found with HT compared with 6MV-3DCRT. Compared directly with IMRT, HT further reduced the IDs to rectum and bladder, at the expense of a slightly higher ID to pelvic bones and NT. The use of 18 MV improved the IDs to NT and the whole body in both 3DCRT and IMRT. Author Disclosure: R. Yang, None; S. Xu, None; W. Jiang, None; G. Zhou, None; J. Wang, None.

3182

Virtual Pre-intra-post Planning for Intraoperative Electron Radiation Therapy (IEORT): Radiance Project 2009 Update

J. A. Santos-Miranda1, J. Pascau1, C. Gonzalez1, C. Ferrer2, M. Desco1, F. A. Calvo1 1

Hospital General Gregorio Maran˜on, Madrid, Spain, 2Castellon Regional Hospital, Castellon, Spain

Purpose/Objective(s): The Radiance project consists of an IOERT patient-specific treatment planning system for virtual surgical simulation and electron beam interaction with modified patient anatomy. Materials/Methods: Development of the system started as an industrial and academic initiative in 2007 (GMV, University Hospital Gregorio Maran˜o´n and Castellon Regional Hospital in Spain). This tool allows planning IOERT interventions from CT studies of a patient. Other modalities can also be used as complementary information. The planning process is as follows: 1) segmentation, user can select several regions to be considered organs at risk, structures to be removed during surgery and high relapse risk areas; 2) simulation of patient positioning during surgery, accomplished by rotating the CT image, allowing virtual definitions of the surgical frame and bone structures that will limit the position of the applicator; 3) selection of applicator parameters (diameter and bevel angle), as well as its positioning; 4) selection of treatment energy with calculation of Dose Volume Histograms for the different regions. The current testing phase has triggered enhancements that are currently under development: designation of a set of landmarks for every anatomical location that will allow automatic pre-positioning of the applicator, and could also serve as references for patient-to-image registration with a tracking device; accumulation of estimated dose distribution from IOERT with planning dose from other Radiotherapy; integration of intraoperative image acquisition for quality assessment of IOERT. Results: 15 patients have been initially evaluated: 13 retrospectively and 2 prospectively. Tumor types were: 8 rectal cancer, 2 sarcomas, 1 breast, 1 chordoma, 3 recurrences. Anatomical fields were: 9 intrapelvic, 3 upper abdominal and 3 external surfaces. Clinical testing has proved feasibility of a) pre-tailoring IOERT target definition in agreement with surgical and radiotherapeutic individualized criteria; b) intra-surgically guided selection and optimization of pre-planning estimated parameters; c) post-planning definitive registration of the actual performed procedure for documentation and record. Conclusions: This virtual pre-intra-post planning system reproduces the real radiosurgical process involved in IOERT. Clinical testing will follow instrumental development with the integration of dosimetric parameters. Predictability of IOERT treatment decision process (including surgical actions) is assessable with this version of Radiance. Acknowledgements: The authors would like to thank GMV for their leadership in the development of Radiance. This project has been funded by Spanish Ministry of Science and Innovation (PI08/90473). Author Disclosure: J.A. Santos-Miranda, None; J. Pascau, None; C. Gonzalez, None; C. Ferrer, None; M. Desco, None; F.A. Calvo, None.

3183

A Free Form Deformation-based 3D Registration Algorithm for Image Guided Breast Radiotherapy

J. Zhou, S. Goyal, S. Kim, A. Khan, S. Jabbour, M. Rao, B. Haffty, N. J. Yue The Cancer Institute of New Jersey & UMDNJ-Robert Wood Johnson Medical School, New Brunswick, NJ Purpose/Objective(s): Accelerated partial breast irradiation (APBI) provides an alternative treatment strategy for early stage breast cancer patients. Image guided radiotherapy (IGRT) has the potential to improve treatment accuracy and quality. However, this potential cannot be fully utilized unless the clinical target volume can be quickly identified and localized at treatment. The purpose of this study is to develop a novel and fast registration method based on discriminating and registering the breast soft tissue vs. the seroma cavity, to capture the clinical target volume on the treatment 3D cone-beam CT (CBCT) images from the planning 3D CT images during the partial breast treatment in IGRT.

S713

I. J. Radiation Oncology d Biology d Physics

S714

Volume 75, Number 3, Supplement, 2009

Materials/Methods: We present a global to local 3D shape registration framework between the planning 3D CT images and treatment 3D CBCT images. The global registration is based on maximizing mutual information and the local registration is based a Bspline based incremental free form deformation model to minimize a sum of squared differences measure. The strengths of this method are that it preserves shape topology during local deformation, develops a novel 3D distance map algorithm and produces smooth, continuous and one-to-one correspondence local registration fields. The method is applied on 7 datasets consisting of both planning CT and CBCT images of breast patients. The target volumes which are used in the registration method in the planning 3D CT images and treatment 3D CBCT images are delineated by radiation oncologists manually and are chosen as the gold standards. Results: The registration method is evaluated using both qualitative and quantitative methods. The qualitative method is based on visualization by radiation oncologists. The quantitative methods are based on distance-based estimators and volume overlap ratio to compare the differences between the gold standard of the treatment CBCT images and the registered planning images. The quantitative results show that between the gold standard of the treatment CBCT images and the registered planning images, the mean discrepancy in distance ranges from 1.21 mm to 2.32 mm, the root-mean-square error (RMSE) ranges from 1.35 mm to 2.54 mm and the mean breast volume overlap ratio ranges from 83.2% to 94%. Conclusions: We present a novel and fast deformable registration method to capture the transformation between the planning and treatment images for external beam radiotherapy. We also present promising results of our method applied to clinical datasets. These preliminary results show that the proposed method is robust and reasonably fast for the registration of the deformable soft tissue of breast, and for deriving the clinical target volume on the treatment 3D CBCT images from the planning 3D CT images during the partial breast treatment. Author Disclosure: J. Zhou, None; S. Goyal, None; S. Kim, None; A. Khan, None; S. Jabbour, None; M. Rao, None; B. Haffty, None; N.J. Yue, None.

3184

Inverse Treatment Planning for Volumetric Modulated Arc Therapy using Compressed Sensing Techniques

L. Zhu, L. Xing Stanford University, Stanford, CA Purpose/Objective(s): The volumetric modulated arc therapy (VMAT) includes the field angle as another degree of freedom in the treatment planning and is therefore able to achieve a superior dose performance. Due to the increased computational complexity and the hardware constraints of beam segments, however, an optimal inverse planning of the VMAT is yet to be found and its advantages are not fully exploited in practice. The conventional beamlet-based algorithms obtain high-complexity fluence maps which are not suitable for delivery in the VMAT, and the segment-based algorithms are computationally intensive with no guarantee on the optimality of the final solution. In this work, a novel VMAT inverse planning algorithm is proposed to overcome the drawbacks of the existing methods. Materials/Methods: The main idea of the proposed algorithm stems from the fact that the VMAT planning problem is highly degenerated. Without compromising the final dose performance, the search space of the optimized solution can be significantly reduced. A new VMAT planning algorithm is then designed using compressed sensing, a method which is commonly used in the field of signal processing to recover compressible signals. We first divide the projection fields of VMAT into several groups of fields as in fix-gantry intensity-modulated radiation therapy (IMRT). Each group is then optimized separately using a previously developed IMRT planning algorithm with total-variation regularization. The derived segments are added into the solution space of the final VMAT plan. Another optimization is then carried out in the generated solution space using L-1 norm regularization on the weights of the segments to find a sparse solution. Results: The proposed algorithm is able to achieve a small number of segments for each projection field. After leaf sequencing, the optimized plan is deliverable using different schemes such as one single arc, multiple full or partial arcs. The algorithm performance is demonstrated using a prostate patient study. As compared to the fixed gantry radiation therapy and the conformal Arc therapy, our approach achieves a much improved target conformity and dose sparing of the sensitive structures, and truly gains the advantages of the VMAT. Conclusions: The compressed sensing techniques reduce the size of the optimization problem without sacrificing the optimality of the final solution, which leads to two major advantages of our VMAT planning algorithm. As compared to beamlet-based algorithms, our approach generates a plan with a small number of segments, which is more readily deliverable in VMAT. As compared to segment-based algorithms, our method has much higher efficiency due to its reduced size of solution space. As arc-based radiation therapy becomes more commonly used, the proposed algorithm is very attractive in clinic. Author Disclosure: L. Zhu, None; L. Xing, None.

3185

Dosimetric Effects of Non-symmetric Openings of Multi-catheter Breast Brachytherapy Applicators

J. E. Reiff1, D. C. Perlingiero2, L. T. Komarnicky1 1

Drexel University College of Medicine, Philadelphia, PA, 2Hahnemann University Hospital, Philadelphia, PA

Purpose/Objective(s): The Strut Adjusted Volume Implant (SAVITM) applicator is an HDR device used for accelerated partial breast irradiation (APBI). It is designed with multiple catheters, or struts, forming an ellipsoid around a central lumen. Occasionally the applicator may not open completely or symmetrically resulting in inverted or splayed struts. To investigate the resulting dosimetric consequences, we have run plans which simulate these abnormalities. Materials/Methods: A CT scan was performed on all four sizes of the SAVITM applicator. In each case the PTV was defined as the volume extending from the periphery of the applicator to 1.0 cm from the ellipsoid formed by the fully opened struts; the prescription dose of 3.40 Gy was prescribed to the outer edge of the PTV. Three plans were run off of each scan. The first plan was for the complete and symmetric opening of the struts. The second plan excluded one of the struts in the dose optimization simulating an inverted or splayed strut. The third plan excluded 2 adjacent struts, thus simulating two struts splayed away from each other. For each plan, the following 8 parameters were studied: the maximum dose encompassing the PTV (D100), V100, V150, V200, V250, V300, V350, and the volume outside the PTV receiving at least the prescribed dose (Vout).