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Rapid Access Palliative Radiation Workflow Using MRI-Guided Single-Session Simulation, Online Adaptation, and Treatment
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International Journal of Radiation Oncology Biology Physics
and the percentage of fractions not meeting the V95% objective was reduced to 12% and 39% for GTV and PTV, respectively (P<0.01). Reoptimized plans exhibited significantly better sparing of OAR and achieved a reduction of 2.1, 2.1 and 2.8 cc for stomach, bowel and duodenum at V35 Gy, with respect to predicted plans (all: P<0.01). Conclusion: Despite breath-hold SABR delivery under MR-guidance, significant volumetric changes, and displacements were observed for OARs. As re-optimization of treatment plans significantly improved target coverage and OAR sparing, our results indicate that online plan adaptation will be beneficial in adrenal SABR, even under MR-guidance. Author Disclosure: M. Palacios: None. O. Bohoudi: None. A. Bruynzeel: Honoraria; ViewRay. B.J. Slotman: Research Grant; Varian Medical Systems Inc. Honoraria; Varian Medical Systems Inc. Travel Expenses; Varian Medical Systems Inc.; American Radium Society, International Stereotactic Radiosurgery Society. F. Lagerwaard: Honoraria; ViewRay. S. Senan: Research Grant; Varian Medical Systems. Honoraria; Varian Medical Systems.
use of both staff and patient time and expedites palliative treatment with similarly successful clinical results. Author Disclosure: A.A. De Costa: None. K.E. Mittauer: Honoraria; ViewRay. H.C. Ko: None. P.M. Hill: None. S.A. Rosenberg: None. M.W. Geurts: None. J. Bayouth: AAPM. P.M. Harari: Education Council; ASTRO Board of Directors. M.F. Bassetti: Travel Expenses; ViewRay. Stock; Seattle genetics.
271 Rapid Access Palliative Radiation Workflow Using MRI-Guided Single-Session Simulation, Online Adaptation, and Treatment A.M.A. De Costa,1 K.E. Mittauer,2 H.C. Ko,1 P.M. Hill,2 S.A. Rosenberg,1 M.W. Geurts,1 J. Bayouth,2 P.M. Harari,2 and M.F. Bassetti2; 1Department of Human Oncology, University of Wisconsin, Madison, WI, 2Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Carbone Cancer Center, Madison, WI Purpose/Objective(s): In the palliative setting, priority is placed on streamlining the process of radiation delivery to avoid unnecessary treatment delay and expedite symptom relief. We hypothesized that using magnetic resonance imaging (MRI) guidance, adaptive planning software, and pre-existing diagnostic computed tomography (CT) imaging, we could deliver palliative radiation without the need for a separate CT simulation scan, thus decreasing the time and steps required to start palliative treatment. Materials/Methods: For patients necessitating urgent palliative radiotherapy, a simple “pre-plan” was created on diagnostic CT imaging prior to patient transport to the treatment machine. For dose calculation purposes, the electron density of the CT was deformed to MRI in the pre-plan or was overridden to water density. In the treatment vault, the patient was imaged in treatment position with volumetric MRI. The pre-plan was then rapidly adapted online to the MRI, updating the target definition, re-defining fields, and re-balancing beam weights. Once the online-adapted plan was finalized and approved, the patient was treated. Results: Eighteen patients with metastatic cancer were treated from October 2015 to November 2016 with urgent palliative radiation for indications such as pain, obstruction, and bleeding. Dose/fractionation regimens included 8 Gy in 1 fraction (8 pts), 25 Gy in 5 fractions (4 pts), and 30 Gy in 10 fractions (6 pts). Median planning target volume (PTV) size was 187cc. Online adaptive MRI-guided radiotherapy enabled plan changes to be made rapidly. Conformal 3D adaptive plans were delivered as quickly as more conventional AP/PA beam arrangements with a median delivery time of 122s. MRI-guided adaptive radiotherapy was planned and delivered in one-hour appointments for each patient, compared with a mean time from CT simulation to delivery of first treatment of 30 hours (95% CI, 24-35) for a similar sample of urgent palliative cases planned and treated with more traditional radiotherapy workflow. Clinical outcomes were similar to historical and sampled controls, with improvement in pain in 11 of 14 patients, relief of obstructive symptoms in 3 of 3 patients, and hemostasis in 1 of 1 patient treated with MRI-guided adaptive radiotherapy. Conclusion: Integrated treatment planning using available MRI-guided online adaptive radiotherapy allows a rapid-access treatment workflow obviating the need for a separate CT simulation. Conformal pre-plans can be created without time pressure and, if necessary, adapted to anatomy at treatment. This streamlined palliative radiation workflow makes efficient
272 A Novel Method of Generating Onboard 4D-MRI for Liver SBRT Target Localization Using Prior 4D-MRI Simulation and Onboard Limited Angle kV Acquisition from a Conventional LINAC C. Wang, W. Harris, F.F. Yin, Z. Chang, J. Cai, and L. Ren; Duke University Medical Center, Durham, NC Purpose/Objective(s): Although on-board MRI has much better soft tissue contrast than x-ray imaging for localizing liver tumors, its availability in the clinics is rather limited. This study aims to develop a novel technique to use conventional LINAC kV imaging system to generate on-board 4D-MRI based on prior 4D-MRI, deformation models, and on-board limited angle kV acquisition. Materials/Methods: To explain the overall workflow, 4D-MRI is acquired during patient simulation. The end of expiration (EOE) phase of the 4DMRI (MREOE) is used to generate a synthetic CT at EOE phase (sCTEOE). Patient on-board volume at any respiratory phase is represented as a deformation of sCTEOE, and the deformation field (DF) is solved based on on-board limited-angle kV projections (data fidelity constraint) and deformation models. The on-board 4D-MRI is generated by deforming MREOE based on DF. To explain in details, a two level motion modeling (MM) and free form deformation (FF) method developed previously is used to model DF: (1) MM. Three major respiratory deformation patterns (RDPs) are extracted by principal component analysis of the deformation field maps generated between EOE and all other phase volumes of prior 4D-MRI acquired during simulation. DF is modeled as a linear combination of RDPs. (2) FF. DF is modeled with free form deformation with minimization of the deformation energy. The method was evaluated using 4D Extended Cardiac-Torso (XCAT) digital phantom with our in-house XCAT-MRI package to simulate deformable diaphragm and chest wall motion of liver SBRT patients. The target was modeled as a spherical lesion (r Z 1.5cm), and the on-board ground-truth 4D-MRI volume was simulated 1) without and 2) with breathing amplitude change from the prior 4D-MRI. On-board kV projections were simulated by XCAT at only orthogonal 30o scan angles for better motion instant capture and less imaging dose. The target localization accuracy at EOE and end of inhalation (EOI) phases were quantitatively evaluated as they represent target location extremes. A liver SBRT patient case with 4D-MRI simulation was retrospectively evaluated for in vivo feasibility. The on-board orthogonal 30 kV acquisition was simulated using the clinical 4DCT. Results: In the XCAT study without breathing amplitude change, the Volume Dice Coefficient (VDC) and Center of Mass Shift (COMS) between ground truth and estimated tumor volumes was 0.93 and 0.5mm for EOE and 0.92 and 1.0 mm for EOI. With breathing amplitude change, the VDC and COMS were 0.96 and 0.7 mm for EOI and 0.93 and 0.5 mm for EOE. In the patient study, the on-board 4D-MRI series was successfully generated. The COMS between generated MRI EOI and clinical 4DCT EOI volumes was about 1.3 mm. Conclusion: The proposed method successfully generated on-board 4DMRI using prior 4D-MRI and on-board limited angle kV projections. The preliminary results showed great potential of MRI-based image guidance for liver SBRT using the conventional LINAC on-board kV imaging system. Author Disclosure: C. Wang: None. W. Harris: None. F. Yin: Patent/ License Fees/Copyright; Varian Medical Systems, Inc. The business and affairs of the ISRS will be managed by or under the direction of the Board of Directors, which will may exercise all such powers of the ISRS and take all lawful actions not prohibited by the Bylaws.; The International
International Journal of Radiation Oncology Biology Physics
and the percentage of fractions not meeting the V95% objective was reduced to 12% and 39% for GTV and PTV, respectively (P<0.01). Reoptimized plans exhibited significantly better sparing of OAR and achieved a reduction of 2.1, 2.1 and 2.8 cc for stomach, bowel and duodenum at V35 Gy, with respect to predicted plans (all: P<0.01). Conclusion: Despite breath-hold SABR delivery under MR-guidance, significant volumetric changes, and displacements were observed for OARs. As re-optimization of treatment plans significantly improved target coverage and OAR sparing, our results indicate that online plan adaptation will be beneficial in adrenal SABR, even under MR-guidance. Author Disclosure: M. Palacios: None. O. Bohoudi: None. A. Bruynzeel: Honoraria; ViewRay. B.J. Slotman: Research Grant; Varian Medical Systems Inc. Honoraria; Varian Medical Systems Inc. Travel Expenses; Varian Medical Systems Inc.; American Radium Society, International Stereotactic Radiosurgery Society. F. Lagerwaard: Honoraria; ViewRay. S. Senan: Research Grant; Varian Medical Systems. Honoraria; Varian Medical Systems.
use of both staff and patient time and expedites palliative treatment with similarly successful clinical results. Author Disclosure: A.A. De Costa: None. K.E. Mittauer: Honoraria; ViewRay. H.C. Ko: None. P.M. Hill: None. S.A. Rosenberg: None. M.W. Geurts: None. J. Bayouth: AAPM. P.M. Harari: Education Council; ASTRO Board of Directors. M.F. Bassetti: Travel Expenses; ViewRay. Stock; Seattle genetics.
271 Rapid Access Palliative Radiation Workflow Using MRI-Guided Single-Session Simulation, Online Adaptation, and Treatment A.M.A. De Costa,1 K.E. Mittauer,2 H.C. Ko,1 P.M. Hill,2 S.A. Rosenberg,1 M.W. Geurts,1 J. Bayouth,2 P.M. Harari,2 and M.F. Bassetti2; 1Department of Human Oncology, University of Wisconsin, Madison, WI, 2Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Carbone Cancer Center, Madison, WI Purpose/Objective(s): In the palliative setting, priority is placed on streamlining the process of radiation delivery to avoid unnecessary treatment delay and expedite symptom relief. We hypothesized that using magnetic resonance imaging (MRI) guidance, adaptive planning software, and pre-existing diagnostic computed tomography (CT) imaging, we could deliver palliative radiation without the need for a separate CT simulation scan, thus decreasing the time and steps required to start palliative treatment. Materials/Methods: For patients necessitating urgent palliative radiotherapy, a simple “pre-plan” was created on diagnostic CT imaging prior to patient transport to the treatment machine. For dose calculation purposes, the electron density of the CT was deformed to MRI in the pre-plan or was overridden to water density. In the treatment vault, the patient was imaged in treatment position with volumetric MRI. The pre-plan was then rapidly adapted online to the MRI, updating the target definition, re-defining fields, and re-balancing beam weights. Once the online-adapted plan was finalized and approved, the patient was treated. Results: Eighteen patients with metastatic cancer were treated from October 2015 to November 2016 with urgent palliative radiation for indications such as pain, obstruction, and bleeding. Dose/fractionation regimens included 8 Gy in 1 fraction (8 pts), 25 Gy in 5 fractions (4 pts), and 30 Gy in 10 fractions (6 pts). Median planning target volume (PTV) size was 187cc. Online adaptive MRI-guided radiotherapy enabled plan changes to be made rapidly. Conformal 3D adaptive plans were delivered as quickly as more conventional AP/PA beam arrangements with a median delivery time of 122s. MRI-guided adaptive radiotherapy was planned and delivered in one-hour appointments for each patient, compared with a mean time from CT simulation to delivery of first treatment of 30 hours (95% CI, 24-35) for a similar sample of urgent palliative cases planned and treated with more traditional radiotherapy workflow. Clinical outcomes were similar to historical and sampled controls, with improvement in pain in 11 of 14 patients, relief of obstructive symptoms in 3 of 3 patients, and hemostasis in 1 of 1 patient treated with MRI-guided adaptive radiotherapy. Conclusion: Integrated treatment planning using available MRI-guided online adaptive radiotherapy allows a rapid-access treatment workflow obviating the need for a separate CT simulation. Conformal pre-plans can be created without time pressure and, if necessary, adapted to anatomy at treatment. This streamlined palliative radiation workflow makes efficient
272 A Novel Method of Generating Onboard 4D-MRI for Liver SBRT Target Localization Using Prior 4D-MRI Simulation and Onboard Limited Angle kV Acquisition from a Conventional LINAC C. Wang, W. Harris, F.F. Yin, Z. Chang, J. Cai, and L. Ren; Duke University Medical Center, Durham, NC Purpose/Objective(s): Although on-board MRI has much better soft tissue contrast than x-ray imaging for localizing liver tumors, its availability in the clinics is rather limited. This study aims to develop a novel technique to use conventional LINAC kV imaging system to generate on-board 4D-MRI based on prior 4D-MRI, deformation models, and on-board limited angle kV acquisition. Materials/Methods: To explain the overall workflow, 4D-MRI is acquired during patient simulation. The end of expiration (EOE) phase of the 4DMRI (MREOE) is used to generate a synthetic CT at EOE phase (sCTEOE). Patient on-board volume at any respiratory phase is represented as a deformation of sCTEOE, and the deformation field (DF) is solved based on on-board limited-angle kV projections (data fidelity constraint) and deformation models. The on-board 4D-MRI is generated by deforming MREOE based on DF. To explain in details, a two level motion modeling (MM) and free form deformation (FF) method developed previously is used to model DF: (1) MM. Three major respiratory deformation patterns (RDPs) are extracted by principal component analysis of the deformation field maps generated between EOE and all other phase volumes of prior 4D-MRI acquired during simulation. DF is modeled as a linear combination of RDPs. (2) FF. DF is modeled with free form deformation with minimization of the deformation energy. The method was evaluated using 4D Extended Cardiac-Torso (XCAT) digital phantom with our in-house XCAT-MRI package to simulate deformable diaphragm and chest wall motion of liver SBRT patients. The target was modeled as a spherical lesion (r Z 1.5cm), and the on-board ground-truth 4D-MRI volume was simulated 1) without and 2) with breathing amplitude change from the prior 4D-MRI. On-board kV projections were simulated by XCAT at only orthogonal 30o scan angles for better motion instant capture and less imaging dose. The target localization accuracy at EOE and end of inhalation (EOI) phases were quantitatively evaluated as they represent target location extremes. A liver SBRT patient case with 4D-MRI simulation was retrospectively evaluated for in vivo feasibility. The on-board orthogonal 30 kV acquisition was simulated using the clinical 4DCT. Results: In the XCAT study without breathing amplitude change, the Volume Dice Coefficient (VDC) and Center of Mass Shift (COMS) between ground truth and estimated tumor volumes was 0.93 and 0.5mm for EOE and 0.92 and 1.0 mm for EOI. With breathing amplitude change, the VDC and COMS were 0.96 and 0.7 mm for EOI and 0.93 and 0.5 mm for EOE. In the patient study, the on-board 4D-MRI series was successfully generated. The COMS between generated MRI EOI and clinical 4DCT EOI volumes was about 1.3 mm. Conclusion: The proposed method successfully generated on-board 4DMRI using prior 4D-MRI and on-board limited angle kV projections. The preliminary results showed great potential of MRI-based image guidance for liver SBRT using the conventional LINAC on-board kV imaging system. Author Disclosure: C. Wang: None. W. Harris: None. F. Yin: Patent/ License Fees/Copyright; Varian Medical Systems, Inc. The business and affairs of the ISRS will be managed by or under the direction of the Board of Directors, which will may exercise all such powers of the ISRS and take all lawful actions not prohibited by the Bylaws.; The International