- Email: [email protected]
Clinical Experience With 2 Cranial Frameless Stereotactic Radiosurgery (fSRS) Systems
Volume 90 Number 1S Supplement 2014 lung cancer. These preliminary results have to be confirmed with more patients and confronted to a clinical application. Moreover, other PET tracers more specific than FDG could be evaluated for this dose painting. Author Disclosure: B. Henriques: None. M. Antoine: None. R. Trouette: None. P. Lagarde: None. J. Benech: None. C. Zacharatou: None. M. Hatt: None. P. Fernandez: None.
3758 Novel Epitaxial Silicon Array for Quality Assurance in Radiation Therapy C. Talamonti,1 M. Zani,1 D. Menichelli,2 F. Friedl,2 M. Scaringella,1 L. Livi,1 M. Bruzzi,1 and M. Bucciolini1; 1University of Florence, Firenze, Italy, 2IBA Dosimetry GmbH, Schwarzenbruck, Germany Purpose/Objective(s): During the last decade silicon dosimeters have found a wide application in radiation therapy due to the dose escalation in the tumor volume which demands accurate quality assurance programs. Silicon devices offer higher spatial resolution and higher performances than other commercial dosimeters like ion chambers, which suffer of limited spatial resolution, and gafchromic films, which are not real time detectors. In this article a novel epitaxial silicon array is described to demonstrate its suitability for measuring the dose properties of photon beams used in stereotactic treatments, Intensity Modulated (IMRT), and Volumetric Modulated Arc Therapy (VMAT) . Materials/Methods: The linear array prototype studied in this work is based on a 64-pixels monolithic silicon sensor made of epitaxial p-type silicon. Array length and pitch are 64mm and 1mm respectively. Sensor design is modular, and more sensors can be placed side by side without breaking pixel pitch. The prototype has four sensors mounted on a printed circuit board and connected to an electrometer based on TERA06 chips. All the pixels of the two central modules are connected to readout electronics. Due to the limited number of readout channels of this prototype (180), only 26 channels have been selected from each external module, with 2mm pitch. A full dosimetric characterization of the detector was performed and the application of the device in the dosimetric verification of clinical plans were verified. Results: Accurate measurements of the dose characteristics of beams as percentage depth doses, beam profiles, output factors and energy response, which are necessary to deliver radiation with high precision and in a trusted manner, were performed. Dose rate independence was verified irradiating the device with flattened and unflattened beams, varying dose per pulse in the range 0.03-2mGy. Results clearly indicate non-dependence of the detector sensitivity on the dose rate in all explored ranges both for flattened and unflattened beams with a variation of at most 0.5%. OFs were obtained for field with a lateral size ranging from 0.8cm to 16cm and the results are in good agreement with ion chamber A1SL (max difference < 1.5%) Field sizes and beam’s penumbra were measured and compared to those of EBT film. Eventually measured dose’s profile were compared with ones predicted by Pinnacle and Monaco TPS showing an excellent characterization of high modulated profiles. Conclusions: The device is a novel and valuable tool for QA in IMRT, VMAT, and especially for stereotactic dose delivery. In fact, all measurements demonstrated the device’s capability to measure with high spatial resolution many crucial properties of the RT beams. Moreover they show the high temporal resolution capability of the detector readout system, which allows to investigate the temporal dose pattern of IMRT and VMAT deliveries. Author Disclosure: C. Talamonti: None. M. Zani: None. D. Menichelli: None. F. Friedl: None. M. Scaringella: None. M. Bruzzi: None. M. Bucciolini: None.
3759 Safety Assessment, Artifact Reduction, and Description of Geometric Distortion Associated With Diffusion Imaging (DWI) With Rigid Head Frame Immobilization for Stereotactic Radiosurgery J.T. Lucas,1 J. DiNotto,1 W. Dolesh,2 Y. Jung,1 C.T. Whitlow,1 J.A. Maldjian,1 M.D. Chan,2 and J. Bourland1; 1Wake Forest Baptist
Poster Viewing Abstracts S903 Medical Center, Winston-Salem, NC, 2Wake Forest University Medical Center, Winston-Salem, NC Purpose/Objective(s): Rigidly-fixed head frames are frequently used for immobilization during single fraction SRS. Biologic imaging sequences to describe the natural history of intracranial disease have been limited to frameless MRI acquisitions due to concern for potential artifacts and MRIinduced thermal injury. We describe an optimized SRS DWI technique that reduces head frame-associated susceptibility artifact/distortion and has RFinduced heating within safe limits. Materials/Methods: Phantoms (melon, skull, and grid) attached to a Model-G, insulated post, SRS head frame were used to characterize spatial, heating, and metal susceptibility artifacts during SRS image acquisition using a 3T clinical MRI scanner. MRI-induced heating was evaluated using fiberoptic temperature probes placed at the head frame screw-melon interface and at sub-surface depth (5 mm from the head frame screw tip) to serially measure the time-temperature profile during the reference (T1, SPGR, etc) & DWI sequences in an axial & oblique orientation. The Bio-Heat transfer equation was used to analyze absorbed power density (watts/cm^3) associated with each sequence. Resistivity of each current loop was assessed using an Ohmmeter. Geometric distortion with single-shot vs. multi-shot (DWI-FSE (Propeller MRI)) EPI acquisition methods were evaluated by estimating differences (mm) in X, Y, & Z coordinates describing localization within the grid & skull phantom. Results: The mean change in temperature at the pin/melon interface at depth for the T1, SPGR, FRFSE were 1.36, 0.08, & 0.17 oC vs. 0.22 & 1.28 oC for the DWI & Propeller-FSE respectively. This change in temperature corresponded to an initial heat transfer estimated at 0.156-0.193 Watts/cm^3 for the T1, 0.15-0.182 Watts/cm^3 for the Propeller-FSE, and an negligible estimate (5 - 10x less) for the SPGR, FRFSE, and DWI. Single shot EPI DWI showed substantial susceptibility artifact in the presence of the SRS head frame while the Propeller-FSE sequence displayed only minimal distortion within 1-1.5cm of the pin-skin interface. Measured brain shift was minimal using the DWI-Propeller FSE sequence with a max X, Y, & Z translation of 1.45, 0.88, & 1.08 mm relative to the max X, Y, & Z translation of 1.21, 0.92, & 0.96 mm with standard DWI. Geometric distortion was similar to the reference T1 (X: 0.85, Y: 0.5, Z: 1.68). Conclusions: DWI-PROPELLER-FSE reduced geometric distortion and had acceptable heating tolerances comparable to standard T1 imaging. Safety of the above sequences is contingent upon the use of insulated pinhead frames. Addition of DWI weighted imaging may improve volume delineation during head frame immobilized single fraction SRS. Author Disclosure: J.T. Lucas: None. J. DiNotto: None. W. Dolesh: None. Y. Jung: None. C.T. Whitlow: None. J.A. Maldjian: None. M.D. Chan: None. J. Bourland: None.
3760 Clinical Experience With 2 Cranial Frameless Stereotactic Radiosurgery (fSRS) Systems G. Li,1 A. Ballangrud,1 M.F. Chan,2 R. Ma,3 K. Beal,1 T.A. Chan,1 Y. Yamada,1 J.G. Mechalakos,1 and M.A. Hunt1; 1Memorial SloanKettering Cancer Center, New York, NY, 2Memorial Sloan-Kettering Cancer Center, Basking Ridge, NJ, 3Memorial Sloan-Kettering Cancer Center, Commack, NY Purpose/Objective(s): The objective of this study is to provide a comprehensive comparison of two cranial fSRS systems. For both systems cone beam computed tomography (CBCT) was used for patient setup and a video-based (or 4-dimensional) optical surface (4DOS) imaging was used for quick initial patient alignment prior to CBCT and for motion monitoring during treatment. Materials/Methods: Two cranial fSRS systems (A and B) are used for patient treatment in our clinic. Both systems use a customized head mold to limit motion in the posterior, superior and lateral directions. In anterior and inferior directions, system A uses a customized mouthpiece, whereas system B uses an open-face mask to restrict motions. System B is also equipped with an adjustable head board to correct pitch and roll rotations. 4DOS was used for quick initial patient alignment to minimize residual
International Journal of Radiation Oncology Biology Physics
S904 Scientific Abstract 3761; Table
Mean values over all patients
DDmean [%]
DV20 [%]
Ipsilateral lung
CTinsp / CTfree
CTexp / CTfree
CTinsp / CTexp
CTinsp / CTfree
CTexp / CTfree
CTinsp / CTexp
3D-CRT VMAT
20.2 7.8 19.4 7.8
12.1 3.9 11.1 4.2
8.2 7.1 8.3 6.9
25.2 9.9 21.8 9.1
14.7 4.5 13.6 5.3
10.4 8.4 8.1 8.7
PTV
Dmean [Gy] PTVfree 49.7 1.2 48.5 0.7
PTVinsp 49.5 1.1 48.1 1.0
PTVexp 49.6 1.2 48.3 0.6
Dmax [Gy] PTVfree 60.8 2.3 59.9 1.4
PTVinsp 60.8 1.9 59.6 1.7
PTVexp 61.0 1.9 59.6 1.2
3D-CRT VMAT
head rotation prior to CBCT, which was used for final patient setup. During treatment, after each couch rotation the patient position was verified with 4DOS, followed by motion monitoring. This study includes 29 patients treated in a single fraction using system A and 8 patients treated in 1-5 fractions with a total of 29 treatments using system B. System B was also evaluated on 8 volunteers to determine the range of deliberate, forced movements and estimate the worst case scenario. Results: At pre-CBCT patient alignment using 4DOS, the residual head rotation was 1.00.5 for system A and 0.6 0.3 for system B. The time for rotation corrections was w5 minutes using system A and 2.5 minutes using system B. After CBCT, on average additional shifts were made with 2.20.5 mm for system A and 1.30.6 mm for system B, due to the differences in residual rotation, imaging modality and registration landmarks. For setup verification at treatment couch angles using 4DOS, the 2 systems were similar in part because of additional uncertainties related to machine/couch accuracy, different camera views and patient topography. The two fSRS systems depict similar patient immobilization capability: in 27 out of the 29 treatments the most mobile patient moved within 1.2mm (95% of the time) for system A and within 1.4mm (95 % of the time) for system B. Two exceptions in both systems showed w2mm intra-fractional motion that was corrected. For system B, the head motion range was 2.10.5mm for deliberate lateral and pitch movements. Conclusions: Both fSRS immobilization systems provide w1.0 mm accuracy for fSRS treatment. System A provides more rigid fixation of patient, with drawbacks of manual rotation correction and discomfort from the mouthpiece. System B provides quick rotation adjustment, improved patient comfort level, and adequate head immobilization. Automatic beam holding via the motion management interface between 4DOS and a Linac is useful to ensure <1 mm motion during treatment in both cases. Author Disclosure: G. Li: None. A. Ballangrud: None. M.F. Chan: None. R. Ma: None. K. Beal: None. T.A. Chan: None. Y. Yamada: None. J.G. Mechalakos: None. M.A. Hunt: None.
3761 Respiratory-Gated Lung Stereotactic Body Radiation Therapy: A Planning Study of 3D-CRT Versus VMAT M. Oechsner, J. Berndt, J.J. Wilkens, and M.N. Duma; Department of Radiation Oncology, Klinikum rechts der Isar, der Technische Universita¨t Mu¨nchen, Munich, Germany Purpose/Objective(s): Volumetric modulated arc therapy (VMAT) is nowadays very widely used and increasingly for stereotactic body radiation therapy (SBRT) as well. Further, 3D conformal radiation therapy (3DCRT) is sometimes combined with gating. The purpose of this study was to assess the dosimetric benefit of gated irradiations (3D-CRT vs. VMAT) in inspiration or expiration for SBRT of lung tumors. Materials/Methods: Datasets of 9 patients were retrospectively included in this study. The lung volume was determined for each of the 10 phases of the 4D-CTs and gating windows were defined as 020% (expiration) or 80-100% (inspiration) of change between maximum and minimum lung volume. By averaging all CT phases which have lung volumes within the defined gating windows, CT data sets in expiration (CTexp) and inspiration (CTinsp) were calculated. An average CT over all phases was also calculated (CTfree). Gross tumor volumes (GTV) were contoured for all CT phases (0-100%)
individually. From the GTVs of the according phases internal target volumes (ITV) and planning target volumes (PTV Z ITV+5mm) were generated for all CT sets. For CTexp, CTinsp and CTfree SBRT plans were optimised using 3D-CRT (7 fields) and VMAT (3 partial arcs) techniques (Disocenter(PTV) Z 100% and Dmin(PTV) Z 60% of the prescription dose). PTV volumes, dosimetric parameters and conformity indices (CI) were determined and compared. Results: The volume of the PTV in inspiration (PTVinsp) was 22.5% 9.3% (meanSD) smaller and the PTV in expiration (PTVexp) was 20.7% 6.8% smaller than PTV of CTfree. Compared to CTfree, CTinsp and CTexp achieved lower lung doses with distinctly lower values for CTinsp. VMATplans resulted in slightly lower doses to the ipsilateral lung (Dmean and V20) and 3D-CRT plans in about 1 Gy higher Dmean and Dmax values (PTV). The CI for 3D-CRT over all plans was 1.40 0.13 according to a larger volume of the 60% isodose (VMAT-CI: 1.27 0.12). Conclusions: Gated irradiation enables smaller PTVs and therefore lower doses to the ipsilateral lung particularly in inspiration as compared to free breathing. 3D-CRT as well as VMAT resulted in similar doses to the lung and dose coverage of the PTV, but better dose conformity for VMAT plans. Author Disclosure: M. Oechsner: A. Employee; Klinikum rechts der Isar (University hospital). J. Berndt: A. Employee; Klinikum rechts der Isar (University hospital). J.J. Wilkens: A. Employee; Klinikum rechts der Isar (University hospital). K. Advisory Board; Scientific Advisory Board of the Pro Health AG. S. Leadership; Associate Editor for the European Journal of Medical Physics. M.N. Duma: A. Employee; Klinikum rechts der Isar (University hospital).
3762 Local Control Evaluation in Bone Metastases Treated With Stereotactic Body Radiation Therapy: Initial Experience R. Pineiro Retif,1 A. Navarro,1 A. Lozano,1 F. Ferrer,1 A. Eraso,1 M. Galdeano,1 D. Najjari,1 R. de Blas Pin˜ol,1 G. Martı´nez Pimienta,2 P. Bavestrello,1 F. Rojas,1 O. Leaman,1 H. Letelier,3 and F. Guedea Edo1; 1 Catalan Institute of Oncology, Barcelona, Spain, 2University Hospital of Bellvitge, Barcelona, Spain, 3Universidad de Valparaiso, Valparaiso, Chile Purpose/Objective(s): Clinical studies have showed the efficacy of SBRT for pain control with consequent improvement of quality of life, and also, secondary to local tumor control, a longer survival in oligometastases and oligo-recurrence disease. We present our initial experience using SBRT for bone metastases in oligometastases and oligo-recurrence patients. Materials/Methods: At the moment, we have treated ten lesions in nine patients. Patients in oligometastases or oligo-recurrence state, with localized bone metastasis, up to three separate sites were included by imaging study (bone scan, PET-CT, CT or MRI), in case of spinal lesions each of the separate sites may have a maximal involvement of two contiguous vertebral bodies. Patients were treated with high precision machines. Eight of them had a single bone lesion and one had two spinal lesions. Primary tumors were treated with curative intent by their respective protocol. The dose prescription was 16Gy in a single fraction or 22.5Gy in three fractions. Follow-up: 1, 3, 6, 12 and 24 months from treatment time, with physical examination, rating the pain at each visit and PET-CT at a second visit (three months from treatment). Results: Currently we have a mean follow-up of six months (r1-19), with no adverse effect detected. The patient who had pain, showed a complete pain relief. All of these patients are in local tumor control.
3758 Novel Epitaxial Silicon Array for Quality Assurance in Radiation Therapy C. Talamonti,1 M. Zani,1 D. Menichelli,2 F. Friedl,2 M. Scaringella,1 L. Livi,1 M. Bruzzi,1 and M. Bucciolini1; 1University of Florence, Firenze, Italy, 2IBA Dosimetry GmbH, Schwarzenbruck, Germany Purpose/Objective(s): During the last decade silicon dosimeters have found a wide application in radiation therapy due to the dose escalation in the tumor volume which demands accurate quality assurance programs. Silicon devices offer higher spatial resolution and higher performances than other commercial dosimeters like ion chambers, which suffer of limited spatial resolution, and gafchromic films, which are not real time detectors. In this article a novel epitaxial silicon array is described to demonstrate its suitability for measuring the dose properties of photon beams used in stereotactic treatments, Intensity Modulated (IMRT), and Volumetric Modulated Arc Therapy (VMAT) . Materials/Methods: The linear array prototype studied in this work is based on a 64-pixels monolithic silicon sensor made of epitaxial p-type silicon. Array length and pitch are 64mm and 1mm respectively. Sensor design is modular, and more sensors can be placed side by side without breaking pixel pitch. The prototype has four sensors mounted on a printed circuit board and connected to an electrometer based on TERA06 chips. All the pixels of the two central modules are connected to readout electronics. Due to the limited number of readout channels of this prototype (180), only 26 channels have been selected from each external module, with 2mm pitch. A full dosimetric characterization of the detector was performed and the application of the device in the dosimetric verification of clinical plans were verified. Results: Accurate measurements of the dose characteristics of beams as percentage depth doses, beam profiles, output factors and energy response, which are necessary to deliver radiation with high precision and in a trusted manner, were performed. Dose rate independence was verified irradiating the device with flattened and unflattened beams, varying dose per pulse in the range 0.03-2mGy. Results clearly indicate non-dependence of the detector sensitivity on the dose rate in all explored ranges both for flattened and unflattened beams with a variation of at most 0.5%. OFs were obtained for field with a lateral size ranging from 0.8cm to 16cm and the results are in good agreement with ion chamber A1SL (max difference < 1.5%) Field sizes and beam’s penumbra were measured and compared to those of EBT film. Eventually measured dose’s profile were compared with ones predicted by Pinnacle and Monaco TPS showing an excellent characterization of high modulated profiles. Conclusions: The device is a novel and valuable tool for QA in IMRT, VMAT, and especially for stereotactic dose delivery. In fact, all measurements demonstrated the device’s capability to measure with high spatial resolution many crucial properties of the RT beams. Moreover they show the high temporal resolution capability of the detector readout system, which allows to investigate the temporal dose pattern of IMRT and VMAT deliveries. Author Disclosure: C. Talamonti: None. M. Zani: None. D. Menichelli: None. F. Friedl: None. M. Scaringella: None. M. Bruzzi: None. M. Bucciolini: None.
3759 Safety Assessment, Artifact Reduction, and Description of Geometric Distortion Associated With Diffusion Imaging (DWI) With Rigid Head Frame Immobilization for Stereotactic Radiosurgery J.T. Lucas,1 J. DiNotto,1 W. Dolesh,2 Y. Jung,1 C.T. Whitlow,1 J.A. Maldjian,1 M.D. Chan,2 and J. Bourland1; 1Wake Forest Baptist
Poster Viewing Abstracts S903 Medical Center, Winston-Salem, NC, 2Wake Forest University Medical Center, Winston-Salem, NC Purpose/Objective(s): Rigidly-fixed head frames are frequently used for immobilization during single fraction SRS. Biologic imaging sequences to describe the natural history of intracranial disease have been limited to frameless MRI acquisitions due to concern for potential artifacts and MRIinduced thermal injury. We describe an optimized SRS DWI technique that reduces head frame-associated susceptibility artifact/distortion and has RFinduced heating within safe limits. Materials/Methods: Phantoms (melon, skull, and grid) attached to a Model-G, insulated post, SRS head frame were used to characterize spatial, heating, and metal susceptibility artifacts during SRS image acquisition using a 3T clinical MRI scanner. MRI-induced heating was evaluated using fiberoptic temperature probes placed at the head frame screw-melon interface and at sub-surface depth (5 mm from the head frame screw tip) to serially measure the time-temperature profile during the reference (T1, SPGR, etc) & DWI sequences in an axial & oblique orientation. The Bio-Heat transfer equation was used to analyze absorbed power density (watts/cm^3) associated with each sequence. Resistivity of each current loop was assessed using an Ohmmeter. Geometric distortion with single-shot vs. multi-shot (DWI-FSE (Propeller MRI)) EPI acquisition methods were evaluated by estimating differences (mm) in X, Y, & Z coordinates describing localization within the grid & skull phantom. Results: The mean change in temperature at the pin/melon interface at depth for the T1, SPGR, FRFSE were 1.36, 0.08, & 0.17 oC vs. 0.22 & 1.28 oC for the DWI & Propeller-FSE respectively. This change in temperature corresponded to an initial heat transfer estimated at 0.156-0.193 Watts/cm^3 for the T1, 0.15-0.182 Watts/cm^3 for the Propeller-FSE, and an negligible estimate (5 - 10x less) for the SPGR, FRFSE, and DWI. Single shot EPI DWI showed substantial susceptibility artifact in the presence of the SRS head frame while the Propeller-FSE sequence displayed only minimal distortion within 1-1.5cm of the pin-skin interface. Measured brain shift was minimal using the DWI-Propeller FSE sequence with a max X, Y, & Z translation of 1.45, 0.88, & 1.08 mm relative to the max X, Y, & Z translation of 1.21, 0.92, & 0.96 mm with standard DWI. Geometric distortion was similar to the reference T1 (X: 0.85, Y: 0.5, Z: 1.68). Conclusions: DWI-PROPELLER-FSE reduced geometric distortion and had acceptable heating tolerances comparable to standard T1 imaging. Safety of the above sequences is contingent upon the use of insulated pinhead frames. Addition of DWI weighted imaging may improve volume delineation during head frame immobilized single fraction SRS. Author Disclosure: J.T. Lucas: None. J. DiNotto: None. W. Dolesh: None. Y. Jung: None. C.T. Whitlow: None. J.A. Maldjian: None. M.D. Chan: None. J. Bourland: None.
3760 Clinical Experience With 2 Cranial Frameless Stereotactic Radiosurgery (fSRS) Systems G. Li,1 A. Ballangrud,1 M.F. Chan,2 R. Ma,3 K. Beal,1 T.A. Chan,1 Y. Yamada,1 J.G. Mechalakos,1 and M.A. Hunt1; 1Memorial SloanKettering Cancer Center, New York, NY, 2Memorial Sloan-Kettering Cancer Center, Basking Ridge, NJ, 3Memorial Sloan-Kettering Cancer Center, Commack, NY Purpose/Objective(s): The objective of this study is to provide a comprehensive comparison of two cranial fSRS systems. For both systems cone beam computed tomography (CBCT) was used for patient setup and a video-based (or 4-dimensional) optical surface (4DOS) imaging was used for quick initial patient alignment prior to CBCT and for motion monitoring during treatment. Materials/Methods: Two cranial fSRS systems (A and B) are used for patient treatment in our clinic. Both systems use a customized head mold to limit motion in the posterior, superior and lateral directions. In anterior and inferior directions, system A uses a customized mouthpiece, whereas system B uses an open-face mask to restrict motions. System B is also equipped with an adjustable head board to correct pitch and roll rotations. 4DOS was used for quick initial patient alignment to minimize residual
International Journal of Radiation Oncology Biology Physics
S904 Scientific Abstract 3761; Table
Mean values over all patients
DDmean [%]
DV20 [%]
Ipsilateral lung
CTinsp / CTfree
CTexp / CTfree
CTinsp / CTexp
CTinsp / CTfree
CTexp / CTfree
CTinsp / CTexp
3D-CRT VMAT
20.2 7.8 19.4 7.8
12.1 3.9 11.1 4.2
8.2 7.1 8.3 6.9
25.2 9.9 21.8 9.1
14.7 4.5 13.6 5.3
10.4 8.4 8.1 8.7
PTV
Dmean [Gy] PTVfree 49.7 1.2 48.5 0.7
PTVinsp 49.5 1.1 48.1 1.0
PTVexp 49.6 1.2 48.3 0.6
Dmax [Gy] PTVfree 60.8 2.3 59.9 1.4
PTVinsp 60.8 1.9 59.6 1.7
PTVexp 61.0 1.9 59.6 1.2
3D-CRT VMAT
head rotation prior to CBCT, which was used for final patient setup. During treatment, after each couch rotation the patient position was verified with 4DOS, followed by motion monitoring. This study includes 29 patients treated in a single fraction using system A and 8 patients treated in 1-5 fractions with a total of 29 treatments using system B. System B was also evaluated on 8 volunteers to determine the range of deliberate, forced movements and estimate the worst case scenario. Results: At pre-CBCT patient alignment using 4DOS, the residual head rotation was 1.00.5 for system A and 0.6 0.3 for system B. The time for rotation corrections was w5 minutes using system A and 2.5 minutes using system B. After CBCT, on average additional shifts were made with 2.20.5 mm for system A and 1.30.6 mm for system B, due to the differences in residual rotation, imaging modality and registration landmarks. For setup verification at treatment couch angles using 4DOS, the 2 systems were similar in part because of additional uncertainties related to machine/couch accuracy, different camera views and patient topography. The two fSRS systems depict similar patient immobilization capability: in 27 out of the 29 treatments the most mobile patient moved within 1.2mm (95% of the time) for system A and within 1.4mm (95 % of the time) for system B. Two exceptions in both systems showed w2mm intra-fractional motion that was corrected. For system B, the head motion range was 2.10.5mm for deliberate lateral and pitch movements. Conclusions: Both fSRS immobilization systems provide w1.0 mm accuracy for fSRS treatment. System A provides more rigid fixation of patient, with drawbacks of manual rotation correction and discomfort from the mouthpiece. System B provides quick rotation adjustment, improved patient comfort level, and adequate head immobilization. Automatic beam holding via the motion management interface between 4DOS and a Linac is useful to ensure <1 mm motion during treatment in both cases. Author Disclosure: G. Li: None. A. Ballangrud: None. M.F. Chan: None. R. Ma: None. K. Beal: None. T.A. Chan: None. Y. Yamada: None. J.G. Mechalakos: None. M.A. Hunt: None.
3761 Respiratory-Gated Lung Stereotactic Body Radiation Therapy: A Planning Study of 3D-CRT Versus VMAT M. Oechsner, J. Berndt, J.J. Wilkens, and M.N. Duma; Department of Radiation Oncology, Klinikum rechts der Isar, der Technische Universita¨t Mu¨nchen, Munich, Germany Purpose/Objective(s): Volumetric modulated arc therapy (VMAT) is nowadays very widely used and increasingly for stereotactic body radiation therapy (SBRT) as well. Further, 3D conformal radiation therapy (3DCRT) is sometimes combined with gating. The purpose of this study was to assess the dosimetric benefit of gated irradiations (3D-CRT vs. VMAT) in inspiration or expiration for SBRT of lung tumors. Materials/Methods: Datasets of 9 patients were retrospectively included in this study. The lung volume was determined for each of the 10 phases of the 4D-CTs and gating windows were defined as 020% (expiration) or 80-100% (inspiration) of change between maximum and minimum lung volume. By averaging all CT phases which have lung volumes within the defined gating windows, CT data sets in expiration (CTexp) and inspiration (CTinsp) were calculated. An average CT over all phases was also calculated (CTfree). Gross tumor volumes (GTV) were contoured for all CT phases (0-100%)
individually. From the GTVs of the according phases internal target volumes (ITV) and planning target volumes (PTV Z ITV+5mm) were generated for all CT sets. For CTexp, CTinsp and CTfree SBRT plans were optimised using 3D-CRT (7 fields) and VMAT (3 partial arcs) techniques (Disocenter(PTV) Z 100% and Dmin(PTV) Z 60% of the prescription dose). PTV volumes, dosimetric parameters and conformity indices (CI) were determined and compared. Results: The volume of the PTV in inspiration (PTVinsp) was 22.5% 9.3% (meanSD) smaller and the PTV in expiration (PTVexp) was 20.7% 6.8% smaller than PTV of CTfree. Compared to CTfree, CTinsp and CTexp achieved lower lung doses with distinctly lower values for CTinsp. VMATplans resulted in slightly lower doses to the ipsilateral lung (Dmean and V20) and 3D-CRT plans in about 1 Gy higher Dmean and Dmax values (PTV). The CI for 3D-CRT over all plans was 1.40 0.13 according to a larger volume of the 60% isodose (VMAT-CI: 1.27 0.12). Conclusions: Gated irradiation enables smaller PTVs and therefore lower doses to the ipsilateral lung particularly in inspiration as compared to free breathing. 3D-CRT as well as VMAT resulted in similar doses to the lung and dose coverage of the PTV, but better dose conformity for VMAT plans. Author Disclosure: M. Oechsner: A. Employee; Klinikum rechts der Isar (University hospital). J. Berndt: A. Employee; Klinikum rechts der Isar (University hospital). J.J. Wilkens: A. Employee; Klinikum rechts der Isar (University hospital). K. Advisory Board; Scientific Advisory Board of the Pro Health AG. S. Leadership; Associate Editor for the European Journal of Medical Physics. M.N. Duma: A. Employee; Klinikum rechts der Isar (University hospital).
3762 Local Control Evaluation in Bone Metastases Treated With Stereotactic Body Radiation Therapy: Initial Experience R. Pineiro Retif,1 A. Navarro,1 A. Lozano,1 F. Ferrer,1 A. Eraso,1 M. Galdeano,1 D. Najjari,1 R. de Blas Pin˜ol,1 G. Martı´nez Pimienta,2 P. Bavestrello,1 F. Rojas,1 O. Leaman,1 H. Letelier,3 and F. Guedea Edo1; 1 Catalan Institute of Oncology, Barcelona, Spain, 2University Hospital of Bellvitge, Barcelona, Spain, 3Universidad de Valparaiso, Valparaiso, Chile Purpose/Objective(s): Clinical studies have showed the efficacy of SBRT for pain control with consequent improvement of quality of life, and also, secondary to local tumor control, a longer survival in oligometastases and oligo-recurrence disease. We present our initial experience using SBRT for bone metastases in oligometastases and oligo-recurrence patients. Materials/Methods: At the moment, we have treated ten lesions in nine patients. Patients in oligometastases or oligo-recurrence state, with localized bone metastasis, up to three separate sites were included by imaging study (bone scan, PET-CT, CT or MRI), in case of spinal lesions each of the separate sites may have a maximal involvement of two contiguous vertebral bodies. Patients were treated with high precision machines. Eight of them had a single bone lesion and one had two spinal lesions. Primary tumors were treated with curative intent by their respective protocol. The dose prescription was 16Gy in a single fraction or 22.5Gy in three fractions. Follow-up: 1, 3, 6, 12 and 24 months from treatment time, with physical examination, rating the pain at each visit and PET-CT at a second visit (three months from treatment). Results: Currently we have a mean follow-up of six months (r1-19), with no adverse effect detected. The patient who had pain, showed a complete pain relief. All of these patients are in local tumor control.