Quality of tri-Co-60 MR-IGRT treatment plans in comparison with VMAT treatment plans for spine SABR

Abstract

FULL PAPERQuality of tri-Co-60 MR-IGRT treatment plans in comparison with VMAT treatment plans for spine SABR Objective: To investigate the plan quality of tri-Co-60 intensity-modulated radiation therapy (IMRT) plans for spine stereotactic ablative radiotherapy (SABR). Methods: A total of 20 patients with spine metastasis were retrospectively selected. For each patient, a tri-Co-60 IMRT plan and a volumetric-modulated arc therapy (VMAT) plan were generated. The spinal cords were defined based on MR images for the tri-Co-60 IMRT, while isotropic 1-mm margins were added to the spinal cords for the VMAT plans. The VMAT plans were generated with 10-MV flattening filter-free photon beams of TrueBeam STx™ (Varian Medical Systems, Palo Alto, CA), while the tri-Co-60 IMRT plans were generated with the ViewRay™ system (ViewRay inc., Cleveland, OH). The initial prescription dose was 18 Gy(1 fraction). If the tolerance dose of the spinal cord was not met, the prescription dose was reduced until the spinal cord tolerance dose was satisfied.Results: The mean dose to the target volumes, conformity index and homogeneity index of the VMAT and tri-Co-60 IMRT were 17.8 6 0.8 vs 13.7 6 3.9 Gy, 0.85 6 0.20 vs 1.58 6 1.29 and 0.09 6 0.04 vs 0.24 6 0.19, respectively. The integral doses and beam-on times were 16,570 6 1768 vs 22,087 6 2.986 Gy cm 3 and 3.95 6 1.13 vs 48.82 6 10.44 min, respectively. Conclusion: The tri-Co-60 IMRT seems inappropriate for spine SABR compared with VMAT. Advances in knowledge: For spine SABR, the tri-Co-60 IMRT is inappropriate owing to the large penumbra, large leaf width and low dose rate of the ViewRay system.

Development of patient‐controlled respiratory gating system based on visual guidance for magnetic‐resonance image‐guided radiation therapy

“…To minimize the target margin compensating for the respiratory motion, various respiratory‐gating techniques to account for the respiratory motion during beam delivery were investigated and clinically applied . Recently, the respiratory‐gating technique based on near‐real‐time magnetic resonance image (MRI) became available with the ViewRay™ system (ViewRay Inc., Cleveland, OH, USA) . The ViewRay system is capable of the near‐real‐time respiratory gated radiation therapy by continuous acquisition of sagittal planar MR images (a single cine image at 4 frames/s or three cine images at 2 frames/s) during treatment .…”

“…In addition, the three Co‐60 are not always used simultaneously during treatment and the use of the Co‐60 source at a particular gantry angle is dependent on the treatment plan . Therefore, the comparable dose‐rate of the ViewRay system to the linac is not always consistently maintained, which results in longer treatment time than with the linac‐based IMRT or VMAT . The increase in the treatment time of the ViewRay system becomes severe when the respiratory‐gating technique is applied.…”

“…The increase in the treatment time of the ViewRay system becomes severe when the respiratory‐gating technique is applied. This long treatment time could be more problematic, especially for stereotactic ablative radiotherapy (SABR), of which the fraction size is large . Therefore, the treatment time reduction in the ViewRay system is an important issue.…”

“…10 Recently, the respiratory-gating technique based on near-real-time magnetic resonance image (MRI) became available with the ViewRay TM system (ViewRay Inc., Cleveland, OH, USA). 8,[11][12][13] The ViewRay system is capable of the near-real-time respiratory gated radiation therapy by continuous acquisition of sagittal planar MR images (a single cine image at 4 frames/s or three cine images at 2 frames/s) during treatment. 8 The cine MRIbased gating technique is beneficial, since the gated radiation therapy with an actual tumor motion is possible without any surrogates.…”

Implementation of AAPM's TG-51 Protocol on Co-60 MRI-Guided Radiation Therapy System

“…[1][2][3][4][5][6][7][8] nology, MR imaging system can be installed in a radiation treatment system and then MR images can be obtained during radiation therapy, which is called MR-IGRT system. 2,[9][10][11] Recently, the most representative MR-IGRT system in the field of radiotherapy is the ViewRay ® system (ViewRay Inc., Cleveland, OH, USA) which consists in a MR scanner of 0.35 T static magnetic field for imaging and tri Co-60 sources for treatment. 1,[11][12][13] The total dose rate of the tri Co-60 sources is 550 cGy/min, which is ideal dose rate in radiotherapy planning system (RTP) and the tri Co-60 sources are positioned at 120-degree intervals in a ring type gantry.…”