An end-to-end test for MR-guided online adaptive radiotherapy

Abstract

In the evolving field of adaptive MR guided radiotherapy, the need for dedicated procedures for acceptance and quality assurance is increasing. Research has been devoted to MR compatible dosimeters and phantoms, but to date no end-to-end test has been presented that covers an MRgRT workflow. Such an end-to-end test should comprise each step of the workflow and include all associated uncertainties. The purpose of this study was to investigate the usability of an anthropomorphic deformable and multimodal pelvis (ADAM-pelvis) phantom in combination with film dosimetry for end-to-end testing of an MRgRT adaptive workflow. The ADAM-pelvis phantom included surrogates for muscle tissue, adipose and bone, as well as deformable silicone organs mimicking a prostate patient. At the interfaces of the critical structures (bladder and rectum), small pieces of GafChromic EBT3 films were placed to measure delivered dose. Pre-treatment MR imaging of the phantom was used to delineate the prostate, rectum and bladder and to generate a treatment plan to deliver 2 Gy to the prostate. Electron density (ED) map from CT imaging was used for dose calculation after deformable image registration (DIR) to the pre-treatment MR scan. At each fraction, bladder- and rectum filling was varied and a new adapted plan was generated. Dose calculation was performed using both a DIR-based ED map and a CT-based ED map after acquisition of a new CT scan of the phantom at each fraction. All dose calculations were performed taking into account the magnetic field. A good agreement between measured and calculated dose was found using both, the CT-derived and the DIR-based ED map (2.0% and 2.8% dose difference, respectively). The gamma index pass-rate (3%/2 mm) varied from 96.4% to 100%.The ADAM-pelvis phantom was suitable for end-to-end testing in MR-guided radiotherapy and a very good agreement with the calculated dose was achieved.

Machine QA for the Elekta Unity system: A Report from the Elekta MR‐linac consortium

“…Reference/adaptive plan QA and end-toend QA equipment are identified but the reader is referred to other publications for testing techniques. 4,29,34,[40][41][42][43] While many of the comments and recommendations will be applicable to other configurations of MR-linac devices, the authors are working with Elekta Unity systems, and thus the tests are designed around this system.…”

“…However, it is expected that many of the tests will be appropriate after a service operation and should be chosen based on the activity performed and based on manufacturer’s recommendations. Reference/adaptive plan QA and end‐to‐end QA equipment are identified but the reader is referred to other publications for testing techniques 4,29,34,40–43 …”

Technical Note: ADAM PETer – An anthropomorphic, deformable and multimodality pelvis phantom with positron emission tomography extension for radiotherapy

“…At this point, we can only estimate the phantom’s potential based on our experience with the ADAM phantom. Hoffmanns et al 8 demonstrated that the ADAM‐phantom was suitable for end‐to‐end testing in MR‐guided online adaptive radiotherapy. In addition, Bohoudi et al 7 used the ADAM phantom to perform an end‐to‐end empirical validation of dose accumulation in MRI‐guided adaptive radiotherapy simulating six MR‐guided prostate SBRT treatment courses.…”

“…For dosimetry measurements, imaging marker points and pockets for dosimetry films are implemented at the surface of rectum and bladder organ surrogates. Hoffmanns et al demonstrated the suitability of the ADAM phantom for end-to-end tests in MR-guided radiotherapy [8]. Bohoudi et al used the phantom for an end-to-end empirical validation of dose accumulation in MRI-guided adaptive radiotherapy for prostate cancer [7].…”

“…Hoffmanns et al demonstrated the suitability of the ADAM phantom for end-to-end tests in MR-guided radiotherapy. 8 Bohoudi et al used the phantom for an end-to-end empirical validation of dose accumulation in MRI-guided adaptive radiotherapy for prostate cancer. 7 In the present note, we describe the extension of the ADAM phantom for compatibility with PET and use in 3T MRI.…”