Abstract gepubliseerd in Elsevier: For patients with intermediate- and high risk prostate cancer, treated with high dose radiotherapy, the CTV generally involves the prostate and (part of) the seminal vesicles (SV) [1,2]. Fiducial markers locate the prostate reliably during radiotherapy [3]. However the SV may move independent from the corpus of the prostate [4–6]. As this should be incorporated in the PTV margin [4,6–8], this may lead to a larger irradiated rectum volume and more gastro-intestinal toxicity [9]. Several studies have shown that rectal and bladder filling are of influence on prostate and SV mobility [10–13]. Using a dietary protocol or applying rectal gas removal could somewhat decrease the prostate and SV mobility [14,15], however, these methods are not very patient friendly. In this study we hypothesize that the vesicles become more rigidly attached to the prostate in case of tumour infiltration. This would imply that in case of extensive infiltration, the prostate and vesicles move as a rigid body and are thus adequately localized by marker-based Image Guided Radiotherapy (IGRT). The aim of this study was to assess the impact of tumour invasion in the SV on their mobility.
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Abstract Background: The benefit of MR-only workflow compared to current CT-based workflow for prostate radiotherapy is reduction of systematic errors in the radiotherapy chain by 2–3 mm. Nowadays, MRI is used for target delineation while CT is needed for position verification. In MR-only workflows, MRI based synthetic CT (sCT) replaces CT. Intraprostatic fiducial markers (FMs) are used as a surrogate for the position of the prostate improving targeting. However, FMs are not visible on sCT. Therefore, a semi-automatic method for burning-in FMs on sCT was developed. Accuracy of MR-only workflow using semi-automatically burned-in FMs was assessed and compared to CT/MR workflow. Methods: Thirty-one prostate cancer patients receiving radiotherapy, underwent an additional MR sequence (mDIXON) to create an sCT for MR-only workflow simulation. Three sources of accuracy in the CT/MR- and MR-only workflow were investigated. To compare image registrations for target delineation, the inter-observer error (IOE) of FM-based CT-to-MR image registrations and soft-tissue-based MR-to-MR image registrations were determined on twenty patients. Secondly, the inter-observer variation of the resulting FM positions was determined on twenty patients. Thirdly, on 26 patients CBCTs were retrospectively registered on sCT with burned-in FMs and compared to CT-CBCT registrations. Results: Image registration for target delineation shows a three times smaller IOE for MR-only workflow compared to CT/MR workflow. All observers agreed in correctly identifying all FMs for 18 out of 20 patients (90%). The IOE in CC direction of the center of mass (COM) position of the markers was within the CT slice thickness (2.5 mm), the IOE in AP and RL direction were below 1.0 mm and 1.5 mm, respectively. Registrations for IGRT position verification in MR-only workflow compared to CT/MR workflow were equivalent in RL-, CC- and AP-direction, except for a significant difference for random error in rotation. Conclusions: MR-only workflow using sCT with burned-in FMs is an improvement compared to the current CT/ MR workflow, with a three times smaller inter observer error in CT-MR registration and comparable CBCT registration results between CT and sCT reference scans. Trial registry Medical Research Involving Human Subjects Act (WMO) does apply to this study and was approved by the Medical Ethics review Committee of the Academic Medical Center. Registration number: NL65414.018.18. Date of registration: 21–08-2018.
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Stereotactische radiotherapie van wervelmetastasen vereist een hoge precisie in alle stappen van de behandeling. Deze techniek werd in het VU medisch centrum in 2009 geïntroduceerd. Data met betrekking tot de behandeling van de eerste 17 klinische patiënten is geëvalueerd. Deze patiënten werden behandeld op een Novalis Tx versneller die beschikt over zowel een kilovolt (kV) cone beam CT (CBCT) scan als het ExacTrac® kV röntgensysteem. De gebruikte methode van de verschillende beeldmodaliteiten voor positionering en verificatie, de behandelingstijd en de intrafractie beweging worden in dit artikel beschreven.
