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Dosimetric Impact of Geometric Distortionsin an MRI-Only Proton Therapy Workflowfor Extracranial Sites

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  1. Tez No: 785515
  2. Yazar: HATİCE SELCEN DUMLU
  3. Danışmanlar: PROF. GUİDO BARONI, PROF. MARCO RIBOLDI, DR. CHİARA PAGANELLI
  4. Tez Türü: Yüksek Lisans
  5. Konular: Biyomühendislik, Bioengineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2020
  8. Dil: İngilizce
  9. Üniversite: Politecnico di Milano
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 148

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Özet (Çeviri)

In a magnetic resonance imaging (MRI) only radiation therapy workflow, dosimetric errors may arise due to system-dependent and patient-dependent geometric distortions introduced by MRI. The aim of this study was to quantify the dosimetric effect of geometric distortions arising from MRI in MRI-only workflow in Intensity Modulated Proton Therapy (IMPT). An approach was developed, in which computer tomography (CT) images were distorted using an MRI displacement map representing MR distortions due to gradient nonlinearities, static magnetic field inhomogeneities and patient susceptibility variations. The maximal mean landmark deformation per image slice was up to 3mm in slice selection direction at a slice shifted 105mm away from the isocenter and mean in-slice landmark deformation was below 1 mm. A retrospective study was conducted on 4DCT/MRI digital phantoms and 4DCT clinical dataset of the thoraco-abdominal site. The treatment plans were designed and separately optimized for each beam field on a beam specific Planning Target Volume (bsPTV) on the distorted CT, and the final dose distribution was obtained as the average. Dose was then recalculated in undistorted CT using the same beam geometry and beam weights. The analysis was performed in terms of Dose Volume Histogram (DVH) parameters of target and organs at risk (OARs). No clinically relevant dosimetric impact was observed on OARs. Small dosimetric changes due to geometric distortions were found in the abdominal and thorax cases, where the tumor was closed or covered by the soft tissue, whereas higher changes were observed for lung cases where the tumor was isolated inside the lung parenchyma due to higher density variations along the beam path. Results suggest the potential applicability of MRI-only proton therapy, provided that further analyses would be performed for isolated lung tumors.

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