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  5. Feasibility of MRI-Only Photon and Proton Dose Calculations for Abdominal Pediatric Patients

Feasibility of MRI-Only Photon and Proton Dose Calculations for Abdominal Pediatric Patients

F Guerreiro1*, L Koivula2 , E Seravalli1 , G Janssens1 , J Maduro3 , C Brouwer3 , E Korevaar3 , A Knopf3 , J Korhonen4 , B Raaymakers1 , (1) University Medical Center Utrecht, Utrecht, The Netherlands, (2) Cancer Center, Helsinki University Hospital, Helsinki, Finland, (3) University Medical Center Groningen, University of Groningen, Groningen, The Netherlands, (4) Kymenlaakso Central Hospital, Kymenlaakso Social and Health Services (Carea), Kotka, Finland

Presentations

(Thursday, 8/2/2018) 1:00 PM - 3:00 PM

Room: Karl Dean Ballroom B1

Purpose: In the current study we developed a technique enabling synthetic computed tomography (sCT) generation of the whole body using magnetic resonance imaging (MRI)-scans of pediatric abdominal patients. The dose calculation accuracy of the sCT was verified for volumetric modulated arc therapy (VMAT) and pencil-beam scanning proton therapy (PBS-PT).

Methods: The proposed sCT method relies on an automatic-atlas-based segmentation of bone and lungs followed by a MRI intensity conversion to synthetic Hounsfield Units (sHU). Separate conversion algorithms were used for the bone, lungs and soft-tissue (muscle, adipose tissue, fluid). Rigidly registered CT and T2-weighted MRI-scans of 20 patients were used for the atlas construction and the conversion algorithms. VMAT and PBS-PT treatment plans (prescription dose <36Gy) were optimized using the planning-CT (3mm dose grid). For both techniques, plans were robust optimized against patient set-up uncertainty (5mm) on an internal target volume (ITV). For the PBS-PT, no robustness against proton range uncertainty was accounted for. The sCT image quality was evaluated by calculating the mean error (ME) between the HU on the CT and sCT. CT and sCT dose calculations were compared by dose-volume statistics.

Results: The mean ME were 1±112, 4±49, and 19±9 HU for the bone, lungs and soft tissue, respectively. Mean differences between CT and sCT dose calculations for the organs at risk were <0.5%/0.1Gy (maximum 1.7%/0.4Gy) and <0.6%/0.1Gy (maximum 5.3%/0.8Gy) for the VMAT and PBS-PT, respectively. Mean differences for the ITV were <0.9%/0.2Gy (maximum 5.0%/0.8Gy) and <0.3%/0.1Gy (maximum 0.7%/0.2Gy) for the VMAT and PBS-PT, respectively.

Conclusion: The present study is the first evaluating the feasibility of generating high-quality sCT-scans for pediatric patients and for any other body parts than pelvis, head & neck and brain. With the proposed whole-body sCT method, results show that accurate MRI-based photon and proton dose calculations are feasible for abdominal pediatric patients.

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