Preparations for photon external beam radiotherapy treatment planning of small animals
(2022) MSFT01 20201Medical Physics Programme
- Abstract
- Introduction:The XenX is a small animal irradiation system that acquires high-resolution cone-beam tomography (CBCT) images of small animals and treats small animals with higher precision than medical linear accelerators. MuriSlice is a software for CBCT image reconstruction. This thesis aims to optimise the CBCT image reconstruction protocol in MuriSlice to enable the segmentation of CBCT images in the μRayStation 8B treatment planning system. In addition, the calculation of absorbed dose performed by the Monte Carlo dose calculation algorithm in μRayStation 8B based on the reconstructed CBCT images is verified by comparison with radiochromic film measurements.
Materials and methods: In the first part of this thesis, the XenX's... (More) - Introduction:The XenX is a small animal irradiation system that acquires high-resolution cone-beam tomography (CBCT) images of small animals and treats small animals with higher precision than medical linear accelerators. MuriSlice is a software for CBCT image reconstruction. This thesis aims to optimise the CBCT image reconstruction protocol in MuriSlice to enable the segmentation of CBCT images in the μRayStation 8B treatment planning system. In addition, the calculation of absorbed dose performed by the Monte Carlo dose calculation algorithm in μRayStation 8B based on the reconstructed CBCT images is verified by comparison with radiochromic film measurements.
Materials and methods: In the first part of this thesis, the XenX's integrated CBCT was used to acquire a set of projections of a cylindrical water phantom, a 3D printed mouse phantom, and a flat field. The acquired projections were used to optimise selected parameters of MuriSlice. First, the voxel size was selected based on the observed signal-to-noise ratio (SNR) in axial images of the cylindrical water phantom and recommendations of voxel size for CT imaging of small animals. Second, three corrections were performed on each projection, including 1) a correction for a distortion introduced by the lens in the digital camera of the CBCT imaging system, 2) a pixel-by-pixel correction to reduce the noise in the individual pixel of the flat field projections, and 3) a ring artefacts reduction using a 2D Butterworth filter. Third, the corrected projections were filtered with different pre-filters for further noise reduction. A pre-filter was selected based on the SNR and the contrast between soft tissue and bone in a transverse slice of the reconstructed images of the 3D printed mouse phantom. In the second part of this thesis, absorbed dose comparisons were carried out in four different slab phantoms containing various combinations of polystyrene, aluminium, and cork. Each phantom was irradiated by a 220 kV circular beam of X-ray photons (Ø = 10 mm). A set of CBCT projections for each slab phantom was acquired, reconstructed with the optimised protocol, and imported into μRayStation 8B. Inside μRayStation 8B, the reconstructed images of the slab phantoms were segmented into regions with the material composition assigned either based on the CBCT’s Hounsfield unit to mass density calibration or by manual identification. The absorbed dose to the assigned material in the CBCT image of each slab phantom was estimated using the Monte Carlo dose calculation algorithm in μRayStation 8B and then compared with radiochromic film measurements.
Results: The reconstruction protocol in Murislice included a voxel size of (100μ〖m)〗^3and a edge-preserving denoising pre-filter. The optimisation of the reconstruction parameters resulted in a significant reduction of noise and near elimination of ring artefacts in the reconstructed image of the 3D printed mouse phantom. Furthermore, the contrast between the structures in the reconstructed CBCT image of the slab phantoms was sufficient to allow for the segmentation of relevant structures in the slab phantoms.
The remaining noise resulted in a large fluctuation in estimated absorbed doses when the reconstructed images of the slab phantoms were segmented into regions with the assignment of the material composition based on the CBCT Hounsfield unit to mass density calibration. With the manual assignment of the material composition, the uncertainty in the estimated absorbed dose was within 1 %. The absorbed dose that was estimated with μRayStation 8B based on manual material assignment to the CBCT images of the slab phantoms was in reasonably good agreement with the film measurements, with a mean (max) of absolute difference in the percentage depth dose of 0.4% (Less) - Popular Abstract (Swedish)
- Extern strålbehandling är en av den viktigaste typen av cancerbehandlingar och administreras till patienter genom användning av en strålbehandlingsapparat som kallas för linjäraccelerator. Linjäracceleratorn producerar bromsstrålning som används för att bota cancern.
För att säkerställa att behandlingen levereras med hög noggrannhet planeras den innan start. Ett viktigt steg i planeringen är beräkning av den absorberade dosen. Den absorberade dosen är mängden energi som deponeras per massenhet. Den absorberade dosen måste beräknas med så hög precision som möjligt för att bota cancern och samtidigt minimera biverkningar från behandlingen. Beräkningen av den absorberade dosen utförs i ett datorprogram som kallas för dosplaneringssystem och... (More) - Extern strålbehandling är en av den viktigaste typen av cancerbehandlingar och administreras till patienter genom användning av en strålbehandlingsapparat som kallas för linjäraccelerator. Linjäracceleratorn producerar bromsstrålning som används för att bota cancern.
För att säkerställa att behandlingen levereras med hög noggrannhet planeras den innan start. Ett viktigt steg i planeringen är beräkning av den absorberade dosen. Den absorberade dosen är mängden energi som deponeras per massenhet. Den absorberade dosen måste beräknas med så hög precision som möjligt för att bota cancern och samtidigt minimera biverkningar från behandlingen. Beräkningen av den absorberade dosen utförs i ett datorprogram som kallas för dosplaneringssystem och baseras på så kallade snittbilder av behandlingsområdet. Behandlingsområdet består av cancern och omkringliggande frisk vävnad. Information om hur strålningen påverkar dessa vävnader kan fås från prekliniska studier som ofta utförs på smådjur och sedan testas på människor innan kliniskt bruk. För att få värdefullt resultat från prekliniska studier är det viktigt att planering av prekliniska studierna efterliknar proceduren vid klinisk extern strålbehandling.
I detta arbete har realistiska mätfantom använts för att optimera bildtagning och utvärdera noggrannheten av ett dosplaneringssystem som används för att beräkna den absorberade dosen som ska ges till smådjur under prekliniska studier. Optimering av biltagningen har gått ut på att generera snittbilder som kan används för sådana beräkningar. Vidare, har noggrannheten i den beräknade absorberade dosen utvärderats genom jämförelse med mätningar. Den dedikerade prekliniska strålbehandlingsapparaten XenX har använts i arbetet.
Detta arbete har visat hur bildtagningen som används för planering av prekliniska studier på smådjur kan optimeras för att få snittbilder med mindre artefakter, mindre brus och högre upplösning. I arbetet har det också visats att för en noggrann beräkning av den absorberade dosen krävs att dosplanneringsystem förses med snittbilder som innehåller så lite artefakter och brus som möjligt. (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9099112
- author
- Diha Guei, Joanie
- supervisor
- organization
- course
- MSFT01 20201
- year
- 2022
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9099112
- date added to LUP
- 2022-09-03 14:51:57
- date last changed
- 2022-09-03 14:51:57
@misc{9099112,
abstract = {{Introduction:The XenX is a small animal irradiation system that acquires high-resolution cone-beam tomography (CBCT) images of small animals and treats small animals with higher precision than medical linear accelerators. MuriSlice is a software for CBCT image reconstruction. This thesis aims to optimise the CBCT image reconstruction protocol in MuriSlice to enable the segmentation of CBCT images in the μRayStation 8B treatment planning system. In addition, the calculation of absorbed dose performed by the Monte Carlo dose calculation algorithm in μRayStation 8B based on the reconstructed CBCT images is verified by comparison with radiochromic film measurements.
Materials and methods: In the first part of this thesis, the XenX's integrated CBCT was used to acquire a set of projections of a cylindrical water phantom, a 3D printed mouse phantom, and a flat field. The acquired projections were used to optimise selected parameters of MuriSlice. First, the voxel size was selected based on the observed signal-to-noise ratio (SNR) in axial images of the cylindrical water phantom and recommendations of voxel size for CT imaging of small animals. Second, three corrections were performed on each projection, including 1) a correction for a distortion introduced by the lens in the digital camera of the CBCT imaging system, 2) a pixel-by-pixel correction to reduce the noise in the individual pixel of the flat field projections, and 3) a ring artefacts reduction using a 2D Butterworth filter. Third, the corrected projections were filtered with different pre-filters for further noise reduction. A pre-filter was selected based on the SNR and the contrast between soft tissue and bone in a transverse slice of the reconstructed images of the 3D printed mouse phantom. In the second part of this thesis, absorbed dose comparisons were carried out in four different slab phantoms containing various combinations of polystyrene, aluminium, and cork. Each phantom was irradiated by a 220 kV circular beam of X-ray photons (Ø = 10 mm). A set of CBCT projections for each slab phantom was acquired, reconstructed with the optimised protocol, and imported into μRayStation 8B. Inside μRayStation 8B, the reconstructed images of the slab phantoms were segmented into regions with the material composition assigned either based on the CBCT’s Hounsfield unit to mass density calibration or by manual identification. The absorbed dose to the assigned material in the CBCT image of each slab phantom was estimated using the Monte Carlo dose calculation algorithm in μRayStation 8B and then compared with radiochromic film measurements.
Results: The reconstruction protocol in Murislice included a voxel size of (100μ〖m)〗^3and a edge-preserving denoising pre-filter. The optimisation of the reconstruction parameters resulted in a significant reduction of noise and near elimination of ring artefacts in the reconstructed image of the 3D printed mouse phantom. Furthermore, the contrast between the structures in the reconstructed CBCT image of the slab phantoms was sufficient to allow for the segmentation of relevant structures in the slab phantoms.
The remaining noise resulted in a large fluctuation in estimated absorbed doses when the reconstructed images of the slab phantoms were segmented into regions with the assignment of the material composition based on the CBCT Hounsfield unit to mass density calibration. With the manual assignment of the material composition, the uncertainty in the estimated absorbed dose was within 1 %. The absorbed dose that was estimated with μRayStation 8B based on manual material assignment to the CBCT images of the slab phantoms was in reasonably good agreement with the film measurements, with a mean (max) of absolute difference in the percentage depth dose of 0.4%}},
author = {{Diha Guei, Joanie}},
language = {{eng}},
note = {{Student Paper}},
title = {{Preparations for photon external beam radiotherapy treatment planning of small animals}},
year = {{2022}},
}