Light delivery and light dosimetry for photodynamic therapy of bronchogenic carcinoma

Photodynamic tllel'apy (PDT) is a treatment modality for malignant (and benign) diseases that combines administration of a chemical compound (photosensitiser) and irradiation with (visible) light of the proper wavelength and fluence to induce tissue necrosis. The mechanisms by. which PDT induces cell death are not yet fully understood. The basic principle is that the iIIumination of the sensitiser causes excitation of the oxygen present in the tissue to the very reactive singlet state that induces damage to the tissue. The oxygen supply in the treated tissue is therefore of paramount importance for the final damage induced. Two types of damage are thought to be most important for the induced necrosis. Firstly, important (tumour)cell structures such as mitochondrial and cellular membranes are damaged with consequent direct cell death. Secondly, through damage of the endothelium of the blood vessels vascular stasis occurs which causes tissue damage as a secondary process

Totale lichaamsbestraling bij hematopoëtische stamceltransplantatie: een vak apart

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Intra-voxel heterogeneity influences the dose prescription for dose-painting with radiotherapy: a modelling study

The purpose of this study was to increase the potential of dose redistribution by incorporating estimates of oxygen heterogeneity within imaging voxels for optimal dose determination. Cellular oxygen tension (pO2) distributions were estimated for imaging-size-based voxels by solving oxygen diffusion-consumption equations around capillaries placed at random locations. The linear-quadratic model was used to determine cell survival in the voxels as a function of pO2 and dose. The dose distribution across the tumour was optimized to yield minimal survival after 30 × 2 Gy fractions by redistributing the dose based on differences in oxygen levels. Eppendorf data of a series of 69 tumours were used as a surrogate of what might be expected from oxygen imaging datasets. Dose optimizations were performed both taking into account cellular heterogeneity in oxygenation within voxels and assuming a homogeneous cellular distribution of oxygen. Our simulations show that dose redistribution based on derived cellular oxygen distributions within voxels result in dose distributions that require less total dose to obtain the same degree of cell kill as dose distributions that were optimized with a model that considered voxels as homogeneous with respect to oxygen. Moderately hypoxic tumours are expected to gain most from dose redistribution. Incorporating cellular-based distributions of radiosensitivity into dose-planning algorithms theoretically improves the potential gains from dose redistribution algorithms. © 2009 Institute of Physics and Engineering in Medicine

Intra-voxel heterogeneity influences the dose prescription for dose-painting with radiotherapy: a modelling study

The purpose of this study was to increase the potential of dose redistribution by incorporating estimates of oxygen heterogeneity within imaging voxels for optimal dose determination. Cellular oxygen tension (pO2) distributions were estimated for imaging-size-based voxels by solving oxygen diffusion-consumption equations around capillaries placed at random locations. The linear-quadratic model was used to determine cell survival in the voxels as a function of pO2 and dose. The dose distribution across the tumour was optimized to yield minimal survival after 30 × 2 Gy fractions by redistributing the dose based on differences in oxygen levels. Eppendorf data of a series of 69 tumours were used as a surrogate of what might be expected from oxygen imaging datasets. Dose optimizations were performed both taking into account cellular heterogeneity in oxygenation within voxels and assuming a homogeneous cellular distribution of oxygen. Our simulations show that dose redistribution based on derived cellular oxygen distributions within voxels result in dose distributions that require less total dose to obtain the same degree of cell kill as dose distributions that were optimized with a model that considered voxels as homogeneous with respect to oxygen. Moderately hypoxic tumours are expected to gain most from dose redistribution. Incorporating cellular-based distributions of radiosensitivity into dose-planning algorithms theoretically improves the potential gains from dose redistribution algorithms. © 2009 Institute of Physics and Engineering in Medicine