Using power loss density and related measures to quantify the dose of tumor treating fields (TTFields)
The planning of treatment using tumor treating fields (TTFields) in a portion of a subject's body (e.g., the subject's head) can be improved by obtaining an image of the body portion, and generating, based on the image, a 3D model of electrical conductivity. A target volume within the 3D model is identified, and a set of model electrodes is added to the 3D model at given locations. Then, for each voxel in the target volume, the power loss density (PLD) that will be present when TTFields are eventually applied is determined. The same process is repeated for a plurality of different electrode locations. Finally, the set of electrode locations that yielded the best PLD is selected, and a description of those locations is output.
1 . A method of planning a treatment using alternating electric fields at a given frequency in a portion of a subject's body, the method comprising the steps of:
(a) obtaining at least one image of the portion;
(b) generating, based on the obtained at least one image, a 3D model of electrical conductivity or resistivity at the given frequency within the portion;
(c) identifying a target volume within the 3D model, the target volume including a plurality of voxels;
(d) adding a first set of model electrodes to the 3D model, with the first set of model electrodes positioned at a first set of locations with respect to the 3D model; and
(e) determining, for each of the voxels in the target volume, a power loss density that will be present when the first set of model electrodes positioned at the first set of locations is used to impose an alternating electric field in the target volume,
wherein step (e) comprises (i) determining, for each of the voxels in the target volume, an electric field intensity that will be present when a respective set of model electrodes positioned at a respective set of locations is used to impose an alternating electric field in the target volume, and (ii) determining a respective power loss density for each voxel in the target volume based on the conductivity of the 3D model at the voxel and the electric field intensity at the voxel.
2 . The method of claim 1 , wherein the power loss density for each voxel in the target volume is determined using the formula L=½ σ |E| 2 , where σ is the conductivity of the 3D model at the voxel and |E| is the electric field intensity at the voxel.
3 . The method of claim 1 , wherein the at least one image of the portion comprises an MRI image of the portion.
4 . The method of claim 1 , wherein the given frequency is between 100 kHz and 300 kHz.
5 . A method of planning a treatment using alternating electric fields at a given frequency in a portion of a subject's body, the method comprising the steps of:
(a) obtaining at least one image of the portion;
(b) generating, based on the obtained at least one image, a 3D model of electrical conductivity or resistivity at the given frequency within the portion;
(c) identifying a target volume within the 3D model, the target volume including a plurality of voxels;
(d) adding a first set of model electrodes to the 3D model, with the first set of model electrodes positioned at a first set of locations with respect to the 3D model; and
(e) determining, for each of the voxels in the target volume, a power loss density that will be present when the first set of model electrodes positioned at the first set of locations is used to impose an alternating electric field in the target volume,
wherein step (e) comprises (i) determining, for each of the voxels in the target volume, an electric field intensity that will be present when a respective set of model electrodes positioned at a respective set of locations is used to impose an alternating electric field in the target volume, and (ii) determining a respective power loss density for each voxel in the target volume based on the resistivity of the 3D model at the voxel and the electric field intensity at the voxel.
6 . The method of claim 5 , wherein the at least one image of the portion comprises an MRI image of the portion.
7 . The method of claim 5 , wherein the given frequency is between 100 kHz and 300 kHz.