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Researchers want to compare proton stopping ratios, used for proton beam therapy planning, calculated based on single energy CT and dual energy CT images; with the intension of improve upon the proton range determination.

The main goal of this study is to compare proton stopping ratios, used for proton beam therapy planning, calculated based on single energy CT and dual energy CT images.

The calculation methods for proton stopping power ratios differs for the two types of CT images, and researchers want to investigate if the proton stopping power ratio can be estimated more accurately by using dual energy CT. A more accurate stopping power ratio calculation gives a more accurate proton range determination in the patient tissue, which again will lead to a better knowledge of the dose distribution in the patient undergoing cancer treatment with proton beam irradiation.

Knowing the accurate dose distribution allows for an uncertainty margin reduction around the tumor, which will result in less normal tissue being irradiated and thereby the risk of side effects is reduced without risking an under-dosage of the tumor.

Inclusion Criteria:

• Cancer patients who are scheduled for a control CT scan

Exclusion Criteria:

• Under 18 years of age

• Patients with a identified tumor referred to curativ intended external beam radiotherapy
• Patients, for who are scheduled for a control CT scan during their treatment course
• Patients above 18 years of age
• Participation will take place on a voluntary basis It is estimated that annually around 1,000 patients will meet the above inclusion criteria

There is no plan to share data with other centers