Improving patient dosimetry under non-reference conditions for proton beams
Improving patient dosimetry under non-reference conditions for proton beams
In radiation therapy of cancer, accuracy is crucial for successful patient treatment. An important ingredient in ensuring accurate treatment delivery is radiation dosimetry, where measurements of the spatial radiation dose distributions are performed. However, the detectors used for these measurements cause perturbations, which must be corrected to obtain accurate dose estimates. While correction strategies for detectors in photon radiation have been widely introduced in the past, additional research on proton dosimetry is needed to reduce measurement uncertainties and thereby improve the accuracy of proton therapy.
This thesis of Jana Kretschmer investigates detectors for various types of dose measurements in proton beams. Perturbation and beam quality correction factors used for absolute dose calibration measurements in proton beams were derived and investigated for several ionization chambers using Monte-Carlo simulations. The calculated factors improved accuracy because a previously used approximation could be omitted.
Also, different types of point detectors were characterized by deriving their lateral dose response functions, which can be used within a convolution model to correct for volume effect perturbations in measured dose distributions. These functions were investigated at different depths and initial proton energies. Afterwards several detectors and their lateral dose response functions were used in measurements of clinical proton radiation fields created with three different proton beam delivery techniques. Detector perturbations were especially pronounced for large volume detectors and in fields created using collimation. While presented approaches require further investigation, the findings of this thesis help to improve the accuracy of proton dosimetry needed for high precision patient treatments.