On the accuracy and effectiveness of dose reconstruction fortomotherapy

Abstract

Dose reconstruction is a process that re-creates the treatment-timedose deposited in a patient provided there is knowledge of the deliveredenergy fluence and the patient's anatomy at the time of treatment. A methodfor reconstructing dose is presented. The process starts with deliveryverification, in which the incident energy fluence from a treatment iscomputed using the exit detector signal and a transfer matrix to convert thedetector signal to energy fluence. With the verified energy fluence and a CTimage of the patient in the treatment position, the treatment-time dosedistribution is computed using any model-based algorithm such asconvolution/superposition or Monte Carlo.The accuracy of dose reconstruction and the ability of the process to revealdelivery errors are presented. Regarding accuracy, a reconstructed dosedistribution was compared with a measured film distribution for a simulatedbreast treatment carried out on a thorax phantom. It was found that thereconstructed dose distribution agreed well with the dose distributionmeasured using film: the majority of the voxels were within the low and highdose-gradient tolerances of 3% and 3 mm respectively. Concerning deliveryerrors, it was found that errors associated with the accelerator, themultileaf collimator and patient positioning might be detected in theverified energy fluence and are readily apparent in the reconstructed dose.For the cases in which errors appear in the reconstructed dose, thepossibility for adaptive radiotherapy is discussed.