ORBIT has been closely integrated with a clinical radiation treatment planning system, which thus combines ORBIT's advanced ability to optimize treatment plans with the clinical versatility and accuracy of forward dose calculation algorithms.
By viewing a fractionated treatment as a dynamical system, the time structure of radiation therapy optimization can be used to organize the calculations in a recursive manner. For this purpose, a new mathematical framework for calculating the probability of complication-free tumor control, and its expectation value, has been constructed. All the main clinical parameters and events that affect P+ are gathered into four sequences of data that describe the delivered energy-fluence distributions, patient geometry, radiobiological response parameters, and time-dose fractionation schedule. Because of the difficulty in measuring all aspects of the intra- and interfractional variations in the patient geometry, such as internal organ displacements and deformations, as well as inter-patient variations in radiation sensitivity, such uncertainties are accounted for by the method of stochastic optimization.
The dynamic optimization approach to radiotherapy planning allows for information feedback so that patient-specific data that are generated as the treatment proceeds (e.g., by in vivo dosimetry, portal imaging, radiotherapeutic computed tomography, PET- and MR-imaging) can be used to refine the beam configurations and beam shapes in the subsequent treatment sessions.