A study of objective functions for organs with parallel and serial architecture

Area of Science:

• Radiation Oncology
• Medical Physics
• Biophysics

Background:

• External beam radiotherapy requires precise targeting, complicated by tumor mobility and positional uncertainty.
• Accurate dose distribution is crucial for maximizing tumor control probability (TCP) while minimizing normal tissue complication probability (NTCP).

Purpose of the Study:

• To develop and analyze an objective function for radiotherapy planning that accounts for tumor motion and positional uncertainty.
• To determine optimal radiation doses (D(R)) that maximize the product of tumor control and normal tissue survival probabilities.

Main Methods:

• Modeled tumor dose distribution with logarithmic dependence on cell density for iso-local TCP.
• Assessed normal tissue response based on homogeneous irradiation at the tumor edge dose, considering serial and parallel organ architectures.
• Constructed a normal tissue survival probability (S0) function and an objective function (TCP * S0).

Main Results:

• Identified optimal D(R) values by maximizing the objective function across various radiobiological parameters (tumor/normal tissue radiosensitivity, functional subunit composition, organ architecture).
• Calculated and discussed corresponding tumor control probability (TCP) and normal tissue survival (S0) values.
• Demonstrated the impact of tumor and normal tissue characteristics on dose optimization.

Conclusions:

• The study provides a framework for optimizing external beam radiotherapy by integrating tumor mobility and normal tissue constraints.
• Optimal dose prescription is highly dependent on specific patient and tumor radiobiological parameters.
• This objective function approach aids in balancing treatment efficacy and patient safety in radiotherapy planning.