Optimization of the dose delivery in a few field techniques using radiobiological objective functions

Area of Science:

• Medical Physics
• Radiation Oncology
• Biophysics

Background:

• External beam radiation therapy (EBRT) planning requires optimizing dose distribution to maximize tumor control while sparing normal tissues.
• Current methods often rely on simplified physical dose metrics, potentially overlooking complex radiobiological effects.
• Developing objective functions that accurately predict complication-free tumor control is crucial for advancing radiation therapy techniques.

Purpose of the Study:

• To develop and present a novel method for determining optimal primary fluence profiles in multiple-field EBRT.
• To utilize a radiobiologically based objective function (P+) that quantifies the probability of achieving complication-free tumor control.
• To investigate the impact of beam orientation and dose delivery non-uniformity on treatment efficacy and safety.

Main Methods:

• A radiobiologically based objective function, P+, was developed to quantify complication-free tumor control probability.
• The P+ function considers both tumor dose escalation and normal tissue complication avoidance, incorporating dose homogeneity within the target volume.
• Patient-specific or library-derived radiobiological parameters were used. The method was applied to determine optimal incident photon fluence profiles and investigate beam orientations for two-beam techniques.

Main Results:

• The P+ objective function effectively balances tumor control and normal tissue complication risks.
• Non-uniform dose delivery strategies revealed that parallel opposed beams are suboptimal in two-beam techniques; a beam angle between 100-120 degrees is generally preferred.
• Symmetry characteristics of the P+ phase space for two-beam techniques were identified, providing insights into optimal planning.

Conclusions:

• The developed method provides a robust framework for optimizing radiation therapy fluence profiles and beam arrangements.
• Radiobiological optimization using P+ leads to improved treatment plans that maximize the probability of complication-free tumor control.
• The findings challenge conventional beam arrangements and highlight the importance of considering non-uniform dose delivery and optimal beam angles in EBRT planning.