Optimum overall times II: Extended modelling for head and neck radiotherapy

Area of Science:

• Radiation oncology
• Cancer treatment optimization
• Radiobiology modeling

Background:

• Previous modeling (Part I) suggested no significant optimum time up to 50 days for radiotherapy schedules.
• UK schedules often yield lower tumor effective doses compared to international standards.
• Part I focused on a limited range of treatment durations and fractions per day.

Purpose of the Study:

• To investigate a wider range of radiotherapy schedules beyond the scope of Part I.
• To correct numerical errors in previous tables and re-evaluate optimal treatment times.
• To determine if using two fractions per day improves tumor control and minimizes complications.

Main Methods:

• Utilized standard linear-quadratic modeling with specific radiobiological parameters (alpha/beta, Tk, Tp).
• Assessed tumor response and acute mucosal reactions using defined dose constraints.
• Explored variations in tumor repopulation rates (Tp=2, 3, or 5 days).

Main Results:

• Optimal treatment durations were identified as 22-32 days for once-daily fractionation and 42-49 days for twice-daily fractionation.
• Tumor repopulation significantly impacted dose reduction after 30 days for once-daily schedules, and after 50 days for twice-daily schedules.
• Twice-daily fractionation showed potential for enhanced tumor dose delivery.

Conclusions:

• Biological modeling can effectively evaluate treatment schedules outside of published clinical data.
• Implementing two fractions per day in radiotherapy reliably enhances tumor control.
• The modeling suggests potential gains equivalent to two 2 Gy fractions, with possibilities for reduced late complications in optimally designed shorter schedules.