Purpose: To investigate how the temporal pattern of dose applied during a single-intensity modulated radiation therapy (IMRT) fraction can be arranged to maximize or minimize cell kill. Methods and Materials: Using the linear-quadratic repair-time model and a simplified IMRT delivery pattern model, the surviving fraction of cells for a single fraction was calculated for all permutations of the dose delivery pattern for an array of clinically based IMRT cases. Maximization of cell kill was achieved by concentrating the highest doses in the middle of a fraction, while minimization was achieved by spreading the highest doses between the beginning and end. The percent difference between maximum and minimum cell kill (%Diffmin/max) and the difference between maximum and minimum total doses normalized to 2 Gy/fx (ΔNTD2 Gy) was calculated for varying fraction durations (T), α/β ratios, and doses/fx. Results: %Diffmin/max and ΔNTD2 Gy both increased with increasing T and with decreasing α/β. The largest increases occurred with dose/fx. With α/β = 3 Gy and 30 min/fx, %Diffmin/max ranged from 2.7-5.3% for 2 Gy/fx to 48.6-74.1% for 10 Gy/fx, whereas ΔNTD2 Gy ranged from 1.2 Gy-2.4 Gy for 30 fractions of 2 Gy/fx to 2.3-4.8 Gy for 2 fractions of 10.84 Gy/fx. Using α/β = 1.5 Gy, an analysis of prostate hypofractionation schemes yielded differences in clinical outcome based on the pattern of applied dose ranging from 3.2%-6.1% of the treated population. Conclusions: Rearrangement of the temporal pattern of dose for a single IMRT fraction could be used to optimize cell kill and to directly, though modestly, affect treatment outcome.
|Number of pages||8|
|Journal||International Journal of Radiation Oncology Biology Physics|
|State||Published - Nov 1 2006|
- Dose protraction
- Linear-quadratic model
- Temporal optimization