NOTE: In the above example, beam 1 delivers 0.8 Gy, and the other beams each deliver 0.4 Gy.  The total dose delivered in each fraction = 0.8 Gy + (3 x 0.4 Gy) = 2.0 Gy.  The fraction delivery time is approximately 4 minutes.  The BSEQ parameter provides a convenient method to swap the order of the beams without changing the RR1 array.

Purpose: Set the sequence of beams used to deliver each fraction.  Use with the RBI keyword to easily swap the sequence (order) of beams.
Data Type: {pointer to array of integer}
Unit: n/a
Default: 1, 2, ..., NBD.
Comments:  In step and shoot intensity modulated radiation therapy (IMRT), fractions are typically delivered in 10 to 20 or 30 minutes using 5 to 9 beams directed at the patient (each beam may be shaped by multiple leaf configurations).  The NBD, RBI, BSEQ and TTO parameters can be used to model the temporal pattern of radiation deliver to some region of the tumor in great details. The total time to deliver each fraction is ~ (NBD-1)*TTO. Some references related to these phenomena are:

• J.Z. Wang, X.A. Li., W. D’Souza, R.D. Stewart. Impacts of prolonged dose-delivery time on tumor control: a note of caution for IMRT, Int. J. Radiat. Oncol. Biol. Phys. Accepted (2003).

• R.D. Stewart and R.J. Traub, Radiobiological Modeling in Voxel Constructs. In A. Kling F. Barão, M. Nakagawa, L. Távora, P. Vaz, eds. Proceedings of the MC2000, An International Conference on Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation and Applications. New York, USA: Springer-Verlag Publishing, 285-290 (2001).
• R.D. Stewart and R.J. Traub, Temporal Optimization of Radiotherapy Treatment Fractions In: Proceedings of the ANS Topical Meeting on Radiation Protection for our National Priorities, Medicine, the Environment, and the Legacy (RPS 2000). Illinois, USA. Published by the American Nuclear Society, Inc. La Grange Park, Illinois, p 372-378 (2000).