A unique feature of the VC is that biological effects can be simulated for exposure conditions of arbitrary temporal complexity (see also the Radiation Delivery Examples).  Several methods are available to setup different kinds of exposure scenarios.  The VC can also perform biological simulations for multiple exposure scenarios in a single computer run.  Information on the temporal delivery of radiation can be specified using two main methods:

1. Exposure information located in the primary VC input file (e.g., information specified with the RADX or SDRX keywords) can be used to generate exposure scenarios on-the-fly (i.e., at runtime).
2. Exposure information can be loaded into memory from an existing (.radx) binary file (see Overview of Program Operation).

If method 1 is used to define the exposure scenario, the VC will automatically create a .radx binary file, and this file can be re-used in future simulations (method 2).  Alternatively, any  ASCII input containing an appropriate set of keywords can be converted to a RADX binary file using the RIO computer code.

Specifying the Temporal Pattern of Radiation Delivery

Within the VC system of computer codes, the temporal pattern of radiation delivery is specified using a series of keywords.  These keywords must be placed in a suitable ASCII input file (see What is an ASCII file? and How do I Edit ASCII files?) and processed by the VC, RIO, XIO, or RXSM computer codes.

The RADX keyword provides a very general method of specifying one or more exposure scenarios of arbitrary temporal complexity.  The SDRX keyword provides a simple way to setup split-dose exposures, the DECAY keyword can be used to specify exponentially decreasing dose rates (e.g., near a radioactive particulate or brachytherapy seed), and the XBRT and DFDM keywords provide a method of setting up exposure scenarios for multi-fraction radiation treatments.