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Tutorial 1.2 split-dose exposures
How to set up radiation exposure scenarios
Examples 1 through 3 illustrate different methods of setting up one or more split-dose exposure scenarios. In a split-dose exposure, the total dose of radiation is sub-divided into two smaller doses (or fractions) that are delivered at different times.  These fractions, usually, but not always, are of equal size.
 
Significance:  By varying the time interval between the first and second dose, the biological response to radiation can be modulated.  The combined effects of the two fractions tends to increase as the time interval between them decreases (see also Split-Dose Exposures in the Examples section of the manual).
 
Instructions: Place the illustrative examples into an ASCII input file (see What is an ASCII file? and How do I Edit ASCII files?) and then use the RIO application, which is typically executed from the command prompt, to convert the input into an ASCII output file (a .radx binary file will also be created but this file can be ignored for now). Compare the processed information in the output file to the desired exposure scenario(s) specified in the input file.  Did the input file generated the desired exposure scenarios in the output file?
 
Example 1 Single split-dose exposure scenario (spd1.inp, spd1.out)
 
! A total dose of 10 Gy is delivered as two 5 Gy fractions. 
! Dose rate: 10,000 Gy/hour Fractions are separated by time
! intervals varying between 0 and 10 hours.
 
SDRX: ADR=10000 TAD=10 TBD=TI1
TI1= 0.00 0.25 0.50 0.75 1.00 2 3 4 5 6 7 8 9 10 /
 
Comment: This example will create 14 split-dose exposure scenarios.
 
 
Example 2 Multiple split-dose exposure scenarios (spd2.inp, spd2.out)
 
! SCENARIO 1: A total dose of 10 Gy as two 5 Gy fractions.
!   Dose Rate: 100 Gy/h. The second dose is delivered at
!   different time intervals varying between 0 and 10 h hours.
! SCENARIO 2:
!   A total dose of 20 Gy as two 10 Gy fractions.
!   Dose Rate: 100Gy/h The second dose is delivered at
!   different time intervals varying between 0 and 10h hours.
 
SDRX: ADR=100 TAD=RX1 TOD=RX2
RX1= 10 20  /
RX2= 0 0.1 0.2 0.3 0.5 1 2 3 4 5 6 7 8 9 10 /
 
 
Example 3 An alternative way to define a multiple split-dose exposure scenario (spd3.inp, spd3.out)
 
! Define multiple split-dose exposure scenarios (see also the s3.inp file). In this
! sample input file, a baseline exposure scenario is defined that delivers a total
! dose of 10 Gy as two 5 Gy fractions. The fractions are delivered using an
! instantaneous dose rate of 10,000 Gy/hour, and the fractions are separated
! by various time intervals from 0 to 10 hours.

SDRX: ADR=10000 TAD=10 TBD=TI1
TI1= 0.00 0.25 0.50 0.75 1.00 2 3 4 5 6 7 8 9 10 / !Array of time intervals (h)
  
Comments: 
  • Time between dose delivery (TBD) is used instead of the Time of  delivery (TOD)
  • Either TOD or TBD can be used to specify the time interval between doses (fractions). However, the methods may not generate the same exact temporal pattern of radiation delivery.  In general, the two methods are only equivalent in the limit as the dose rate used to deliver each fraction becomes very larger (fraction delivery time is very short).
 
Suggested Problems: For all of the sample problems, use RIO to process the input file into an output file.  Verify that the RIO application generates the desired exposure scenario.  Debug as necessary.
  1. What happens if both TBD and TOD parameters are inadvertently used in the same input file (which one takes precedence)?
  2. Define a split-dose exposure scenario that cannot be specified using the TBD parameter but can be specified using the TOD parameter.
  3. Derive a mathematical equation for the relationship between TOD and TBD. Test the formula by defining several hypothetical split-dose exposure scenario using both methods.
  4. In Example 2.3, the TBD parameter is used to setup several split-dose exposure scenarios.  Setup an input file to generate a similar set of exposure scenarios using the TOD parameter.
  5. Setup an exposure that delivers two doses of radiation separated by 15 minutes.  Each dose is delivered at 10 Gy/h for 10 minutes.  What is the total absorbed dose delivered in the exposure scenario? Use the information from the output file to plot the absorbed dose rate (y-axis) versus time (x-axis).
  6. Create an input file that generates four split-dose exposure scenarios in which two 10 Gy doses are delivered at a dose rate of 10 Gy/h.  The time intervals between the doses are 10, 30 , 40 and 50 minutes, respectively.  What are the average dose rates in each of the four exposures scenarios (Hint: total dose is the same for all four scenarios but the overall irradiation time is different)?
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Last updated: 10 June, 2011
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