# TDF Plan: Recovery from Late Reactions

Some late reactions may be capable of recovery and repair of radiation damage. For instance, regarding spinal cord, in the chapter Clinical Response of Normal Tissues in his textbook Radiobiology for the Radiologist Eric Hall states: "As far as re-treatment is concerned, animal data suggest that by about two years, the majority of damage from a prior exposure has been repaired; the extent of the repair depends very much on the level of the initial injury." To estimate recovery from a past treatment: 1. In the IMR group, select course #1 (yellow highlight), name it something like "old previous treatment" and then click the Set... button in the TDF Plan repopulation biology group and enter the estimated fractional repair per year in the biology and repopulation settings window. In this example, if recovery from radiation damage is estimated to be about 20% per year, then enter a factor of 0.2 and then click the Enable checkbox to allow this calculation. Note: the late repair factor is assumed to be zero and repair calculations are disabled by default. This calculation is speculative at best for human use and must be explicitly enabled in this way on a per course basis. |

2. In the IMR group, select course #1 (yellow highlight) and enter the previous treatment regimen (e.g. 25 fractions of 180 cGy, total dose 4500 cGy delivered in August of 2005), include course 1 by checking the course Include box and also be sure to check the course RTP complete checkbox. Use the Calendar window to set the date of this previous treatment.

3. In the IMR group, enter the new treatment as simulated course #2 (green highlight) and use the Calendar window to set the proposed date of the new treatment (e.g. August 2008). Include course 2 by checking the course Include box and also be sure to check the course Simulation checkbox to prevent the current course BED calculations from being totaled. The gap in days between the previous course and the current simulated course will be displayed (e.g. 1060 days in this example).

4. In the IMR Repopulation group check the repopulation Include chechbox. The repair factor and effective late BED will be calculated and displayed. In this example the original late BED for course #1 was 72 Gy3.0 and the effective late BED for course #1 after 1060 days of recovery is 30.21 Gy3.0

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