(1) Loss of all of 3rd week (5F)
of a treatment schedule of 70Gy / 35F / 46Days
Assuming that treatment began on a Monday, intended overall treatment time is 46 days. After gap (missed 3rd week), treatment resumes on Monday of 4th week. 10F have been given, 25 left to deliver. If treatment is to be complated on prescribed finishing date, available number of days (incl. weekends) is 26.
Thus the missed dose in the gap can be compensated for by delivering the remainder of the treatment on weekdays (20F) and on 5 of the remaining 6 weekend days. This does not involve changing the fraction size, as the treatment is not extended and is "good" compensation.
If weekend treatments are not feasible, good compensationis still possible if, on 5 of the remaining 20 treatment days, 2F are delivered instead of 1F. The important proviso is that the twice-daily fractions must be dfelivered with a minimum time gap of 6 hours. It is also recommended that the days on which 2F are delivered are NOT consecutive, but spaced throughout the available time period. Fridays are a good choice for delivery of some 2F treatments as there is a greater opportunity for completion of repair before treatment resumes the following week.
Where fraction size is >2Gy, care needs to be taken with twice-daily fractionation.
(2) Loss of entire 6th week (5F)
of treatment schedule of 70Gy / 35F / 46Days
After the gap, treatment resumes on Monday of 7th week. 25F have been delivered and 10F remain. Ideally, these 10F should be delivered over the 5 remaining treatment days, so treatment is not extended. The missed dose can therefore be compensated for by delivering the remainder of the treatment as twice-daily fractions (at least 6 hours apart), in each weekday of the final week.
This does not involve changing fraction size and as treatment length is not extended, also constitutes "good" compensation. A better solution would be to also make use of the weekend before the final week of treatment, thus providing 7 days to deliver 10F. Bi-daily fractionation could be used on Mon, Wed, Fri and single fractions on the other 4 days. This reduces the likelihood of creating excess normal tissue damage in the event that there is incomplete repair between fractions.
Solutions 1 and 2 do not involve changing fraction size or overall time and provided there is reasonable spacing between treatment days on which 2F are given, do NOT invoke any quantitative evaluations or significant radiobiological issues.
(3) More complex case - loss of
7th week (5F) in schedule of 70Gy / 35F / 46Days
In this case, the unscheduled gap extends to the time when treatment should have finished and ANY form of compensation will therefore extend the overall treatment time. It is thus necessary to use calculations to first determine how much normal tissue BED there is still to deliver after the gap.
