In [

The authors use a model for calculating the probability of killing all tumour cells presented earlier by the same authors [

In a reply to the comment [

In this case, one has to keep in mind that microdosimetrical measurements show large variations in specific energy for the same expectation/average value. If we refer to the cell nucleus, the variations could be even higher.

It is of course impossible that “large variations in specific energy” could lead to large variations in the “expectation/average value” (i.e., the absorbed dose) because the latter was supposed to be constant (“the same”).

However, there is no theoretical or experimental support for the occurrence of large and statistically independent variations of absorbed dose over distances of a cell diameter.

For example, as a reasonable model of a clinical radiation field, assume a threedimensional space filled with water for

If

Assume that on the average

If ^{−1} [^{−2}, corresponding to 2 Gy, then the relative standard deviation caused by the random variation of the photons can be calculated. The result is less than

Hereby it is shown that the random distribution of the photons has a small effect on the random variations of absorbed dose, so that (

However, even if it is hypothetically (and contrary to experimental and theoretical evidence) assumed that dose variations as described by Wiklund et al. should occur, they would not influence the probability of cell survival and hence would not influence the probability of tumour control in the way described by the model of [

This is shown as follows. The radiation sensitivity of the cells is described by the function

Therefore, the conclusion remains that the model presented in [

The authors also treat the case of heterogeneous radiation sensitivity of the cells of a tumor, subject to radiation treatment. To that end equation 12 of [

If the variations in radiation sensitivity stem from variations in intrinsic radiation sensitivity, then the sensitivity of the same cell in different fractions will not be independent. Another important cause of variations in sensitivity is variations in oxygenation. In this case cells close to each other will have similar oxygenation, so that their sensitivity variations from this cause are not independent.

Because of this, the results regarding variations in radiation sensitivity using equation 12 are not applicable to radiation treatment.

The author declares that there is no conflict of interests regarding the publication of this paper.