Discrepancy in rounded exposure time with gamma knife treatment

We investigated the discrepancy between the sums of calculated time down to two places of decimals by gamma plan and those of exposure time taken a figure up one place on gamma knife. The average among the ninety-nine cases having one lesion was +0.11%. It was a very good value and we thought probable that the mean would decrease as the cases would increase. It does not come into question if we use the numerical value of one place of decimals for setting up exposure time. There were, however, about 25% cases which exceeded the difference of 0.35%. In spite of these cases, the discrepancy affect little in dose delivery and dose distribution. If we want to achieve more accuracy, it is necessary to install the timer to be capable of setting two places of decimals. (author)