CLINICAL IMPLEMENTATION OF AN OBJECTIVE COMPUTER-AIDED PROTOCOL FOR INTERVENTION IN INTRA-TREATMENT CORRECTION USING ELECTRONIC PORTAL IMAGING

In order to test the feasibility of a protocol for intra-fractional ad justment of the patient position, during radiation therapy treatment i n the pelvic region, a two-fold study is carried out. The protocol inv olves an objective quantitative measurement of the error in positionin g starting from the comparison of a portal image with a reference imag e. The first part of the study applies the protocol to determine the e fficacy of adjustment using subjective determination of the positionin g errors by a clinician by measuring the residual errors after adjustm ent. A group of 13 patients was followed extensively throughout their treatment, analyzing 240 fields. In the second part the measurement it self determines the extent of readjustment of the position. Throughout the procedure elapsed time is measured to determine the extra time in volved in using this procedure. For this part a group of 21 patients w as followed yielding statistics on 218 fields. Using this computer aid ed protocol it is shown that systematic as well as random errors can b e reduced to standard deviations of the order of 1 mm. The price to pa y however is additional treatment time up to 58% of the treatment time without the protocol. Time analysis shows that the largest part of th e added time is spent on the readjustment of the patients' position ad ding a mean of 37% of time to the treatment of one field. This is desp ite the fact that the readjustment was performed using a remote couch controller. Finally a statistical analysis shows that it is possible t o select patients benefiting from the use of such a protocol after a l imited number of fractions.