When using TMS for the treatment of Major Depressive Disorder in adult patients who have failed to receive satisfactory improvement from prior antidepressant medication in the current episode, it is important to be able to correctly position the coil of the Dorsal Laterla PreFrontal Cortex (DLPFC). There are many different methods available that clinicians use to locate the treatement area. Early studies used a "5 cm" rule which involved moving the coil 5 cm to the motor cortex where the motor threshold evoke potential was determined. This method has limitations as it does not take into affect variability in head size and other variables that change between individuals. As the left DLPFC corresponds to the F3 location of the international 10-20 EEG system, it is possible to take measurements of the individual and use an algorithm to determine the desired placement of the TMS coil.
Using the Beam protocol, named after William Beam, a clinician can take three measurements (tragus to tragus, nasion to inion and head circumfrence) and input them into the free software that provides the position of the F3 - DLPFC position that corresponds to that individual.
The software is availble for both Windows and Mac on the Clincal Researcher website.
The publication, An efficient and accurate new method for locating the F3 position for prefrontal TMS applications is available for review.
An alternative method to mapping the international 10-20 EEG measurements involves using the Borckardt/Hanlon System. The system works similar to the beam protocol which uses three measurements (tragus to tragus, nasion to inion and head circumfrence). The free software than allowes you to choose the desired point of interest and the algorithm provides the mapping to the location.