Patient setup and verification for intensity-modulated radiation therapy (IMRT).

Intensity Modulated Radiation Therapy (IMRT) is now widely used in the radiation therapy community. The ability of IMRT to deliver complex dose distributions has allowed dose escalation to targets while sparing normal tissues. In IMRT the roles of the physicist, dosimetrist, and physician are changed. Inverse planning, which is inherent to IMRT, requires that the final dose solution be defined at the beginning of the planning process. The physician must define specific dose volume constraints for the target as well as normal tissues. The physicist and dosimetrist must evaluate the final plan and determine if it meets the goals of the treatment, even if it does not completely satisfy the initial constraints. Once a plan is decided upon, the ability of the clinic to safely and accurately deliver that plan to the patient must be confirmed. As with any new technology, IMRT has created a need for new quality assurance procedures. Here we describe our IMRT process from simulation through planning and treatment. By standardizing our simulations we have decreased setup times and decreased the threat of collisions. Comparison of pseudo-DRR's and multiple-exposure port films allows confirmation of patient positioning on the linac. Our treatment delivery quality assurance program using film and MOSFET detectors in a polystyrene phantom is also described. We provide insight on how to overcome some of the common problems encountered in treatment planning and delivery such as isocenter location, collision avoidance, table indexing, dose confirmation, and plan analysis.