Dose verification for patients undergoing IMRT

At Emory Clinic intensity-modulated radiation therapy (IMRT) was started by using dynamic multileaf collimators (dMLC) as electronic tissue compensators in August 1998. Our IMRT program evolved with the inclusion of a commercially available inverse treatment planning system in September 1999. While the introduction of electronic tissue compensators into clinical use did not affect the customary radiation oncology practice, inverse treatment planning does alter our basic routines. Basic concepts of radiation therapy port designs for inverse treatment planning are different from conventional or 3D conformal treatments. With inverse treatment planning, clinicians are required to outline a gross tumor volume (GTV), a clinical target volume (CTV), critical normal structures, and to design a planning target volume (PTV). Clinicians do not designate the volume to be shielded. Because each IMRT radiation portal is composed of many beamlets with varying intensities, methods and practice used to verify delivered dose from IMRT portals are also different from conventional treatment portals. Often, the validity of measured data is in doubt. Therefore, checking treatment planning computer output with measurements are confusing and fruitless, at times. Commissioning an IMRT program and routine patient dose verification of IMRT require films and ionization chamber measurements in phantom. Additional specialized physics instrumentation is not required other than those available in a typical radiation oncology facility. At this time, we consider that routine quality assurance prior to patient treatments is necessary.