Table 5.1 presents SRS/SBRT-specific linac-related quality assurance requirements, which include the standard linear accelerator tests described in TG-142 and additional tests listed in “Quality and safety considerations in SRS and SBRT” in ASTRO [4]. Daily, monthly, and annual tests in Table 5.1 have specific recommendations based on the nature of the treatments delivered on the individual machine and are supplemented and modified as needed. Several tests deserve additional discussion. First, in addition to mechanical and safety tests in TG-142, a “Winston-Lutz” type of test provides the fundamental assessment of radiation isocenter and should be performed daily. The Winston-Lutz test can be performed by use of a film or an amorphous silicon electronic portal imaging device (EPID). Second, if image guidance is used for either cranial or extracranial localization, a test that verifies proper calibration and operation of those systems should also be performed daily. The Winston-Lutz test for both cones and MLC, covering complete range of gantry, couch, and collimator positions should be performed monthly. A hidden target test using SRS frame and/or IGRT system is performed monthly. Finally, end-to-end tests of both localization and dosimetric capabilities should be performed annually to assess the accuracy and integrity of the SRS/SBRT processes in an integrated manner.

Table 5.2 presents SRS/SBRT-specific imaging-related quality assurance requirements, which include the standard linear accelerator tests described in both the AAPM Task Group 142 report and ASTRO. The tests that verify geometrical arraignment, imaging quality, and imaging dose for planner kV and MV (EPID) imaging and cone-beam CT (kV and MV) should be performed appropriate frequency.

These SRS/SBRT-specific quality assurance requirements recommend annual evaluation of these characteristics. In addition, the report of AAPM task group 101 (TG-101) provides a number of excellent references for medical physicists, clinicians, and therapists in order to outline the best practice guidelines for SBRT [5]. The report of AAPM task group 135 will provide specific guidance for QA of robotic radiosurgery devices [6]. Similarly, the report of AAPM TG-148 describes QA for helical tomotherapy devices [7].

In addition to these major features, there are other characteristics that distinguish SBRT from conventional radiation therapy (Table 5.3). These include a general increase in the number of beams used for treatment, the frequent use of noncoplanar beam arrangements, small or no beam margins for penumbra, and the use of inhomogeneous dose distributions and dose-painting techniques (including IMRT). All of these technology improvements result in the highly conformal dose distribution that characterizes the SBRT technique.