What is the recommended tolerance for locating the isocenter in rotations of the collimator, gantry, and couch top?

The recommended tolerance for locating the isocenter during rotations of the collimator, gantry, and couch is 2 mm in diameter. This standard is established to ensure that the targeted area of treatment receives precise radiation doses and minimizes exposure to surrounding healthy tissue. A 2 mm tolerance is considered a practical balance between the high level of accuracy needed for effective treatment planning and delivery, while also accommodating the operational capabilities and limitations of radiotherapy equipment.

In clinical practice, achieving a tolerance of 2 mm allows for sufficient alignment fidelity in typical patient setups, given various factors such as patient movement or slight changes in anatomy. This tolerance level reflects an understanding of the complexity of maintaining isocentric alignment across multiple axes and the need for a margin that still allows for effective delivery of the prescribed dose.

Selecting a tolerance that is tighter, such as 1 mm or 0.5 mm, might be desirable in specific advanced techniques or highly conformal treatments, but 2 mm is widely accepted as a standard that supports efficient workflow while ensuring clinical efficacy. It is important for dosimetrists and radiation therapists to be aware of these tolerances in order to maintain quality assurance and treatment precision.