Table 1.

Some practical requirements for a four‐dimensional intensity‐modulated (IMRT) / stereotactic body radiation therapy (SBRT) quality assurance device

Requirement	Explanation
1. Electronic (filmless)	Given the resource and time constraints of modern clinics, any new device—hardware or software—should hold efficiency paramount. In intensity‐modulated quality assurance, this requirement implies filmless dosimetry to avoid processing and scanning time.
2. High resolution (sub‐mm3 detector size)	Intrafraction motion kernels are typically on the order of several centimeters in the direction of maximum motion, and motion cycles can be fast. To capture dosimetry accurately, volume averaging must be avoided. A small active detector size is therefore required.
3. Sufficient detector density (detectors/area)	To capture sufficient data and generate meaningful statistics, the number of detectors per unit area (two‐dimensional) must be maximized within practical device limits.
4. Quantify absolute dose	Absolute dose errors are necessary to build a clinical database and to make any assumptions about biologic effects using today's strategies.
5. Programmable motion	The detectors must move, and they must be able to move in exact or very close correlation with the beam's‐eye‐view of the target motion. Conformal radiation therapy is very customized, and a four‐dimensional dose quality assurance device must also be customizable. Motion acceleration and speed must accommodate the full range of breathing motion.
6. Integration with gating methods	Gating methodologies use different fiducial and image triggers. A programmable four‐dimensional dose quality assurance device that moves in two‐dimensions must be able to integrate with standard gatingmechanisms.
7. Integration with existing two‐dimensional array devices	To help reduce costs while still making new technologies available, new devices should, if possible, integrate with existing tools. A four‐dimensional dose quality assurance device should integrate with an existing, accepted two‐dimensional array product.
8. Use of familiar analysis methods	A four‐dimensional dose quality assurance device should, when possible, use the language and methods accepted by medical physicists—for example, percent difference, distance‐to‐agreement, gamma statistics, and so on. This approach would accelerate understanding and appropriate application of new devices.