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Intensity-modulated photon beams can be used to obtain homogeneous concave dose distributions. They allow the creation of intentionally non-homogeneous dose distributions for the prescription of multiple dose levels to be delivered during the same fraction. Dose gradients can be delivered with controlled steepness and location. Unwanted dosimetrical effects of loss of electron equilibrium near interfaces between lower and higher density tissues can be counteracted by IMRT but the appropriate planning technology is not generally available yet. Simple and straightforward is the use of intensity-modulated beams for missing tissue compensation. Dose distributions can be generated to match brachytherapy or electron beam plans. Mixed intensity and energy modulated electron-photon beams with steep dose-fall off and sharp depth-independent penumbra can be created.

Routine QA in traditional radiation therapy involves numerous redundancy checks that are sometimes repeated for every patient. Extrapolation of this ‘attitude’ to IMRT is untenable. Instead, focused QA procedures that test the vulnerable links, are needed in the triad of routine patient-specific QA, periodic equipment QA and thorough class-solution QA. The physics team is encouraged to aim at a balance between the triad using the conceptual approach that has been presented to optimize and streamline QA procedures within class solutions, rather than proliferating redundant QA checks. Multi-center co-operation and QA networking can be helpful and stimulating. Rather than a burden to the physics team, QA should be a passionate professional activity of combining the appropriate instruments and strategy to ensure or even manage the radiation physics quality of the implemented IMRT planning and delivery processes. One might expect that new dedicated delivery technologies like tomotherapy and image guided robotic IMRT have the potential of shortening the loop of planning and delivery, and hence will allow the QA activities to be condensed and further streamlined. In the mean time, QA of the longer treatment chain remains mandatory and will further stimulate familiarization with IMRT and keep the level of alertness and vigilance.