**7. Discussion**

The modern radiotherapy in HNC have revolutionized treatment outcome especially in terms of acute and late toxicity. It thus brings about a clear change in treatment outcome. One important aspect in preserving the QOL is the OAR's. We, as radiation oncologist are much aware about the importance of accurate delineation of these structures. Only an accurate delineation can lead to effective sparing and thus a desirable outcome in terms of QOL. There were several isolated guidelines available. In this chapter we tried to summarize all the available guidelines. For certain organs like temporal lobe, multiple guidelines are available in the literature. We have tried to incorporate them together to put forward a single uniform consensus. Having said that the delineation and the attempted dose constraints should also be evaluated based on the target volume and tumor control. In case of parallel structures, the target volume coverage should be made priority and the risks and side effects of the same should be communicated to the patients. In such cases the volume of OARs outside the planning target volume (PTV) may be delineated separately and similar dose constrains may be aimed for. It should also be kept in mind that even with the most sophisticated of technologies, not all of the dose constraints might not be achieved due the basic physics of the photon beam. In such situations a trade-off should be agreed upon. However, such liberties, should not be attempted with serial structures like spinal cord and brain stem. Organs such as these should always be given hard constraints. If the PTV is overlapping such structures, under dose the area is accepted.
