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The major potential advantages of IMRT have been addressed in a number of preliminary clinical investigations/trials which have generated encouraging results that salivary gland sparing can be achieved with improvements in xerostomia without risking increased failure rates. Dose escalation trials, although documenting the potential of IMRT as a tool for dose escalation, require refinement and intense physician involvement but have produced encouraging loco-regional tumor control rates. Finally, the ability of generating plans with outstanding dose conformality in the radiotherapeutic management of HNSCCs of the OP/(OC) has been clearly established.

IMRT offers exciting potential for improving the radiation therapy of NSCLC, a disease that generally responds poorly to conventional RT. NSCLC is in many aspects a textbook example of a treatment site for which IMRT was designed, as it is a disease for which dose-escalation is clearly required, but for which improved normal tissue dose sparing is also critically important. It is also a site where significant improvements over conventional RT are clearly needed, being the most common cause of cancer death in the US. Even with implementation of IMRT, however, there are still many technical details that could mitigate any possible benefits of increased radiation doses. In particular, conventional RT does poorly in NSCLC in large part because of poor initial identification of the tumor volume, and errors associated with respiratory motion. Thus, this chapter has highlighted that the application of IMRT to NSCLC must be clinically tested in conjunction with other cutting edge technologies such as FDG-PET imaging, respiratory gating, and EPID-based treatment verification. Such a multi-faceted approach represents the best, and perhaps the only possibility for improved outcome in the treatment of this disease with radiation.

The use of IMRT in the treatment of breast cancer is increasing across the U.S. as a result of the improvements provided in dose homogeneity and normal tissue avoidance. The application of IMRT offers reduced soft tissue toxicity in isolated breast treatment and the potential for improved local-regional control without an increase in lung and heart toxicity in those requiring loco-regional treatment. When standard tangential fields are used to define the target volume, the focus of IMRT is primarily to optimize dose homogeneity. Although long term outcome studies are needed to make definitive statements, many have already accepted this treatment approach as a preferred method of treatment delivery. However, when dose conformality becomes a primary focus, many uncertainties arise that require additional study prior to widespread adoption. By generating highly conformal fields with severe dose gradients, the accuracy of treatment delivery becomes increasingly dependant on set up error and breathing motion. This is not an issue when standard tangents are used for isolated breast treatment as the generous field design allows the target to remain in the field despite inter or intra-fraction motion. However, this is a critical issue when dose shaping with the goal of maximizing target coverage and normal tissue avoidance. Future investigation will need to address these challenges before IMRT can be considered for widespread adoption. Additionally, long term followup is needed to determine whether the improvements in dose homogeneity and conformality will translate into improvements in disease control and/or a reduction in toxicity.