Purpose: The aim of this study was to assess whether intensity-modulated radiation therapy (RT; IMRT) can reduce dose to normal tissues (organs at risk) while maintaining equivalent target coverage.
Patients and methods: A 9-field, non-coplanar, 1-cm beamlet IMRT plan was designed for 9 patients who were previously treated for anal cancer with conventional field arrangements. Clinical target volumes and organs at risk (OARs) were defined. Target coverage was assigned highest priority for optimization, followed sequentially by organ at risk. The genitalia and perineal skin were the highest priority OARs. Lexicographic ordering-based IMRT optimization was used to generate a conformal plan, which was compared with the conventional, previously delivered RT plan.
Results: The IMRT and conventional RT plan achieved homogeneous dose coverage of all target volumes. Intensity-modulated RT produced highly conformal dose distributions compared with conventional techniques, with avoidance of critical normal structures. Statistically significant reductions in mean doses to the perineal skin and to the genitalia were seen with IMRT, with only a modest increase in mean dose to the bony pelvis.
Conclusion: Intensity-modulated RT, with lexicographic ordering, allows for substantial reduction of dose to OARs while maintaining adequate target coverage. These encouraging findings might translate into reductions of treatment-related toxicity, gains in local control, or improvements in quality of life.