Purpose/Objective: Some patients with head and neck cancer are treated with intensity modulated radiation therapy (IMRT). We designated this as “firstirradiation”. If they later develop disease, “second-irradiation” therapy would be challenging. We have developed a technique that limits the cumulative dose to the spinal cord and brainstem while maximizing coverage of a new planning target volume (PTV) in the new treatment region.
Materials and methods: Three patients who previously received IMRT and later developed a recurrence were selected to demonstrate this technique. A CT simulation scan was performed and then the original plan was applied. Fluence from outside of the spinal cord and brainstem with a 1.0 cm margin (SCBM) was removed. This modified plan was then used as a base plan for optimization. The original plan was summed with a new second-irradiation plan to evaluate the cumulative dose received by the spinal cord and brainstem. The second-irradiation plan alone was used to evaluate for coverage of the new PTV.
Results: For all patients, the maximum cumulative doses to the spinal cord with 0.5 cm margin (SCM) and brainstem with 0.5 cm margin (BSM) met the National Cancer Institute of Canada Clinical Trials Group head and neck clinical protocol dose limitations. For the second-irradiation plan alone, 100% of the prescribed dose covered 95% of PTV.
Conclusion: The use of a fluence modified IMRT plan as base plan is an effective planning technique that accounts for the cumulative dose to the spinal cord and brainstem while allowing coverage of a new PTV.
Fred Cao1, Carson Leong,Peter Steiner and Joy Schroeder
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