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SU‐FF‐T‐417: The Effect of Target Volume Depth On Surface Dose for Inverse Planned IMRT Treatments of Head and Neck Cancers
Author(s) -
Parker W,
Poli E,
Evans M,
Campos L Lucente,
Podgorsak E
Publication year - 2006
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2241336
Subject(s) - imaging phantom , nuclear medicine , medicine , multileaf collimator , dosimetry , head and neck , supine position , radiation therapy , radiation treatment planning , radiology , surgery
This work evaluates the surface dose as a function of PTV proximity to the surface for inverse planned head‐and‐neck IMRT patients and compares the results to measurements performed for a conventional treatment technique. Methods and Materials: An anthropomorphic phantom was CT scanned in the supine treatment position with thermoplastic mask immobilization covering the entire head‐and‐neck excluding the supra‐clavicular region. A CTV including the cervical, low neck, and supra‐clavicular lymph nodes, as well a 5 mm margin was outlined. Inverse IMRT plans were generated using a 7 field coplanar technique with 6 MV photons. Plans were created for PTVs defined at 0, 5, and, 10 mm depth from the phantom surface (PTV skin , PTV 5 , PTV 10 ). The treatments were delivered using a dynamic multileaf collimator sliding window technique. Measurements at up to 8 locations on the surface of the phantom and at 2 locations near the center of the PTVs were performed using TLD and MOSFET dosimeters. Results were compared to measurements performed for a conventional 3‐field geometry (opposed laterals and anterior supra‐clavicular field planned to cover the PTV skin ). Results: and Discussion: The average surface dose for the IMRT plans in the neck region was measured to be 59%, 78%, and 92% of the prescription dose for the PTV 10 , PTV 5 , and PTV skin plans respectively, and likewise, 53%, 55%, and 73%, respectively in the supra‐clavicular region. Average surface doses from the conventional field arrangement were measured to be 100% and 36% of the prescription dose for the neck and supra‐clavicular region respectively. Conclusion: For the IMRT plans the surface dose increased as a function of the PTV proximity to the surface. For an equivalent prescription dose, the conventional 3‐field technique yielded a higher average skin dose in the neck region and lower dose in the supraclavicular region in comparison with the IMRT plans.