AbstractID: 9718 Title: A Novel Technique for Matching Head-and-Neck IMRT Fields with
Supraclavicular Field
Intensity modulated radiation therapy (IMRT) for head-and-neck (HN) cancer often adopts conventional supraclavicular field to treat lymph nodes
in the lower neck and supraclavicular areas. A technique using single-isocenter and half-beam (SIHB) had been employed in our clinic for matching
supraclavicular and IMRT fields. However, this technique requires perfect jaw calibration and limits the IMRT field size to only half of the available
size. We propose a wedge junction method for matching supraclavicular with HN IMRT fields to overcome these shortfalls. During treatment, the
superior border of the supraclavicular field, shaped with dynamic MLC, moves continuously from 1.5cm inferior to 1.5cm superior to the match
line, producing a 3cm-wide wedge at the junction. The IMRT fields, which are extended inferiorly by 1.5cm, are optimized by including the dose
contribution from the supraclavicular filed, thereby forming another wedge at the junction to complement the supraclavicular field. Treatment plans
generated with this method demonstrated dose homogeneity better than 3% at the junction. Radiation dose at the junction is insensitive to calibration
errors of the jaws or MLC leaves. Cold/hot spots generated by 1 and 2 mm overlap/underlap are less than 3% and 6%, respectively, as compared to
>10% and >20% with the SIHB technique. The proposed method facilitates seamless match between supraclavicular and HN IMRT fields. It allows
field sizes larger than half beam for IMRT fields and substantially reduces cold/hot spots caused by imperfect jaw or MLC leaf calibration.