Defining the role of intensity modulation in electron conformal therapy for the treatment of head and neck cancer.

Bolus electron conformal therapy (BECT) in the treatment of cancers of the head and neck is often limited by an inability to reduce dosimetric hot spots resulting from surface irregularity or tissue heterogeneity. We examined the potential benefits of using intensity modulation for electron therapy (IM-BECT) to reduce hotspots in patients undergoing electron beam therapy for superficial cancers of the head and neck (HN). Twenty patients with HN cancer previously treated with BECT were identified. Each case included the treatment targets and a primary organ at risk (OAR) that were defined by the radiation oncologist. A target +2 cm rind structure was created for analysis of the dose deposition in areas surrounding the target volume as a measure of conformality. Each patient plan was transferred into the novel IM-BECT planning software and each case was recomputed as per the original parameters. Next, each case was replanned with the inclusion of intensity modulation, as well as a new custom conformal bolus that was redesigned for optimized range compensation when paired with an intensity modulator. The plans were then normalized to prescription dose and compared for target coverage/dose and OAR dose. For patients who had a hotspot of 125% or greater, the hotspot was on average reduced by 13.1% with IM-BECT. For IM-BECT, the average primary OAR means dose and target+2cm rind mean dose increased slightly by 10.6% and 6.4%, respectively (primary OAR mean [p = 0.0001], and Target+2cm rind mean [p = 0.0001], paired t-test). IM-BECT is an effective method of reducing hotspots in patients with superficial HN cancer. Improvements came at the expense of slight increases in dose to the underlying tissues. This retrospective planning study represents the first example of IM-BECT to actual HN patient cases. Expanding the role of IM-BECT in other disease sites could potentially compared to conventional BECT.