SU‐F‐T‐442: Dose Distribution Comparison for Post‐Laryngectomy Stoma Area Between Conventional AP and VMAT Plans with Or Without Bolus

Abstract

Purpose:To compare dose distributions of conventional AP vs. VMAT treatment plans with or without bolus around post‐laryngectomy stoma.Methods:Radiation dose coverage for post‐laryngectomy stoma was analyzed using a set of real‐case CT‐simulation images. After meticulous contouring of the catheter cuff, stoma lumen, peri‐stoma skin and subclinical tumor bed at the larynx, the resulting dosimetry plans were analyzed with or without a 5 mm bolus placement. Wet gauze was used to minimize the effect of any air gap. Four plans were generated: AP superclavicular (SCV) plan with or without bolus, and VMAT plan with or without bolus. A dose of 60Gy in 30 fractions was prescribed at 3 cm depth for AP SCV plan, and to 95% of the PTV volume for VMAT plan.Results:For the conventional AP SCV plan, the peri‐stoma skin dose is sensitive to bolus placement as well as air gap compensation by wetted gauze (V95% of 20.7%, 33.0% and 94.8% for no bolus, bolus without and with air gap compensation, respectively). For stoma lumen, the dose drops off rapidly in depth. The catheter cuff may have certain dose‐buildup effect, but air gap around it and under the bolus placed can pose a more serious problem. The dose distributions of the two VMAT plans are moderately different for peri‐stoma skin (V95% of 95.0% with bolus and air gap compensation, and 82.3% without bolus), but nearly identical for stoma lumen (V95% of 91.5% and 92.0%, respectively). VMAT allows beamlets with different angles of incidence that helped achieve such dose distribution around the stoma even without bolus placement.Conclusion:Overall, the dose coverage around the stoma in the VMAT plan is better than the conventional AP SCV plan. To achieve optimal dose distribution, it is still recommended to place physical bolus and reduce the air gaps.