Effect of Inconsistent Virtual Bolus Thickness On Superficial Dose Distribution
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Purpose: Bolus is used in Radiotherapy to improve dose coverage close to skin. Irregular skin surfaces can cause the intended uniform virtual bolus thickness to be inconsistent with the virtual bolus thickness generated for dose calculation in the treatment planning system (TPS). To correct for this, planners manually edit virtual bolus thickness in TPS to match the intended bolus thickness, otherwise calculated dose in TPS and delivered dose will be different: this is very time consuming and susceptible to error. This study investigated the effect of inconsistent bolus thickness on superficial dose distributions in electron conformal radiotherapy and proposes a solution to this problem.
Methods: Three different kinds of cases were analyzed in this study (chest wall, ear, and cheek). First, plans for all cases were calculated using an inserted 1cm thick virtual bolus, irregular skin surface causes virtual bolus thickness greater than 1cm at certain locations. Plans were recalculated using manually corrected bolus. To evaluate the dose distribution to the skin, a 4 mm thick skin was profiled, and statistical analysis was performed by studying the dosimetric parameters (i.e. mean and maximum dose) of skin.
Results: Bolus thickness inconsistency had an impact on the maximum and mean doses for all three different kinds cases. The effect on the maximum dose is significant for the ear case, the difference is as high as 14.7% between the plans with uncorrected and corrected bolus thicknesses.
Conclusion: This study demonstrated that electron conformal therapy using virtual bolus with inconsistent thickness leads to varying dose distribution, which could result in normal tissue complications or tumor regrowth. Reliable solutions to this problem include scanning the patient with physical bolus present or generate a 3D printed bolus.
Keywords
Taxonomy
TH- External Beam- Electrons: General (most aspects)
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