An evaluation of ankle and foot bolus in paediatric modulated arc total body irradiation (MATBI)

Introduction

This retrospective planning study aimed to evaluate the role of bolus in achieving dose uniformity in the ankles and feet in paediatric patients undergoing Modulated Arc Total Body Irradiation (MATBI) treatment and to identify patient factors that may negate or warrant its use.

Methods

The clinically treated plans of 20 paediatric patients who received MATBI treatment utilising ankle and foot bolus (Bolus plan) were compared with two retrospectively generated plans; a plan with bolus removed and no re-optimisation (No Bolus plan), and a re-optimised plan without bolus attempting to achieve equal dosimetry to the clinical plan via monitor unit adjustment (MU plan). Descriptive statistics were used to evaluate the dose uniformity criteria of ±10% coverage of the reference dose (RD) for each subregion of the ankle and foot for the three plans. The impact of patient height, weight, and age at the time of treatment was evaluated using Spearman's correlation.

Results

Variation in doses >10% RD was minimal across the three plans, with an average D1cc difference < 0.4Gy. For the ankle and foot regions in the Bolus plans, the volume receiving at least 90% of the RD (V90) was on average > 92%. In No Bolus and MU plans, there was an average reduction of 24.5% and 23.2% V90 coverage respectively in the toes. Spearman's correlation suggests height has the strongest relationship to D1cc.

Conclusion

This study validated the continued use of ankle and foot bolus to achieve dosimetric goals for paediatric MATBI treatments, particularly V90 coverage across all heights.