Exhibit Hall | Forum 7
Purpose: To compare the effect of conformal brass mesh bolus (BMB) to that of 3 mm tissue-equivalent bolus (TEB) on superficial dose when using a pseudo-flash VMAT technique for postmastectomy chest wall radiotherapy (PMRT).
Methods: For PMRT, bolus is commonly used to increase superficial dose. BMB has been shown to be an acceptable alternative to TEB for tangential delivery, but it has not been investigated for VMAT delivery. Treatment plans for three of the common VMAT PMRT beam arrangements used in our clinic were optimized on the CIRS IMRT thorax phantom. Each treatment plan used 7 mm of pseudo-flash for robust delivery. Point measurements with OSLDs and planar measurements with film were used to evaluate the superficial dose under three conditions: no bolus (NB), 3 mm TEB, and BMB.
Results: The superficial dose ranged from 46 - 72% of prescription dose with NB when measured with film. For the three delivery techniques, OSLD measurements yielded an average superficial dose of 98.1 +/- 3.6% of prescription for BMB, while 3 mm TEB averaged 103 +/- 2.0% of prescription. OSLD measurements showed an increase in superficial dose of 22 +/- 2% for BMB and 27 +/- 3% for 3 mm TEB. Film measurements ranged from 77 – 107% for BMB and from 92 - 113% for 3 mm TEB.
Conclusion: BMB provides similar superficial dose enhancement to 3 mm TEB regardless of beam arrangement. BMB has the benefits of being more conformal to the chest wall and not significantly impacting the dose at depth. Therefore, BMB is a suitable alternative to 3 mm TEB for VMAT PMRT that presents multiple advantages while providing a similar enhancement of the superficial dose.