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. 2023 Sep;24(9):e14054.
doi: 10.1002/acm2.14054. Epub 2023 Jun 7.

Comparing brass mesh to tissue equivalent bolus materials for volumetric modulated arc therapy chest wall irradiation

Timothy D Keiper  1   2 , Kelly Kisling  1 , Patricia Hua  1 , Ryan P Manger  1
Affiliations

Comparing brass mesh to tissue equivalent bolus materials for volumetric modulated arc therapy chest wall irradiation

Timothy D Keiper et al. J Appl Clin Med Phys. 2023 Sep.

Abstract

Purpose: To compare the superficial dose when using brass mesh bolus (BMB), no bolus, or 3 mm tissue-equivalent bolus with a pseudo-flash volumetric modulated arc therapy (VMAT) breast treatment planning technique.

Methods: Two different beam arrangements for right-sided irradiation and one beam arrangement for bilateral irradiation were planned on an inhomogeneous thorax phantom in accordance with our clinical practice for VMAT postmastectomy radiotherapy (PMRT). Plans were optimized using pseudo-flash and representative critical organ optimization structures were used to shape the dose. Plans were delivered without bolus, with 3 mm tissue-equivalent bolus (TEB), or with one-layer BMB. Optically stimulated luminescence dosimeter (OSLD) and radiochromic film measurements were taken and analyzed to determine the superficial dose in each case and the relative enhancement from the no bolus delivery.

Results: Superficial dose measured with OSLDs was found to be 76.4 ± 4.5%, 103.0 ± 6.1%, and 98.1 ± 5.8% of prescription for no physical bolus (NB), TEB, and BMB, respectively. Superficial dose was observed to increase from lateral to medial points when measured with film. However, the relative increase in superficial dose from NB was consistent across the profile with an increase of 43 ± 2.1% and 34 ± 3.3% of prescription for TEB and BMB, respectively. The results are in good agreement with expectations from the literature and the experience with tangential radiotherapy.

Conclusion: Three millimeter TEB and one-layer BMB were shown to provide similar enhancement to the superficial dose compared to delivery without bolus. BMB, which does not significantly affect dose at depth and is more conformal to the patient surface, is an acceptable alternative to 3 mm TEB for chest wall PMRT patients treated with pseudo-flash PMRT.

Keywords: VMAT breast; brass bolus; brass mesh.

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Conflict of interest statement

This investigation was reported at the 2022 AAPM Annual Meeting. Authors have no COI to declare.

Figures

FIGURE 1
FIGURE 1
VMAT planning process showing (A, D, G) the arc angles and control points, (B, E, H) the structure delineation used in optimization, and (C, F, I) the dose color wash to the 70% coverage level showing clinically acceptable organ sparing and dose conformality for (top) Plan A, (middle) Plan B, and (bottom) Plan C arrangements.
FIGURE 2
FIGURE 2
Phantom setup for delivery and measurement. (A) Phantom aligned to BBs before IGRT. (B) Phantom aligned after applying IGRT (CBCT) shifts for the bilateral case with OSLDs placed on either side of isocenter. (C) Film measurement placement for Plan C. (D) 3 mm TEB placed on the phantom for irradiation. (E) BMB placed on the phantom for irradiation. (F) OSLD Placement for unilateral measurements. (G) Film placement after irradiation of unilateral setup.
FIGURE 3
FIGURE 3
Film (line) and OSLD (markers) dosimetry for the three plan delivery types for each bolus option. (A) Plan A, (B) Plan B, and (C) Plan C deliveries show similar trends and good agreement between OSLD and film measurements.
See this image and copyright information in PMC

References

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