Highlights
- •Bolus material is required for superficial dose delivery with MV radiation therapy.
- •Conventional bolus can be inadequate for irregular surfaces in the head & neck region.
- •Non-rigid translucent 3-dimensional printed bolus (3DB) improves surface conformity.
- •3DB has more uniform material properties than conventional bolus.
- •3DB provides accurate surface dose, verified by MOSFET, in clinical patients.
Abstract
Purpose
Megavoltage radiotherapy to irregular superficial targets is challenging due to the
skin sparing effect. We developed a three-dimensional bolus (3DB) program to assess
the clinical impact on dosimetric and patient outcomes.
Materials and Methods
Planar commercial bolus (PCB) and 3DB density, clarity, and net bolus effect were
rigorously evaluated prior to clinical implementation. After IRB approval, patients
with cutaneous or locally advanced malignancies deemed to require bolus for radiotherapy
treatment were treated with custom 3DB.
Results
The mean density of 3DB and PCB was of 1.07 g/cm 3 and 1.12 g/cm3, respectively. 3DB
optic clarity was superior versus PCB at any material thickness. Phantom measurements
of superficial dose with 3DB and PCB showed excellent bolus effect for both materials.
3DB reduced air gaps compared with PCB - particularly in irregular areas such as the
ear, nose, and orbit. A dosimetric comparison of 3DB and PCB plans showed equivalent
superficial homogeneity for 3DB and PCB (3DB median HI 1.249, range 1.111–1.300 and
PCB median HI 1.165, range 1.094–1.279), but better conformity with 3DB (3DB median
CI 0.993, range 0.962–0.993) versus PCB (PCB median CI 0.977, range 0.601–0.991).
Patient dose measurements using 3DB confirm the delivered superficial dose was within
1% of the intended prescription (95% CI 97–102%; P = 0.11).
Conclusions
3DB improves radiotherapy plan conformity, reduces air gap volume in irregular superficial
areas which could affect superficial dose delivery, and provides excellent dose coverage
to irregular superficial targets.
Keywords
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Article info
Publication history
Published online: August 20, 2020
Accepted:
August 9,
2020
Received in revised form:
August 6,
2020
Received:
February 24,
2020
Identification
Copyright
© 2020 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
