Highlights
- •Not applying any pseudo skin flash strategy in VMAT compromises the CTV irradiation.
- •A valid strategy is to optimise the plan using an extended CT with a virtual bolus.
- •A methodology to assign optimal thickness and HU for the virtual bolus is provided.
- •We determined the optimal virtual bolus thickness based on isocenter shifts.
- •We determined the optimal HU value based on minimum changes in plan normalization.
Abstract
Purpose
Optimisation strategies for volumetric modulated arc therapy (VMAT) in most treatment
planning systems for breast cancer do not account for patient positioning, breathing,
or anatomical changes. To overcome this limitation, a pseudo-skin flash strategy using
a virtual bolus has been proposed. Using this strategy, we determined optimal thickness
and value of Hounsfield units (HU) assigned to the virtual bolus to ensure adequate
CTV irradiation.
Materials and methods
We modified the original computed tomography data (CT0) by adding combinations of thicknesses and densities of a virtual bolus on PTVs (CT’)
of seven bilateral breast cancer patients. Using a single optimization objective template,
we obtained a VMAT plan on CT’ and recalculated this on the CT0. Optimal CT’ parameters were defined as those that minimized dose differences between
CT’ and CT0 plans regarding PTV and OAR dose-volume parameters. We studied bolus parameters regarding
robustness by shifting the isocenter 5 and 10 mm in the breathing direction for each
CT0 plan.
Results
The minimal dosimetric impact was between −400 and −600 HU depending on bolus thickness.
OARs doses were not significantly affected. Best robustness was found for −500 HU
and 15 mm bolus thickness against shifts of up to 10 mm in the breathing direction.
Conclusion
Our results support a bolus thickness equal to the CTV-PTV margin plus 5 mm and a
virtual bolus HU value around −500 and −400 depending on the bolus thickness chosen.
These findings could play a useful role in maximising robustness and minimising the need for plan renormalization.
Keywords
To read this article in full you will need to make a payment
Purchase one-time access:
Academic and PersonalCorporate R&D ProfessionalsOne-time access price info
- For academic or personal research use, select 'Academic and Personal'
- For corporate R&D use, select 'Corporate R&D Professionals'
Subscribe:
Subscribe to Physica Medica: European Journal of Medical PhysicsAlready a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
References
- Potential advantages of volumetric arc therapy in head and neck cancer.Head Neck. 2015; 37: 909-914https://doi.org/10.1002/hed.23685
- Volumetric modulated arc therapy: a review of current literature and clinical use in practice.Br J Radiol. 2011; 84: 967-996https://doi.org/10.1259/bjr/22373346
- Clinical utility of RapidArcTM radiotherapy technology.Cancer Manage Res. 2015; 7: 345-356https://doi.org/10.2147/CMAR.S72775
- A dosimetric comparison of 3D-CRT, IMRT, and static tomotherapy with an SIB for large and small breast volumes.Med Dosim. 2014; 39: 163-168https://doi.org/10.1016/j.meddos.2013.12.003
- The feasibility and benefits of using volumetric arc therapy in patients with brain metastases: a systematic review.J Med Radiat Sci. 2014; 61: 267-276https://doi.org/10.1002/jmrs.69
- Critical appraisal of the role of volumetric modulated arc therapy in the radiation therapy management of breast cancer.Radiat Oncol. 2017; 12: 200https://doi.org/10.1186/s13014-017-0935-4
- Simultaneous integrated boost radiotherapy for bilateral breast: a treatment planning and dosimetric comparison for volumetric modulated arc and fixed field intensity modulated therapy.Radiat Oncol. 2009; 4: 27https://doi.org/10.1186/1748-717X-4-27
- Radiation therapy of synchronous bilateral breast carcinoma (SBBC) using multiple techniques.Med Dosim. 2018; 43: 55-68https://doi.org/10.1016/j.meddos.2017.08.003
- Synchronous bilateral breast cancer irradiation: clinical and dosimetrical issues using volumetric modulated arc therapy and simultaneous integrated boost.Radiol Medica. 2017; 122: 464-471https://doi.org/10.1007/s11547-017-0741-y
- Second cancer risk after 3D-CRT, IMRT and VMAT for breast cancer.Radiother Oncol. 2014; 110: 471-476https://doi.org/10.1016/j.radonc.2013.12.002
- VMAT radiation-induced nausea and vomiting in adjuvant breast cancer radiotherapy: the incidental effect of low-dose bath exposure.Clin Transl Radiat Oncol. 2017; 7: 43-48https://doi.org/10.1016/j.ctro.2017.09.009
- The delivery of intensity modulated radiotherapy to the breast using multiple static fields.Radiother Oncol. 2000; 57: 79-89https://doi.org/10.1016/s0167-8140(00)00263-2
- Intensity modulation to improve dose uniformity with tangential breast radiotherapy: initial clinical experience.Int J Radiat Oncol Biol Phys. 2000; 48: 1559-1568https://doi.org/10.1016/s0360-3016(00)01396-1
- Intensity-modulated tangential beam irradiation of the intact breast.Int J Radiat Oncol Biol Phys. 1999; 44: 1155-1164https://doi.org/10.1016/S0360-3016(99)00132-7
ICRU Report 83. Prescribing, Recording, and Reporting Photon-Beam Intensity-Modulated Radiation Therapy (IMRT). J ICRU 2010; 10: 1–106. doi:10.1179/rmt.2003.14.1.5.
- Dosimetric effects of anatomical deformations and positioning errors in VMAT breast radiotherapy.J Appl Clin Med Phys. 2018; 19: 506-516https://doi.org/10.1002/acm2.12409
- Planning strategies in volumetric modulated arc therapy for breast.Med Phys. 2011; 38: 4025-4031https://doi.org/10.1118/1.3598442
- Tangential volumetric modulated arc therapy technique for left-sided breast cancer radiotherapy.Radiat Oncol. 2015; https://doi.org/10.1186/s13014-015-0392-x
- An assessment of the use of skin flashes in helical tomotherapy using phantom and in-vivo dosimetry.Radiother Oncol. 2007; 84: 34-39https://doi.org/10.1016/j.radonc.2007.06.003
- Safety and benefit of using a virtual bolus during treatment planning for breast cancer treated with arc therapy.J Appl Clin Med Phys. 2018; 19: 463-472https://doi.org/10.1002/acm2.12398
White J, Tai A, Arthur D, Buchholz T, Macdonald S, Marks L, et al. Breast Cancer Atlas for Radiation Therapy Planning: Consensus Definitions n.d. https://www.rtog.org/LinkClick.aspx?fileticket=SQhssxHu7Jg%3D&tabid=227 (accessed January 7, 2019).
RStudio Team. RStudio: integrated development environment for R. (Version 1.1.463). Boston, MA 2015. https://www.rstudio.com/ (accessed January 7, 2019).
Article Info
Publication History
Published online: May 29, 2019
Accepted:
May 18,
2019
Received in revised form:
April 15,
2019
Received:
February 7,
2019
Identification
Copyright
© 2019 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
