Abstract
Purpose
Nasopharyngeal brachytherapy is limited in part by the radiotolerance of nearby organs
like the soft palate. This study explores several novel shielding designs for an intracavitary
applicator to significantly reduce soft palate dose while adhering to the constraints
of standard treatment procedure.
Methods
The Monte Carlo code TOPAS is used to characterize each prototype under typical high-dose-rate
treatment conditions. Mucosal surface dose maps are collected to evaluate the shields
on their dose reduction to the central and soft palate planning points and uniformity
in their shielding profile. Practicality with respect to patient comfort and pretreatment
imaging is discussed. History-by-history standard deviations are calculated for each
simulation.
Results
A design with elliptical tubing containing bundles of tantalum wires provides the
most significant attenuation with 39% and 27% dose reduction to the center and soft
palate locations, respectively. Another design utilizing miniature lead spheres loaded
into a constructed cavity shows 27% and 24% dose reduction to the same locations while
providing more uniform shielding and several practical benefits. Both shields are
designed to be completely removable for applicator insertion and pretreatment imaging.
The mean and maximum standard error of relative dose measurements was 0.36 and 1.14
percentage points, respectively.
Conclusion
Each shielding design presented in this study provides a novel approach to safely
and effectively shield healthy tissue during intracavitary nasopharyngeal brachytherapy.
Analysis performed using Monte Carlo suggests that the design using metal spheres
most practically shields the soft palate and should be advanced to the next stages
of clinical optimization.
Keywords
To read this article in full you will need to make a payment
Purchase one-time access:
Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online accessOne-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 BrachytherapyAlready a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
References
- Managing nasopharyngeal carcinoma with intracavitary brachytherapy: one institution's 45-year experience.Brachytherapy. 2002; 1: 74-82https://doi.org/10.1016/s1538-4721(02)00013-2
- A new applicator design for endocavitary brachytherapy of cancer in the nasopharynx.Radiother Oncol. 1997; 45 (PMID: 9364638): 95-98https://doi.org/10.1016/s0167-8140(97)00105-9
- High dose rate brachytherapy for cancer of the head and neck.in: Nag S High dose rate brachytherapy: a textbook. Futura Publishing Co., Armonk, NY1994: 237-273
- A novel applicator design for intracavitary brachytherapy of the nasopharynx: simulated reconstruction, image-guided adaptive brachytherapy planning, and dosimetry.Brachytherapy. 2018; 17 (Epub 2018 May 11. PMID: 29759328): 709-717https://doi.org/10.1016/j.brachy.2018.03.004
- Analysis of 80 cases of nasopharyngeal carcinoma treated by intracavitary brachytherapy using a new-type applicator.Chin J Clin Oncol. 2007; 4: 52-55https://doi.org/10.1007/s11805-007-0052-5
- TOPAS: an innovative proton Monte Carlo platform for research and clinical applications.Med Phys. 2012; 39: 6818https://doi.org/10.1118/1.4758060
Faddegon B, Ramos-Mendez J, Schuemann J, McNamara A, Shin J, Perl J, Paganetti H, The TOPAS Tool for Particle Simulation, a Monte Carlo Simulation Tool for Physics, Biology and Clinical Research, Physica Medica, doi:10.1016/j.ejmp.2020.03.019.
- Variations in proton scanned beam dose delivery due to uncertainties in magnetic beam steering.Med Phys. 2009; 36: 3693-3702https://doi.org/10.1118/1.3175796
- Accurate Monte Carlo simulations for nozzle design, commissioning and quality assurance for a proton radiation therapy facility.Med Phys. 2004; 31: 2107-2118https://doi.org/10.1118/1.1762792
- Plastic scintillation dosimetry: optimal selection of scintillating fibers and scintillators.Med Phys. 2005; 32: 2271-2278https://doi.org/10.1118/1.1943807
- Dosimetric characterization of a novel intracavitary mold applicator for 192Ir high dose rate endorectal brachytherapy treatment.Med Phys. 2006; 33: 4515-4526https://doi.org/10.1118/1.2364054
Francisco Berumen, Yunzhi Ma, Jose Ramos-Mendez, Joseph Perl, Luc Beaulieu. “Validation of the TOPAS Monte Carlo toolkit for HDR brachytherapy simulations.” Brachytherapy (in press). doi:10.1016/j.brachy.2020.12.007.
- Gamma ray attenuation properties of common shielding materials.PG Research Foundation, 2018 (Available at: https://www.eichrom.com/wp-content/uploads/2018/01/gamma-ray-attenuation-white-paper-by-d.m.-rev-4.pdf, last accessed on June 30, 2021)
- Comparative study of the effect of impurities on the ductility of tantalum and tungsten based on atomistic and first principles calculations.The University of North Carolina at Charlotte, Charlotte, NC2012
- PubChem Compound Summary for CID 23956.Tantalum. 2021; (Available at:) (Accessed February 16, 2021)
- Mitigating the Effects of the Space Radiation Environment: a novel approach of using graded-Z materials.in: AIAA SPACE 2013 conference and exposition. 2013https://doi.org/10.2514/6.2013-5385
- Ir-192 Hdr sources.in: 2019 (, last accessed on June 30, 2021)
Gafchromic. 2019. “Gafchromic dosimetry media, type Ebt-3.” Available at: http://www.gafchromic.com/documents/EBT3_Specifications.pdf, last accessed on June 30, 2021.
AbuAlRoos N.J., Azman M.N., Amin N.A.B., Zainon R., Tungsten-based material as promising new lead-free gamma radiation shielding material in nuclear medicine, Physical Medica, doi:10.1016/j.ejmp.2020.08.017.
Article info
Publication history
Published online: January 20, 2022
Accepted:
December 20,
2021
Received in revised form:
December 18,
2021
Received:
July 16,
2021
Footnotes
Disclosure: This work was partially funded from a scholarship by the American Association of Physicists in Medicine (AAPM) Summer Undergraduate Fellowship Program. One author reports grants from National Sciences and Engineering Council of Canada (NSERC) Grant Numbers: IRCPJ 491776-15 and RGPIN-2019-05038, during the conduct of the study.
✰Research data are stored in an institutional repository and will be shared upon request to the corresponding author.
Identification
Copyright
© 2021 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.
