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A method for generating intensity-modulated radiation therapy fields for small animal irradiators utilizing 3D-printed compensator molds.

Publication ,  Journal Article
Yoon, SW; Kodra, J; Miles, DA; Kirsch, DG; Oldham, M
Published in: Med Phys
September 2020

PURPOSE: The purpose of this study was to investigate the feasibility of using fused deposition modeling (FDM) three-dimensional (3D) printer to generate radiation compensators for high-resolution (~1 mm) intensity-modulated radiation therapy (IMRT) for small animal radiation treatment. We propose a novel method incorporating 3D-printed compensator molds filled with NaI powder. METHODS: The inverse planning module of the computational environment for radiotherapy research (CERR) software was adapted to simulate the XRAD-225Cx irradiator, both geometry and kV beam quality (the latter using a phase space file provided for XRAD-225Cx). A nine-field IMRT treatment was created for a scaled-down version of the imaging and radiation oncology core (IROC) Head and Neck IMRT credentialing test, recreated on a 2.2-cm-diameter cylindrical phantom. Optimized fluence maps comprising nine fields and a total of 2564 beamlets were calculated at resolution of 1.25 × 1.25 mm2 . A hollow compensator mold was created (using in-house software and algorithm) for each field using 3D printing with polylactic acid (PLA) filaments. The molds were then packed with sodium iodide powder (NaI, measured density ρNaI  = 2.062 g/cm3 ). The mounted compensator mold thickness was limited to 13.8 mm due to clearance issues with couch collision. At treatment delivery, each compensator was manually mounted to a customized block tray attached to the reference 40 × 40 mm2 collimator. Compensator reproducibility among three repeated 3D-printed molds was measured with Radiochromic EBT2 film. The two-dimensional (2D) dose distributions of the nine fields were compared to calculated 2D doses from CERR using gamma comparisons with distance-to-agreement criteria of 0.5-0.25 mm and dose difference criteria of 3-5%. RESULTS: Good reproducibility of 3D-printed compensator manufacture was observed with mean error of ±0.024 Gy and relative dose error of ±4.2% within the modulated part of the beam. Within the limit of 13.8 mm compensator height, a maximum radiation blocking efficiency of 91.5% was achieved. Per field, about 45.5 g of NaI powder was used. Gamma analysis on each of the nine delivered IMRT fields using radiochromic films resulted in eight of nine treatment fields with >90% pass rate with 5%/0.5 mm tolerances. However, low gamma passing rate of 49-66% (3%/0.25 mm to 5%/0.5 mm) was noted in one field, attributed to fabrication errors resulting in over-filling the mold. The nine-field treatment plan was delivered in under 30 min with no mechanical or collisional issues. CONCLUSIONS: We show the feasibility of high spatial resolution IMRT treatment on a small animal irradiator utilizing 3D-printed compensator shells packed with NaI powder. Using the PLA mold with NaI powder was attractive due to the ease of 3D printing a PLA mold at high geometric resolution and the well-balanced attenuation properties of NaI powders that prevented the mold from becoming too bulky. IMRT fields with 1.25-mm resolution are capable with significant fluence modulation with relative dose accuracy of ±4.2%.

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Published In

Med Phys

DOI

EISSN

2473-4209

Publication Date

September 2020

Volume

47

Issue

9

Start / End Page

4363 / 4371

Location

United States

Related Subject Headings

  • Reproducibility of Results
  • Radiotherapy, Intensity-Modulated
  • Radiotherapy Planning, Computer-Assisted
  • Radiotherapy Dosage
  • Radiometry
  • Printing, Three-Dimensional
  • Nuclear Medicine & Medical Imaging
  • Animals
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
 

Citation

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MLA
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Yoon, S. W., Kodra, J., Miles, D. A., Kirsch, D. G., & Oldham, M. (2020). A method for generating intensity-modulated radiation therapy fields for small animal irradiators utilizing 3D-printed compensator molds. Med Phys, 47(9), 4363–4371. https://doi.org/10.1002/mp.14175
Yoon, Suk W., Jacob Kodra, Devin A. Miles, David G. Kirsch, and Mark Oldham. “A method for generating intensity-modulated radiation therapy fields for small animal irradiators utilizing 3D-printed compensator molds.Med Phys 47, no. 9 (September 2020): 4363–71. https://doi.org/10.1002/mp.14175.
Yoon, Suk W., et al. “A method for generating intensity-modulated radiation therapy fields for small animal irradiators utilizing 3D-printed compensator molds.Med Phys, vol. 47, no. 9, Sept. 2020, pp. 4363–71. Pubmed, doi:10.1002/mp.14175.

Published In

Med Phys

DOI

EISSN

2473-4209

Publication Date

September 2020

Volume

47

Issue

9

Start / End Page

4363 / 4371

Location

United States

Related Subject Headings

  • Reproducibility of Results
  • Radiotherapy, Intensity-Modulated
  • Radiotherapy Planning, Computer-Assisted
  • Radiotherapy Dosage
  • Radiometry
  • Printing, Three-Dimensional
  • Nuclear Medicine & Medical Imaging
  • Animals
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering