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An iterative convex relaxation method for proton LET optimization.

Wangyao Li1, Yuting Lin1, Harold Li1

  • 1Department of Radiation Oncology, University of Kansas Medical Center, Kansas City, Kansas, KS 66160, United States of America.

Physics in Medicine and Biology
|February 2, 2023
PubMed
Summary
This summary is machine-generated.

Iterative convex relaxation (ICR) optimizes proton radiotherapy by minimizing high linear energy transfer (LET) in normal tissues. This novel method improves biological dose accuracy and treatment planning efficiency compared to traditional approaches.

Keywords:
IMPTLETinverse optimizationproton therapy

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Area of Science:

  • Medical Physics
  • Radiation Oncology
  • Computational Biology

Background:

  • Current proton radiotherapy (RT) clinical practice uses a simplified relative biological effectiveness (RBE) of 1.1, potentially underestimating biological dose to normal tissues near Bragg peaks.
  • High linear energy transfer (LET) in these regions necessitates advanced treatment planning to accurately assess and minimize biological dose.
  • LET optimization is crucial for reducing normal tissue complications but presents significant computational challenges due to its nonlinear and nonconvex nature.

Purpose of the Study:

  • To develop an effective optimization method, Iterative Convex Relaxation (ICR), to address the nonlinear and nonconvex challenges in LET optimization for proton RT.
  • To improve the accuracy of biological dose calculations and minimize potential hot spots in normal tissues.
  • To enhance the efficiency and quality of proton treatment planning.

Main Methods:

  • Developed ICR, a novel optimization method tailored for LET modeling and optimization, contrasting with generic nonlinear methods like Quasi-Newton (QN).
  • ICR iteratively linearizes nonlinear dose-averaged LET terms, transforming the problem into a sequence of convex subproblems.
  • Utilized a 1 cm normal-tissue expansion of the clinical target volume (CTV1cm) to specifically minimize LET in critical regions near the target.

Main Results:

  • ICR demonstrated effectiveness in LET optimization across abdomen, lung, and head-and-neck cases.
  • ICR significantly reduced LET and biological dose within the CTV1cm, while maintaining dose conformity to the CTV.
  • Compared to QN, ICR achieved superior results with lower LET, physical, and biological doses in CTV1cm, higher conformity indices, and was approximately 3 times faster computationally.

Conclusions:

  • A novel LET-specific optimization method, ICR, has been successfully developed for proton RT.
  • ICR offers superior computational efficiency and improved treatment plan quality regarding LET, biological dose, and physical dose conformity compared to generic nonlinear optimizers.
  • This advancement holds significant promise for more precise and safer proton therapy by accurately accounting for biological effectiveness.