Mitigating dosimetric perturbations from large metal implants utilizing spot-scanning proton arc therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Conventional intensity modulated proton therapy (IMPT) is sensitive to setup and range uncertainties, particularly with high-density metal implants.
• Metal artifacts significantly challenge the precision of proton therapy delivery near implants.

Purpose of the Study:

• To introduce and evaluate a novel spot-scanning proton arc (SPArc) approach for proton therapy in the presence of metal implants.
• To improve nominal plan quality, target coverage, homogeneity, and robustness compared to conventional IMPT.

Main Methods:

• Generated 4-field IMPT and single-arc SPArc plans for 5 patients with metal implants near target volumes.
• Utilized robust optimization with ± 3.5% range and ± 3/5 mm setup uncertainties.
• Assessed plan quality using dose-volume histograms (DVHs), target coverage, hotspot metrics, homogeneity indices, and robustness quantification.

Main Results:

• SPArc significantly improved target coverage and reduced hotspots (V105%) compared to IMPT.
• SPArc plans demonstrated superior homogeneity (e.g., reduced standard deviation, interquartile range, homogeneity index) and robustness to uncertainties.
• SPArc achieved greater generalized equivalent uniform dose (gEUD) and favorable DVH profiles, indicating better dose distribution.

Conclusions:

• SPArc therapy offers a novel and effective solution for challenging clinical scenarios involving metal artifacts in proton therapy.
• The SPArc approach significantly enhances homogeneity, robustness, and target coverage compared to conventional IMPT near metal implants.