AI Article Synopsis

  • The Elekta Unity MR linac's limitations in couch motion and laser positioning make it challenging to perform patient-specific quality assurance (PSQA) for lateral targets in intensity-modulated radiotherapy (IMRT).
  • This study presents a method using the Sun Nuclear ArcCheck-MR phantom, allowing PSQA at lateral positions without requiring extra equipment or construction.
  • The proposed method showed high gamma pass rates over 94% for patient plans, enhancing measurement flexibility for offset targets, especially when the planning target volume (PTV) edge is further from the isocenter than the diagonal array's radius.

Article Abstract

The Elekta Unity magnetic resonance (MR) linac is limited to longitudinal couch motion and a sagittal-only laser, which restricts the ability to perform patient-specific quality assurance (PSQA) intensity-modulated radiotherapy (IMRT) measurements for very lateral targets. This work introduces a simple method to perform PSQA using the Sun Nuclear ArcCheck-MR phantom at left and right lateral positions without additional equipment or in-house construction. The proposed setup places the center of the phantom 1.3 cm vertical and 12.9 cm lateral to isocenter in either the left or right direction. Computed tomography (CT) scans are used to simulate the setup and create a QA plan template in the Monaco treatment planning system (TPS). The workflow is demonstrated for four patients, with an average axial distance from the center of the bore to the planning target volume (PTV) of 12.4 cm. Gamma pass rates were above 94% for all plans using global 3%/2 mm gamma criterion with a 10% threshold. Setup uncertainties are slightly larger for the proposed lateral setup compared to the centered setup on the Elekta platform (∼1 mm compared to ∼0.5 mm), but acceptable pass rates are achievable without optimizing shifts in the gamma analysis software. In general, adding the left and right lateral positions increases the axial area in the bore encompassed by the cylindrical measurement array by 147%, substantially increasing the flexibility of measurements for offset targets. Based on this work, we propose using the lateral QA setup if the closest distance to the PTV edge from isocenter is larger than the array radius (10.5 cm) or the percent of the PTV encompassed by the diode array would be increased with the lateral setup compared to the centered setup.

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Source
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC11005970PMC
http://dx.doi.org/10.1002/acm2.14323DOI Listing

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