Correlation Engine 2.0
Clear Search sequence regions

  • d c (2)
  • dmax (1)
  • phantoms imaging (1)
  • phenylpropionates (2)
  • ssd (1)
  • tg 51 (6)
  • Sizes of these terms reflect their relevance to your search.

    Methods for accurate absolute dose (AD) calibration are essential for the proper functioning of radiotherapy treatment machines. Many systems do not conform to TG-51 calibration standards, and modifications are required. TG-21 calibration is also a viable methodology for these situations with the appropriate setup, equipment, and factors. It has been shown that both these methods result in minimal errors. A similar approach has been taken in calibrating the dose for a recent vault-free radiosurgery system. To evaluate modified TG-21 and TG-51 protocols for AD calibrations of the ZAP-X radiosurgery system using ion chambers, film, and thermoluminescent dosimeters (TLDs). The current treatment planning system for ZAP-X requires AD calibration at dmax (7 mm) and 450 mm source-to-axis distance. Both N D , w 60 C o [ G y / C ] $N_{D,w}^{{60}Co}[ {Gy/C} ]$ and Nx [R/C] calibration coefficients were provided by an accredited dosimetry calibration laboratory for a physikalisch technische werkstatten (PTW) 31010 chamber (0.125 cc). The vendor provides an f-bracket that can be mounted on the collimator. Various phantoms can then be attached to the f-bracket. A custom acrylic phantom was designed based on recommendations from TG-21 and technical report series-398 that places the chamber at 500 mm from the source with a depth of 44-mm acrylic and 456-mm SSD. Nx along with other TG-21 parameters was used to calculate the AD. Measurements using a PTW MP3-XS water tank and the same chamber were used to calculate AD using N D , w 60 C o $N_{D,w}^{{60}Co}$ and TG-51 factors. Dose verification was performed using Gafchromic film and 3rd party TLDs. Measurements from TG-51, TG-21 (utilizing the custom acrylic phantom), film, and TLDs agreed to within ± 2%. A modified TG-51 AD calculation in water is preferred but may not be practical due to the difficulty in tank setup. The TG-21 modified protocol using a custom acrylic phantom is an accurate alternative option for dose calibration. Both of these methods are within acceptable agreement and provide confidence in the system's AD calibration. © 2022 American Association of Physicists in Medicine.


    Stephen P Sorensen, Shyam S Jani, Dilini S Pinnaduwage, Xiangsheng Yan, Shiv P Srivastava. Technical note: Absolute dose measurements of a vault-free radiosurgery system. Medical physics. 2022 Dec;49(12):7733-7741

    Expand section icon Mesh Tags

    Expand section icon Substances

    PMID: 35964159

    View Full Text