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Usefulness of Vaginal/Rectal Cylinders or Interstitial Needles for Dosimetric Verification and Uncertainty Analysis of Brachytherapy Treatment



The point doses for HDR treatment using vaginal/rectal cylinders or interstitial needles are verified by comparing the results for the planned dose, manual calculations using TG-43 and the actual measurements from radiochromic film. The dosimetric uncertainty associated with the calibration of the source strength, the treatment plan and the reconstructed seed-positions are analyzed.

Materials and Methods

An interstitial implant tube was placed on a 30 × 30 × 5 cm3 polystyrene phantom and above them were placed a 1 cm thick 30 × 30 cm2 bolus, then a 1 cm thick 30 × 30 cm2 RW3 plate, an EBT2 film, and one other 30 × 30 × 5 cm3 polystyrene phantom. The source seed was arranged to stop at nine positions, 0.5 cm apart. Prescribed 3 Gy was planned to be delivered to the prescription points, which were 2 cm away from the seeds. After delivery, the film dose was compared with the planned dose and a manual calculation using TG-43. Finally, the combined dosimetric uncertainty was determined by manual calculation using the uncertainty for the reconstructed seed position and the propagation uncertainty determined by TG-138/GEC-ESTRO.


The results agree to within 3%. Due to the uncertainty in the seed-position reconstruction, the difference in doses is determined to be mostly around 5% from manual calculation using TG-43. All combined dosimetric uncertainties with the cover factor of two are less than 9.5%, satisfying the criteria for TG-56.


This method is practical for routine QA to verify the dose for a HDR treatment plan with uncertainty analysis.

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This work was supported by the Ministry of Science and Technology of Taiwan (MOST 105-2221-E-214-013 and MOST 108-2221-E-214-006).

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Correspondence to Pang-Yu Chen or Hueisch-Jy Ding.

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Chang, L., Ho, SY., Lee, TF. et al. Usefulness of Vaginal/Rectal Cylinders or Interstitial Needles for Dosimetric Verification and Uncertainty Analysis of Brachytherapy Treatment. J. Med. Biol. Eng. (2021).

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  • Brachytherapy
  • TG-43
  • TG-138
  • Dosimetric verification; uncertainty