Machine characterization and central axis depth dose data of a superficial x-ray radiotherapy unit

Zhenyu Xiong, Yuncheng Zhong, Thomas I. Banks, Robert Ray Reynolds Jr., Tsuicheng Chiu, Jun Tan, You Zhang, David D Parsons, Yulong Yan, Andrew Godley, Strahinja Stojadinovic

Research output: Contribution to journalArticlepeer-review


Objectives. The purpose of this study is to present data from the clinical commissioning of an Xstrahl 150 x-ray unit used for superficial radiotherapy, Methods. Commissioning tasks included vendor acceptance tests, timer reproducibility, linearity and end-effect measurements, half-value layer (HVL) measurements, inverse square law verification, head-leakage measurements, and beam output calibration. In addition, percent depth dose (PDD) curves were determined for different combinations of filter/kV settings and applicators. Automated PDD water phantom scans were performed utilizing four contemporary detectors: a microDiamond detector, a microSilicon detector, an EDGE detector, and a PinPoint ionization chamber. The measured PDD data were compared to the published values in BJR Supplement 25, Results. The x-ray unit’s mechanical, safety, and radiation characteristics were within vendor-stated specifications. Across sixty commissioned x-ray beams, the PDDs determined in water using solid state detectors were in excellent agreement with the BJR 25 data. For the lower (<100 kVp) and medium-energy (≥100 kVp) superficial beams the average agreement was within [−3.6,+0.4]% and [−3.7,+1.4]% range, respectively. For the high-energy superficial (low-energy orthovoltage) x-rays at 150 kVp, the average difference for the largest 20 × 20 cm2 collimator was (−0.7 ± 1.0)%, Conclusions. This study presents machine characterization data collected for clinical use of a superficial x-ray unit. Special focus was placed on utilizing contemporary detectors and techniques for the relative PDD measurements using a motorized water phantom. The results in this study confirm that the aggregate values published in the BJR 25 report still serve as a valid benchmark when comparing data from site-specific measurements, or the reference data for clinical utilization without such measurements, Advances in knowledge. This paper presents comprehensive data from the acceptance and commissioning of a modern kilovoltage superficial x-ray radiotherapy machine. Comparisons between the PDD data measured in this study using different detectors and BJR 25 data are highlighted.

Original languageEnglish (US)
Article number015005
JournalBiomedical Physics and Engineering Express
Issue number1
StatePublished - Jan 2023


  • commissioning of superficial radiotherapy unit
  • kV percent depth dose
  • superficial radiotherapy

ASJC Scopus subject areas

  • Biophysics
  • Bioengineering
  • Biomaterials
  • Physiology
  • Biomedical Engineering
  • Radiology Nuclear Medicine and imaging
  • Computer Science Applications
  • Health Informatics


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