Abstract
This study provides the authors' experience along with dosimetric data from the commissioning of two Sensus SRT‐100 50‐100 kV X‐ray units. Data collected during the commissioning process included: a) HVL, b) output (dose rate), c) applicator cone factors, and d) percentage depth dose. A Farmer‐type chamber (PTW‐N23333), and a thin‐window parallel plate ion chamber (PTW‐N23342) were used for dose rate measurements and dose profiles were measured with EBT3 GafChromic film. The average HVL values for 50, 70, and 100 kV of the two treatment units were found to be 0.52, 1.15, and 2.20 mm Al, respectively. The HVL's were 5%–9% lower when measured with the Farmer chamber, as compared to measurements with the parallel plate chamber, for energies of 70 and 100 kV. Dose rates were also measured to be 3%–4% lower with the Farmer chamber. The dose rate variation between the two units was found to be 2%–9% for 50, 70, and 100 kV. The dose uniformity over a circle of 2 cm diameter was within 4% in four cardinal directions; however, the dose profiles for the 5 cm applicator were nonuniform, especially in the cathode–anode direction. Measurements indicated as much as 15% lower dose for the 50 kV beam at field edge on the anode side, when normalized to the center. The crossline profile was relatively more symmetric, with a maximum deviation of 10% at the field edge. All ion chamber readings agreed with film measurements within 3%. The nonuniform profile produced by these units may introduce uncertainty in dose rate measurements, especially for larger applicators. Since there is no intrinsic tool (crosshair or field light) for alignment with the beam axis, the user should take care when positioning the chamber for output measurements. The data obtained with a Farmer‐type chamber should be used cautiously and as a reference only for the SRT‐100 X‐ray treatment unit.PACS number: 87.53.Bn
Highlights
162 Sheu et al.: Commissioning a kV skin treatment unit radiation oncology department expands the lineup of treatment modalities and, for many cases, gives more suitable treatments
To commission the SRT-100 skin treatment machine, we followed the protocol for 40-300 kV X-ray beam dosimetry, AAPM Task Group 61.(4) TG-61 describes the details of reference dosimetry for low-energy X-rays
The values measured by the Farmer chamber were 3%–4% lower than those measured by the parallel plate chamber
Summary
To commission the SRT-100 skin treatment machine, we followed the protocol for 40-300 kV X-ray beam dosimetry, AAPM Task Group 61.(4) TG-61 describes the details of reference dosimetry for low-energy X-rays. A study by Rong and Welsh[5] can serve as a practical source of useful information and detailed procedures for the calibration and commissioning of low energy X-ray skin treatment machines. Devising an appropriate commissioning procedure for a superficial treatment unit is important as the accuracy of measurements are dependent on several factors, such as chamber calibration factor, chamber position, and target to surface distance. Uncertainties in dose rate measurement can be large at low kilovoltage energies. The accuracy of ion chamber positioning will affect dose calibration due to non uniformities across the field. The lack of a tool for alignment or reproducible positioning of the chamber for output measurements compounds this difficulty
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
