The influence of lack of reference conditions on dosimetry in pre-clinical radiotherapy with medium energy x-ray beams

Subiel, Anna; Patallo, Ileana Silvestre; Barry, M; Tulk, Amanda; Soultanidis, Georgios; Greenman, John; Green, Victoria L.; Cawthorne, Christopher; Schettino, Giuseppe

doi:10.1088/1361-6560/ab7b30

Cited by 10 publications

(17 citation statements)

References 29 publications

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“…For accurate kV dosimetry, in-air air-kerma calibration as specified by TG-61 15 or IAEA TRS 398 27 is recommended. Corrections considering the field size, depth, and backscatter material thickness have been developed 11,12 based on in-air air-kerma. Therefore, while it is possible to develop correction factors off the vendor-defined calibration condition, it is ideal for the vendor to follow commonly adopted calibration protocols using in-air airkerma.…”

Section: Discussionmentioning

confidence: 99%

“…The “delivered dose” displayed on the preclinical irradiator’s touchscreen simply reflects the quantity of radiation fluence delivered (which can be viewed similarly as a monitor unit (MU) in radiation therapy) independent of field size, shelf height, sample size or shape, etc. However, the dose deposited to the point of interest depends on field size, depth, and backscatter material thickness 11,12 . For a typical cell irradiation experiment with only shelf providing backscatter, the dose deposited can drop by 10% as field size change from 20 × 20 cm 2 to 1 × 1 cm 2 11 .…”

Section: Discussionmentioning

confidence: 99%

“…However, the dose deposited to the point of interest depends on field size, depth, and backscatter material thickness. 11,12 For a typical cell irradiation experiment with only shelf providing backscatter, the dose deposited can drop by 10% as field size change from 20 × 20 cm 2 to 1 × 1 cm 2 . 11 Increasing supporting material by 1-cm thickness can also bring more than 10% increase in deposited dose at 20 × 20 cm 2 field size.…”

Section: Discussionmentioning

confidence: 99%

“…As a result, dose calculation in the region of interest can vary significantly depending on the radiation field sizes and the material located downstream from the dose point. 11,12 Additionally, dosimeters such as clinically used ionization chambers require energy-specific recalibration due to their energy-dependent response. Even with the help of a clinical physicist, it is still challenging to achieve accurate kV dosimetry as most clinical physicists may not have the proper training for the specific type of equipment or the appropriately calibrated measurement equipment required for the task.…”

Section: Introductionmentioning

confidence: 99%

“…In the orthovoltage energy range, backscatter photons have a more dominant contribution to radiation dose calculation, compared to those in megavoltage energies where the scattered photons are more forward‐peaked. As a result, dose calculation in the region of interest can vary significantly depending on the radiation field sizes and the material located downstream from the dose point 11,12 . Additionally, dosimeters such as clinically used ionization chambers require energy‐specific recalibration due to their energy‐dependent response.…”

Section: Introductionmentioning

confidence: 99%

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Technical Note: Vendor miscalibration of preclinical orthovoltage irradiator identified through independent output check

et al. 2020

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Purpose: Accurate radiation dosimetry in radiobiological experiments is crucial for preclinical research in advancement of cancer treatment. Vendors of cell irradiators often perform calibration for end-users. However, calibration accuracy remains unclear due to missing detailed information on calibration equipment and procedures. In this study, we report our findings of a vender miscalibration of the radiation output and our investigation on the root cause of the discrepancy. Methods: Independent calibration verification for a commercial preclinical orthovoltage irradiator was conducted. Initially, in the absence of ionization chambers calibrated at kV energy, radiochromic films (EBT3) was first calibrated at MV energy. Energy correction factors from literature were used to create an in-house kV dosimetry system. The miscalibration identified with the in-house kV EBT3 dosimetry was later confirmed by ADCL calibrated ionization chambers (Exradin A1SL and PTW 30013) at kV energy. Ionization chambers were suspended in-air following TG-61 recommendation for output calibration. To investigate the root cause of the miscalibration, additional measurements were performed with ionization chambers placed on the shelf. A validated Monte Carlo simulation code was also used to investigate the impact of placing the ionization chamber on the shelf instead of suspending it in air during the vendor-performed calibration process. Results: Up to a 6% dosimetry error was observed when comparing the vendor calibrated output of the preclinical irradiator with our independent calibration check. Further investigation showed incorrect setups in the vendor's calibration procedure which may result in dose errors up to 11% from the backscatter of the shelf board during calibration, and up to 5% from omitting temperature and pressure corrections to ionization chamber readings. Conclusion: Our study revealed large dose calibration errors caused by incorrect setup and the omission of temperature/pressure correction in the vendor's calibration procedure. The findings also highlighted the importance of performing an independent check of the dose calibration for preclinical kV irradiators. More absolute dosimetry training is needed for both vendors and end users for establishing accurate absolute dosimetry.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Technical Note: Vendor miscalibration of preclinical orthovoltage irradiator identified through independent output check

et al. 2020

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Dose calculations for preclinical radiobiology experiments conducted with single‐field cabinet irradiators

et al. 2022

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Purpose To provide percentage depth dose (PDD) data along the central axis for dosimetry calculations in small‐animal radiation biology experiments performed in cabinet irradiators. The PDDs are provided as a function of source‐to‐surface distance (SSD), field size, and animal size. Methods The X‐ray tube designs for four biological cabinet irradiators, the RS2000, RT250, MultiRad350, and XRAD320, were simulated using the BEAMnrc Monte Carlo code to generate 160, 200, 250, and 320 kVp photon beams, respectively. The 320 kVp beam was simulated with two filtrations: a soft F1 aluminium filter and a hard F2 thoraeus filter made of aluminium, tin, and copper. Beams were collimated into circular fields with diameters of 0.5–10 cm at SSDs of 10–60 cm. Monte Carlo dose calculations in 1–5‐cm diameter homogeneous (soft tissue) small‐animal phantoms as well as in heterogeneous phantoms with 3‐mm diameter cylindrical lung and bone inserts (rib and cortical bone) were performed using DOSXYZnrc. The calculated depth doses in three test‐cases were estimated by applying SSD, field size, and animal size correction factors to a reference case (40‐cm SSD, 1‐cm field, and 5‐cm animal size), and these results were compared with the specifically simulated (i.e., expected) doses to assess the accuracy of this method. Dosimetry for two test‐case scenarios of 160 and 250 kVp beams (representative of end‐user beam qualities) was also performed, whereby the simulated PDDs at two different depths were compared with the results based on the interpolation from reference data. Results The depth doses for three test‐cases calculated at 200, 320 kVp F1, and 320 kVp F2 with half value layers (HVLs) ranging from ∼0.6 to 3.6 mm Cu, agreed well with the expected doses, yielding dose differences of 1.2%, 0.1%, and 1.0%, respectively. The two end‐user test‐cases for 160 and 250 kVp beams with respective HVLs of ∼0.8 and 1.8 mm Cu yielded dose differences of 1.4% and 3.2% between the simulated and the interpolated PDDs. The dose increase at the bone‐tissue proximal interface ranged from 1.2 to 2.5 times the dose in soft tissue for rib and 1.3 to 3.7 times for cortical bone. The dose drop‐off at 1‐cm depth beyond the bone ranged from 1.3% to 6.0% for rib and 3.2% to 11.7% for cortical bone. No drastic dose perturbations occurred in the presence of lung, with lung‐tissue interface dose of >99% of soft tissue dose and <3% dose increase at 1‐cm depth beyond lung. Conclusions The developed dose estimation method can be used to translate the measured dose at a point to dose at any depth in small‐animal phantoms, making it feasible for preclinical calculation of dose distributions in animals irradiated with cabinet‐style irradiators. The dosimetric impact of bone must be accurately quantified as dramatic dose perturbations at and beyond the bone interfaces can occur due to the relative importance of the photoelectric effect at kilovoltage energies. These results will help improve dosimetric accuracy in preclinical experiments.

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Use of calculations to validate beam quality and relative dose measurements for a kilovoltage X-ray therapy unit

Healy

Hill

2022

Phys Eng Sci Med

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The influence of lack of reference conditions on dosimetry in pre-clinical radiotherapy with medium energy x-ray beams

Cited by 10 publications

References 29 publications

Technical Note: Vendor miscalibration of preclinical orthovoltage irradiator identified through independent output check

Technical Note: Vendor miscalibration of preclinical orthovoltage irradiator identified through independent output check

Dose calculations for preclinical radiobiology experiments conducted with single‐field cabinet irradiators

Use of calculations to validate beam quality and relative dose measurements for a kilovoltage X-ray therapy unit

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