AAPM Task Group 329: Reference dose specification for dose calculations: Dose‐to‐water or dose‐to‐muscle?

Kry, Stephen F; Feygelman, Vladimir; Balter, Peter A; Knöös, Tommy; Charlie, C.‐M.; Snyder, Michael; Tonner, B. P.; Vassiliev, Oleg N

doi:10.1002/mp.13995

Cited by 50 publications

(68 citation statements)

References 42 publications

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“…These algorithms partially account for material of the voxels by applying material specific mass attenuation coefficients for photon attenuation, which adjusts the water based kernel. Due to the lack of clarity in the literature [21,22,24,37,38], these algorithms have been analysed using both D m,m and D w,w .…”

Section: Sbrt Spine Dosimetry Auditmentioning

confidence: 99%

“…As the literature recommends avoiding the stopping power/energy deposition ratio based conversion of dose to water in a medium (D w,m ) [17,18,22,24], we have not modelled correction factors for this methodology. Additionally, no SBRT spine plans were submitted to this study using this calculation method.…”

Section: Sbrt Spine Dosimetry Auditmentioning

confidence: 99%

“…Absorbed dose is traditionally defined as D w,w [23] and radiotherapy detectors are traditionally calibrated in terms of absorbed dose to water (D w,w ) which creates challenges in dose verification for calculations in bony material. With the aim of a consistent definition of dose, and in particular, only one definition of absorbed dose to water, we propose a methodology for measuring dose in bone as either as D m,m or D w,w , based on the primary reporting mode of the calculation algorithm [24]. The methodology is applied in the context of an end-to-end clinical dosimetry audit of SBRT spine treatments.…”

Section: Introductionmentioning

confidence: 99%

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Measuring the dose in bone for spine stereotactic body radiotherapy

Shaw

Lye

Alves³

et al. 2021

Physica Medica

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Current quality assurance of radiotherapy involving bony regions generally utilises homogeneous phantoms and dose calculations, ignoring the challenges of heterogeneities with dosimetry problems likely occurring around bone. Anthropomorphic phantoms with synthetic bony materials enable realistic end-to-end testing in clinical scenarios. This work reports on measurements and calculated corrections required to directly report dose in bony materials in the context of comprehensive end-to-end dosimetry audit measurements (63 plans, 6 planning systems). Materials and methods: Radiochromic film and microDiamond measurements were performed in an anthropomorphic spine phantom containing bone equivalent materials. Medium dependent correction factors, k med , were established using 6 MV and 10 MV Linear Accelerator Monte Carlo simulations to account for the detectors being calibrated in water, but measuring in regions of bony material. Both cortical and trabecular bony material were investigated for verification of dose calculations in dose-to-medium (D m,m ) and dose-to-water (D w,w ) scenarios. Results: For D m,m calculations, modelled correction factors for cortical and trabecular bone in film measurements, and for trabecular bone in microDiamond measurements were 0.875(±0.1%), 0.953(±0.3%) and 0.962(±0.4%), respectively. For D w,w calculations, the corrections were 0.920(±0.1%), 0.982(±0.3%) and 0.993(±0.4%), respectively. In the audit, application of the correction factors improves the mean agreement between treatment plans and measured microDiamond dose from − 2.4%(±3.9%) to 0.4%(±3.7%). Conclusion: Monte Carlo simulations provide a method for correcting the dose measured in bony materials allowing more accurate comparison with treatment planning system doses. In verification measurements, algorithm specific correction factors should be applied to account for variations in bony material for calculations based on D m,m and D w,w .

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Section: Sbrt Spine Dosimetry Auditmentioning

confidence: 99%

Section: Sbrt Spine Dosimetry Auditmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Measuring the dose in bone for spine stereotactic body radiotherapy

Shaw

Lye

Alves³

et al. 2021

Physica Medica

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“…A conversion from “dose‐to‐air” to “dose‐to‐water” or “dose‐to‐muscle” would be needed as “dose‐to‐water” and “dose‐to‐muscle” are two most frequently used dose specifications in radiation dosimetry. The conversion factor for dose‐to‐water (ratio of average mass energy‐absorption coefficients water to air, free in air) is 1.04 for X225 Al and 1.07 for X225 Cu according to TG‐61 15 and 1% smaller for dose‐to‐muscle conversion 16 …”

Section: Methodsmentioning

confidence: 99%

“…The conversion factor for dose-to-water (ratio of average mass energy-absorption coefficients water to air, free in air) is 1.04 for X225 Al and 1.07 for X225 Cu according to TG-61 15 and 1% smaller for dose-to-muscle conversion. 16…”

Section: A Description Of the X-rad 225xl Preclinical Irradiatormentioning

confidence: 99%

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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Integration of automation into an existing clinical workflow to improve efficiency and reduce errors in the manual treatment planning process for total body irradiation (TBI)

Thomas

Miller

Rabinovitch

et al. 2020

J Applied Clin Med Phys

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Purpose To identify causes of error, and present the concept of an automated technique that improves efficiency and helps to reduce transcription and manual data entry errors in the treatment planning of total body irradiation (TBI). Methods Analysis of incidents submitted to incident learning system (ILS) was performed to identify potential avenues for improvement by implementation of automation of the manual treatment planning process for total body irradiation (TBI). Following this analysis, it became obvious that while the individual components of the TBI treatment planning process were well implemented, the manual ‘bridging’ of the components (transcribing data, manual data entry etc.) were leading to high potential for error. A C#‐based plug‐in treatment planning script was developed to remove the manual parts of the treatment planning workflow that were contributing to increased risk. Results Here we present an example of the implementation of “Glue” programming, combining treatment planning C# scripts with existing spreadsheet calculation worksheets. Prior to the implementation of automation, 35 incident reports related to the TBI treatment process were submitted to the ILS over a 6‐year period, with an average of 1.4 ± 1.7 reports submitted per quarter. While no incidents reached patients, reports ranged from minor documentation issues to potential for mistreatment if not caught before delivery. Since the implementation of automated treatment planning and documentation, treatment planning time per patient, including documentation, has been reduced; from an average of 45 min pre‐automation to <20 min post‐automation. Conclusions Manual treatment planning techniques may be well validated, but they are time‐intensive and have potential for error. Often the barrier to automating these techniques becomes the time required to “re‐code” existing solutions in unfamiliar computer languages. We present the workflow here as a proof of concept that automation may help to improve clinical efficiency and safety for special procedures.

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AAPM Task Group 329: Reference dose specification for dose calculations: Dose‐to‐water or dose‐to‐muscle?

Cited by 50 publications

References 42 publications

Measuring the dose in bone for spine stereotactic body radiotherapy

Measuring the dose in bone for spine stereotactic body radiotherapy

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

Integration of automation into an existing clinical workflow to improve efficiency and reduce errors in the manual treatment planning process for total body irradiation (TBI)

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