Density Scaling Artifacts in Dosimetry Calculations

Dickof, Peter

doi:10.1120/jacmp.2025.25342

Cited by 2 publications

(2 citation statements)

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“…However, the median of gDD using ED (1.159) was not between that using PD (1.19) and DSF (1.13). This may be due to the coarse resolution of the mass attenuation coefficient in an older version of Pinnacle 3 , as pointed out by Dickof . Except for AXB within PMMA, the pass rates of gGI increased and median of gDD moved close to 0% from the PD to DSF .…”

Section: Resultsmentioning

confidence: 91%

Density scaling of phantom materials for a 3D dose verification system

Tani

Fujita

Wakita³

et al. 2018

J Applied Clin Med Phys

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In this study, the optimum density scaling factors of phantom materials for a commercially available three‐dimensional (3D) dose verification system (Delta4) were investigated in order to improve the accuracy of the calculated dose distributions in the phantom materials. At field sizes of 10 × 10 and 5 × 5 cm2 with the same geometry, tissue‐phantom ratios (TPRs) in water, polymethyl methacrylate (PMMA), and Plastic Water Diagnostic Therapy (PWDT) were measured, and TPRs in various density scaling factors of water were calculated by Monte Carlo simulation, Adaptive Convolve (AdC, Pinnacle3), Collapsed Cone Convolution (CCC, RayStation), and AcurosXB (AXB, Eclipse). Effective linear attenuation coefficients (μ eff) were obtained from the TPRs. The ratios of μ eff in phantom and water ((μ eff)pl,water) were compared between the measurements and calculations. For each phantom material, the density scaling factor proposed in this study (DSF) was set to be the value providing a match between the calculated and measured (μ eff)pl,water. The optimum density scaling factor was verified through the comparison of the dose distributions measured by Delta4 and calculated with three different density scaling factors: the nominal physical density (PD), nominal relative electron density (ED), and DSF. Three plans were used for the verifications: a static field of 10 × 10 cm2 and two intensity modulated radiation therapy (IMRT) treatment plans. DSF were determined to be 1.13 for PMMA and 0.98 for PWDT. DSF for PMMA showed good agreement for AdC and CCC with 6 MV x ray, and AdC for 10 MV x ray. DSF for PWDT showed good agreement regardless of the dose calculation algorithms and x‐ray energy. DSF can be considered one of the references for the density scaling factor of Delta4 phantom materials and may help improve the accuracy of the IMRT dose verification using Delta4.

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Section: Resultsmentioning

confidence: 91%

Density scaling of phantom materials for a 3D dose verification system

Tani

Fujita

Wakita³

et al. 2018

J Applied Clin Med Phys

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“…Comparison between the use of the standard CT-to-density table and the use of density overrides within the Pinnacle 3 TPS indicated that planned doses computed using the CT-to-density table matched values obtained when applying a density override of approximately 1.03 gcm −3 , very close to the actual physical density of 1.04 gcm −3 . It was notable that the dose predicted by Pinnacle 3 v9.0 does not change smoothly as the density override is changed but followed a stepped pattern as discussed by Dickof (2005), and that this stepping effect dominated the difference between calculations based on the CT scan and calculations based on density overrides. CT scans of the initial prototype phantom highlighted a manufacturing issue which resulted in the presence of internal voids, and this was corrected during the manufacture of a second prototype.…”

Section: Basic Evaluation Of Phantom Materials and Designmentioning

confidence: 89%

Marvin: an anatomical phantom for dosimetric evaluation of complex radiotherapy of the head and neck

Aitkenhead¹,

Rowbottom²,

Mackay³

2013

Phys. Med. Biol.

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We report on the design of Marvin, a Model Anatomy for Radiotherapy Verification and audit In the head and Neck and present results demonstrating its use in the development of the Elekta volumetric modulated arc therapy (VMAT) technique at the Christie, and in the audit of TomoTherapy and Varian RapidArc at other institutions. The geometry of Marvin was generated from CT datasets of eight male and female patients lying in the treatment position, with removable inhomogeneities modelling the sinuses and mandible. A modular system allows the phantom to be used with a range of detectors, with the locations of the modules being based on an analysis of a range of typical treatment plans (27 in total) which were mapped onto the phantom geometry. Results demonstrate the use of Gafchromic EBT2/EBT3 film for measurement of relative dose in a plane through the target and organs-at-risk, and the use of a small-volume ionization chamber for measurement of absolute dose in the target and spinal cord. Measurements made during the development of the head and neck VMAT protocol at the Christie quantified the improvement in plan delivery resulting from the installation of the Elekta Integrity upgrade (which permits an effectively continuously variable dose rate), with plans delivered before and after the upgrade having 88.5 ± 9.4% and 98.0 ± 2.2% respectively of points passing a gamma analysis (at 4%, 4 mm, global). Audits of TomoTherapy and Varian RapidArc neck techniques at other institutions showed a similar quality of plan delivery as for post-Integrity Elekta VMAT: film measurements for both techniques had >99% of points passing a gamma analysis at the clinical criteria of 4%, 4 mm, global, and >95% of points passing at tighter criteria of 3%, 3 mm, global; and absolute dose measurements in the PTV and spinal cord were within 1.5% and 3.5% of the planned doses respectively for both techniques. The results demonstrate that Marvin is an efficient and effective means of assessing the quality of delivery of complex radiotherapy in the head and neck, and is a useful tool to assist development and audit of these techniques.

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Density Scaling Artifacts in Dosimetry Calculations

Cited by 2 publications

References 0 publications

Density scaling of phantom materials for a 3D dose verification system

Density scaling of phantom materials for a 3D dose verification system

Marvin: an anatomical phantom for dosimetric evaluation of complex radiotherapy of the head and neck

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