Dose calculation for photon‐emitting brachytherapy sources with average energy higher than 50 keV: Report of the AAPM and ESTRO

The aim of this work is to evaluate the performance of a commercial brachytherapy treatment planning system (TPS) with TG‐43 Vendors Input Data (VID), analyze possible discrepancies with respect to a proper reference source and its implications for standard treatments, and judge the effectiveness of certain widespread recommended quality controls to find potential errors related with the interpolations of TG‐43 VID tables. The TPS evaluated was a BrachyVision 8.6 loaded with TG‐43 VID for a VariSource high‐dose‐rate 192Ir source (Vs2000). The reference data chosen were the TG‐43 data published in the literature. In the first step, we compared TG‐43 VID with respect to the chosen reference data. Next, we used percent dose‐rate differences in a point array matrix to compare the outcomes of the TPS on standard treatment setup with respect to an in‐house developed program (MATLAB R2009a‐based) loaded with the chosen full TG‐43 reference data. The cases with major discrepancies were evaluated using the gamma‐index analysis. The comparison with the reference data indicated a lack of sample in the angles between near to the tip (between 165<θ<180) and cable (0<θ<15) of the F(r,θ)VID, which causes a dose underestimation of approximately 17% in the investigated points due to inaccurate interpolations. The differences over 2% encompassed approximately 17% of the surrounding source volume. These results have special relevance in treatment using one applicator with a few dwell steps or in Fletcher treatments where 10% dose underestimates were identified within the tumor or in organs at risk, respectively. Our results suggest that the differences found in the TPS under study are created by a lack of information on the angles in high‐gradient zones in the F(r,θ)VID, which generates important differences in dosimetric results. In contrast, the gamma analysis shows very good results (between 90% and 100% of passed points) in the analyzed treatments (one dwell and Fletcher). Further studies are required to exclude the possibility of finding noticeable effects in the DVH of treatment plans caused by the discrepancies here described. To achieve more strict control over the TPS dose‐rate calculation, we recommend using QA test thinking in a source with nonaxial symmetry, adding a control point on the angles of the high‐dose gradient zones (e.g., between 0° and 15° and between 165° and 180°). More studies are required to achieve full understanding of the clinical implication of such discrepancies.PACS number: 87.55.Qr

^{192} Ir

Flexisource); however, this recommendation may require revision for other

^{192} Ir

sources.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

\overset{D}{true} false(r, θ false) = S_{k} Λ \frac{G_{L} false(r, θ false)}{G_{L} false(r_{0}, θ_{0} false)} g_{L} false(r false) F false(r, θ false)

where

S_{K}

is the air kerma strength of the source, Λ is the dose rate constant,

g_{L} (r)

is the radial dose function for a LSA,

F (r, θ)

is the anisotropy function, and

G_{L} (r, θ)

\begin{matrix} left \\ left G_{L} false(r, θ false) = \\ left {\begin{matrix} left \\ left \frac{{italiccos}^{- 1} (\frac{r italiccos θ - \frac{L}{2}}{\sqrt{r^{2} + {(\frac{L}{2})}^{2} - L r italiccos θ}}) - {italiccos}^{- 1} (\frac{r italiccos θ + \frac{L}{2}}{\sqrt{r^{2} + {(\frac{L}{2})}^{2} - L r italiccos θ}})}{L r italicsin θ}, & left i f θ \neq 0 \\ left {(r^{2} - \frac{L^{2}}{4})}^{- 1}, & left i f θ = 0 \end{matrix} \end{matrix}

…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Brachytherapy treatment planning commissioning: effect of the election of proper bibliography and finite size of TG‐43 input data on standard treatments

Valdés

Piriz

Lozano

2015

“…A 0.1 cm thick waterproof buildup cap was screwed over the Markus chamber. The water tank was filled so as to provide about 15 cm depth of water for backscatter, as suggested in the joint AAPM‐ESTRO TG‐229 report (8) . The chamber was affixed to a custom holder mounted to the tank's one‐dimensional motion system and then centered at a given depth in water using the simulator's lasers and graticule.…”

Section: Methodsmentioning

confidence: 99%

Commissioning and quality assurance for the treatment delivery components of the AccuBoost system

Iftimia

Talmadge

Ladd

et al. 2015

The objective for this work was to develop a commissioning methodology for the treatment delivery components of the AccuBoost system, as well as to establish a routine quality assurance program and appropriate guidance for clinical use based on the commissioning results. Various tests were developed: 1) assessment of the accuracy of the displayed separation value; 2) validation of the dwell positions within each applicator; 3) assessment of the accuracy and precision of the applicator localization system; 4) assessment of the combined dose profile of two opposed applicators to confirm that they are coaxial; 5) measurement of the absolute dose delivered with each applicator to confirm acceptable agreement with dose based on Monte Carlo modeling; 6) measurements of the skin‐to‐center dose ratio using optically stimulated luminescence dosimeters; and 7) assessment of the mammopad cushion's effect on the center dose. We found that the difference between the measured and the actual paddle separation is <0.1 cm for the separation range of 3 cm to 7.5 cm. Radiochromic film measurements demonstrated that the number of dwell positions inside the applicators agree with the values from the vendor, for each applicator type and size. The shift needed for a good applicator‐grid alignment was within 0.2 cm. The dry‐run test using film demonstrated that the shift of the dosimetric center is within 0.15 cm. Dose measurements in water converted to polystyrene agreed within 5.0% with the Monte Carlo data in polystyrene for the same applicator type, size, and depth. A solid water‐to‐water (phantom) factor was obtained for each applicator, and all future annual quality assurance tests will be performed in solid water using an average value of 1.07 for the solid water‐to‐water factor. The skin‐to‐center dose ratio measurements support the Monte Carlo‐based values within 5.0% agreement. For the treatment separation range of 4 cm to 8 cm, the change in center dose would be <1.0% for all applicators when using a compressed pad of 0.2 cm to 0.3 cm. The tests performed ensured that all treatment components of the AccuBoost system are functional and that a treatment plan can be delivered with acceptable accuracy. Based on the commissioning results, a quality assurance manual and guidance documents for clinical use were developed.PACS numbers: 87.55.Qr, 87.56.Da, 87.90.+y

“…The high‐energy, photon‐emitting brachytherapy dosimetry protocol is described by the joint AAPM/ESTRO High Energy Brachytherapy Dosimetry Working Group Report (14) . A detailed description of the formalism involved is available in that literature.…”

Section: Methodsmentioning

confidence: 99%

Brachytherapy dose‐volume histogram commissioning with multiple planning systems

Gossman

Hancock

Kudchadker

et al. 2014

The first quality assurance process for validating dose‐volume histogram data involving brachytherapy procedures in radiation therapy is presented. The process is demonstrated using both low dose‐rate and high dose‐rate radionuclide sources. A rectangular cuboid was contoured in five commercially available brachytherapy treatment planning systems. A single radioactive source commissioned for QA testing was positioned coplanar and concentric with one end. Using the brachytherapy dosimetry formalism defined in the AAPM Task Group 43 report series, calculations were performed to estimate dose deposition in partial volumes of the cuboid structure. The point‐source approximation was used for a 125I source and the line‐source approximation was used for a 192Ir source in simulated permanent and temporary implants, respectively. Hand‐calculated, dose‐volume results were compared to TPS‐generated, dose‐volume histogram (DVH) data to ascertain acceptance. The average disagreement observed between hand calculations and the treatment planning system DVH was less than 1% for the five treatment planning systems and less than 5% for 1 cm≤r≤5 cm. A reproducible method for verifying the accuracy of volumetric statistics from a radiation therapy TPS can be employed. The process satisfies QA requirements for TPS commissioning, upgrading, and annual testing. We suggest that investigations be performed if the DVHnormal%VolTPS “actual variance” calculations differ by more than 5% at any specific radial distance with respect to normal%VolTG−43, or if the “average variance” DVH DVHnormal%VolTPS calculations differ by more than 2% over all radial distances with respect to normal%VolTG−43.PACS numbers: 87.10.+e, 87.55.‐x, 87.53.Jw, 07.05.Tp