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Improved source path localisation in ring applicators and the clinical impact for gynecological brachytherapy.

Humer I, Kirisits C, Berger D, Trnková P, Pötter R, Nesvacil N - J Contemp Brachytherapy (2015)

Bottom Line: Videos of the exact motion of the source wire through three different (r = 26, 30, 34 mm) computed tomography/magnetic resonance (CT/MR) compatible plastic ring applicators were recorded.Autoradiography analysis showed a positional accuracy within ± 3 mm (extended standard deviation k = 2).For shifts of ± 2.5 mm for even all dwell positions, the systematic and random variation of the D2cm(3) for bladder, rectum, and sigmoid was within 3%, while the impact on DVH uncertainties was much smaller for clinical target volume (CTV)HR and gross tumour volume (GTV).

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna.

ABSTRACT

Purpose: The path of subsequent dwell positions of an afterloader source being moved through a ring applicator for cervix cancer brachytherapy deviates from an ideal circle and the position of marker wires. This can lead to deviations of several millimetres between real and assumed dwell positions for treatment planning with simplified source path models. The aim of this study was to test video- and autoradiography-based methods for source path determination, and to study the influence of dwell position accuracy on dose-volume histogram (DVH)-parameters.

Material and methods: Videos of the exact motion of the source wire through three different (r = 26, 30, 34 mm) computed tomography/magnetic resonance (CT/MR) compatible plastic ring applicators were recorded. Observed dwell positions covering the whole length of each applicators channel were used to adjust the circular source path model. The agreement of the true source positions derived from video analysis with those of the corrected circular source path was verified using autoradiography. The impact of an accurate source path definition on dose planning was analysed by simulating clinically relevant uncertainties in 10 clinical treatment plans.

Results: Depending on the ring size, source path diameters had to be increased by 0.5-1.0 mm in order to achieve acceptable maximum differences between observed and corrected dwell positions (1.3-2.0 mm). Autoradiography analysis showed a positional accuracy within ± 3 mm (extended standard deviation k = 2). For shifts of ± 2.5 mm for even all dwell positions, the systematic and random variation of the D2cm(3) for bladder, rectum, and sigmoid was within 3%, while the impact on DVH uncertainties was much smaller for clinical target volume (CTV)HR and gross tumour volume (GTV).

Conclusions: It is strongly advised to verify the real source path for ring applicators during acceptance testing in order to assure accurate source path definition and dose planning. Autoradiography can be used for source path verification with acceptable accuracy for treatment planning and dose reporting.

No MeSH data available.


Related in: MedlinePlus

Template for the R34 ring applicator, showing the inner and outer diameter (dashed lines), positions of the holes for interstitial needles (grey circles), dwell positions observed in video analysis (blue circles), positions predicted by the corrected source path model (red crosses), the nominal path (solid line), and most frequently active dwell positions (black circles) of a standard loading pattern
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Figure 0001: Template for the R34 ring applicator, showing the inner and outer diameter (dashed lines), positions of the holes for interstitial needles (grey circles), dwell positions observed in video analysis (blue circles), positions predicted by the corrected source path model (red crosses), the nominal path (solid line), and most frequently active dwell positions (black circles) of a standard loading pattern

Mentions: Three CT-/MR-compatible Vienna ring applicators (Elekta AB, Sweden) with nominal diameters d = 26, 30 and 34 mm (R26, R30, and R34, hereafter) were investigated. In order to be able to reconstruct the real source path with high precision, a detailed video analysis of the motion of the source through the applicator channel was performed. For this purpose, the applicators were cut open and covered with a transparent plate (Figure 1 in [7]). This allowed to record the stepwise motion of the source through the ring during irradiation with a microSelectron® afterloader (Elekta AB, Sweden), with a digital camera mounted in front of the applicator. For each applicator, the selected dwell position sequence was repeated 10 times in order to evaluate possible random variations between individual irradiations. Each sequence included a maximum of 33 dwell positions distributed over the whole length of the ring. The dwell time for each position was set to 2.0 s.


Improved source path localisation in ring applicators and the clinical impact for gynecological brachytherapy.

Humer I, Kirisits C, Berger D, Trnková P, Pötter R, Nesvacil N - J Contemp Brachytherapy (2015)

Template for the R34 ring applicator, showing the inner and outer diameter (dashed lines), positions of the holes for interstitial needles (grey circles), dwell positions observed in video analysis (blue circles), positions predicted by the corrected source path model (red crosses), the nominal path (solid line), and most frequently active dwell positions (black circles) of a standard loading pattern
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4499519&req=5

Figure 0001: Template for the R34 ring applicator, showing the inner and outer diameter (dashed lines), positions of the holes for interstitial needles (grey circles), dwell positions observed in video analysis (blue circles), positions predicted by the corrected source path model (red crosses), the nominal path (solid line), and most frequently active dwell positions (black circles) of a standard loading pattern
Mentions: Three CT-/MR-compatible Vienna ring applicators (Elekta AB, Sweden) with nominal diameters d = 26, 30 and 34 mm (R26, R30, and R34, hereafter) were investigated. In order to be able to reconstruct the real source path with high precision, a detailed video analysis of the motion of the source through the applicator channel was performed. For this purpose, the applicators were cut open and covered with a transparent plate (Figure 1 in [7]). This allowed to record the stepwise motion of the source through the ring during irradiation with a microSelectron® afterloader (Elekta AB, Sweden), with a digital camera mounted in front of the applicator. For each applicator, the selected dwell position sequence was repeated 10 times in order to evaluate possible random variations between individual irradiations. Each sequence included a maximum of 33 dwell positions distributed over the whole length of the ring. The dwell time for each position was set to 2.0 s.

Bottom Line: Videos of the exact motion of the source wire through three different (r = 26, 30, 34 mm) computed tomography/magnetic resonance (CT/MR) compatible plastic ring applicators were recorded.Autoradiography analysis showed a positional accuracy within ± 3 mm (extended standard deviation k = 2).For shifts of ± 2.5 mm for even all dwell positions, the systematic and random variation of the D2cm(3) for bladder, rectum, and sigmoid was within 3%, while the impact on DVH uncertainties was much smaller for clinical target volume (CTV)HR and gross tumour volume (GTV).

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, Comprehensive Cancer Center, Medical University of Vienna.

ABSTRACT

Purpose: The path of subsequent dwell positions of an afterloader source being moved through a ring applicator for cervix cancer brachytherapy deviates from an ideal circle and the position of marker wires. This can lead to deviations of several millimetres between real and assumed dwell positions for treatment planning with simplified source path models. The aim of this study was to test video- and autoradiography-based methods for source path determination, and to study the influence of dwell position accuracy on dose-volume histogram (DVH)-parameters.

Material and methods: Videos of the exact motion of the source wire through three different (r = 26, 30, 34 mm) computed tomography/magnetic resonance (CT/MR) compatible plastic ring applicators were recorded. Observed dwell positions covering the whole length of each applicators channel were used to adjust the circular source path model. The agreement of the true source positions derived from video analysis with those of the corrected circular source path was verified using autoradiography. The impact of an accurate source path definition on dose planning was analysed by simulating clinically relevant uncertainties in 10 clinical treatment plans.

Results: Depending on the ring size, source path diameters had to be increased by 0.5-1.0 mm in order to achieve acceptable maximum differences between observed and corrected dwell positions (1.3-2.0 mm). Autoradiography analysis showed a positional accuracy within ± 3 mm (extended standard deviation k = 2). For shifts of ± 2.5 mm for even all dwell positions, the systematic and random variation of the D2cm(3) for bladder, rectum, and sigmoid was within 3%, while the impact on DVH uncertainties was much smaller for clinical target volume (CTV)HR and gross tumour volume (GTV).

Conclusions: It is strongly advised to verify the real source path for ring applicators during acceptance testing in order to assure accurate source path definition and dose planning. Autoradiography can be used for source path verification with acceptable accuracy for treatment planning and dose reporting.

No MeSH data available.


Related in: MedlinePlus