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Progress in Medical Physics 2024; 35(4): 116-124

Published online December 31, 2024

https://doi.org/10.14316/pmp.2024.35.4.116

Copyright © Korean Society of Medical Physics.

A Commissioning Report on the Magnetic Resonance-Compatible Geneva Brachytherapy Applicator

Yoonsuk Huh1,2 , Hyojun Park1,2 , Jin Jegal1,2 , Inbum Lee1,2 , Jaeman Son1,2,3,4 , Seonghee Kang1,2,3 , Chang Heon Choi1,2,3 , Jung-in Kim1,2,3 , Hyeongmin Jin1,2,3,4

1Department of Radiation Oncology, Seoul National University Hospital, Seoul, 2Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, 3Biomedical Research Institute, Seoul National University Hospital, Seoul, 4Project Group of the Gijang Heavy Ion Medical Accelerator, Seoul National University Hospital, Seoul, Korea

Correspondence to:Hyeongmin Jin
(hmjin@snu.ac.kr)
Tel: 82-2-2072-4160
Fax: 82-2-765-3317

Received: September 30, 2024; Revised: November 26, 2024; Accepted: December 11, 2024

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Purpose: Brachytherapy is essential for treating gynecological cancers as it offers precise radiation delivery to tumors while minimizing radiation exposure to surrounding healthy tissues. The Geneva applicator, introduced in 2020 as a replacement for older models like the Utrecht applicator, enhances MRI-based brachytherapy with improved imaging capabilities and more accurate applicator placement. In 2021, updates to non-reimbursement policies in Korea for MRI-based 3D brachytherapy planning further promoted the adoption of advanced techniques such as the Geneva applicator. This study aims to commission the Geneva applicator, focusing on wall thickness, dummy marker positions, and source dwell positions to ensure accurate dose delivery and safety.
Methods: The commissioning process involved measuring wall thickness in both the longitudinal and transverse directions for the tandem and lunar-shaped ovoid tubes and comparing these measurements with the manufacturer’s specifications. Dummy marker positions were verified using CT imaging, with a focus on alignment tolerances of ±1 mm. Source dwell positions were planned using the Oncentra treatment planning system, with measurements taken using EBT4 film and analyzed with RIT software.
Results: Wall thickness measurements and dummy marker positions were within the specified tolerance ranges, confirming their accuracy. The source dwell positions, measured and analyzed through multiple tests, were all within the ±1 mm tolerance, ensuring the applicator’s reliability.
Conclusions: The Geneva applicator met all standards for safe and effective use in brachytherapy. The use of a 3D-printed holder was crucial for precise alignment and measurement. With updated reimbursement policies in Korea for MRI-based brachytherapy, the Geneva applicator is expected to significantly impact the future of advanced brachytherapy treatments and research.

KeywordsMRI-based brachytherapy, Geneva applicator, EBT4 film, 3D-printed holder

Brachytherapy is a critical modality in cancer treatment, particularly for gynecological malignancies [1-3]. This technique allows for the precise delivery of high doses of radiation directly to the tumor while minimizing exposure to surrounding normal tissues. Such treatment is crucial for improving patient outcomes as it reduces side effects and enhances the effectiveness of therapy.

MRI-based brachytherapy offers significant advantages over traditional brachytherapy methods. The superior imaging capabilities of MRI provide better visualization and more accurate placement of the applicator, resulting in improved dose distribution. This leads to more effective treatment, potentially better clinical outcomes, and a reduction in complications. MRI-based techniques also enable the most accurate assessment of the cervix and any residual lesions, ensuring precise and safe treatment planning [4-6].

In 2021, the non-reimbursement system in Korea was updated for MRI-based 3D brachytherapy planning for cervical cancer following a new health technology assessment. Before this update, reimbursement policies favored traditional 2D or CT-based methods, hindering the adoption of MRI-guided techniques essential for precise tumor targeting and dose optimization. The updated system replaced traditional methods with MRI imaging, enhancing the precision and safety of treatment. Clinical textbooks and guidelines recognize MRI-based 3D brachytherapy planning as the most accurate method for evaluating the cervix and surrounding tissues while reducing the risk of damage to nearby organs [7-10]. This recognition underscores the technology’s effectiveness and safety, offering a more precise and efficient approach to brachytherapy planning for cervical cancer patients.

Commissioning the Geneva applicator (Elekta), introduced in 2020 as a replacement for the Utrecht and several other older applicators, is crucial to ensure its proper functioning and accurate dose delivery. This process involves verifying the device’s operation, detecting any manufacturing defects, and ensuring compliance with safety standards. It also helps medical physicists become familiar with the new equipment. This study aims to commission the Geneva applicator, focusing on wall thickness, dummy marker positions, and source dwell positions to ensure accurate dose delivery and safety.

1. Geneva applicator

The Geneva applicator is a versatile gynecological device designed for both intracavitary and interstitial brachytherapy treatments, specifically targeting the cervix and endometrium. Key features of the applicator include an integrated cervical stopper to prevent slippage from the intrauterine tandem, an interstitial template for the effective treatment of asymmetric diseases, and the ability to insert a flexible interstitial tube through the cervical stopper. Additionally, the applicator features a rotating and click mechanism for faster assembly compared to traditional screw mechanisms, such as the Utrecht applicator. A notable advantage of the Geneva applicator is its compatibility with various imaging modalities, including ultrasound, X-ray, CT, and MRI. Its nonmetallic construction ensures distortion-free images, which is crucial for accurate imaging and effective treatment planning [11].

The applicator primarily consists of several components, including an intrauterine tube (tandem tube), ovoid tubes, and interstitial ovoid pairs designed to accommodate optional needles. These components can be combined with compatible devices to reach a wide range of target areas. The minimum configuration includes two ovoid tubes with ovoid pairs inserted into the vagina and attached to a tandem tube. These tubes contain channels to guide a radioactive source to precise positions within the patient’s body (Fig. 1).

Figure 1.A Geneva applicator (Elekta) set comprising an intrauterine tube and a pair of ovoid tubes.

2. Commissioning parameters

The commissioning of the Geneva applicator can be broadly divided into three categories: General Inspection, Wall Thickness, and Distal Dwell Position. General inspection involves visual checks to detect possible cracks, verifying external dimensions using a caliper, checking for potential obstructions in the insertion items, and confirming the mechanical integrity of the applicator. Although crucial, this process is omitted in this paper. Instead, this paper focuses on two key processes: Wall Thickness and Distal Dwell Position. To accurately measure the transverse wall thickness of the tandem tube, a 3D-printed holder model provided by Elekta was used during commissioning. This holder minimizes tandem tube movement and ensures proper alignment during CT imaging, allowing for precise measurements.

Fig. 2 illustrates the 3D-printed holder designed for tandem tubes of varying tip lengths, as well as a holder for securing a pair of ovoid tubes. The holder includes a film insertion slot at the top (Fig. 2), which is used to secure the film for measuring the source dwell position. Specifically, the EBT4 film (Ashland) is pushed fully into the insertion slot, while the ovoid and tandem are inserted completely to ensure alignment between the starting points of the film and the tips. These holders were manufactured using the Fused Deposition Modeling method, as recommended in the white paper, utilizing polylactic acid filament. Upon completion, the holder’s dimensions were verified to ensure that both the film and the tubes could be fully inserted into their respective slots.

Figure 2.3D-printed holders for a pair of ovoid tubes (green) and tandem tubes with varying tip lengths (gray). Film insertion slots are located at the top of each holder for measuring the dwell position.

3. Wall thickness and known length verification

Accurate measurement of wall thickness and proper positioning of dummy markers are critical components of the commissioning process for the Geneva applicator, as these factors directly influence the applicator’s performance and the precision of radiation delivery during brachytherapy treatments. The wall thickness of the tandem tube and the lunar-shaped ovoid tube was measured in both longitudinal and transverse directions to compare with the manufacturer’s specifications and confirm that the measurements fell within the specified tolerance range.

In the longitudinal direction, wall thickness was determined by measuring the distance between the outer tip and the inner tip of the tandem and ovoid tubes. In the transverse direction, particular attention was required due to the asymmetrical positioning of the inner wall within the tandem tube. The pixel width of the image to be measured was configured based on the CT DICOM header, and the window level was adjusted to the recommended settings of 50/1,200, as outlined in the white paper. Interpolation was applied to ensure a pixel width and height of 0.02 mm. Reference diameters, such as an outer diameter of 3.85 mm and an inner diameter of 2.55 mm, were used to draw circles. The distance between the centers of these circles was then calculated to determine the wall thickness.

Additionally, X-ray dummy markers were attached to the tandem and ovoid tubes to verify measurements against known lengths, and the locations of these markers were assessed. Special care was taken during the measurement of dummy marker positions, particularly for the ovoid tubes, as the size of the first marker differed in each dummy (Fig. 3). Although not a mandatory parameter for commissioning, and with no specified tolerance, the angle of curvature between the ovoid and tandem was also measured using CT imaging.

Figure 3.X-ray dummy markers for ovoid tubes (1, 2) and tandem tubes (3).

For quantitative verification of wall thickness and dummy marker position measurements, a Brilliance Big Bore CT scanner (Philips Healthcare) was used to ensure precise alignment of the setup. The longitudinal wall thickness and dummy marker positions were measured directly from the CT image viewer, while the transverse wall diameter was analyzed using ImageJ software (National Institutes of Health) according to the methods provided in the white paper.

4. Source position verification

Source position commissioning ensures that the applicator’s performance aligns with the planned treatment parameters, minimizing the risk of dose delivery errors and enhancing the overall safety and efficacy of brachytherapy. To verify the dwell positions of the tandem tube and a pair of ovoid tubes, a treatment plan was generated using the Oncentra treatment planning system (Elekta), utilizing the applicator library model. As recommended in the white paper, it is essential to verify the first two clinically used source positions within the ovoid tubes during commissioning. Therefore, the source positions were set at 8 mm and 15 mm for the tandem tube and at 6 mm and 15 mm for the ovoid tube from the outer wall. The dwell time and activity were calibrated accordingly.

For source position measurements, as mentioned above, the EBT4 film was fully inserted into the film insertion slot to align the starting point of the applicator’s outer edge with the starting point of the film. This film was securely fixed to prevent movement, and the setup was positioned on the bed of the microSelectron (Elekta) system (Fig. 4). Each tandem and ovoid tube pair underwent three separate measurements. The resulting film images were scanned using a flatbed scanner (Expression 10000 XL; Epson) at a resolution of 300 dots per inch and converted into TIFF files. Distances were then measured using RIT software (Radiological Imaging Technology) to ensure accurate determination of the source positions.

Figure 4.Applicator setups with EBT4 film (Ashland) for source dwell position measurements. (a) A pair of ovoid and a tandem on the table for measurement of the source dwell position and side views for them (b).

The applicator model and the dummy marker positions captured by the CT scan were verified (Fig. 5). The dummy markers were correctly positioned within the tandem and ovoid tubes, and the red dots in the model corresponded to these positions, confirming alignment between the model and the actual markers.

Figure 5.The dummy marker position comparison between the applicator model in the treatment planning system and CT images.

Fig. 6a displays the longitudinal wall thickness and the positions of the dummy markers. The thicknesses of the outer shell, inner shell, and dummy marker positions were all within the specified tolerance ranges, as summarized in Table 1.

Table 1 Comparison of longitudinal wall thickness, marker position, and curvature angles among the reference, applicator model, and CT images

DistanceReference distance (mm)Applicator model (mm)*Deviation (mm)CT image (mm)†Deviation (mm)Angle (°)
Tandem tubeOuter to inner tip2.42.40.02.40.014.9
Inner tip to the most distal dwell position5.95.60.35.90.0
Outer to the most distal dwell position8.38.00.38.30.0
Ovoid tube 1Outer to inner tip1.01.00.01.00.0119.6
Inner tip to the most distal dwell position5.05.00.04.80.2
Outer to the most distal dwell position6.06.00.05.80.2
Ovoid tube 2Outer to inner tip1.01.00.01.00.0120.2
Inner tip to the most distal dwell position5.05.00.05.30.3
Outer to the most distal dwell position6.06.00.06.30.3

Figure 6.Example images for the measurement of the longitudinal wall thickness of the tandem and ovoid (a) and the transverse wall thickness measurement of the tandem tube and the measurement of the angle of curvatures using the ImageJ (National Institutes of Health) tool (b: left, outer; right, inner; c: ovoids and a tandem).

During the measurement of the transverse wall thickness of the tandem, the coordinates obtained from ImageJ corresponded to the vertices of a square surrounding the circles representing the external surface and the inner lumen. Based on these coordinates, the centers of the circles were calculated, and the shift between the two centers was determined using Pythagoras’ theorem. Finally, we calculated the minimum wall thickness in millimeters using the nominal wall thickness of 0.65 mm. The minimum distance value was calculated to be 0.57 mm, exceeding the minimum tolerance of 0.47 mm, thereby meeting the required specifications (Fig. 6b). Fig. 6c shows the sagittal view of the ovoids and tandem, with the bending angles analyzed using ImageJ. The ovoids have an angle of approximately 120°, and the tandem approximately 15°. Although no specific tolerance information is available, these values align closely with the specifications provided in the manual.

Fig. 7 illustrates the film used for source dwell position measurements and provides an example of the analysis software utilized for this process. Based on the results of three measurements for each setup, a Region of Interest was defined in the analysis software. The relevant areas were then analyzed, focusing on vertical and horizontal positions. The distance from the lowest point (assumed to be the source position) was calculated. The results of these measurements are summarized in Table 2, confirming that all values were within the specified tolerance range (within 1 mm), meeting the required standards.

Table 2 Comparison of source dwell positions between reference values and measured data for tandem and ovoid tubes

Source positionReference (mm)1st (mm)2nd (mm)3rd (mm)Average (mm)Deviation (mm)
Tandem18.307.828.498.488.26–0.04
215.0015.0715.0115.0315.040.04
Ovoid 116.005.996.136.156.090.09
215.0015.0014.9915.0015.000.00
Ovoid 216.006.116.046.106.080.08
215.0014.9914.9815.0415.000.00

Figure 7.Measured film sets for the source dwell position of the tandem and ovoid tubes. (a) EBT4 films (Ashland) and (b, c) examples for the dwell position analysis for ovoid and tandem with RIT software (Radiological Imaging Technology).

Commissioning the applicator is an essential procedure to ensure its performance and safety in clinical practice. According to international guidelines [12], comprehensive commissioning is critical for verifying that all components meet the technical specifications required for accurate dose delivery. These guidelines emphasize that deviations in applicator performance, such as inaccurate source dwell positions or misaligned markers, can significantly impact patient outcomes. In this study, we report the commissioning results of the Geneva applicator, introduced as a replacement for older models like the Utrecht applicator, through a comprehensive evaluation of its physical dimensions and dose delivery positions. This process included verifying the device, detecting any defects, and ensuring compliance with safety standards, thereby facilitating its consistent and reliable use in clinical settings. In this study, we conducted the commissioning process for wall thickness, dummy marker positions, and source dwell positions, confirming that all measurements fell within the specified tolerance ranges. While the commissioning process generally proceeds smoothly, it is important to exercise great caution in alignment due to the tight tolerance criteria of ±1 mm or less. Utilizing a 3D-printed holder can significantly aid in achieving accurate measurements.

With recent updates to reimbursement policies in Korea for 3D brachytherapy planning in 2021, there is a strong expectation for an increase in treatments and further research in this field. The careful commissioning of the Geneva applicator will be crucial in supporting these advancements, ensuring that the technology can be utilized effectively and safely in clinical practice.

This study was supported by a grant from the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2022R1F1A1063779) and a grant No. 0720233109 from the SNUH Research fund.

Chang Heon Choi and Jin Jegal are members of the editorial board of the Progress in Medical Physics, but have no role in the decision to publish this article. The other authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

All relevant data are within the paper and its Supporting Information files.

Conceptualization: Jung-in Kim, Hyeongmin Jin. Methodology: Yoonsuk Huh, Jaeman Son, Seonghee Kang, Chang Heon Choi, Hyeongmin Jin. Project administration: Jung-in Kim. Measurement: Yoonsuk Huh, Hyojun Park, Jin Jegal, Inbeom Lee, Hyeongmin Jin. Validation: Yoonsuk Huh, Hyojun Park, Jin Jegal, Inbeom Lee, Hyeongmin Jin. Writing – original draft: Yoonsuk Huh. Writing – review & editing: Hyeongmin Jin.

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Article

Original Article

Progress in Medical Physics 2024; 35(4): 116-124

Published online December 31, 2024 https://doi.org/10.14316/pmp.2024.35.4.116

Copyright © Korean Society of Medical Physics.

A Commissioning Report on the Magnetic Resonance-Compatible Geneva Brachytherapy Applicator

Yoonsuk Huh1,2 , Hyojun Park1,2 , Jin Jegal1,2 , Inbum Lee1,2 , Jaeman Son1,2,3,4 , Seonghee Kang1,2,3 , Chang Heon Choi1,2,3 , Jung-in Kim1,2,3 , Hyeongmin Jin1,2,3,4

1Department of Radiation Oncology, Seoul National University Hospital, Seoul, 2Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, 3Biomedical Research Institute, Seoul National University Hospital, Seoul, 4Project Group of the Gijang Heavy Ion Medical Accelerator, Seoul National University Hospital, Seoul, Korea

Correspondence to:Hyeongmin Jin
(hmjin@snu.ac.kr)
Tel: 82-2-2072-4160
Fax: 82-2-765-3317

Received: September 30, 2024; Revised: November 26, 2024; Accepted: December 11, 2024

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose: Brachytherapy is essential for treating gynecological cancers as it offers precise radiation delivery to tumors while minimizing radiation exposure to surrounding healthy tissues. The Geneva applicator, introduced in 2020 as a replacement for older models like the Utrecht applicator, enhances MRI-based brachytherapy with improved imaging capabilities and more accurate applicator placement. In 2021, updates to non-reimbursement policies in Korea for MRI-based 3D brachytherapy planning further promoted the adoption of advanced techniques such as the Geneva applicator. This study aims to commission the Geneva applicator, focusing on wall thickness, dummy marker positions, and source dwell positions to ensure accurate dose delivery and safety.
Methods: The commissioning process involved measuring wall thickness in both the longitudinal and transverse directions for the tandem and lunar-shaped ovoid tubes and comparing these measurements with the manufacturer’s specifications. Dummy marker positions were verified using CT imaging, with a focus on alignment tolerances of ±1 mm. Source dwell positions were planned using the Oncentra treatment planning system, with measurements taken using EBT4 film and analyzed with RIT software.
Results: Wall thickness measurements and dummy marker positions were within the specified tolerance ranges, confirming their accuracy. The source dwell positions, measured and analyzed through multiple tests, were all within the ±1 mm tolerance, ensuring the applicator’s reliability.
Conclusions: The Geneva applicator met all standards for safe and effective use in brachytherapy. The use of a 3D-printed holder was crucial for precise alignment and measurement. With updated reimbursement policies in Korea for MRI-based brachytherapy, the Geneva applicator is expected to significantly impact the future of advanced brachytherapy treatments and research.

Keywords: MRI-based brachytherapy, Geneva applicator, EBT4 film, 3D-printed holder

Introduction

Brachytherapy is a critical modality in cancer treatment, particularly for gynecological malignancies [1-3]. This technique allows for the precise delivery of high doses of radiation directly to the tumor while minimizing exposure to surrounding normal tissues. Such treatment is crucial for improving patient outcomes as it reduces side effects and enhances the effectiveness of therapy.

MRI-based brachytherapy offers significant advantages over traditional brachytherapy methods. The superior imaging capabilities of MRI provide better visualization and more accurate placement of the applicator, resulting in improved dose distribution. This leads to more effective treatment, potentially better clinical outcomes, and a reduction in complications. MRI-based techniques also enable the most accurate assessment of the cervix and any residual lesions, ensuring precise and safe treatment planning [4-6].

In 2021, the non-reimbursement system in Korea was updated for MRI-based 3D brachytherapy planning for cervical cancer following a new health technology assessment. Before this update, reimbursement policies favored traditional 2D or CT-based methods, hindering the adoption of MRI-guided techniques essential for precise tumor targeting and dose optimization. The updated system replaced traditional methods with MRI imaging, enhancing the precision and safety of treatment. Clinical textbooks and guidelines recognize MRI-based 3D brachytherapy planning as the most accurate method for evaluating the cervix and surrounding tissues while reducing the risk of damage to nearby organs [7-10]. This recognition underscores the technology’s effectiveness and safety, offering a more precise and efficient approach to brachytherapy planning for cervical cancer patients.

Commissioning the Geneva applicator (Elekta), introduced in 2020 as a replacement for the Utrecht and several other older applicators, is crucial to ensure its proper functioning and accurate dose delivery. This process involves verifying the device’s operation, detecting any manufacturing defects, and ensuring compliance with safety standards. It also helps medical physicists become familiar with the new equipment. This study aims to commission the Geneva applicator, focusing on wall thickness, dummy marker positions, and source dwell positions to ensure accurate dose delivery and safety.

Materials and Methods

1. Geneva applicator

The Geneva applicator is a versatile gynecological device designed for both intracavitary and interstitial brachytherapy treatments, specifically targeting the cervix and endometrium. Key features of the applicator include an integrated cervical stopper to prevent slippage from the intrauterine tandem, an interstitial template for the effective treatment of asymmetric diseases, and the ability to insert a flexible interstitial tube through the cervical stopper. Additionally, the applicator features a rotating and click mechanism for faster assembly compared to traditional screw mechanisms, such as the Utrecht applicator. A notable advantage of the Geneva applicator is its compatibility with various imaging modalities, including ultrasound, X-ray, CT, and MRI. Its nonmetallic construction ensures distortion-free images, which is crucial for accurate imaging and effective treatment planning [11].

The applicator primarily consists of several components, including an intrauterine tube (tandem tube), ovoid tubes, and interstitial ovoid pairs designed to accommodate optional needles. These components can be combined with compatible devices to reach a wide range of target areas. The minimum configuration includes two ovoid tubes with ovoid pairs inserted into the vagina and attached to a tandem tube. These tubes contain channels to guide a radioactive source to precise positions within the patient’s body (Fig. 1).

Figure 1. A Geneva applicator (Elekta) set comprising an intrauterine tube and a pair of ovoid tubes.

2. Commissioning parameters

The commissioning of the Geneva applicator can be broadly divided into three categories: General Inspection, Wall Thickness, and Distal Dwell Position. General inspection involves visual checks to detect possible cracks, verifying external dimensions using a caliper, checking for potential obstructions in the insertion items, and confirming the mechanical integrity of the applicator. Although crucial, this process is omitted in this paper. Instead, this paper focuses on two key processes: Wall Thickness and Distal Dwell Position. To accurately measure the transverse wall thickness of the tandem tube, a 3D-printed holder model provided by Elekta was used during commissioning. This holder minimizes tandem tube movement and ensures proper alignment during CT imaging, allowing for precise measurements.

Fig. 2 illustrates the 3D-printed holder designed for tandem tubes of varying tip lengths, as well as a holder for securing a pair of ovoid tubes. The holder includes a film insertion slot at the top (Fig. 2), which is used to secure the film for measuring the source dwell position. Specifically, the EBT4 film (Ashland) is pushed fully into the insertion slot, while the ovoid and tandem are inserted completely to ensure alignment between the starting points of the film and the tips. These holders were manufactured using the Fused Deposition Modeling method, as recommended in the white paper, utilizing polylactic acid filament. Upon completion, the holder’s dimensions were verified to ensure that both the film and the tubes could be fully inserted into their respective slots.

Figure 2. 3D-printed holders for a pair of ovoid tubes (green) and tandem tubes with varying tip lengths (gray). Film insertion slots are located at the top of each holder for measuring the dwell position.

3. Wall thickness and known length verification

Accurate measurement of wall thickness and proper positioning of dummy markers are critical components of the commissioning process for the Geneva applicator, as these factors directly influence the applicator’s performance and the precision of radiation delivery during brachytherapy treatments. The wall thickness of the tandem tube and the lunar-shaped ovoid tube was measured in both longitudinal and transverse directions to compare with the manufacturer’s specifications and confirm that the measurements fell within the specified tolerance range.

In the longitudinal direction, wall thickness was determined by measuring the distance between the outer tip and the inner tip of the tandem and ovoid tubes. In the transverse direction, particular attention was required due to the asymmetrical positioning of the inner wall within the tandem tube. The pixel width of the image to be measured was configured based on the CT DICOM header, and the window level was adjusted to the recommended settings of 50/1,200, as outlined in the white paper. Interpolation was applied to ensure a pixel width and height of 0.02 mm. Reference diameters, such as an outer diameter of 3.85 mm and an inner diameter of 2.55 mm, were used to draw circles. The distance between the centers of these circles was then calculated to determine the wall thickness.

Additionally, X-ray dummy markers were attached to the tandem and ovoid tubes to verify measurements against known lengths, and the locations of these markers were assessed. Special care was taken during the measurement of dummy marker positions, particularly for the ovoid tubes, as the size of the first marker differed in each dummy (Fig. 3). Although not a mandatory parameter for commissioning, and with no specified tolerance, the angle of curvature between the ovoid and tandem was also measured using CT imaging.

Figure 3. X-ray dummy markers for ovoid tubes (1, 2) and tandem tubes (3).

For quantitative verification of wall thickness and dummy marker position measurements, a Brilliance Big Bore CT scanner (Philips Healthcare) was used to ensure precise alignment of the setup. The longitudinal wall thickness and dummy marker positions were measured directly from the CT image viewer, while the transverse wall diameter was analyzed using ImageJ software (National Institutes of Health) according to the methods provided in the white paper.

4. Source position verification

Source position commissioning ensures that the applicator’s performance aligns with the planned treatment parameters, minimizing the risk of dose delivery errors and enhancing the overall safety and efficacy of brachytherapy. To verify the dwell positions of the tandem tube and a pair of ovoid tubes, a treatment plan was generated using the Oncentra treatment planning system (Elekta), utilizing the applicator library model. As recommended in the white paper, it is essential to verify the first two clinically used source positions within the ovoid tubes during commissioning. Therefore, the source positions were set at 8 mm and 15 mm for the tandem tube and at 6 mm and 15 mm for the ovoid tube from the outer wall. The dwell time and activity were calibrated accordingly.

For source position measurements, as mentioned above, the EBT4 film was fully inserted into the film insertion slot to align the starting point of the applicator’s outer edge with the starting point of the film. This film was securely fixed to prevent movement, and the setup was positioned on the bed of the microSelectron (Elekta) system (Fig. 4). Each tandem and ovoid tube pair underwent three separate measurements. The resulting film images were scanned using a flatbed scanner (Expression 10000 XL; Epson) at a resolution of 300 dots per inch and converted into TIFF files. Distances were then measured using RIT software (Radiological Imaging Technology) to ensure accurate determination of the source positions.

Figure 4. Applicator setups with EBT4 film (Ashland) for source dwell position measurements. (a) A pair of ovoid and a tandem on the table for measurement of the source dwell position and side views for them (b).

Results

The applicator model and the dummy marker positions captured by the CT scan were verified (Fig. 5). The dummy markers were correctly positioned within the tandem and ovoid tubes, and the red dots in the model corresponded to these positions, confirming alignment between the model and the actual markers.

Figure 5. The dummy marker position comparison between the applicator model in the treatment planning system and CT images.

Fig. 6a displays the longitudinal wall thickness and the positions of the dummy markers. The thicknesses of the outer shell, inner shell, and dummy marker positions were all within the specified tolerance ranges, as summarized in Table 1.

Table 1 . Comparison of longitudinal wall thickness, marker position, and curvature angles among the reference, applicator model, and CT images.

DistanceReference distance (mm)Applicator model (mm)*Deviation (mm)CT image (mm)†Deviation (mm)Angle (°)
Tandem tubeOuter to inner tip2.42.40.02.40.014.9
Inner tip to the most distal dwell position5.95.60.35.90.0
Outer to the most distal dwell position8.38.00.38.30.0
Ovoid tube 1Outer to inner tip1.01.00.01.00.0119.6
Inner tip to the most distal dwell position5.05.00.04.80.2
Outer to the most distal dwell position6.06.00.05.80.2
Ovoid tube 2Outer to inner tip1.01.00.01.00.0120.2
Inner tip to the most distal dwell position5.05.00.05.30.3
Outer to the most distal dwell position6.06.00.06.30.3


Figure 6. Example images for the measurement of the longitudinal wall thickness of the tandem and ovoid (a) and the transverse wall thickness measurement of the tandem tube and the measurement of the angle of curvatures using the ImageJ (National Institutes of Health) tool (b: left, outer; right, inner; c: ovoids and a tandem).

During the measurement of the transverse wall thickness of the tandem, the coordinates obtained from ImageJ corresponded to the vertices of a square surrounding the circles representing the external surface and the inner lumen. Based on these coordinates, the centers of the circles were calculated, and the shift between the two centers was determined using Pythagoras’ theorem. Finally, we calculated the minimum wall thickness in millimeters using the nominal wall thickness of 0.65 mm. The minimum distance value was calculated to be 0.57 mm, exceeding the minimum tolerance of 0.47 mm, thereby meeting the required specifications (Fig. 6b). Fig. 6c shows the sagittal view of the ovoids and tandem, with the bending angles analyzed using ImageJ. The ovoids have an angle of approximately 120°, and the tandem approximately 15°. Although no specific tolerance information is available, these values align closely with the specifications provided in the manual.

Fig. 7 illustrates the film used for source dwell position measurements and provides an example of the analysis software utilized for this process. Based on the results of three measurements for each setup, a Region of Interest was defined in the analysis software. The relevant areas were then analyzed, focusing on vertical and horizontal positions. The distance from the lowest point (assumed to be the source position) was calculated. The results of these measurements are summarized in Table 2, confirming that all values were within the specified tolerance range (within 1 mm), meeting the required standards.

Table 2 . Comparison of source dwell positions between reference values and measured data for tandem and ovoid tubes.

Source positionReference (mm)1st (mm)2nd (mm)3rd (mm)Average (mm)Deviation (mm)
Tandem18.307.828.498.488.26–0.04
215.0015.0715.0115.0315.040.04
Ovoid 116.005.996.136.156.090.09
215.0015.0014.9915.0015.000.00
Ovoid 216.006.116.046.106.080.08
215.0014.9914.9815.0415.000.00


Figure 7. Measured film sets for the source dwell position of the tandem and ovoid tubes. (a) EBT4 films (Ashland) and (b, c) examples for the dwell position analysis for ovoid and tandem with RIT software (Radiological Imaging Technology).

Discussion

Commissioning the applicator is an essential procedure to ensure its performance and safety in clinical practice. According to international guidelines [12], comprehensive commissioning is critical for verifying that all components meet the technical specifications required for accurate dose delivery. These guidelines emphasize that deviations in applicator performance, such as inaccurate source dwell positions or misaligned markers, can significantly impact patient outcomes. In this study, we report the commissioning results of the Geneva applicator, introduced as a replacement for older models like the Utrecht applicator, through a comprehensive evaluation of its physical dimensions and dose delivery positions. This process included verifying the device, detecting any defects, and ensuring compliance with safety standards, thereby facilitating its consistent and reliable use in clinical settings. In this study, we conducted the commissioning process for wall thickness, dummy marker positions, and source dwell positions, confirming that all measurements fell within the specified tolerance ranges. While the commissioning process generally proceeds smoothly, it is important to exercise great caution in alignment due to the tight tolerance criteria of ±1 mm or less. Utilizing a 3D-printed holder can significantly aid in achieving accurate measurements.

Conclusions

With recent updates to reimbursement policies in Korea for 3D brachytherapy planning in 2021, there is a strong expectation for an increase in treatments and further research in this field. The careful commissioning of the Geneva applicator will be crucial in supporting these advancements, ensuring that the technology can be utilized effectively and safely in clinical practice.

Funding

This study was supported by a grant from the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 2022R1F1A1063779) and a grant No. 0720233109 from the SNUH Research fund.

Conflicts of Interest

Chang Heon Choi and Jin Jegal are members of the editorial board of the Progress in Medical Physics, but have no role in the decision to publish this article. The other authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Availability of Data and Materials

All relevant data are within the paper and its Supporting Information files.

Author Contributions

Conceptualization: Jung-in Kim, Hyeongmin Jin. Methodology: Yoonsuk Huh, Jaeman Son, Seonghee Kang, Chang Heon Choi, Hyeongmin Jin. Project administration: Jung-in Kim. Measurement: Yoonsuk Huh, Hyojun Park, Jin Jegal, Inbeom Lee, Hyeongmin Jin. Validation: Yoonsuk Huh, Hyojun Park, Jin Jegal, Inbeom Lee, Hyeongmin Jin. Writing – original draft: Yoonsuk Huh. Writing – review & editing: Hyeongmin Jin.

Fig 1.

Figure 1.A Geneva applicator (Elekta) set comprising an intrauterine tube and a pair of ovoid tubes.
Progress in Medical Physics 2024; 35: 116-124https://doi.org/10.14316/pmp.2024.35.4.116

Fig 2.

Figure 2.3D-printed holders for a pair of ovoid tubes (green) and tandem tubes with varying tip lengths (gray). Film insertion slots are located at the top of each holder for measuring the dwell position.
Progress in Medical Physics 2024; 35: 116-124https://doi.org/10.14316/pmp.2024.35.4.116

Fig 3.

Figure 3.X-ray dummy markers for ovoid tubes (1, 2) and tandem tubes (3).
Progress in Medical Physics 2024; 35: 116-124https://doi.org/10.14316/pmp.2024.35.4.116

Fig 4.

Figure 4.Applicator setups with EBT4 film (Ashland) for source dwell position measurements. (a) A pair of ovoid and a tandem on the table for measurement of the source dwell position and side views for them (b).
Progress in Medical Physics 2024; 35: 116-124https://doi.org/10.14316/pmp.2024.35.4.116

Fig 5.

Figure 5.The dummy marker position comparison between the applicator model in the treatment planning system and CT images.
Progress in Medical Physics 2024; 35: 116-124https://doi.org/10.14316/pmp.2024.35.4.116

Fig 6.

Figure 6.Example images for the measurement of the longitudinal wall thickness of the tandem and ovoid (a) and the transverse wall thickness measurement of the tandem tube and the measurement of the angle of curvatures using the ImageJ (National Institutes of Health) tool (b: left, outer; right, inner; c: ovoids and a tandem).
Progress in Medical Physics 2024; 35: 116-124https://doi.org/10.14316/pmp.2024.35.4.116

Fig 7.

Figure 7.Measured film sets for the source dwell position of the tandem and ovoid tubes. (a) EBT4 films (Ashland) and (b, c) examples for the dwell position analysis for ovoid and tandem with RIT software (Radiological Imaging Technology).
Progress in Medical Physics 2024; 35: 116-124https://doi.org/10.14316/pmp.2024.35.4.116

Table 1 Comparison of longitudinal wall thickness, marker position, and curvature angles among the reference, applicator model, and CT images

DistanceReference distance (mm)Applicator model (mm)*Deviation (mm)CT image (mm)†Deviation (mm)Angle (°)
Tandem tubeOuter to inner tip2.42.40.02.40.014.9
Inner tip to the most distal dwell position5.95.60.35.90.0
Outer to the most distal dwell position8.38.00.38.30.0
Ovoid tube 1Outer to inner tip1.01.00.01.00.0119.6
Inner tip to the most distal dwell position5.05.00.04.80.2
Outer to the most distal dwell position6.06.00.05.80.2
Ovoid tube 2Outer to inner tip1.01.00.01.00.0120.2
Inner tip to the most distal dwell position5.05.00.05.30.3
Outer to the most distal dwell position6.06.00.06.30.3

Table 2 Comparison of source dwell positions between reference values and measured data for tandem and ovoid tubes

Source positionReference (mm)1st (mm)2nd (mm)3rd (mm)Average (mm)Deviation (mm)
Tandem18.307.828.498.488.26–0.04
215.0015.0715.0115.0315.040.04
Ovoid 116.005.996.136.156.090.09
215.0015.0014.9915.0015.000.00
Ovoid 216.006.116.046.106.080.08
215.0014.9914.9815.0415.000.00

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Korean Society of Medical Physics

Vol.35 No.4
December 2024

pISSN 2508-4445
eISSN 2508-4453
Formerly ISSN 1226-5829

Frequency: Quarterly

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