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Original Article

Progress in Medical Physics 2024; 35(2): 52-57

Published online June 30, 2024 https://doi.org/10.14316/pmp.2024.35.2.52

Copyright © Korean Society of Medical Physics.

Simulating the Effect of Junction Setup Error in Dual-Isocentric Volumetric Modulated Arc Therapy for Pelvic Radiotherapy with a Large Target

Hojeong Lee1 , Dong Woon Kim1 , Ji Hyeon Joo1,2 , Yongkan Ki1,2 , Wontaek Kim2,3 , Dahl Park3 , Jiho Nam3 , Dong Hyeon Kim2,3 , Hosang Jeon1

1Department of Radiation Oncology and Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Yangsan, 2Department of Radiation Oncology, Pusan National University School of Medicine, Yangsan, 3Department of Radiation Oncology, Pusan National University Hospital, Busan, Korea

Correspondence to:Hosang Jeon
(hjeon316@gmail.com)
Tel: 82-55-360-2693
Fax: 82-55-360-3449

Received: March 4, 2024; Revised: May 24, 2024; Accepted: June 10, 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: The use of two adjacent radiation beams to treat a lesion that is larger than the maximum field of a machine may lead to higher or lower dose distribution at the junction than expected. Therefore, evaluation of the junction dose is crucial for radiotherapy. Volumetric modulated arc therapy (VMAT) can effectively protect surrounding normal tissues by implementing a complex dose distribution; therefore, two adjacent VMAT fields can effectively treat large lesions. However, VMAT can lead to significant errors in the junction dose between fields if setup errors occur due to its highly complex dose distributions.
Methods: In this study, setup errors of ±1, ±3, and ±5 mm were assumed during radiotherapy for treating large lesions in the lower abdomen, and their effects on the treatment dose distribution and target coverage were analyzed using gamma pass rate (GP) and homogeneity index (HI). All studies were performed using a computational simulation method based on our radiation treatment planning software.
Results: Consequently, when the setup error was more than ±3 mm, most GP values using a 3%/3-mm criterion decreased by <90%. GP was independent of the direction of the field gap (FG), whereas HI values were relatively more affected by negative values for FG.
Conclusions: Therefore, the size and direction of setup errors should be carefully managed when performing dual-isocentric VMATs for large targets.

KeywordsLarge target, Radiation therapy, Volumetric modulated arc therapy, Setup error, Homogeneity index

When employing two adjacent radiation therapy beams, the nature of the dose distribution at their junction is a long-standing topic of study because of the risk of the dose becoming higher or lower than the expected dose (i.e., forming hot or cold spots). This is particularly pertinent when treating very large lesions using a linear accelerator with a limited maximum field size, as more than two fields are required to cover the whole lesion. The cranio–spinal irradiation technique introduced by Faiz M. Khan is a representative example of this, and other cases have been described wherein radiation therapy for the lower abdominal region requires dealing with large lesions [1-4].

Volumetric modulated arc therapy (VMAT) [5,6] is a widely used technique in modern radiation therapy. VMAT employs the benefits of two other techniques namely, intensity modulated radiation therapy (IMRT), which allows for complex dose distribution, and rotational therapy, which enables rapid dose delivery and minimizes damage to the surrounding normal tissues; at our institution, VMAT has been adopted and used as a standard technique for IMRT. In addition, when large lesions exceed the maximum field size of the linear accelerator, treatment is performed using two adjacent VMAT fields to maximize its benefits. In particular, the radiation treatment planning (RTP) system in our institute can simultaneously optimize two VMAT beams with different beam centers, so the planning stage does not need to consider hot/cold spots that may occur at the junction.

This study aimed to analyze the effect of patient setup errors on dose distribution when using two adjacent VMAT fields for treatment. When treating with two adjacent fields, the patient must be positioned exactly where each field specifies, particularly for VMAT techniques that deliver complex modulated dose distributions to the patient. However, a degree of patient setup error is inevitable, and, consequently, the relative setup error between the two VMAT fields crucially requires prior analysis of how such errors affect dose distribution. Computational simulations using RTP system were performed to exclude the possible experimental errors and accurately evaluate the effect of patient setup errors on dose delivery. Finally, the calculated dose distributions for each situation were compared and analyzed.

1. Plan conditions

The three scan ranges of computed tomography images used in different VMAT plans for setup error simulation in this study were >50 cm along the cranial–caudal direction, and the total volumes of the planning target volumes (PTVs) were 861–3,638 cm3. MONACO (v6.1.2; Elekta) RTP was used to generate the plan. To cover a large treatment area, fields A and B were used with different field centers while their field borders were in contact with each other (Fig. 1). The details of the three planning parameters are presented in Table 1.

Table 1 Plan parameters for the three patients

PatientTargetMUCalculation time (s)


RangeVolume (cm3)Field AField B
1L-spine, femur3,6382,0171,1361,724
2T-spine, S-spine9868677951,387
3C-spine, L-spine8616741,028980

MU, monitor unit.


Figure 1.Description of field gap (FG) simulation between fields A and B. (a) Negative FG, (b) golden standard, and (c) positive FG.

2. Simulation of setup error

To computationally simulate setup errors, verification plans for the three patients were created. Furthermore, to implement the setup error when a patient was moved to field B position after being treated in field A, the position of field B was moved by x cm in the axis direction to create the corresponding verification plan with a field gap (FG). Finally, the dose was recalculated to obtain a dose distribution with the setup error. Six FGs, viz., −5, −3, −1, 1, 3, and 5 mm were used, and plans having FGs for the three patients were generated so the total number of plans with non-zero FGs was 18. The setup error conditions established are depicted in Fig. 1.

3. Analysis

To analyze the effect of the size of setup error on dose distribution, gamma evaluation was performed using seven gamma criteria of 3%/3, 3%/2, 2%/3, 2%/2, 2%/1, 1%/2, and 1%/1 mm. Homogeneity index (HI) was calculated as shown in Equation 1 using the dose D_(2%) that occupies <2%, dose D_(98%) that occupies >98%, and dose D_(50%) that occupies 50% of PTV volume.

HI= D2 %D98 %D50 %

HI has a value of 0 in the ideal case and it increases as the uniformity of the target dose coverage decreases, making it a representative factor to assess the homogeneity of dose distribution delivered to PTV. Both the gamma pass rate (GP) and HI were determined to comprehensively analyze the effects of changes in FG size on dose distribution and target coverage.

1. GP

Several dose distributions computationally simulated for FGs and gamma evaluation results are shown in Figs. 2 and 3, respectively. All GP using a gamma criterion of 3%/3 mm were >90% at an FG of less than or equal to ±3 mm. However, when the FG was ±5 mm, all GPs were <90%. Furthermore, GPs were <90% for most FG conditions when the GP criteria were stricter than 3%/3 mm (Table 2). GP of patient 2 was lower than that of other patients (Fig. 3) because the PTV occupancy ratio of field B over field A was the highest for patient 2.

Table 2 Gamma pass rates and homogeneity indices

PatientFG (mm)Gamma pass rate (%)HI

3/3*3/22/32/22/11/21/1
1−586.180.983.577.063.970.055.30.17451
−391.686.589.282.668.675.059.40.13080
−197.795.196.291.876.584.165.40.09601
197.694.895.991.676.784.165.90.09524
392.086.989.883.069.275.660.00.11476
586.380.983.677.264.870.556.30.14643
2−576.871.073.567.059.261.552.30.25927
−390.481.387.076.765.769.756.60.15625
−198.797.298.095.079.388.666.40.06975
198.797.198.094.779.388.266.30.06311
390.081.586.776.865.970.157.30.12905
576.671.373.767.860.162.653.00.19547
3−586.480.984.276.863.970.353.20.36541
−393.288.491.484.970.678.058.40.28887
−199.197.598.395.481.689.366.50.22989
198.997.198.194.881.288.766.60.21641
393.588.691.684.870.778.258.90.22386
587.181.384.877.364.571.154.40.23933

FG, field gap; HI, homogeneity index.

*Gamma criteria are presented as percent dose/distance to agreement.


Figure 2.Comparison of calculated dose distribution with five examples for patient 1 having different field gap (FG) values in the dose range of 80%–110%. (a) –5.0 mm (FG), (b) –3.0 mm, (c) 0 mm, (d) 3.0 mm, and (e) 5.0 mm.

Figure 3.Gamma pass rates of all plans using the gamma criteria of (a) 3%/3 mm, (b) 2%/2 mm, and (c) 1%/1 mm with different setup errors.

2. HI

The highest HI values were 0.26639 and 0.19374 on an average for FGs of −5 and 5 mm, respectively. The lowest HI values were 0.13188 and 0.12492 on an average for FGs of −1 and 1 mm, respectively. Fig. 4 shows a comparison of HI across all plans. HI increased with increased absolute value of FG, which was higher when FG had negative values.

Figure 4.Homogeneity indices of all plans with different setup errors.

GP values were <90% with a gamma criterion of 3%/3 mm, which is one of the widely used GP criteria in our simulation study. Furthermore, when stricter GP criteria were applied, GP values dropped further, with values approaching 50% at 1%/1 mm. This suggests that reducing setup errors when performing VMAT while using two different fields is vital for precisely covering large PTVs.

The decrease in GP with increasing FG was independent of the sign of FG values (Fig. 4), which indicates the direction of setup errors. However, HI seemed to be more affected when FG had negative values (Fig. 4). This implies that PTV coverage is likely to be poorer when two neighboring VMAT fields overlap each other because of setup errors, which must be considered during patient setup in clinical settings.

Although PTV volumes of the three patients differed, this difference did not significantly affect GP results. In the treatment scenario assumed in this study, field A was delivered after accurate patient setup via image guidance and assuming that some setup errors may occur while moving the patient to field B. Therefore, GP value would be lower with a higher PTV ratio occupied by field B rather than the absolute PTV volume. In this study, patient 2 had the highest PTV percentage in field B among the three patients and the lowest GP values with FGs of ±3 and ±5 mm.

This study has several limitations. We considered only one specific target that spanned the pelvis and femur regions; therefore, further research may be needed on different regions. However, as the types of targets with size greater than 40×40 cm2 are quite rare, the trends derived from this study are considered sufficiently meaningful. In addition, only setup errors in the longitudinal direction were considered to evaluate the effects between two adjacent fields along the longitudinal axis. The effects of setup errors in the anterior–posterior and lateral directions must be investigated in further study.

The effect of setup error sizes between neighboring fields on dose distribution and target coverage in treatments involving large pelvic areas requiring two VMAT fields was computationally simulated. Setup errors that exceed approximately 3 mm could severely aggravate both GP and target coverage. Therefore, caution must be exercised to navigate setup errors between fields within ≤3 mm for large-area VMAT treatments.

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea, funded by the Korean government (2022R1F1A1064176), and a 2023 research grant from Pusan National University Yangsan Hospital.

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

Conceptualization: Hojeong Lee, Hosang Jeon. Data curation: Hojeong Lee, Dong Woon Kim. Formal analysis: Dong Woon Kim, Dong Hyeon Kim. Funding acquisition: Ji Hyeon Joo, Dong Hyeon Kim. Investigation: Dong Woon Kim, Wontaek Kim. Methodology: Hojeong Lee, Jiho Nam. Project administration: Yongkan Ki, Hosang Jeon. Resources: Hojeong Lee, Wontaek Kim. Software: Hojeong Lee, Dahl Park. Supervision: Ji Hyeon Joo, Yongkan Ki. Validation: Hojeong Lee, Hosang Jeon. Visualization: Hojeong Lee, Dahl Park. Writing – original draft: Hojeong Lee, Hosang Jeon. Writing – review & editing: Hosang Jeon, Jiho Nam.

  1. Cao F, Harrop S, Cooper N, Steiner P, Karvat A. The dose junction issue associated with photon beams for large volume radiation therapy and the sensitivity to set-up error. J Med Phys Appl Sci. 2017;2:8.
  2. Zhou Y, Ai Y, Han C, Zheng X, Yi J, Xie C, et al. Impact of setup errors on multi-isocenter volumetric modulated arc therapy for craniospinal irradiation. J Appl Clin Med Phys. 2020;21:115-123.
    Pubmed KoreaMed CrossRef
  3. Prabhu RS, Dhakal R, Piantino M, Bahar N, Meaders KS, Fasola CE, et al. Volumetric modulated arc therapy (VMAT) craniospinal irradiation (CSI) for children and adults: a practical guide for implementation. Pract Radiat Oncol. 2022;12:e101-e109.
    Pubmed CrossRef
  4. Morrison CT, Symons KL, Woodings SJ, House MJ. Verification of junction dose between VMAT arcs of total body irradiation using a Sun Nuclear ArcCHECK phantom. J Appl Clin Med Phys. 2017;18:177-182.
    Pubmed KoreaMed CrossRef
  5. Semenenko VA, Reitz B, Day E, Qi XS, Miften M, Li XA. Evaluation of a commercial biologically based IMRT treatment planning system. Med Phys. 2008;35:5851-5860.
    Pubmed CrossRef
  6. Teoh M, Clark CH, Wood K, Whitaker S, Nisbet A. Volumetric modulated arc therapy: a review of current literature and clinical use in practice. Br J Radiol. 2011;84:967-996.
    Pubmed KoreaMed CrossRef

Article

Original Article

Progress in Medical Physics 2024; 35(2): 52-57

Published online June 30, 2024 https://doi.org/10.14316/pmp.2024.35.2.52

Copyright © Korean Society of Medical Physics.

Simulating the Effect of Junction Setup Error in Dual-Isocentric Volumetric Modulated Arc Therapy for Pelvic Radiotherapy with a Large Target

Hojeong Lee1 , Dong Woon Kim1 , Ji Hyeon Joo1,2 , Yongkan Ki1,2 , Wontaek Kim2,3 , Dahl Park3 , Jiho Nam3 , Dong Hyeon Kim2,3 , Hosang Jeon1

1Department of Radiation Oncology and Research Institute for Convergence of Biomedical Science and Technology, Pusan National University Yangsan Hospital, Yangsan, 2Department of Radiation Oncology, Pusan National University School of Medicine, Yangsan, 3Department of Radiation Oncology, Pusan National University Hospital, Busan, Korea

Correspondence to:Hosang Jeon
(hjeon316@gmail.com)
Tel: 82-55-360-2693
Fax: 82-55-360-3449

Received: March 4, 2024; Revised: May 24, 2024; Accepted: June 10, 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: The use of two adjacent radiation beams to treat a lesion that is larger than the maximum field of a machine may lead to higher or lower dose distribution at the junction than expected. Therefore, evaluation of the junction dose is crucial for radiotherapy. Volumetric modulated arc therapy (VMAT) can effectively protect surrounding normal tissues by implementing a complex dose distribution; therefore, two adjacent VMAT fields can effectively treat large lesions. However, VMAT can lead to significant errors in the junction dose between fields if setup errors occur due to its highly complex dose distributions.
Methods: In this study, setup errors of ±1, ±3, and ±5 mm were assumed during radiotherapy for treating large lesions in the lower abdomen, and their effects on the treatment dose distribution and target coverage were analyzed using gamma pass rate (GP) and homogeneity index (HI). All studies were performed using a computational simulation method based on our radiation treatment planning software.
Results: Consequently, when the setup error was more than ±3 mm, most GP values using a 3%/3-mm criterion decreased by <90%. GP was independent of the direction of the field gap (FG), whereas HI values were relatively more affected by negative values for FG.
Conclusions: Therefore, the size and direction of setup errors should be carefully managed when performing dual-isocentric VMATs for large targets.

Keywords: Large target, Radiation therapy, Volumetric modulated arc therapy, Setup error, Homogeneity index

Introduction

When employing two adjacent radiation therapy beams, the nature of the dose distribution at their junction is a long-standing topic of study because of the risk of the dose becoming higher or lower than the expected dose (i.e., forming hot or cold spots). This is particularly pertinent when treating very large lesions using a linear accelerator with a limited maximum field size, as more than two fields are required to cover the whole lesion. The cranio–spinal irradiation technique introduced by Faiz M. Khan is a representative example of this, and other cases have been described wherein radiation therapy for the lower abdominal region requires dealing with large lesions [1-4].

Volumetric modulated arc therapy (VMAT) [5,6] is a widely used technique in modern radiation therapy. VMAT employs the benefits of two other techniques namely, intensity modulated radiation therapy (IMRT), which allows for complex dose distribution, and rotational therapy, which enables rapid dose delivery and minimizes damage to the surrounding normal tissues; at our institution, VMAT has been adopted and used as a standard technique for IMRT. In addition, when large lesions exceed the maximum field size of the linear accelerator, treatment is performed using two adjacent VMAT fields to maximize its benefits. In particular, the radiation treatment planning (RTP) system in our institute can simultaneously optimize two VMAT beams with different beam centers, so the planning stage does not need to consider hot/cold spots that may occur at the junction.

This study aimed to analyze the effect of patient setup errors on dose distribution when using two adjacent VMAT fields for treatment. When treating with two adjacent fields, the patient must be positioned exactly where each field specifies, particularly for VMAT techniques that deliver complex modulated dose distributions to the patient. However, a degree of patient setup error is inevitable, and, consequently, the relative setup error between the two VMAT fields crucially requires prior analysis of how such errors affect dose distribution. Computational simulations using RTP system were performed to exclude the possible experimental errors and accurately evaluate the effect of patient setup errors on dose delivery. Finally, the calculated dose distributions for each situation were compared and analyzed.

Materials and Methods

1. Plan conditions

The three scan ranges of computed tomography images used in different VMAT plans for setup error simulation in this study were >50 cm along the cranial–caudal direction, and the total volumes of the planning target volumes (PTVs) were 861–3,638 cm3. MONACO (v6.1.2; Elekta) RTP was used to generate the plan. To cover a large treatment area, fields A and B were used with different field centers while their field borders were in contact with each other (Fig. 1). The details of the three planning parameters are presented in Table 1.

Table 1 . Plan parameters for the three patients.

PatientTargetMUCalculation time (s)


RangeVolume (cm3)Field AField B
1L-spine, femur3,6382,0171,1361,724
2T-spine, S-spine9868677951,387
3C-spine, L-spine8616741,028980

MU, monitor unit..



Figure 1. Description of field gap (FG) simulation between fields A and B. (a) Negative FG, (b) golden standard, and (c) positive FG.

2. Simulation of setup error

To computationally simulate setup errors, verification plans for the three patients were created. Furthermore, to implement the setup error when a patient was moved to field B position after being treated in field A, the position of field B was moved by x cm in the axis direction to create the corresponding verification plan with a field gap (FG). Finally, the dose was recalculated to obtain a dose distribution with the setup error. Six FGs, viz., −5, −3, −1, 1, 3, and 5 mm were used, and plans having FGs for the three patients were generated so the total number of plans with non-zero FGs was 18. The setup error conditions established are depicted in Fig. 1.

3. Analysis

To analyze the effect of the size of setup error on dose distribution, gamma evaluation was performed using seven gamma criteria of 3%/3, 3%/2, 2%/3, 2%/2, 2%/1, 1%/2, and 1%/1 mm. Homogeneity index (HI) was calculated as shown in Equation 1 using the dose D_(2%) that occupies <2%, dose D_(98%) that occupies >98%, and dose D_(50%) that occupies 50% of PTV volume.

HI= D2 %D98 %D50 %

HI has a value of 0 in the ideal case and it increases as the uniformity of the target dose coverage decreases, making it a representative factor to assess the homogeneity of dose distribution delivered to PTV. Both the gamma pass rate (GP) and HI were determined to comprehensively analyze the effects of changes in FG size on dose distribution and target coverage.

Results

1. GP

Several dose distributions computationally simulated for FGs and gamma evaluation results are shown in Figs. 2 and 3, respectively. All GP using a gamma criterion of 3%/3 mm were >90% at an FG of less than or equal to ±3 mm. However, when the FG was ±5 mm, all GPs were <90%. Furthermore, GPs were <90% for most FG conditions when the GP criteria were stricter than 3%/3 mm (Table 2). GP of patient 2 was lower than that of other patients (Fig. 3) because the PTV occupancy ratio of field B over field A was the highest for patient 2.

Table 2 . Gamma pass rates and homogeneity indices.

PatientFG (mm)Gamma pass rate (%)HI

3/3*3/22/32/22/11/21/1
1−586.180.983.577.063.970.055.30.17451
−391.686.589.282.668.675.059.40.13080
−197.795.196.291.876.584.165.40.09601
197.694.895.991.676.784.165.90.09524
392.086.989.883.069.275.660.00.11476
586.380.983.677.264.870.556.30.14643
2−576.871.073.567.059.261.552.30.25927
−390.481.387.076.765.769.756.60.15625
−198.797.298.095.079.388.666.40.06975
198.797.198.094.779.388.266.30.06311
390.081.586.776.865.970.157.30.12905
576.671.373.767.860.162.653.00.19547
3−586.480.984.276.863.970.353.20.36541
−393.288.491.484.970.678.058.40.28887
−199.197.598.395.481.689.366.50.22989
198.997.198.194.881.288.766.60.21641
393.588.691.684.870.778.258.90.22386
587.181.384.877.364.571.154.40.23933

FG, field gap; HI, homogeneity index..

*Gamma criteria are presented as percent dose/distance to agreement..



Figure 2. Comparison of calculated dose distribution with five examples for patient 1 having different field gap (FG) values in the dose range of 80%–110%. (a) –5.0 mm (FG), (b) –3.0 mm, (c) 0 mm, (d) 3.0 mm, and (e) 5.0 mm.

Figure 3. Gamma pass rates of all plans using the gamma criteria of (a) 3%/3 mm, (b) 2%/2 mm, and (c) 1%/1 mm with different setup errors.

2. HI

The highest HI values were 0.26639 and 0.19374 on an average for FGs of −5 and 5 mm, respectively. The lowest HI values were 0.13188 and 0.12492 on an average for FGs of −1 and 1 mm, respectively. Fig. 4 shows a comparison of HI across all plans. HI increased with increased absolute value of FG, which was higher when FG had negative values.

Figure 4. Homogeneity indices of all plans with different setup errors.

Discussion

GP values were <90% with a gamma criterion of 3%/3 mm, which is one of the widely used GP criteria in our simulation study. Furthermore, when stricter GP criteria were applied, GP values dropped further, with values approaching 50% at 1%/1 mm. This suggests that reducing setup errors when performing VMAT while using two different fields is vital for precisely covering large PTVs.

The decrease in GP with increasing FG was independent of the sign of FG values (Fig. 4), which indicates the direction of setup errors. However, HI seemed to be more affected when FG had negative values (Fig. 4). This implies that PTV coverage is likely to be poorer when two neighboring VMAT fields overlap each other because of setup errors, which must be considered during patient setup in clinical settings.

Although PTV volumes of the three patients differed, this difference did not significantly affect GP results. In the treatment scenario assumed in this study, field A was delivered after accurate patient setup via image guidance and assuming that some setup errors may occur while moving the patient to field B. Therefore, GP value would be lower with a higher PTV ratio occupied by field B rather than the absolute PTV volume. In this study, patient 2 had the highest PTV percentage in field B among the three patients and the lowest GP values with FGs of ±3 and ±5 mm.

This study has several limitations. We considered only one specific target that spanned the pelvis and femur regions; therefore, further research may be needed on different regions. However, as the types of targets with size greater than 40×40 cm2 are quite rare, the trends derived from this study are considered sufficiently meaningful. In addition, only setup errors in the longitudinal direction were considered to evaluate the effects between two adjacent fields along the longitudinal axis. The effects of setup errors in the anterior–posterior and lateral directions must be investigated in further study.

Conclusions

The effect of setup error sizes between neighboring fields on dose distribution and target coverage in treatments involving large pelvic areas requiring two VMAT fields was computationally simulated. Setup errors that exceed approximately 3 mm could severely aggravate both GP and target coverage. Therefore, caution must be exercised to navigate setup errors between fields within ≤3 mm for large-area VMAT treatments.

Funding

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea, funded by the Korean government (2022R1F1A1064176), and a 2023 research grant from Pusan National University Yangsan Hospital.

Conflicts of Interest

The authors have nothing to disclose.

Availability of Data and Materials

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

Author Contributions

Conceptualization: Hojeong Lee, Hosang Jeon. Data curation: Hojeong Lee, Dong Woon Kim. Formal analysis: Dong Woon Kim, Dong Hyeon Kim. Funding acquisition: Ji Hyeon Joo, Dong Hyeon Kim. Investigation: Dong Woon Kim, Wontaek Kim. Methodology: Hojeong Lee, Jiho Nam. Project administration: Yongkan Ki, Hosang Jeon. Resources: Hojeong Lee, Wontaek Kim. Software: Hojeong Lee, Dahl Park. Supervision: Ji Hyeon Joo, Yongkan Ki. Validation: Hojeong Lee, Hosang Jeon. Visualization: Hojeong Lee, Dahl Park. Writing – original draft: Hojeong Lee, Hosang Jeon. Writing – review & editing: Hosang Jeon, Jiho Nam.

Fig 1.

Figure 1.Description of field gap (FG) simulation between fields A and B. (a) Negative FG, (b) golden standard, and (c) positive FG.
Progress in Medical Physics 2024; 35: 52-57https://doi.org/10.14316/pmp.2024.35.2.52

Fig 2.

Figure 2.Comparison of calculated dose distribution with five examples for patient 1 having different field gap (FG) values in the dose range of 80%–110%. (a) –5.0 mm (FG), (b) –3.0 mm, (c) 0 mm, (d) 3.0 mm, and (e) 5.0 mm.
Progress in Medical Physics 2024; 35: 52-57https://doi.org/10.14316/pmp.2024.35.2.52

Fig 3.

Figure 3.Gamma pass rates of all plans using the gamma criteria of (a) 3%/3 mm, (b) 2%/2 mm, and (c) 1%/1 mm with different setup errors.
Progress in Medical Physics 2024; 35: 52-57https://doi.org/10.14316/pmp.2024.35.2.52

Fig 4.

Figure 4.Homogeneity indices of all plans with different setup errors.
Progress in Medical Physics 2024; 35: 52-57https://doi.org/10.14316/pmp.2024.35.2.52

Table 1 Plan parameters for the three patients

PatientTargetMUCalculation time (s)


RangeVolume (cm3)Field AField B
1L-spine, femur3,6382,0171,1361,724
2T-spine, S-spine9868677951,387
3C-spine, L-spine8616741,028980

MU, monitor unit.


Table 2 Gamma pass rates and homogeneity indices

PatientFG (mm)Gamma pass rate (%)HI

3/3*3/22/32/22/11/21/1
1−586.180.983.577.063.970.055.30.17451
−391.686.589.282.668.675.059.40.13080
−197.795.196.291.876.584.165.40.09601
197.694.895.991.676.784.165.90.09524
392.086.989.883.069.275.660.00.11476
586.380.983.677.264.870.556.30.14643
2−576.871.073.567.059.261.552.30.25927
−390.481.387.076.765.769.756.60.15625
−198.797.298.095.079.388.666.40.06975
198.797.198.094.779.388.266.30.06311
390.081.586.776.865.970.157.30.12905
576.671.373.767.860.162.653.00.19547
3−586.480.984.276.863.970.353.20.36541
−393.288.491.484.970.678.058.40.28887
−199.197.598.395.481.689.366.50.22989
198.997.198.194.881.288.766.60.21641
393.588.691.684.870.778.258.90.22386
587.181.384.877.364.571.154.40.23933

FG, field gap; HI, homogeneity index.

*Gamma criteria are presented as percent dose/distance to agreement.


References

  1. Cao F, Harrop S, Cooper N, Steiner P, Karvat A. The dose junction issue associated with photon beams for large volume radiation therapy and the sensitivity to set-up error. J Med Phys Appl Sci. 2017;2:8.
  2. Zhou Y, Ai Y, Han C, Zheng X, Yi J, Xie C, et al. Impact of setup errors on multi-isocenter volumetric modulated arc therapy for craniospinal irradiation. J Appl Clin Med Phys. 2020;21:115-123.
    Pubmed KoreaMed CrossRef
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Korean Society of Medical Physics

Vol.35 No.2
June 2024

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

Frequency: Quarterly

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