Tolerance levels of mass density for adaptive helical tomotherapy using MVCT

Tsunemine, Shogo; Ozawa, Shogo; Nakao, Minoru; Miura, Hideharu; Saito, A.; Kawahara, Daisuke; Onishi, Yasuhiko; Onishi, Takashi; Okawa, Fumito; Terai, Atsushi; Hashiguchi, Taiki; Yamasaki, Hidetoshi; Maruta, Tsutomu; Murakami, Yuji; Nagata, Yasushi

doi:10.1093/jrr/rrac071

Cited by 3 publications

(9 citation statements)

References 14 publications

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“…Furthermore, the entire ρ for adipose/muscle was underestimated for Tomotherapy because the CT‐ ρ of the real water (CT number: 0 HU, ρ : 1.0 g/cm 3 ) was lower than that obtained from the calibration curve based on human tissue (Figure 7). The average Δ ρ m value for adipose/muscle was 2.1% for Tomotherapy TPSs, which is comparable to the target dose difference of 1%–2% for prostate cancer 11 …”

Section: Discussionmentioning

confidence: 63%

“…The average Δρ m value for adipose/muscle was 2.1% for Tomotherapy TPSs,which is comparable to the target dose difference of 1%-2% for prostate cancer. 11 Dosimetry audits for density inhomogeneity were implemented through end-to-end tests with an anthropomorphic or inhomogeneous phantom. 2,3,5 If the dose deviation at their institute exceeded the tolerance level of the dosimetry audit, the participating institutes attempted to detect the cause.…”

Section: Presented In Table 2 Was Established Based On Internationalmentioning

confidence: 99%

“…A CT number calibration survey was conducted using TEMs within the European Particle Therapy Network, 7 indicating that CT number calibration curve deviations among various institutes led to dose deviations. [8][9][10][11] The tolerance levels of CT number,ρ, and ρ e in photon radiation therapy have been suggested in guidance documentations 12 and a previous study. 13,14 The symbols ρ, ρ e , and stopping-power ratio of TEMs must be consistent with those of human tissues 15 ; hence, inconsistencies in the TEMs owing to insufficient material investigation can cause undesirable influences on the CT number calibration audit.…”

Section: Introductionmentioning

confidence: 99%

“…Since the accuracy of the dose calculation by the participating institutions provides an accurate assessment of the survival curves for a clinical trial, 6 it is reasonable to verify the inhomogeneous corrections in the TPS by comparing the CT number calibration curves with human tissue. A CT number calibration survey was conducted using TEMs within the European Particle Therapy Network, 7 indicating that CT number calibration curve deviations among various institutes led to dose deviations 8–11 . The tolerance levels of CT number, ρ , and ρ e in photon radiation therapy have been suggested in guidance documentations 12 and a previous study 13,14 …”

Section: Introductionmentioning

confidence: 99%

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CT number calibration audit in photon radiation therapy

Nakao,

Ozawa,

Miura

et al. 2023

Medical Physics

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BackgroundInadequate computed tomography (CT) number calibration curves affect dose calculation accuracy. Although CT number calibration curves registered in treatment planning systems (TPSs) should be consistent with human tissues, it is unclear whether adequate CT number calibration is performed because CT number calibration curves have not been assessed for various types of CT number calibration phantoms and TPSs.PurposeThe purpose of this study was to investigate CT number calibration curves for mass density (ρ) and relative electron density (ρe).MethodsA CT number calibration audit phantom was sent to 24 Japanese photon therapy institutes from the evaluating institute and scanned using their individual clinical CT scan protocols. The CT images of the audit phantom and institute‐specific CT number calibration curves were submitted to the evaluating institute for analyzing the calibration curves registered in the TPSs at the participating institutes. The institute‐specific CT number calibration curves were created using commercial phantom (Gammex, Gammex Inc., Middleton, WI, USA) or CIRS phantom (Computerized Imaging Reference Systems, Inc., Norfolk, VA, USA)). At the evaluating institute, theoretical CT number calibration curves were created using a stoichiometric CT number calibration method based on the CT image, and the institute‐specific CT number calibration curves were compared with the theoretical calibration curve. Differences in ρ and ρe over the multiple points on the curve (Δρm and Δρe,m, respectively) were calculated for each CT number, categorized for each phantom vendor and TPS, and evaluated for three tissue types: lung, soft tissues, and bones. In particular, the CT‐ρ calibration curves for Tomotherapy TPSs (ACCURAY, Sunnyvale, CA, USA) were categorized separately from the Gammex CT‐ρ calibration curves because the available tissue‐equivalent materials (TEMs) were limited by the manufacturer recommendations. In addition, the differences in ρ and ρe for the specific TEMs (ΔρTEM and Δρe,TEM, respectively) were calculated by subtracting the ρ or ρe of the TEMs from the theoretical CT‐ρ or CT‐ρe calibration curve.ResultsThe mean ± standard deviation (SD) of Δρm and Δρe,m for the Gammex phantom were −1.1 ± 1.2 g/cm3 and −0.2 ± 1.1, −0.3 ± 0.9 g/cm3 and 0.8 ± 1.3, and −0.9 ± 1.3 g/cm3 and 1.0 ± 1.5 for lung, soft tissues, and bones, respectively. The mean ± SD of Δρm and Δρe,m for the CIRS phantom were 0.3 ± 0.8 g/cm3 and 0.9 ± 0.9, 0.6 ± 0.6 g/cm3 and 1.4 ± 0.8, and 0.2 ± 0.5 g/cm3 and 1.6 ± 0.5 for lung, soft tissues, and bones, respectively. The mean ± SD of Δρm for Tomotherapy TPSs was 2.1 ± 1.4 g/cm3 for soft tissues, which is larger than those for other TPSs. The mean ± SD of Δρe,TEM for the Gammex brain phantom (BRN‐SR2) was −1.8 ± 0.4, implying that the tissue equivalency of the BRN‐SR2 plug was slightly inferior to that of other plugs.ConclusionsLatent deviations between human tissues and TEMs were found by comparing the CT number calibration curves of the various institutes.

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Section: Discussionmentioning

confidence: 63%

Section: Presented In Table 2 Was Established Based On Internationalmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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CT number calibration audit in photon radiation therapy

Nakao,

Ozawa,

Miura

et al. 2023

Medical Physics

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“…Tomotherapy is equipped with a megavolt-CT (MVCT) system, and the acquisition of an MVCT image is a prerequisite before each treatment fraction (12). MVCT can be used for IGRT and dose recalculation (13)(14)(15). The present study aimed to compare the dosimetric consequences of robust and PTV-margin-based optimization to assess the efficacy of optimization technique on helical tomotherapy plans for prostate cancer in the presence of interfractional anatomical variations.…”

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confidence: 99%

Comparing Efficacy Between Robust and PTV Margin-based Optimizations for Interfractional Anatomical Variations in Prostate Tomotherapy

YAGIHASHI,

INOUE,

SHIBA

et al. 2023

In Vivo

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Background/Aim: Interfractional anatomical variations cause considerable differences between planned and actual radiotherapy doses. This study aimed to investigate the efficacy of robust and planning target volume (PTV) margin-based optimizations for the anatomical variations in helical tomotherapy for prostate cancer. Patients and Methods: Ten patients underwent treatment-planning kilovolt computed tomography (kVCT) and daily megavolt computed tomography (MVCT). Two types of nominal plans, with a prescription of 60 Gy/20 fractions, were created using robust and PTV margin-based optimizations on kVCT for each patient. Subsequently, the daily estimated doses were recalculated using nominal plans, and all available MVCTs modified the daily patient-setup errors. Due to the difference in dose calculation accuracy between kVCT and MVCT, three scenarios with dose corrections of 1, 2, and 3% were considered in the recalculation process. The dosimetric metrics, including target coverage with the prescription dose, Paddick's conformity index, homogeneity index, and mean dose to the rectum, were analyzed. Results: A dosimetric comparison of the nominal plans demonstrated that the robust plans had better dose conformity, lower target coverage, and dose homogeneity than the PTV plans. In the daily estimated doses of any dose-corrected scenario, the target coverage and dose sparing to the rectum in the robust plans were significantly higher than those in the PTV plans, whereas dose conformity and homogeneity were identical to those of the nominal case. Conclusion: Robust optimization is recommended as it accounts for anatomical variations during treatment regarding target coverage in helical tomotherapy plans for prostate cancer.

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Analysis of Geometry Verification of X, Y, Z Correction Values with Megavoltage Computed Tomography Using Lower Extremity Positioning System in Prostate Cancer

Apriantoro,

Dewi,

Rubiyanto

2023

JIAE

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The immobilization tool is used to minimize the movement caused while doing irradiation, one of the immobilization tools is the Lower Extremity Positioning System (LEPS) which is used to minimize movement in the Pelvis area. This research was conducted at Dr. Cipto Mangunkusumo Central General Hospital. The type of this research is analytics quantitative. This research used 15 samples with secondary data, which were selected based on inclusion and exclusion criteria’s. The secondary data will be analyzed namely the consistency between the Set-Up value (Couch Position before verification) and the MVCT (Couch Position after verification) value using the Non-Parametric Wilcoxon statistical test, and evaluating the shifting values of X, Y and Z with tolerance standards from AAPM TG-148 which is 2 mm. The results obtained are based on statistical analysis of the Set-Up value with the MVCT results obtained that there is no significant difference, and based on the overall substance, the total that exceeds the tolerance of X coordinates is 92 times with a percentage of 68%, from Y coordinates that is 80 times with a percentage of 59%, from the Z coordinate which is 51 times with a percentage of 38% there is a shift that exceeds tolerance. The conclusion is that the results of MVCT verification still occur that exceed the tolerance standard so that LEPS is still not effective in preventing shifts that occur during radiation therapy.

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Tolerance levels of mass density for adaptive helical tomotherapy using MVCT

Cited by 3 publications

References 14 publications

CT number calibration audit in photon radiation therapy

CT number calibration audit in photon radiation therapy

Comparing Efficacy Between Robust and PTV Margin-based Optimizations for Interfractional Anatomical Variations in Prostate Tomotherapy

Analysis of Geometry Verification of X, Y, Z Correction Values with Megavoltage Computed Tomography Using Lower Extremity Positioning System in Prostate Cancer

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