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.

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.

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.

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.

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.

Purpose: To assess risk factors of disease progression after salvage radiation therapy (SRT) with androgen deprivation therapy (ADT) in case of prostate-specific antigen (PSA) persistence after radical prostatectomy (RP). Materials and Methods: We analyzed 57 patients who received SRT with ADT between 2013 and 2019 due to PSA persistence after RP. The endpoint was disease progression defined by biochemical recurrence or clinical recurrence. Age, Pre-RP PSA level, Gleason score, pathologic stage, presence of pelvic lymph node dissection, surgical margins, and PSA at 6-8 weeks after RP were analyzed as predictive factors for disease progression. Kaplan-Meier method and Cox regression models were used for data analysis. Results: At a median follow-up of 38 months (interquartile range, 26–61), 17 patients had disease progression. Pathologic T stage (pT3b vs. pT3a or lower; hazard ratio [HR] = 9.20; p = 0.035) and PSA level at 6-8 weeks after RP (≥2.04 vs. <2.04 ng/mL; HR = 5.85; p = 0.002) were predictors of disease progression. The 5-year disease progression-free survival rate was 46.7% in pT3b group as compared to 92.9 % in pT3a or lower group, and 18.4% for PSA ≥2.04 ng/mL after RP as compared to 79.2% for PSA <2.04 ng/mL. Conclusion Pathological T stage (pT3b) and post RP PSA ≥2.04 ng/mL are independent risk factors of disease progression after SRT with ADT in patients with PSA persistence after RP.

Purpose: This study evaluates the radiation shielding performance of a new lead-free tungsten-based sheet to reduce the radiation exposure of operators and patients under C-arm fluoroscopy. Materials and Methods: A non-lead radiation shielding sheet (ROO201128; Pentas, Korea) was fabri-cated using tungsten and bismuth. The dose measurements were conducted using a C-arm fluoroscopy machine at 64 kVp and 1.5 mA, assuming two possible scenarios according to the position of the sheet. In each scenario, measurements were conducted at three distances (30, 60, and 90 cm) away from the beam center and in three directions (cephal, caudal, and operator’s direction). Results: In the area within a radius of 60 cm from the beam center, the measured doses were reduced by 66.3% on mean, and the doses measured at distances more than 60 cm were less than 0.1 mSv/h in both scenarios. The most beneficial utilization of the lead-free shielding sheet was verified during C-arm fluoroscopy by placing the sheet on the X-ray tube. The operator’s radiation exposure was reduced by 56.6% when the sheet was placed under the phantom, and by 81.0% when the sheet was placed on the X-ray tube. Conclusion The use of lead-free radiation shielding sheets under C-arm fluoroscopy was effective in reducing radiation exposure, and the most beneficial scenario in which the sheet can be utilized was verified when the sheet was placed on the X-ray tube.

Background and Objectives: 18F-fluorodeoxyglucose PET/CT scans can be a useful method to detect recurrence. However, its role in locally advanced head and neck squamous cell carcinomas (HNSCCs) patients after definitive chemoradiotherapy (CRT) has not yet been determined. The current study was performed to identify the role of therapeutic response evaluation using PET/CT after definitive CRT.Subjects and Method We conducted a retrospective review of patients with locally advanced HNSCCs, and who have undergone definitive CRT from 2009 to 2017 at a single institution. The patients were divided into two groups according to their responses to the treatment (metabolic complete remission [mCR] group or non-mCR group), assessed by PET/CT scans after definitive CRT. Results: Twenty-eight patients were consecutively enrolled. The most common primary site of cancer was the oropharynx, followed by the oral cavity, hypopharynx, and nasal cavity. The therapeutic response assessed by PET/CT scans was mCR in 14 patients. The median progression- free survival (PFS) was not reached in the mCR group but was 13.3 months for the non-mCR group (p=0.001). The median overall survival was significantly longer for the mCR group (52.5 months) than for the non-mCR group (15.2 months, p=0.002). A multivariate analysis showed PET/CT response and high-sensitivity C-reactive protein (hsCRP) as independent prognostic factors for PFS (mCR: p=0.027; hsCRP: p=0.042) and for the overall survival (mCR: p=0.006; hsCRP: p=0.020). Conclusion PET/CT scans after definitive CRT predicted the prognosis in patients with locally advanced HNSCCs. CRP was a prognostic factor affecting the outcomes of treatments.

Purpose: To evaluate the prognostic value of the pretreatment maximum standardized uptake value (SUVmax) for locoregional control (LRC) of early glottic cancer treated with primary radiotherapy. Materials and Methods: We retrospectively reviewed the medical records of 101 patients with T1-T2N0 glottic cancer treated with helical tomotherapy between 2013 and 2016. The clinical T-stages were T1 in 87 (86.1%) and T2 in 14 (13.9%) patients. The median total dose was 63 Gy (63–67.5 Gy) in 2.25 Gy per fraction. The survival outcomes were plotted using Kaplan-Meier curves. Receiver operating characteristic curves were used to assess the optimal SUVmax cut-off value for predicting locoregional recurrence. Results: The median follow-up period was 58 months (range, 11 to 90 months). The 5-year overall survival (OS) and locoregional recurrence-free survival rates were 96.8% and 85.4%, respectively. The median pretreatment SUVmax of the primary tumor for all 101 patients was 2.3 (range, 1.1 to 9.1). The best cut-off value for SUVmax for predicting LRC was 3.3, with a sensitivity of 78.6% and specificity of 73.6%. Univariate analysis showed that T-stage, overall treatment time (≥43 days), and high SUVmax (≥3.3) were significant predictors of LRC. Multivariate analysis showed that LRC was independently affected by a high SUVmax (≥3.3) (hazard ratio = 5.505, p = 0.020). Conclusion High pretreatment SUVmax (≥3.3) is a negative prognostic factor for LRC in early glottic cancer patients treated with primary radiotherapy.

Purpose: Dedicated breast CT is an emerging volumetric X-ray imaging modality for diagnosis that does not require any painful breast compression. To improve the detection rate of weakly enhanced lesions, an adaptive image rescaling (AIR) technique was proposed. Materials and Methods: Two disks containing five identical holes and five holes of different diameters were scanned using 60/100 kVp to obtain single-energy CT (SECT), dual-energy CT (DECT), and AIR images. A piece of pork was also scanned as a subclinical trial. The image quality was evaluated using image contrast and contrast-to-noise ratio (CNR). The difference of imaging performances was confirmed using student’s t test. Results: Total mean image contrast of AIR (0.70) reached 74.5% of that of DECT (0.94) and was higher than that of SECT (0.22) by 318.2%. Total mean CNR of AIR (5.08) was 35.5% of that of SECT (14.30) and was higher than that of DECT (2.28) by 222.8%. A similar trend was observed in the subclinical study. Conclusion The results demonstrated superior image contrast of AIR over SECT, and its higher overall image quality compared to DECT with half the exposure. Therefore, AIR seems to have the potential to improve the detectability of lesions with dedicated breast CT.