What is the optimal isodose line for stereotactic radiotherapy for single brain metastases using HyperArc?

PURPOSE: The study aimed to investigate the optimal isodose line (IDL) in linear accelerator-based stereotactic radiotherapy for single brain metastasis, using HyperArc. We compared the dosimetric parameters for target and normal brain tissue among six plans with different IDLs. METHODS: This study included 30 patients with single brain metastasis. We retrospectively generated six plans for each tumor with different IDLs (80%, 70%, 60%, 50%, 40%, and 33%) using HyperArc. All treatment plans were normalized to the prescription dose of 35 Gy in five fractions which was covered by 95% of the planning target volume (PTV), defined by adding a 1.0 mm margin to the gross tumor volume (GTV). The dosimetric parameters were compared among the six plans. RESULTS: For GTV > 0.1 cm3, the ratio of brain-GTV volumes receiving 25 Gy to PTV (V25Gy/PTV) was significantly lower at IDL 40%-70% than at IDL 80% and 33% (p < 0.01, retrospectively). For GTV < 0.1 cm3, V25Gy/PTV decreased continuously as IDL decreased. The values of D99% and D80% for GTV increased with decreasing IDL. An IDL of 50% or less was required to achieve D99% of greater than 43 Gy and D80% of greater than 50 Gy. The mean values of D99% and D80% for IDL 50% were 44.3 and 51.9 Gy. CONCLUSION: The optimal IDL is 40%-50% for GTV > 0.1 cm3. These lower IDLs could increase D99% and D80% of GTV while lowering V25Gy of normal brain tissue, which may help reduce the risk of radiation necrosis and improve local control.

Feasibility of a portable respiratory training system with a gyroscope sensor.

OBJECTIVES: A portable respiratory training system with a gyroscope sensor (gyroscope respiratory training system [GRTS]) was developed and the feasibility of respiratory training was evaluated. METHODS: Simulated respiratory waveforms from a respiratory motion phantom and actual respirator waveforms from volunteers were acquired using the GRTS and Respiratory Gating for Scanners system (RGSC). Respiratory training was evaluated by comparing the stability and reproducibility of respiratory waveforms from patients undergoing expiratory breath-hold radiation therapy, with and without the GRTS. The stability and reproducibility of respiratory waveforms were assessed by root mean square error and gold marker placement-based success rate of expiratory breath-hold, respectively. RESULTS: The absolute mean difference for sinusoidal waveforms between the GRTS and RGSC was 2.0%. Among volunteers, the mean percentages of errors within ±15% of the respiratory waveforms acquired by the GRTS and RGSC were 96.1% for free breathing and 88.2% for expiratory breath-hold. The mean root mean square error and success rate of expiratory breath-hold (standard deviation) with and without the GRTS were 0.65 (0.24) and 0.88 (0.89) cm and 91.0% (6.9) and 89.1% (11.6), respectively. CONCLUSIONS: Respiratory waveforms acquired by the GRTS exhibit good agreement with waveforms acquired by the RGSC. Respiratory training with the GRTS reduces inter-patient variability in respiratory waveforms, thereby improving the success of expiratory breath-hold radiation therapy. ADVANCES IN KNOWLEDGE: A respiratory training system with a gyroscope sensor is inexpensive and portable, making it ideal for respiratory training. This is the first report concerning clinical implementation of a respiratory training system.

The effects of distance between the imaging isocenter and brain center on the image quality of cone-beam computed tomography for brain stereotactic irradiation.

In linear accelerator-based stereotactic irradiation (STI) for brain metastasis, cone-beam computed tomography (CBCT) image quality is essential for ensuring precise patient setup and tumor localization. However, CBCT images may be degraded by the deviation of the CBCT isocenter from the brain center. This study aims to investigate the effects of the distance from the brain center to the CBCT isocenter (DBI) on the image quality in STI. An anthropomorphic phantom was scanned with varying DBI in right, anterior, superior, and inferior directions. Thirty patients undergoing STI were prospectively recruited. Objective metrics, utilizing regions of interest included contrast-to-noise ratio (CNR) at the centrum semiovale, lateral ventricle, and basal ganglia levels, gray and white matter noise at the basal ganglia level, artifact index (AI), and nonuniformity (NU). Two radiation oncologists assessed subjective metrics. In this phantom study, objective measures indicated a degradation in image quality for non-zero DBI. In this patient study, there were significant correlations between the CNR at the centrum semiovale and lateral ventricle levels (rs = - 0.79 and - 0.77, respectively), gray matter noise (rs = 0.52), AI (rs = 0.72), and NU (rs = 0.91) and DBI. However, no significant correlations were observed between the CNR at the basal ganglia level, white matter noise, and subjective metrics and DBI (rs < ± 0.3). Our results demonstrate the effects of DBI on contrast, noise, artifacts in the posterior fossa, and uniformity of CBCT images in STI. Aligning the CBCT isocenter with the brain center can aid in improving image quality.

Impact of magnetic resonance imaging-related geometric distortion of dose distribution in fractionated stereotactic radiotherapy in patients with brain metastases.

PURPOSE: The geometric distortion related to magnetic resonance (MR) imaging in a diagnostic radiology (MRDR) and radiotherapy (MRRT) setup is evaluated, and the dosimetric impact of MR distortion on fractionated stereotactic radiotherapy (FSRT) in patients with brain metastases is simulated. MATERIALS AND METHODS: An anthropomorphic skull phantom was scanned using a 1.5­T MR scanner, and the magnitude of MR distortion was calculated with (MRDR-DC and MRRT-DC) and without (MRDR-nDC and MRRT-nDC) distortion-correction algorithms. Automated noncoplanar volumetric modulated arc therapy (HyperArc, HA; Varian Medical Systems, Palo Alto, CA, USA) plans were generated for 53 patients with 186 brain metastases. The MR distortion at each gross tumor volume (GTV) was calculated using the distance between the center of the GTV and the MR image isocenter (MIC) and the quadratic regression curve derived from the phantom study (MRRT-DC and MRRT-nDC). Subsequently, the radiation isocenter of the HA plans was shifted according to the MR distortion at each GTV (HADC and HAnDC). RESULTS: The median MR distortions were approximately 0.1 mm when the distance from the MIC was < 30 mm, whereas the median distortion varied widely when the distance was > 60 mm (0.23, 0.47, 0.37, and 0.57 mm in MRDR-DC, MRDR-nDC, MRRT-DC, and MRRT-nDC, respectively). The dose to the 98% of the GTV volume (D98%) decreased as the distance from the MIC increased. In the HADC plans, the relative dose difference of D98% was less than 5% when the GTV was located within 70 mm from the MIC, whereas the underdose of GTV exceeded 5% when it was 48 mm (-26.5% at maximum) away from the MIC in the HAnDC plans. CONCLUSION: Use of a distortion-correction algorithm in the studied MR diagnoses is essential, and the dosimetric impact of MR distortion is not negligible, particularly for tumors located far away from the MIC.

Dual-energy computed tomography-based iodine concentration as a predictor of histopathological response to preoperative chemoradiotherapy for pancreatic cancer.

To explore predictors of the histopathological response to preoperative chemoradiotherapy (CRT) in patients with pancreatic cancer (PC) using dual-energy computed tomography-reconstructed images. This retrospective study divided 40 patients who had undergone preoperative CRT (50-60 Gy in 25 fractions) followed by surgical resection into two groups: the response group (Grades II, III and IV, evaluated from surgical specimens) and the nonresponse group (Grades Ia and Ib). The computed tomography number [in Hounsfield units (HUs)] and iodine concentration (IC) were measured at the locations of the aorta, PC and pancreatic parenchyma (PP) in the contrast-enhanced 4D dual-energy computed tomography images. Logistic regression analysis was performed to identify predictors of histopathological response. Univariate analysis did not reveal a significant relation between any parameter and patient characteristics or dosimetric parameters of the treatment plan. The HU and IC values in PP and the differences in HU and IC between the PP and PC (ΔHU and ΔIC, respectively) were significant predictors for distinguishing the response (n = 24) and nonresponse (n = 16) groups (P < 0.05). The IC in PP and ΔIC had a higher area under curve values [0.797 (95% confidence interval, 0.659-0.935) and 0.789 (0.650-0.928), respectively] than HU in PP and ΔHU [0.734 (0.580-0.889) and 0.721 (0.562-0.881), respectively]. The IC value could potentially be used for predicting the histopathological response in patients who have undergone preoperative CRT.

Dosimetric Comparison of Helical Tomotherapy and HyperArc Treatment Plans for Angiosarcoma of the Scalp.

BACKGROUND/AIM: Angiosarcoma of the scalp (AS) is a rare tumor that has often been treated by total scalp irradiation (TSI). TSI has technical and dosimetric challenges. This study aimed to compare the dosimetric performance of helical tomotherapy (HT) plans with that of HyperArc (HA) plans for TSI in AS. PATIENTS AND METHODS: A planning study was conducted for 11 patients with AS (70 Gy/35 fr). HT and HA planning was performed using TomoHDA and TrueBeam Edge systems, respectively. The performance of three different plans were compared: HT, HA, and HA with half-field beams (HF-HA). The dose distribution and dosimetric parameters for each plan were evaluated. RESULTS: All constraint parameters for the target and organs at risk (OARs) met the goals within acceptable limits for the three techniques. The HA and HF-HA plans provided significantly lower mean brain dose (12.46±2.48 Gy and 8.02±1.48 Gy) than did the HT plan (17.59±3.47 Gy). The doses receiving 0.1 cc of the volume for brainstem and chiasm were significantly lower in the HA and HF-HA plans than those in the HT plan. The HA and HF-HA plans provided a shorter beam-on time (155±3 s and 181±14 s) than did the HT plan (962±221 s). CONCLUSION: The HA plan provided significantly better OARs sparing than the HT plan for TSI in AS and had an advantage to using half-field beams.

Improvement of target coverage using automated non-coplanar volumetric modulated arc therapy planning in stereotactic radiotherapy for cervical metastatic spinal tumors.

This study aimed to compare dosimetric parameters for targets and organs at risk (OARs) between volumetric modulated arc therapy (VMAT) and automated VMAT (HyperArc, HA) plans in stereotactic radiotherapy for patients with cervical metastatic spine tumors. VMAT plans were generated for 11 metastases using the simultaneous integrated boost technique to deliver 35 to 40 and 20 to 25 Gy for high dose and elective dose planning target volume (PTVHD and PTVED), respectively. The HA plans were retrospectively generated using 1 coplanar and 2 noncoplanar arcs. Subsequently, the doses to the targets and OARs were compared. The HA plans provided significantly higher (p < 0.05) Dmin (77.4 ± 13.1%), D99% (89.3 ± 8.9%), and D98% (92.5 ± 7.7%) for gross tumor volume (GTV) than those of the VMAT plans (73.4 ± 12.2%, 84.2 ± 9.6 and 87.3 ± 8.8% for Dmin, D99% and D98%, respectively). In addition, D99% and D98% for PTVHD were significantly higher in the HA plans, whereas dosimetric parameters were comparable between the HA and VMAT plans for PTVED. The Dmax values for the brachial plexus, esophagus, and spinal cord were comparable, and no significant difference was observed in the Dmean for the larynx, pharyngeal constrictor, thyroid, parotid grand (left and right), and Submandibular gland (left and right). The HA plans provided significantly higher target coverage of GTV and PTVHD, with a comparable dose for OARs with VMAT plans. The results of this study may contribute to the improvement of local control in clinical practice.

Comparison of dosimetric parameters and robustness for rotational errors in fractionated stereotactic irradiation using automated noncoplanar volumetric modulated arc therapy for patients with brain metastases: single- versus multi-isocentric technique.

To compare the dosimetric parameters of automated noncoplanar volumetric modulated arc therapy plans using single-isocentric (SIC) and multi-isocentric (MIC) techniques for patients with two brain metastases (BMs) in stereotactic irradiation and to evaluate the robustness of rotational errors. The SIC and MIC plans were retrospectively generated (35 Gy/five fractions) for 58 patients. Subsequently, a receiver operating characteristic curve analysis between the tumor surface distance (TSD) and V25Gy was performed to determine the thresholds for the brain tissue. The SIC and MIC plans were recalculated based on the rotational images to evaluate the dosimetric impact of rotational error. The MIC plans showed better brain tissue sparing for TSD > 6.6 cm. The SIC plans provided a significantly better conformity index for TSD ≤ 6.6 cm, while significantly lower gradient index was obtained (3.22 ± 0.56vs. 3.30 ± 0.57, p < 0.05) in the MIC plans with TSD > 6.6 cm. For organs at risk (OARs) (brainstem, chiasm, lens, optic nerves, and retinas), D0.1 cc was significantly lower (p < 0.05) in the MIC plans than in the SIC plans. The prescription dose could be delivered (D99%) to the gross tumor volume (GTV) for patients with TSD ≤ 6.6 cm when the rotational error was < 1°, whereas 31% of the D99% of GTV fell below the prescription dose with TSD > 6.6 cm. MIC plans can be an optimal approach for reducing doses to OARs and providing robustness against rotational errors in BMs with TSD > 6.6 cm.

Automated Non-coplanar Volumetric Modulated Arc Therapy Planning for Maxillary Sinus Carcinoma.

BACKGROUND/AIM: Dosimetric parameters in volumetric modulated arc therapy (VMAT), non-coplanar VMAT (NC-VMAT), and automated NC-VMAT (HyperArc, HA) were compared for patients with maxillary sinus carcinoma (MSC). PATIENTS AND METHODS: Twenty HA plans were generated to deliver 70.4, 64, and 46 Gy for planning target volumes with high (PTV1), intermediate (PTV2), and low risk (PTV3), respectively. The VMAT and NC-VMAT plans were retrospectively generated using the same optimized parameters as those used in the HA plans. RESULTS: For PTV1, the three treatment plans provided comparable target coverages. For PTV2, the D95%, D99%, and Dmin in the HA plans (64.7±1.2, 62.7±2.1 and 54.6±6.2 Gy, respectively) were significantly higher (p<0.05) than those in the VMAT plans (64.3±1.7, 61.9±2.4 and 52.9±6.4 Gy, respectively). The NC-VMAT and HA plans provided significantly higher (p<0.05) dosimetric parameters for PTV3 than those in the VMAT plans, and D99% in the HA was significantly higher than that in the NC-VMAT plans (52.5±3.0 vs. 51.8±2.7 Gy, p<0.05). The doses to the brain and brainstem were lowest in the HA plans (p<0.05). Moreover, dosimetric parameters of the contralateral organs (lens, optic nerve, retina, and parotid) were lower in the HA plans than in the VMAT and NC-VMAT plans. CONCLUSION: The HA plans provided the best target coverage and OAR sparing compared with VMAT and NC-VMAT plans for patients with MSC.

Dose reduction of hippocampus using HyperArc planning in postoperative radiotherapy for primary brain tumors.

To compare dosimetric parameters for the hippocampus, organs at risk (OARs), and targets of volumetric modulated arc therapy (VMAT), noncoplanar VMAT (NC-VMAT), and HyperArc (HA) plans in patients undergoing postoperative radiotherapy for primary brain tumors. For 20 patients, HA plans were generated to deliver 40.05 to 60 Gy for the planning target volume (PTV). In addition, doses for the hippocampus and OARs were minimized. The VMAT and NC-VMAT plans were retrospectively generated using the same optimization parameters as those in the HA plans. For the hippocampus, the equivalent dose to be administered in 2 Gy fractions (EQD2) was calculated assuming α/ß = 2. Dosimetric parameters for the PTV, hippocampus, and OARs in the VMAT, NC-VMAT, and HA plans were compared. For PTV, the HA plans provided significantly lower Dmax and D1% than the VMAT and NC-VMAT plans (p < 0.05), whereas the D99% and Dmin were significantly higher (p < 0.05). For the contralateral hippocampus, the dosimetric parameters in the HA plans (8.1 ± 9.6, 6.5 ± 7.2, 5.6 ± 5.8, and 4.8 ± 4.7 Gy for D20%, D40%, D60% and D80%, respectively) were significantly smaller (p < 0.05) than those in the VMAT and NC-VMAT plans. Except for the optic chiasm, the Dmax in the HA plans (brainstem, lens, optic nerves, and retinas) was the smallest (p < 0.05). In addition, the doses in the HA plans for the brain and skin were the smallest (p < 0.05) among the 3 plans. HA planning, instead of coplanar and noncoplanar VMAT, significantly reduces the dosage to which the contralateral hippocampus as well as other OARs are exposed without compromising on target coverage.

Setup accuracy and dose attenuation of a wooden immobilization system for lung stereotactic body radiotherapy.

Background: We evaluated the setup error and dose absorption of an immobilization system with a shell and wooden baseplate (SW) for lung stereotactic body radiotherapy (SBRT). Materials and methods: Setup errors in 109 patients immobilized with an SW or BodyFix system (BF) were compared. Dose attenuation rates of materials for baseplates were measured with an ion-chamber. Ionization measurements were performed from 90° to 180° gantry angle in 10° increments, with the ball water equivalent phantom placed at the center of the wood and carbon baseplates whose effects on dose distribution were compared using an electron portal imaging device. Results: The ratio for the anterior-posterior, cranial-caudal, and right-left of the cases within 3-mm registered shifts in interfractional setup error were 90.9%, 89.2%, and 97.4% for the SW, and 93.2%, 91.6%, and 98.0% for the BF, respectively. For intrafractional setup error, 98.3%, 97.4%, and 99.1% for the SW and 96.6%, 95.8%, and 98.7% for the BF were within 3-mm registered shifts, respectively. In the center position, the average (minimum/maximum) dose attenuation rates from 90° to 180° for the wooden and carbon baseplates were 0.5 (0.1/2.8)% and 1.0 (-0.1/10.1)% with 6 MV, respectively. The gamma passing rates of 2%/2 mm for the wooden and carbon baseplates were 99.7% and 98.3% (p < 0.01). Conclusions: The immobilization system with an SW is effective for lung SBRT since it is comparable to the BF in setup accuracy. Moreover, the wooden baseplate had lower radiation attenuation rates and affected the dose distribution less than the carbon baseplate.

Intra-fractional motion error during HyperArc stereotactic radiosurgery on patients with brain metastases: Comparison of open and full-face clamshell-style immobilization devices.

PURPOSE: To compare the intrafractional motion error (IME) during stereotactic irradiation (STI) in patients with brain metastases immobilized using open- (Encompass) and full-face (DSPS) clamshell-style immobilization devices. METHODS: Encompass (38 patients) and DSPS (38 patients) were used for patient immobilization, and HyperArc plans with three to four non-coplanar beams were generated to deliver 25 to 35 Gy in three to five fractions. Cone-beam computed tomography (CBCT) was performed on patients before and after the treatment. Moreover, the difference in patient position between the two CBCT images was considered as the IME. The margins to compensate for IME were calculated using the van Herk margin formula. RESULTS: For Encompass, the mean values of IME in the translational setup were 0.1, 0.2, and 0.0 mm in the anterior-posterior, superior-inferior, and left-right directions, respectively, and the mean values of IME about rotational axes were -0.1, 0.0, and 0.0° for the Pitch, Roll, and Yaw rotations, respectively. For DSPS, the mean values of IME in the translational setup were 0.2, 0.2, and 0.0 mm in the anterior-posterior, superior-inferior, and left-right directions, respectively, and the mean values of IME about rotational axes were -0.1, -0.1, and 0.0° for the Pitch, Roll, and Yaw rotations, respectively. No statistically significant difference was observed between the IME of the two immobilization systems except in the anterior-posterior direction (p = 0.02). Moreover, no statistically significant correlation was observed between three-dimensional IME and treatment time. The margin compensation for IME was less than 1 mm for both immobilization devices. CONCLUSIONS: The IME during STI using open- and full-face clamshell-style immobilization devices is approximately equal considering the adequate accuracy in patient positioning.

Dose Reduction and Low-Contrast Detectability Using Iterative CBCT Reconstruction Algorithm for Radiotherapy.

Introduction: Several studies have reported the relation between the imaging dose and secondary cancer risk and have emphasized the need to minimize the additional imaging dose as low as reasonably achievable. The iterative cone-beam computed tomography (iCBCT) algorithm can improve the image quality by utilizing scatter correction and statistical reconstruction. We investigate the use of a novel iCBCT reconstruction algorithm to reduce the patient dose while maintaining low-contrast detectability and registration accuracy. Methods: Catphan and anthropomorphic phantoms were analyzed. All CBCT images were acquired with varying dose levels and reconstructed with a Feldkamp-Davis-Kress algorithm-based CBCT (FDK-CBCT) and iCBCT. The low-contrast detectability was subjectively assessed using a 9-point scale by 4 reviewers and objectively assessed using structure similarity index (SSIM). The soft tissue-based registration error was analyzed for each dose level and reconstruction technique. Results: The results of subjective low-contrast detectability found that the iCBCT acquired at two-thirds of a dose was superior to the FDK-CBCT acquired at a full dose (6.4 vs 5.4). Relative to FDK-CBCT acquired at full dose, SSIM was higher for iCBCT acquired at one-sixth dose in head and head and neck region while equivalent with iCBCT acquired at two-thirds dose in pelvis region. The soft tissue-based registration was 2.2 and 0.6 mm for FDK-CBCT and iCBCT, respectively. Conclusion: Use of iCBCT reconstruction algorithm can generally reduce the patient dose by approximately two-thirds compared to conventional reconstruction methods while maintaining low-contrast detectability and accuracy of registration.

Machine log file-based dose verification using novel iterative CBCT reconstruction algorithm in commercial software during volumetric modulated arc therapy for prostate cancer patients.

PURPOSE: To evaluate the utility of the use of iterative cone-beam computed tomography (CBCT) for machine log file-based dose verification during volumetric modulated arc therapy (VMAT) for prostate cancer patients. METHODS: All CBCT acquisition data were used to reconstruct images with the Feldkamp-Davis-Kress algorithm (FDK-CBCT) and the novel iterative algorithm (iCBCT). The Hounsfield unit (HU)-electron density curves for CBCT images were created using the Advanced Electron Density Phantom. The I'mRT and anthropomorphic phantoms were irradiated with VMAT after CBCT registration. Subsequently, fourteen prostate cancer patients received VMAT after CBCT registration. Machine log files and both CBCT images were exported to the PerFRACTION software, and a 3D patient dose was reconstructed. Mean dose for planning target volume (PTV), the bladder, and rectum and the 3D gamma analysis were evaluated. RESULTS: For the phantom studies, the variation of HU values was observed at the central position surrounding the bones in FDK-CBCT. There were almost no changes in the difference of doses at the isocenter between measurement and reconstructed dose for planning CT (pCT), FDK-CBCT, and iCBCT. Mean dose differences of PTV, rectum, and bladder between iCBCT and pCT were approximately 2% lower than those between FDK-CBCT and pCT. For the clinical study, average gamma analysis for 2%/2 mm was 98.22% ± 1.07 and 98.81% ± 1.25% in FDK-CBCT and iCBCT, respectively. CONCLUSIONS: A similar machine log file-based dose verification accuracy is obtained for FDK-CBCT and iCBCT during VMAT for prostate cancer patients.

Customization of a Model For Knowledge-Based Planning to Achieve Ideal Dose Distributions in Volume Modulated arc Therapy for Pancreatic Cancers.

PURPOSE: To evaluate customizing a knowledge-based planning (KBP) model using dosimetric analysis for volumetric modulated arc therapy for pancreatic cancer. MATERIALS AND METHODS: The first model (M1) using 56 plans and the second model (M2) using 31 plans were created in the first 7 months of the study. The ratios of volume of both kidneys overlapping the expanded planning target volume to the total volume of both kidneys (Voverlap/Vwhole) were calculated in all cases to customize M1. Regression lines were derived from Voverlap/Vwhole and mean dose to both kidneys. The third model (M3) was created using 30 plans which data put them below the regression line. For validation, KBP was performed with the three models on 21 patients. RESULTS: V18 of the left kidney for M1 plans was 7.3% greater than for clinical plans. Dmean of the left kidney for M2 plans was 2.2% greater than for clinical plans. There was no significant difference between all kidney doses in M3 and clinical plans. Dmean of the left kidney for M2 plans was 2.2% greater than for clinical plans. Dmean to both kidneys did not differ significantly between the three models in validation plans with Voverlap/Vwhole lower than average. In plans with larger than average volumes, the Dmean of validation plans created by M3 was significantly lower for both kidneys by 1.7 and 0.9 Gy than with M1 and M2, respectively. CONCLUSIONS: Selecting plans to register in a model by analyzing dosimetry and geometry is an effective means of improving the KBP model.

Evaluation of two-dimensional electronic portal imaging device using integrated images during volumetric modulated arc therapy for prostate cancer.

BACKGROUND: The aim of the study was to evaluate analysis criteria for the identification of the presence of rectal gas during volumetric modulated arc therapy (VMAT) for prostate cancer patients by using electronic portal imaging device (EPID)-based in vivo dosimetry (IVD). MATERIALS AND METHODS: All measurements were performed by determining the cumulative EPID images in an integrated acquisition mode and analyzed using PerFRACTION commercial software. Systematic setup errors were simulated by moving the anthropomorphic phantom in each translational and rotational direction. The inhomogeneity regions were also simulated by the I'mRT phantom attached to the Quasar phantom. The presence of small and large air cavities (12 and 48 cm3) was controlled by moving the Quasar phantom in several timings during VMAT. Sixteen prostate cancer patients received EPID-based IVD during VMAT. RESULTS: In the phantom study, no systematic setup error was detected in the range that can happen in clinical (< 5-mm and < 3 degree). The pass rate of 2% dose difference (DD2%) in small and large air cavities was 98.74% and 79.05%, respectively, in the appearance of the air cavity after irradiation three quarter times. In the clinical study, some fractions caused a sharp decline in the DD2% pass rate. The proportion for DD2% < 90% was 13.4% of all fractions. Rectal gas was confirmed in 11.0% of fractions by acquiring kilo-voltage X-ray images after the treatment. CONCLUSIONS: Our results suggest that analysis criteria of 2% dose difference in EPID-based IVD was a suitable method for identification of rectal gas during VMAT for prostate cancer patients.

Impact of Multileaf Collimator Width on Dose Distribution in HyperArc Fractionated Stereotactic Irradiation for Multiple (-) Brain Metastases.

BACKGROUND/AIM: To assess the impact of the width of multileaf collimator (MLC) on dose distributions on HyperArc fractionated stereotactic irradiation for multiple (5-10) brain metastases. PATIENTS AND METHODS: Twenty-one HyperArc (HA) plans were generated using the high definition (HD) MLC (2.5 mm) to deliver 30-35 Gy in 3-5 fractions (HA-HD). The HyperArc plans using Millennium (ML) MLC (5 mm) were retrospectively generated (HA-ML) using the same planning parameters with HA-HD. Dosimetric parameters between the planning target volume (PTV) and organs at risk (OARs) were compared. RESULTS: The conformity index was significantly higher (p<0.0001) in the HA-HD plans (0.95±0.04) than that in the HA-ML plans (0.92±0.06). The HA-HD provided significantly lower (p<0.0001) gradient index (5.6±2.5) than HA-ML (6.2±3.5). For the brainstem and retina (right), a statistically significant difference (p<0.05) was observed between the HA-HD (12.8±10.9 and 2.8±1.7 Gy, for brainstem and retina, respectively) and HA-ML (13.6±11.1 and 3.0±1.8 Gy) plans. For the brain tissue, the HA-HD plans statistically significantly reduced dosimetric parameters (p<0.0001) in all evaluated dose range (V6Gy-V28Gy). CONCLUSION: The narrower MLC provided significantly higher conformity, steeper dose gradient, and better normal tissue sparing.

Accuracy of dose calculation on iterative CBCT for head and neck radiotherapy.

PURPOSE: To evaluate the feasibility of the use of iterative cone-beam computed tomography (CBCT) for dose calculation in the head and neck region. METHODS: This study includes phantom and clinical studies. All acquired CBCT images were reconstructed with Feldkamp-Davis-Kress algorithm-based CBCT (FDK-CBCT) and iterative CBCT (iCBCT) algorithm. The Hounsfield unit (HU) consistency between the head and body phantoms was determined in both reconstruction techniques. Volumetric modulated arc therapy (VMAT) plans were generated for 16 head and neck patients on a planning CT scan, and the doses were recalculated on FDK-CBCT and iCBCT with Anisotropic Analytical Algorithm (AAA) and Acuros XB (AXB). As a comparison of the accuracy of dose calculations, the absolute dosimetric difference and 1%/1 mm gamma passing rate analysis were analyzed. RESULTS: The difference in the mean HU values between the head and body phantoms was larger for FDK-CBCT (max value: 449.1 HU) than iCBCT (260.0 HU). The median dosimetric difference from the planning CT were <1.0% for both FDK-CBCT and iCBCT but smaller differences were found with iCBCT (planning target volume D50%: 0.38% (0.15-0.59%) for FDK-CBCT, 0.28% (0.13-0.49%) for iCBCT, AAA; 0.14% (0.04-0.19%) for FDK-CBCT, 0.07% (0.02-0.20%) for iCBCT). The mean gamma passing rate was significantly better in iCBCT than FDK-CBCT (AAA: 98.7% for FDK-CBCT, 99.4% for iCBCT; AXB: 96.8% for FDK_CBCT, 97.5% for iCBCT). CONCLUSION: The iCBCT-based dose calculation in VMAT for head and neck cancer was accurate compared to FDK-CBCT.

Dual-energy computed tomography image-based volumetric-modulated arc therapy planning for reducing the effect of contrast-enhanced agent on dose distributions.

To compare the effect of a contrast-enhanced (CE) agent on volumetric-modulated arc therapy plans based on four types of images-virtual monochromatic images (VMIs) captured at 70 and 140 keV (namely VMI70 and VMI140, respectively), water density image (WDI), and virtual non-contrast image (VNC) generated using a dual-energy computed tomography (DECT) system. A tissue characterization phantom and a multi-energy phantom were scanned, and VMI70, VMI140, WDI, and VNC were retrospectively reconstructed. For each image, a lookup table (LUT) was created. For 13 patients with nasopharyngeal cancer, non-CE and CE scans were performed, and volumetric-modulated arc therapy plans were generated on the basis of non-CE VMI70. Subsequently, the doses were re-calculated using the four types of DECT images and their corresponding LUTs. The maximum differences in the physical density estimation were 21.3, 5.2, -3.9, and 0.5% for VMI70, VMI140, WDI, and VNC, respectively. Compared with VMI70, the WDI approach significantly reduced (p < 0.05) the dosimetric difference due to the CE agent for the planning target volume (PTV) (D50%), whereas the difference was significantly increased for D1%. Except for PTV (D1%), the differences were significantly lower (p < 0.05) in the treatment plans based on VMI140 and VNC than that based on VMI70. For the VNC, the mean difference was less than 0.2% for all dosimetric parameters for the PTV. For patients with NPC, treatment plans based on the VNC derived from CE scan showed the best agreement with those based on the non-CE VMI70. Ideally, the effect of CE agent on dose distribution does not appear in treatment planning procedures.

A Third-Generation Adaptive Statistical Iterative Reconstruction for Contrast-Enhanced 4-Dimensional Dual-Energy Computed Tomography for Pancreatic Cancer.

OBJECTIVES: The objective of this study was to assess the objective and subjective qualities of the contrast-enhanced 4-dimensional dual-energy computed tomography using adaptive statistical iterative reconstruction (ASiR) and ASiR-V. METHODS: The virtual monochromatic images at 60 keV were reconstructed using filtered back projection, ASiR, and ASiR-V (10%-100%) for 14 patients with pancreatic cancer. The contrast-to-noise ratio (CNR) was calculated, and the subjective measurements were compared based on a 5-point score scale. RESULTS: The ASiR-V yielded a significantly higher CNR than ASiR (P < 0.05). The subjective image quality (peak) was significantly improved (P < 0.01) with ASiR (50%) (3.8, 3.5, and 4.0; overall image quality, tumor delineation, and noise, respectively) and with ASiR-V (50%) (3.9, 3.5, and 4.2, respectively) compared with the filtered back projection (3.2, 3.2, and 3.0, respectively). CONCLUSIONS: The ASiR-V yielded higher CNR than ASiR and provided the highest subjective scores regarding the overall image quality.