Setup Errors Research Articles

Optical Surface Management System and BladderScan for Patient Setup During Radiotherapy of Postoperative Prostate Cancer.

Background: The precision of postoperative prostate cancer radiotherapy is significantly influenced by setup errors and alterations in bladder morphology. Utilizing daily cone beam computed tomography (CBCT) imaging allows for the correction of setup errors. However, this naturally leads to the question of the issue of peripheral dose and workload. Thus, a zero-dose, noninvasive technique to reproduce the bladder volume and improve patient setup accuracy was needed. Purpose: The aim of this study is to investigate if the setup method by combining Optical Surface Management System (OSMS) and BladderScan can improve the accuracy of setup and accurately reproduce the bladder volume during radiotherapy of postoperative prostate cancer and to guide CTV-PTV margins for clinic. Method: The experimental group consisted of 15 postoperative prostate cancer patients who utilized a setup method that combined OSMS and BladderScan. This group recorded 103 setup errors, verified by CBCT. The control group comprised 25 patients, among whom 114 setup errors were recorded using the conventional setup method involving skin markers; additionally, patients in this group also exhibited spontaneous urinary suppression. The errors including lateral (Lat), longitudinal (Lng), vertical directions (Vrt), Pitch, Yaw, and Roll were analyzed between the two methods. The Dice similarity coefficient (DSC) and volume differences of the bladder between CBCT and planning CT were compared as the bladder concordance indicators. Results: The errors in the experimental group at Vrt, Lat, and Lng were 0.17 ± 0.12, 0.22 ± 0.17, and 0.18 ± 0.12 cm, and the control group were 0.25 ± 0.15, 0.31 ± 0.21, 0.34 ± 0.22 cm. The rotation errors of Pitch, Roll, and Yaw in the experimental group were 0.18 ± 0.12°, 0.11 ± 0.1°, and 0.18 ± 0.13°, and in the control group, they were 0.96 ± 0.89°, 1.01 ± 0.86°, and 1.02 ± 0.84°. The DSC and volume differences were 92.52 ± 1.65% and 39.99 ± 28.75 cm3 in the patients with BladderScan, and in the control group, they were 62.98 ± 22.33%, 273.89 ± 190.62 cm3. The P < 0.01 of the above performance indicators indicates that the difference is statistically significant. Conclusion: The accuracy of the setup method by combining OSMS and BladderScan was validated by CBCT in our study. The method in our study can improve the setup accuracy during radiotherapy of postoperative prostate cancer compared to the conventional setup method.

Dosimetric effect of rotational setup errors in volumetric modulated arc therapy and field-in-field treatment of left-sided breast cancer

Setup errors are an important factor in the dosimetric accuracy of radiotherapy delivery. In this study, we investigated how rotational setup errors influence the dose distribution in volumetric modulated arc therapy (VMAT) and tangential field-in-field (FiF) treatment of left-sided breast cancer with supraclavicular lymph node involvement in deep inspiration breath hold. Treatment planning computed tomography images and radiotherapy plans of 20 patients were collected retrospectively for the study. Rotational setup errors up to 3° were simulated by rotating the planning images, and the resulting dosimetric changes were calculated. With rotational setup errors up to 3°, the median decrease of V95% to clinical target volume was less than 0.8 percentage point in both VMAT and FiF plans. The dose distribution of the heart and left anterior descending artery was more stable with respect to rotations in VMAT plans compared to FiF plans. Correction of ≥1° setup errors is recommended due to increased doses to the heart and left anterior descending artery after 1° setup errors.

Margins of Planning Target Volume and Set-up Errors based on Megavoltage Cone-Beam CT Image Guided Radiotherapy with Helical Tomotherapy: Importance of Automatic Registration Plus Manual Registration

Margins of Planning Target Volume and Set-up Errors based on Megavoltage Cone-Beam CT Image Guided Radiotherapy with Helical Tomotherapy: Importance of Automatic Registration Plus Manual Registration

Estimation of Uncertainty of the VMAT Absolute Dose Measurement Due to the Phantom Setup Error Using a Treatment Planning System

When performing single-point dose verification in VMAT, it is necessary to avoid the regions with steep dose gradient. We propose a method to obtain the estimated value ( Uplan) of uncertainty of the absolute dose measurement due to the phantom setup error by using dose gradient calculated from treatment planning system (TPS), for evaluating the appropriate measurement points. The dose gradient was calculated from the planned dose values in the vicinity of the isocenter point using TPS. The phantom setup error was estimated. The Uplan was calculated using the proposed formula after estimating the phantom setup error. Then, the dose gradient was calculated from the measured dose values in the vicinity of the isocenter point specified by TPS using the Tough water phantom with ionization chamber (IC), and Umeas was calculated as in Uplan. The correlation coefficient between Uplan and Umeas was 0.984, which indicates a high correlation. The average of the difference between Umeas and Uplan was -0.24%. We considered that this result was caused by the influence of volume averaging effect of IC. The Uplan obtained from this proposed method reflects the uncertainty of the absolute dose measurement due to the phantom setup error and is useful for evaluating the appropriate measurement points for absolute dose measurement.

Unmasking anxiety: a head-to-head comparison of open and closed masks in head and neck cancer radiotherapy.

Facemasks accurately immobilise patients with head and neck cancer (HNC) receiving radiotherapy (RT). However, such masks are associated with treatment related distress, a prognostic factor for poorer survival. Open masks offer increased comfort and patient satisfaction. We investigated whether open masks could immobilise patients without affecting treatment accuracy. Over an 18-month period, all HNC RT patients with anxiety were offered open masks. Once 30 patients had completed treatment, set-up data was compared to patients in closed masks. The mean displacement and one-dimensional standard deviations (SD) of the mean, systematic and random set-up errors were calculated for translational directions: anterior-posterior (x), superior-inferior (y), medial-lateral (z). The mean and SD of the mean was calculated for rotational displacements. Mann-Whitney U was used to determine any significant differences between set-up data. Sixty patients were included (30 open & 30 closed masks). There was no statistically significant difference found in the x (p = 0.701), y (p = 0.246) or z (p = 0.535) direction for the SD of the mean displacements between both masks. No statistically significant difference was found in the SD of means for rotational displacements. The calculated planning target volume (PTV) margin requirements were minimally less for the closed masks 3.5, 2.6, and 2.7 mm (x, y, z, respectively) versus 4.2, 3.2, and 3.7 mm, respectively, for open masks. Our study demonstrates that open masks maintain accuracy at levels comparable to closed masks in patients with anxiety. The minor difference in the calculated PTV margin could be rectified with daily on-line imaging or surface guided imaging.

Dosimetric impact of rotational errors in trigeminal neuralgia radiosurgery using CyberKnife.

Trigeminal neuralgia (TN) can be treated on the CyberKnife system using two different treatment delivery paths: the general-purpose full path corrects small rotations, while the dedicated trigeminal path improves dose fall-off but does not allow rotational corrections. The study evaluates the impact of uncorrected rotations on brainstem dose and the length of CN5 (denoted as Leff) covered by the prescription dose. A proposed model estimates the delivered dose considering translational and rotational delivery errors for TN treatments on the CyberKnife system. The model is validated using radiochromic film measurements with and without rotational setup error for both paths. Leff and the brainstem dose is retrospectively assessed for 24 cases planned using the trigeminal path. For 15 cases, plans generated using both paths are compared for the target coverage and toxicity to the brainstem. In experimental validations, measured and estimated doses agree at 1%/1mm level. For 24 cases, the treated Leff is 5.3±1.7mm, reduced from 5.9±1.8mm in the planned dose. Constraints for the brainstem are met in 23 cases for the treated dose but require frequent treatment interruption to maintain rotational corrections<0.5° using the trigeminal path. The treated length of CN5, and plan quality metrics are similar for the two paths, favoring the full path where rotations are corrected. We validated an analytical model that can provide patient-specific tolerances on rotations to meet plan objectives. Treatment using the full path can reduce treatment time and allow for rotational corrections.

Uncertainty assessment of machine tool squareness error identification using on-machine measurement

Identification and compensation of geometric errors in the machine tool are widely performed to increase machining accuracy. Periodic verification of the geometric errors, as introduced in ISO 230-2, helps monitor the machine tool accuracy during continued manufacturing operation and detect accuracy degradation early on. While interferometry-based error identification techniques are commonly applied, on-machine measurement (OMM), with its increasing availability to machine tools, can be used to identify geometric errors as an alternative to traditional interferometry-based techniques. As geometric errors also contribute to OMM error, assessment of the uncertainty of error identification is essential to ensure the reliability of the identification. This work presents a method to evaluate the uncertainty in the OMM-based geometric error identification process by Monte Carlo simulation. The error ellipse model, which represents OMM errors with better accuracy, is utilized to improve the identification uncertainty. The squareness errors, as position-independent geometric errors that contribute to machining inaccuracy, are taken as an example to demonstrate the presented method. The influence of the artifact setup errors on the error identification is also investigated. A series of experiments are conducted to evaluate the uncertainty of the OMM-based identification method. The geometric error obtained with the presented method is found to deviate by less than 10% from that obtained with an interferometry-based commercial instrument. The uncertainty obtained from the proposed Monte Carlo simulation method matches well with the uncertainty results obtained by the Guide to the Expression of Uncertainty in Measurement method and repeated measurements.

Target movement according to cervical lymph node level in head and neck cancer and its clinical significance.

To evaluate set-up error for head and neck cancer (HNC) patients according to each neck lymph node (LN) level. And clinical factors affecting set-up error were analyzed. Reference points (RP1, RP2, RP3, and RP4) representing neck LN levels I to IV were designated. These RP were contoured on simulation computed tomography (CT) and cone-beam CT of 89 HNC patients with the same standard. After image registration was performed, movement of each RP was measured. Univariable logistic regression analyses were performed to analyze clinical factors related to measured movements. The mean value of deviation of all axes was 1.6 mm, 1.3 mm, 1.8 mm, and 1.5 mm for RP1, RP2, RP3, and RP4, respectively. Deviation was over 3 mm in 24 patients. Movement of more than 3 mm was observed only in RP1 and RP3. In RP1, it was related to bite block use. Movement exceeding 3 mm was most frequently observed in RP3. Primary tumor and metastatic LN volume change were clinical factors related to the RP3 movement. Planning target volume margin of 4 mm for neck LN level I, 3 mm for neck LN level II, 5 mm for neck LN level III, and 3 mm for neck LN level IV was required to include all movements of each LN level. In patients using bite block, changes in primary tumor volume, and metastatic LN volume were related to significant movement.

Automated image quality assessment for selecting among multiple magnetic resonance image acquisitions in the German National Cohort study

In magnetic resonance imaging (MRI), the perception of substandard image quality may prompt repetition of the respective image acquisition protocol. Subsequently selecting the preferred high-quality image data from a series of acquisitions can be challenging. An automated workflow may facilitate and improve this selection. We therefore aimed to investigate the applicability of an automated image quality assessment for the prediction of the subjectively preferred image acquisition. Our analysis included data from 11,347 participants with whole-body MRI examinations performed as part of the ongoing prospective multi-center German National Cohort (NAKO) study. Trained radiologic technologists repeated any of the twelve examination protocols due to induced setup errors and/or subjectively unsatisfactory image quality and chose a preferred acquisition from the resultant series. Up to 11 quantitative image quality parameters were automatically derived from all acquisitions. Regularized regression and standard estimates of diagnostic accuracy were calculated. Controlling for setup variations in 2342 series of two or more acquisitions, technologists preferred the repetition over the initial acquisition in 1116 of 1396 series in which the initial setup was retained (79.9%, range across protocols: 73–100%). Image quality parameters then commonly showed statistically significant differences between chosen and discarded acquisitions. In regularized regression across all protocols, ‘structured noise maximum’ was the strongest predictor for the technologists’ choice, followed by ‘N/2 ghosting average’. Combinations of the automatically derived parameters provided an area under the ROC curve between 0.51 and 0.74 for the prediction of the technologists’ choice. It is concluded that automated image quality assessment can, despite considerable performance differences between protocols and anatomical regions, contribute substantially to identifying the subjective preference in a series of MRI acquisitions and thus provide effective decision support to readers.

Dosimetric effects of rotational errors for single isocenter multiple targets in HyperArc plans: A phantom and retrospective imaging analysis study.

This study uses a phantom to investigate the dosimetric impact of rotational setup errors for Single Isocenter Multiple Targets (SIMT) HyperArc plans. Additionally, it evaluates intra-fractional rotational setup errors in patients treated with Encompass immobilization system. The Varian HyperArc system (Varian Medical systems) was used to create plans targeting spherical PTVs with diameters of 5, 10, and 15mm and with offsets of 1.3-5.3cm from the isocenter. Dosimetric parameters, including mean and maximum dose, D99% and D95% were evaluated for various rotational setup errors ranging from 0.5° to 2° for the PTVs and certain CTVs created within PTVs. These rotational errors were applied in an order and direction that resulted in the maximum displacement of targets. The rotation was applied both uniformly around all three axes and individually around each axis. Furthermore, to link the findings to actual treatment scenarios, the intra-fractional rotational setup errors were obtained for stereotactic cranial patients treated with the Encompass system using CBCT images acquired during treatments. The maximum displacement of 2.7mm was observed for targets located at 4.4 and 4.5cm from the isocenter with rotational setup errors of 2°. The dose reduction for D99% values corresponding to this displacement were about 50%, 40%, and 30% for PTVs with diameters of 5, 10, and 15mm, respectively. Both D99% and D95% showed a consistent trend of dose reduction across various rotational errors and PTV volumes. While the maximum dose remained consistent for different targets with various rotational errors, the mean dose decreased by approximately 25%, 12%, and 6% for PTVs with diameters of 5, 10, and 15cm, respectively, with rotational errors of 2°. In addition, by analyzing CBCT images, the absolute mean rotational setup errors obtained during treatment with Encompass for pitch, roll, and yaw were 0.17°±0.13°, 0.11°±0.10°, and 0.12°±0.10° respectively. This data, combined with existing studies, suggest that a 0.5° rotational setup error is a safe choice to consider for calculating additional PTV margin to ensure adequate CTV coverage. Therefore, the assessment of maximum displacement and dosimetric parameters in this study, for a 0.5° rotational error, highlights the need for an additional 0.7mm PTV margin for targets positioned at distances of 4.4cm or greater from the isocenter. For SIMT Plans, a 0.5° rotational setup error is recommended as a basis for calculating additional PTV margins to ensure adequate CTV coverage when using the Encompass system.

A Dose Accumulation Assessment of Alignment Errors During Spatially Fractionated Radiation Therapy

IntroductionSpatially fractionated radiotherapy (SFRT) techniques produce high-dose peaks and low-dose valleys within a tumor. Lattice stereotactic body radiation therapy (SBRT) is a form a SFRT delivered across five fractions. Due to the high spatial dose gradients associated with SFRT, it is critical for fractionated SFRT patients to be aligned correctly for treatment. Here we investigate the dosimetric impact of daily alignment uncertainty through a dose accumulation study. MethodsDose accumulation was retrospectively performed for ten patients enrolled on a Phase I trial. Lattice SBRT was completed in 5 fractions with 20Gy prescribed to the entire tumor and a simultaneous integrated boost of 66.7Gy prescribed to a set of regularly spaced high-dose spheres. Daily alignment error was quantified through manually selected landmarks in both the planning computed tomography (CT) scan and daily cone-beam CT. The dosimetric impact of alignment errors was quantified by translating the isocenter in the treatment planning system by the daily average alignment error. Large errors were simulated by translating isocenter 5mm and 10mm for one and two fractions, independently assessing errors in the superior-inferior and axial directions. The reduction of dose gradients was quantified using the dose ratio (DR) of the mean dose in the high-dose and low-dose spheres. ResultsThe average alignment error was 1.8mm across the patient population resulting in minor smoothing of the high- and low-dose distributions in the dose accumulation. Quantitatively, the DR decreased from 3.42 to 3.32 (p=0.093) in the dose accumulation study. The simulated worst case was an inferior-superior shift of 10mm for two fractions where the average DR decreased to 2.72 (p=0.0001). ConclusionsThe dose accumulation study revealed on average DR only decreased from 3.42 to 3.32. However, setup errors >5mm resulted in larger dosimetric degradation, reflecting a larger impact for individual high dose spheres within regions exhibiting larger displacements.

Single isocenter HyperArc treatment of multiple intracranial metastases: Targeting accuracy.

(A) To examine the alignment accuracy of CBCT guidance for brain metastases with off centered isocenters, (B) to test dose delivery and targeting accuracy for single isocenter treatments with multiple brain metastases. We report the results of the end-to-end test for Truebeam stereotactic radiosurgery (SRS). An anthropomorphic CT head phantom was drilled with five MOSFET inserts and two PTW Pinpoint chamber inserts. The phantom was simulated, planned, and delivered. For the purpose of comparing the accuracy of alignment, CBCTs were acquired with the isocenter centered and offset superiorly 8cm, inferiorly 8cm, anteriorly 7cm, posteriorly 7cm, and right 5cm. There were six degrees of freedom corrections applied to the plans, as well as intentional rotational and translational errors for dose comparisons. Dose accuracy checks were performed with MOSFET and PTW Pinpoint chamber, and targeting accuracy was assessed with GafChromic films. (A) Compared to centered CBCT, off-centered CBCT scan showed some alignment errors, with a maximum difference of 0.6-degree pitch and 0.9mm translation when the phantom was placed 8cm inferior off center. (B) For the single isocenter plan, measured doses of the five MOSFET were 95%-100% of the planned dose, whereas the multiple isocenter plans were 96%-100%. With intentional setup errors of 1-degree pitch, doses were 97.1%-100.4% compared to the perfect setup. The same was found for the two pinpoint chamber readings with 1-degree rotation and 1mm translation. (C) Targeting accuracy for targets at the isocenter is 0.67mm, within the machine specification of 0.75mm. Targeting accuracy for isocenters 6-12cm away from the target is in the range 0.67-1.18mm. (A) Single isocenter HyperArc treatments for multiple brain metastases are feasible and targeting accuracy is clinically acceptable. (B) The vertex in a cranial scan is very important for proper alignment.

Setup error of electronic portal image device in IMRT for thoracic tumors and its influence.

The aim of this study was to analyze the setup error of the electronics portal image device (EPID) in intensity-modulated radiation therapy (IMRT) for thoracic tumors and the influence on the outward expansion distance of the target area. A total of 202 patients with chest tumors admitted to our hospital from March 2016 to March 2018 were selected as the observation subjects. All patients were treated with IMRT. The original plan was developed based on the SM90 obtained by the planning target volume (PTV) expansion method, and the new plan was obtained by shifting the isocenter coordinates of the treatment plan according to the positioning error value obtained by EPID. Before the treatment, EPID scans were performed. The electronic radiation field images (ERIs) were registered with the digitally reconstructed radiographic images (DRRs) generated by the treatment planning system using the image registration software, and the setup errors in the X, Y, and Z directions were further measured. The PTV was developed according to ERIs, and the setup error was simulated to obtain the PTV with 95% internal target volume (ITV) reaching the prescribed dose under the condition of a setup error. The outward expansion distance of clinical target volume (CTV) → PTV was calculated. In this experiment, the setup errors in X, Y, and Z directions were (-2.00±1.16) mm, (0.16±1.14) mm, and (-0.55±1.16) mm, respectively. The systematic error in the Z direction was -3.00 mm, and the random error in the X direction was 3.30 mm. The CTV → PTV outward expansion distance was set as 7, 8 and 7 mm in the X direction, Y direction and Z direction, respectively. At this time, under the presence of setup error, the PTV D95 and the ITV V100 in the new plan were (62.23±3.85) Gy and (97.51±1.56) %, respectively, effectively ensuring that 95% ITV of 90% patients reached the prescribed dose. In contrast, the ITV D95 and ITV V100 in the presence of setup error were (56.11±5.26) Gy and (90.15±3.12) %, respectively, at a CTV → PTV outward expansion distance of 5 mm, which could not guarantee that 95% ITV of 90% patients reached the prescribed dose. In the presence of a setup error, the double-lung 5 Gy irradiation of the total heart volume (V5), the double-lung 20 Gy irradiation of the total heart volume (V20), mean lung dose (MLD), mean heart dose (MHD), and D1 cm3 of the new plan increased by 0.89%, 0.29%, 0.13%, 0.06%, and 5 Gy, respectively, compared with the original plan. In general, the first treatment of radiotherapy in thoracic tumors mostly has a certain degree of setup error, which is most evident in the X direction. When the CTV → PTV outward expansion distance is set at 7, 8, and 7 mm in the X direction, Y direction, and Z direction, respectively, it can effectively ensure that 95% ITV reach the prescribed dose in 90% of patients in the presence of a setup error. EPID helps to achieve the desired effect of radiotherapy, improves the efficacy of radiotherapy, and reduces the side effects caused by radiotherapy errors.

Application of customisable 3D-printed bite blocks combined with nano head, neck and shoulder mask to head and neck neoplasm radiotherapy

This study investigated the effectiveness of customisable 3D-printed bite blocks combined with nano head, neck and shoulder mask in radiotherapy for head and neck neoplasms. The images of 50 patients with head and neck neoplasms treated at our hospital from 2020 to 2022 were collected using CBCT. The patients were divided into two groups: 25 in the mask group and 25 in the combination group. The mask group utilized thermoplastic polyurethane (TPU) nanofiber membrane to stabilize the position of the patients’ head, shoulder, and neck. On the other hand, the combined group added a personalized bite block produced by 3D printing technology on the basis of the mask group. Cone beam CT (CBCT) was used to calibrate any errors, and the set-up errors and number of head rotations after image calibration were analyzed between the two groups. The conformation number (CN) and heterogeneity index (HI) in the target area of the intensity-modulated radiation therapy (IMRT) plan of the two groups were calculated, and the dose-volume parameters of the tongue and other organs at risk, including Dmax and Dmean, were compared using paired tests. Follow-up observations were performed to assess the occurrence of adverse reactions to radiation damage among the patients. The findings revealed a statistically significant difference in the Y -axis set-up error between the combination group and the mask group (P &lt; 0.05). Additionally, the combination group exhibited a higher proportion of set-up errors &lt; 2 mm in both the Y -axis and Z-axis directions compared to the mask group. Significantly fewer images showed head rotation in the combination group than in the mask group. In terms of the target area, there were no significant differences observed in the conformation number (CN) and heterogeneity index (HI) between the two groups. However, wearing the personalized bite block resulted in significantly lower Dmax and Dmean values for the tongue. In contrast, the mask group experienced a higher incidence of oral mucositis and taste disorders. By utilizing customizable 3D-printed bite blocks in conjunction with a nano-mask, accurate repositioning for chemotherapy was achieved, leading to a reduction in set-up error and a significant decrease in radiation dose to the tongue and its surface oral mucosa. Consequently, the occurrence of adverse reactions such as oral mucositis and taste disorders was also reduced. The production of personalized bite blocks is simple, with accurate radiotherapy, making it a technique that should be widely adopted.

Going from 3D/3D to 2D/3D registration for noncoplanar setup verification in intracranial single-isocenter multiple-target hypofractionated stereotactic radiotherapy: comparison between kilo-voltage/mega-voltage image pairs and noncoplanar cone-beam computed tomography.

Single-isocenter (SI) noncoplanar volumetric modulated arc therapy (NC-VMAT) has been widely used in stereotactic radiosurgery (SRS) or hypofractionated stereotactic radiotherapy (HSRT) for multiple brain metastases (BMs). However, it is critical to verify patient positioning at a noncoplanar couch angle. This study aimed to compare the noncoplanar setup discrepancies between kilo-voltage/mega-voltage image (kV/MV) orthogonal image pairs with a 2-dimensional/3-dimensional (2D/3D) matching mode and noncoplanar cone-beam computed tomography (NC-CBCT) with a 3D/3D matching mode in SI NC-VMAT HSRT for multiple BMs. Twenty patients with multiple BMs [2-5] who underwent SI NC-VMAT HSRT were enrolled in this study. Prior to each noncoplanar field delivery, both kV/MV orthogonal image pairs and NC-CBCT were used to determine setup errors. The setup error values reported by NC-CBCT were defined as the gold standard and compared to those reported by kV/MV orthogonal image pairs. The Bland-Altman analysis method was utilized to assess the agreement of the two positioning modalities. In total, 104 kV/MV image pairs and NC-CBCT scans were acquired. The mean setup error differences (SEDs; absolute values) between the two positioning systems were 0.17 mm, 0.21 mm, 0.16 mm, 0.22°, 0.18°, and 0.17° in the vertical, longitudinal, lateral, yaw, pitch, and roll directions, respectively. The maximum SEDs regarding translation and rotation occurred in the longitudinal and yaw directions at 0.60 mm and 0.8°, respectively. Bland-Altman analysis showed excellent agreement between the two positioning modalities, and the 95% limits of agreement (LOAs) never exceeded 0.6 mm and 0.6° in the translational and rotational directions, respectively. Only 4.80% of SEDs exceeded the tolerance of 0.5 mm/0.5°. Orthogonal kV/MV image pairs with 2D/3D matching mode could provide comparable accuracy for noncoplanar positioning as NC-CBCT with 3D/3D matching mode.

Proton pencil beam scanning craniospinal irradiation (CSI) with a single posterior brain beam: Dosimetry and efficiency

This study explores the feasibility and potential dosimetric and time efficiency benefit of proton Pencil Beam Scanning (PBS) craniospinal irradiation with a single posterior-anterior (SPA) brain field. The SPA approach was compared to our current clinical protocol using Bilateral Posterior Oblique brain fields (BPO). Ten consecutive patients were simulated in the head-first supine position on a long BOS frame and scanned using 3 mm CT slice thickness. A customized thermoplastic mask immobilized the patient's head, neck, and shoulders. A vac-lock was used to secure the legs. PBS proton plans were robustly optimized with 3mm setup errors and 3.5% range uncertainties in the Eclipse V15.6 treatment planning system (n = 12 scenarios). In order to achieve a smooth gradient dose match at the junction area, at least 5 cm overlap region was maintained between the segments and 5 mm uncertainty along the cranial-cauda direction was applied to each segment independently as additional robust optimization scenarios. The brain doses were planned by SPA or BPO fields. All spine segments were planned with a single PA field. Dosimetric differences between the BPO and SPA approaches were compared, and the treatment efficiency was analyzed according to timestamps of beam delivery. Results: The maximum brain dose increases to 111.1 ± 2.1% for SPA vs. 109.0 ± 1.7% for BPO (p < 0.01). The dose homogeneity index (D5/D95) in brain CTV was comparable between techniques (1.037 ± 0.010 for SPA and 1.033 ± 0.008 for BPO). Lens received lower maximum doses by 2.88 ± 1.58 Gy (RBE) (left) and 2.23 ± 1.37 Gy (RBE) (right) in the SPA plans (p < 0.01). No significant cochlea dose change was observed. SPA reduced the treatment time by more than 4 minutes on average and ranged from 2 to 10 minutes, depending on the beam waiting and allocation time. SPA is dosimetrically comparable to BPO, with reduced lens doses at the cost of slightly higher dose inhomogeneity and hot spots. Implementation of SPA is feasible and can help to improve the treatment efficiency of PBS CSI treatment.

A robust treatment planning approach for chest motion in postmastectomy chest wall intensity modulated radiation therapy.

Chest wall postmastectomy radiation therapy (PMRT) should consider the effects of chest wall respiratory motion. The purpose of this study is to evaluate the effectiveness of robustness planning intensity modulated radiation therapy (IMRT) for respiratory movement, considering respiratory motion as a setup error. This study analyzed 20 patients who underwent PMRT (10 left and 10 right chest walls). The following three treatment plans were created for each case and compared. The treatment plans are a planning target volume (PTV) plan (PP) that covers the PTV within the body contour with the prescribed dose, a virtual bolus plan (VP) that sets a virtual bolus in contact with the body surface and prescribing the dose that includes the PTV outside the body contour, and a robust plan (RP) that considers respiratory movement as a setup uncertainty and performs robust optimization. The isocenter was shifted to reproduce the chest wall motion pattern and the doses were recalculated for comparison for each treatment plan. No significant difference was found between the PP and the RP in terms of the tumor dose in the treatment plan. In contrast, VP had 3.5% higher PTV Dmax and 5.5% lower PTV V95% than RP (p<0.001). The RP demonstrated significantly higher lung V20Gy and Dmean by 1.4% and 0.4Gy, respectively, than the PP. The RP showed smaller changes in dose distribution affected by chest wall motion and significantly higher tumor dose coverage than the PP and VP. We revealed that the RP demonstrated comparable tumor doses to the PP in treatment planning and was robust for respiratory motion compared to both the PP and the VP. However, the organ at risk dose in the RP was slightly higher; therefore, its clinical use should be carefully considered.

The performance of a new type accelerator uRT-linac 506c evaluated by a quality assurance automation system.

The purpose of this study was to evaluate the performance of our quality assurance (QA) automation system and to evaluate the machine performance of a new type linear accelerator uRT-linac 506c within 6months using this system. This QA automation system consists of a hollow cylindrical phantom with 18 steel balls in the phantom surface and an analysis software to process electronic portal imaging device (EPID) measurement image data and report the results. The performance of the QA automation system was evaluated by the tests of repeatability, archivable precision, detectability of introduced errors, and the impact of set-up errors on QA results. The performance of this linac was evaluated by 31 items using this QA system over 6months. This QA system was able to automatically deliver QA plan, EPID image acquisition, and automatic analysis. All images acquiring and analysis took approximately 4.6min per energy. The preset error of 0.1mm in multi-leaf collimator (MLC) leaf were detected as 0.12±0.01mm for Bank A and 0.10±0.01mm in Bank B. The 2mm setup error was detected as -1.95±0.01mm, -2.02±0.01mm, 2.01±0.01mm for X, Y, Z directions, respectively. And data from the tests of repeatability and detectability of introduced errors showed the standard deviation were all within 0.1mm and 0.1°. and data of the machine performance were all within the tolerance specified by AAPM TG-142. The QA automation system has high precision and good performance, and it can improve the QA efficiency. The performance of the new accelerator has also performed very well during the testing period.

Setup Uncertainty of Pediatric Brain Tumor Patients Receiving Proton Therapy: A Prospective Study.

This study quantifies setup uncertainty in brain tumor patients who received image-guided proton therapy. Patients analyzed include 165 children, adolescents, and young adults (median age at radiotherapy: 9 years (range: 10 months to 24 years); 80 anesthetized and 85 awake) enrolled in a single-institution prospective study from 2020 to 2023. Cone-beam computed tomography (CBCT) was performed daily to calculate and correct manual setup errors, once per course after setup correction to measure residual errors, and weekly after treatments to assess intrafractional motion. Orthogonal radiographs were acquired consecutively with CBCT for paired comparisons of 40 patients. Translational and rotational errors were converted from 6 degrees of freedom to a scalar by a statistical approach that considers the distance from the target to the isocenter. The 95th percentile of setup uncertainty was reduced by daily CBCT from 10 mm (manual positioning) to 1-1.5 mm (after correction) and increased to 2 mm by the end of fractional treatment. A larger variation existed between the roll corrections reported by radiographs vs. CBCT than for pitch and yaw, while there was no statistically significant difference in translational variation. A quantile mixed regression model showed that the 95th percentile of intrafractional motion was 0.40 mm lower for anesthetized patients (p=0.0016). Considering additional uncertainty in radiation-imaging isocentricity, the commonly used total plan robustness of 3 mm against positional uncertainty would be appropriate for our study cohort.

Comparison of passive-scattered and intensity-modulated proton beam therapy of craniospinal irradiation with proton beams for pediatric and young adult patients with brain tumors

PurposeTo investigate the dose stability of craniospinal irradiation based on irradiation method of proton beam therapy (PBT).Methods and materialsTwenty-four pediatric and young adult brain tumor patients (age: 1–24 years) were examined. Treatment method was passive-scattered PBT (PSPT) in 8 patients and intensity-modulated PBT (IMPT) in 16 patients. The whole vertebral body (WVB) technique was used in 13 patients whose ages were younger than 10, and vertebral body sparing (VBS) technique was used for the remaining 11 patients aged 10 and above. Dose stability of planning target volume (PTV) against set-up error was investigated.ResultsThe minimum dose (Dmin) of IMPT was higher than that of PSPT (p = 0.01). Inhomogeneity index (INH) of IMPT was lower than that of PSPT (p = 0.004). When the irradiation field of the cervical spinal cord level (C level) was shifted, the maximum dose (Dmax) was lower in IMPT, and mean dose (Dmean) was higher than PSPT as movement became greater to the cranial–caudal direction (p = 0.000–0.043). Dmin was higher and INH was lower in IMPT in all directions (p = 0.000–0.034). When the irradiation field of the lumber spinal cord level (L level) was shifted, Dmax was lower in IMPT as movement became greater to the cranial direction (p = 0.000–0.028). Dmin was higher and INH was lower in IMPT in all directions (p = 0.000–0.022).ConclusionsThe PTV doses of IMPT and PSPT are robust and stable in both anterior–posterior and lateral directions at both C level and L level, but IMPT is more robust and stable than PSPT for cranial–caudal movements.Trial registryClinical Trial Registration number: No. 04-03.