Interfractional Setup Errors Research Articles

Utility of a skin marker-less setup procedure using surface-guided imaging: a comparison with the traditional laser-based setup in extremity irradiation.

This study aimed to assess the feasibility of a skin marker-less patient setup using a surface-guided radiotherapy (SGRT) system for extremity radiotherapy. Twenty-five patients who underwent radiotherapy to the extremities were included in this retrospective study. The first group consisted of 10 patients and underwent a traditional setup procedure using skin marks and lasers. The second group comprised 15 patients and had a skin marker-less setup procedure that used an SGRT system only. To compare the two setup procedures for setup accuracy, the mean 3D vector shift magnitude was 0.9mm for the traditional setup procedure and 0.5mm for the skin marker-less setup procedure (p < 0.01). In addition, SGRT systems have been suggested to improve the accuracy and reproducibility of patient setups and consistently reduce interfractional setup errors. These results indicate that a skin marker-less patient setup procedure using an SGRT system is useful for extremity irradiation.

CBCT Guided Interfraction Absolute Displacement and Setup Error Assessment during Breast Prone Radiotherapy

To calculate interfraction absolute displacement/shift and setup error using cone beam computed tomography (CBCT) during breast prone radiotherapy. Fifty-nine patients undergoing prone whole breast-irradiation after breast-conserving surgery (BCS) were studied as part of an institutional review board- approved prospective trial. Setup precision was monitored using a daily online CBCT. Translational shifts in 3 axes (AP: anterior posterior; LR: left right; and SI: superior inferior) and 3 rotations (pitch, roll, and rtn) after CBCT were analyzed for 1062 treatment fractions. The random and systematic setup errors (SE) were calculated and were analyzed for time trends during the course of radiotherapy. For absolute inter-fractional shifts, the numbers of fractions exceeding 10 mm in the AP, LR, and SI directions were 6.5%, 17.42% and 8.92%, respectively; 0%, 0% and 1.31% fractions exceeded 3°for pitch, roll, and Rtn, respectively. The population systematic errors were 1.89/2.91/1.98 mm in AP/SI/LR directions, while the random error were 2.72/3.99/3.31 mm. In pitch, roll, rtn rotations, the population systematic error were 0.64°/0.49°/0.46°, and 0.89°/0.90°/0.93° for the random error. Without correction these would correspond to a clinical to planning target volume margin of 6.64/10.08/7.26 mm in AP/SI/LR directions and 2.22°/1.79°/1.8° in pitch, roll, rtn rotations. The magnitude of inter-fraction motion was not correlated with patient treatment time accept in AP direction (P = 0.000). SE was larger in prone position in breast cancer patients, attributable mostly to random errors, which emphasize the need for on-line imaging guidance in breast prone radiotherapy. 10mm margins would adequately cover the target volume and account for setup errors in the absence of IGRT.

Assessment of dosimetric impact of interfractional 6D setup error in tongue cancer treated with IMRT and VMAT using daily kV-CBCT.

This study aimed to evaluate the dosimetric influence of 6-dimensional (6D) interfractional setup error in tongue cancer treated with intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) using daily kilovoltage cone-beam computed tomography (kV-CBCT). This retrospective study included 20 tongue cancer patients treated with IMRT (10), VMAT (10), and daily kV-CBCT image guidance. Interfraction 6D setup errors along the lateral, longitudinal, vertical, pitch, roll, and yaw axes were evaluated for 600 CBCTs. Structures in the planning CT were deformed to the CBCT using deformable registration. For each fraction, a reference CBCT structure set with no rotation error was created. The treatment plan was recalculated on the CBCTs with the rotation error (RError), translation error (TError), and translation plus rotation error (T+RError). For targets and organs at risk (OARs), the dosimetric impacts of RError, TError, and T+RError were evaluated without and with moderate correction of setup errors. The maximum dose variation ΔD (%) for D98% in clinical target volumes (CTV): CTV-60, CTV-54, planning target volumes (PTV): PTV-60, and PTV-54 was -1.2%, -1.9%, -12.0%, and -12.3%, respectively, in the T+RError without setup error correction. The maximum ΔD (%) for D98% in CTV-60, CTV-54, PTV-60, and PTV-54 was -1.0%, -1.7%, -9.2%, and -9.5%, respectively, in the T+RError with moderate setup error correction. The dosimetric impact of interfractional 6D setup errors was statistically significant (p < 0.05) for D98% in CTV-60, CTV-54, PTV-60, and PTV-54. The uncorrected interfractional 6D setup errors could significantly impact the delivered dose to targets and OARs in tongue cancer. That emphasized the importance of daily 6D setup error correction in IMRT and VMAT.

In Vivo Dosimetry in the Urethra During Prostate Carbon Ion Radiotherapy.

In vivo dosimetry can prevent dose delivery errors by directly measuring the dose of radiation administered to a patient. However, a method for in vivo dosimetry during carbon ion radiotherapy (CIRT) has not been established. Therefore, we investigated data from in vivo dosimetry of the urethra during CIRT for prostate cancer using small spherical diode dosimeters (SSDDs). This study included five patients enrolled in a clinical trial (jRCT identifier: jRCTs032190180) on which the use of four-fraction CIRT for prostate cancer was examined. The urethral dose during CIRT for prostate cancer was measured using the SSDDs inserted into the ureteral catheter. The relative error between the in vivo and calculated doses obtained using the Xio-N treatment planning system was determined. Additionally, a dose-response stability test for the in vivo dosimeter was performed under clinical conditions. The relative error between the in vivo and calculated urethral doses ranged from 6 to 12%. The dose-response stability under clinical conditions of the measured dose was ≤1%. Therefore, an error >1% would be due to an interfractional patient setup error in the large dose gradient in the urethra. The usefulness of in vivo dosimetry using SSDDs in CIRT and SSDDs' potential for detecting dose delivery errors during CIRT is herein highlighted.

Robustness of VMAT to setup errors in postmastectomy radiotherapy of left-sided breast cancer: Impact of bolus thickness.

Volumetric modulated arc therapy (VMAT) with varied bolus thicknesses has been employed in postmastectomy radiotherapy (PMRT) of breast cancer to improve superficial target coverage. However, impact of bolus thickness on plan robustness remains unclear. The study enrolled ten patients with left-sided breast cancer who received radiotherapy using VMAT with 5 mm and 10 mm bolus (VMAT-5B and VMAT-10B). Inter-fractional setup errors were simulated by introducing a 3 mm shift to isocenter of the original plans in the anterior-posterior, left-right, and inferior-superior directions. The plans (perturbed plans) were recalculated without changing other parameters. Dose volume histograms (DVH) were collected for plan evaluation. Absolute dose differences in DVH endpoints for the clinical target volume (CTV), heart, and left lung between the perturbed plans and the original ones were used for robustness analysis. VMAT-10B showed better target coverage, while VMAT-5B was superior in organs-at-risk (OARs) sparing. As expected, small setup errors of 3 mm could induce dose fluctuations in CTV and OARs. The differences in CTV were small in VMAT-5B, with a maximum difference of -1.05 Gy for the posterior shifts. For VMAT-10B, isocenter shifts in the posterior and right directions significantly decreased CTV coverage. The differences were -1.69 Gy, -1.48 Gy and -1.99 Gy, -1.69 Gy for ΔD95% and ΔD98%, respectively. Regarding the OARs, only isocenter shifts in the posterior, right, and inferior directions increased dose to the left lung and the heart. Differences in VMAT-10B were milder than those in VMAT-5B. Specifically, mean heart dose were increased by 0.42 Gy (range 0.10 ~ 0.95 Gy) and 0.20 Gy (range -0.11 ~ 0.72 Gy), and mean dose for the left lung were increased by 1.02 Gy (range 0.79 ~ 1.18 Gy) and 0.68 Gy (range 0.47 ~ 0.84 Gy) in VMAT-5B and VMAT-10B, respectively. High-dose volumes in the organs were increased by approximate 0 ~ 2 and 1 ~ 3 percentage points, respectively. Nevertheless, most of the dosimetric parameters in the perturbed plans were still clinically acceptable. VMAT-5B appears to be more robust to 3 mm setup errors than VMAT-10B. VMAT-5B also resulted in better OARs sparing with acceptable target coverage and dose homogeneity. Therefore 5 mm bolus is recommended for PMRT of left-sided breast cancer using VMAT.

Verification of patient-setup accuracy using a surface imaging system with steep measurement angle.

We evaluate an SGRT device (Voxelan HEV-600M/RMS) installed with Radixact, with the view angle of the Voxelan's camera at 74 degrees. The accuracy of Voxelan with this steep angle was evaluated with phantom experiments and inter-fractional setup errors of patients. In the phantom experiments, the difference between the measured values of Voxelan from the truth was evaluated for translations and rotations. The inter-fractional setup error between the setup using skin markers with laser localizer (laser setup: LS) and the setup using Voxelan (surface setup: SS) was compared for head and neck (N=19), chest (N=7) and pelvis (N=9) cases. The inter-fractional setup error was calculated by subtracting from bone matching by megavoltage computed tomography (MVCT) as ground truth. From the phantom experiments, the average difference between the measured values of Voxelan from the truth was within 1mm and 1 degree. In all cases, inter-fractional setup error based on MVCT was not significantly different between LS and SS by Welch's t-test (P>0.05). The vector offset of the LS for head and neck, chest, and pelvis were 6.5, 9.6, and 9.6mm, respectively, and that of the SS were 5.8, 8.6, and 12.6mm, respectively. Slight improvement was observed for the head and neck, and chest cases, however, pelvis cases were not improved because the umbilical region could not be clearly visualized as a reference. The results show that SS in Voxelan with an installation angle of 74 degrees is equal to or better than LS.

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

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). 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. 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). 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.

Evaluation of the dosimetric influence of interfractional 6D setup error in hypofractionated prostate cancer treated with IMRT and VMAT using daily kV-CBCT

IntroductionProstate cancer is one of the most common malignant tumors in men and is usually treated with advanced intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). Significant uncorrected interfractional 6-Dimensional setup errors could impact the delivered dose. The aim of this study was to assess the dosimetric impact of 6D interfractional setup errors in hypofractionated prostate cancer using daily kilovoltage cone-beam computed tomography (kV-CBCT). MethodsThis retrospective study comprised twenty prostate cancer patients treated with hypofractionated IMRT (8) and VMAT (12) with daily kV-CBCT image guidance. Interfraction 6D setup errors along lateral, longitudinal, vertical, pitch, roll, and yaw axes were evaluated for 400 CBCTs. For targets and organs at risk (OARs), the dosimetric impact of rotational error (RError), translational error (TError), and translational plus rotational error (T+RError) were evaluated on kV-CBCT images. ResultsThe single fraction maximum TError ranged from 12–20 mm, and the RError ranged from 2.80–3.00. The maximum mean absolute dose variation ΔD in D98% (dose to 98% volume) of CTV-55 and PTV-55 was -0.66±0.82 and -5.94±3.8 Gy, respectively, in the T+RError. The maximum ΔD (%) for D98% and D0.035cc in CTV-55 was -4.29% and 2.49%, respectively, while in PTV-55 it was -24.9% and 2.36%. The mean dose reduction for D98% in CTV-55 and D98% and D95% in PTV-55 was statistically significant (p<0.05) for TError and T+RError. The mean dose variation for Dmean and D50% in the rectum was statistically significant (p<0.05) for TError and T+RError. ConclusionThe uncorrected interfractional 6D setup error results in significant target underdosing and OAR overdosing in prostate cancer. This emphasizes the need to correct interfractional 6D setup errors daily in IMRT and VMAT.

Setup error and residual error analysis of ExacTrac X-ray image guidance system in stereotactic radiotherapy for brain metastases

ObjectiveThis study aims to analyze the setup errors of the ExacTrac X-ray image guidance system in stereoscopic radiotherapy for brain metastases and discuss the necessity of setup error verification after bed angle movement. MethodsTwelve patients with brain metastases were treated with stereotactic radiotherapy. ExacTrac X-ray image guidance system was used to register and verify the image. Besides, the intra- and inter-fractional setup errors and residual errors were analyzed. ResultsTwelve patients received head stereotactic radiotherapy 56 times. The inter-fractional setup errors and residual errors were x (1.04 ± 0.16) and (0.15 ± 0.05) mm in left and right directions, y (1.25 ± 0.28) and (0.18 ± 0.07) mm in head and foot direction, and z (0.93 ± 0.81) and (0.14 ± 0.13) mm in abdominal and dorsal direction, respectively; Rx (0.81 ± 0.24) and (0.24 ± 0.09) degree in the sagittal plane, Ry (0.95 ± 0.19), (0.22 ± 0.06) degree in the cross-section, and Rz (1.03 ± 0.26), (0.22 ± 0.06) in the coronal plane. The difference was statistically significant (P < 0.05). Only 19.6% of the intra-fractional non-coplanar arc setup verification passed without correction for the first time, and the others were significantly improved after correction, presenting statistical significance (P < 0.05). The inter-fractional setup errors and residual errors were x (0.82 ± 0.25) and (0.13 ± 0.04) mm in left and right directions, y (0.67 ± 0.23) and (0.18 ± 0.08) mm in head and foot direction, and z (0.74 ± 0.21) and (0.19 ± 0.08) mm in abdominal and dorsal direction, respectively; Rx (0.67 ± 0.13) and (0.20 ± 0.08) degree in the sagittal plane, Ry (0.68 ± 0.13) and (0.17 ± 0.10) degree in the cross-section, and Rz (0.60 ± 0.28) and (0.19 ± 0.07) degree in the coronal plane. The difference was statistically significant (P < 0.05). ConclusionThe ExacTrac image guidance system enhanced the accuracy of setup in stereoscopic radiotherapy for brain metastases and satisfied the clinical requirements. It is necessary to verify the non-coplanar arc setup.

Evaluation of Hybrid VMAT Advantages and Robustness Considering Setup Errors Using Surface Guided Dose Accumulation for Internal Lymph Mammary Nodes Irradiation of Postmastectomy Radiotherapy

ObjectivesSetup error is a key factor affecting postmastectomy radiotherapy (PMRT) and irradiation of the internal mammary lymph nodes is the most investigated aspect for PMRT patients. In this study, we evaluated the robustness, radiobiological, and dosimetric benefits of the hybrid volumetric modulated arc therapy (H-VMAT) planning technique based on the setup error in dose accumulation using a surface-guided system for radiation therapy.MethodsWe retrospectively selected 32 patients treated by a radiation oncologist and evaluated the clinical target volume (CTV), including internal lymph node irradiation (IMNIs), and considered the planning target volume (PTV) margin to be 5 mm. Three different planning techniques were evaluated: tangential-VMAT (T-VMAT), intensity-modulated radiation therapy (IMRT), and H-VMAT. The interfraction and intrafraction setup errors were analyzed in each field and the accumulated dose was evaluated as the patients underwent daily surface-guided monitoring. These parameters were included while evaluating CTV coverage, the dose required for the left anterior descending artery (LAD) and the left ventricle (LV), the normal tissue complication probability (NTCP) for the heart and lungs, and the second cancer complication probability (SCCP) for contralateral breast (CB).ResultsWhen the setup error was accounted for dose accumulation, T-VMAT (95.51%) and H-VMAT (95.48%) had a higher CTV coverage than IMRT (91.25%). In the NTCP for the heart, H-VMAT (0.04%) was higher than T-VMAT (0.01%) and lower than IMRT (0.2%). However, the SCCP (1.05%) of CB using H-VMAT was lower than that using T-VMAT (2%) as well as delivery efficiency. And T-VMAT (3.72) and IMRT (10.5).had higher plan complexity than H-VMAT (3.71).ConclusionsIn this study, based on the dose accumulation of setup error for patients with left-sided PMRT with IMNI, we found that the H-VMAT technique was superior for achieving an optimum balance between target coverage, OAR dose, complication probability, plan robustness, and complexity.

Technical challenges in the treatment of mediastinal lymphomas by proton pencil beam scanning and deep inspiration breath-hold

PurposeTo comprehensively describe the treatment of mediastinal lymphoma by pencil beam scanning (PBS) proton therapy. MethodsFourteen patients underwent PBS proton treatment in a supine position in deep inspiration breath-hold (DIBH). Three DIBH computed tomography (CT) scans were acquired for each patient to delineate the Internal Target Volume (ITV). Intensity-modulated proton therapy (IMPT) was planned by min–max robust optimization on the ITV, with a 6 mm setup and 3.5% range uncertainties. Robustness analysis was performed and dose coverage was visually inspected on the corresponding voxel-wise minimum map. Layer repainting was set equal to 5 to compensate for cardiac motion. Intra-fraction reproducibility during treatment was assessed by repeated daily DIBH X-ray imaging. Finally, an additional CT was acquired at half treatment to estimate the impact of inter-fraction dosimetric reproducibility. ResultsIMPT guaranteed robust mediastinal target coverage and organs-at-risk sparing. However, visual voxel-wise robustness evaluation showed that in five patients a second optimization with focused objectives in the cost-function was necessary to achieve a robust coverage of the target regions at the interface between lungs and soft tissue. In six patients, repainting was not used due to excessive treatment time length and poor patient compliance. Intra-fraction average reproducibility was within 1 mm/1degree. On repeated CT scans, inter-fraction setup errors and/or anatomical changes showed minimal dosimetric differences in CTV coverage. ConclusionIMPT in DIBH is effective and reproducible to treat mediastinal lymphomas. Caution is recommended to guarantee robust dose delivery to high-risk regions at the interface between lungs and soft tissue.

Characterization and commissioning of a Leksell Gamma Knife ICON system for framed and frameless stereotactic radiosurgery.

PurposeThe Leksell Gamma Knife Icon unit (IU) was introduced recently as an upgrade to the Perfexion unit (PU) at our Gamma Knife practice. In the current study, we sought mainly to characterize dosimetry and targeting accuracy of the IU treatment deliveries using both invasive frame and frameless treatment workflows.MethodsRelative output factors were measured by delivering single‐shot 4, 8 and 16 mm radiation profiles in the manufacturer's acrylonitrile butadiene styrene spherical phantom in coronal and sagittal planes using EBT3 film. Resultant dosimetry was compared with the manufacturer's dose calculation and derived output factors were compared with the manufacturer's published value. Geometric consistency of stereotactic coordinates based on cone‐beam computed tomography (CBCT) versus the traditional conventional CT‐based method was characterized using a rigid phantom containing nine fiducial indicators over four separate trials. End‐to‐end (E2E) testing using EBT3 film was designed to evaluate both dosimetric and geometric accuracy for hypothetical framed and frameless workflows.ResultsRelative output factors as measured by the manufacturer were independently confirmed using EBT3 film measurements to within 2%. The mean 3D radial discrepancy in stereotactic space between CBCT and CT‐based definition over the sampled locations in our rigid geometry phantom was demonstrated to be between 0.40 mm and 0.56 mm over the set of trials, larger than prior reported values. E2E performed in 2D demonstrates sub‐mm (and typically < 0.5 mm) accuracy for framed and frameless workflows; geometric accuracy of framed treatments using CBCT‐defined stereotactic coordinates was shown to be slightly improved in comparison with those defined using conventional CT. Furthermore, in phantom, frameless workflows exhibited better accuracy than framed workflows for fractionated treatments, despite large magnitudes of introduced interfraction setup error. Accuracy of dosimetric delivery was confirmed in terms of qualitative comparisons of dose profiles and in terms of 2D gamma pass rates based on 1%/1 mm criteria.ConclusionThe IU was commissioned for clinical use of frameless and framed treatment protocols. The present study outlines an extensive E2E methodology for confirmation of dosimetric and geometric treatment accuracy.

Original Knee Fixation Device as a Useful Fixation Method during Prostate Intensity-Modulated Radiation Therapy.

Purpose:The purpose of he study was to reduce setup errors during intensity-modulated radiation therapy (IMRT) with an original knee fixation device (KFD) and evaluate the clinical target volume (CTV) coverage.Methods:Participants were classified into two groups: knee flexion (KF) group (n = 16), wherein participants' knees were fixed in a flexed position using the proposed KFD during planning computed tomography, and knee extension group (KE; n = 15), wherein no KFD was used. We investigated the residual rotational errors and inter-fractional setup errors with or without KFD. Furthermore, inter-fractional margins were calculated using logistic regression analysis, and CTV coverage was evaluated.Results:The residual rotational errors in the yaw and roll directions (P < 0.02) and the inter-fractional error in the anterior-posterior (A-P) direction (P < 0.02) improved significantly in the KF group compared with the KE group. Repeatability was improved for the pitch direction. The inter-fractional margins were 6.68 mm and 4.87 mm in the A-P and superior-inferior (S-I) directions, respectively, in the KF group, representing reductions (mm) of 20.8% and 12.6% compared with the KE group, respectively. The odds ratios for CTV coverage in the KF group compared to the KE group were 2.76 (P < 0.001) and 1.74 (P < 0.05) in the A-P and S-I directions, respectively.Conclusions:The IMRT fixation method using an original KFD improved the residual rotational error in the three directions and the inter-fractional error in the A-P direction, reduced the interfractional margins in the A-P, and S-I directions and improved CTV coverage. Our original KFD may be a useful fixation method during prostate IMRT.

The Effect of Cone-Beam CT Image-Guidance Strategies on the Delivered Dose for Spine Metastases Radiotherapy

This article will investigate the appropriate image-guidance (IG) strategy for spine metastases (SpM) radiotherapy by analyzing the delivered dose under different IG strategies with setup errors from daily cone-beam computed tomography (CBCT).A total of 720 CBCT scans about 36 vertebrae lesions from 2017 to 2019 were enrolled. All lesions were divided into two groups, twenty for simultaneous boost (PTV 40 Gy/20f, GTV 60 Gy/20f) and sixteen for conventional fractionated (PTV 40 Gy/20f). The actual fractionated plan was recalculated after transferring the isocenter of the original plan according to the inter-fraction setup error. Then under no daily image-guidance (no-DIG) strategies, like twice imaging guidance weekly (TIG), initial 5 days then weekly imaging guidance (5D+WIG), weekly imaging guidance (WIG) and no imaging guidance (NIG), the dose deviation was calculated between the delivered dose accumulated by each actual fractionated plan and the original RT-plan which is regarded as the dose distribution under daily image guidance (DIG). The tolerance of dose deviation for the target is within ± 5% and the Dmax of the spinal cord is limited below 45 Gy.When conventional fractionated radiotherapy, under strategies of image-guidance like TIG, 5D+WIG, WIG and NIG, the median dose deviations are 0% (-1.0% ∼ 1.2%), 0.2% (-0.8% ∼ 1.2%), 0.4% (-0.6% ∼ 1.8%), 0.8% (-0.2% ∼ 2.4%) for the Dmax of spinal cord; -0.2% (-1.4% ∼ 0%), -0.4% (-1.4% ∼ 0%), -0.8% (-2.3% ∼ -0.4%), -1.6% (-3.2% ∼ -0.8%) for the CTV D95; -6.0% (-8.4% ∼ -4.6%), -5.9% (-8.3% ∼ -4.6%), -8.0% (-11.3% ∼ -6.4%), -10.8% (-14.4% ∼ -8.7%) for the PTV D95. When simultaneous boosting, the median dose deviations correspondingly are 9.5% (7.2% ∼ 12.4%), 9.3% (7.0% ∼ 11.9%), 11.2% (9.3% ∼ 16.4%), 14.2% (11.6% ∼ 20.2%) and the proportions of case whose maximum irradiated dose of spinal cord is more than 45 Gy are all beyond 70% for the Dmax of spinal cord; -5.1% (-7.9% ∼ -4.2%), -4.7% (-7.4% ∼ -4.2%), -7.0% (-10.3% ∼ -6.0%), -8.6% (-13.1% ∼ -7.3%) for the GTV D95; -3.5% (-7.3% ∼ -2.1%), -3.4% (-6.8% ∼ -1.7%), -6.2% (-11.1% ∼ -3.9%), -9.0% (-16.5% ∼ -5.6%) for the PTV D95.When conventional fractionated radiotherapy, the image-guidance strategies could be chosen according to the clinical practice. However, it is necessary to do daily IGRT for spine metastases radiotherapy when simultaneous boosting because the dose deviations for the Dmax of spinal cord, GTV D95 are all out of the tolerance.C.Jia: None. B. Zhao: None. X. Gao: None. Y. Bai: None. Z. Shang: None.

Influence of Clinical and Tumor Factors on Interfraction Setup Errors With Rotation Correction for Vacuum Cushion in Lung Stereotactic Body Radiation Therapy.

PurposeTo explore the influence of clinical and tumor factors over interfraction setup errors with rotation correction for non-small cell lung cancer (NSCLC) stereotactic body radiation therapy (SBRT) patients immobilized in vacuum cushion (VC) to better understand whether patient re-setup could further be optimized with these parameters.Materials and MethodsThis retrospective study was conducted on 142 NSCLC patients treated with SBRT between November 2017 to July 2019 in the local institute. Translation and rotation setup errors were analyzed in 732 cone-beam computed tomography (CBCT) scans before treatment. Differences between groups were analyzed using independent sample t-test. Logistic regression test was used to analyze possible correlations between patient re-setup and clinical and tumor factors.ResultsMean setup errors were the largest in anterior–posterior (AP) direction (3.2 ± 2.4 mm) compared with superior–inferior (SI) (2.8 ± 2.1 mm) and left–right (LR) (2.5 ± 2.0 mm) directions. The mean values were similar in pitch, roll, and rtn directions. Of the fractions, 83.7%, 90.3%, and 86.6% satisfied setup error tolerance limits in AP, SI, and LR directions, whereas 95% had rotation setup errors of <2° in the pitch, roll, or rtn directions. Setup errors were significantly different in the LR direction when age, body mass index (BMI), and “right vs. left” location parameters were divided into groups. Both univariate and multivariable model analyses showed that age (p = 0.006) and BMI (p = 0.002) were associated with patient re-setup.ConclusionsAge and BMI, as clinical factors, significantly influenced patient re-setup in the current study, whereas all other clinical and tumor factors were not correlated with patient re-setup. The current study recommends that more attention be paid to setup for elderly patients and patients with larger BMI when immobilized using VC, especially in the left–right direction.

Benefits and challenges of standard ceiling-mounted surface guided radiotherapy systems for breast treatments on Halcyon™

The present work investigates the benefits and challenges of applying surface guided radiation therapy (SGRT) to breast cancer treatments on the Halcyon™ (Varian, USA). Inter-fraction setup accuracy and treatment time were assessed by comparing CBCT shifts registered following SGRT-based vs. standard tattoo-based patient setup in two randomly selected groups of ten breast patients. Next, using a torso phantom and a volunteer, intra-fraction motion tracking accuracy and surface coverage were assessed for 3 adjusted central ceiling camera positions. SGRT was shown to significantly reduce setup errors (mostly within ± 2 mm) compared to tattoos (up to 2.1 cm) in all translational directions (p-value &lt; 0.001). Treatment throughput and efficiency were also significantly improved with SGRT (p = 0.038). Meanwhile, intra-bore surface coverage with an adjusted central SGRT camera proved insufficient, suffering from patient self-occlusions (invisible body parts occluded by patients’ own morphology such as breasts, bellies, arms, etc.) and bore-induced camera obstructions. Tracking accuracy remained satisfactory (sub-0.5 mm) but 6 degrees-of-freedom motion monitoring, critical in stereotactic radiosurgery, stereotactic body radiation therapy and deep inspiration breath hold techniques and clinical applications, was not possible. Standard ceiling-mounted SGRT systems reduce inter-fraction breast setup errors and treatment duration while intra-fraction motion tracking is insufficient for O-ring linear accelerators.

Intrafraction stability using full head mask for brain stereotactic radiotherapy.

PurposeWe investigated the immobilization accuracy of a new type of thermoplastic mask—the Double Shell Positioning System (DSPS)—in terms of geometry and dose delivery.MethodsThirty‐one consecutive patients with 1–5 brain metastases treated with stereotactic radiotherapy (SRT) were selected and divided into two groups. Patients were divided into two groups. One group of patients was immobilized by the DSPS (n = 9). Another group of patients was immobilized by a combination of the DSPS and a mouthpiece (n = 22). Patient repositioning was performed with cone beam computed tomography (CBCT) and six‐degree of freedom couch. Additionally, CBCT images were acquired before and after treatment. Registration errors were analyzed with off‐line review. The inter‐ and intrafractional setup errors, and planning target volume (PTV) margin were also calculated. Delivered doses were calculated by shifting the isocenter according to inter‐ and intrafractional setup errors. Dose differences of GTV D99% were compared between planned and delivered doses against the modified PTV margin of 1 mm.ResultsInterfractional setup errors associated with the mouthpiece group were significantly smaller than the translation errors in another group (p = 0.03). Intrafractional setup errors for the two groups were almost the same in all directions. PTV margins were 0.89 mm, 0.75 mm, and 0.90 mm for the DSPS combined with the mouthpiece in lateral, vertical, and longitudinal directions, respectively. Similarly, PTV margins were 1.20 mm, 0.72 mm, and 1.37 mm for the DSPS in the lateral, vertical, and longitudinal directions, respectively. Dose differences between planned and delivered doses were small enough to be within 1% for both groups.ConclusionsThe geometric and dosimetric assessments revealed that the DSPS provides sufficient immobilization accuracy. Higher accuracy can be expected when the immobilization is combined with the use of a mouthpiece.

Practical aspects of the application of helical tomotherapy for craniospinal irradiation

We investigated the practical aspects of the application of craniospinal irradiation using helical tomotherapy (HT-CSI) by evaluating interfractional setup errors and intrafractional movement during each treatment in 83 patients undergoing HT-CSI between January 2014 and December 2018. Interfractional setup errors in each axis (mediolateral; ML, craniocaudal; CC, and anteroposterior; AP) were assessed as differences between pre-treatment megavoltage computed tomography (MVCT) images scanned (zygomatic arch to the C4 spine) and planning CT images. Intrafractional movements were evaluated as the difference between pre-treatment and post-treatment MVCT (T12–L4 spine) images at each fraction. Median interfractional setup error was acceptable in every axis (ML: 1.6 mm, CC: 1.9 mm, AP: 3.1 mm). Seven patients (8.4%) experienced significant intrafractional displacement from 1 to 10 fractions (0.34% for ML, 0.74% for CC, 1.21% for AP). Weight loss grade 1+ during treatment (p = 0.016) was an independent risk factor for significant intrafractional displacement. The risk factor for significant intrafractional movement in pediatric patients was weight loss grade 1+ (p = 0.020), while there was no factor in adults. HT-CSI could be a feasible treatment modality with acceptable setup verification. Inter- and intrafractional errors were acceptable; paying attention to weight loss during treatment is necessary, especially in pediatric patients.

Comparison of Setup Variations and Defining a CTV-PTV Margin in Fractionated Radiotherapy of Brain Tumor Using Novalis Tx Orthogonal OBI (kv) Versus Brain Lab ExacTrac (kv) Imaging Systems with Brain Lab Mask

The objective of this study is to evaluate the setup discrepancy between Brain Lab ExacTrac (kv) and Orthogonal Novalis Tx (kv) imaging systems and to obtain an optimal CTV-PTV margin. We recruited 35 consecutive brain tumor patients, immobilized with non-invasive thermoplastic BrainLab mask, between August 2016 and August 2017. The position verification done by ExacTrac, Infrared Positioning System was followed by a set of images by OBI at 0° and 90° position. The images were autofused and compared with DRR generated by TPS. The extent of translational and rotational shift was then applied and documented. The translational inter-fractional setup error (mean ± SD) in X-axis detected by OBI and ET was 0.002 ± 0.227 and −0.042 ± 0.084, respectively. In Y-axis, the error detected was −0.01 ± 0.176 and 0.075 ± 0.079, respectively, whereas in Z-axis the error with OBI and ET was 0.329 ± 0.521 and 0.051 ± 0.091, respectively. The P-value of inter-fractional errors in X, Y, and Z axes was 0.294, 0.013, and 0.004, which is statistically significant in Y- and Z-axes. Rotational inter-fractional setup errors (mean ± SD) for OBI and ET were −0.101 ± 0.257 and −0.076 ± 0.102, respectively. The rotational setup errors detected by ET in pitch and roll dimension are −0.003 ± 0.084 and −0.085 ± 0.073, respectively. The data obtained were put in Van Herk’s formula (PTV margin = 2.5 ∑ + 0.74 σ), and CTV-PTV margin was calculated. CTV-PTV margin for ET was 2.70, 2.72, and 2.94 mm and 3.38o, 2.84o, and 2.51o in lateral, longitudinal, vertical and pitch, roll, yaw dimension, respectively. The CTV-PTV margin for OBI was 7.40, 6.20, and 5.30 mm and 7.27o in lateral, longitudinal, vertical, and yaw dimension, respectively. Daily setup verifications that use the Brain LAB Exac Trac 6D image-guided system are very useful for brain tumor treatment; nevertheless, OBI kv imaging can be used for FRT of brain tumor with extended margin.

Use of surface-guided radiation therapy in combination with IGRT for setup and intrafraction motion monitoring during stereotactic body radiation therapy treatments of the lung and abdomen.

Background and purposeMultiple techniques can be used to assist with more accurate patient setup and monitoring during Stereotactic body radiation therapy (SBRT) treatment. This study analyzes the accuracy of 3D surface mapping with Surface‐guided radiation therapy (SGRT) in detecting interfraction setup error and intrafraction motion during SBRT treatments of the lung and abdomen.Materials and MethodsSeventy‐one patients with 85 malignant thoracic or abdominal tumors treated with SBRT were analyzed. For initial patient setup, an alternating scheme of kV/kV imaging or SGRT was followed by cone beam computed tomography (CBCT) for more accurate tumor volumetric localization. The CBCT six degree shifts after initial setup with each method were recorded to assess interfraction setup error. Patients were then monitored continuously with SGRT during treatment. If an intrafractional shift in any direction >2 mm for longer than 2 sec was detected by SGRT, then CBCT was repeated and the recorded deltas were compared to those detected by SGRT.ResultsInterfractional shifts after SGRT setup and CBCT were small in all directions with mean values of <5 mm and < 0.5 degrees in all directions. Additionally, 25 patients had detected intrafraction motion by SGRT during a total of 34 fractions. This resulted in 25 (73.5%) additional shifts of at least 2 mm on subsequent CBCT. When comparing the average vector detected shift by SGRT to the resulting vector shift on subsequent CBCT, no significant difference was found between the two.ConclusionsSurface‐guided radiation therapy provides initial setup within 5 mm for patients treated with SBRT and can be used in place of skin marks or planar kV imaging prior to CBCT. In addition, continuous monitoring with SGRT during treatment was valuable in detecting potentially clinically meaningful intrafraction motion and was comparable in magnitude to shifts from additional CBCT scans. PTV margin reduction may be feasible for SBRT in the lung and abdomen when using SGRT for continuous patient monitoring during treatment.