Megavoltage Research Articles

Investigation of the Dose-Enhancement Effects of Spherical and Rod-Shaped Gold Nanoparticles on the HeLa Cell Line.

Background: Cervical cancer cells are known as radioresistant cells. Current treatment methods have not improved the patients’ survival efficiently; thus, new therapeutic strategies are needed to enhance the efficacy of radiotherapy. Gold nanomaterials with different shapes and sizes have been explored as radiosensitizers. The present study compared the radiosensitizing effects of gold nanorods (AuNRs) with spherical gold nanoparticles (AuNPs) on the HeLa cell line irradiated with megavoltage X-rays. Materials and Methods: The cytotoxicity of AuNRs and AuNPs on HeLa cells in the presence and absence of 6-MV X-ray was investigated using the MTT assay. For this aim, HeLa cells were incubated with and AuNPs and AuNRs at various concentrations (5, 10, and 15 µg/mL) for 6 hours. Afterward, HeLa cells were irradiated with 6-MV X-ray at a single dose of 2 Gy. Results: The results showed that the addition of AuNRs and AuNPs could enhance the radiosensitivity of HeLa cells. Both AuNRs and AuNPs showed low toxicity on HeLa cells, while AuNRs were more toxic than AuNPs at the examined concentrations. Moreover, it was found that AuNRs could enhance the radiosensitivity of HeLa cells more than spherical-shaped AuNPs. Conclusion: This study revealed that the shape of nanoparticles is an effective factor when they are used as radiosensitizing agents during radiotherapy.

RETRACTED: 68. FRAMELESS, VAULT-FREE RADIOSURGERY: INITIAL CLINICAL EXPERIENCE WITH THE ZAP-X STEREOTACTIC SYSTEM

The Zap-X is a novel self-contained and self-shielded dedicated radiosurgery system developed and manufactured by ZAP Surgical Systems, Inc. of San Carlos, California. Intended for the stereotactic radiosurgery (SRS) treatment of benign and malignant intracranial and cervical spine lesions, this gyroscopically stabilized 3 megavolt (MV) linear accelerator (LINAC) provides a unique radiosurgical alternative for selected patients. Beginning in January 2019, a total of 38 metastatic lesions in 24 patients were treated in our facility. Radiation prescription doses ranged from 1500–1900 cGy (single fraction) to 2500 cGy (five fractions), with treatment volumes ranging from .04 to 15.3 cc. Daily treatment times averaged 45 minutes or less. Target coverage, dose homogeneity, and conformality were comparable to the existing Gamma Knife, CyberKnife and LINAC-based radiosurgery treatment systems in daily use at our facility. As with other frameless radiosurgery platforms, the Zap-X proved particularly useful in situations where either surgery or single-fraction radiosurgery was considered a less desirable treatment option; or when fractionated radiosurgery was thought to be radiobiologically advantageous. All treatments were completed without complication. At two months post-treatment, all lesions showed a complete or partial response to therapy based on MRI scan. None of our patients experienced treatment-related skin reaction, cognitive deficit, fatigue or steroid dependency. Among patients who had previously undergone Gamma Knife treatment, there was a clear preference for frameless radiosurgery. In our experience, the Zap-X delivery system offers a high-precision, patient-friendly and cost-effective alternative to traditional dedicated radiosurgical platforms.

Direct measurement and correction of both megavoltage and kilovoltage scattered x-rays for orthogonal kilovoltage imaging subsystems with dual flat panel detectors.

PurposeTo measure the scattered x‐rays of megavoltage (MV) and kilovoltage (kV) beams (MV scatter and kV scatter, respectively) on the orthogonal kV imaging subsystems of Vero4DRT.MethodsImages containing MV‐ and kV‐scatter from another source only (i.e., MV‐ and kV‐scatter maps) were acquired for each investigated flat panel detector. The reference scatterer was a water‐equivalent cuboid phantom. The maps were acquired by changing one of the following parameters from the reference conditions while keeping the others fixed: field size: 10.0 × 10.0 cm2; dose rate: 400 MU/min; gantry and ring angles: 0°; kV collimator aperture size at isocenter: 10.0 × 10.0 cm2: tube voltage: 110 kV; and exposure: 0.8 mAs. The average pixel values of MV‐ and kV‐scatter (i.e., the MV‐ and kV‐scatter values) at the center of each map were calculated and normalized to the MV‐scatter value under the reference conditions (MV‐ and kV‐scatter value factor, respectively). In addition, an MV‐ and kV‐scatter correction experiment with intensity‐modulated beams was performed using a phantom with four gold markers (GMs). The ratios between the intensities of the GMs and those of their surroundings were calculated.ResultsThe measurements showed a strong dependency of the MV‐scatter on the field size and dose rate. The maximum MV‐scatter value factors were 2.0 at a field size of 15.0 × 15.0 cm2 and 2.5 at a dose rate of 500 MU/min. The maximum kV‐scatter value was 0.48 with a fully open kV collimator aperture. In the phantom experiment, the intensity ratios of kV images with MV‐ and kV‐scatter were decreased from the reference ones. After correction of kV‐scatter only, MV‐scatter only, and both MV‐ and kV‐scatter, the intensity ratios gradually improved.ConclusionsMV‐ and kV‐scatter could be corrected by subtracting the scatter maps from the projections, and the correction improved the intensity ratios of the GMs.

Automated MV markerless tumor tracking for VMAT

Tumor tracking during radiotherapy treatment can improve dose accuracy, conformity and sparing of healthy tissue. Many methods have been introduced to tackle this challenge utilizing multiple imaging modalities, including a template matching based approach using the megavoltage (MV) on-board portal imager demonstrated on 3D conformal treatments. However, the complexity of treatments is evolving with the introduction of VMAT and IMRT, and successful motion management is becoming more important due to a trend towards hypofractionation.We have developed a markerless lung tumor tracking algorithm, utilizing the electronic portal imager (EPID) of the treatment machine. The algorithm has been specifically adapted to track during complex treatment deliveries with gantry and MLC motion. The core of the algorithm is an adaptive template matching method that relies on template stability metrics and local relative orientations to perform multiple feature tracking simultaneously. Only a single image is required to initialize the algorithm and features are automatically added, modified or removed in response to the input images. This algorithm was evaluated against images collected during VMAT arcs of a dynamic thorax phantom. Dynamic phantom images were collected during radiation delivery for multiple lung SBRT breathing traces and an example patient data set. The tracking error was 1.34 mm for the phantom data and 0.68 mm for the patient data.A multi-region, markerless tracking algorithm has been developed, capable of tracking multiple features simultaneously without requiring any other a priori information. This novel approach delivers robust target localization during complex treatment delivery. The reported tracking error is similar to previous reports for 3D conformal treatments.

Clinical Development and Evaluation of Megavoltage Topogram for Fast Patient Alignment on Helical Tomotherapy

PurposeTo develop and evaluate a fast patient localization tool using megavoltage (MV)-topogram on helical tomotherapy. Methods and MaterialsEighty-one MV-topogram pairs for 18 pelvis patients undergoing radiation were acquired weekly under an institutional review board–approved clinical trial. The MV-topogram imaging protocol requires 2 orthogonal acquisitions at static gantry angles of 0 degrees and 90 degrees for a programed scan length. A MATLAB based in-house software was developed to reconstruct the MV-topograms offline. Reference images (digitally reconstructed topograms, digitally reconstructed topograms) were generated using the planning computed tomography and tomotherapy geometry. The MV-topogram based alignment was determined by registering the MV-topograms to the digitally reconstructed topogram using bony landmark on commercial MIM software. The daily shifts in 3 translational directions determined from MV-topograms were compared with the megavoltage computed tomography (MVCT) based patient shifts. Linear-regression and two one-sided tests equivalence tests were performed to investigate the relation and equivalence between the 2 techniques. Seventy-eight MV-topogram pairs for 19 head and neck patients were included to validate the finding. ResultsThe magnitudes of alignment differences of (MVCT − MV-topogram) (and standard deviations) were −0.3 ± 2.1, −0.8 ± 2.4, and 1.6 ± 1.7 mm for pelvis and 0.6 ± 1.2, 0.8 ± 4.2, 1.6 ± 2.6 mm for head and neck; the linear-regression coefficients between 2 imaging techniques were 1.18, 1.10, 0.94, and 0.86, 0.63, 0.38 in the lateral, longitudinal, vertical directions for pelvis and head and neck, respectively. The acquisition time for a pair of MV-topograms was up to 12.7 times less than MVCT scans (coarse scan mode) while covering longer longitudinal length. ConclusionsMV-topograms showed equivalent clinical performance to the standard MVCT with significantly less acquisition time for pelvis and H&N patients. The MV-topogram can be used as an alternative or complimentary tool for bony landmark-based patient alignment on tomotherapy.

3D printing for dosimetric optimization and quality assurance in small animal irradiations using megavoltage X-rays

PurposeNew therapeutic options in radiotherapy (RT) are often explored in preclinical in-vivo studies using small animals. We report here on the feasibility of modern megavoltage (MV) linear accelerator (LINAC)-based RT for small animals using easy-to-use consumer 3D printing technology for dosimetric optimization and quality assurance (QA). MethodsIn this study we aimed to deliver 5×2Gy to the half-brain of a rat using a 4MV direct hemi-field X-ray beam. To avoid the beam's build-up in the target and optimize dosimetry, a 1cm thick, customized, 3D-printed bolus was used. A 1:1 scale copy of the rat was 3D printed based on the CT dataset as an end-to-end QA tool. The plan robustness to HU changes was verified. Thermoluminescent dosimeters (TLDs), for both MV irradiations and for kV imaging doses, and a gafchromic film were placed within the phantom for dose delivery verifications. The phantom was designed using a standard treatment planning software, and was irradiated at the LINAC with the target aligned using kV on-board imaging. ResultsThe plan was robust (dose difference<1% for HU modification from 0 to 250). Film dosimetry showed a good concordance between planned and measured dose, with the steep dose gradient at the edge of the hemi-field properly aligned to spare the contralateral half-brain. In the treated region, the mean TLDs percentage dose differences (±2 SD) were 1.3% (±3.8%) and 0.9% (±1.7%) beneath the bolus. The mean (±2 SD) out-of-field dose measurements was 0.05Gy (±0.02Gy) for an expected dose of 0.04Gy. Imaging doses (2mGy) still spared the contralateral-brain. ConclusionsUse of consumer 3D-printers enables dosimetry optimization and QA assessment for small animals MV RT in preclinical studies using standard LINACS.

Technical note: development and validation of a Monte Carlo tool for analysis of patient-generated photon scatter

Scattered radiation unavoidably generated in the patient will negatively impact both kilovoltage (KV) and megavoltage (MV) imaging applications. Recently, ‘hybrid’ methods (i.e. combining analytical and Monte Carlo (MC) techniques) are being investigated as a solution to accurately yet quickly calculate the scattered contribution for both KV and MV images. We have developed a customized MC simulation user code for investigating the individual components of patient-scattered photon fluence, which serves as a valuable tool in this area of research. The MC tool is based on the EGSnrc/DOSXYZnrc user code. The IAUSFL flag options associated with subroutine AUSGAB, combined with LATCH tracking, are used to classify the various interactions of particles with the media. Photons are grouped into six different categories: primary, 1st Compton scatter, 1st Rayleigh scatter, multiple scatter, bremsstrahlung, and positron annihilation. We take advantage of the geometric boundary check in DOSXYZnrc, to write exiting photon particle information to a phase-space file. The tool is validated using homogeneous and heterogeneous phantom configurations with monoenergetic and polyenergetic beams under parallel and divergent beam geometry, comparing MC-simulated exit primary fluence and singly-scattered fluence to corresponding analytical calculations. This MC tool has been validated to separately score the primary and scatter fluence components of the KV and MV imaging applications in the field of radiation therapy. The results are acceptable for the various configurations and beam energies tested here. Overall, the mean percentage differences are less than 0.2% and standard deviations less than 1.6%. This will be a critical test instrument for research in photon scatter applications and particularly for the development of hybrid methods, and is freely available from the authors for research purposes.

Evaluating the radioprotective effect of arbutin on mice exposed to megavoltage X-rays based on hematological parameters and lymphocytes micronucleus assay

Evaluating the radioprotective effect of arbutin on mice exposed to megavoltage X-rays based on hematological parameters and lymphocytes micronucleus assay

Assessment of polarization and ion recombination correction factors and leakage of small megavoltage photon beams

Assessment of polarization and ion recombination correction factors and leakage of small megavoltage photon beams

Impact of radiopacified bone cement on radiotherapy dose calculation.

Background and purposeRadiopacifiers are introduced to bone cements to provide the appearance of bone in kilovoltage (kV) radiographic images. For higher energy megavoltage (MV) radiotherapy treatment beams, however, these radiopacifiers do not cause a bone-like perturbation of dose. This study therefore aimed to determine the impact of the barium-contrasted plastic-based cement materials on radiotherapy dose calculations.Materials and methodsThe radiological properties of a physical sample of bone cement were characterised by computed tomography (CT) imaging and transmission measurements. Monte Carlo simulations of percentage depth-dose profiles were performed to determine the possible dose error for MV treatment beams. Dose differences were then investigated for clinical volumetric modulated radiotherapy treatment plans, with and without density overrides applied.ResultsDifferences of up to 7% were observed at the downstream interface of a 0.6 cm thick bone cement layer, compared to bone. Differences in planning target volume dose-volume metrics varied between −0.5% and 2.0%.ConclusionBefore planning radiotherapy treatments for patients who have undergone cranioplasty, every effort should be made to identify whether a radiopacified bone cement has been implanted. Density overrides should be applied to minimise dose calculation errors, whenever bone cement is used.

Setup error with and without image guidance using two canine intracranial positioning systems for radiation therapy.

Daily image guidance reduces inter-fractional variation in patient position for intracranial radiation therapy. However, the ability to detect and correct positioning errors is limited below a certain level. Because of these limitations, the accuracy achieved with a positioning system prior to image guidance may affect the error remaining after image guidance (the residual setup error). The objective of this study was to compare the setup accuracy achieved before and after megavoltage (MV) and cone-beam computed tomography (CBCT) guidance between two intracranial positioning systems. Equipment included a four degrees-of-freedom couch capable of 1 mm translational moves. Six dog cadavers were positioned 24 times as for clinical treatment in a head re-positioner (HPS), and the coordinates of five fiducial markers were measured before and after image-guided correction. The values obtained for the HPS were compared with those previously reported for the standard positioning system (SPS) used at this facility. The mean three-dimensional distance vector (3DDV) was lower for the HPS than for the SPS when no image guidance was used (P = .019). The mean 3DDV after MV guidance was lower for the HPS than for the SPS (P = .027), but not different after CBCT guidance (P = .231). The 95th percentiles of the 3DDV after MV and CBCT guidance were 2.1 and 2.9 mm, respectively, for the HPS, and 2.8 and 3.6 mm for the SPS. The setup error after MV guidance was lower for the positioning system that achieved a more accurate patient position before image guidance.

Synchrotron-Based Infrared Microscopy Studies of the Radiosensitization Effects of Nanoparticles used in Radiotherapy

Radiotherapy (RT) is the most important non-surgical modality for cancer and the recent technological advances brought a substantial gain in the balance between the probability of tumor control and the risk of normal tissue complications. However, the clinical management of some radioresistant tumors (such as brain gliomas) continues being a challenge since tumor doses are constrained by the surrounding healthy tissue tolerances. Within this context, new modalities such as radiosensitization in the presence of high atomic number nanoparticles (NP) are extensively evaluated, with the main goal of enhancing the differential effect between tumors and healthy tissues. In the present work, Synchrotron based Fourier Transform Infrared Microspectroscopy (SR-FTIRM), a vibrational spectroscopic technique for the biochemical cell analysis on a microscopic scale, provides relevant information on the treatment-induced modifications of the main biomolecules (nucleic acids, proteins and lipids). A series of treatments, including various NP sized, typed and chemical natured (3 nm gadolinium (GdNP), 1.9 nm gold (AuNP) nanoparticles), cell line used (F98 murine and U87-MG human glioma cells) and radiotherapy configuration (megavoltage X-ray photon energy (MV) normaly used in clinics, with respect to kilovoltage photons (kV)), were assessed for their induced cell macromolecular damages (Martinez-Rovira et al. (2019) Analyst 144, 5511 and DOI: 10.1039/c9an01109a). Additionally, alongside X-ray photon RT, the possible cell damages caused by several charged particle beams (proton, helium, carbon and oxygen) were also considered. Briefly, the biochemical information provided by the highly brilliant infrared light source produced at ALBA Synchrotron leads to a clear advantage in spectral quality at a cellular level and allow better characterization of NP induced damage in cells.

Megavoltage Radiosensitization of Gold Nanoparticles on a Glioblastoma Cancer Cell Line Using a Clinical Platform.

Gold nanoparticles (GNPs) have demonstrated significant dose enhancement with kilovoltage (kV) X-rays; however, recent studies have shown inconsistent findings with megavoltage (MV) X-rays. We propose to evaluate the radiosensitization effect on U87 glioblastoma (GBM) cells in the presence of 42 nm GNPs and irradiated with a clinical 6 MV photon beam. Cytotoxicity and radiosensitization were measured using MTS and clonogenic cellular radiation sensitivity assays, respectively. The sensitization enhancement ratio was calculated for 2 Gy (SER2Gy) with GNP (100 μg/mL). Dark field and MTS assays revealed high co-localization and good biocompatibility of the GNPs with GBM cells. A significant sensitization enhancement of 1.45 (p = 0.001) was observed with GNP 100 μg/mL. Similarly, at 6 Gy, there was significant difference in the survival fraction between the GBM alone group (mean (M) = 0.26, standard deviation (SD) = 0.008) and the GBM plus GNP group (M = 0.07, SD = 0.05, p = 0.03). GNPs enabled radiosensitization in U87 GBM cells at 2 Gy when irradiated using a clinical platform. In addition to the potential clinical utility of GNPs, these studies demonstrate the effectiveness of a robust and easy to standardize an in-vitro model that can be employed for future studies involving metal nanoparticle plus irradiation.

Patient setup variations in computed tomography-based treatment planning for left-sided breast cancer using electronic portal images

Background and Aim: This study deals with isocentric variations along with the setup reproducibility and determines the random and systematic errors in a cohort of 25 (females) left-sided breast cancer patients treated with megavoltage X-rays using an online electronic portal imaging (EPI) protocol. Materials and Methods: This is a hospital-based cross-sectional observational study which was carried out on 25 female patients of carcinoma breast (left sided) who had undergone modified radical mastectomy. After completion of the planned chemotherapy, all patients underwent virtual three-dimensional (3D) computed tomography (CT) simulation, and an external beam radiotherapy treatment was planned on these 3D CT images on a treatment planning system (TPS) using two (coplanar)/conventional tangential fields for a total dose of 50 Gy in 25 fractions. Analysis of 150 EPIs determined changes in the treatment fields during setup of these 25 patients. The online assessment included setup deviations in all the three directions (anteroposterior [AP], superoinferior [SI], and mediolateral [ML]) and variations in central lung distance (CLD) during the first three fractions. Results: Random errors ranged from 1 to 5 mm for the chest wall (medial and lateral) tangential treatments and 1 mm for the anterior supraclavicular nodal field. Systematic errors ranged from 2.5 to 4.5 mm in the AP direction for the tangential fields and from 2.5 to 7.5 mm in the SI and Mediolateral directions for the anterior supraclavicular nodal field. For 25 (left-sided) patients, the CLD (TPS) was 20–30 mm, CLD (EPIs) was 25–40 mm showing variations of 5–10 mm, V20 was 1.0–6.0 Gy, maximum total lung dose was 43 Gy, V30 was 2.0–4.0 Gy, maximum heart dose was 52 Gy, and maximum spine dose was 45 Gy. Conclusions: Online assessment of patient position with matching of EPIs with digitally reconstructed radiographs is a useful method in evaluation of interfraction reproducibility of tangential fields in breast irradiation, thereby improving upon the quality of treatment delivery for our patient population.

Use of Megavoltage (MV) Computed Tomography (CT) to account for anatomical variations during radiotherapy treatment

Use of Megavoltage (MV) Computed Tomography (CT) to account for anatomical variations during radiotherapy treatment

Technical Note: Accuracy of MTF measurements with an edge phantom at megavoltage x-ray energies.

Measurement of the modulation transfer function (MTF) is performed by evaluating the response of an imaging system to a predefined input. To obtain accurate results when using an edge phantom, the detector input signal must resemble an ideal step function. The MTF of megavoltage (MV) imagers used in radiotherapy has been measured with highly absorbing edge phantoms fabricated from thick metal blocks. This study investigates the influence of the edge phantom design on the accuracy of the resulting MTF. The MTF of an electronic portal imaging device (EPID) was measured at 6MV beam quality with four edge phantoms made of lead with 1.3, 3.3, 5.0, and 10.0cm thickness. Monte Carlo simulations were carried out for these and a selection of tungsten phantoms to determine the photon fluence at the imaging plane and quantify the systematic error in the MTF introduced by the edge phantom design. The measured MTF depends on the design of the edge phantom. The detector input signal of a thin phantom is affected by secondary radiation from the phantom itself, causing an overestimation of the MTF. The amount of secondary radiation can be reduced by increasing the phantom thickness or introducing an air gap between the phantom and the detector. Both methods introduce geometric unsharpness, which can result in an underestimation of the true MTF. Edge phantoms made from 4.0cm thick tungsten or 5.0cm thick lead induce comparatively small systematic errors of below 3% or 5%, respectively. When MTF measurements are conducted at MV energies, even a highly absorbing edge phantom will introduce a systematic error of several percent. Direct comparison of MTFs obtained with different edge phantoms should therefore be treated with caution.

The role and mechanisms of zinc oxide nanoparticles in the improvement of the radiosensitivity of lung cancer cells in clinically relevant megavoltage radiation energies in-vitro

Objective(s): Semiconductor zinc oxide nanoparticles (ZnO NPs) have unique properties, such as inherent selectivity and photosensitization effects under ultraviolet (UV) radiation. ZnO NPs serve as promising anticancer agents. However, UV radiation limits their penetration into the body. In most clinical settings, it is essential to use high-energy photons in the treatment of deep-seated tumors. The present study aimed to evaluate the radiosensitization effects of ZnO NPs on human lung cancer cells under megavoltage (MV) X-ray irradiation. Materials and Methods: ZnO NPs with the mean diameter of seven nanometers were synthesized and characterized. The cytotoxicity and cellular uptake of ZnO NPs were evaluated in SKLC-6 lung cancer and MRC-5 normal lung cells using the 3-(4,5-dimethylthiazol-yl)-5(3-carboxymethoxyphenyl)-2H-tetrazolium (MTT) and inductively coupled plasma-mass spectrometry assays, respectively. In addition, the radiosensitization effects of ZnO NPs were investigated under MV irradiation using a clonogenic survival assay. Apoptosis induction and DNA damage were also evaluated using flow cytometry and cytokinesis-block micronucleus assay, respectively.Results: ZnO NPs were taken up and reduced the viability of the cancer cells at a higher rate compared to the normal cells. Moreover, ZnO NPs significantly enhanced the radiosensitivity of the cancer cells with the sensitizer enhancement ratios of 1.23 and 1.31 at the concentrations of 10 and 20 μg/ml, respectively. However, they had no significant effect on the radiosensitivity of the normal cells. Apoptosis induction and DNA damage also improved at a higher rate in the cancer cells compared to the normal cells with the combination of ZnO NPs with MV radiation.Conclusion: According to the results, ZnO NPs had the potential to be a selective radiosensitizer for lung cancer radiotherapy under MV X-ray irradiation. Some of the cytotoxic and genotoxic mechanisms in radiosensitization by ZnO NPs were elevated apoptosis induction and DNA damage levels.

Efficient quality assurance method with automated data acquisition of a single phantom setup to determine radiation and imaging isocenter congruence.

We developed a quality assurance (QA) method to determine the isocenter congruence of Optical Surface Monitoring System (OSMS, Varian, CA, USA), kilovoltage (kV), and megavoltage (MV) imaging, and the radiation isocenter using a single setup of the OSMS phantom for frameless Stereotactic Radiosurgery (SRS) treatment. After aligning the phantom to the OSMS isocenter, a cone‐beam computed tomography (CBCT) of the phantom was acquired and registered to a computed tomography (CT) scan of the phantom to determine the CBCT isocenter. Without moving the phantom, MV and kV images were simultaneously acquired at four gantry angles to localize MV and kV isocenters. Then, Winston‐Lutz (W‐L) test images of the central BB in the phantom were acquired to analyze the radiation isocenter. The gantry and couch were automatically controlled using the TrueBeam Developer Mode during MV, kV, and W‐L image acquisition. All the images were acquired weekly for 17 weeks to track the congruence of all the imaging modalities' isocenter in six‐dimensional (6D) translations and rotations, and the radiation isocenter in three‐dimensional (3D) translations. The shifts of isocenters of all imaging modalities and the radiation isocenter from the OSMS isocenter were within 0.2 mm and 0.2° on average over 17 weeks. The maximum discrepancy between OSMS and other imaging modalities or radiation isocenters was 0.8 mm and 0.3°. However, systematic shifts of radiation isocenter anteriorly and laterally relative to the OSMS isocenter were observed. The measured discrepancies were consistent from week‐to‐week except for two weeks when the isocenter discrepancies of 0.8 mm were noted due to drifts of the OSMS isocenter. Once recalibration was performed on OSMS, the discrepancy was reduced to 0.3 mm and 0.2°.By performing the proposed QA on a weekly basis, the isocenter congruencies of multiple imaging systems and radiation isocenter were validated for a linear accelerator.

Residual setup error in the canine intracranial region after megavoltage, kilovoltage, or cone-beam computed tomographic image guidance for radiation therapy.

Sources of residual setup error after image guidance include image localization accuracy, errors associated with image registration, and inability of some treatment couches to correct submillimeter translational errors and/or pitch and roll errors. The purpose of this experimental study was to measure setup error after image-guided correction of the canine intracranial region, using a four degrees-of-freedom couch capable of 1 mm translational moves. Six cadaver dogs were positioned 45 times as for clinical treatment using a vacuum deformable body cushion, a customizable head cushion, a thermoplastic mask and an indexed maxillary plate with a dental mould. The location of five fiducial markers in the skull bones was compared between the reference position and after megavoltage (MV), kilovoltage (kV) and cone-beam computed tomography (CBCT)-guided correction using orthogonal kV images. The mean three-dimensional distance vectors (3DDV) after MV, kV and CBCT-guided correction were 1.7, 1.5 and 2.2 mm, respectively. All values were significantly different (P < .01). The 95th percentiles of the 3DDV after online MV, kV and CBCT-guided correction were 2.8, 2.6 and 3.6 mm, respectively. Residual setup error in the clinical scenario examined was on the order of millimetres and should be considered when choosing PTV margins for image-guided radiation therapy of the canine intracranial region.

Comparison of Workflow Efficiency of VMAT Craniospinal Irradiation Between Adult and Pediatric Settings

Assessing radiation therapy (RT) delivery workflow efficiency of volumetric-modulated arc therapy (VMAT) craniospinal irradiation (CSI) in children and adult groups. A retrospective review of patients treated at a children’s hospital (CH) and an adult cancer hospital (AH) with supine VMAT CSI between June 2013 and November 2018 was conducted. Treatment planning was centralized. Both sites utilized linear accelerators. The CH had surface guidance radiation therapy (SGRT) while AH did not. Image-guided radiation therapy (IGRT) time was defined as the duration from kilovoltage (kV) IGRT start time to megavoltage (MV) beam-on time. Total radiation time (TT) was defined as kV IGRT start time to beam-off time of the final MV beam. Time stamped data were collected. Age, gender, height, diagnosis, number of isocenters, RT fraction number, sedation status, IGRT modality and SGRT vs. non-SGRT were recorded. Data from 662 VMAT CSI treatment sessions from the CH and AH (614 and 48, respectively) in 47 patients (41 and 6, respectively) were analyzed. The overall median TT was significantly shorter at the CH vs. the AH (21.07 vs. 37.23 min, p < 0.05). Overall median IGRT time was 12.58 vs. 24.82 min (p < 0.05) with fewer median number of images acquired of 3 vs. 7 (p < 0.05). Re-imaging rate after beam-on time was significantly higher at the AH at 16.7%. Subgroup data for non-sedated patients was analyzed. Median TT was performed on 3-isocenter patients (n=175 vs. n=48, 23.13 vs. 37.23 min, p < 0.05), and with the same IGRT modality (n=24 vs. n=44, 25.22 vs. 34.19 min, p < 0.05). Significantly lower durations were observed at the CH vs. the AH. At the CH, all treatment sessions were preceded by SGRT which may be a significant factor. For patients at the CH, the TT and IGRT durations decreased after the first three fractions, with a smaller proportion of TT less than the median (30.9% vs. 54.0%, p < 0.05) for the first three fractions compared to the remaining fractions. This did not hold true at the AH (33.3% vs. 57.6%, p=0.119). A multiple linear regression model applied to the TT at the CH showed significant (p < 0.001) impact of height, number of isocenters, and RT fraction number, but not sedation status. Median TT and IGRT times were significantly shorter at the CH vs. the AH, even when subgroup analyses compared plans adjusted for the same number of isocenters and IGRT modality in non-sedated patients. At the CH, after the first three treatments, TT tended to decrease. Differences in workflow efficiency between sites may be explained in part by supplemental SGRT or by greater experience with VMAT CSI at the CH. By tracking TT, clinics may optimize staffing resources.