Radiation Dose Delivery Research Articles

Dosimetric validation of the couch and coil model for high-field MR-linac treatment planning

PurposeThe precision of the dose delivery in radiation therapy with high-field MR-linacs is challenging due to the substantial variation in the beam attenuation of the patient positioning system (PPS) (the couch and coils) as a function of the gantry angle. This work aimed to compare the attenuation of two PPSs located at two different MR-linac sites through measurements and calculations in the treatment planning system (TPS). MethodsAttenuation measurements were performed at every 1° gantry angle at the two sites with a cylindrical water phantom with a Farmer chamber inserted along the rotational axis of the phantom. The phantom was positioned with the chamber reference point (CRP) at the MR-linac isocentre. A compensation strategy was applied to minimise sinusoidal measurement errors due to, e.g. air cavity or setup. A series of tests were performed to assess the sensitivity to measurement uncertainties. The dose to a model of the cylindrical water phantom with the PPS added was calculated in the TPS (Monaco v5.4 as well as in a development version Dev of an upcoming release), for the same gantry angles as for the measurements. The TPS PPS model dependency of the dose calculation voxelisation resolution was also investigated. ResultsA comparison of the measured attenuation of the two PPSs yielded differences of less than 0.5% for most gantry angles. The maximum deviation between the attenuation measurements for the two different PPSs exceeded ±1% at two specific gantry angles 115° and 245°, where the beam traverses the most complex PPS structures. The attenuation increases from 0% to 25% in 15° intervals around these angles. The measured and calculated attenuation, as calculated in v5.4, was generally within 1-2% with a systematic overestimation of the attenuation for gantry angles around 180°, as well as a maximum error of 4-5% for a few discrete angles in 10° gantry angle intervals around the complex PPS structures. The PPS modelling was improved compared to v5.4 in Dev, especially around 180°, and the results of those calculations were within ±1%, but with a similar 4% maximum deviation for the most complex PPS structures. ConclusionsGenerally, the two tested PPS structures exhibit very similar attenuation as a function of the gantry angle, including the angles with a steep change in attenuation. Both TPS versions, v5.4 and Dev delivered clinically acceptable accuracy of the calculated dose, as the differences in the measurements were overall better than ±2%. Additionally, Dev improved the accuracy of the dose calculation to ±1% for gantry angles around 180°.

Large scale crowdsourced radiotherapy segmentations across a variety of cancer anatomic sites

Clinician generated segmentation of tumor and healthy tissue regions of interest (ROIs) on medical images is crucial for radiotherapy. However, interobserver segmentation variability has long been considered a significant detriment to the implementation of high-quality and consistent radiotherapy dose delivery. This has prompted the increasing development of automated segmentation approaches. However, extant segmentation datasets typically only provide segmentations generated by a limited number of annotators with varying, and often unspecified, levels of expertise. In this data descriptor, numerous clinician annotators manually generated segmentations for ROIs on computed tomography images across a variety of cancer sites (breast, sarcoma, head and neck, gynecologic, gastrointestinal; one patient per cancer site) for the Contouring Collaborative for Consensus in Radiation Oncology challenge. In total, over 200 annotators (experts and non-experts) contributed using a standardized annotation platform (ProKnow). Subsequently, we converted Digital Imaging and Communications in Medicine data into Neuroimaging Informatics Technology Initiative format with standardized nomenclature for ease of use. In addition, we generated consensus segmentations for experts and non-experts using the Simultaneous Truth and Performance Level Estimation method. These standardized, structured, and easily accessible data are a valuable resource for systematically studying variability in segmentation applications.

Simultaneous Integrated Boost (SIB) vs. Sequential Boost in Head and Neck Cancer (HNC) Radiotherapy: A Radiomics-Based Decision Proof of Concept.

Artificial intelligence (AI) and in particular radiomics has opened new horizons by extracting data from medical imaging that could be used not only to improve diagnostic accuracy, but also to be included in predictive models contributing to treatment stratification of cancer. Head and neck cancers (HNC) are associated with higher recurrence rates, especially in advanced stages of disease. It is considered that approximately 50% of cases will evolve with loco-regional recurrence, even if they will benefit from a current standard treatment consisting of definitive chemo-radiotherapy. Radiotherapy, the cornerstone treatment in locally advanced HNC, could be delivered either by the simultaneous integrated boost (SIB) technique or by the sequential boost technique, the decision often being a subjective one. The principles of radiobiology could be the basis of an optimal decision between the two methods of radiation dose delivery, but the heterogeneity of HNC radio-sensitivity makes this approach difficult. Radiomics has demonstrated the ability to non-invasively predict radio-sensitivity and the risk of relapse in HNC. Tumor heterogeneity evaluated with radiomics, the inclusion of coarseness, entropy and other first order features extracted from gross tumor volume (GTV) in multivariate models could identify pre-treatment cases that will benefit from one of the approaches (SIB or sequential boost radio-chemotherapy) considered the current standard of care for locally advanced HNC. Computer tomography (CT) simulation and daily cone beam CT (CBCT) could be chosen as imaging source for radiomic analysis.

MRI-LINAC: A transformative technology in radiation oncology.

Advances in radiotherapy technologies have enabled more precise target guidance, improved treatment verification, and greater control and versatility in radiation delivery. Amongst the recent novel technologies, Magnetic Resonance Imaging (MRI) guided radiotherapy (MRgRT) may hold the greatest potential to improve the therapeutic gains of image-guided delivery of radiation dose. The ability of the MRI linear accelerator (LINAC) to image tumors and organs with on-table MRI, to manage organ motion and dose delivery in real-time, and to adapt the radiotherapy plan on the day of treatment while the patient is on the table are major advances relative to current conventional radiation treatments. These advanced techniques demand efficient coordination and communication between members of the treatment team. MRgRT could fundamentally transform the radiotherapy delivery process within radiation oncology centers through the reorganization of the patient and treatment team workflow process. However, the MRgRT technology currently is limited by accessibility due to the cost of capital investment and the time and personnel allocation needed for each fractional treatment and the unclear clinical benefit compared to conventional radiotherapy platforms. As the technology evolves and becomes more widely available, we present the case that MRgRT has the potential to become a widely utilized treatment platform and transform the radiation oncology treatment process just as earlier disruptive radiation therapy technologies have done.

Real-time, volumetric imaging of radiation dose delivery deep into the liver during cancer treatment.

Ionizing radiation acoustic imaging (iRAI) allows online monitoring of radiation's interactions with tissues during radiation therapy, providing real-time, adaptive feedback for cancer treatments. We describe an iRAI volumetric imaging system that enables mapping of the three-dimensional (3D) radiation dose distribution in a complex clinical radiotherapy treatment. The method relies on a two-dimensional matrix array transducer and a matching multi-channel preamplifier board. The feasibility of imaging temporal 3D dose accumulation was first validated in a tissue-mimicking phantom. Next, semiquantitative iRAI relative dose measurements were verified in vivo in a rabbit model. Finally, real-time visualization of the 3D radiation dose delivered to a patient with liver metastases was accomplished with a clinical linear accelerator. These studies demonstrate the potential of iRAI to monitor and quantify the 3D radiation dose deposition during treatment, potentially improving radiotherapy treatment efficacy using real-time adaptive treatment.

Respiratory motion prediction based on deep artificial neural networks in CyberKnife system: A comparative study.

In external beam radiotherapy, a prediction model is required to compensate for the temporal system latency that affects the accuracy of radiation dose delivery. This study focused on a thorough comparison of seven deep artificial neural networks to propose an accurate and reliable prediction model. Seven deep predictor models are trained and tested with 800 breathing signals. In this regard, a nonsequential-correlated hyperparameter optimization algorithm is developed to find the best configuration of parameters for all models. The root mean square error (RMSE), mean absolute error, normalized RMSE, and statistical F-test are also used to evaluate network performance. Overall, tuning the hyperparameters results in a 25%-30% improvement for all models compared to previous studies. The comparison between all models also shows that the gated recurrent unit (GRU) with RMSE=0.108±0.068mm predicts respiratory signals with higher accuracy and better performance. Overall, tuning the hyperparameters in the GRU model demonstrates a better result than the hybrid predictor model used in the CyberKnife VSI system to compensate for the 115ms system latency. Additionally, it is demonstrated that the tuned parameters have a significant impact on the prediction accuracy of each model.

A case report on the abscopal effect of liver-directed GRID radiotherapy

GRID radiotherapy is a form of spatially fractionated radiotherapy that allows delivery of high radiation doses to bulky tumours. A grid splits the beam into multiple beamlets to give a heterogenous dose to the tumour, while stimulating the immune system to improve tumour response through the abscopal effect. However, this has fallen out of favour in recent times due to the presence of more modern techniques. Here we present a case of a large liver metastasis from a rectal neuroendocrine primary treated with GRID radiotherapy with an abscopal response seen in a portal vein tumour thrombus.

CTNI-51. FEASIBILITY AND SAFETY OF NEUROSURGICAL RESECTION AND INTRA-OPERATIVE RADIATION THERAPY USING THE XOFT AXXENT ELECTRONIC BRACHYTHERAPY SYSTEM AND BEVACIZUMAB IN RECURRENT GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most common and aggressive primary brain tumor. External beam radiation therapy (EBRT) is widely recognized as an effective treatment for primary GBM. EBRT applied after GBM resection is associated with an increase in overall survival. Beyond upfront therapy with radiation and temozolomide chemotherapy, there is no standard therapy that has been proven effective. Re-irradiation with ERBT is minimally effective and with significant comorbidities. Our study uses IORT at the time of re-resection in patients who have recurrent, operable GBM after failure of who received primary EBRT and temozolamide in their first course of treatment. IORT allows the delivery of a large effective radiation dose applied directly to the tumor bed at the time of resection. This affords direct radiation to be delivered to the micro- and macroscopic tumor remnants in the vicinity of the resection cavity immediately following gross resection. In contrast, the more distant, surrounding brain tissue does not receive high radiation exposure. This Phase II study continues to accrue subjects with the primary endpoint of overall survival and several secondary endpoints that includes progression free survival, quality of life, and adverse events/safety. To date, five patients have been treated on this protocol. The technical feasibility and safety of administering intraoperative radiation with the Xoft System has been established in this cohort. Preliminary GLIOX Trial findings demonstrate the safety and feasibility of using the Xoft Axxent® Electronic Brachytherapy System to administer intracranial radiation during resection of recurrent glioblastomas. We will report new and expansive study results to include these early findings.

Dose Escalation for Posterior Fossa Ependymomas: Analysis of Prospective Pediatric Proton/Photon Consortium Registry

<h3>Purpose/Objective(s)</h3> A dose of 54 Gy is considered a minimum dose required for local control (LC) in an adjuvant setting for posterior fossa (PF) ependymomas; however, a higher dose may be more desirable given that the primary mode of relapse is local failure. Proton therapy (PT) may allow for safer delivery of higher radiation doses, although data on safety and efficacy of dose-escalation for posterior fossa tumors with PT are currently limited. We analyzed the Pediatric Proton/Photon Consortium Registry (PPCR), the largest United States database of pediatric patients treated with PT, to examine the safety and efficacy of dose-escalation (≥55.8 Gy) for PF ependymoma. <h3>Materials/Methods</h3> All consecutive patients enrolled on the PPCR with PF ependymomas who received adjuvant radiation with PT between 2002 and 2020 were assessed. Survival and toxicity outcomes between patients who received a standard dose (SD) of 54 Gy and a high dose (HD) ≥55.8 Gy were compared. Overall survival (OS), LC, and progression-free survival (PFS) were estimated using Kaplan Meier analysis. <h3>Results</h3> A total of 171 children with PF ependymoma were treated with PT: 111 (65%) received SD and 60 (35%) received HD. Of those in HD cohort, 43 (72%) received a dose of 59.4 Gy [range, 55.8-59.4]. The median follow-up time was 35.6 months. Median age was 3.2 years [range, 0.5-21.2]. Patients in the HD cohort were older (median 4.25 vs 2.73 years, p=0.008). A higher proportion of HD children had a subtotal resection of their primary tumor (30.5% vs 17.4%) although not statistically significant (p=0.112). More patients in the HD arm received chemotherapy following the completion of PT (83.3% vs. 45.5%, p=0.075). No statistically significant differences in neurologic (82.4% vs. 89.5%), auditory (30.6% vs. 29.8%), visual (50.5% vs. 45.6%), endocrine (15.7% vs. 15.8%), or cutaneous (86.1% vs. 75.4%) toxicities were noted between SD and HD patients, respectively. Median OS and median PFS were not reached for both cohorts. The 5-year OS were 78.4% (95% CI: 67.5-91.2) and 74.9% (95% CI: 61.2-91.7) for SD and HD, respectively (p=0.082). The 5-year LC were 79.9% (95% CI: 71.1-89.9) and 70.1% (95% CI: 57.5-85.4) (p=0.069), and the 5-year PFS were 58.4% (95% CI: 47.1-72.4) and 63.8% (95% CI: 50.8-80.2) (p=0.54) for SD and HD, respectively. Among the subset of HD patients receiving 59.4 Gy, there similarly was no LC, PFS, or OS advantage when compared to SD (all p>0.05). <h3>Conclusion</h3> Dose-escalation (≥55.8 Gy) did not result in higher rates of radiation-induced toxicities in children with PF ependymomas treated with PT on PPCR. At the same time, higher doses did not lead to superior LC or survival when compared to a standard dose of 54 Gy. Randomized studies are needed to provide a definitive answer on the value of dose-escalation in pediatric PF ependymoma and identify a subset of children who may benefit from higher RT doses.

A Dosimetric Analysis of Single Fraction Lattice Radiotherapy as a Boost for the Palliative Treatment of Bulky Head and Neck Tumors

<h3>Purpose/Objective(s)</h3> This study investigates the dosimetry achieved in VMAT/IMRT-planned lattice radiotherapy (LRT) for bulky, palliative head and neck tumors. LRT allows for the delivery of higher radiation doses without dramatically increasing toxicity by using high-dose spheres within the tumor while directing high dose away from OAR's. Our objective was to analyze LRT using 3 dose levels as a boost for palliative treatment of bulky head and neck tumors. The clinical goal of LRT boost would be to increase the effectiveness of treatment while minimizing the burden of care for patients requiring a quick palliation of symptoms associated with bulky tumors. <h3>Materials/Methods</h3> Six bulky palliative head and neck cases were used for this study. A 3D lattice of 0.75 cm spheres spaced 0.85 cm apart was applied to the planning scan and restricted to the area inside the lattice inward contour (GTV was contracted by 0.5 mm). Each case was planned with three different dose prescriptions (15 Gy, 20 Gy and 25 Gy in a single fraction) to the lattice of spheres. In addition, a standard IMRT plan was also created to deliver a uniform 20 Gy in 5 fractions to a defined PTV. The margins (CTV + PTV expansions) used were between 0.5 to 1 cm. A total of 7 plans were created for each case, which included the three single fraction doses, the five fractions of standard treatment, and a combination of the single and five fraction plans. <h3>Results</h3> The average planned tumor volume was 209.77 mL (range 137.80 – 411.01). The number of spheres used in the LRT plan ranged from 13 to 41. The median maximum dose (Dmax) and dose statistics achieved are listed in Table 1. The median ipsilateral carotid dose was high for the 25 Gy (single fraction) plan, so our results suggest that a neoadjuvant LRT boost with of a single fraction of 20 Gy would likely be safe. <h3>Conclusion</h3> Lattice radiotherapy is a viable treatment option for bulky head and neck cases treated with palliative intent. We were able to achieve acceptable dosimetric plans in both the 15 and 20 Gy boosts (single fraction) followed by 20 Gy in 5 fractions, a combination that would be expected to provide more favorable tumor control and symptom relief than traditional palliative regimens of 20-30 Gy. A clinical application with prospective dose escalation trial is under consideration.

Long-Term Outcomes of Pediatric Patients with Chordomas Treated with Proton Beam Radiation Therapy

<h3>Purpose/Objective(s)</h3> Chordomas are rare tumors that arise from embryonic remnants of the notochord and can arise anywhere along the spine or the base of skull. This condition is even more uncommon within the pediatric population, and standard of care treatment includes maximal safe resection with subsequent radiation. The use of proton radiation allows for a conformal delivery of radiation dose that potentially minimizes the exposure of sensitive nearby structures to harmful treatment effects. The purpose of this study is to evaluate the long-term survival and toxicity of pediatric patients with base of skull or cervical spine chordomas treated at this institution with proton-based radiation therapy. <h3>Materials/Methods</h3> This IRB-approved single-institution study examines a cohort of 36 pediatric patients (≤ 18 years old) with 39 lesions treated with proton radiation between 1994 and 2016. Patients were included if they were treated with definitive intent and had at least five years of time since completing radiation treatment. Median age at treatment of patients was 10.9 years old. 79% of lesions received subtotal resection, while 21% received gross total resection. 10 patients received chemotherapy. The vast majority of tumors was treated to 72-77.4Gy in 40-43 fractions. Two patients were treated to 66.6Gy in 37 fractions. <h3>Results</h3> Median follow-up time was 100 months. The 5-year overall survival for the entire cohort was 26/36 (72%), further stratified by gender to reveal 68% in the female cohort and 75% in the male cohort. Seven patients (19%) developed distant metastases and subsequent passed away from their disease. GTV over size of 25cc and poorly differentiated histology were associated with decreased overall survival and local control. Of the 30 patients with base of skull lesions, at most recent follow-up, 15 patients (50%) had ototoxicity with 12 of those cases related to adjuvant treatment. 17 patients had confirmed pituitary dysfunction or required pituitary hormone replacement at some timepoint after treatment, 7 patients had no dysfunction, 5 patients died without evidence of pituitary dysfunction, 1 patient did not have pituitary function tests available. No instances of brain or brainstem necrosis were seen. Of the 21 survivors, 20 were either in school or employed with no cognitive or learning disabilities present. <h3>Conclusion</h3> This single-institution experience shows the efficacy and safety of proton radiation in pediatric patients with chordomas. Limitations include small number of patients and retrospective nature of the study. Future directions include analysis at 10-year follow-up and further evaluation of long-term toxicity.

Radiation Treatment Timing and Dose Delivery: Effects on Bladder Cancer Cells in 3D in Vitro Culture

While radical cystectomy remains the primary treatment of choice for bladder cancer, increased evidence supports the use of bladder-preservation strategies based on adjuvant radiotherapy. This highlights the need for a better understanding of bladder cancer radiosensitivity to different types of treatment deliveries. The purpose of this study is to analyze the effect of treatment time, dose and fractionation on the number and sizes of grown three-dimensional (3D) bladder cancer spheres, and to assess the capacity of the linear-quadratic model in describing the response of cells cultured in 3D. 3D MatrigelTM-based cultures were employed to enrich for cancer stem cells (CSCs) from three human bladder cancer cell lines, RT4, T24 and UM-UC-3. Three single dose radiation treatments were performed at different time points after plating, and sphere number and sizes were assessed. Anti-CD44 immunofluorescence, clonogenic assay and anti-γH2AX staining were also performed to analyze the cell lines’ radiosensitivity. The radiosensitivity of spheres was dependent on the treatment timing after plating. Current linear quadratic dose fractionation models were shown to over-estimate radiosensitivity in 3D models. Our results showed the importance of treatment timing on the radio-response of bladder cancer spheres. We also demonstrated that bladder cancer spheres are more resistant to dose-fractionation than the estimation from the theoretical linear-quadratic model.

A phantom-based analysis for tracking intra-fraction pancreatic tumor motion by ultrasound imaging during radiation therapy.

PurposeIn this study, we aim to further evaluate the accuracy of ultrasound tracking for intra-fraction pancreatic tumor motion during radiotherapy by a phantom-based study.MethodsTwelve patients with pancreatic cancer who were treated with stereotactic body radiation therapy were enrolled in this study. The displacement points of the respiratory cycle were acquired from 4DCT and transferred to a motion platform to mimic realistic breathing movements in our phantom study. An ultrasound abdominal phantom was placed and fixed in the motion platform. The ground truth of phantom movement was recorded by tracking an optical tracker attached to this phantom. One tumor inside the phantom was the tracking target. In the evaluation of the results, the monitoring results from the ultrasound system were compared with the phantom motion results from the infrared camera. Differences between infrared monitoring motion and ultrasound tracking motion were analyzed by calculating the root-mean-square error.ResultsThe 82.2% ultrasound tracking motion was within a 0.5 mm difference value between ultrasound tracking displacement and infrared monitoring motion. 0.7% ultrasound tracking failed to track accurately (a difference value > 2.5 mm). These differences between ultrasound tracking motion and infrared monitored motion do not correlate with respiratory displacements, respiratory velocity, or respiratory acceleration by linear regression analysis.ConclusionsThe highly accurate monitoring results of this phantom study prove that the ultrasound tracking system may be a potential method for real-time monitoring targets, allowing more accurate delivery of radiation doses.

Linac natW target close-in geometry photoneutron study by nuclear track distribution function

During electron beam stopping on natW target in a linear accelerator, photonuclear (γ, xn) reactions occur; the tungsten converter provides a non-negligible neutron yield with an energy spectrum that significantly depends on surrounding mass nuclei. Reduction of the neutron radiation field is convenient to limit the side-effects that accompany the tumor or cancer radiotherapy. A close-in irradiation geometry is proposed to improve therapy effectiveness. The convenience of the proposed experimental arrangement is assessed using Monte Carlo simulation and experimental results based on nuclear track-etch methodology. Photoneutron yield for two energy groups (thermal and epithermal) are determined experimentally via boron (98%) converter and cadmium-filter employing a passive detector (poly allyl di-glicol carbonate polimer). Etched track diameter histograms are described by distribution functions to determine the ratio between thermal and higher energy neutrons. New insights are given into therapy beam quality and radiotherapy dose delivery based on bar histograms unfolding.

Self-supervised inter- and intra-slice correlation learning for low-dose CT image restoration without ground truth

Training a convolutional neural network (CNN) to reduce noise in low-dose CT (LDCT) images typically relies on supervised learning, which requires input–target pairs of noisy LDCT and corresponding full-dose CT (FDCT) images. Although previous approaches have shown promising results in LDCT image denoising, it is difficult to acquire clinical datasets of LDCT-FDCT image pairs, which require additional and unnecessary radiation dose delivery to patients. In this paper, we propose a self-supervised learning approach to training a CNN-based denoiser with LDCT images alone. As a means of self-supervision, the proposed approach searches inter-pixel correlation of LDCT images in z-direction as well as in-plane direction. To regularize the CNN-based denoiser, thicker LDCT slices are used as image priors during the self-supervised training process in our approach. For efficient self-supervised learning, we adopt a two-stage training strategy with offline pretraining and online finetuning. The proposed approach is thoroughly evaluated with public and private clinical LDCT datasets. Both image quality measures and clinical assessments indicate that the self-supervised denoising model simultaneously reduces noise level and restores anatomical information in LDCT images from the images alone. The experimental results also show that our online finetuning scheme can improve the denoising performance of supervised learning models as well as self-supervised learning models at test time.

Geometrical source modeling of 6MV flattening-filter-free (FFF) beam from TrueBeam linear accelerator and its commissioning validation using Monte Carlo simulation approach for radiotherapy

PurposeTo study geometrical source modeling of 6 MV flattening-filter-free (FFF) beam from TrueBeam linear accelerator and its commissioning validation using Monte Carlo simulation approach. Methods & materialSource modeling of 6MVFFF beam from TrueBeam linear accelerator has been accomplished by using PRIMO as the Monte-Carlo (MC) simulation software based on PENELOPE code. Initially, source modeling of 6MVFFF beam was validated against experimentally measured Percentage-depth-dose (PDD) and profile for 10 × 10cm2 field. Followed by commissioning validation of 6MVFFF beam has been carried out by simulating PDDs, profiles and output factors for range of field sizes. Besides, verification of absolute dose, beam quality index, performance analysis of dose distribution in heterogeneous phantom and simulation of radiation treatment plan for validation of Treatment planning system (TPS) was performed. Simulated results compared against measured; dose distributions were analyzed using gamma analysis with acceptance criteria of 2% Dose-difference (DD) and 2 mm Distance-to-agreement (DTA). ResultsGamma analysis for all the simulated and measured PDDs and profiles shows minimum passing rate of 100% and 98.04% respectively. Simulated values of absolute point dose, beam quality index and output factors shows good agreements with measurements. Gamma analysis of depth dose distribution in heterogeneous phantom obtained using MC simulation and calculated with Analytical anisotropic algorithm (AAA) agreed within 95.89%. However, heterogeneous medium of very high and low-density region shows larger dose discrepancy between MC and AAA due to the poor modeling of AAA compared to MC. The percentage of 99.81% of gamma passing and comparison of predicted Dose-volume-histogram (DVH) shows good resemblance between PRIMO simulated and AAA calculated plan. ConclusionStudy concludes that PRIMO is an independent MC simulation tools for verification and commissioning validation of external beam radiotherapy in treatment of cancer. The MC validation of external beam therapy modules grants higher confidence in accuracy of radiation dose delivery.

A feasibility and pilot study of the clinical efficacy of a custom designed handgrip device to improve patient immobilisation for the external beam radiotherapy of oesophageal cancers

The primary aim of radiotherapy is to eradicate tumour cells within the clinical target volume (CTV), at the same time while sparing surrounding organs at risk (OAR) which is often accomplished by conforming to the treatment fields, i.e. target volume and by using appropriate margins for accounting the treatment uncertainties. Furthermore, for accurate radiation dose delivery, perfect immobilisation is required to keep the patient within the same position at each treatment fraction. There has always been a need for perfect immobilisation which should provide minimal patient movement, patient comfort, reproducible patient positioning during radiotherapy and be less expensive. The main objective of the present study was to design, fabricate and evaluate a handgrip board immobilisation device for the thorax region to boost the efficiency of the external beam radiotherapy in oesophageal cancer patients and evaluate the set-up error. Our indigenously fabricated handgrip baseboard device is made of poly-methyl methacrylate (PMMA), which consists of the main baseboard with an adjustable central T-bar and separate right and left single hand poles. In the present study, fifteen patients with oesophageal tumours were included. Patients were positioned using the indigenously fabricated handgrip immobilisation device; portal images were performed prior to the treatment and matched with the digitally reconstructed radiographs (DRR). The population systematic (Σ) and random (σ) patient set-up errors were calculated along the direc­tions of Anterior-Posterior (AP), Medial-Lateral (ML) and Superior-Inferior (SI). The values for the planning target volume (PTV) margins were calculated using ICRU 62, Van Herk’s and Stroom’s formulae. The population systematic (Σ) errors of AP, ML and SI were 0.12, 0.20 and 0.20 cm, respectively while the population random (σ) errors of AP, ML, SI were 0.17, 0.31 and 0.17 cm, respectively. The PTV margins were calculated according to ICRU 62, Van Herk’s, and Stroom’s and it was observed in the range of 0.2–0.7 cm in the three acquisition directions. The use of a handgrip immobilisation device allowed for relatively small set-up errors and ensured the patient’s comfort. Also, the technique showed satisfactory accuracy and reproducibility.

Systematic analysis of volumetric ultrasound parameters for markerless 4D motion tracking

ObjectivesMotion compensation is an interesting approach to improve treatments of moving structures. For example, target motion can substantially affect dose delivery in radiation therapy, where methods to detect and mitigate the motion are widely used. Recent advances in fast, volumetric ultrasound have rekindled the interest in ultrasound for motion tracking. We present a setup to evaluate ultrasound based motion tracking and we study the effect of imaging rate and motion artifacts on its performance.MethodsWe describe an experimental setup to acquire markerless 4D ultrasound data with precise ground truth from a robot and evaluate different real-world trajectories and system settings toward accurate motion estimation. We analyze motion artifacts in continuously acquired data by comparing to data recorded in a step-and-shoot fashion. Furthermore, we investigate the trade-off between the imaging frequency and resolution.ResultsThe mean tracking errors show that continuously acquired data leads to similar results as data acquired in a step-and-shoot fashion. We report mean tracking errors up to 2.01 mm and 1.36 mm on the continuous data for the lower and higher resolution, respectively, while step-and-shoot data leads to mean tracking errors of 2.52 mm and 0.98 mm.ConclusionsWe perform a quantitative analysis of different system settings for motion tracking with 4D ultrasound. We can show that precise tracking is feasible and additional motion in continuously acquired data does not impair the tracking. Moreover, the analysis of the frequency resolution trade-off shows that a high imaging resolution is beneficial in ultrasound tracking.

PO-1462 High radiation dose delivery by lattice-rt to hypoxic areas in bulky tumours: a multicentric study.

PO-1462 High radiation dose delivery by lattice-rt to hypoxic areas in bulky tumours: a multicentric study.

Versatile Detection and Monitoring of Ionizing Radiation Treatment Using Radiation-Responsive Gel Nanosensors.

Modern radiation therapy workflow involves complex processes intended to maximize the radiation dose delivered to tumors while simultaneously minimizing excess radiation to normal tissues. Safe and accurate delivery of radiation doses is critical to the successful execution of these treatment plans and effective treatment outcomes. Given extensive differences in existing dosimeters, the choice of devices and technologies for detecting biologically relevant doses of radiation has to be made judiciously, taking into account anatomical considerations and modality of treatment (invasive, e.g., interstitial brachytherapy vs noninvasive, e.g., external-beam therapy radiotherapy). Rapid advances in versatile radiation delivery technologies necessitate new detection platforms and devices that are readily adaptable into a multitude of form factors in order to ensure precision and safety in dose delivery. Here, we demonstrate the adaptability of radiation-responsive gel nanosensors as a platform technology for detecting ionizing radiation using three different form factors with an eye toward versatile use in the clinic. In this approach, ionizing radiation results in the reduction of monovalent gold salts leading to the formation of gold nanoparticles within gels formulated in different morphologies including one-dimensional (1D) needles for interstitial brachytherapy, two-dimensional (2D) area inserts for skin brachytherapy, and three-dimensional (3D) volumetric dose distribution in tissue phantoms. The formation of gold nanoparticles can be detected using distinct but complementary modes of readout including optical (visual) and photothermal detection, which further enhances the versatility of this approach. A linear response in the readout was seen as a function of radiation dose, which enabled straightforward calibration of each of these devices for predicting unknown doses of therapeutic relevance. Taken together, these results indicate that the gel nanosensor technology can be used to detect ionizing radiation in different morphologies and using different detection methods for application in treatment planning, delivery, and verification in radiotherapy and in trauma care.