Computed Tomography Treatment Planning Research Articles

Prostate segmentation accuracy using synthetic MRI for high-dose-rate prostate brachytherapy treatment planning

Objective. Both computed tomography (CT) and magnetic resonance imaging (MRI) images are acquired for high-dose-rate (HDR) prostate brachytherapy patients at our institution. CT is used to identify catheters and MRI is used to segment the prostate. To address scenarios of limited MRI access, we developed a novel generative adversarial network (GAN) to generate synthetic MRI (sMRI) from CT with sufficient soft-tissue contrast to provide accurate prostate segmentation without MRI (rMRI). Approach. Our hybrid GAN, PxCGAN, was trained utilizing 58 paired CT-MRI datasets from our HDR prostate patients. Using 20 independent CT-MRI datasets, the image quality of sMRI was tested using mean absolute error (MAE), mean squared error (MSE), peak signal-to-noise ratio (PSNR) and structural similarity index (SSIM). These metrics were compared with the metrics of sMRI generated using Pix2Pix and CycleGAN. The accuracy of prostate segmentation on sMRI was evaluated using the Dice similarity coefficient (DSC), Hausdorff distance (HD) and mean surface distance (MSD) on the prostate delineated by three radiation oncologists (ROs) on sMRI versus rMRI. To estimate inter-observer variability (IOV), these metrics between prostate contours delineated by each RO on rMRI and the prostate delineated by treating RO on rMRI (gold standard) were calculated. Main results. Qualitatively, sMRI images show enhanced soft-tissue contrast at the prostate boundary compared with CT scans. For MAE and MSE, PxCGAN and CycleGAN have similar results, while the MAE of PxCGAN is smaller than that of Pix2Pix. PSNR and SSIM of PxCGAN are significantly higher than Pix2Pix and CycleGAN (p < 0.01). The DSC for sMRI versus rMRI is within the range of the IOV, while the HD for sMRI versus rMRI is smaller than the HD for the IOV for all ROs (p ≤ 0.03). Significance. PxCGAN generates sMRI images from treatment-planning CT scans that depict enhanced soft-tissue contrast at the prostate boundary. The accuracy of prostate segmentation on sMRI compared to rMRI is within the segmentation variation on rMRI between different ROs.

Estimation of cancer risks due to chest radiotherapy treatment planning computed tomography (CT) simulations.

The objective of our study was to determine organ doses to estimate the lifetime attributable risk (LAR) of cancer incidence related to chest tomography simulations for Radiotherapy Treatment Planning (RTTP) using patient-specific information. Patient data were used to calculate organ doses and effective dose. The effective dose (E) was calculated by two methods. First, to calculate effective dose in a standard phantom, the collected dosimetric parameters were used with the ImPACT CT Patient Dosimetry Calculator and E was calculated by applying related correction factors. Second, using the scanner-derived Dose Length Product, LARs were computed using the US National Academy of Sciences (BEIR VII) model for age- and sex-specific risks at each exposure. DLP, CTDIvol, and scan length were 507 ± 143mGy.cm, 11 ± 4mGy, and 47 ± 7cm, respectively. The effective dose was 10 ± 3mSv using ImPACT patient dosimetry calculator software and 9 ± 2mSv using the scanner-derived Dose Length Product. The LAR of cancer incidence for all cancers, all solid cancers and leukemia were 65 ± 29, 62 ± 27, 7 ± 2 cases per 100,000 individuals, respectively. Radiation exposure from the usage of CT for radiotherapy treatment planning (RTTP) causes non-negligible increases in lifetime attributable risk. The results of this study can be used as a guide by physicians to implement strategies based on the As Low As Reasonably Achievable (ALARA) principle that lead to a reduction dose without sacrificing diagnostic information.

Sunday, June 19, 202211:30 AM - 12:30 PMPSOR1 Presentation Time: 11:30 AM: MRI-Guided Neurovascular Bundle Avoidance in HDR Prostate Brachytherapy

<h3>Purpose</h3> Ultrasound or computed tomography (CT) are typically used for treatment planning in HDR prostate brachytherapy. However, the neurovascular bundles (NVB), which are hypothesized to have a role in erectile function, are not well visualized in these studies. Our group has shown that magnetic resonance imaging (MRI) can be used to segment the NVB as an avoidance structure for external beam radiation. In this study we hypothesize that treatment planning MRI will allow avoidance of the NVB during HDR prostate brachytherapy. <h3>Materials and Methods</h3> A retrospective chart review of all individuals with prostate cancer treated with radiation therapy at a single institution was used to identify patients who had HDR brachytherapy as monotherapy. All patients underwent TRUS-guided HDR catheter placement followed by CT and MRI for treatment planning. Patients were treated with two 13.5 Gy fractions utilizing standard clinical plans that optimized prostate coverage and minimized irradiation of the standard organs at risk (OARs) - bladder, rectum, and urethra. When applicable, MRI-defined GTVs were targeted for dose escalation to 150%. Experimental NVB-sparing plans were generated to maintain target coverage and OAR constraints but also to add avoidance of the NVBs. The left and right NVB were contoured on the treatment planning MRI and used as avoidance structures with 0 margin. Differences between target and OAR doses in the original and NVB-sparing plans were assessed pairwise using a two-tailed t-test. <h3>Results</h3> 15 prostate cancer patients at a single institution were treated with HDR monotherapy were included. Segmentation of the left and right NVB was feasible for all patients and 13 MRI-defined GTVs were targeted for dose escalation in 11 patients. Compared to their paired original plans, NVB-sparing plans reduced NVB D0.01cc (18.2 vs 14.6 Gy, p<0.01) and V100 (0.1 cc vs 0.0 cc, p<0.01). There was no difference in prostate D90 (108% vs 108%, p=0.19) and V100 (96.7 vs 95.9%, p=0.17) between plans; prostate V150% (36.5% vs. 34.3%, p<0.01) and V200% (14.4% vs 13.5%, p<0.01) slightly decreased in the NVB-sparing plans. Bladder V75 (0.3 cc vs 0.3 cc, p=1.0), rectum V75 (0.2 cc vs. 0.2 cc, p=0.75), and urethra V125 (0.03 cc vs. 0.03 cc, p=0.33) were similar between plans. In the subset of patients with GTVs, the mean GTV V150 decreased from 80.9% to 74.8% (p = 0.04) in the NVB-sparing plans; in one case NVB-sparing led to GTV min dose less than 100%. <h3>Conclusions</h3> NVB-sparing prostate HDR brachytherapy is feasible. Treatment planning MRI should be considered for NVB delineation. NVB-sparing should be approached with caution if GTVs are in close proximity. Evaluation of the clinical impact of MRI-delineated NVB irradiation is underway.

CT and cone-beam CT of ablative radiation therapy for pancreatic cancer with expert organ-at-risk contours

We describe a dataset from patients who received ablative radiation therapy for locally advanced pancreatic cancer (LAPC), consisting of computed tomography (CT) and cone-beam CT (CBCT) images with physician-drawn organ-at-risk (OAR) contours. The image datasets (one CT for treatment planning and two CBCT scans at the time of treatment per patient) were collected from 40 patients. All scans were acquired with the patient in the treatment position and in a deep inspiration breath-hold state. Six radiation oncologists delineated the gastrointestinal OARs consisting of small bowel, stomach and duodenum, such that the same physician delineated all image sets belonging to the same patient. Two trained medical physicists further edited the contours to ensure adherence to delineation guidelines. The image and contour files are available in DICOM format and are publicly available from The Cancer Imaging Archive (https://doi.org/10.7937/TCIA.ESHQ-4D90, Version 2). The dataset can serve as a criterion standard for evaluating the accuracy and reliability of deformable image registration and auto-segmentation algorithms, as well as a training set for deep-learning-based methods.

Validation of four-dimensional computed tomography without external reference respiratory signals for radiation treatment planning of lung tumors

Deviceless four-dimensional (4D) computed tomography (CT) allows the acquisition of respiratory signals from six features without requiring an external device for cine CT processing. This method has been recently introduced in radiation treatment planning of lung tumors. To validate deviceless 4D CT, it must be compared with conventional 4D CT, which requires an external monitoring device. We compared the two methods using a multicell 4D phantom that simulates patient’s movement during respiration regarding the target volume (TV), target position (TP), and internal TV for lung tumor radiation therapy. We retrospectively obtained images of 10 patients who underwent radiation treatment planning of lung tumors and compared the two methods, as in the phantom study. For the phantom study, the mean TV, root mean square errors of the TP, and mean internal TV differences between the two methods ranged from −4.5% to 1.2%, 0.7 to 2.6 mm, and −1.1% to 3.4%, respectively. The corresponding results of the clinical study ranged from −1.5% to 14.9%, 0.1 to 5.9 mm, and −9.7% to 10.1%, respectively. The results of deviceless 4D CT for the clinical study were consistent with those of conventional 4D CT, except for target movements with high excursions. Therefore, deviceless 4D CT can be an alternative to conventional 4D CT for radiation treatment planning of lung tumors.

A Contouring Strategy and Reference Atlases for the Full Abdominopelvic Bowel Bag on Treatment Planning and Cone Beam Computed Tomography Images

PurposeTo establish a practical contouring strategy with reference atlases for the abdominopelvic bowel bag on treatment planning computed tomography (TPCT) and cone beam computed tomography (CBCT) images. Methods and MaterialsA scoping literature review was done to evaluate the existing definitions and contouring guidelines for bowel bag and small bowel planning-at-risk volume–like structures. A comprehensive definition was proposed for the abdominopelvic bowel bag that expanded the Radiation Therapy Oncology Group Pelvic Normal Tissue Consensus definition. Seven patients with TPCT and first-treatment-day CBCT images were selected from an institutional database to represent a range of normal anatomy and CBCT image quality. The TPCT and CBCT images were contoured using the proposed definition. During contouring, the Radiation Therapy Oncology Group definition's list of inclusion and exclusion structures was expanded. For areas with limited visibility of the bowel bag on either TPCT or CBCT, a set of operational definitions was developed based on consistently visible reference structures. ResultsA literature review showed that previously existing bowel bag definitions predominantly focused on the pelvic region and did not provide a complete and practical description of the full abdominopelvic contour relative to structures consistently visible in all radiation therapy images. The proposed contouring strategy had 4 components: a definition, a list of inclusion and exclusion structures, 15 tabulated operational definitions, and a set of atlases. The bowel bag was defined as the peritoneal cavity and retroperitoneal duodenum and ascending and descending colon, as visualized at the time of image acquisition. The operational definitions formalized the location of the peritoneal fascial planes through a simple look-up table. The proposed contouring strategy and reference atlases were successfully used on both TPCT and CBCT images. ConclusionsThis study produced a practical contouring strategy and reference atlases to enable reproducible delineation of the full bowel bag on TPCT and CBCT images. The strategy is a necessary first step toward consensus contouring with reduced observer variability, which is a prerequisite for evaluation of cumulative dose and its correlation with toxic effects, adaptive planning strategies, and automated contouring potential.

Generative models for reproducible coronary calcium scoring.

Purpose: Coronary artery calcium (CAC) score, i.e., the amount of CAC quantified in CT, is a strong and independent predictor of coronary heart disease (CHD) events. However, CAC scoring suffers from limited interscan reproducibility, which is mainly due to the clinical definition requiring application of a fixed intensity level threshold for segmentation of calcifications. This limitation is especially pronounced in non-electrocardiogram-synchronized computed tomography (CT) where lesions are more impacted by cardiac motion and partial volume effects. Therefore, we propose a CAC quantification method that does not require a threshold for segmentation of CAC. Approach: Our method utilizes a generative adversarial network (GAN) where a CT with CAC is decomposed into an image without CAC and an image showing only CAC. The method, using a cycle-consistent GAN, was trained using 626 low-dose chest CTs and 514 radiotherapy treatment planning (RTP) CTs. Interscan reproducibility was compared to clinical calcium scoring in RTP CTs of 1662 patients, each having two scans. Results: A lower relative interscan difference in CAC mass was achieved by the proposed method: 47% compared to 89% manual clinical calcium scoring. The intraclass correlation coefficient of Agatston scores was 0.96 for the proposed method compared to 0.91 for automatic clinical calcium scoring. Conclusions: The increased interscan reproducibility achieved by our method may lead to increased reliability of CHD risk categorization and improved accuracy of CHD event prediction.

Traumatic rupture of an intracranial dermoid cyst: A case report

Intracranial dermoid cyst is a very rare primary intracranial tumor accounting for &lt;0.5% of intracranial masses. They are usually congenital and benign. Rupture of intracranial dermoid may occur spontaneously or with trivial trauma. Most cases of rupture are spontaneous. There are very few reported cases of traumatic rupture of intracranial dermoid cysts in world medical literature. The presentation can range from headache to signs of meningeal irritation and focal neurological deficit. Computed tomography (CT) and magnetic resonance imaging (MRI) of the brain is of paramount importance for early diagnosis and prompt treatment planning which can reduce both morbidity and mortality. The following case report gives an account of a 49-year-old female who presented with complaints of headache after an episode of fall. She was examined and no neurological deficit was found. Examination of the neurological system was within normal limits. She underwent a CT and MRI of the brain and was subsequently diagnosed as traumatic rupture of dermoid cyst based on the findings. She was treated with high-dose steroids until resolution of her symptoms and then discharged with the advice of regular follow-up. This case report highlights the role of CT and MRI in early diagnosis and treatment planning of patients with ruptured dermoid cysts which leads to a decrease in mortality and morbidity and also the ability of the same to rule out other more sinister causes of headache in patients.

Accurate Delineation of Mucosal Lesions in Treatment-Planning Computed Tomography Using Iodine Paste Markers for Oral Mucosal Melanoma

This technical report introduces the utility of iodine paste markers using endodontic materials for the accurate contouring of mucosal lesions of oral mucosal melanoma, which are difficult to delineate on imaging during the planning of carbon-ion radiation therapy (CIRT). The patient had a primary oral mucosal melanoma located in the palatal mucosa without palatal or maxillary bone invasion. A dental root canal filling material, which is a calcium hydroxide/iodoform nonhardenable paste, was used as a marker. We first performed treatment-planning computed tomography (CT) without an iodine paste marker for mucosal lesions. Subsequently, we placed an iodine paste marker on the palatal mucosal lesion to accurately delineate the mucosal lesions of the palate. Finally, we obtained a reference CT image with an iodine paste marker. Computed tomography without the marker was fused to the reference CT with markers during treatment planning, and the gross tumor volume was contoured. Thereafter, CIRT was delivered without markers. During CIRT, expected acute mucositis was observed in the area of the planning target volume, including melanosis, in accordance with the dose distribution. The use of iodine paste markers for localized mucosal lesions, which are difficult to delineate on CT and magnetic resonance imaging, may be useful for accurately contouring gross tumor volumes on treatment-planning CT.

Computed Tomography-Based Assessment of Transvalvular Pressure Gradient in Aortic Stenosis.

Background: In patients with aortic stenosis, computed tomography (CT) provides important information about cardiovascular anatomy for treatment planning but is limited in determining relevant hemodynamic parameters such as the transvalvular pressure gradient (TPG).Purpose: In the present study, we aimed to validate a reduced-order model method for assessing TPG in aortic stenosis using CT data.Methods: TPGCT was calculated using a reduced-order model requiring the patient-specific peak-systolic aortic flow rate (Q) and the aortic valve area (AVA). AVA was determined by segmentation of the aortic valve leaflets, whereas Q was quantified based on volumetric assessment of the left ventricle. For validation, invasively measured TPGcatheter was calculated from pressure measurements in the left ventricle and the ascending aorta. Altogether, 84 data sets of patients with aortic stenosis were used to compare TPGCT against TPGcatheter.Results: TPGcatheter and TPGCT were 50.6 ± 28.0 and 48.0 ± 26 mmHg, respectively (p = 0.56). A Bland–Altman analysis revealed good agreement between both methods with a mean difference in TPG of 2.6 mmHg and a standard deviation of 19.3 mmHg. Both methods showed good correlation with r = 0.72 (p < 0.001).Conclusions: The presented CT-based method allows assessment of TPG in patients with aortic stenosis, extending the current capabilities of cardiac CT for diagnosis and treatment planning.

Determination of reproducibility of end-exhaled breath-holding in stereotactic body radiation therapy.

ABSTRACTMethods to evaluate the positional reproducibility of breath-hold irradiation mostly require manual operation. The purpose of this study is to propose a method to determine the reproducibility of breath-hold irradiation of lung tumors between fractions using non-artificial methods. This study included 13 patients who underwent terminal exhaled breath-hold irradiation for primary and metastatic lung cancer. All subjects received a prescribed dose of 60 Gy/8 fractions. The contours of the gross tumor volume (GTV) were extracted by threshold processing using treatment-planning computed tomography (CT) and cone-beam CT (CBCT), which was done just before the beginning of the treatment. The method proposed in this study evaluates the dice similarity coefficient (DSC) and Hausdorff distance (HD) by comparing two volumes, the GTVCTS (GTV obtained from treatment-planning CT) and GTVCBCT (GTV obtained from CBCT). The reference contours for DSC and HD are represented by GTVCTS. The results demonstrated good visual agreement for cases with a DSC of ~0.7. However, apparent misalignment occurred when the DSC was <0.5. HD was >2 mm in 3 out of 13 cases, and when the DSC was ~0.7, the HD was ~1 mm. In addition, cases with greater HD also demonstrated more significant variability. It was found that the DSC and HD evaluation methods for the positional reproducibility of breath-hold irradiation proposed in this study are straightforward and can be performed without the involvement of humans. Our study is of extreme significance in the field of radiation studies.

Estimation of Hounsfield unit conversion parameters for pelvic CT images.

Linear scaling is used to convert raw computed tomography (CT) pixel values into Hounsfield units corresponding to different tissue values. Analysis of a benchmarking study, presented here, where the same CT scan was imported into and then exported from multiple radiotherapy treatment planning systems, found inconsistencies in HU scaling parameter values exported along with the images, particularly when images were exported using the Radiation Therapy Oncology Group format. Several methods of estimating conversion parameters, based on estimating pixel values corresponding to air and water within the image, for pelvic CT images from a large multi-centre trial were compared against original Digital Imaging and Communications in Medicine export parameters. In general using the mean of a sample region at the centroid of the bladder to estimate the value of water was more accurate than using the minimum or maximum or a single value at the centroid. Accuracy of methods of air estimation tested were dependent in part on features of the CT scanners and treatment planning systems, making it difficult to pick one method as superior that was independent of scanner and treatment planning system type. Based on the above analysis, methods for estimating air and water were selected for use in performing linear scaling of a set of pelvic CT images prior to their use in an interpatient image registration application. The selected methods were validated against a more recent and homogeneous dataset. Estimation error was found to be much lower within the validation set.

Strategies for prediction and mitigation of radiation-induced liver toxicity.

Although well described in the 1960s, liver toxicity secondary to radiation therapy, commonly known as radiation-induced liver disease (RILD), remains a major challenge. RILD encompasses two distinct clinical entities, a ‘classic’ form, composed of anicteric hepatomegaly, ascites and elevated alkaline phosphatase; and a ‘non-classic’ form, with liver transaminases elevated to more than five times the reference value, or worsening of liver metabolic function represented as an increase of 2 or more points in the Child–Pugh score classification. The risk of occurrence of RILD has historically limited the applicability of radiation for the treatment of liver malignancies. With the development of 3D conformal radiation therapy, which allowed for partial organ irradiation based on computed tomography treatment planning, there has been a resurgence of interest in the use of liver irradiation. Since then, a large body of evidence regarding the liver tolerance to conventionally fractionated radiation has been produced, but severe liver toxicities has continued to be reported. More recently, improvements in diagnostic imaging, radiation treatment planning technology and delivery systems have prompted the development of stereotactic body radiotherapy (SBRT), by which high doses of radiation can be delivered with high target accuracy and a steep dose gradient at the tumor – normal tissue interface, offering an opportunity of decreasing toxicity rates while improving tumor control. Here, we present an overview of the role SBRT has played in the management of liver tumors, addressing the challenges and opportunities to reduce the incidence of RILD, such as adaptive approaches and machine-learning–based predictive models.

Anatomical and Dosimetric Changes during IMRT for Oropharyngeal Cancer Detected by Weekly Cone-Beam CT With Deformable Image Registration

Re-planning is often necessary during IMRT for head and neck cancer due to tumor regression and changes of body contour. CBCT was obtained for patients with OPC once a week to confirm anatomical and dosimetric changes of tumor and organs at risk (OAR). Ten patients with OPC treated by a two-step IMRT method were included. For all patients, treatment-planning computed tomography (CT) was done twice before and at the fourth week for initial and boost IMRT, respectively. All 10 patients were given 70 Gy/35 fractions with concurrent chemotherapy (CDDP; 5, Cetuximab; 4, CBDCA 1). On board CBCTs were obtained on days 1, 8, 15, 22, and 29 of IMRT. Deformed volumes of tumor and OARs in the CBCT were compared with those in the planning CT. Dose distribution at the isocenter level was recalculated based on weekly CBCT image and compared with the initial planned dose distribution. Area of body surface, PTV D2, D50 and D98, and Dmax of the spinal cord on the isocenter level were selected for analysis. After volumes on initial treatment-planning CT were deformed into CBCT images on days 1-29, change rates from CBCT images on day1 were determined for CBCT images from day 8 to day 29. Change rates of more than 5% in area or dose were regarded as significant change. Results: Average change rates and number of patients with significant change were shown in Table 1. Area of body surface decreased gradually. After day 22, five of the 10 patients showed decrease of body area of more than 5%. Area of body surface and Dmax of the spinal cord were inversely correlated (r = -0.47). After day 22, Dmax of the spinal cord increased more than 5% for eight patients (80%). Notably, PTV D2, D50 and D98 were not changed during the period from day 1 to day 29. In patients with OPC treated by a two-step IMRT method, weekly CBCT demonstrated decrease of body surface and increase of Dmax of the spinal cord after 22-29 days of treatment. Although changes in PTV doses were minimal, re-planning may be necessary to protect spinal cord toxicity when significant decrease of body area was noted.Abstract 2812; Table 1Average change rate and number of patients with significant changeAverage change rateNumber of patients with significant changeDay1Day8Day15Day22Day29Day1Day8Day15Day22Day29Body surface(cm2)100%97%97%96%96%Body surface(cm2)03356PTV D98 (Gy)100%99%99%99%98%PTV D98 (Gy)00001PTV D50100%100%100%100%100%PTV D5000000PTV D2100%100%100%100%100%PTV D200001Spinal cordDmax (Gy)100%101%102%101%104%Spinal cordDmax (Gy)02589 Open table in a new tab

SU‐F‐J‐81: Evaluation of Automated Deformable Registration Between Planning Computed Tomography (CT) and Daily Cone Beam CT Images Over the Course of Prostate Cancer Radiotherapy

Purpose:To compute daily dose delivered during radiotherapy, deformable registration needs to be relatively fast, automated, and accurate. The aim of this study was to evaluate the performance of commercial deformable registration software for deforming between two modalities: planning computed tomography (pCT) images acquired for treatment planning and cone beam (CB) CT images acquired prior to each fraction of prostate cancer radiotherapy.Methods:A workflow was designed using MIM Software™ that aligned and deformed pCT into daily CBCT images in two steps: (1) rigid shifts applied after daily CBCT imaging to align patient anatomy to the pCT and (2) normalized intensity‐based deformable registration to account for interfractional anatomical variations. The physician‐approved CTV and organ and risk (OAR) contours were deformed from the pCT to daily CBCT over the course of treatment. The same structures were delineated on each daily CBCT by a radiation oncologist. Dice similarity coefficient (DSC) mean and standard deviations were calculated to quantify the deformable registration quality for prostate, bladder, rectum and femoral heads.Results:To date, contour comparisons have been analyzed for 31 daily fractions of 2 of 10 of the cohort. Interim analysis shows that right and left femoral head contours demonstrate the highest agreement (DSC: 0.96±0.02) with physician contours. Additionally, deformed bladder (DSC: 0.81±0.09) and prostate (DSC: 0.80±0.07) have good agreement with physician‐defined daily contours. Rectum contours have the highest variations (DSC: 0.66±0.10) between the deformed and physician‐defined contours on daily CBCT imaging.Conclusion:For structures with relatively high contrast boundaries on CBCT, the MIM automated deformable registration provided accurate representations of the daily contours during treatment delivery. These findings will permit subsequent investigations to automate daily dose computation from CBCT. However, improved methods need to be investigated to improve deformable results for rectum contours.

Image Guided Planning for Prostate Carcinomas With Incorporation of Anti-3-[18F]FACBC (Fluciclovine) Positron Emission Tomography: Workflow and Initial Findings From a Randomized Trial

(18)F-Fluciclovine (anti-1-amino-3-[(18)F]fluorocyclobutane-1-carboxylic acid) is a novel positron emission tomography (PET)/computed tomography (CT) radiotracer that has demonstrated utility for detection of prostate cancer. Our goal is to report the initial results from a randomized controlled trial of the integration of (18)F-fluciclovine PET-CT into treatment planning for defining prostate bed and lymph node target volumes. We report our initial findings from a cohort of 41 patients, of the first enrolled on a randomized controlled trial, who were randomized to the (18)F-fluciclovine arm. All patients underwent (18)F-fluciclovine PET-CT for the detection of metabolic abnormalities and high-resolution CT for treatment planning. The 2 datasets were registered first by use of a rigid registration. If soft tissue displacement was observable, the rigid registration was improved with a deformable registration. Each (18)F-fluciclovine abnormality was segmented as a percentage of the maximum standard uptake value (SUV) within a small region of interest around the lesion. The percentage best describing the SUV falloff was integrated in planning by expanding standard target volumes with the PET abnormality. In 21 of 55 abnormalities, a deformable registration was needed to map the (18)F-fluciclovine activity into the simulation CT. The most selected percentage was 50% of maximum SUV, although values ranging from 15% to 70% were used for specific patients, illustrating the need for a per-patient selection of a threshold SUV value. The inclusion of (18)F-fluciclovine changed the planning volumes for 46 abnormalities (83%) of the total 55, with 28 (51%) located in the lymph nodes, 11 (20%) in the prostate bed, 10 (18%) in the prostate, and 6 (11%) in the seminal vesicles. Only 9 PET abnormalities were fully contained in the standard target volumes based on the CT-based segmentations and did not necessitate expansion. The use of (18)F-fluciclovine in postprostatectomy radiation therapy planning was feasible and led to augmentation of the target volumes in the majority (30 of 41) of the patients studied.

Evaluation of Non-Rigid Image-Registration Algorithms Using Discrepancy Distance Between Organ Contours

Purpose: Non-rigid image registration (NIR) is useful for adaptive radiotherapy. However, no method has been established for evaluating the quality of the algorithms used in NIR. To remedy this situation, we demonstrate herein a novel method to evaluate NIR algorithms. Methods: We define the NIR error as the discrepancy distance between (i) the organ contours obtained from computed tomography (CT) images acquired during the treatment period (reference contours) and (ii) the contours obtained from the treatment-planning CT images that are constructed by automated propagation during the treatment period (evaluation contours). However, the continuous positional relationship between the points where the reference contour intersects the evaluation contour is assumed to be maintained. In addition, we adapt the proposed method so that it can be applied to the contours of complex organs such as spherical and tubular organs. To demonstrate this method, we measure the contours of the prostate, right seminal vesicle, left seminal vesicle, urinary bladder, and rectum. The obtained NIR error presented in two-dimensional (2D) discrepancy maps. Results: The 2D discrepancy maps show the difference between the reference and evaluation contours from CT images. The proposed method measures the difference between the contours of spherical and tubular organs and evaluates the NIR error based on the positional relationship between the points constituting the contours. Conclusions: This study accounts for and measures the continuous positional relationship between corresponding points in the contours of complex-shaped spherical and tubular organs with irregularities and evaluates NIR algorithms based on these organ contours.

Validation of a novel robot-assisted 3DUS system for real-time planning and guidance of breast interstitial HDR brachytherapy.

In current clinical practice, there is no integrated 3D ultrasound (3DUS) guidance system clinically available for breast brachytherapy. In this study, the authors present a novel robot-assisted 3DUS system for real-time planning and guidance of breast interstitial high dose rate (HDR) brachytherapy treatment. For this work, a new computer controlled robotic 3DUS system was built to perform a hybrid motion scan, which is a combination of a 6 cm linear translation with a 30° rotation at both ends. The new 3DUS scanner was designed to fit on a modified Kuske assembly, keeping the current template grid configuration but modifying the frame to allow the mounting of the 3DUS system at several positions. A finer grid was also tested. A user interface was developed to perform image reconstruction, semiautomatic segmentation of the surgical bed as well as catheter reconstruction and tracking. A 3D string phantom was used to validate the geometric accuracy of the reconstruction. The volumetric accuracy of the system was validated with phantoms using magnetic resonance imaging (MRI) and computed tomography (CT) images. In order to accurately determine whether 3DUS can effectively replace CT for treatment planning, the authors have compared the 3DUS catheter reconstruction to the one obtained from CT images. In addition, in agarose-based phantoms, an end-to-end procedure was performed by executing six independent complete procedures with both 14 and 16 catheters, and for both standard and finer Kuske grids. Finally, in phantoms, five end-to-end procedures were performed with the final CT planning for the validation of 3DUS preplanning. The 3DUS acquisition time is approximately 10 s. A paired Student t-test showed that there was no statistical significant difference between known and measured values of string separations in each direction. Both MRI and CT volume measurements were not statistically different from 3DUS volume (Student t-test: p > 0.05) and they were significantly correlated to 3DUS measurement (Pearson test: MRI p < 0.05 and CT p < 0.001). The mean angular separation distance between catheter trajectories segmented from 3DUS and CT images was 0.42° ± 0.24°, while the maximum and mean trajectory separations were 0.51 ± 0.19 and 0.37 ± 0.17 mm, respectively. Overall, the new finer grid has performed significantly better in terms of dosimetric indices. The planning target volume dosimetric indices were not found statistically different between 3DUS and CT planning (Student t-test, p > 0.05). Both the skin and the pectoral muscle dosimetric indices were within ABS guidelines. A novel robot-assisted 3DUS system was designed and validated. To their knowledge, this is the first system capable of performing real-time guidance and planning of breast multicatheter HDR brachytherapy treatments. Future investigation will test the feasibility of using the system in the clinic and for permanent breast brachytherapy.

Monte Carlo comparison of x-ray and proton CT for range calculations of proton therapy beams

Proton computed tomography (CT) has been described as a solution for imaging the proton stopping power of patient tissues, therefore reducing the uncertainty of the conversion of x-ray CT images to relative stopping power (RSP) maps and its associated margins. This study aimed to investigate this assertion under the assumption of ideal detection systems. We have developed a Monte Carlo framework to assess proton CT performances for the main steps of a proton therapy treatment planning, i.e. proton or x-ray CT imaging, conversion to RSP maps based on the calibration of a tissue phantom, and proton dose simulations. Irradiations of a computational phantom with pencil beams were simulated on various anatomical sites and the proton range was assessed on the reference, the proton CT-based and the x-ray CT-based material maps. Errors on the tissue’s RSP reconstructed from proton CT were found to be significantly smaller and less dependent on the tissue distribution. The imaging dose was also found to be much more uniform and conformal to the primary beam. The mean absolute deviation for range calculations based on x-ray CT varies from 0.18 to 2.01 mm depending on the localization, while it is smaller than 0.1 mm for proton CT. Under the assumption of a perfect detection system, proton range predictions based on proton CT are therefore both more accurate and more uniform than those based on x-ray CT.

Analysis of reproducibility and field size using gating system in 4D computed tomography

Differences exist in each reproduced image since the scan types are different for the images acquired by axial, helical and cine scanning in accordance with computed tomography. This study was aimed to examine reproducibility using drive phantom in order to identify how accurately each scan type of computed tomography describes the movement of table. This study evaluated gating-based four-dimensional (4D)-computed tomography treatment planning by a comparison with common three-dimensional (3D)-computed tomography treatment planning and examining the change in treatment field size. The study used a self-manufactured drive phantom and a respiration gated drive motor to reproduce movements in the upward/downward direction and in the top/bottom direction. Following this, breathing-induced movement was applied to the self-manufactured model phantom and images were taken by Axial, Helical and cine scanning according to each computed tomography scan type. Reproducibility of the model and volume reflecting the movement was compared and analysed for accuracy using the RPT equipment. The scanning conditions according to each computed tomography scan type were set equally as follows: tube voltage 120 kV, tube current 200 mA, slice thickness and gap between slices 2·5 mm, inter scan delay 1·3, and pitch 1. The 3D-computed tomography and gating-based 4D-computed tomography images were obtained from patients who had undergone radiation treatment for chest and abdomen tumours in the oncology department. From the study results, the total volume of the marker was 88·2 cm3 and when a 3 cm shift in the top/bottom direction and a 0·3 cm shift in the upward/downward direction were taken into account, the total volume was 184·3 cm3. Total volumes by different computed tomography scan types were 135 cm3 for axial scanning, 164·9 cm3 for helical scanning and 181·7 cm3 for cine scanning. Regarding the presentation of reproducibility for movement, the cine scan type depicted the marker as closely as possible. The treatment field size was smaller in volume in the case of 4D-computed tomography treatment planning.