Craniocaudal Direction Research Articles

Heart-Sparing Capability and Positional Reproducibility of Continuous Positive Airway Pressure in Left-Sided Breast Radiation Therapy

PurposeOur purpose was to investigate the interfraction and intrafraction reproducibility and practical applicability of continuous positive airway pressure (CPAP) for left breast volumetric modulated arc therapy (VMAT). Methods and MaterialsInterfraction reproducibility of the position of the heart was evaluated by measuring the heart-to-target distance on 20 planning computed tomography (CT) and 300 daily cone beam CT of 20 patients with left breast cancer treated with a 15-fraction VMAT. The dosimetric metrics of the whole heart and its substructures were compared between CPAP and free-breathing based VMAT plans. Intrafraction reproducibility was evaluated by measuring the motions of the breast target and diaphragm in 4-dimensional CT of 20 female patients with nonbreast cancer. Lastly, we analyzed the CPAP compliance data of 237 consecutive patients with left-sided breast cancer with and without internal mammary node irradiation (IMNI). ResultsThe heart position was reproducible as evidenced by an absolute average heart-to-target distance error of 2.0 ± 2.0 mm. Compared with free-breathing, CPAP significantly reduced the mean heart dose and the dose to the left ventricle and left anterior descending artery. The average intrafraction position variation of the breast target was 0.5 ± 0.5, 2.5 ± 2.0, and 1.8 ± 1.4 mm in the mediolateral, craniocaudal, and anteroposterior directions, respectively. CPAP was successfully applied in 221 patients (93%), with a mean heart dose of 1.6 ± 0.7 Gy (IMNI: 2.0 Gy and no IMNI: 1.1 Gy). ConclusionsCPAP has adequate heart-sparing capability and sufficient reproducibility in VMAT for left-sided breast cancer treatment, with a high compliance rate. Thus, CPAP is applicable in routine practice for left-sided breast cancer radiation therapy.

Segmental composition of the porcine iliopsoas muscle and influence of the body size and posture on the composition of the iliopsoas muscle

The iliopsoas muscle (IPM) of the pig consists of the iliacus muscle (IM) and the psoas major muscle (PMM). Due to the differences in posture and size between animal species, the musculoskeletal system is subjected to different functional demands, which affects the morphological characteristics of the musculoskeletal system. The aim of this study was to determine the muscle fiber type composition in pigs IPM, as pigs are large quadrupeds that differ in body size and posture from humans and small mammals, and to determine the influence of body size and posture on the composition of IPM. Muscle samples were collected from the Pietrain Landrace pigs, a sample from IM and a samples at four segments of the PMM. Samples were analyzed with monoclonal antibodies specific for different isoforms of the myosin heavy chain. The percentages and cross-sectional area (CSA) of type I, IIA, and IIX/IIB muscle fibers were calculated. Our studies revealed that in pigs IPM, type IIX/IIB muscle fibers were predominant with the largest CSA. A decrease in the proportion of type IIX/IIB muscle fibers, an increase in type I and IIA muscle fibers, and a decrease in the CSA of all muscle fiber types from the cranial to the caudal part of the PMM were observed. The pig IPM has primarily a dynamic function. The function of the PMM in the cranio-caudal direction changes from a dynamic to a static role. Body size and posture influence the composition of the IPM.

Patient setup accuracy in DIBH radiotherapy of breast cancer with lymph node inclusion using surface tracking and image guidance.

Studying setup accuracy in breast cancer patients with axillary lymph node inclusion in deep inspiration breath-hold (DIBH) after patient setup with surface-guided radiotherapy (SGRT) and image-guided radiotherapy (IGRT). Breast cancer patients (N = 51) were treated (50 Gy in 25 fractions) with axillary lymph nodes within the planning target volume (PTV). Patient setup was initiated with tattoos and lasers, and further adjusted with SGRT. The DIBH guidance was based on SGRT. Orthogonal and/or tangential imaging was analyzed for residual position errors of bony landmarks, the breath-hold level (BHL), the skin outline, and the heart; and setup margins were calculated for the PTV. The calculated PTV margins were 4.3 to 6.3 and 2.8 to 4.6 mm before and after orthogonal imaging, respectively. The residual errors of the heart were 3.6 ± 2.2 mm and 2.5 ± 2.4 mm before and 3.0 ± 2.5 and 2.9 ± 2.3 mm after orthogonal imaging in the combined anterior-posterior/lateral and the cranio-caudal directions, respectively, in tangential images. The humeral head did not benefit from daily IGRT, but SGRT guided it to the correct location. We presented a slightly complicated but highly accurate workflow for DIBH treatments. The residual position errors after both SGRT and IGRT were excellent compared to previous literature. With well-planned SGRT, IGRT brings only slight improvements to systematic accuracy. However, with the calculated PTV margins and the number of outliers, imaging cannot be omitted despite SGRT, unless the PTV margins are re-evaluated.

The factors of fiducial marker motions and individual margin assessment in postoperative breast cancer radiotherapy.

As a surrogate for the breast tumor bed, individual fiducial markers frequently move during radiotherapy. This study aimed to classify the motions and calculate the individualized target margin. The mammary basal diameters (D) and heights (H) were measured to represent breast sizes for 15 patients after breast-conserving surgery. The clinical target volume (CTV) was divided into 4 quadrants by a coordinate system with the center of mass of the tumor bed as the origin. The lateral, anteroposterior, and craniocaudal motions of markers were calculated (MLR, MAP, MSI) based on the difference of the setup errors between the spine matching and the fiducial markers matching. The distances between markers and the innermost, foremost, and uppermost borders of CTV (DSLR, DSAP, DSSI) were recorded. In the first quadrant, MAP was strongly correlated with D×H (r>0.80) when D×H <99.89 cm2. Both MLR and MAP were positively linearly related to DSLR, DSAP, DSSI (r>0.85, R2>0.75). MSI was also positively linearly correlated with DSAP and DSLR (r>0.90, R2>0.80). In the fourth quadrant with D×H <90.71 cm2, only MLR and DSLR showed a linear positive correlation (r>0.90, R2>0.75), whereas the others showed linear negative correlations (r>-0.90, R2>0.80). The planning target volume (PTV) margin varied significantly between the first and fourth quadrant (P<0.05), and the largest margin was 12.4 mm in the craniocaudal direction of the first quadrant with D×H ≥99.89 cm2. Fiducial motion is susceptible to breast size and fiducial position, and the individualized PTV margins should take the above factors into account.

Impact on liver position under breath-hold by computed tomography contrast agents in stereotactic body radiotherapy of liver cancer.

BackgroundWe investigated variations in liver position relative to the vertebral bone for liver cancer treated with stereotactic body radiation therapy under expiratory phase breath-hold (BH) for treatment with contrast-enhanced-computed tomography (CECT), non-CECT, and cone-beam computed tomography (CBCT).Materials and methodsSeventeen consecutive patients using a contrast enhancement (CE) agent for the CT simulation session for this retrospective study were selected. The first computed tomography (CT) scan without the use of CE agent in the expiratory phase was used for treatment planning (pCT). The remaining three CT scans without a CE agent under expiratory phase BH were acquired successively without repositioning to evaluate the intra-fraction variation in liver position. Furthermore, a three-phase CT scan (arterial, portal, and late phases) accompanied by a CE agent under expiratory phase BH was acquired for target delineation. CBCT scans without the use of a CE agent under expiratory phase BH were acquired for treatment. Inter-fractional variations (non-CECT or CECT) in liver position were measured using the difference between CBCT and pCT or each 3 phase CECT images, respectively.ResultsThe average ± standard deviations for intrafractional, non-CECT interfractional variations, and CECT interfractional variations were 1.0 ± 1.3, 2.5 ± 2.6, and 6.4 ± 6.4 mm, respectively, in the craniocaudal (CC) direction. Intra- and inter-fractional variations in liver position were relatively small for non-CECT. However, significant inter-fractional liver position variations in CECT were observed in the expiratory phase BH. The position of the liver should be carefully considered when applying CECT images for image-guided radiotherapy.

Degree of reduction in normal liver complication probability from free-breathing to breath-hold liver SBRT: a dose-escalation strategy using radiation dose-volume effect

Introduction. This study aimed to analyze the degree of reduction in normal liver complication probability (NTCP) from free-breathing (FB) to breath-hold (BH) liver SBRT. The effect of the radiation dose-volume on the mean liver dose (MLD) was also analyzed due to dose prescription, normal liver volume (NLV), and PTV. Materials and Methods. Thirty-three stereotactic body radiation therapy (SBRT) cases of hepatocellular carcinoma were selected, retrospectively. For FB, the treatments were planned on average intensity projection scan (CTavg), and patient-specific internal target volume (ITV) margins were applied. To simulate the BH treatment, computed tomography (CT) scan correspond to the 40%—50% of the respiratory cycle (CT40%-50%) was chosen, and an appropriate intrafraction margin of 2 mm, 1.5 mm, and 1.5 mm were given in craniocaudal (CC), superior-inferior (SI), and lateral direction to generate the final iGTV. As per RTOG 1112, all organs at risk (OAR’s) were considered during the optimization of treatment plans. NTCP was calculated using LKB fractionated model. Multivariate regression analysis was performed to see the effect of EQD2Gy, NLV, and PTV on MLD2Gy. Results. A significant dosimetric difference was observed in the normal liver (liver-ITV/iGTV). A reduction of 1.7% in NTCP was observed from FB to BH technique. The leverage of dose escalation is more in BH because MLD2Gy corresponds to 5%, 10%, 20%, and 50% NTCP was 0.099 Gy, 0.41 Gy, 1.21 Gy, and 3.432 Gy more in BH as compared to FB technique. In MVRA, the major factor which was attributed to a change in MLD2Gy is EQD2Gy. Conclusion. From FB to BH technique, a significant reduction in NTCP was observed. The dose prescription is a major factor attributed to the change in MLD2Gy. Advances in knowledge: If feasible, prefer BH treatment either for tumor dose escalation or for the reduction in NTCP.

ANATOMICAL STUDY OF THE IDEAL POSITIONING OF THE S2 ILIAC SCREW

ABSTRACT Objective: To evaluate the morphometry of the pelvis to determine the safe trajectory for the insertion of the S2-iliac screw, and to correlate it with studies reported in the literature for other populations. Method: The computed tomography (CT) pelvic exams of 36 Brazilian patients without congenital malformations, tumors, pelvic ring fractures or dysplasias were selected from the database of a radiological clinic. To define the ideal trajectory of the S2-iliac screw, the following variables were measured: 1- maximum sacroiliac screw length; 2- thickness of the iliac dipole for planning the choice of screw dimensions (length and diameter); 3 - distance between the insertion point of the iliac S2 screw and the posterior sacral cortex; 4 - angulation for insertion of the screw in the mediolateral direction, representing the angle formed between the “iliac line” and the anatomical sagittal plane; 5- Angulation for insertion of the screw in the craniocaudal direction. The Pearson's chi squared and student's t tests were used for statistical analysis. Results: The sample consisted of 36 patients, 50% (18/36) of whom were women. The mean age was 63.7 years, ranging from 23 to 96 years. All the pelvic morphometric variables analyzed presented values similar to those described in the literature for other populations. Conclusion: Prior evaluation of the tomography exams was important for preoperative planning, and there was a statistically significant difference between the sexes only in relation to the variables left craniocaudal and length of the left internal table. Level of evidence III; Observational cross-sectional study.

Radiological characteristics and diagnostic impact of duplicated right adrenal veins on adrenal venous sampling in primary aldosteronism.

We aimed to analyze the prevalence and radiological characteristics of duplicated right adrenal veins (DRAVs) and evaluate the diagnostic impact of adrenal venous sampling (AVS) in primary aldosteronism. DRAVs were retrospectively identified among patients who underwent segmental AVS between April 2017 and March 2020. DRAVs were defined as main or accessory according to the drainage area. The diameter, position, hormone levels, and treatment plan based on AVS were compared between main and accessory RAVs, using the Wilcoxon rank-sum test. Fourteen of 432 patients (3.2%) were diagnosed with DRAVs. On venography, the mean diameters of the main and accessory side were 3±0.63 mm and 2.1±0.41 mm, respectively, and were significantly different (p < 0.001). The mean relative position in craniocaudal direction of main and accessory veins from the adrenal caudal edge on computed tomography was 65.5%±16.0%, and 48.1%±16.8%, respectively, which was significantly different (p = 0.007). The left-right positions and hormone levels were not significantly different. Based on conventional AVS, the treatment plan between DRAVs was not changed in six of eight patients, but changed from surgery to medication in two patients with right aldosterone-producing adenoma (APA)/microadenoma based on segmental AVS findings. DRAVs, in which the main RAV was thicker and more cranially located than the accessory RAV were rare. Depending on blood sampled from either of DRAVs, the diagnosis made through conventional AVS might change treatment approach from surgery to medication, especially with right APA. Hence, their identification is important to make an accurate subtyping by AVS.

Cervical intervertebral separation caused by trauma on post-mortem computed tomography: Possibility of a diagnosis based on intervertebral gas

ObjectivesGas is a common finding in cervical intervertebral separation. However, intervertebral gas is also found in many decedents without intervertebral separation. Here, we quantified intervertebral gas and examined its value in the diagnosis of cervical intervertebral separation. MethodsWe retrospectively reviewed data from 1118 decedents who underwent post-mortem computed tomography (CT) and autopsy from May 2011 to July 2016 and selected those with cervical intervertebral gas with or without intervertebral separation. These data comprised 56 cervical intervertebral spaces with gas [intervertebral separation in 19 (33.9%)] in 43 subjects [intervertebral separation in 17 (39.5%)]. We categorised the decedents according to gas volume, position, and shape and determined the significance of the differences between the decedents with and without separation. ResultsThe gas volume did not differ significantly between decedents with and without separation (p = 0.063). However, there were significant differences in the gas position between decedents with and without separation. In the sagittal plane: gas was seen in the “centred” position in the ventral-to-dorsal direction in more decedents without separation than in those with separation (p = 0.018). Gas was seen in the ventral-to-dorsal positions in more decedents with separation than in those without separation (p = 0.049). In the cranio-caudal direction, gas in the upper position was more common in decedents with separation than in those without separation in the sagittal plane (p = 0.03).In the coronal plane: gas was seen in the upper position more frequently in decedents with separation in the cranio-caudal direction than in those without separation (p = 0.001). A significant difference in gas shape was observed only in the coronal plane (p = 0.024); irregular gas was associated with decedents without separation. ConclusionGas in the ventral-to-dorsal and upper positions in the sagittal plane and in the upper position in the coronal plane was rather indicative of cervical intervertebral separation. An irregular gas shape in the coronal plane was indicative of degenerative changes.

Quantification of the\xa0spatial distribution of primary tumors in the lung to develop new prognostic biomarkers for locally advanced NSCLC

The anatomical location and extent of primary lung tumors have shown prognostic value for overall survival (OS). However, its manual assessment is prone to interobserver variability. This study aims to use data driven identification of image characteristics for OS in locally advanced non-small cell lung cancer (NSCLC) patients. Five stage IIIA/IIIB NSCLC patient cohorts were retrospectively collected. Patients were treated either with radiochemotherapy (RCT): RCT1* (n = 107), RCT2 (n = 95), RCT3 (n = 37) or with surgery combined with radiotherapy or chemotherapy: S1* (n = 135), S2 (n = 55). Based on a deformable image registration (MIM Vista, 6.9.2.), an in-house developed software transferred each primary tumor to the CT scan of a reference patient while maintaining the original tumor shape. A frequency-weighted cumulative status map was created for both exploratory cohorts (indicated with an asterisk), where the spatial extent of the tumor was uni-labeled with 2 years OS. For the exploratory cohorts, a permutation test with random assignment of patient status was performed to identify regions with statistically significant worse OS, referred to as decreased survival areas (DSA). The minimal Euclidean distance between primary tumor to DSA was extracted from the independent cohorts (negative distance in case of overlap). To account for the tumor volume, the distance was scaled with the radius of the volume-equivalent sphere. For the S1 cohort, DSA were located at the right main bronchus whereas for the RCT1 cohort they further extended in cranio-caudal direction. In the independent cohorts, the model based on distance to DSA achieved performance: AUCRCT2 [95% CI] = 0.67 [0.55–0.78] and AUCRCT3 = 0.59 [0.39–0.79] for RCT patients, but showed bad performance for surgery cohort (AUCS2 = 0.52 [0.30–0.74]). Shorter distance to DSA was associated with worse outcome (p = 0.0074). In conclusion, this explanatory analysis quantifies the value of primary tumor location for OS prediction based on cumulative status maps. Shorter distance of primary tumor to a high-risk region was associated with worse prognosis in the RCT cohort.

A Novel Immobilization Method Using 3D Printing for the Treatment of Head and Neck Cancer

<h3>Purpose/Objective(s)</h3> Radiation therapy requires immobilization hardware that may produce significant anxiety for a patient under treatment, particularly when covering the face. In cases where such anxiety is treatment limiting, 3D printing can provide for a better tolerated custom immobilization. The technical hurdles, fidelity of positioning, and clinical outcomes are reviewed for the treatment of oropharyngeal cancer in a patient who was unable to tolerate traditional mask-based immobilization. <h3>Materials/Methods</h3> A 3D printer was used to create a custom immobilization cradle for the treatment of squamous cell carcinoma of the oropharynx. This was used in the treatment of a patient who was unable to be simulated despite nine separate attempts, using a variety of open-faced immobilization techniques, anxiolytics, and coaching. Operative management was not feasible due to the patient's habitus and comorbidities. Despite acknowledging the severity of the situation, the patient could not complete simulation. Thus, after he was confirmed to still have locoregionally limited disease, we proposed creation of a 3D-printed cradle for the back of his head and neck, based on CT imaging without immobilization. Three separate attempts were made to complete the printing of the cradle. Major issues stemmed from the need to find a set of support structures that would allow for the proper printing of the area supporting the ears, as well as the back of the head. Ultimately, a dense array of column supports was successful, but still required buttressing of the columns with tape at several points during the print. In total, 664g of polylactic acid filament was used, as well as 525g of polyvinyl alcohol, a water soluble support material. Total print time was just under 78 hours for the final successful print. <h3>Results</h3> The patient was able to tolerate simulation and the full course of fractionated chemoradiotherapy. The cradle provided for a setup requiring mean absolute shift of 0.35 mm in the anterior-posterior direction, 0.17 cm in the cranio-caudal direction, and 0.36 cm in the lateral direction, and a couch kick of 1.28 degrees to bring the patient into alignment on final imaging. The patient is currently in stable condition and following up with both medical oncology and radiation oncology at regular intervals. Imaging and laryngoscopy, conducted at multiple time points following completion, shows him to have no evidence of disease, now at 10 months. <h3>Conclusion</h3> The full uses of 3D printing are still developing, as evidenced by the difficulty of creating a workable print, both in terms of prototyping and the time needed to create a print. The impact of 3D printing within the context of radiation oncology, as well as in other specialties, will undoubtedly continue to increase the variety of viable treatment options available to patients as the technology improves.

A Comparative Study Between AI-Generated, Real-Life Clinical as Well as Reference Rectal Volumes Defined in Accordance With the Swedish National STRONG Guidelines in Prostate Cancer Radiotherapy

Successful delivery of radiotherapy (RT) relies on correct and consistent definition of organs at risk (OAR). Artificial intelligence (AI) auto-segmentation based on deep learning (DL) is emerging as a means to reduce variability of OARs. Knowledge about how auto-segmentation tools perform on standardized datasets is limited. Our aim is to evaluate the quality of rectal volumes defined by an existing DL auto-contouring algorithm on a standardized dataset for rectal volumes in prostate cancer RT as proposed by the Swedish STRONG guidelines for male pelvis [1][2][3]. [1] Olsson et al. PhIRO 2019:11:88 [2] Gay et al. IJROBP 2012:83:e353 [3] Salembier et al. RO 2018:127:49 MATERIALS/METHODS: DICOM-RT datasets for 19 patients extracted from a treatment planning system at one institution in Sweden was used. The patients were treated for prostate cancer in 2018-2019 using 15 MV photon beams to total doses of 50-70Gy@2-3Gy/fraction. Rectal volumes were defined on planning CT images clinically (clinical), according to proposed standard (reference), and auto-contoured using the existing version of the MVision software. The degree of variation between volumes was investigated. Statistics included dose volume histogram metrics, the Jaccard index, and the Dice similarity coefficient with comparisons between groups based on hypothesis testing with a two-sided P-value≤0.05 indicating a statistically significant difference.The clinical and the MVision DVH points were in general closer to each other than to the points of the reference DVH. Clinical and MVision volumes were also somewhat larger than the reference volume (83cc and 84cc versus 80cc; P > > 0.05). Overall, mean doses were 0.8/0.9Gy lower for clinical/MVision compared with the reference (21.9 ± 5.1/21.8 ± 5.1Gy versus 22.7 ± 5.9Gy; P > > 0.05) whilst maximum doses were similar for all (67.8-67.9 ± 4.3). Both overlap metrics were similar for volume comparisons between MVision and reference and for MVision and clinical but somewhat higher for clinical and reference (Jaccard index/Dice coefficient: 0.74/0.85 versus 0.73/0.83 versus 0.90/0.95, respectively). Differences were primarily found in cranio-caudal direction between any two data sets.This is the first systematic comparison of an auto-contouring algorithm's performance on a standardized OAR dataset in RT. Our results need to be confirmed on a larger patient cohort, but indicate that the MVision algorithm did very well since the size of identified differences generally was small both with respect to clinical and to reference volumes. However, to increase the use of AI-algorithms for clinical studies and research, retraining them on standardized reference datasets has the potential to improve performance further.

Mid-Treatment Intrafraction Motion Assessment During LINAC-Based Stereotactic Radiosurgery: A Single Institution Experience of Over 600 Treatments

Intrafraction motion, if not mitigated, may pose a significant challenge to the delivery of frameless intracranial stereotactic radiosurgery. The current study presents a 7-year mid-treatment intrafraction motion assessment experience on 300 patients treated with a relocatable mask system.668 lesions, each treated using a mono-isocentric technique, comprised the current retrospective analysis from April 2012 to April 2019. Patient immobilization was by means of a 3-point hybrid thermoplastic mask system (Orfit industries). Orthogonal stereoscopic were acquired pre-beam and approximately mid-way through each treatment session, and at the same nominal 0° couch angle, for intrafraction motion assessment on a six-degree of freedom robotically actuated couch system.Mean/median time between each stereoscopic image pair was 6.05/6.10 s (SD = 1.10; range: 3.90-7.98). Mean/median translational motion (SD) was 0.19/0.12 mm (max = 1.97; SD = 0.22), 0.25/0.17 mm (max = 1.99; SD = 0.27), and 0.24/0.16 mm (max = 2.24; SD = 0.27) in the antero-posterior, cranio-caudal and medio-lateral directions, respectively. Mean/median 3D displacement 0.46/0.35 mm (max = 2.31; SD = 0.39). Mean/median rotational was 0.20/0.16o (max = 1.11; SD = 0.17), 0.15/0.10o (max = 1.09; SD = 0.16), and 0.21/0.14o (max = 2.07; SD = 0.24) in the yaw, roll and pitch directions, respectively. Frequencies of 2D and 3D intrafraction translational motion exceeding 1 mm/1.5 mm/2 mm were 5.24%/1.50%/0.15% and 7.78%/3.14%/1.20%, respectively. Rotational motion greater than 1o/1.5o/2o were 1.95%/0.60%/0.15%, respectively. No correlation between laterality/anatomic location/time vs. intrafraction motion was observed (P > 0.1).Mid-treatment intrafraction motion assessment revealed 1 mm or greater shift in 3D for 7.78% of cases. This frequency was small, but non-trivial. Our findings have implications on PTV margin setting and underscore the importance of intrafraction motion monitoring.R. Boopathy: None. C.M. Kato: None. K. Gallagher: None. J.J. Jaboin: None. C. Kubicky: None. C.M. Marquez: None. M. Fuss: None. J.A. Tanyi: None.

Heart-Sparing Capability and Reproducibility of Continuous Positive Airway Pressure (CPAP) in Left-Sided Breast Radiation Therapy

<h3>Purpose/Objective(s)</h3> CPAP is a novel method to avoid heart radiation exposure during radiation therapy, recently proposed as an alternative to the current standard-of-care deep inspiration breath-hold technique. In this study, the heart dose, inter- and intrafraction motions in CPAP-based treatment were investigated. <h3>Materials/Methods</h3> A retrospective study on heart dose level and CPAP compliance included 237 left-sided breast cancer patients treated with CPAP-based VMAT in hypofractionation (with (n = 116) and without (n = 105) internal mammary node irradiation (IMNI)) between June 2020 and January 2021. During simulation, CT was obtained with free breathing (FB) and CPAP. For each treatment fraction, CBCT was acquired to confirm geometric accuracy within 3 mm tolerance. Two different datasets were used for reproducibility evaluations. Dataset 1: interfraction reproducibility was evaluated by measuring heart-to-PTV distance (MinHD), defined as the minimum distance between the line posteriorly tangential to the PTV and the heart, on 300 CBCT and 20 planning CT data of 20 women. Using dataset 1, heart-sparing effect was further explored by comparing dosimetric metrics of the whole heart and its substructures (e.g., atrium, ventricles, and vessels) between CPAP- and FB-based VMAT plans. Dataset 2: intrafraction reproducibility was evaluated in 20 women who were treated for different malignancies and underwent 4D CT with CPAP. <h3>Results</h3> Among 237 patients recruited, the CPAP compliance was 93% with a mean heart dose of 1.6 ± 0.7 Gy (no IMNI, 1.1 Gy; IMNI 2.0 Gy). The use of CPAP during treatment did not require additional time resource. The analysis of dataset 1 (i.e., total of 300 CBCT and 20 planning CT images) showed small variations of MinHD (0.6 ± 0.2 cm), demonstrating a reasonable agreement of the heart-to-PTV distance between the planning CT and CBCTs (MinHD difference < 0.2 cm, on average, for all patients). Compared with FB, the use of CPAP significantly reduced the mean heart dose (2.1 to 1.7 Gy), the mean dose to the left ventricle, the maximum dose to the left anterior descending artery, and the mean lung dose by 21%, 23%, 36%, and 23%, respectively. In dataset 2, the breast surface motion amplitude was 0.5 ± 0.5, 2.5 ± 2.0, and 1.8 ± 1.4 mm across the patients in the mediolateral, craniocaudal, and anteroposterior directions, respectively, and exceeded 5 mm for only two patients. <h3>Conclusion</h3> To the best of our knowledge, this is the first and largest study to evaluate the heart-sparing capability and reproducibility of CPAP-based VMAT for left-sided breast cancer treatment. A large population study confirmed a reasonably low irradiation to the heart with CPAP. This heart-sparing effect can be consistent across treatment fractions as demonstrated in sub-centimeter reproducibility of the heart position. For most of the women, the intrafraction breast motion with CPAP was minimal.

Minimizing the need for coil attenuation correction in integrated PET/MRI at 1.5 T using low-density MR-linac receive arrays

The simultaneous use of positron emission tomography (PET) and magnetic resonance imaging (MRI) requires attenuation correction (AC) of photon-attenuating objects, such as MRI receive arrays. However, AC of flexible, on-body arrays is complex and therefore often omitted. This can lead to significant, spatially varying PET signal losses when conventional MRI receive arrays are used. Only few dedicated, photon transparent PET/MRI arrays exist, none of which are compatible with our new, wide-bore 1.5 T PET/MRI system dedicated to radiotherapy planning. In this work, we investigated the use of 1.5 T MR-linac (MRL) receive arrays for PET/MRI, as these were designed to have a low photon attenuation for accurate dose delivery and can be connected to the new 1.5 T PET/MRI scanner. Three arrays were assessed: an 8-channel clinically-used MRL array, a 32-channel prototype MRL array, and a conventional MRI receive array. We experimentally determined, simulated, and compared the impact of these arrays on the PET sensitivity and image reconstructions. Furthermore, MRI performance was compared. Overall coil-induced PET sensitivity losses were reduced from 8.5% (conventional) to 1.7% (clinical MRL) and 0.7% (prototype MRL). Phantom measurements showed local signal errors of up to 32.7% (conventional) versus 3.6% (clinical MRL) and 3.5% (prototype MRL). Simulations with data of eight cancer patients showed average signal losses were reduced from 14.3% (conventional) to 1.2% (clinical MRL) and 1.0% (prototype MRL). MRI data showed that the signal-to-noise ratio of the MRL arrays was slightly lower at depth (110 versus 135). The parallel imaging performance of the conventional and prototype MRL arrays was similar, while the clinical MRL array’s performance was lower. In conclusion, MRL arrays reduce in-vivo PET signal losses >10×, which decreases, or eliminates, the need for coil AC on a new 1.5 T PET/MRI system. The prototype MRL array allows flexible coil positioning without compromising PET or MRI performance. One limitation of MRL arrays is their limited radiolucent PET window (field of view) in the craniocaudal direction.

Intra-fraction motion monitoring during fast modulated radiotherapy delivery in a closed-bore gantry linac.

New closed-bore linacs allow for highly streamlined workflows and fast treatment delivery resulting in brief treatment sessions. Motion management technology has only recently been integrated inside the bore, yet is required in future online adaptive workflows. We measured patient motion during every step of the workflow: image acquisition, evaluation and treatment delivery using surface scanning. Nineteen patients treated for breast, lung or esophageal cancer were prospectively monitored from the end of setup to the end of treatment delivery in the Halcyon linac (Varian Medical Systems). Motion of the chest was tracked by way of 6 degrees-of-freedom surface tracking. Baseline drift and rate of drift were determined. The influence of fraction number, patient and fraction duration were analyzed with multi-way ANOVA. Median fraction duration was 4min 48 s including the IGRT procedure (kV-CBCT acquisition and evaluation) (N=221). Baseline drift at the end of the fraction was -1.8±1.5mm in the anterior-posterior, -0.0±1.7mm in the cranio-caudal direction and 0.1±1.8mm in the medio-lateral direction of which 75% occurred during the IGRT procedure. The highest rate of baseline drift was observed between 1 and 2min after the end of patient setup (-0.62mm/min). Baseline drift was patient and fraction duration dependent (p<0.001), but fraction number was not significant (p=0.33). Even during short treatment sessions, patient baseline drift is not negligible. Drift is largest during the initial minutes after completion of patient setup, during verification imaging and evaluation. Patients will need to be monitored during extended contouring and re-planning procedures in online adaptive workflows.

Quantitative assessment of the vertebral pneumaticity in an anhanguerid pterosaur using micro-CT \ufeffscanning

Research on the postcranial skeletal pneumaticity in pterosaurs is common in the literature, but most studies present only qualitative assessments. When quantitative, they are done on isolated bones. Here, we estimate the Air Space Proportion (ASP) obtained from micro-CT scans of the sequence from the sixth cervical to the fourth dorsal vertebra of an anhanguerine pterosaur to understand how pneumaticity is distributed in these bones. Pneumatisation of the vertebrae varied between 68 and 72% of their total volume. The neural arch showed higher ASP in all vertebrae. Anhanguerine vertebral ASP was generally higher than in sauropod vertebrae but lower than in most extant birds. The ASP observed here is lower than that calculated for the appendicular skeleton of other anhanguerian pterosaurs, indicating the potential existence of variation between axial and appendicular pneumatisation. The results point to a pattern in the distribution of the air space, which shows an increase in the area occupied by the trabecular bone in the craniocaudal direction of the vertebral series and, in each vertebra, an increase of the thickness of the trabeculae in the zygapophyses. This indicates that the distribution of pneumatic diverticula in anhanguerine vertebrae may not be associated with stochastic patterns.

Baş-Boyun ve Beyin Tümörü IMRT Uygulamasında Vakumlu Boyun Yastığı (VBY)’ nın Set Up Doğruluğuna Katkısı

Aim: An effective immobilization is warranted to minimize set up deviations while treating head &amp;amp; neck (HN) and brain tumors with intensity modulated radiotherapy (IMRT). In this study we evaluated the effectiveness of thermoformable vacuum head cushion (TVHC) on immobilization of these patients via weekly electronic digital port films (EDPF). Material and Method: Twenty patients treated with IMRT for HN and Brain tumors were enrolled in the study. Thermoplastic mask with additional standard plastic head rest (n:10) in Group A or TVHC supporting the head and neck region (n:10) in Group B were used for immobilization. Weekly EDPF images were obtained on the linear accelerator. Set-up displacements in latero-medial, anteroposterior and cranio-caudal directions in these images were compared with variation data of first treatment. Results: When each group was analyzed in terms of deviations in all 3 directions, deviations calculated in anteroposterior and craniocaudal directions were significantly higher for TVHC group (p:0.039 and p:0.002 respectively). Deviations &amp;gt;4mm in all three directions were also analyzed and similarly, higher rates of &amp;gt;4mm deviations were recorded for TVHC group in anteroposterior and craniocaudal directions (p:0.023 and p:&amp;lt;0.001 respectively) which of both were also statistically significant. Conclusion: We found that TVHC utilization in HN and brain IMRT for immobilization leads to significantly higher set-up deviations so future investigations with larger patient populations and evaluating set up accuracy via more sensitive alignments are needed to suggest TVHC for utilization in daily clinical practice.

Direct visualization and correlation of liver stereotactic body radiation therapy treatment delivery accuracy with interfractional motion.

This study used the visualization of hypo‐intense regions on liver‐specific MRI to directly quantify stereotactic body radiation therapy (SBRT) spatial delivery accuracy. Additionally, the interfractional motion of the liver region was determined and compared with the MRI‐based evaluation of liver SBRT spatial treatment delivery accuracy. Primovist®‐enhanced MRI scans were acquired from 17 patients, 8–12 weeks following the completion of liver SBRT treatment. Direct visualization of radiation‐induced focal liver reaction in the form of hypo‐intensity was determined. The auto‐delineation approach was used to localize these regions, and center‐of‐mass (COM) discrepancy was quantified between the MRI hypo‐intensity and the CT‐based treatment plan. To assess the interfractional motion of the liver region, a planning CT was registered to a Cone Beam CT obtained before each treatment fraction. The interfractional motion assessed from this approach was then compared against the localized hypo‐intense MRI regions. The mean ± SD COM discrepancy was 1.4 ± 1.3 mm in the left‐right direction, 2.6 ± 1.8 mm in an anteroposterior direction, and 1.9 ± 2.6 mm in the craniocaudal direction. A high correlation was observed between interfractional motion of visualized hypo‐intensity and interfractional motion of planning treatment volume (PTV); the quantified Pearson correlation coefficient was 0.96. The lack of correlation was observed between Primovist® MRI‐based spatial accuracy and interfractional motion of the liver, where Pearson correlation coefficients ranged from −0.01 to −0.26. The highest random and systematic errors quantified from interfractional motion were in the craniocaudal direction. This work demonstrates a novel framework for the direct evaluation of liver SBRT spatial delivery accuracy.

Organ motion in linac-based SBRT for glottic cancer

PurposeThe purpose of this study is to evaluate inter- and intra-fraction organ motion as well as to quantify clinical target volume (CTV) to planning target volume (PTV) margins to be adopted in the stereotactic treatment of early stage glottic cancer.Methods and materialsStereotactic body radiotherapy (SBRT) to 36 Gy in 3 fractions was administered to 23 patients with early glottic cancer T1N0M0. Patients were irradiated with a volumetric intensity modulated arc technique delivered with 6 MV FFF energy. Each patient underwent a pre-treatment cone beam computed tomography (CBCT) to correct the setup based on the thyroid cartilage position. Imaging was repeated if displacement exceeded 2 mm in any direction. CBCT imaging was also performed after each treatment arc as well as at the end of the delivery. Swallowing was allowed only during the beam-off time between arcs. CBCT images were reviewed to evaluate inter- and intra-fraction organ motion. The relationships between selected treatment characteristics, both beam-on and delivery times as well as organ motion were investigated.ResultsFor the population systematic (Ʃ) and random (σ) inter-fraction errors were 0.9, 1.3 and 0.6 mm and 1.1, 1.3 and 0.7 mm in the left-right (X), cranio-caudal (Y) and antero-posterior (Z) directions, respectively. From the analysis of CBCT images acquired after treatment, systematic (Ʃ) and random (σ) intra-fraction errors resulted 0.7, 1.6 and 0.7 mm and 1.0, 1.5 and 0.6 mm in the X, Y and Z directions, respectively. Margins calculated from the intra-fraction errors were 2.4, 5.1 and 2.2 mm in the X, Y and Z directions respectively. A statistically significant difference was found for the displacement in the Z direction between patients irradiated with > 2 arcs versus ≤ 2 arcs, (MW test, p = 0.038). When analyzing mean data from CBCT images for the whole treatment, a significant correlation was found between the time of delivery and the three dimensional displacement vector (r = 0.489, p = 0.055), the displacement in the Y direction (r = 0.553, p = 0.026) and the subsequent margins to be adopted (r = 0.626, p = 0.009). Finally, displacements and the subsequent margins to be adopted in Y direction were significantly greater for treatments with more than 2 arcs (MW test p = 0.037 and p = 0.019, respectively).ConclusionsIn the setting of controlled swallowing during treatment delivery, intra-fraction motion still needs to be taken into account when planning with estimated CTV to PTV margins of 3, 5 and 3 mm in the X, Y and Z directions, respectively. Selected treatments may require additional margins.