Median Target Research Articles

Point estimation in sign-restricted SVARs based on independence criteria with an application to rational bubbles

The median and median target estimates in sign-restricted SVARs are driven by a highly informative prior for the set-identified structural parameters. This paper proposes an approach for point elicitation by minimizing the evidence against the null hypothesis of independence with respect to the orthogonalized residuals implied by the identified set. Finite sample properties of the estimator are studied in a Monte Carlo experiment. As an empirical illustration, we analyze monetary policy effects within the rational bubble model of equity valuation (Galí, 2014). The detected monetary policy shocks lead to distinct response profiles of the fundamental and bubble components of asset prices.

Conventionally fully fractionated Gamma Knife Icon re-irradiation of primary recurrent intracranial tumors: the first report indicating feasibility and safety.

With the incorporation of real-time image guidance on the Gamma Knife system allowing for mask-based immobilization (Gamma Knife Icon [GKI]), conventionally fully fractionated (1.8-3.0 Gy/day) GKI radiation can now be delivered to take advantage of an inherently minimal margin for delivery uncertainty, sharp dose falloff, and inhomogeneous dose distribution. This case series details the authors' preliminary experience in re-irradiating 7 complex primary intracranial tumors, which were considered to have been previously maximally radiated and situated adjacent to critical organs at risk. The authors retrospectively reviewed all patients who received fractionated re-irradiation using GKI at the Sunnybrook Health Sciences Centre, University of Toronto, Ontario, Canada, between 2016 and 2021. Patients with brain metastases, and those who received radiotherapy courses in 5 or fewer fractions, were excluded. All radiotherapy doses were converted to the equivalent total dose in 2-Gy fractions (EQD2), with the assumption of an α/β ratio of 2 for late normal tissue toxicity and 10 for the tumor. A total of 7 patients were included in this case series. Three patients had recurrent meningiomas, as well as 1 patient each with ependymoma, intracranial sarcoma, pituitary macroadenoma, and papillary pineal tumor. Six patients had undergone prior linear accelerator-based conventional fractionated radiotherapy and 1 patient had undergone prior proton therapy. Patients were re-irradiated with a median (range) total dose of 50.4 (30-63.4) Gy delivered in a median (range) of 28 (10-38) fractions with GKI. The median (range) target volume was 6.58 (0.2-46.3) cm3. The median (range) cumulative mean EQD2 administered to the tumor was 121.1 (107.9-181.3) Gy, and the median (range) maximum point EQD2 administered to the brainstem, optic nerves, and optic chiasm were 91.6 (74.0-111.5) Gy, 58.9 (6.3-102.9) Gy, and 59.9 (36.7-127.3) Gy, respectively. At a median (range) follow-up of 15 (6-42) months, 6 of 7 patients were alive with 4 having locally controlled disease. Only 3 patients experienced treatment-related toxicities, which were self-limited. Fractionated radiotherapy using GKI may be a safe and effective method for the re-irradiation of complex progressive primary intracranial tumors, where the aim is to minimize the potential for serious late effects.

Hypofractionated stereotactic radiosurgery (HSRS) as a salvage treatment for brain metastases failing prior stereotactic radiosurgery (SRS)

Various treatment options exist to salvage stereotactic radiosurgery (SRS) failures for brain metastases, including repeat SRS and hypofractionated SRS (HSRS). Our objective was to report outcomes specific to salvage HSRS for brain metastases that failed prior HSRS/SRS. Patients treated with HSRS to salvage local failures (LF) following initial HSRS/SRS, between July 2010 and April 2020, were retrospectively reviewed. The primary outcomes were the rates of LF, radiation necrosis (RN), and symptomatic radiation necrosis (SRN). Univariable (UVA) and multivariable (MVA) analyses using competing risk regression were performed to identify predictive factors for each endpoint. 120 Metastases in 91 patients were identified. The median clinical follow up was 13.4 months (range 1.1-111.1), and the median interval between SRS courses was 13.1 months (range 3.0-56.5). 115 metastases were salvaged with 20-35Gy in 5 fractions and the remaining five with a total dose ranging from 20 to 24Gy in 3-fractions. 67 targets (56%) were postoperative cavities. The median re-treatment target volume and biological effective dose (BED10) was 9.5cc and 37.5Gy, respectively. The 6- and 12- month LF rates were 18.9% and 27.7%, for RN 13% and 15.6%, and for SRN were 6.1% and 7.0%, respectively. MVA identified larger re-irradiation volume (hazard ratio [HR] 1.02, p = 0.04) and shorter interval between radiosurgery courses (HR 0.93, p < 0.001) as predictors of LF. Treatment of an intact target was associated with a higher risk of RN (HR 2.29, p = 0.04). Salvage HSRS results in high local control rates and toxicity rates that compare favorably to thosesingle fraction SRS re-irradiationexperiences reported in the literature.

Enhanced Recognition Confidence of Millimeter-Sized Intrahepatic Targets by Real-Time Virtual Sonography.

Real-time virtual sonography (RVS) is an artificial-intelligence-assisted ultrasonographic navigation system that displays synchronized preoperative computed tomography (CT) images corresponding to real-time intraoperative ultrasonograms (IOUS). This study aimed to investigate whether RVS can enhance IOUS identification of small intrahepatic targets found in preoperative CT. Patients with small intrahepatic targets detected by preoperative thin-slice dynamic CT before liver resection were included. The targets included millimeter-sized liver tumors or a third-order or more distal portal branch and were marked on CT images using 3D simulation software. After laparotomy, the targets were searched using fundamental IOUS, and participating liver surgeons subjectively scored the target identifying confidence on a scale of 1-5 (5 points for detection with the highest confidence and one point for undetectable). Then, the search procedure was repeated using the RVS, and the scores were compared. Totally, 55 patients with 117 small targets were investigated. The median target size was 6.0 mm, and the median registration time was 3.6 seconds. The target identification confidence score significantly increased from 2.78 to 4.52 points after using RVS. Seventeen targets (14.5%) were undetectable in fundamental IOUS, and 14 of them were identified by RVS. The detectability of small liver tumors (2-5 points of identification confidence) by IOUS was 81.1 and 96.7% by RVS. RVS enhanced surgeons' confidence in identifying millimeter-sized intrahepatic targets found in preoperative CT.

Non-invasive stereotactic arrhythmia radiotherapy for ventricular tachycardia: results of the prospective STARNL-1 trial.

Stereotactic arrhythmia radiotherapy (STAR) is suggested as potentially effective and safe treatment for patients with therapy-refractory ventricular tachycardia (VT). However, the current prospective knowledge base and experience with STAR is limited. In this study we aimed to prospectively evaluate the efficacy and safety of STAR. The StereoTactic Arrhythmia Radiotherapy in the Netherlands no.1 was a pre-post intervention study to prospectively evaluate efficacy and safety of STAR. In patients with therapy-refractory VT, the pro-arrhythmic region was treated with a 25 Gy single radiotherapy fraction. The main efficacy measure was a reduction in the number of treated VT-episodes by ≥50%, comparing the 12 months before and after treatment (or end of follow-up, excluding a 6-week blanking period). The study was deemed positive when ≥50% of patients would meet this criterion. Safety evaluation included left ventricular ejection fraction, pulmonary function, and adverse events. Six male patients with an ischaemic cardiomyopathy were enrolled, and median age was 73 years (range 54-83). Median left ventricular ejection fraction was 38% (range 24-52). The median planning target volume was 187 mL (range 93-372). Four (67%) patients completed the 12-month follow-up, and two patients died (not STAR related) during follow-up. The main efficacy measure of ≥50% reduction in treated VT-episodes at the end of follow-up was achieved in four patients (67%). The median number of treated VT-episodes was reduced by 87%. No reduction in left ventricular ejection fraction or pulmonary function was observed. No treatment related serious adverse events occurred. STAR resulted in a ≥ 50% reduction in treated VT-episodes in 4/6 (67%) patients. No reduction in cardiac and pulmonary function nor treatment-related serious adverse events were observed during follow-up. Netherlands Trial Register-NL7510.

Oncologic outcomes after MRI-assisted image-guided brachytherapy with hybrid interstitial and intra-cavitary applicators under moderate sedation for locally advanced cervix cancer.

To report outcomes of using image-guided hybrid intra-cavitary/interstitial applicators under moderate sedation for locally advanced cervical cancer patients in our institution. A total of 69 fractions of brachytherapy with hybrid applicators were performed in 33 patients from January 2017 to April 2021. All patients underwent MRI pelvis 1 week pre-brachytherapy to determine suitability for interstitial brachytherapy and pre-plan needle placement. All insertion of applicators were performed under moderate sedation with midazolam and/or fentanyl. Fifty-eight (84.1%) fractions were planned with CT alone. Clinical outcomes, dose volume parameters, and toxicities were analyzed. The median follow-up was 28 months. A total of 320 needles (median, 5 needles per fraction) were implanted, with a median insertion depth of 3 cm (range, 1.5-4 cm). The median high-risk clinical target volume (HR-CTV) during initial brachytherapy was 34.5 cc (range, 17.8-74.7 cc). The median total EQD2 D2cc of the rectum, bladder, sigmoid, and small intestine colon was 71.8 Gy, 81.5 Gy, 69 Gy, and 58.3 Gy, respectively. The 2-year local control and overall survival were 80.7% and 77.7%, respectively. Larger volume HR-CTV was significantly associated with worse local control (HR = 1.08, p = 0.005) and overall survival (HR = 1.04, p = 0.015). None of the patients required in-patient admission or blood transfusion post-procedure. Late grade 3 gastrointestinal and genitourinary toxicities were observed in 4 patients (12.2%). Hybrid applicators inserted under moderate sedation are feasible and safe. Image-guided interstitial brachytherapy with CT planning aided by MRI performed 1 week pre-brachytherapy is associated with favorable outcomes and modest toxicities.

Results of hypofractionated stereotactic radiotherapy for resected and intact large brain metastases

To compare the results of post-resection or isolated HF-SRT in patients with LBMs. A prospective study included 115 patients with 129 intact LBMs and 133 patients with 149 resected LBMs who underwent HF-SRT. Median baseline focal size was 22.5 and 28 mm, median target volume - 8.3 and 23.7 cm3, respectively. Median follow-up was 13.9 months, median overall survival - 19.1 months. After 12 months, local recurrences developed in 17 and 31% of patients, respectively (p=0.0078). Local recurrence after 12 months developed in 23% of patients with residual tumor in postoperative cavity compared to 16% of patients after total resection (p=0.0073). After 12 months, incidence of leptomeningeal progression was 27 and 11%, respectively (p=0.033), incidence of symptomatic radiation-induced necrosis - 4 and 23%, respectively (p=0.0006). Post-resection HF-SRT demonstrated better local control and less severe symptomatic radiation-induced necrosis compared to patients with intact LBMs. Incidence of leptomeningeal progression is significantly higher after resection of LBMs.

619. Pharmacokinetic-Pharmacodynamic (PK-PD) Target Attainment Analyses to Support Epetraborole Dose Selection for the Treatment of Patients with Mycobacterium avium Complex (MAC) Lung Disease

619. Pharmacokinetic-Pharmacodynamic (PK-PD) Target Attainment Analyses to Support Epetraborole Dose Selection for the Treatment of Patients with <i>Mycobacterium avium</i> Complex (MAC) Lung Disease

Early Toxicity and Patient-Reported Cosmetic Outcomes in Patients Treated With Adjuvant Proton-Based Radiotherapy After Breast-Conserving Surgery

IntroductionTo evaluate the dosimetric data, early toxicity, and patient-reported cosmetic outcomes in breast cancer patients treated with adjuvant proton-based radiotherapy (RT) after breast-conserving surgery. Materials and MethodsWe performed a retrospective review of our institutional database to identify breast cancer patients treated with breast-conserving surgery followed by proton-based RT from 2015 to 2020. Patient-reported cosmetic outcomes were graded as excellent, good, fair, or poor. Early toxicity outcomes were graded by the treating physician during treatment. Dose-volume histograms were reviewed to obtain dosimetry data. ResultsWe identified 21 patients treated with adjuvant proton-based RT. Median whole breast dose delivered was 46.8 Gy (range, 40.0-50.4 Gy). Target volumes included the regional lymph nodes in 17 patients (81%). Seventeen patients (81%) received a lumpectomy boost. The median planning target volume V95 was 94% (range, 77%-100%), V100 71% (range, 60%-97%), V110 2% (range 0%-18%), and median max point dose was 115% (range, 105%-120%). The median ipsilateral breast V105 was 367.3 cc (range, 0-1172 cc) and V110 was 24.1 cc (range, 0-321.3 cc). Grade 2 and 3 dermatitis occurred in 62% and 14% of patients, respectively. Grade 2 and 3 pain was reported by 33% and 10% of patients, respectively. Median follow-up at the time of cosmetic evaluation was 27 months (range, 5-42 months). Four patients (21%) reported fair cosmetic outcome and 15 patients (79%) reported good or excellent cosmetic outcome. No poor cosmesis was reported. ConclusionAdjuvant proton-based radiotherapy after breast-conserving surgery is well tolerated with acceptable rates of acute toxicities and a high rate of good-to-excellent patient-reported cosmetic outcomes.

Efficacy and safety of lifileucel, a one-time autologous tumor-infiltrating lymphocyte (TIL) cell therapy, in patients with advanced melanoma after progression on immune checkpoint inhibitors and targeted therapies: pooled analysis of consecutive cohorts of the C-144-01 study

BackgroundPatients with advanced melanoma have limited treatment options after progression on immune checkpoint inhibitors (ICI). Lifileucel, a one-time autologous tumor-infiltrating lymphocyte (TIL) cell therapy, demonstrated an investigator-assessed objective response rate...

Through an Ice Sheet, Darkly

Through an Ice Sheet, Darkly

Dosimetric comparison of volumetric modulated arc therapy with TrueBeam LINAC and hypofractionated radiosurgery with gamma knife ICON for large (>10 cm3) skull base meningiomas.

Multi Fractionated stereotactic radiosurgery (MF-SRS) of Linac has an essential role in the treatment of skull base meningiomas (sbMNG). However, Gamma Knife Icon (GK) allows MF-SRS using mask immobilization with onboard image guidance. This dosimetric study aims to investigate whether equivalent plan quality can be achieved with Volumetric Modulated Arc Therapy (VMAT) in patients with large sbMNG (>10 cm3) previously treated with GK. Twenty patients with the median target volume of 19.7cm3 are re-planned by using VMAT with 20 Gy in 5 fractions. Plan qualities are compared to tumor coverage, paddick conformity index (PCI), gradient index (GI), V4 Gy, V10 Gy, V12 Gy, optic chiasm V20 Gy, brainstem V23 Gy, optic nerve V25 Gy volumes, and maximum doses for all. Additionally, beam-on time and approximate planning time are also analyzed and compared. All plans provide adequate clinical requirements. First, the CI is comparable for the GK and VMAT (0.99±0.01 vs. 1.13±0.20; p = 0.18). Second, VMAT has a significantly higher GI than GK (3.81±0.35 vs. 2.63±0.09; p < 0.001). Third, the PCI is significantly higher in GK than VMAT (0.76±0.05 vs. 0.70±0.07; p < 0.001). The lower GI of the GK also results in significantly lower V4 Gy (156.1±43.8 vs. 207.5±40.1 cm3, p < 0.001) and V10 Gy (26.1±9.0 vs. 28.9±7.7 cm3, p < 0.001) compared to VMAT. Last, the VMAT reduces beam-on time (4.8±0.5 vs. 19±1.1 min.; p < 0.001). Although both systems have succeeded in creating effective plans in clinical practice, the GK reveals more effective lower normal brain tissue doses. However, the shorter treatment time with LINAC, excluding the total procedure time, can be considered advantageous over GK.

Effective clinical applications of Monte Carlo-based independent secondary dose verification software for helical tomotherapy

PurposeTo investigate the scope of the effective clinical application of Monte Carlo (MC)-based independent dose verification software for helical tomotherapy. MethodsDoseCHECK was selected as the MC-based dose calculation software. First, the dose calculation accuracy of DoseCHECK was evaluated with film and chamber measurements in a water-equivalent phantom. Second, the dose calculation accuracy was examined in several heterogeneous materials. Finally, dosimetric comparisons between DoseCHECK and the treatment planning system (TPS) were performed for clinical patient plans. Prostate IMRT, head and neck IMRT (HN), total body irradiation (TBI), and brain stereotactic radiotherapy (SRT) were evaluated. ResultThe DoseCHECK calculations agreed with the chamber and film measurements in the homogenous phantom. For heterogeneous phantom cases, the dose differences between DoseCHECK and TPS were within 3 %, except in air, in which large dose differences of 20 % were observed. In clinical patient plans, the median dose differences between the lung Dmean in TBI cases and the normal brain Dmean in brain SRT cases were significantly >3 %. For HN and brain SRT cases, the median target dose differences were >3 %. ConclusionOur results show that independent dose verification with the MC algorithm can detect systematic errors caused by the lack of heterogeneity correction in the TPS. In particular, MC-based independent dose verification is required for HN, TBI, and brain SRT cases in helical tomotherapy.

RADT-39. STAGED GAMMA KNIFE STEREOTACTIC RADIOSURGERY FOR LARGE INTACT AND RESECTED BRAIN TUMORS; THE MUSC EXPERIENCE

Abstract Stereotactic radiosurgery (SRS) is a well-established treatment modality for management of both benign and malignant central nervous tumors. One limiting factor in the use of SRS is tumor size. Staged radiosurgery treatment is an option to utilize this treatment modality while still limiting associated toxicity. This involves treating each target in 2 separate sessions, spaced apart by approximately 30 days. We describe a series of 17 patients with 20 unique lesions treated using this technique in our department from January of 2019 through December of 2021. 18 treated lesions were malignant brain metastases and 2 were meningiomas. For 13 lesions, SRS was the primary treatment, and for 7 lesions, SRS was adjuvant treatment after surgery. The median target size for fraction 1 was 18.40 cm^3 with a median dose of 12.65 Gy. The median target size for fraction 2 was 14.50 cm^3 with a median dose of 12.08 Gy. All but one target was prescribed to the 50% isodose line. Median follow up was 7.12 months. Local control at the site of treated lesions was 90%. 3 patients with local control at the site of the fractionated treatment were noted to have additional progression within the CNS. There were 2 patient deaths within 30 days of treatment. One death was due to respiratory failure. The other cause of death was unknown. Treatment was well tolerated with no grade 3 or higher acute toxicity. 50% of patients went on to receive additional systemic therapy. 55% of patients are known to have died at the time of latest follow up. Overall, staged gamma knife radiosurgery appears to be an effective option for treating both intact and resected tumors with an acceptable toxicity profile.

Volume staging for arteriovenous malformation SRS treatment using VMAT.

Volume staging involves dividing the target volume into smaller parts and treating each part separately. In this study, the feasibility of volume-staged stereotactic radiosurgery (VS-SRS) on a linear accelerator using volumetric modulated arc therapy (VMAT) and a frameless patient positioning system is investigated. Ten patients, previously treated with hypofractionated stereotactic radiotherapy with arteriovenous malformation (AVM) sized from 1.6 to 4.0cm in diameter, were selected. VS-SRS plans were created with the VMAT technique on the Varian Eclipse treatment planning system (TPS) using the TrueBeam STx linear accelerator. For each patient, an AVM-VMAT set was planned with the AVM as the target and a PTV-VMAT set using the (PTV=AVM+1mm) as the target. All targets were divided into two sub-volumes. The TPS data from the AVM-VMAT plans was compared to Gamma Knife (GK) VS-SRS plan data available in the literature. The AVM-VMAT and PTV-VMAT plans were compared to investigate the effect of a 1mm PTV margin on normal brain (NB) dose. End-to-end testing was performed using a GaFchromic EBT3 film and point-dose measurements. Dosimetric effects of multiple setups were investigated through film-to-film comparisons. Median target dose coverage, NB V12Gy , and conformity index for the AVM-VMAT plans were 97.5%, 17cm3 , and 0.8, respectively. PTV-VMAT plans attained comparable target dose coverage, but the average NB V12Gy increased by 48.9% when compared to the AVM-VMAT plans. Agreement of point-dose measurements with TPS calculations was -0.6% when averaged over all patients. Gamma analysis passing rates were above 90% for all film-to-film comparisons (2%/1mm criteria), and for the film to TPS comparison (5%/1mm). This work suggests that VMAT is capable of producing VS-SRS plans with similar dose falloff characteristics as GK plans. NB dose depends on PTV margin size, and two-stage treatment setups do not appear to contribute additional uncertainty to treatment delivery.

Abstract 15340: Association of Serum Lipoprotein (a) Levels and Lipid Burden by Near Infrared Spectroscopy in Intermediate Coronary Artery Disease

Introduction: The relationship between elevated lipoprotein (a) (Lp(a)) and poor prognosis in coronary artery disease (CAD) has been addressed for decades. However, data of mechanism of increased risk with plaque lipid burden has not been established. Hypothesis: This study aimed to investigate the association between Lp(a) and lipid burden in patients with intermediate CAD by Near Infrared Spectroscopy (NIRS). Methods: We retrospectively analyzed 128 patients with intermediate CAD who performed intravascular ultrasound (IVUS) during coronary angiography and checked Lp(a) level. The lipid core burden index (LCBI) for the 4-mm segments at the target lesion was calculated by NIRS. We divided the patients into 3 groups by calculating baseline Lp(a) tertile level. A mixed model adjusted for baseline sex, age, weight, pre-minimal luminal area, lesion length, apolipoprotein (Apo) E, Apo A1, Apo B100, total cholesterol, triglyceride, high density lipoprotein (HDL), low density lipoprotein (LDL), fasting glucose, past history, current medication including statin use was used to calculate the risk-adjusted target LCBI. Results: We enrolled 128 patients (60 years; male, 114; mean Lp(a) 21.03±20.84 mg/dl, Figure 1) and NIRS was taken in 90 patients among them. Mean and median target LCBI by NIRS were 78.4±60.3 and 62.0. Target LCBI significantly higher in the intermediate Lp(a) group than low Lp(a) group in risk-adjusted analyses (Lp(a)&lt;9; 45.7 versus 9≤Lp(a)&lt;19; 111.48, p =0.026, Table 1). However, between intermediate and high Lp(a) groups, there was no statistical difference (9≤Lp(a)&lt;19; 111.48 versus 19≤Lp(a); 86.41, p =0.774). Conclusions: Elevated Lp(a) level is independently associated with increased lipid burden of target lesion in intermediate CAD, and it’s important for treatment decision. Further investigation is needed to clarify the effect of Lp(a) in various type and severity of plaque.

Vestibular Schwannoma Hypofractionated Stereotactic Radiation Therapy in Five Fractions

AimTo retrospectively analyse the long-term results of hypofractionated stereotactic radiation therapy (HSRT) applied in five fractions for vestibular schwannomas. Materials and methodsOne hundred and thirty-four patients with vestibular schwannomas underwent medical treatment of HSRT. The median follow-up time interval was 54 months (range 6–121 months). All patients had a prescribed dose of 22 Gy in five fractions to D90. Restaging was carried out by thin-slice contrast-enhanced T1 magnetic resonance imaging. Progression was defined as 2 mm post-treatment tumour enlargement. Progression or death for any reason was counted as an event in progression-free survival rates. Acute toxicity was defined as adverse events occurring within 3 months of HSRT; long-term toxicity was defined as such events occurring after 3 months. ResultsIn 74/128 patients who had >6 months of follow-up (54%), the HSRT resulted in a partial or a complete response. The mean time interval for response in 50% of these was 4 years, whereas in 49 patients (38%) vestibular schwannomas failed to show any response, resulting in stable disease. Five of 128 patients (4%) showed marked progressive vestibular schwannomas after treatment in the first 3 years; two of them received conventionally fractionated radiation therapy. Local control at 3, 5 and 7 years was 96%, 95% and 94%, respectively. Seven were lost to follow-up. The median planning target volume was 2.1 ml (range 0.78–8.66). The 3- and 5-year progression-free survival rates were 95% and 94%, respectively. Seven patients reported a marked deterioration in hearing ability. Post-radiation therapy magnetic resonance imaging showed variability in oedema collection, but no patient suffered from radio-necrosis. Grade 2 temporary facial nerve disorders were observed in 10 patients (8%) 3–6 months after HSRT. ConclusionDelivering HSRT in five fractions for vestibular schwannoma appears safe and efficient, combining both efficiency and short treatment time while optimising neurological function preservation.

Cross-Modality Image Registration Using a Training-Time Privileged Third Modality.

In this work, we consider the task of pairwise cross-modality image registration, which may benefit from exploiting additional images available only at training time from an additional modality that is different to those being registered. As an example, we focus on aligning intra-subject multiparametric Magnetic Resonance (mpMR) images, between T2-weighted (T2w) scans and diffusion-weighted scans with high b-value (DWI [Formula: see text]). For the application of localising tumours in mpMR images, diffusion scans with zero b-value (DWI [Formula: see text]) are considered easier to register to T2w due to the availability of corresponding features. We propose a learning from privileged modality algorithm, using a training-only imaging modality DWI [Formula: see text], to support the challenging multi-modality registration problems. We present experimental results based on 369 sets of 3D multiparametric MRI images from 356 prostate cancer patients and report, with statistical significance, a lowered median target registration error of 4.34 mm, when registering the holdout DWI [Formula: see text] and T2w image pairs, compared with that of 7.96 mm before registration. Results also show that the proposed learning-based registration networks enabled efficient registration with comparable or better accuracy, compared with a classical iterative algorithm and other tested learning-based methods with/without the additional modality. These compared algorithms also failed to produce any significantly improved alignment between DWI [Formula: see text] and T2w in this challenging application.

MRI-Guided Real-Time Online Adaptive Gated Stereotactic Body Radiation Therapy for Liver Tumors

<h3>Purpose/Objective(s)</h3> Liver tumors (primary or metastases) are commonly encountered in Oncology. Single breathing phase Magnetic resonance imaging (MRI)-guided gated and possible adaptive stereotactic body radiation therapy (SBRT) for liver tumors offer dosimetric advantages and facilitate safe dose escalation compared to non- MRI-guided SBRT (MRgSBRT). We aimed to evaluate the impact of MRgSBRT on treatment outcomes and report treatment related adverse events. <h3>Materials/Methods</h3> This IRB approved retrospective study included liver tumors patients treated consecutively with MRgSBRT between 2019 and 2021. All patients received Gadoxetate disodium contrast followed by single phase post-exhale CT and MRI simulations utilizing 0.35 T MRI-guided linear accelerator. MRI images (hybrid T1-T2 sequence) were used as the primary set of images for contouring and planning. Real-time online adaptive SBRT plans were generated to account for daily anatomical changes of nearby organs at risk (OARs) when indicated. Patients were followed up every 3 to 6 months with a brief history, physical examination and imaging as indicated. Patients' data were analyzed based on age, sex, histology, tumor volume and delivered biologically equivalent dose (BED <100 Gy vs BED > 100 Gy). Kaplan Meier curves were generated for freedom from local progression (FFLP) and overall survival (OS). <h3>Results</h3> The study included 35 eligible patients with 49 liver tumors (hepatocellular carcinoma 21 lesions, liver metastases 28 lesions). The median age was 69.5 years (range 25 - 95). The median planning target volume (PTV) was 43.5 cm³ (4.9 - 344.8 cm³). Most patients (80%) were prescribed 50 Gy in 5 fractions (median 50 Gy, range 35 - 50Gy) to PTV. A total of 255 fractions were delivered for patients who completed treatment, 22 of which were adapted (8.6%). The median follow up was 19.4 months (range 1-37 months). The median OS was 25.9 months with 95% confidence intervals (CI) (22.1 - 29.6). The 1-year OS rate was 77.7%, 3-year OS rate was 47.9%. Local control was a driver for OS with patients with durable local control having a median OS of 27.8 months [95%CI (23.8-31.6)] vs 13.5 months [95%CI (5.6-21.3), p=0.007] in patients with local progression. The median FFLP was 29.8 months [95%CI (27.2-32.3]. The estimated 1-year FFLP was 95.6 % and 3-year FFLP was 87.1%. The FFLP in patients with BED>100Gy was 30.9 months [95%CI (28.7-33.1)] vs 13.3 months [95%CI (5.3-21.3), p value=0.004] in patients who received <100Gy BED. Most patients tolerated treatment well, no acute grade 3 toxicity. Two patients developed late grade 3 toxicity (gastric ulcer and non-classic radiation induced liver disease). <h3>Conclusion</h3> In our study, Gated MRgSBRT with real-time online adaptive planning is feasible, provides durable local control and impacts overall survival in a heavily pretreated older group of liver tumor patients, with remarkably good safety profile. BED>100Gy improved local control. Improved local control seems to drive overall survival benefit in liver tumors.

An Essential Treatment Pattern of Lung Cancer: Magnetic Resonance-Guided Stereotactic Body Radiotherapy

<h3>Purpose/Objective(s)</h3> Stereotactic body radiation therapy (SBRT) has emerged as an important treatment for non-resectable lung cancer. MR-Linac can offer superior soft-tissue contrast, have the ability to visualize cancer physiology and daily on-table treatment adaptation. Obviously combined SBRT with MR-Linac holds the promise to improve the accuracy of radiotherapy and reduce the toxicity of organs-at-risk (OAR). However, data on treatment effect and patient acceptance is still limited. <h3>Materials/Methods</h3> Between July 2019 and October 2021,14 patients with lung cancer were treated with an MRI-Linac guided SBRT, of them, 6 in left upper lobe, 1 in left lower lobe, 2 in right upper lobe and 5 in right lower lobe. The CT simulation used a Siemens big-bore CT scanner (syngo CT VA62A) for all patients. All patients were treated with step and shoot intensity modulated radiotherapy (IMRT). The online plan was created while the patient was on the treatment table and based on the online MRI images; pre-treatment CT was deformably registered to the online MRI to obtain position error. All patients used adapt to position (ATP) workflow. The curative effect and adverse reactions in the process of treatment need to be paid close attention to, and the adverse reactions should be treated and recorded in time. <h3>Results</h3> Fourteen patients (with n=2 metastases; n=12 primary tumor) received MR-guided SBRT. Median prescribed does was 60Gy(range:54Gy-70Gy) and median planning target volume was 28.8cc (range:11.1-93.4cc). Two patients occurred grade I bone marrow suppression and two occurred grade II bone marrow suppression. One patient occurred grade I gastrointestinal toxicity. No patient occurred grade III or higher toxicity. Only one patient developed left lung recurrence and left hilar lymph node metastasis ten months after treatment, one patient was not re-examined, and others were controlled locally. <h3>Conclusion</h3> In summary, MR-guided SBRT of lung cancer is well-effective and well-accepted. The results are promising that it holds with prominent local control and mild adverse events. The influence of magnetic field on dosimetry remains to be studied. The relevant work is also conducted.