BACKGROUND:Spatially fractionated radiation therapy (SFRT) has shown incredible potential in sparing normal tissues and activating mechanisms of tumor control distinct from conventional radiotherapy. However, the optimal spatial configuration of SFRT as well as the optimal peak and valley dose values have not been established. This poses a barrier to widespread clinical implementation and efficacy. PURPOSE:To facilitate greater SFRT optimization, this work establishes a simple, readily customizable, and cost-effective approach for fabricating SFRT collimators with different spatial configurations as well as peak and valley dose values. METHODS:The approach involves fabrication of custom SFRT collimators, each consisting of a 3D-printed plastic shell filled with tungsten. Once fabricated, the collimator dosimetry is characterized using a combination of Gafchromic film and ion chamber measurements. Monte Carlo simulations are used to verify SFRT dosimetry and assess positional uncertainties. The collimators are applied in preclinical mouse experiments demonstrating how they can be used to deliver SFRT. RESULTS:Five collimators were fabricated for use at kilovoltage energies and one collimator was fabricated for use at megavoltage energies. Across all collimators, the peak widths ranged from 1.2 to 10.1 mm and the valley widths ranged from 1.1 to 10.6 mm. For the kilovoltage collimators, the highest peak-to-valley dose ratio was 32.4 at the surface and this dropped to 29.5 at 10 mm depth. For the megavoltage collimator, at 95 cm SSD, the peak-to-valley dose ratio was 2.7 at 15 mm depth and this dropped to 2.2 at 100 mm depth. In the mouse experiments, out of multiple SFRT parameters, the mean tumor valley dose had the strongest correlation with change in tumor volume (p = 0.02). The Monte Carlo simulations indicated a 5 mm translation of the mouse tumor relative to the beam led to a 44.8% change in the mean tumor dose, underlying the importance of precise positioning for SFRT. CONCLUSIONS:This work establishes a novel approach for custom 3D printing of SFRT collimators and their subsequent characterization. The developed collimators are capable of SFRT delivery at both kilovoltage and megavoltage photon beam energies. This approach facilitates patient specific customization as well as optimization of the peak and valley doses for more effective SFRT.

Abstract Background Biochemical recurrence (BCR) occurs in up to 40% of men following radical prostatectomy (RP). Current risk models rely primarily on clinicopathologic variables and may not fully capture the biological heterogeneity associated with recurrence. The Decipher Genomic Classifier (DGC), prostate-specific membrane antigen positron emission tomography (PSMA-PET), and multiparametric magnetic resonance imaging (mpMRI) provide complementary prognostic information that may improve prediction. Objective To develop and evaluate machine learning (ML) models integrating DGC, PSMA-PET, and mpMRI for preoperative prediction of BCR following RP. Methods This retrospective study included patients with available preoperative DGC, PSMA-PET, mpMRI, and clinicopathologic data. Logistic regression (LR), random forest (RF), and XGBoost models were developed using single- and multimodality feature combinations. Early- and intermediate-fusion strategies were evaluated. Performance was assessed using an area under the receiver operating characteristic curve (AUC) and accuracy. Clinical utility was evaluated using decision curve analysis. Results XGBoost consistently outperformed LR and RF. DGC achieved the highest single-modality performance (AUC 0.94, accuracy 86.7%). Among multimodal models, DGC combined with PSMA-PET using intermediate fusion achieved the best overall performance (AUC 0.93, accuracy 87.0%). Addition of mpMRI reduced performance (AUC 0.85, accuracy 83.0%). Decision curve analysis demonstrated positive net benefit across clinically relevant thresholds. Conclusion XGBoost-based multimodal fusion improved preoperative BCR prediction following RP. DGC was the strongest individual predictor, while integration with PSMA-PET provided the best overall performance, supporting the potential of radiogenomic ML models for personalized risk stratification.

Purpose : Hypoxia is a well-known major factor contributing to the radioresistance of prostate cancer, which could be counteracted by increasing the dose. This study aimed to demonstrate the dosimetric feasibility of a dose-painting radiation therapy plan for prostate cancer, using a novel ring gantry system, based on the localization of tumoral and hypoxic areas. Methods and Materials : Seven patients from the PAIR prostate study, who underwent external-beam radiation therapy for intermediate-risk prostate cancer and exhibited pre-therapeutic F-MISO PET uptake in the tumor, were selected. The Gross Tumor Volume (GTV) was delineated on the MRI and the hypoxic region within the Planning Target Volume (PTV) was delineated based on F-MISO PET uptake. Intensity-modulated radiation therapy planning was performed based on three different prescriptions: standard fractionation (77 Gy in 35 fractions to the PTV), with an integrated boost of 95 Gy and 118 Gy in 35 fractions to the GTV and the hypoxic region, moderate hypofractionation (60 Gy in 20 fractions) with a boost of 67 Gy and 91 Gy to the GTV and the hypoxic region, and high hypofractionation (40 Gy in 5 fractions) with a boost of 50 Gy to the GTV and as high as possible to the hypoxic region. Planning was performed on the research version of the RefleXion Treatment Planning System (X1-TPS). Results : We achieved the prescribed dose in all seven patients while respecting the usual dose limits for organs at risk. Conclusions : This study demonstrated the dosimetric feasibility of dose escalation in both the tumor and hypoxic regions in patients with prostate cancer using the RefleXion X1 TPS, without compromising the dose limits for OARs.

Purpose: Hypoxia is a well-known major factor contributing to the radioresistance of prostate cancer, which could be counteracted by increasing the dose. This study aimed to demonstrate the dosimetric feasibility of a dose-painting radiation therapy plan for prostate cancer, using a novel ring gantry system, based on the localization of tumoral and hypoxic areas. Methods and Materials: Seven patients from the Programme d’Action Intégré de Recherche-prostate study, who underwent external-beam radiation therapy for intermediate-risk prostate cancer and exhibited pretherapeutic fluromisonodazole positron emission tomography (PET) uptake in the tumor, were selected. The gross tumor volume (GTV) was delineated on the magnetic resonance imaging, and the hypoxic region within the planning target volume was delineated based on fluromisonodazole PET uptake. Intensity modulated radiation therapy planning was performed based on 3 different prescriptions: standard fractionation (77 Gy in 35 fractions to the planning target volume), with an integrated boost of 95 Gy and 118 Gy in 35 fractions to the GTV and the hypoxic region, moderate hypofractionation (60 Gy in 20 fractions) with a boost of 67 Gy and 91 Gy to the GTV and the hypoxic region, and high hypofractionation (40 Gy in 5 fractions) with a boost of 50 Gy to the GTV and as high as possible to the hypoxic region. Planning was performed on the research version of the RefleXion treatment planning system. Results: We achieved the prescribed dose in all 7 patients while respecting the usual dose limits for organs at risk. Conclusions: This study demonstrated the dosimetric feasibility of dose escalation in both the tumor and hypoxic regions in patients with prostate cancer using the RefleXion treatment planning system, without compromising the dose limits for organs at risks.

PurposeThis study explores the feasibility of employing Generative Adversarial Networks (GANs) to model the RefleXion X1 Linac. The aim is to investigate the accuracy of dose simulation and assess the potential computational benefits.MethodsThe X1 Linac is a new radiotherapy machine with a binary multi-leaf collimation (MLC) system, facilitating innovative biology-guided radiotherapy. A total of 34 GAN generators, each representing a desired MLC aperture, were developed. Each generator was trained using a phase space file generated underneath the corresponding aperture, enabling the generation of particles and serving as a beam source for Monte Carlo simulation. Dose distributions in water were simulated for each aperture using both the GAN and phase space sources. The agreement between dose distributions was evaluated. The computational time reduction from bypassing the collimation simulation and storage space savings were estimated.ResultsThe percentage depth dose at 10 cm, penumbra, and full-width half maximum of the GAN simulation agree with the phase space simulation, with differences of 0.4 % ± 0.2 %, 0.32 ± 0.66 mm, and 0.26 ± 0.44 mm, respectively. The gamma passing rate (1 %/1mm) for the planar dose exceeded 90 % for all apertures. The estimated time-saving for simulating an plan using 5766 beamlets was 530 CPU hours. The storage usage was reduced by a factor of 102.ConclusionThe utilization of the GAN in simulating the X1 Linac demonstrated remarkable accuracy and efficiency. The reductions in both computational time and storage requirements make this approach highly valuable for future dosimetry studies and beam modeling.

BACKGROUND:Biology-guided radiotherapy (BgRT) is a novel technology that uses positron emission tomography (PET) data to direct radiotherapy delivery in real-time. BgRT enables the precise delivery of radiation doses based on the PET signals emanating from PET-avid tumors on the fly. In this way, BgRT uniquely utilizes radiotracer uptake as a biological beacon for controlling and adjusting dose delivery in real-time to account for target motion. PURPOSE:To demonstrate using real-time PET for BgRT delivery on the RefleXion X1 radiotherapy machine. The X1 radiotherapy machine is a rotating ring-gantry radiotherapy system that generates a nominal 6MV photon beam, PET, and computed tomography (CT) components. The system utilizes emitted photons from PET-avid targets to deliver effective radiation beamlets or pulses to the tumor in real-time. METHODS:This study demonstrated a real-time PET BgRT delivery experiment under three scenarios. These scenarios included BgRT delivering to (S1) a static target in a homogeneous and heterogeneous environment, (S2) a static target with a hot avoidance structure and partial PET-avid target, and (S3) a moving target. The first step was to create stereotactic body radiotherapy (SBRT) and BgRT plans (offline PET data supported) using RefleXion's custom-built treatment planning system (TPS). Additionally, to create a BgRT plan using PET-guided delivery, the targets were filled with 18F-Fluorodeoxyglucose (FDG), which represents a tumor/target, that is, PET-avid. The background materials were created in the insert with homogeneous water medium (for S1) and heterogeneous water with styrofoam mesh medium. A heterogeneous background medium simulated soft tissue surrounding the tumor. The treatment plan was then delivered to the experimental setups using a pre-commercial version of the X1 machine. As a final step, the dosimetric accuracy for S1 and S2 was assessed using the ArcCheck analysis tool-the gamma criteria of 3%/3 mm. For S3, the delivery dose was quantified using EBT-XD radiochromic film. The accuracy criteria were based on coverage, where 100% of the clinical target volume (CTV) receives at least 97% of the prescription dose, and the maximum dose in the CTV was ≤130% of the maximum planned dose (97 % ≤ CTV ≤ 130%). RESULTS:For the S1, both SBRT and BgRT deliveries had gamma pass rates greater than 95% (SBRT range: 96.9%-100%, BgRT range: 95.2%-98.9%), while in S2, the gamma pass rate was 98% for SBRT and between 95.2% and 98.9% for BgRT plan delivering. For S3, both SBRT and BgRT motion deliveries met CTV dose coverage requirements, with BgRT plans delivering a very high dose to the target. The CTV dose ranges were (a) SBRT:100.4%-120.4%, and (b) BgRT: 121.3%-139.9%. CONCLUSIONS:This phantom-based study demonstrated that PET signals from PET-avid tumors can be utilized to direct real-time dose delivery to the tumor accurately, which is comparable to the dosimetric accuracy of SBRT. Furthermore, BgRT delivered a PET-signal controlled dose to the moving target, equivalent to the dose distribution to the static target. A future study will compare the performance of BgRT with conventional image-guided radiotherapy.

Purpose/Objective(s) The PAIR prostate study aims to demonstrate the dosimetric feasibility of tumoral and hypoxia-guided dose escalated radiation therapy in prostate cancer on a novel ring gantry system TPS, based on conventionally fractionated and hypofractionated regimens. Materials/Methods The GTV was delineated on MRI and the hypoxic region (biological tumor volume [BTV]) within the PTV on F-MISO PET uptake was delineated on pre-therapeutic F-MISO PET scans of 7 patients showing uptake in the tumor before undergoing external-beam RT for intermediate-risk prostate cancer. IMRT planning was performed using three different prescriptions regimen 1) Standard fractionation (SF) 77Gy/35 fractions (fx) to PTV, with a boost to 95Gy and 118Gy in 35 fx to the GTV and to the hypoxic region defined by F-MISO PET, respectively, 2) moderate hypofractionation (MH) 60 Gy/20 fx with a boost to 67Gy and 91Gy in 20 fx to the GTV and to the hypoxic region, respectively, and 3) high hypofractionation (HH) 40 Gy/5 fx with a boost to 50Gy in 5 fx to the GTV and as high as possible to the hypoxic region (SBRT). Planning was performed on a treatment planning system. Results The average size of the GTV and BTV was 11.4 ± 11.3 cc, and 1.30 ± 1.20 cc, respectively. For the SF regimen, the average D98% and D2% to the PTV, GTV and BTV were 71.3 ± 11.7 Gy and 105.0 ± 7.6 Gy; 90.3 ± 6.9 Gy and 113.2 ± 6.9 Gy; and 107.4 ± 5.6 Gy, and 116.0 ± 5.6 Gy, respectively. For the MH and HH techniques, the average D98% to the PTV was 54.3 ± 2.5 Gy, and 31.7 ± 5.3 Gy, and the average D2% was 83.6 ± 7.0 Gy, and 55.8 ± 2.9 Gy. In addition, the average D98%, and D2% to the GTV was 61.2 ± 6.2 Gy, and 89.8 ± 5.9 Gy using the MH treatment technique, while the average D98%, and D2% to the BTV was 85.2 ± 4.1 Gy, and 92.3 ± 3.2 Gy, respectively. Also, for the HH treatment planning method, the average D98%, and D2% to the GTV was 45.7 ± 4.9 Gy, and 59.2 ± 3.2 Gy, while the average D98%, and D2% to the BTV was 53.6 ± 4.2 Gy and 60.6 ± 2.5 Gy, respectively. The average D50% of the bladder, rectum, and femoral heads was 12.6 ± 5.4 Gy, 24.8 ± 9.9 Gy, and 9.6 ± 2.5 Gy, while the average V15Gy was 43.0 ± 11.5%, 59.4 ± 12.5 %, and 12.5 ± 14.1%, respectively. Conclusion This study showed the dosimetric feasibility of dose-escalating the tumor and the hypoxic region in patients with prostate cancer using standard, moderate and high hypofractionated regimen on a treatment planning system while keeping the doses within acceptable limits for the organs at risk.

Purpose/Objective(s) This study investigated the performance of machine learning-derived nomograms utilizing logistic regression (LR) and random forest (RF) algorithms, along with biomarkers from 68Ga-PSMA-11 PET, MRI, and the Decipher test, in predicting side-specific extraprostatic extension (EPE) in radical prostatectomy (RP) patients. Materials/Methods In this retrospective study, data from prostate cancer patients who underwent RP at Indiana University Hospital, alongside their 68Ga-PSMA-11 PET, MRI, and Decipher results were analyzed. This included their clinical information (fraction of positive cores on biopsy, prostate-specific antigen density, and ISUP biopsy grade) alongside results from three biomarkers: 68Ga-PSMA-11 PET, MRI, and the Decipher test. Several machine learning-derived nomogram models were developed using LR and RF algorithms. These models incorporated various combinations of the biomarkers (PET-only, MRI-only, Decipher-only, Decipher-only, PET+Decipher, PET+MRI, MRI+Decipher, and PET+MRI+Decipher) along with the clinical data. The performance of each model was assessed using the area under the receiver operating characteristic curve (AUC-ROC). Results In the nomogram development and validation process, we selected 110 patients with a median age of 61.5 years (range = 48 –77 years), PSA score of 2.7–7.15 ng/mL, ISUP biopsy grade of 1–5, and a fraction of positive cores of 0.50 ± 0.36. For the PET-only, MRI-only, Decipher-only, PET+Decipher, PET+MRI, MRI+Decipher, and PET+MRI+Decipher variables, the performance of the RF models was 0.82, 0.76, 0.65, 0.83, 0.76, 0.73, and 0.83, respectively. In addition, the performance of the LR models was 0.80, 0.71, 0.62, 0.78, 0.79, 0.78, and 0.63, respectively. Conclusion From this study, the RF algorithm generally outperformed LR algorithm in this task. 68Ga-PSMA PET-only variables provided better EPE prediction than MRI or Decipher variables used individually among the evaluated biomarkers. However, the most accurate predictions were achieved by combining Decipher and MRI data with PET data, particularly within the RF models. This suggests that a combined approach using multiple biomarkers holds promise for improving EPE prediction. Hence to guide treatment decisions, such as nerve-sparing RP. Further study with a larger patient population is needed to refine the model’s accuracy and validate its clinical utility.

The AI-based auto segmentation system showed improved agreement with manual contouring when using kVCT images from the BgRT capable machine compared to MVCT or CBCT images. However, manual correction is necessary on auto-segmentation results from all imaging modalities especially for organs with limited contrast from surrounding tissues.

73 Background: This study aimed at demonstrating the dosimetric feasibility of tumoral and hypoxia-guided dose escalated radiation therapy in prostate cancer on a novel ring gantry system TPS, based on conventionally fractionated and hypofractionated regimens. Methods: Three patients who underwent external-beam RT for intermediate-risk prostate cancer in the PAIR prostate study and had pre-therapeutic F-MISO PET uptake in the tumor, were selected. The GTV and the hypoxic region (biological tumor volume [BTV]) within the PTV on F-MISO PET uptake were delineated. IMRT planning based on three different prescriptions was performed: 1) Standard fractionation (SF)- 77Gy/35 fractions (fx) to PTV, with a boost to 95Gy and 118Gy in 35 fx to the GTV and to the hypoxic region defined by F-MISO PET, respectively, 2) moderate hypofractionation (MH)- 60 Gy/20 fx with a boost to 67Gy and 91Gy in 20 fx to the GTV and to the hypoxic region, respectively, and 3) high hypofractionation (HH)- 40 Gy/5 fx with a boost to 50Gy in 5 fx to the GTV and as high as possible to the hypoxic region (SBRT). Planning was performed on the research version of the RefleXion treatment planning system (X1-TPS). Results: The average size of the GTV and BTV was 6.03±2.05 cc, and 1.90±1.64 cc, respectively. For the SF regimen, the average D98% and D2% to the PTV, GTV and BTV were 71.33±0.15 Gy and 110.43±8.57 Gy; 91.43±1.12 Gy and 108.53± 10.29 Gy; and 112.33±3.54 Gy, and 121.37±1.31 Gy, respectively. For the MH and HH techniques, the average D98% to the PTV was 56.13±0.51 Gy, and 37.03± 1.81 Gy, and the average D2% was 85.53±8.52 Gy, and 58.47±1.90 Gy. In addition, the average D98%, and D2% to the GTV was 65.67±0.15 Gy, and 80.27±10.20 Gy using the MH treatment technique, while the average D98%, and D2% to the BTV was 85.87±5.00 Gy, and 94.9±1.15 Gy, respectively. Also, for the HH treatment planning method, the average D98%, and D2% to the GTV was 50.33±3.79 Gy, and 57.23±4.75 Gy, while the average D98%, and D2% to the BTV was 54.57±3.67 Gy and 61.00±2.17 Gy, respectively. The average D50% of Bladder, Rectum, and Femoral heads was 12.28±11.39 Gy, 26.09±5.89 Gy, and 11.44±2.92 Gy, while the average V15Gy was 43.07±18.68%, 72.39±8.81 %, and 23.43±20.44%, respectively. Conclusions: This study showed the dosimetric feasibility of dose-escalating the tumor and the hypoxic region in patients with prostate cancer on the RefleXion X1 TPS without compromising the OARs dose limits.

An increasing number of elderly prostate cancer patients with high-density material hip prostheses are referred for external beam Radiotherapy (EBRT). Radiation treatment of pelvis cancer patients with high-density hip prostheses needs special attention due to the artifacts created in the computed tomography (CT) field of view and the radiotherapy dosimetry challenges. This study investigated the pelvic prostate point dose with and without titanium hip prosthesis using a 0.6 cc PTW Farmer ionization chamber, EBT3 Gafchromic films, compared with the EGSnrc Monte Carlo (MC) simulation dose distribution. The doses were measured and simulated in a locally made pelvic phantom. MC and measured doses were compared with the Treatment Planning System (TPS) calculated prostate point dose. The ionization chamber, EBT3 Gafchromic films, and MC doses have a maximum deviation of 6.3 %, 5.7 %, and 7.4% for 6 MV and 4.2 %, 4.7 %, and 5.5 % for 15 MV photon beam, respectively, when compared with TPS calculated dose. There is a significant difference between the prostate point dose measured with ionization chamber, EBT3 Gafchromic film in comparison MC simulated doses. The MC simulation dose shows the highest deviation especially on the lateral field passing through the prosthesis.

PURPOSE:Biology-guided radiation therapy (BgRT) uses real-time line-of-response data from on-board positron emission tomography (PET) detectors to guide beamlet delivery during therapeutic radiation. The current workflow requires 18F-fluorodeoxyglucose (FDG) administration daily before each treatment fraction. However, there are advantages to reducing the number of tracer injections by using a PET tracer with a longer decay time. In this context, we investigated 89Zr-panitumumab (89Zr-Pan), an antibody PET tracer with a half-life of 78 hours that can be imaged for up to 9 days using PET. METHODS AND MATERIALS:The BgRT workflow was evaluated preclinically in mouse colorectal cancer xenografts (HCT116) using small-animal positron emission tomography/computed tomography (PET/CT) for imaging and image-guided kilovoltage conformal irradiation for therapy. Mice (n = 5 per group) received 7 MBq of 89Zr-Pan as a single dose 2 weeks after tumor induction, with or without fractionated radiation therapy (RT; 6 × 6.6 Gy) to the tumor region. The mice were imaged longitudinally to assess the kinetics of the tracer over 9 days. PET images were then analyzed to determine the stability of the PET signal in irradiated tumors over time. RESULTS:Mice in the treatment group experienced complete tumor regression, whereas those in the control group were killed because of tumor burden. PET imaging of 89Zr-Pan showed well-delineated tumors with minimal background in both groups. On day 9 postinjection, tumor uptake of 89Zr-Pan was 7.2 ± 1.7 in the control group versus 5.2 ± 0.5 in the treatment group (mean percentage of injected dose per gram of tissue [%ID/g] ± SD; P = .07), both significantly higher than FDG uptake (1.1 ± 0.5 %ID/g) 1 hour postinjection. To assess BgRT feasibility, the clinical eligibility criteria was computed using human-equivalent uptake values that were extrapolated from preclinical PET data. Based on this semiquantitative analysis, BgRT may be feasible for 5 consecutive days after a single 740-MBq injection of 89Zr-Pan. CONCLUSIONS:This study indicates the potential of long-lived antibody-based PET tracers for guiding clinical BgRT.

Background and Purpose: A recently developed biology-guided radiotherapy platform, equipped with positron emission tomography (PET) and computed tomography (CT), provides both anatomical and functional image guidance for radiotherapy. This study aimed to characterize performance of the kilovoltage CT (kVCT) system on this platform using standard quality metrics measured on phantom and patient images, using CT simulator images as reference. Materials and Methods: Image quality metrics, including spatial resolution/modular transfer function (MTF), slice sensitivity profile (SSP), noise performance and image uniformity, contrast-noise ratio (CNR) and low-contrast resolution, geometric accuracy, and CT number (HU) accuracy, were evaluated on phantom images. Patient images were evaluated mainly qualitatively. Results: On phantom images the MTF10% is about 0.68 lp/mm for kVCT in PET/CT Linac. The SSP agreed with nominal slice thickness within 0.7 mm. The diameter of the smallest visible target (1% contrast) is about 5 mm using medium dose mode. The image uniformity is within 2.0 HU. The geometric accuracy tests passed within 0.5 mm. Relative to CT simulator images, the noise is generally higher and the CNR is lower in PET/CT Linac kVCT images. The CT number accuracy is comparable between the two systems with maximum deviation from the phantom manufacturer range within 25 HU. On patient images, higher spatial resolution and image noise are observed on PET/CT Linac kVCT images. Conclusions: Major image quality metrics of the PET/CT Linac kVCT were within vendor-recommended tolerances. Better spatial resolution but higher noise and better/comparable low contrast visibility were observed as compared to a CT simulator when images were acquired with clinical protocols.

The results of a comparative study on vitamin compositions of unripe C. papaya showed that vitamin A and C contents of aqueous and ethanol leaves and seeds extracts respectively, was higher than that of vitamin E. However, vitamin A and C contents in the aqueous leaves and seeds extracts respectively, was significantly (p < 0.05) higher than that of ethanol leaves and seeds extracts.The in vitro antifungal activity was examined against Candida albicans, Aspergillus niger, Penicilliumnotatum and Rhizopus stolonifera by using the surface plate method.The aqueous leaves extract observation of the fungi plates after 48 h of incubation showed clear zones of inhibition at higher concentrations and little or no zone of inhibition observed in P. notatumand R. stolonifer at lower concentrations of aqueous leaves and seeds extracts.Therefore, aqueous leaves extract is of great importance in the discovery of new drugs for the pharmaceutical industry.

Purpose: To assess the fiducial motion in abdominal stereotactic body radiotherapy (SBRT) using the cone-beam computed tomography (CBCT) projections acquired for pre-treatment patient set-up. Materials and Methods: Pre-treatment CBCT projections and anterior-posterior (AP) and lateral (LAT) pair of fluoroscopic sequences of 7 pancreatic and 6 liver SBRT patients with implanted fiducials were analyzed for 49 treatment fractions retrospectively. A tracking algorithm based on template matching and sequential stereo triangulation algorithms was used to track the fiducials in the CBCT projections and the fluoro sequence pairs. We predicted the clinical couch adjustment from CBCT tracking and compared it with the clinical couch decision made during the patient's treatment. Results: In 3D coordinate, the fiducial motion ranges for pancreas cases were 9.90+/-3.52 mm, 10.65+/-5.91 mm, and 10.74+/-6.24 mm for CBCT, AP, and LAT fluoro, respectively, while in the liver, they were 13.93+/-3.39 mm, 11.17+/-3.75 mm, and 11.52+/-4.33 mm, respectively. Prediction of couch adjustment in LAT, SI, and AP coordinates from CBCT tracking agrees with the actual clinical couch correction within 0.92+/-0.74 mm, 1.37+/-1.26 mm, and 0.68+/-0.56 mm for pancreas cases and within 1.12+/-0.96 mm, 1.15+/-0.92 mm and 0.90+/-0.86 mm for liver cases, respectively. Conclusion: Tracking pre-treatment CBCT projections using template matching and sequential stereo triangulation is suitable for assessing fiducial motion and adjusting the patient setup for abdominal SBRT. CBCT can be used for motion modeling, potentially eliminating the need for additional fluoroscopic pair acquisition and thus reducing the imaging dose to the patient and the total treatment time.

Purpose We investigated the feasibility of biology-guided radiotherapy (BgRT), a technique that utilizes real-time positron emission imaging to minimize tumor motion uncertainties, to spare nearby organs at risk. Methods Volumetric modulated arc therapy (VMAT), intensity-modulated proton (IMPT) therapy, and BgRT plans were created for a paratracheal node recurrence (case 1; 60 Gy in 10 fractions) and a primary peripheral left upper lobe adenocarcinoma (case 2; 50 Gy in four fractions). Results For case 1, BgRT produced lower bronchus V40 values compared to VMAT and IMPT. For case 2, total lung V20 was lower in the BgRT case compared to VMAT and IMPT. Conclusions BgRT has the potential to reduce the radiation dose to proximal critical structures but requires further detailed investigation.

Purpose/Objective(s) A novel fast ring-gantry radiotherapy system delivers radiation beamlets using a high-speed binary multi-leaf collimator (100 transitions /sec). This study investigated plan quality and delivery efficiency of IMRT Head and Neck (H&N) cancer cases using the novel radiotherapy system. Materials/Methods Three IMRT H&N cases were planned on the novel radiotherapy treatment planning system using the ICRU 83 guidelines to deliver 54 Gy to the planning target volume (PTV) in 30 fractions. Each H&N case was planned with 1 and 2 cm field width (FW). The treatment time-PTV correlation coefficient (C2TT-PTV), homogeneity index (HI), conformity index (CI), mean dose (Dmean), Dnear-max (D2%), Dnear-min (D98%) of the PTVs and the mean dose to the 19 organs-at-risk (OARs) were investigated. Results All the H&N plans met the ICRU 83 guidelines. The C2TT-PTV for 1 cm FW and 2 cm FW were 0.95 and 0.99, respectively. In addition, the average HI and CI for 1 cm FW were 1.20±0.00 and 1.23±0.15, while the average HI and CI for 2 cm FW were 1.23±0.06 and 1.30±0.17. The average Dmean, D98% and D2% were 57.65±0.36, 50.56±4.07 and 62.63±1.17 Gy for 1 cm FW. Also, the average Dmean, D98% and D2% for 2 cm FW were 57.68±0.69, 50.77±3.53 and 63.2±1.95 Gy, respectively. Conclusion The novel radiotherapy system can be used to deliver H&N cancer radiotherapy treatment efficiently while meeting dosimetric constraints and achieving homogenous dose distribution to the PTV structures. A novel fast ring-gantry radiotherapy system delivers radiation beamlets using a high-speed binary multi-leaf collimator (100 transitions /sec). This study investigated plan quality and delivery efficiency of IMRT Head and Neck (H&N) cancer cases using the novel radiotherapy system. Three IMRT H&N cases were planned on the novel radiotherapy treatment planning system using the ICRU 83 guidelines to deliver 54 Gy to the planning target volume (PTV) in 30 fractions. Each H&N case was planned with 1 and 2 cm field width (FW). The treatment time-PTV correlation coefficient (C2TT-PTV), homogeneity index (HI), conformity index (CI), mean dose (Dmean), Dnear-max (D2%), Dnear-min (D98%) of the PTVs and the mean dose to the 19 organs-at-risk (OARs) were investigated. All the H&N plans met the ICRU 83 guidelines. The C2TT-PTV for 1 cm FW and 2 cm FW were 0.95 and 0.99, respectively. In addition, the average HI and CI for 1 cm FW were 1.20±0.00 and 1.23±0.15, while the average HI and CI for 2 cm FW were 1.23±0.06 and 1.30±0.17. The average Dmean, D98% and D2% were 57.65±0.36, 50.56±4.07 and 62.63±1.17 Gy for 1 cm FW. Also, the average Dmean, D98% and D2% for 2 cm FW were 57.68±0.69, 50.77±3.53 and 63.2±1.95 Gy, respectively. The novel radiotherapy system can be used to deliver H&N cancer radiotherapy treatment efficiently while meeting dosimetric constraints and achieving homogenous dose distribution to the PTV structures.