Radiobiological evaluation of the stepping-source effect in single-fraction monotherapy high-dose-rate prostate brachytherapy.

Introduction: The continued reliance upon the traditional biologically effective dose (BED) formalism of BED=nd(1+d/(α/β)) may be one possible contributor to the poor clinical outcomes observed with single-fraction 19-20 Gy prescriptions in prostate high-dose-rate (HDR) brachytherapy because BED does not consider intrafraction sublethal damage repair (iSLDR). This, along with low α/β and repair half-times comparable to delivery time, could reduce the biological effect predicted using BED.

Methods And Materials: BED was recalculated with a model accounting for iSLDR, using time-averaged uniform dose rate (BED) patterns and time-variable dose rate (BED) patterns inherent to stepping-source delivery.

Early Ophthalmology Findings in Nonsyndromic Craniosynostosis.

Craniosynostosis (CS) occurs 1 in 2500 births and surgical intervention is indicated partly due to risk for elevated intracranial pressure (EICP). Ophthalmological examinations help identify EICP and additional vision concerns. This study describes preoperative and postoperative ophthalmic findings in CS patients (N=314) from chart review.

Preliminary dosimetric comparison between fixed and rotating source stereotactic radiosurgery systems.

Purpose: The Akesis Galaxy RTi (AK) is a novel rotational Co-based cranial stereotactic radiosurgery (SRS) system. While similar systems have been compared against the fixed-source Leksell Gamma Knife (GK) system using stylized phantoms, dosimetric plan quality with realistic anatomy has yet to be characterized for this or any other rotating system versus GK. This study aims to benchmark AK dosimetric performance against GK by retrospectively replanning previously-treated GK patients at our institution.

Implementing a simulation-based curriculum for hybrid intracavitary/interstitial brachytherapy using a new, commercially available, US/MR/CT-compatible gynecologic phantom.

Purpose: To establish a simulation-based workshop for teaching hybrid intracavitary/interstitial (IC/IS) brachytherapy skills using a new, commercially available US/CT/MRI-compatible gynecologic phantom prototype.

Methods And Materials: The VIOMERSE gynecological trainer phantom consisted of tissue-like colloid material and was US, CT, and MRI-compatible. We designed a hands-on workshop incorporating the phantom prototype to teach skills for hybrid IC/IS brachytherapy including pre-implant planning, procedural steps of implant placement, and post-implant evaluation.

Single application hybrid interstitial brachytherapy for cervical cancer: an institutional approach during the COVID-19 pandemic.

Purpose: To ease anesthesia and inpatient strain during the COVID-19 pandemic, our institution's policy for hybrid intracavitary-interstitial brachytherapy (IC/ISBT) for cervical cancer (CC) was modified from multiple applications (MA) treated over 2 separate weeks (7 Gy × 4) to a single-application (SA), treated within 1 week (8 Gy × 3). Here, we assessed dosimetric quality of the SA hybrid IC/ISBT approach and report our early outcomes.

Material And Methods: This was an IRB-approved retrospective review of CC patients treated with magnetic resonance imaging (MRI)-guided hybrid IC/ISBT between April 1, 2020 and December 31, 2020 (COVID cohort).

Dosimetric study of Varian Universal Multi-Channel Cylinder System for High-Dose-Rate Ir Brachytherapy.

Purpose: Recently, the Varian multichannel vaginal cylinder (MCVC) set for high-dose-rate Ir brachytherapy was commercially released. This MCVC was distinct from our existing MCVC in its peripheral channel layout and tip design. This investigation sought to assess the dosimetric impact of these changes.

Impact of tissue heterogeneity correction on Gamma Knife stereotactic radiosurgery of acoustic neuromas.

Purpose/objectives: Treatment planning systems (TPS) for Gamma Knife stereotactic radiosurgery (GK-SRS) include TMR10 algorithms, which assumes tissue homogeneity equivalent to water, and collapsed-cone convolutional (CCC) algorithms, which accounts for tissue inhomogeneity. This study investigated dosimetric differences between TMR10 and CCC TPS for acoustic neuromas (ANs) treated with GK-SRS.

Materials/methods: A retrospective review of 56 AN treated with GK-SRS was performed.

Clinically-implementable template plans for multidwell treatments using Leipzig-style applicators in Ir surface brachytherapy.

Purpose: Multiple dwell positions ("multidwell") within a Leipzig-style applicator can be used to increase dose uniformity and treatment area. Model-based dose calculation algorithms (MBDCAs) are necessary for accurate calculations involving these applicators because of their nonwater equivalency and complex geometry. The purpose of this work was to create template plans from MBDCA calculations and present their dwell times and positions for users of these applicators without access to MBDCAs.

Associating dose-volume characteristics with theoretical radiobiological metrics for rapid Gamma Knife stereotactic radiosurgery plan evaluation.

Purpose: To examine general dose-volume characteristics in Gamma Knife (GK) plans which may be associated with higher tumor control probability (TCP) and equivalent uniform dose (EUD) using characteristic curve sets.

Methods: Two sets of dose-volume histograms (DVHs) were exported alongside an analytical purpose-generated DVH: (a) single-shot large collimator (8 or 16 mm) emulated with multiple shots of 4 mm collimator. (b) shot-within-shot (SWS) technique with isodose lines (IDLs) of 40-75%.

A prototype open-ended multichannel intracavitary-interstitial hybrid applicator for gynecological high-dose-rate brachytherapy.

This manuscript introduces a novel open-ended, multichannel intracavitary-interstitial hybrid applicator for gynecological high-dose-rate brachytherapy. A prototype was three-dimensionally (3D) printed using polylactic acid. The device was 25 mm in diameter and 150 mm in length, with eight evenly spaced peripheral channels around a central tandem channel, each 2.

Feasibility of using multiple-dwell positions in Ir Leipzig-style brachytherapy surface applicators to expand target coverage and clinical application.

Purpose: Leipzig-style applicators for surface brachytherapy are traditionally used with a single-source dwell position. This study explores the feasibility of using multiple-source dwell positions ("multidwell") to improve the dose coverage and applicability of Leipzig-style applicators.

Methods And Materials: A virtual model of the Leipzig-style applicator was commissioned for a model-based dose calculation algorithm (MBDCA) and compared against American Association of Physicists in Medicine working group 186 benchmarking data sets and ionization chamber point measurements.

Role of Gamma Knife Radiosurgery in Small Cell Lung Cancer: A Multi-Institutional Retrospective Study of the International Radiosurgery Research Foundation (IRRF).

Background: Despite a high incidence of brain metastases in patients with small-cell lung cancer (SCLC), limited data exist on the use of stereotactic radiosurgery (SRS), specifically Gamma Knife™ radiosurgery (Elekta AB), for SCLC brain metastases.

Objective: To provide a detailed analysis of SCLC patients treated with SRS, focusing on local failure, distant brain failure, and overall survival (OS).

Methods: A multi-institutional retrospective review was performed on 293 patients undergoing SRS for SCLC brain metastases at 10 medical centers from 1991 to 2017.

Deployment and performance of model-based dose calculation algorithm in Ir shielded cylinder brachytherapy.

Purpose: The purpose of the study was to integrate model-based dose calculation algorithm (MBDCA) and 3-D planning into our institutional capabilities for clinical cases with inherent heterogeneities, namely shielded cylinder cases, which were previously performed using templates.

Methods And Materials: AcurosBV (Varian Medical Systems) was selected as MBDCA, and we compared results against the American Association of Physicists in Medicine working group (WG) reference Test Case #4, which contains a 36-mm-diameter 180-degree shielded cylinder. The last five clinically used template plans, as generated with ABACUS (Varian Medical Systems), were compared against MBDCA results.

High-dose-rate brachytherapy as monotherapy for prostate cancer: The impact of cellular repair and source decay.

Purpose: This work quantifies the influence of intrafraction DNA damage repair and cellular repopulation on biologically effective dose (BED) in Ir-192 high-dose-rate brachytherapy for prostate cancer. In addition, it examines the effect of source-decay-induced BED variation for patients treated at different time points in a source exchange cycle.

Materials And Methods: Current fractionation schemes are based on simplified-form BED = nd(1 + d/(α/β)), which assumes that intrafraction repair, interfraction repair, and repopulation are negligible.

Extended duration of dilator use beyond 1 year may reduce vaginal stenosis after intravaginal high-dose-rate brachytherapy.

Background: Vaginal dilators (VD) are recommended following vaginal or pelvic radiotherapy for patients with endometrial carcinoma (EC) to prevent vaginal stenosis (VS). The time course of VS is not fully understood and the optimal duration of VD use is unknown.

Methods: We reviewed 243 stage IA-II EC patients who received adjuvant brachytherapy (BT) at an academic tertiary referral center.

Incorporating patient-specific CT-based ophthalmic anatomy in modeling iodine-125 eye plaque brachytherapy dose distributions.

Purpose: To quantify the dosimetric impact of incorporating patient-specific CT-based models rather than the conventional stylized-standard model for eye plaque brachytherapy planning.

Methods And Materials: Plaque Simulator was used to plan 16 patients using both CT-based patient-specific eye model and stylized-standard (SS) eye models. Plaque position was initially based on the SS model and compared against their patient-specific model without changing the plaque loading pattern and seed strength.

Monte Carlo simulations of adult and pediatric computed tomography exams: validation studies of organ doses with physical phantoms.

Purpose: To validate the accuracy of a Monte Carlo source model of the Siemens SOMATOM Sensation 16 CT scanner using organ doses measured in physical anthropomorphic phantoms.

Methods: The x-ray output of the Siemens SOMATOM Sensation 16 multidetector CT scanner was simulated within the Monte Carlo radiation transport code, MCNPX version 2.6.

Optically stimulated luminescent dosimetry for high dose rate brachytherapy.

Purpose: The objective was to determine whether optically stimulated luminescent dosimeters (OSLDs) were appropriate for in vivo measurements in high dose rate brachytherapy. In order to make this distinction, three dosimetric characteristics were tested: dose linearity, dose rate dependence, and angular dependence. The Landauer nanoDot™ OSLDs were chosen due to their popularity and their availability commercially.

A methodology for direct quantification of over-ranging length in helical computed tomography with real-time dosimetry.

In helical computed tomography (CT), reconstruction information from volumes adjacent to the clinical volume of interest (VOI) is required for proper reconstruction. Previous studies have relied upon either operator console readings or indirect extrapolation of measurements in order to determine the over-ranging length of a scan. This paper presents a methodology for the direct quantification of over-ranging dose contributions using real-time dosimetry.

Construction of anthropomorphic phantoms for use in dosimetry studies.

This paper reports on the methodology and materials used to construct anthropomorphic phantoms for use in dosimetry studies, improving on methods and materials previously described by Jones et al. [Med Phys. 2006;33(9):3274-82].