Impact of robust optimization on patient specific error thresholds for high dose rate prostate brachytherapy source tracking.

Purpose: The purpose of this study was to compare the effect of catheter shift errors and determine patient specific error thresholds (PSETs) for different high dose rate prostate brachytherapy (HDRPBT) plans generated by different forms of inverse optimization.

Methods: Three plans were generated for 50 HDRPBT patients and PSETs were determined for each of the 3 plans. Plan 1 was the original Oncentra Prostate (v4.

Potential anatomical triggers for plan adaptation of cervical cancer external beam radiotherapy.

This study aimed to identify potential anatomical variation triggers using magnetic resonance imaging for plan adaption of cervical cancer patients to ensure dose requirements were met over an external beam radiotherapy course. Magnetic resonance images (MRIs) acquired before and during treatment were rigidly registered to a pre-treatment computerised tomography (CT) image for 11 retrospective cervix cancer datasets. Target volumes (TVs) and organs at risk (OARs) were delineated on both MRIs and propagated onto the CT.

HDR brachytherapy afterloader quality assurance optimization using monolithic silicon strip detectors.

Background: There currently exists no widespread high dose-rate (HDR) brachytherapy afterloader quality assurance (QA) tool for simultaneously assessing the afterloader's positional, temporal, transit velocity and air kerma strength accuracy.

Purpose: The purpose of this study was to develop a precise and rigorous technique for performing daily QA of HDR brachytherapy afterloaders, incorporating QA of: dwell position accuracy, dwell time accuracy, transit velocity consistency and relative air kerma strength (AKS) of an Ir-192 source.

Method: A Sharp ProGuide 240 mm catheter (Elekta Brachytherapy, Veenendaal, The Netherlands) was fixed 5 mm above a 256 channel epitaxial diode array 'dose magnifying glass' (DMG256) (Centre for Medical and Radiation Physics, University of Wollongong).

Electron streaming dose measurements and calculations on a 1.5 T MR-Linac.

Purpose: To evaluate the accuracy of different dosimeters and the treatment planning system (TPS) for assessing the skin dose due to the electron streaming effect (ESE) on a 1.5 T magnetic resonance (MR)-linac.

Method: Skin dose due to the ESE on an MR-linac (Unity, Elekta) was investigated using a solid water phantom rotated 45° in the x-y plane (IEC61217) and centered at the isocenter.

Development of patient and catheter specific error thresholds for high dose rate prostate brachytherapy.

Background: In-vivo source tracking has been an active topic of research in the field of high-dose rate brachytherapy in recent years to verify accuracy in treatment delivery. Although detection systems for source tracking are being developed, the allowable threshold of treatment error is still unknown and is likely patient-specific due to anatomy and planning variation.

Purpose: The purpose of this study was to determine patient and catheter-specific shift error thresholds for in-vivo source tracking during high-dose-rate prostate brachytherapy (HDRPBT).

Investigation of in vivo source tracking error thresholds for interstitial and intra-cavitary high-dose-rate cervical brachytherapy.

Purpose: The purpose of this study was to determine a comprehensive source tracking error thresholds in high-dose-rate (HDR) brachytherapy for cervical cancer. Achieving this enables the definition of an action level for imminent source tracking technologies and treatment monitoring devices, preventing clinically relevant changes to the applied dose.

Material And Methods: Retrospective HDR interstitial ( = 10) and intra-cavitary ( = 20) cervical brachytherapy patients were randomly selected to determine the feasibility of implementing source tracking error thresholds.

Feasibility of online adaptive HDR prostate brachytherapy: A novel treatment concept.

Purpose: The purpose of this study was to determine the feasibility of online adaptive transrectal ultrasound (TRUS)-based high-dose-rate prostate brachytherapy (HDRPBT) through retrospective simulation of source positioning and catheter swap errors on patient treatment plans.

Method: Source positioning errors (catheter shifts in 1 mm increments in the cranial/caudal, anterior/posterior, and medial/lateral directions up to ±6 mm) and catheter swap errors (between the most and least heavily weighted) were introduced retrospectively into DICOM treatment plans of 20 patients that previously received TRUS HDRPBT. Dose volume histogram (DVH) indices were monitored as errors were introduced sequentially into individual catheters, simulating potential errors throughout treatment.

HDR prostate brachytherapy plan robustness and its effect on in-vivo source tracking error thresholds: A multi-institutional study.

Purpose: The purpose of this study was to examine the effect of departmental planning techniques on appropriate in-vivo source tracking error thresholds for high dose rate (HDR) prostate brachytherapy (BT) treatments, and to determine if a single in-vivo source tracking error threshold would be appropriate for the same patient anatomy.

Methods: The prostate, rectum, and urethra were contoured on a single patient transrectal ultrasound (TRUS) dataset. Anonymized DICOM files were disseminated to 16 departments who created an HDR prostate BT treatment plan on the dataset with a prescription dose of 15 Gy in a single fraction.

Characterizing magnetically focused contamination electrons by off-axis irradiation on an inline MRI-Linac.

Purpose: The aim of this study is to investigate off-axis irradiation on the Australian MRI-Linac using experiments and Monte Carlo simulations. Simulations are used to verify experimental measurements and to determine the minimum offset distance required to separate electron contamination from the photon field.

Methods: Dosimetric measurements were performed using a microDiamond detector, Gafchromic EBT3 film, and MOSkin .

The use of collimator angle optimization and jaw tracking for VMAT-based single-isocenter multiple-target stereotactic radiosurgery for up to six targets in the Varian Eclipse treatment planning system.

Purpose: Island blocking occurs in single-isocenter multiple-target (SIMT) stereotactic radiotherapy (SRS) whenever targets share multi-leaf collimator (MLC) leaf pairs. This study investigated the effect on plan quality and delivery, of reducing island blocking through collimator angle optimization (CAO). In addition, the effect of jaw tracking in this context was also investigated.

eXaSkin: A novel high-density bolus for 6MV X-rays radiotherapy.

Purpose: To evaluate eXaSkin, a novel high-density bolus alternative to commercial tissue-equivalent Superflab, for 6MV photon-beam radiotherapy.

Materials And Methods: We delivered a 10 × 10 cm open field at 90° and head-and-neck clinical plan, generated with the volumetric modulated arc therapy (VMAT) technique, to an anthropomorphic phantom in three scenarios: with no bolus on the phantom's surface, with Superflab, and with eXaSkin. In each scenario, we measured dose to a central planning target volume (PTV) in the nasopharynx region with an ionization chamber, and we measured dose to the skin, at three different positions within the vicinity of a neck lymph node PTV, with MOSkin™, a semiconductor dosimeter.

Towards real time in-vivo rectal dosimetry during trans-rectal ultrasound based high dose rate prostate brachytherapy using MOSkin dosimeters.

Purpose: To compare the dose measured by MOSkin dosimeters coupled to a trans-rectal ultrasound (TRUS) probe to the dose predicted by the brachytherapy treatment planning system (BTPS) during high dose rate (HDR) prostate brachytherapy (pBT), and to examine the feasibility of performing real-time catheter-by-catheter analysis of in-vivo rectal dosimetry during TRUS based HDR pBT.

Method: Four MOSkin dosimeters were coupled to a TRUS probe during 20 TRUS-based HDR pBT treatment fractions. The measured MOSkin doses were retrospectively compared to those predicted by the BTPS for the total treatment fraction, as well as on a per catheter basis.

A novel quality assurance system for eye plaque brachytherapy.

Eye Plaque brachytherapy pre-treatment quality assurance (QA) conducted clinically involves an activity verification of individual seeds via well chamber and does not include a physical measurement of dose-rate of the final assembly. A novel spectroscopic, dose-rate detection system, was evaluated for pre-treatment QA of eye plaque brachytherapy. The system includes a water phantom with sterility management.

Experimental characterization of magnetically focused electron contamination at the surface of a high-field inline MRI-linac.

Purpose: The fringe field of the Australian MRI-linac causes contaminant electrons to be focused along the central axis resulting in a high surface dose. This work aims to characterize this effect using Gafchromic film and high-resolution detectors, MOSkin and microDiamond. The secondary aim is to investigate the influence of the inline magnetic field on the relative dose response of these detectors.

Characterisation of out-of-field dose at shallow depths for external beam radiotherapy: implications for eye lens dose.

Re-evaluation of the eye lens radio-sensitivity by the ICRP in 2011 resulted in a significant reduction of the threshold for lens opacities from 8 Gy to 0.5 Gy. This has led to an increase in concern for eye lens doses from treatment sites further from the eye than previously considered.

Derivation of in vivo source tracking error thresholds for TRUS-based HDR prostate brachytherapy through simulation of source positioning errors.

Purpose: The purpose of this study was to simulate treatment planning source positioning errors in transrectal ultrasound-based real-time high-dose-rate prostate brachytherapy treatments and determine appropriate in vivo source tracking error thresholds.

Methods And Materials: Treatment planning source positioning errors were simulated for 20 patient plans in the brachytherapy treatment planning system by manually adjusting the dwell position coordinates within selected catheters without plan reoptimization. The change in dose-volume histogram (DVH) indices was calculated as a function of the source positioning error.

Dose verification for liver target volumes undergoing respiratory motion.

Respiratory motion has a significant impact on dose delivered to abdominal targets during radiotherapy treatment. Accurate treatment of liver tumours adjacent to the diaphragm is complicated by large respiratory movement, as well as differing tissue densities at the lung-liver interface. This study aims to evaluate the accuracy of dose delivered to superior liver tumours using passive respiratory monitoring, in the absence of gating technology, for a range of treatment techniques.

A Monte Carlo study on the feasibility of real-time in vivo source tracking during ultrasound based HDR prostate brachytherapy treatments.

Purpose: This study aims to assess the accuracy of in-vivo source tracking during real-time trans-rectal ultrasound (TRUS) based high dose rate (HDR) prostate brachytherapy (pBT) through Monte Carlo simulations of multiple HDR pBT treatments with a two-dimensional (2D) diode array, the Magic Plate 900 (MP900), embedded below the patient in a carbon-fibre couch.

Method: Monte Carlo simulations of source positions representing three separate real-time TRUS based HDR pBT treatments were performed using the Geant4 toolkit. For each source position, an Ir-192 source was simulated inside a voxelized patient geometry.

An innovative gynecological HDR brachytherapy applicator system for treatment delivery and real-time verification.

The multichannel vaginal cylinder (MVC) applicator employed for gynecological high dose rate (HDR) brachytherapy increases dose delivery complexity, and thus makes the treatment more prone to errors. A quality assurance (QA) procedure tracking the source throughout dose delivery can detect dwell position and time errors in the multiple channels of the applicator. A new MVC system with integrated real time in vivo treatment delivery QA has been developed based on diodes embedded on the outer surface of the MVC.

Dosimetric effects of brass mesh bolus on skin dose and dose at depth for postmastectomy chest wall irradiation.

Purpose: To investigate the feasibility of using the brass mesh bolus as an alternative to tissue- equivalent bolus for post mastectomy chest wall cancer by characterizing the dosimetric effects of the 2-mm fine brass bolus on both the skin dose, the dose at depth and spatial distribution.

Materials And Methods: Surface dose and percent depth dose data were acquired for a 6 MV photon beam in a solid water phantom using MOSkin™, Gafchromic EBT3 film and an Advanced Markus ionization chamber. Data were acquired for the case of: no bolus, Face-up bass bolus, Face-down brass bolus, double brass bolus, 0.

HDR brachytherapy in vivo source position verification using a 2D diode array: A Monte Carlo study.

Purpose: This study aims to assess the accuracy of source position verification during high-dose rate (HDR) prostate brachytherapy using a novel, in-house developed two-dimensional (2D) diode array (the Magic Plate), embedded exactly below the patient within a carbon fiber couch. The effect of tissue inhomogeneities on source localization accuracy is examined.

Method: Monte Carlo (MC) simulations of 12 source positions from a HDR prostate brachytherapy treatment were performed using the Geant4 toolkit.

Semiconductor real-time quality assurance dosimetry in brachytherapy.

With the increase in complexity of brachytherapy treatments, there has been a demand for the development of sophisticated devices for delivery verification. The Centre for Medical Radiation Physics (CMRP), University of Wollongong, has demonstrated the applicability of semiconductor devices to provide cost-effective real-time quality assurance for a wide range of brachytherapy treatment modalities. Semiconductor devices have shown great promise to the future of pretreatment and in vivo quality assurance in a wide range of brachytherapy treatments, from high-dose-rate (HDR) prostate procedures to eye plaque treatments.

Comparison of phantom materials for use in quality assurance of microbeam radiation therapy.

Microbeam radiation therapy (MRT) is a promising radiotherapy modality that uses arrays of spatially fractionated micrometre-sized beams of synchrotron radiation to irradiate tumours. Routine dosimetry quality assurance (QA) prior to treatment is necessary to identify any changes in beam condition from the treatment plan, and is undertaken using solid homogeneous phantoms. Solid phantoms are designed for, and routinely used in, megavoltage X-ray beam radiation therapy.

Influence of exposure and geometric parameters on absorbed doses associated with common neuro-interventional procedures.

Purpose: The purpose of this study was to investigate the effects of routine exposure parameters on patient's dose during neuro-interventional radiology procedures.

Methods: We scrutinized the routine radiological exposure parameters during 58 clinical neuro-interventional procedures such as, exposure direction, magnification, frame rate, and distance between image receptor to patient's body and evaluate their effects on patient's dose using an anthropomorphic phantom. Radiation dose received by the occipital region, ears and eyes of the phantom were measured using MOSkin detectors.

Real-time in vivo rectal wall dosimetry using MOSkin detectors during linac based stereotactic radiotherapy with rectal displacement.

Background: MOSFET dosimetry is a method that has been used to measure in-vivo doses during brachytherapy treatments and during linac based radiotherapy treatment. Rectal displacement devices (RDDs) allow for safe dose escalation for prostate cancer treatment. This study used dual MOSkin detectors to assess real-time in vivo rectal wall dose in patients with an RDD in place during a high dose prostate stereotactic body radiation therapy (SBRT) boost trial.