Dosimetric impact of rotational errors in trigeminal neuralgia radiosurgery using CyberKnife.

Purpose: Trigeminal neuralgia (TN) can be treated on the CyberKnife system using two different treatment delivery paths: the general-purpose full path corrects small rotations, while the dedicated trigeminal path improves dose fall-off but does not allow rotational corrections. The study evaluates the impact of uncorrected rotations on brainstem dose and the length of CN5 (denoted as L) covered by the prescription dose.

Methods And Materials: A proposed model estimates the delivered dose considering translational and rotational delivery errors for TN treatments on the CyberKnife system.

4D Monte Carlo dose reconstructions using surface motion measurements.

Purpose: To investigate the feasibility of a 4D Monte Carlo based dose reconstruction method to study the dosimetric impact of respiratory motion using surface motion measurements for patients undergoing VMAT treatments for Non-Small Cell Lung Cancer.

Methods: The 4Ddefdosxyznrc/EGSnrc algorithm was used to reconstruct VMAT doses delivered to the patients using machine log files and respiratory traces measured with the RADPOS 4D dosimetry system. The RADPOS sensor was adhered to the patient's abdomen prior to each treatment fraction and its position was used as a surrogate for tumour motion.

A dose perturbation tool for robotic radiosurgery: Experimental validation and application to liver lesions.

Background: An analytical tool is empirically validated and used to assess the delivered dose to liver lesions accounting for different types of errors in robotic radiosurgery treatment.

Material And Methods: A tool is proposed to estimate the target doses taking into account the translation, rotation, and deformation of a target. Translational errors are modeled as a spatial convolution of the planned dose with a probability distribution function derived from treatment data.

Patient-specific PTV margins for liver stereotactic body radiation therapy determined using support vector classification with an early warning system for margin adaptation.

Purpose: An adaptive planning target volume (PTV) margin strategy incorporating a volumetric tracking error assessment after each fraction is proposed for robotic stereotactic body radiation therapy (SBRT) liver treatments.

Methods And Materials: A supervised machine learning algorithm employing retrospective data, which emulates a dry-run session prior to planning, is used to investigate if motion tracking errors are <2 mm, and consequently, planning target volume (PTV) margins can be reduced. A fraction of data collected during the beginning of a treatment course emulates a dry-run session (mock) before planning.

Validation of 4D Monte Carlo dose calculations using a programmable deformable lung phantom.

Purpose: To validate the accuracy of 4D Monte Carlo (4DMC) simulations to calculate dose deliveries to a deforming anatomy in the presence of realistic respiratory motion traces. A previously developed deformable lung phantom comprising an elastic tumor was modified to enable programming of arbitrary motion profiles. 4D simulations of the dose delivered to the phantom were compared with the measurements.

AAPM TG 191: Clinical use of luminescent dosimeters: TLDs and OSLDs.

Thermoluminescent dosimeters (TLD) and optically stimulated luminescent dosimeters (OSLD) are practical, accurate, and precise tools for point dosimetry in medical physics applications. The charges of Task Group 191 were to detail the methodologies for practical and optimal luminescence dosimetry in a clinical setting. This includes: (a) to review the variety of TLD/OSLD materials available, including features and limitations of each; (b) to outline the optimal steps to achieve accurate and precise dosimetry with luminescent detectors and to evaluate the uncertainty induced when less rigorous procedures are used; (c) to develop consensus guidelines on the optimal use of luminescent dosimeters for clinical practice; and (d) to develop guidelines for special medically relevant uses of TLDs/OSLDs such as mixed photon/neutron field dosimetry, particle beam dosimetry, and skin dosimetry.

Dosimetric and radiobiological investigation of permanent implant prostate brachytherapy based on Monte Carlo calculations.

Purpose: Permanent implant prostate brachytherapy plays an important role in prostate cancer treatment, but dose evaluations typically follow the water-based TG-43 formalism, ignoring patient anatomy and interseed attenuation. The purpose of this study is to investigate advanced TG-186 model-based dose calculations via retrospective dosimetric and radiobiological analysis for a new patient cohort.

Methods And Materials: A cohort of 155 patients treated with permanent implant prostate brachytherapy from The Ottawa Hospital Cancer Centre is considered.

Geometrical tracking accuracy and appropriate PTV margins for robotic radiosurgery of liver lesions by SBRT.

To assess the geometrical accuracy and estimate adequate PTV margins for liver treatments using the Synchrony respiratory tracking system. : Treatment log files are analyzed for 72 liver patients to assess tracking accuracy. The tracking error is calculated as the quadratic sum of the correlation, the predictor and the beam positioning errors.

Monte Carlo and analytic modeling of an Elekta Infinity linac with Agility MLC: Investigating the significance of accurate model parameters for small radiation fields.

Purpose: To explain the deviation observed between measured and Monaco calculated dose profiles for a small field (i.e., alternating open-closed MLC pattern).

Evaluation of the 4D RADPOS dosimetry system for dose and position quality assurance of CyberKnife.

Purpose: The Synchrony respiratory motion tracking of the CyberKnife system purports to provide real-time tumor motion compensation during robotic radiosurgery. Such a complex delivery system requires thorough quality assurance. In this work, RADPOS applicability as a dose and position quality assurance tool for CyberKnife treatments is assessed quantitatively for different phantom types and breathing motions, which increase in complexity to more closely resemble clinical situations.

Development of a deformable phantom for experimental verification of 4D Monte Carlo simulations in a deforming anatomy.

Purpose: To verify the accuracy of 4D Monte Carlo (MC) simulations, using the 4DdefDOSXYZnrc user code, in a deforming anatomy. We developed a tissue-equivalent and reproducible deformable lung phantom and evaluated 4D simulations of delivered dose to the phantom by comparing calculations against measurements.

Methods: A novel deformable phantom consisting of flexible foam, emulating lung tissue, inside a Lucite external body was constructed.

Experimental verification of 4D Monte Carlo simulations of dose delivery to a moving anatomy.

Purpose: To evaluate a novel 4D Monte Carlo simulation tool by comparing calculations to physical measurements using a respiratory motion phantom.

Methods: We used a dynamic Quasar phantom in both stationary and breathing states (sinusoidal motion of amplitude of 1.8 cm and period of 3.

Evaluation of a new commercial Monte Carlo dose calculation algorithm for electron beams.

Purpose: In this report the authors present the validation of a Monte Carlo dose calculation algorithm (XiO EMC from Elekta Software) for electron beams.

Methods: Calculated and measured dose distributions were compared for homogeneous water phantoms and for a 3D heterogeneous phantom meant to approximate the geometry of a trachea and spine. Comparisons of measurements and calculated data were performed using 2D and 3D gamma index dose comparison metrics.

Real-time measurement of urethral dose and position during permanent seed implantation for prostate brachytherapy.

Purpose: The in vivo dosimetry tool, RADPOS, has been modified to include a metal oxide-silicon semiconductor field effect transistor (MOSFET) array with an electromagnetic positioning sensor. This allows dose monitoring at five points rather than just at single dose point as in the other versions of the device. The detector has been used in a clinical trial, which is the first to measure both urethral dose and internal motion concurrently during permanent seed implantation for prostate brachytherapy using a single probe.

In vivo dosimetry in brachytherapy.

In vivo dosimetry (IVD) has been used in brachytherapy (BT) for decades with a number of different detectors and measurement technologies. However, IVD in BT has been subject to certain difficulties and complexities, in particular due to challenges of the high-gradient BT dose distribution and the large range of dose and dose rate. Due to these challenges, the sensitivity and specificity toward error detection has been limited, and IVD has mainly been restricted to detection of gross errors.

Generalized eMC implementation for Monte Carlo dose calculation of electron beams from different machine types.

The electron Monte Carlo (eMC) dose calculation algorithm available in the Eclipse treatment planning system (Varian Medical Systems) is based on the macro MC method and uses a beam model applicable to Varian linear accelerators. This leads to limitations in accuracy if eMC is applied to non-Varian machines. In this work eMC is generalized to also allow accurate dose calculations for electron beams from Elekta and Siemens accelerators.

The effect of different bleaching wavelengths on the sensitivity of Al(2)O(3):C optically stimulated luminescence detectors (OSLDs) exposed to 6 MV photon beams.

Purpose: To determine the effect of different bleaching wavelengths on the response of Al(2)O(3):C optically stimulated luminescence detectors (OSLDs) exposed to accumulated doses of 6 MV photon beams.

Methods: In this study the authors used nanoDot OSLDs readout with a MicroStar reader. The authors first characterized the dose-response, fading, and OSL signal loss of OSLDs exposed to doses from 0.

Clinical use of a novel in vivo 4D monitoring system for simultaneous patient motion and dose measurements.

Purpose: A new 4D in vivo dosimetry tool, RADPOS, has been used on lung cancer patients to evaluate the feasibility of using the detectors to characterize variations in patient breathing patterns as well as to monitor daily variations in dose.

Methods And Materials: The RADPOS system combines a MOSFET dosimeter with an electromagnetic positioning sensor for simultaneous measurement of real-time dose and spatial coordinates. Three RADPOS sensors were placed on patients' chest and abdomen during a 4DCT and daily treatments.

4D dose-position verification in radiation therapy using the RADPOS system in a deformable lung phantom.

Purpose: A novel 4D in vivo dosimetry system (RADPOS), in conjunction with a deformable lung phantom, has been evaluated as a potential quality assurance tool for 4D radiotherapy.

Methods: RADPOS detectors, which consist of a MOSFET dosimeter combined with an electromagnetic positioning probe, were placed inside the deformable lung phantom. One detector was positioned directly inside a tumor embedded in the lung phantom and another was positioned inside the lung portion of the phantom, outside the tumor.

Penile brachytherapy: technical aspects and postimplant issues.

Purpose: Squamous carcinoma (SCC) of the penis affects about 1 in 100,000 men in western societies. Interstitial brachytherapy can be an effective penis-conserving modality for T1, T2, and selected T3 tumors. Unfortunately, few radiation oncology trainees have the opportunity to treat a case of penile cancer during their residency, and few centers have brachytherapy expertise for this tumor site.

Report of the AAPM Task Group No. 105: Issues associated with clinical implementation of Monte Carlo-based photon and electron external beam treatment planning.

The Monte Carlo (MC) method has been shown through many research studies to calculate accurate dose distributions for clinical radiotherapy, particularly in heterogeneous patient tissues where the effects of electron transport cannot be accurately handled with conventional, deterministic dose algorithms. Despite its proven accuracy and the potential for improved dose distributions to influence treatment outcomes, the long calculation times previously associated with MC simulation rendered this method impractical for routine clinical treatment planning. However, the development of faster codes optimized for radiotherapy calculations and improvements in computer processor technology have substantially reduced calculation times to, in some instances, within minutes on a single processor.

MOSFET detectors in quality assurance of tomotherapy treatments.

Background And Purpose: The purpose of this work was to characterize metal oxide semiconductor field-effect transistors (MOSFETs) in a 6 MV conventional linac and investigate their use for quality assurance of radiotherapy treatments with a tomotherapy Hi-Art unit.

Materials And Methods: High sensitivity and standard sensitivity MOSFETs were first calibrated and then tested for reproducibility, field size dependence, and accuracy of measuring surface dose in a 6 MV beam as well as in a tomotherapy Hi-Art unit. In vivo measurements were performed on both a RANDO phantom and several head and neck cancer patients treated with tomotherapy and compared to TLD measurements and treatment plan doses to evaluate the performance of MOSFETs in a high gradient radiation field.

Feasibility study of using MOSFET detectors for in vivo dosimetry during permanent low-dose-rate prostate implants.

Purpose: To investigate the feasibility of using new micro-MOSFET detectors for QA and in vivo dosimetry of the urethra during transperineal interstitial permanent prostate implants (TIPPB).

Methods And Materials: This study involves measurements for several patients who have undergone the implant procedure with iodine-125 seeds. A new micro-MOSFET detector is used as a tool for in vivo measurement of the initial dose rate within the urethra.

First macro Monte Carlo based commercial dose calculation module for electron beam treatment planning--new issues for clinical consideration.

The purpose of this study is to present our experience of commissioning, testing and use of the first commercial macro Monte Carlo based dose calculation algorithm for electron beam treatment planning and to investigate new issues regarding dose reporting (dose-to-water versus dose-to-medium) as well as statistical uncertainties for the calculations arising when Monte Carlo based systems are used in patient dose calculations. All phantoms studied were obtained by CT scan. The calculated dose distributions and monitor units were validated against measurements with film and ionization chambers in phantoms containing two-dimensional (2D) and three-dimensional (3D) type low- and high-density inhomogeneities at different source-to-surface distances.

Interstitial low-dose-rate brachytherapy in the treatment of recurrent head and neck malignancies.

Background: Recurrent head and neck malignancies are therapeutically challenging. Brachytherapy is a retreatment alternative to external-beam radiation therapy (EBRT).

Methods: Patients receiving brachytherapy during 1987-2004 for recurrent head and neck cancer were identified.