Design and characterization of a new high-dose-rate brachytherapy Valencia applicator for larger skin lesions.

Purpose: The aims of this study were (i) to design a new high-dose-rate (HDR) brachytherapy applicator for treating surface lesions with planning target volumes larger than 3 cm in diameter and up to 5 cm in size, using the microSelectron-HDR or Flexitron afterloader (Elekta Brachytherapy) with a (192)Ir source; (ii) to calculate by means of the Monte Carlo (MC) method the dose distribution for the new applicator when it is placed against a water phantom; and (iii) to validate experimentally the dose distributions in water.

Methods: The penelope2008 MC code was used to optimize dwell positions and dwell times. Next, the dose distribution in a water phantom and the leakage dose distribution around the applicator were calculated.

Novel tools for stepping source brachytherapy treatment planning: enhanced geometrical optimization and interactive inverse planning.

Purpose: Dose optimization for stepping source brachytherapy can nowadays be performed using automated inverse algorithms. Although much quicker than graphical optimization, an experienced treatment planner is required for both methods. With automated inverse algorithms, the procedure to achieve the desired dose distribution is often based on trial-and-error.

Prostate volume and implant configuration during 48 hours of temporary prostate brachytherapy: limited effect of oedema.

Background: In pulsed-dose rate prostate brachytherapy the dose is delivered during 48 hours after implantation, making the treatment sensitive to oedematic effects possibly affecting dose delivery. The aim was to study changes in prostate volume during treatment by analysing catheter configurations on three subsequent scans.

Methods: Prostate expansion was determined for 19 patients from the change in spatial distribution of the implanted catheters, using three CT-scans: a planning CT (CT1) and two CTs after 24 and 48 hours (CT2, CT3).

A comparison of inverse optimization algorithms for HDR/PDR prostate brachytherapy treatment planning.

Purpose: Graphical optimization (GrO) is a common method for high-dose-rate/pulsed-dose-rate (PDR) prostate brachytherapy treatment planning. New methods performing inverse optimization of the dose distribution have been developed over the past years. The purpose is to compare GrO and two established inverse methods, inverse planning simulated annealing (IPSA) and hybrid inverse treatment planning and optimization (HIPO), and one new method, enhanced geometric optimization-interactive inverse planning (EGO-IIP), in terms of speed and dose-volume histogram (DVH) parameters.

Review of clinical brachytherapy uncertainties: analysis guidelines of GEC-ESTRO and the AAPM.

Background And Purpose: A substantial reduction of uncertainties in clinical brachytherapy should result in improved outcome in terms of increased local control and reduced side effects. Types of uncertainties have to be identified, grouped, and quantified.

Methods: A detailed literature review was performed to identify uncertainty components and their relative importance to the combined overall uncertainty.

Deviations from the planned dose during 48 hours of stepping source prostate brachytherapy caused by anatomical variations.

Background And Purpose: To determine the uncertainties in planned dose associated with catheter and organ movement during 48 hours of stepping source prostate brachytherapy.

Material And Methods: Pulsed-dose rate (PDR) prostate brachytherapy as a boost is given in 24 pulses every 2 hours, making the total treatment last 48 hours. The entire treatment is based on one plan, created on the planning CT (CT1).

Improved tumour control probability with MRI-based prostate brachytherapy treatment planning.

Background: Due to improved visibility on MRI, contouring of the prostate is improved compared to CT. The aim of this study was to quantify the benefits of using MRI for treatment planning as compared to CT-based planning for temporary implant prostate brachytherapy.

Material And Methods: CT and MRI image data of 13 patients were used to delineate the prostate and organs at risk (OARs) and to reconstruct the implanted catheters (typically 12).

Dosimetric characterization of Ir-192 LDR elongated sources.

Ir-192 wires have been used in low-dose-rate brachytherapy for many years. Commercially available treatment planning systems approximate the dose rate distribution of the straight or curved wires applying the superposition principle using one of the following methods: (i) The wire is modeled as a set of point sources, (ii) the wire is modeled as a set of small straight segment wires, (iii) the values of the parameters and functions of the American Association of Physicists in Medicine (AAPM) Task Group 43 protocol are obtained for wire lengths between 3 and 7 cm assuming some simplifications. The dose rate distributions obtained using these methods for linear wires of different lengths and U-shaped wires present significant deviations compared to those obtained by Monte Carlo.

Design and evaluation of a HDR skin applicator with flattening filter.

The purposes of this study are: (i) to design field flattening filters for the Leipzig applicators of 2 and 3 cm of inner diameter with the source traveling parallel to the applicator contact surface, which are accessories of the microSelectron-HDR afterloader (Nucletron, Veenendaal, The Netherlands). These filters, made of tungsten, aim to flatten the heterogeneous dose distribution obtained with the Leipzig applicators. (ii) To estimate the dose rate distributions for these Leipzig+filter applicators by means of the Monte Carlo (MC) method.

Technique for routine output verification of Leipzig applicators with a well chamber.

The H-type Leipzig applicators are accessories of the microSelectron-HDR system (Nucletron, Veenendaal, The Netherlands) for treatment of superficial malignancies. Recently, the dose rate distributions in liquid water for the whole set of applicators using both source models available for the microSelectron-HDR afterloaders have been obtained by means of the experimentally validated Monte Carlo (MC) code GEANT4. Also an output table (cGy/hU) at 3 mm depth on the applicator central axis was provided.

Influence of dose point and inverse optimization on interstitial cervical and oropharyngeal carcinoma brachytherapy.

Background And Purpose: Evaluation of the use of optimization methods in interstitial cervical and oropharyngeal brachytherapy; evaluation of the conformal index (COIN) and the natural dose ratio (NDR) to quantify the implant quality.

Material And Methods: CT-based dose distributions were obtained for seven implants according to the Paris system. CT-based implants were used to assess the dose point and inverse optimization methods.

The combined use of the natural and the cumulative dose-volume histograms in planning and evaluation of permanent prostatic seed implants.

Background And Purpose: To investigate prostate dose coverage and overdosage in planned and realized permanent iodine seed prostate implants and to explore the use of the natural dose-volume histogram (NDVH) and the cumulative dose-volume histogram (CDVH) as tools to optimize prostate implants.

Materials And Methods: The optimal prescription dose (PD) or natural prescription dose (NPD) was derived from the NDVH. The mismatch between the NPD and the given PD was called the natural dose ratio (NDR).

CT-based software for 3-D localization and reconstruction in stepping source brachytherapy.

This paper describes innovative software for catheter localization and three-dimensional (3-D) reconstruction in stepping source brachytherapy applications. Patient information is a set of computed tomography (CT) slices scanned during the implantation of brachytherapy catheters. Catheter geometry and patient anatomy are exported for use with dose calculation software modules.

Dependence of the tray transmission factor on collimator setting and source-surface distance.

When blocks are placed on a tray in megavoltage x-ray beams, generally a single correction factor for the attenuation by the tray is applied for each photon beam quality. In this approach, the tray transmission factor is assumed to be independent of field size and source-surface distance (SSD). Analysis of a set of measurements performed in beams of 13 different linear accelerators demonstrates that there is, however, a slight variation of the tray transmission factor with field size and SSD.

Effect of electron contamination on scatter correction factors for photon beam dosimetry.

Physical quantities for use in megavoltage photon beam dose calculations which are defined at the depth of maximum absorbed dose are sensitive to electron contamination and are difficult to measure and to calculate. Recently, formalisms have therefore been presented to assess the dose using collimator and phantom scatter correction factors, Sc and Sp, defined at a reference depth of 10 cm. The data can be obtained from measurements at that depth in a miniphantom and in a full scatter phantom.

A consistent formalism for the application of phantom and collimator scatter factors.

A coherent system for the use of scatter correction factors, determined at 10 cm depth, is described for dose calculations on the central axis of arbitrarily shaped photon beams. The system is suitable for application in both the fixed source-surface distance (SSD) and in the isocentric treatment set-up. This is in contrast to some other proposals where only one of these approaches forms the basis of the calculation system or where distinct quantities and data sets are needed.

A three-Gaussian fit of phantom scatter correction data.

The phantom scatter correction factor Sp of megavoltage photon beams can be accurately described using a three-Gaussian fit. The model leads to six parameters, with which Sp(r) is described as a smooth function of the field radius r for beam qualities in the range from 60Co up to 25 MV. The parameters allow Sp values to be calculated at intermediate beam energies and for any field shape.

Is there a need for a revised table of equivalent square fields for the determination of phantom scatter correction factors?

The use of the British Journal of Radiology (BJR) (supplement 17) tables of equivalent square fields for dose calculations is widespread. A revised version of the supplement was published recently, with a more elaborate discussion, but without changes in data given in these tables (Br. J.

Comparison of parametrization methods of the collimator scatter correction factor for open rectangular fields of 6-25 MV photon beams.

Purpose: To facilitate the use of the collimator scatter correction factor, Sc, parametrization methods that relate Sc to the field size by fitting were investigated.

Materials And Methods: Sc was measured with a mini-phantom for five types of dual photon energy accelerators with energies varying between 6 and 25 MV. Using these Sc-data six methods of parametrizing Sc for square fields were compared, including a third-order polynomial of the natural logarithm of the field size normalized to the field size of 10 cm2.

The determination of phantom and collimator scatter components of the output of megavoltage photon beams: measurement of the collimator scatter part with a beam-coaxial narrow cylindrical phantom.

The separation of the total scatter correction factor Sc,p in a collimator scatter component, Sc, and a phantom scatter component, Sp, has proven to be an useful concept in megavoltage photon beam dose calculations in situations which differ from the standard treatment geometry. A clinically applicable method to determine Sc is described. Measurements are carried out with an ionization chamber, placed at a depth beyond the range of contaminant electrons, in a narrow cylindrical polystyrene phantom with a diameter of 4 cm of which the axis coincides with the beam axis.

Discrepancies in dose and dose specification in interstitial implants.

The first step in the execution of an interstitial implant is the decision on size and location of the target volume. Several implant systems, e.g.