Verification of treatment parameter transfer by means of electronic portal dosimetry.

Electronic portal imaging devices (EPIDs) are mainly used for patient setup verification during treatment but other geometric properties like block shape and leaf positions are also determined. Electronic portal dosimetry allows dosimetric treatment verification. By combining geometric and dosimetric information, the data transfer between treatment planning system (TPS) and linear accelerator can be verified which in particular is important when this transfer is not carried out electronically.

Clinical dosimetry with MOSFET dosimeters to determine the dose along the field junction in a split beam technique.

Background And Purpose: We report on the accuracy of metal oxide-silicon semiconductor field effect transistor (MOSFET) detectors to measure dose distributions in the region of a field junction in a split beam technique, compared to ionisation chamber and photographic film. We present a study on five patients receiving loco-regional treatment for breast cancer.

Materials And Methods: The dose variation at the junction was measured with the patient dose verification system model TN-RD-50 (MOSFET system).

Monitor unit calculations for wedged asymmetric photon beams.

Algorithms for calculating monitor units (MUs) in wedged asymmetric high-energy photon beams as implemented in treatment planning systems have their limitations. Therefore an independent method for MU calculation is necessary. The aim of this study was to develop an empirical method to determine MUs for points at the centre of wedged fields, asymmetric in two directions.

An improved technique for breast cancer irradiation including the locoregional lymph nodes.

Purpose: To find an irradiation technique for locoregional irradiation of breast cancer patients which, compared with a standard technique, improves the dose distribution to the internal mammary-medial supraclavicular (IM-MS) lymph nodes. The improved technique is intended to minimize the lung dose and reduce the dose to the heart.

Methods And Materials: The standard technique consists of an anterior mixed electron/photon IM-MS field.

A treatment planning method to correct dose distributions distorted by setup verification fields.

Purpose: Portal images of conformal treatment fields are often not suitable for setup verification purposes because they contain insufficient bony structures. Therefore, additional rectangular fields are frequently applied for setup verification purposes. It is the aim of this study to reduce the dose distortions induced by these extra fields by appropriately adjusting the beam weights and wedge angles of the treatment fields.

A semi-empirical method for calculating the effect of air gap space on output factors on electron beam dose distributions.

Background: A simple approach to calculate the effect of air gap on output factors on electron beam dose distribution is presented.

Methods: The method accounts for variations of pencil beam parameters using a model developed by Bruinvis et al. [4,5].

A fast and accurate treatment planning method for boron neutron capture therapy.

Background And Purpose: The aim of this study was to test the applicability of conventional semi-empirical algorithms for the treatment planning of boron neutron capture therapy (BNCT).

Materials And Methods: Beam data of a clinical epithermal BNCT beam obtained in a large cuboid water phantom were introduced into a commercial treatment planning system (TPS). For the calculation of thermal neutron fluence distributions, the Gaussian pencil beam model of the electron beam treatment planning algorithm was used.

Characteristics of scattered electron beams shaped with a multileaf collimator.

Characteristics of dual-foil scattered electron beams shaped with a multileaf collimator (MLC) (instead of an applicator system) were studied. The electron beams, with energies between 10 and 25 MeV, were produced by a racetrack microtron using a dual-foil scattering system. For a range of field sizes, depth dose curves, profiles, penumbra width, angular spread in air, and effective and virtual source positions were compared.

Electron dose calculations using the Method of Moments.

The Method of Moments is generalized to predict the dose deposited by a prescribed source of electrons in a homogeneous medium. The essence of this method is (i) to determine, directly from the linear Boltzmann equation, the exact mean fluence, mean spatial displacements, and mean-squared spatial displacements, as functions of energy; and (ii) to represent the fluence and dose distributions accurately using this information. Unlike the Fermi-Eyges theory, the Method of Moments is not limited to small-angle scattering and small angle of flight, nor does it require that all electrons at any specified depth z have one specified energy E(z).

Influence of shape on the accuracy of grid-based volume computations.

The influence of the shape of a region of interest (ROI) on the uncertainty in the sampled volume of the ROI is investigated for computations with regular Cartesian grids. Both mathematically defined volumes and clinically relevant ROIs were studied. The sampling uncertainty is shown to depend on the compactness of the ROI and on effects of grid matching and translational symmetry.

Quantification of patient to patient variation of skin erythema developing as a response to radiotherapy.

A method is described to determine accurately skin redness during a course of radiotherapy using reflectance spectroscopy utilizing information from across the visible spectrum according to the L*a*b* color coordinate system. The method was used to quantify the development of skin erythema during and after electron beam irradiation of the chest wall following mastectomy. A number of factors were identified which could influence the wide variation in response seen between patients.

Calculation of electron beam depth-dose curves and output factors for arbitrary field shapes.

A previously presented method to calculate depth-dose curves and output factors for arbitrarily shaped electron beams is evaluated. The method employs a Gaussian pencil model for direct incident and applicator scattered electrons; the parameter values are derived from measured central axis depth-dose distributions. In addition, an empirical model is used to compute the dose due to electrons scattered by field-defining frames.

Comparison of ionisation measurements in water and polystyrene for electron beam dosimetry.

For the determination of absorbed dose to water in electron beams, dosimetry protocols advocate ionisation measurements in plastic phantoms instead of water for practical reasons. The chamber readings in polystyrene at the depth of maximum ionisation must be corrected for the difference in physical properties between the two materials. This correction factor was determined for a Farmer 0.

Calculation of electron beam dose distributions for arbitrarily shaped fields.

A method for the calculation of absorbed dose distributions of arbitrarily shaped electron beams is presented. Isodose distributions and output factors of treatment fields can be predicted with good accuracy, without the need for any dose measurement in the actual field. A Gaussian pencil beam model is employed with two different pencil beams for each electron beam energy.

Dose calculations for arbitrarily shaped electron beams.

A method for the calculation of absorbed dose distributions of arbitrarily shaped electron beams is described. Isodose distributions and the output factor of a newly designed treatment field can be predicted with good accuracy, without the need for any dose measurement in the actual field. Two different Gaussian pencil beams are used as building elements for the treatment beams of each electron energy.

Wall-scattering effects in electron beam collimation.

This report describes now a set of applicators, convering fields with dimensions of 4 to 20 cm, for the 6 to 20 MeV electron beams of a MEL SL75-20 linear accelerator was developed. The electron scatter contribution of the applicator walls to the treatment field was investigated, varying the applicator entrance opening and the scattering foil, with the aim of optimizing the resulting field flatness, with a minimum loss of depth dose. Experiments with field defining end frames and additional perspex scatterers for large field sizes are also reported.