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Radiation-induced cardiovascular disease: impact of dose and volume.

The radiation-induced cardiovascular pathology represents a major cause of morbidity and mortality in patients undergoing therapeutic chest irradiation. There is a broad range of clinical manifestations probably associated with dose, volume and technique of irradiation. From the assumption that prevention is the best way to manage radiation-induced cardiotoxicity, based on the pathophysiogenesis of heart structures, a number of reports of the literature are reviewed. They consider the incidence of cardiovascular disease in patients affected by Hodgkin's lymphoma and breast cancer. The dosimetric prevention is takled in terms of therapeutic procedures and doses (IMRT, 3DCRT) with particular reference to the impact on cardiotoxicity of parameters as maximum heart distance (MHD), mean lung dose (MLD), normal tissue complication probability (NTCP) and V30. The different evaluation criteria of cardiotoxicity are reported, based on the review of the major scoring scales of acute and late complications, which have been worked out in the course of time (LENT-SOMA, RTOG, CTC v.2.0 and CTC v.3.0). The monitoring system of late toxicity used by the authors is presented.

Breast Neoplasms↗
PubMed1991

[Evaluation of irradiation techniques in breast carcinoma using dose-volume histograms. Comparison of the heart and lung exposure].

For irradiation of the internal mammary lymph nodes (IMN), together with irradiation of the breast the commonly used treatment techniques are of three types: 1. two tangential opposed fields, 2. three field plans with a separate "straight on" IMN-field, or 3. with a separate "angled" IMN-field. To determine lung and heart volumes and doses for these techniques, dose-volume-histograms in 30 patients were analyzed. The optimum dose distribution was achieved with the "angled" field technique and an appropriate combination of electrons and 60Co gamma radiation for the IMN-field. (The beam mixture used was 40% 60Co beam and 60% electron beam.) The least possible dose to the lung was obtained with the "straight-on" field technique and the least possible dose to the heart with the separate "angled" IMN-field technique.

Breast Neoplasms↗
PubMed1983

Fluence and absorbed dose in high energy electron beams.

The depth dependence of fluence, vectorial and planar fluence, energy fluence, vectorial and planar energy fluence and absorbed dose has been calculated in 5 and 20 MeV electron beams in water. The shape of these distributions has been compared with analytic expressions for fluence and absorbed dose and the general mechanisms governing the shape of the depth dose curve have been explained. In particular it is demonstrated that the depth dependence of planar energy fluence and mean energy is very similar, and so is the case for fluence and absorbed dose and primary fluence and absorbed dose from primaries with inclusion of fast secondaries. The results are useful for dosimetry and dose planning in high energy electron beams.

Computers↗
PubMed1983

Comparison of broad beam central axis depth dose curves from different accelerators using the universal depth dose curve model.

Electron beam central axis depth dose distribution can be transformed to fluence distributions with geometric depth replaced by a measure of the state of angular dispersion of the beam. A transformed central axis depth dose distribution was called a 'fluence curve.' The transformation was applied to a set of central axis depth dose curves calculated by Monte Carlo code for broad electron beams of energies ranging from 1 to 60 MeV in homogeneous phantoms of water, aluminium, and copper. For the energies and compositions likely to be encountered in external beam radiation therapy, the resulting fluence curves, were found to belong to a single parameter family. A collimator scatter parameter was introduced to take into account the initial angular dispersion produced by the collimator of an accelerator. Given the energy of the beam, the medium in which the beam is passing through, and the collimator scatter parameter, the fluence curve associated with the beam can easily be transformed back to a calculated depth dose curve. The collimator scatter parameter necessary to fit the depth dose curves measured on different accelerators was investigated. The results for the Clinac 18, LMR-13, Mevatron XII, Mevatron 80, Microtron, Sagittaire, Siemens Betatron, and the Therac 20 are presented.

Computers↗
PubMed1983

Characteristic functions of point monodirectional electron beams.

Narrow electron beams with approximately Gaussian radial fluence distributions were extracted from a clinical 42 MeV betatron by means of a special multi-diaphragm lead collimator with either 3 or 7.5 mm diameter of the effective diaphragm. From each narrow beam the dose distribution in water, was measured with an automated scanning system, and the corresponding dose distribution of the point monodirectional source was obtained by deconvolution. As a reference, the fluence distribution in air at the same distance z was used, corrected for multiple scattering in air where necessary. At 10, 20 and 40 MeV, non-linear pear-shaped curves for the root mean square radial excursion, sigma(z), as functions of the depth, with maxima of 12, 19.7 and 27.8 mm at about 70 per cent of the practical range were obtained. The second characteristic function, I(z), the integral of the dose over the transverse plane at depth z, was obtained from the measured broad beam depth dose curve and the associated transverse dose distributions.

Computers↗
PubMed1983

Absorbed dose distribution of electron beams in uniform and inhomogeneous media.

The absorbed dose at dose maximum in different materials or tissues irradiated by a given electron fluence can vary considerably depending on scattering and stopping properties of the media. A simple expression relating the dose levels in different materials have been derived and is found to be in good agreement with published experimental results for different phantom materials. This expression has been used to calculate the ratio of the absorbed dose to different tissues to that in water. The absorbed dose behind different inhomogeneities has been investigated experimentally. Based on this expression correction factors and scaling laws have been derived which allow the calculation of the absorbed dose distribution behind the inhomogeneity with good accuracy. The procedure only uses tabulated mass scattering and total stopping power data and the dose distribution in the uniform medium. The shift in penetration behind the inhomogeneity independent of its depth is shown to be accurately determined by the equivalent thickness of the inhomogeneity as obtained by multiplying the real thickness by the total stopping power ratio at the incident mean energy.

Adipose Tissue↗
PubMed1983

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. The dose distributions of the pencil beams are derived from measurements of broad beam dose distributions; in this way the influence of electrons scattered by the applicator walls is taken into account. The contribution to the dose by electrons scattered from a high Z metal frame which defines the treatment field contour is calculated separately and added. This calculation is based on experimentally derived data. The method has been tested for electron beams with 6, 10, 14 and 20 MeV nominal energy. The distance between calculated and measured isodose lines with values between 90 and 10 per cent of the maximum dose did not exceed a limit of 0.3 cm. The difference between calculated and measured output factors remained within 2 per cent.

Computers↗