A method of in vivo measurement of the elastic properties of skin in radiotherapy patients.

A portable apparatus which measures the force-displacement or elastic characteristics of skin in vivo has been constructed. A displacement transducer between two arms measures the extension of the skin as the arms are driven apart by means of a lead screw, and the force exerted on the skin is measured by means of two electrical resistance strain gauges attached at a reduced section on each of the arms. The apparatus was designed for compactness and lightness to enable it to be hand held. Illustrative results obtained on patients during and after courses of radiotherapy are presented.

The dosimetry of bone irradiated by fast neutrons.

The previous work on the dosimetry of bone is briefly reviewed. A dosimetric theory for the response of detectors irradiated by fast neutrons is applied to the problem of bone dosimetry. In the theory the detector or cavity shape is characterised by distributions of chord lengths along which the neutron-produced charged particles travel and deposit energy. Cavities of different convex geometries can be treated. A simplified version of the theory uses a single mean chord length to characterise the cavity. The absorbed dose to individual marrow cavities in trabecular bone is calculated over a large range of marrow cavity size for monoenergetic neutrons ranging from 0.5 to 7.0 MeV and for 252Cf neutrons. The influence of cavity shape is explored by considering spheres and cylinders of different elongation. The difference in absorbed dose is not great. Also the simplified model using a single mean chord length gives results in close agreement with the results obtained with chord length distributions. The mean marrow dose to different human bones has been calculated in three ways. First by using measured chord length distributions for the marrow cavities in the bones, second by using a sphere with the same mean chord length as the measured distribution and third by applying the measured single mean chord length. The difference between the three approaches is small and the agreement is good with results obtained by other workers who used the Monte Carlo technique. The dose to the endosteal cell layer has also been calculated by approximating the layer with an infinite slab.

The dosimetry of radioisotopes incorporated in bone using cavity ionization theory.

Cavity ionization theory is applied to the dosimetry of bones incorporating beta- and gamma-emitting radioactive isotopes. The assumptions inherent in different theoretical approaches to bone dosimetry are reviewed and compared with those adopted in cavity theory. In presenting the theory attention is given to the effects of electron and photon attenuation and to the absence of electronic equilibrium which may occur in bone. The mean marrow dose is calculated for a range of cavity size and gamma-ray energies and for a beta-ray emitter. The mean marrow dose and the mean endosteal dose are calculated for a human lumbar vertebra and some comparisons made with the results of other workers. It is concluded that cavity theory provides a useful approach to the dosimetry problems of bone-seeking beta- and gamma-ray radioactive isotopes.

The effects of split dose radiations on the mechanical properties of the skin.

A series of split dose experiments in which the interval between doses was varied from 1 to 7 d is reported. In vitro measurements of the mechanical properties of skin are made 50 and 120 d after the first irradiation. The variation of the skin thickness, load at rupture, extension at rupture, stress at rupture and skin stiffness with dose and with time interval between doses is examined. The results suggest that after the highest doses of irradiation the skin is matted in structure and the fractionation pattern is insignificant. Different fractionation patterns only influence the radiation effects at lower doses where the skin retains an open mesh structure. The experiments indicate that a maximum skin sparing effect is obtained with a two day interval between the split doses.

The effects of x-irradiation on the mechanical properties of skin.

The elastic properties of rat skin previously irradiated with single doses form 1000 to 3000 rad have been studied. The measurements were made 50 and 120 d after irradiation on skin specimens immersed in saline at 37 degrees c. The tests were carried out on a tensile testing machine. The load extension curve, which was plotted to the point of rupture, exhibits two portions which are identified with the aligment of the collagen fibres and then their subsequent stretching. The elastic properties associated with fibre alignment are little affected by these doses of radiation but the stiffness of the collagen itself tends to decrease with increasing dose, exhibiting a shoulder in the dose response curve.

Cavity ionisation theory applied to the design of a maximum permissible fluence instrument.

The maximun permissible fluence is proposed as a practical concept in radiological monitoring of photon fields. It is virtually this concept that is used for monitoring neutron fields. The practicability of designing instruments with a required response function over a large energy range is examined. Cavity isonisation theory is employed to examine the effect of gas filling, wall material, chamber size and wall thickness on response function and the optimum parameters for the design of an ionisation chamber are thus identified. An experimental chamber of parameters close to the optimum has been constructed and its response compared with the response calculated from cavity ionisation theory. It is concluded that it is possible to design an instrument, the energy response of which follows the maximum permissible fluence. The approach and data in this paper will facilitate any necessary design changes which would arise in the event of national regulation being modified.

The dosimetry of bone incorporating alpha-emitting radionuclides.

The previous work on the dosimetry of alpha-emitting radionuclides incorporated in bone is briefly reviewed. The application of cavity ionisation theory to problems of bone dosimetry is propounded and recent developments of the cavity theory for alpha particle fields are applied to bone dosimetry problems. The mean marrow dose over a large range of bone cavity size calculated by a simple theory using a mean chord length to characterise a cavity is compared with results of a more elaborate theory employing the chord length distribution for a sphere. The difference is not great. The influence of the shape of the cavity is explored by considering cylindrical cavities of different elongation. Data are presented for both volume-seeking and surface-seeking radioactive nuclides. The endosteal dose to a 10 mu layer is calculated as a function of cavity size for both volume-seeking and surface-seeking radioactive nuclides. The endosteal dose is also calculated for a surface seeker as a function of endosteal layer thickness. Finally, the results of these calculations are shown to be generally in good agreement with those of the calculations of earlier workers. It is concluded that a simple and reliable method of calculating the mean marrow dose and endosteal dose for both volume- and surface-seeking alpha emitters has been established.

Experimental examination of cavity ionisation theory applied to alpha-particle fields.

The form of a general theory of cavity ionisation is outlined and its applications to alpha-particle fields considered. The attenuation of the alpha particles within the cavity, which gives rise to the weighting factor in general cavity theory, is considered in detail and an appropriate treatment for alpha-particle fields developed. Apparatus, consisting of an ionisation chamber composed of electrodes emitting alpha rays, was constructed in order to impose a rigorous test on the theory in the most critical region of cavity size. The general theory of cavity ionisation as applied to alpha-particle fields is shown to be in close agreement with the experimental results. As in the case of photon and electron fields, it is possible to characterise a cavity by a single chord length (path length) but the charged particle energy spectrum and the variation of stopping power with energy must be considered in detail.

A comparison of different treatment regimes on the visual appearance and mechanical properties of mouse skin.

Four different regimes of radiotherapy employed in the treatment of basal cell epitheliomas were compared in order to assess their effect on the visual appearance and mechanical properties of skin. Three groups of mice received exposures identical to those given in the radiotherapy treatments; three months after completion of the radiation the visual and mechanical properties of the skin and its appendages were examined. The skin scarring, coat condition, greying of hair, skin, thickness, load at rupture, extension at rupture, mechanical stress at rupture and stiffness were used as cirteria for comparing the four treatments. The treatment regime which caused the least damage to normal skin was identified.

Effects of radiation on the visual appearance and mechanical properties of mouse skin.

A study of the long term effects of radiation on the visual appearance and mechanical properties of mouse skin is presented. The effects associated with the hair follicle (greying and alopecia) increase monotonically with exposure. Other effects (load, extension and stress at rupture and scarring of the skin) all show a reversal at the highest exposures. The skin thickness changes little with exposure, while the skin stiffness exhibits a shoulder on the response curve. Possible mechanisms underlying these effects are discussed.