Characterisation of dosimetry in electron radiotherapy under different bolus applications

Radiation therapy with electron beams is a technique that continues to be used by many clinics. The characteristic depth dose with a dose build up and rapid dose drop off beyond the peak dose permits a lesion to be treated with a relatively uniform dose whilst sparing deeper normal tissue. <br><br>There are three general methods employed to modulate electron beams; a)Intensity Modulated Electron Therapy b) Segmented-field Electron Conformal Therapy, c) Bolus Electron Conformal Therapy, which can be used to achieve one or a combination of three aims; 1) level an irregular surface and improve dose distributions (missing tissue compensator), 2) reduce the penetration of the electron beam in certain areas (shaping isodoses closer to the distal edge of the target volume), 3) increase the surface dose at energies below 10MeV.<br><br>The most commonly employed method in a general radiotherapy practice to modify an electron beam is the application of a tissue like material (bolus) to the skin surface, in the strictest sense this is not Bolus Electron Conformal Therapy (BolusECT) but rather an element of the method as the bolus applied usually lacks sophisticated contouring. The first two methods mentioned are both technically and resource challenging for a general radiotherapy clinic. Unfortunately the application of bolus does have some limitations; it is not usually sterile and the daily application in areas where there may be ulcerated, necrotic or haemorrhaging tissue can lead to an unhygienic situation. In addition there are times when it is difficult to mould or reproducibly position the bolus to the particular surface irregularities leading to suboptimal treatment delivery.<br><br>Moving the bolus to the applicator level alleviates the contact and positional reproducibility difficulties however it does introduce new challenges in understanding how this will affect the electron beam dosimetry for the clinical treatment. This thesis provides the reader with some of the information necessary to understand the new challenges.