[en] Incidence of post-radiotherapy pericarditis has been studied in 579 patients treated by mantle fields with Cobalt gamma rays for Hodgkin's Disease. The pericarditis was the most serious and frequent complication found after these irradiations. The most important factor is the dose received at the anterior pericardial surface: the incidence of pericarditis is zero for a dose of less than 4,500 rads at this level, 9.2% at 4,500 rads and nearly 20% at 5,000 rads. The factors which increase the dose at the anterior pericardium are the nominal dose in the mediastinum (zero incidence of pericarditis at less than 4,000 rads, 3% at 4,000 rads and nearly 20% at 4,500 rads and above) and the distribution of dose between the anterior and posterior incident beams (it is important not to give more than 60% by the anterior field). Thickness (separation) of the patient and width of the field are of relatively less importance. On the other hand the patient's age and overall time (pericarditis appears above a dose corresponding to 1,355 rets in the mediastinum) are more important. A new protocol, which associates initial intensive chemotherapy, allowing irradiation to be given to a mediastinum cleared of tumour, and therefore avoiding doses above 4,000 rads, and even more important modification of the dose distribution so that not more than 60% of the dose is given by the anterior field, have reduced the incidence of pericarditis to zero. A rigorous dosimetric study is necessary in every case, and it is desirable to use a radiation beam of energy greater than that provided by cobalt 60, if the thickness of the subject makes this necessary

[en] In this paper, we present the principle and the studies for a new type of Compton polarimeter based on the use of power buildup Fabry-Perot cavity to get a 3% measurement of the Jefferson Lab electron polarization within minutes