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Purpose: The EQUAL-ESTRO laboratory was set up in 1998 to perform external audits of radiotherapy beams for all the European centres. Until the end of the year 2003, it was funded by EC projects. The external quality control is based on measurements performed with thermoluminescent dosimeters (TLD) sent by postal mail to the participating centre in order to be irradiated on axis in reference conditions and in conditions close to clinical conditions for photon and electron beams. The EQUAL-ESTRO laboratory also started in 2002, a new TLD control allowed to check the dosimetry of complex clinical fields for photon beams with multileaf collimator (MLC). New geometric and dosimetric checks have also been developed for brachytherapy., Material and Methods: The participating centre irradiates TLDs (7LiF: Na, mg, Ti, TLD 937 [Philitec]) in water at a dose of 2 Gy, calculated with the TPS used clinically, following the EQUAL-ESTRO protocol., Results: Since the beginning of the activities, 46% of the French radiotherapy centres and 55% of the European radiotherapy centres applied to participate to the EQUAL quality control programme. In France, the EQUAL-ESTRO laboratory checked, from 1998 and June 2004, 283 photon beams, 180 electron beams and 61 photon beams with MLC. For all the French beams checks, the following results have been observed: for the photon beams, the results show that about 1% of the measured doses in the reference conditions on axis have been detected outside the tolerance level (deviation between the measured dose and the stated dose > +/- 5%) after a first or a second check. For points checked in photon beams with wedge filter, 2.5% of the beams checked show a deviation > +/- 5% after a first or a second check. For the electron beams, the check has been set up in January 1999. For the 180 electron beams checked, 5% of the measured doses in the reference conditions have been found outside the tolerance level (> +/- 5%)., Conclusion: These results show clearly the importance of the quality control in radiotherapy in the frame of an external audit. This audit should now be a part of a quality assurance programme in the radiotherapy centres in addition to the internal quality control as planned in the French law (02/03/2004) concerning the external quality control conditions of the radiotherapy treatment units.

The potential benefit of the introduction of californium-252 in interstitial and intracavitary therapy is related to the greater efficiency of its neutron emission against anoxic cancer cells. In that respect, the oxygen enhancement ratio (OER) of the 252Cf emission has been determined for a continuous low dose rate irradiation. The biological system is growth inhibition in Vicia faba bean roots. A new Vicia faba "BelB" strain has been used, which better tolerates long periods (up to about 10 hours) of anoxia. In a first series of experiments, for a 252Cf (Dn + gamma) dose rate of 0.11 Gy . h-1, an OER of 1.4 +/- 0.1 was observed (the gamma contribution of D gamma to the total absorbed dose Dn + gamma was 0.35 at the position of the root tips). In a second series of experiments, in somewhat different geometrical conditions with a 252Cf (Dn + gamma) dose rate of 0.13 Gy . h-1, an OER of 1.5 +/- 0.1 was observed (D gamma/Dn + gamma = 0.42). The OER values observed for similar irradiation times, with iridium-192 gamma-rays, were 2.3 +/- 0.2 and 2.6 +/- 0.1 respectively, which leads to therapeutic gain factors (GF) of 1.6 and 1.7 respectively. These GF values are slightly lower than those previously obtained (GF = 1.8) on the same system, with d(50)-Be, p(75)-Be and 15 MeV neutron beams.

Relative biological effectiveness (RBE) of 252Cf, with respect to 192Ir, has been determined at the low dose rates commonly used in interstitial and intracavitary therapy. The biological criterion was growth reduction in Vicia faba bean roots. Two varieties of Vicia faba were used. For Vicia faba Sutton's seeds, an RBE of 5.7 to 6.6 was obtained for 252Cf Dn + gamma doses of 0.5 to 0.2 Gy respectively and at a Dn + gamma dose rate of 0.11 Gy-1. The gamma contribution D gamma/Dn + gamma at the level of the root tipes was 0.35 and the derived RBE of the neutron emission of 252Cf was then 8.2 to 9.7. For Vicia faba Be1B and in the same irradiation conditions, an RBE of 5.1 to 6.2 was obtained for the total (n + gamma) 252Cf emission and for Dn + gamma doses of 0.4 to 0.2 Gy respectively. These values lead to an RBE of 7.4 to 9.0 for the neutron emission of 252Cf. For Vicia faba BelB, but for another source arrangement (Dn + gamma dose rate of 0.13 Gy . h-1 for 252Cf), an RBE of 5.6 to 7.5 was obtained for the total (n + gamma) emission of 252Cf and for Dn + gamma doses of 0.4 to 0.1 Gy respectively. The gamma contribution (D gamma/Dn + gamma) at the level of the root tips was 0.42, and the derived RBE of the neutron emission of 252Cf was then 8.9-12.3.