The ESTRO-QUALity assurance network (EQUAL) for European radiotherapy centers

An ESTRO (European Society for Therapeutic Radiology and Oncology) Quality Assurance network for radiotherapy (EQUAL) has been set up for 23 European and 2 Mediterranean Basin Countries. The network deals with measurements performed with mailed TLD irradiated in reference and non reference conditions, for on-axis points. The checks include the reference beam output, beam output variation with collimator opening, depth dose data and wedge transmission factors, using 10 TLDs per beam. The Philitech LiF DTL937 was used and read with the FIMEL-PCL3 automatic reader. The participating centers irradiate the TLD capsules to an absorbed dose of 2 Gy estimated with the Treatment Planning System used in clinical routine. During 1998-1999, the EQUAL has checked 180 out of 450 accepted centers including 422 beams, 65 ⁶⁰Co beams and 357 X-ray beams. The results show that 3% of the beam outputs in reference conditions and 3% of the percentage depth doses are outside tolerance level (deviation >±5%). The standard deviation for the beam outputs is 2%, 6% of the beam outputs for beams other than 10 cm× 10 cm and 10% of the wedge transmission factors show deviations >±5%. The global results analysis shows deviations >±5% in at least 1 point for 61 out of the 422 beams, mainly for large and rectangular fields and for wedged beams. The results of the EQUAL program show the importance of a quality assurance network in Radiotherapy, especially for the non reference conditions. The EQUAL program for electron beams has been initiated in 1999