Dosimetric verification of gynecological implants

Over the past 100 years brachytherapy has been used for the treatment of gynecological malignancies. These treatments have evolved from a manual to after loading to mechanical device based treatments. Various treatment schemes have been developed such as Stockholm, Paris and Manchester systems for the source loading. For the treatment of cervical tumors. The Manchester system has proved popular and simple in the USA. In conjunction with the Manchester system, the Fletcher-Suit applicator is frequently used for the treatment. In this system, dose is specified to a point A, which is defined as a point 2 cm lateral to the central canal or tandem and 2 cm up from lateral fornix in the same axis of the uterus. For practical reasons this definition has also been modified to include either fornix or cervical os or the tip of the flange of the intrauterine source. Nath et al. (1991) provided a dosimetric comparison among various methods for the brachytherapy treatment of carcinoma of the cervix. ICRU-38 recommended that dose be specified to a volume, however, in a clinical practice dose is often specified to point A. Various rule of thumb methods have been proposed for calculating dose rate to point A with respect to source strength 3-5, however these studies did not provide relationship between bladder and rectum dose with respect to the source strength. In this study, simple analytical expressions are provided to estimate dose to point A, bladder and rectum with a given source strengths. It is concluded that dose rate to point A, rectum and bladder can be accurately calculated by simple analytical methods for a given source activity. This method can be used for a quick check for the computer-generated results as well as it can be used for simple quality assurance method for dose calculation. This method is accurate to within 3%. Deviation may be noted if the implant geometry is extremely distorted due to bulky tumor or a poor implant