Prostate irradiation in patients with hip prostheses – a retrospective analysis
There are several clinically useful techniques for delivering radical radiotherapy to the prostate. One such beam arrangement is a conformal four-field box technique. Patients who have undergone a total hip replacement have in place a metallic prosthesis, which presents challenges in achieving a homogenous dose distribution. This is due to the increased density of the metal in comparison to bone and soft tissue. The resultant effect is additional attenuation of the X-ray beam as it passes through the prosthesis. The interaction of the photons with the metal also causes increased scatter. Thus, the dose delivered to the tumour is reduced if it is not corrected for. Due to the uncertainty in the amount of attenuation, it is recommended to avoid irradiating through the hip concerned. This means that the four-field box technique cannot be used. Instead, different field arrangements are used such as three or four oblique fields. This is a retrospective investigation into which field arrangement would be the most appropriate for early stage prostate cancer patients. Ten previously treated prostate patients were planned with different beam arrangements avoiding the prosthesis. The results were analysed and are presented with reference to the doses to the organs at risk and the planning target volume. The results indicate that the beam arrangement of choice should be three fields (anterior, posterior and lateral) or a three-field oblique beam arrangement. It has been proved that these plans are acceptable as a solution in this scenario.(Published Online September 27 2006)
Key Words: Hip; prostate; total hip replacement; prosthesis; dosimetry; heterogeneity.
c1 Correspondence to: L. James, Treatment Planning, Christie Hospital NHS Trust, 550 Wilmslow Road, Manchester M20 4BX, UK. E-mail: Laura.James@physics.cr.man.ac.uk