Value of a multileaf prescription preparation system for palliative external beam irradiation

In palliative treatment, irregularly shaped fields are used to reduce side- effects and can improve, or avoid, field matching. We investigated the effe ctiveness of a multileaf collimator (MLC) supported by a digitizing data en try system in the palliative radiotherapy treatment of 66 patients and comp ared it with conventional shielding with geometrically shaped blocks. After conventional simulation of rectangular fields: irregular field shapes were marked on the simulator film in 17 patients (27%) to reduce radiotherapy r elated side-effects. Individual leading was performed with an MLC. Digitizi ng and fitting of the optimum leaf position were carried out using a multil eaf preparation system (MLP, Elekta, Crawley, UK). Target volumes included bone metastases in the pelvis, spine and extremities, mediastinal soft tiss ues, lymph nodes and central nervous system. In 10 patients, treated with a parallel pair for pelvic metastases, MLC and conventional shielding were p rospectively compared with regard to time requirements and area shielded. C ompared with conventional blocking, the mean simulation, preparation and tr eatment time required for MLP fields was shorter (9.55+/-1.44 min vs 16.90/-2.64 min, and 5.50+/-1.14 min vs 8.97+/-1.75 min). The mean shielded area was 31 cm(2) larger for MLC fields compared with geometrically shaped bloc ks (p<0.05). Compared with cerrobend blocking, the use of an MLC, supported by preparation data entry software, is more flexible and reduces radiother apy resources. Therefore, a preparation data entry system as a separate dev ice, or integrated into the treatment planning system, is a useful tool in palliative treatment.