Value of conformal planning in the radiotherapy of soft tissue sarcoma

The late complications and subsequent limb function seen following treatment of extremity sarcoma are related to the radiation dose used and the volume of tissue irradiated. The potential value of the use of 3D-planning and conformal blocking has been studied in 11 patients with lower limb sarcoma. Tumour, target and normal tissue volumes were reconstructed in 3D following a CT planning scan. Dose calculations were performed for conventional and conformal plans, using customized blocks with a margin of 6 mm around the target volume. No compromise of target dosimetry was permitted. The volumes of tissue receiving 50%, 80% and 90% of the prescribed dose were compared using cumulative volume dose histograms. The treatment volume was reduced in all patients, and by greater than 20% in four of five with thigh tumours. The mean volume of muscle outside the target volume which was irradiated to the 50% isodose was 4.2 litres. The volume irradiated to 90% or greater isodose was reduced by greater than 30% in five of eight patients with thigh and lower leg tumours. Similarly, the volumes of femur, tibia/fibula and ilium were reduced by 38%, 18% and 14% respectively by conformal blocking. Considerable sparing was achieved in the volumes of pelvic contents irradiated, including gonads and rectum. This simple, but time consuming, technique can achieve major reductions in normal tissue irradiation with potential improvements in limb function. To confirm its value and safety, prospective randomized trials must be performed and similar advances in patient immobilization and treatment verification are essential.