Clinical dosimetry optimization in spinal metastases

Introduction: Radiotherapy is commonly used to treat spinal metastases. The aim of this study was to compare conventional dosimetry (posterior–anterior fields) with an optimized three-dimensional conformal plan (using oblique fields). Material and Methods: Fifteen patients were selected, and split into three groups of five based on tumour localization: cervical, dorsal and lumbar. Reference planning comprised of two fields: anterior–posterior. The planning target volume (PTV) was covered with 90% of the prescribed doses, minimizing anterior field weight and not exceeding 120%. The alternative consisted of three fields: two oblique posterior fields with wedge and anterior field. The PTV was covered with 95% of the prescription dose, minimizing the anterior field weight with 107% of overdose as a limit. The patient received 8 Gy in one fraction; retreatment with an additional fraction was feasible, safe and effective if persistent or recurrent bone pain was present. Five fractions of 4 Gy were used for cervical cases. To consider the future patients toxicity we evaluated the mean dose, V90 and V70 parameters in each plan. Results: Dosimetric parameters of organs at risk were not significantly different from one trial to another. The optimized plan followed ICRU criteria, reaching PTV coverage of 95–107% range of the prescription dose. In the conventional plan, high dose had to be accepted to obtain 90% of coverage in the target. Conclusions: In contrast with the anterior–posterior configuration, oblique fields improve dose conformity and limit high dose all of the body except the spinal cord.