Journal of Experimental & Clinical Cancer Research 2009, 28:2 http://www.jeccr.com/content/28/1/2 Background External beam radiotherapy is a well-recognized and effec- tive modality in the palliation of symptomatic bone metastases and complication control [1]. Under- or over- dosing the target volume and dose heterogeneity may not be major concerns, since many patients treated for pallia- tive purposes have short survival. However, long term symptom control associated with bone involvement and normal tissue complications becomes more vital in cancer patients with long life-expectancy. Some breast and pros- tate cancer patients even with spinal cord compression may live for several years after radiotherapy. Single posterior field or two opposed anterior-posterior fields (AP-PA) conventional two-dimensional (2D) radio- therapy planning without dose volume information is widely used for palliative spinal bone irradiation using the International Commission on Radiation Units and Measurements reference points (ICRUrps) and the Inter- national Bone Metastasis Consensus Working Party refer- ence points (IBMCrps) [2,3]. To our knowledge, dosimetric assessment of conventional 2D palliative spinal bone irradiation using three-dimen- sional (3D) dose information has not been reported. This study aimed to analyze 3D dosimetric data of palliative spinal bone irradiation using different reference points and treatment plans with respect to the International Commission on Radiation Units and Measurements (ICRU) Report 50 [2]. Methods CT simulation Forty-five simulation CT scans of 39 patients previously treated for thoraco-lumbar spinal bone metastases were used for treatment planning. CT scanning was performed with a 6 detector helical CT (Brilliance, Philips Medical Systems, Netherlands) and with a 5-mm slice thickness. Volumes of interest Target volumes were contoured in corresponding CT slices (Figure 1). One vertebra above and below the involved vertebra(e) were included in the clinical target volume (CTV). However, the upper end-plate of the upper verte- bra and the lower end-plate of the lower vertebra were not included in the CTV, to limit the distal and proximal bor- ders of the treatment fields in the inter-vertebral space. To determine the planning target volume (PTV), 10 mm was added to CTV in lateral directions and 5 mm in anterior- posterior and superior-inferior directions. Treatment fields were determined by adding 7–10 mm to the PTV using multi-leaf collimators. Portions of the esophagus located in thoracic radiother- apy fields, the intestines located in lumbar radiotherapy fields and the medulla spinalis in all fields were deline- ated as critical organs. Treatment planning Precise PLAN®2.11 (Elekta, Crawley, UK) treatment plan- ning system (TPS), which enables 3D conformal radio- therapy planning, was used for treatment plans. To calculate the dose distribution of the photon beam, the TPS uses an irregular field algorithm, for different depths and field sizes, based on data measures in a phantom. The algorithm takes into account the inhomogeneity of the patient's tissue and uses an integration scheme to evaluate the scatter component of the dose. The dose calculation grid is set to 2.5 mm. Three different treatment plans were created (1) single posterior field treatment plans using ICRUrps; (2) single posterior field treatment plans using IBMCrps; and (3) two opposed anterior-posterior (AP-PA) field plans using ICRUrps. The ICRUrp was defined as the center of the PTV, the IBM- Crp was defined as the mid-vertebral body point in the central plane, and the prescription dose was normalized to these points (Figure 1). Dose distributions of treatment plans in one case are shown in Figure 2. The nominal prescribed dose was 2000 cGy in 5 fractions using 6-MV photons for posterior fields and 18-MV for anterior fields. In AP-PA field plans, beam weights were used as 1 and 1.5–2 in AP and PA fields, while assuring the intended dose range of 90% to 110% of the prescribed dose for the PTV. No dose constraint was used in single posterior field plans. Cumulative dose-volume histograms (DVH) were gener- ated for each plan, and minimum, maximum and mean doses to the PTV, medulla spinalis, esophagus and intes- tines were calculated for both single posterior fields and AP-PA field plans. Cumulative dose-volume histograms of treatment plans in one case for PTV and medulla spinalis are shown in Fig- ure 3. Statistical analysis The mean, minimum and maximum dose levels were compared using the Paired-Samples T test for parametric data on the PTV and medulla spinalis and the Wilcoxon test for non-parametric data on the esophagus and intes- tines. P-values of less than 0.05 were considered statisti- Page 2 of 7 (page number not for citation purposes)