A dosimetric comparison of different treatment plans of palliative spinal bone irradiation: analysis of dose coverage with respect to ICRU 50 report

BACKGROUND: This study aimed to analyze three-dimensional (3D) dosimetric data of conventional two-dimensional (2D) 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. METHODS: Forty-five simulation CT scans of 39 patients previously treated for thoraco-lumbar spinal bone metastases were used. Three different treatment plans were created: (1) single posterior field plans using the ICRU reference points (ICRUrps); (2) single posterior field plans using the International Bone Metastasis Consensus Working Party reference points (IBMCrps); (3) two opposed anterior-posterior (AP-PA) field plans using the ICRUrps. The intended dose range for planning target volume (PTV) was 90% to 110% of the prescribed dose for AP-PA field plans. Cumulative dose-volume histograms were generated for each plan, and minimum, maximum and mean doses to the PTV, medulla spinalis, esophagus and intestines were analyzed. RESULTS: The mean percentages of minimum, maximum and mean PTV doses ± standard deviation were, respectively, 91 ± 1.3%, 108.8 ± 1.3% and 99.7 ± 1.3% in AP-PA field plans; 77.3 ± 2.6%, 122.2 ± 4.3% and 99.8 ± 2.6% in ICRUrp single field plans; and 83.7 ± 3.3%, 133.9 ± 7.1% and 108.8 ± 3.3% in IBMCrp single field plans. Minimum doses of both single field plans were significantly lower (p < 0.001) while maximum doses were significantly higher (p < 0.001) than AP-PA field plans. Minimum, maximum and mean doses were higher in IBMCrp single field plans than in ICRUrp single field plans (p < 0.001). The mean medulla spinalis doses were lower in AP-PA field plans than single posterior field plans (p < 0.001). Maximum doses for medulla spinalis were higher than 120% of the prescribed dose in 22 of 45 (49%) IBMCrp single field plans. Mean esophagus and intestinal doses were higher (p < 0.001) in AP-PA field plans than single field plans, however, less than 95% of the prescribed dose. CONCLUSION: In palliative spinal bone irradiation, 2D conventional single posterior field radiotherapy did not accomplish the ICRU Report 50 recommendations for PTV dose distribution, while the AP-PA field plans did achieve the intended dose ranges with a homogenous distribution and reasonable doses to the medulla spinalis, esophagus and intestines.