Minimums Maximums Means Single field-ICRUrp 77.3 (72–81) ± 2.6 122.2 (114–130) ± 4.3 99.8 (94–107) ± 2.6 plished the ICRU Report 50 recommendations for dose distribution, while the AP-PA field plans achieved the intended dose ranges and homogeneity. The ICRU Report 50 recommends selecting a reference point that is clinically relevant and representative of the dose distribution throughout the PTV, where the dose can be accurately determined and where there is no large dose gradient [2]. The point located at the center or central part of the PTV generally fulfills these requirements and is rec- ommended as the ICRU reference point (ICRUrp). While a homogeneous dose within 95% to 107% of the pre- scribed dose is recommended for the target volume, a var- iation of ± 10% from the prescribed dose is widely used in clinical practice and was used in the present study for AP- PA field plans [2]. Thoracic and lumbar spinal irradiation is performed either with a single posterior field or two opposed AP-PA fields [4]. The International Bone Metastasis Consensus Working Party recommends dose prescriptions to the mid-vertebral body for single-posterior fields and includ- ing at least one vertebral body above and below the involved vertebra(e) in the treatment volumes [3]. How- ever, these recommendations are not supported with dosi- metric data or treatment outcomes. Radiotherapy planning and delivery, and dose distribu- tion may affect treatment outcome by dose coverage and dose heterogeneity in the target volume. Although several studies investigated optimal radiotherapy fractionation, the dose-volume effect on radiotherapy outcome, in terms Mean dose (range) % ± SD Single field-IBMCrp 83.7 (74–89) ± 3.3 133.9 (115–147) ± 7.1 108.8 (95–116) ± 3.3 Two opposed fields 91 (90–95) ± 1.3 108.8 (104–110) ± 1.3 99.7(97–102) ± 1.3 of pain relief and duration of response, has not been eval- uated [5-13]. Furthermore, higher re-treatment rates have been reported in single-fraction palliative radiotherapy than in multifraction radiotherapy [12-14]. The relation between higher re-treatment rates and physician bias, pri- mary site, pain severity and duration of symptoms has been evaluated, but the relation between high re-treat- ment rates and dose coverage has not been investigated. Studies investigating the relationship between radiother- apy technique and treatment outcome would provide important information, particularly for patients with long life-expectancies. Dose heterogeneity may become vitally important in patients with long life expectancies. Minimum target vol- ume doses as low as 70% of the prescribed dose may diminish treatment success, while maximum target vol- ume doses reaching as high as 130% of the prescribed dose may cause serious normal-tissue side effects in such patients. In the present study, the mean minimum dose for PTV in the ICRUrp single field plans was 77.3% (72– 81%) ± 2.6% of the prescribed dose, and the mean maxi- mum dose for PTV in the IBMCrp single field plans was 133.9% (115–147%) ± 7.1% of the prescribed dose. When the medulla spinalis doses were assed, maximum doses were higher than 120% of the prescribed dose in 22 of 45 (49%) IBMCrp single field plans but lower than 106% of prescribed dose in all AP-PA field plans. When the dose distribution to the esophagus and intestines were evaluated, mean doses were higher in the AP-PA field plans than the single field plans, but less than 95% of the prescribed dose. Journal of Experimental & Clinical Cancer Research 2009, 28:2 http://www.jeccr.com/content/28/1/2 Table 1: The mean percentages of minimum, maximum and mean planning target volume (PTV) doses ± standard deviation for all plans ICRUrp, the International Commission on Radiation Units and Measurements reference point; IBMCrp, the International Bone Metastasis Consensus Working Party reference point; SD, standard deviation. Table 2: The mean percentages of minimum, maximum and mean medulla spinalis doses ± standard deviation for all plans Minimums Maximums Means Single field-ICRUrp 94.2 (85–102) ± 3.0 108.8 (101–118) ± 3.6 102 (95–112) ± 3.1 Mean dose (range) % ± SD Single field-IBMCrp 103.4 (96–109) ± 3.3 120.1 (115–129) ± 3.5 112.7 (107–117) ± 2.3 Two opposed fields 96.2 (94–101) ± 1.5 103.2 (101–106) ± 1.4 100.3 (98–104) ± 1.3 ICRUrp, the International Commission on Radiation Units and Measurements reference point; IBMCrp, the International Bone Metastasis Consensus Working Party reference point; SD, standard deviation. Page 6 of 7 (page number not for citation purposes)