Variability in the point to which single direct field irradiation is prescribed for spinal bone metastases: a survey of practice patterns in Japan

Direct single fields are commonly used in radiotherapy for spinal bone metastases, and it is crucial to define the point for which the dose is prescribed. According to the guidelines from the International Bone Metastases Consensus Working Party (IBMCWP) updated in 2010, different opinions exist on whether this therapy should be prescribed to the mid-vertebral or anterior vertebral body. To our knowledge, no previous studies have surveyed practice patterns regarding this discrepancy. Therefore, we performed an Internet-based survey of members of the Japanese Radiation Oncology Study Group (JROSG) to investigate the current practice patterns in Japan. The respondents mentioned the point to which they prescribed radiotherapy for a single direct field. A total of 52 radiation oncologists from 50 institutions (36% of JROSG institutions) responded. Respondent prescription for radiotherapy varied widely. Only 21% and 6% of respondents prescribed irradiation to the mid-vertebral body and anterior vertebral body, respectively. A larger proportion of respondents (27%) prescribed irradiation to the spinal cord (center of the spinal canal). Still another group of respondents (27%) stated that they never use a single direct field. In conclusion, the point to which irradiation dosages are prescribed varies widely for a single direct field in cases of spinal bone metastases. This variation may lead some radiation oncologists to misunderstand the tolerance dosage of the spinal cord, especially in cases of re-irradiation. Thus, careful consideration is required before any prescriptions are made.