Variability in the Point to Which Single Direct Field Irradiation is Prescribed for Spinal Bone Metastases: A Survey of Practice Patterns in Japan

Abstract

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 reirradiation. Thus, careful consideration is required before any prescriptions are made.

Palliative radiotherapy for thoracic spine metastases: Dosimetric advantage of three-dimensional conformal plans

“…Regarding the prescription point in this method, opinions in the guidelines from the International Bone Metastases Consensus Working Party were split between the mid-vertebral body and anterior vertebral body, although concerns regarding toxicity were raised for the latter (3). A survey regarding the practice patterns for this RT method concluded that a significantly higher number of respondents used dose prescription to the mid-vertebral body (17). Irrespective of these prescription points, the single PA field is inferior to AP/PA fields in terms of accomplishing homogeneous target dose distribution (18).…”

A dosimetric comparison of craniospinal irradiation using TomoDirect radiotherapy, TomoHelical radiotherapy and 3D conventional radiotherapy

“…Prescription dose was normalised to the reference point located at the geometric centre of PTVbrain. Spinal field dose normalisation point was placed in the central axis, at depth of the spinal canal 18 19 For patients with PTV lengths within 65 cm, one spinal field was used using a source-to-skin distance (SSD) of 100–110 cm.…”

“…Spinal field dose normalisation point was placed in the central axis, at depth of the spinal canal. 18,19 For patients with PTV lengths within 65 cm, one spinal field was used using a source-to-skin distance (SSD) of 100-110 cm. For patients with longer spinal lengths, two direct posterior spinal fields (SSD 100 cm) were dosimetrically matched at spine depth.…”