Irradiation has constituted a traditional therapeutic option for palliation of lumbar metastases. Historically, extensive research has explored optimal dose-fractionation relationships for his modality. However, despite the modern revolution in treatment planning there is limited information on sophisticated field configuration for the irradiation of the lumbar spine. Our results indicate that similar PTV coverage can be achieved in the three comparative plans selected but that the optimal dose distribution is associated with the 3-D plan which was developed.
Approximately 70% of cancer patients have metastatic disease at death. The spine is involved in up to 40% of those patients. Spinal cord compression may develop in 5% to 10% of cancer patients and up to 40% of patients with preexisting nonspinal bone metastasis (>25,000 cases/y). Given the increasing survival times of patients with cancer, greater numbers of patients are likely to develop this complication
. Such lesions are most frequently encountered in the management of patients diagnosed with cancers of the breast and prostate. Patients with bone metastases that arise from the latter two primary malignancies can enjoy median survival times that are measured in years while mean survival times as low as 6 months from bronchogenic carcinoma are seen in contemporary series
External beam irradiation constitutes a time-honored intervention for the treatment of bone metastases; especially those situated in the spine. Controversies surrounding dose fractionation schedules for bone metastases have preoccupied radiation oncologists for years
. Not only retrospective series but also numerous randomized controlled clinical trials have stated that similar pain relief outcomes are achievable with short and long course of radiotherapy. Prescriptions for radiation treatment, however, require more specification than the delineation of dosage, beam energy and notation of total and fractional dose.
Despite the abundance of information regarding dose-fractionation regimens for spinal metastases, limited data exist regarding the comparison of various techniques in the treatment of the spine
. Although sophisticated approaches such as stereotactic body irradiation for spinal metastases have been readily adopted by many institutions
 such technologies are not available to all users around the world. Therefore, a formal assessment must be made of more accessible technologies.
Radiation oncologists have always concerned themselves with both components that comprise the “therapeutic index”. Our data underscore the value of the 3D conformal approach for spinal metastases as a palliative tool. When treating the lumbar spine; however, several organs are at a risk for expressing radiation-related damage. In term of anticipated acute small bowel toxicity Baglan et al. showed that irradiation of more than 15 Gy to at least 150 cm3 is associated with an incidence of grade 3 acute small bowel toxicity approximating 30% using the Common Toxicity Criteria scale
[15, 16]. The mean radiation dose at which diarrhea grade 2–3 occurred was 27 Gy according to
Gunnlaugsson A et al. . Comprehensive review of the radiation dose- volume effects in small bowel was published by Kavanagh et al. in 2010
. According to those authors, following doses on the order of 50 Gy, late small-bowel obstruction or perforation rates of 2% to 9% were observed after partial organ irradiation. A dose of 25 Gy in five fractions of preoperative radiation therapy is associated with the same rate of late toxicity. It was also underscored in the review that small bowel obstruction occurred in 30% when fields were extended to the level of L1 or L2 versus 9% with pelvic- only therapeutic strategies
. Reports on the probability of the late small bowel damage could not be identified in correlation with the radiation dose- volume function. Notwithstanding, we reasoned that maximum effort should be invested to spare as much small bowel from the radiation field as possible. As a surrogate, we reported in our study the mean volume of the bowel irradiated and V15.
It must be acknowledged that one of the possible disadvantages in conformal 3D radiation techniques which employ a paired set of oblique wedged fields is the deposition of higher doses within the kidneys. The risks of radiation damage to the kidneys were comprehensively summarized by Dawson et al. The dose associated with a 5% risk for toxicity at 5 years was 18–23 Gy regardless of the fractionation scheme used
. It was within the context of these criteria that we carried out a comparative assessment of potential renal damage from radiation treatment.
Although the beam arrangements evaluated herein were not associated with optimal renal sparing, the dose volume histograms which paid attention to the kidney suggest that such treatments can be delivered without inducing nephropathy
. Moreover, vis-à-vis other adjacent critical organs (e.g., bowel, spinal cord) the conformal approach offered significant improvement. As indicated, none of the 3 approaches evaluated was associated with advantages in terms of target coverage.
A recently published trial by the RTOG (97–14) assessed quality of life endpoints among patients suffering from bone metastases
[20, 21]. As predicted, radiation therapy was highly effective in reducing bone pain. The framers of the protocol allowed physicians to treat patients who presented with spinal metastases via AP-PA or posterior-only portals. Despite the availability of conformal approaches during the recruitment period of the protocol, no allowance was made for selecting such an option. While this decision may have successfully isolated the dose fractionation question (i.e., by eliminating the variability in radiation treatment approaches) it is possible that patients enrolled in the study were impacted upon from a QOL perspective due to the use of non-optimized portal arrangements.
The RTOG is about to open the phase III component of protocol l 06–31 which will randomize patients diagnosed with bone metastases between SBRT and other forms of external beam radiation therapy. While the protocol does stipulate
 that for those randomized to the conventional treatment arm “field arrangements to treat the target lesion may be chosen at the discretion of the treating radiation oncologist” the study goes on to provide detailed suggestions for treating the spine via 2-field approaches (AP-PA for thoraco-lumbar spine; lateral beams for cervical spine) with only cursory mention of the possibility of using oblique beams.
The absence of rigorous comparisons of portal selection is also evident in reference textbooks
 as well as the recent evidence-based ASTRO guidelines on palliative radiotherapy for bone metastases
 which provide extensive information on dose volume relationships but fail to bring up the matter of optimal field arrangements when conventional irradiation is employed. The reality is that 3D conformal RT is already the standard procedure for irradiation in many institutions worldwide. However, even in the most recently published update of the International Consensus on palliative RT endpoints for future clinical trials in bone metastases opinion was split between prescribing the dose to the mid-vertebral body or anterior vertebral body for a single direct field and the guidelines for conformal radiotherapy and stereotactic radiotherapy were subsumed under the rubric of “future research areas”
. Ironically, the same guidelines devote extensive space towards consideration of SBRT techniques despite the fact that the use of the latter is not yet justifiable with level 1 evidence. Since the authors of these guidelines do not yet consider SBRT to be a standard of care, we believe that data must still be collected regarding the merits of modern as well as conventional beam arrangements.
It is troubling to reflect on the current reality of extremes. Today’s clinician seems to be left with polarized options for treating bone metastases of the spine. Specifically, physicians can avail themselves of the most modern variants of SBRT; however, there are certainly many palliative cases which do not require this level of sophistication. Conversely, alternative options that are documented in the literature include the most rudimentary radiation techniques (i.e. Posterior beams or combination of AP and PA fields). The rationale for presenting our results is to re-orient the clinician to an intermediate level of sophistication in the palliative approach to this entity.