3D conformal treatment planning “significantly better” for spinal cord and bowel exposure than traditional approaches

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A study published in Radiation  Oncology (by Viacheslav Soyfer, Radiation Oncology Department, Tel Aviv Souraskiy Medical Center, Tel Aviv, Israel, and others) indicated that 3D conformal treatment planning of lumbar vertebral metastases was significantly better in terms of bowel and spinal cord exposure compared with traditional approaches.

Soyfer et al reported that the traditional methods of treating spinal metastases include external beam radiation through a single posterior beam or through anterior-posterior portals (depending on the distance between the skin and the target lesion). However, they added that newer methods, such as 3D radiotherapy, are now being used.

The authors commented: “Although these methods have been readily adopted by senior clinicians, it is difficult to identify peer-reviewed articles discussing the advantages of these new techniques above classical anterior-posterior or single posterior-anterior beam treatment of vertebral column metastases.” Therefore, the aim of their study was to assess “several straightforward external beam approaches for treating spinal metastases with respect to target volume coverage and the potential influence of these respective beam arrangements on normal tissue tolerance.”

Soyer et al assessed 10 comparative plans from randomly chosen patients who were treated for lumbar spine metastases between 2007 and 2010. For each patient, a series of plans (posterior-anterior, anterior-posterior, or 3D) was assessed. They wrote: “Data was collected for clinical treatment volume coverage, mean dose, and V15 exposure of the bowel, mean dose for both kidneys, and maximal dose of the spinal cord for every patient in all comparative plans.”

They found with all plans, that clinical treatment volume was similar for all plans and stated: “It is evident that the 3D plan offers improvement in maximum dose deposited to the spinal cord while maintaining the kidney dose within tolerable limits.” The authors explained that the V15 of the bowel was significantly lower with the 3D plan (6.7%) compared with the traditional approaches (39.9% for anterior-posterior and 37.3% for posterior-anterior; p<0.0001). The lowest maximum spinal dose was also observed with the 3D plan—30.6Gy for 3D vs. 33.1Gy for anterior-posterior vs. 37.7Gy for posterior-anterior. However, the mean dose to both kidneys was significantly higher with the 3D plan compared with the other approaches (p=0.009). Soyer et al wrote “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 kidney.” But, they added that the doses observed with the 3D plan suggested that “such treatments can be delivered without inducing nephropathy.”

The authors concluded clinicians should “continue to avail themselves of 3D conformal approaches as dictated by the complexity of the case being evaluated.”

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