SU-F-T-512: A Dosimetric Comparison for Palliative Spine Metastasis Treatments: 3-D Vs. Conformal Arc

Authors


Abstract

Purpose:

Spine metastases have traditionally been treated using a parallel opposed 3-D technique: an anterior field and a posterior field (AP/PA). This has proven to give the lesions adequate coverage. The downside to this type of treatment is that the full prescription dose covers a large area of the patient and can go through critical organs such as the heart, spine, lungs, bowel, and others depending on the vertebrae being treated. Conformal arc therapy can also be used for this type of treatment. These two techniques will be compared for target coverage and doses to organs at risk (OARs).

Methods:

20 multi-vertebra metastases patients were chosen for this study, with a range of vertebrae being treated amongst each case. The original AP/PA treatments were re-planned with 1–3 conformal arcs placed depending on the location of nearby OARs. The GTV coverage was normalized so that both techniques had equal coverage. The OAR doses and the volume of the 50% prescription dose value were then compared between the two planning techniques.

Results:

Initial results on average show lower doses for the heart maximum, heart mean, lung V20, spinal cord maximum, and bowel maximum for the conformal arc plans. The AP/PA plans however on average showed lower kidney mean dose, liver mean dose, and parotid mean dose. The 50% prescription dose volume was smaller in all the conformal arc plans except for one.

Conclusion:

From the preliminary results the conformal arc plans spare critical OARs better than the two field technique, except when treating the vertebrae near the kidneys, liver, and parotids. The conformal arc plans also have a lower volume of the 50% prescription dose value. The data suggests that conformal arcs can be used for certain palliative spine treatments and that this technique should be considered when beginning planning.

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