Prog Med Phys.  2013 Dec;24(4):230-236. 10.14316/pmp.2013.24.4.230.

A Smart Setup for Craniospinal Irradiation

• Peterson J
• Vallow LA
• Kim S
• Casale HE
• Tzou KS

• KMID: 1910563
• DOI: http://doi.org/10.14316/pmp.2013.24.4.230

Abstract

Our purpose is to present a novel technique for delivering craniospinal irradiation in the supine position using a perfect match, field-in-field (FIF) intrafractional feathering, and simple forward-optimization technique. To achieve this purpose, computed tomography simulation was performed with patients in the supine position. Half-beam, blocked, opposed, lateral, cranial fields with a collimator rotation were matched to the divergence of the superior border of an upper-spinal field. Fixed field parameters were used, and the isocenter of the upper-spinal field was placed at the same source-to-axis distance (SAD), 20 cm inferior to the cranial isocenter. For a lower-spinal field, the isocenter was placed 40 cm inferior to the cranial isocenter at a constant SAD. Both gantry and couch rotations for the lower-spinal field were used to achieve perfect divergence match with the inferior border of the upper-spinal field. A FIF technique was used to feather the craniospinal and spinal-spinal junction daily by varying the match line over 2 cm. The dose throughout the target volume was modulated using the FIF simple forward optimization technique to obtain homogenous coverage. Daily, image-guided therapy was used to assure and verify the setup. This supine-position, perfect match craniospinal irradiation technique with FIF intrafractional feathering and dose modulation provides a simple and safe way to deliver treatment while minimizing dose inhomogeneity.

Keyword

Dose modulation; Field matching; Intrafractional feathering; Daily feathering

MeSH Terms

Animals
Craniospinal Irradiation*
Feathers
Humans
Supine Position

Figure

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  Fig. 1. Sagittal representation of the cranial field, upper-spinal field, and lower-spinal field, with each isocenter at a constant source-to-axis distance (illustrated by the star, square, and circle, respectively). Calculation points for each field are indicated by triangles.

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  Fig. 2. Couch and gantry rotation for the spinal fields. (a) Upper spine (couch, 0o; gantry, 180o). (b) Lower spine (couch, 270o; gantry, 191o).

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  Fig. 3. (a) Cranial treatment field. (b) and (c), Illustration of the field-in-field technique used to feather the match of the craniospinal junction.

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  Fig. 4. (a) Upper-spinal treatment field. (b) and (c), Illustration of the field-in-field technique used to feather the match of the craniospinal junction superiorly and the spinal-spinal junction inferiorly. (d) and (e) Illustration of the field- infield technique used to modulate the dose throughout the upper-spinal field.

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  Fig. 5. (a) Lower-spinal treatment field. (b) and (c), Illustration of the field-in-field technique used to feather the match of the spinal spinal junction.

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  Fig. 6. Sagittal reconstruction of dose distribution. (a) Without dose modulation. (b) With field-in-field dose modulation. Target volume is green, 100% isodose line is red.

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