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Craniospinal irradiation using a forward planned segmented field technique

¹ Regional Medical Physics Department, ² Northern Centre for Cancer Treatment, Newcastle General Hospital, Newcastle upon Tyne NE4 6BE, UK

View larger version (83K): [in this window] [in a new window]   Figure 1. The simple spinal planning target volume(PTV) defined as a box.

View larger version (52K): [in this window] [in a new window]   Figure 2. Multiplanar reconstruction(MPR) showing the uncompensated isodose distribution achieved with three large spinal fields intended to permit a moving gap. The 105% isodose line is orange, the 100% isodose line is green and the 90% isodose blue.

View larger version (51K): [in this window] [in a new window]   Figure 3. A typical field arrangement for a spinal field<45 cm in length. The central axis is indicated by the dashed green line. The extent of the maximum radiation field is indicated by the solid green lines. The extent of the additional segment in the upper cervicothoracic region is indicated by blue lines, that in the lower lumber region by the yellow lines and the three segments added to the upper cervical region are defined by the red lines. The solid red line indicates the position of the lower limit of the three segments, the dotted lines indicate the position of the upper extent of the fields which also corresponds to the positions of the moving junctions.

View larger version (53K): [in this window] [in a new window]   Figure 4. Multiplanar reconstruction(MPR) showing the compensated isodose distribution with the 110% isodose line in yellow, 100% isodose in green and the 90% isodose blue.

View larger version (49K): [in this window] [in a new window]   Figure 5. For a spinal field45 cm a multiplanar reconstruction (MPR) showing the uncompensated isodose distribution, with the 115% isodose line in dull yellow, 100% isodose in green, the 90% in blue and the 85% isodose in grey.

View larger version (65K): [in this window] [in a new window]   Figure 6. A typical field arrangement for a spinal field45 cm. The central axis of the open fields is indicated by the solid green line. The extent of the open radiation fields is indicated by the dashed green lines, the two junctions in the upper cervicothoracic region. The extent of the two additional segments, one in the thoracolumbar region and the other in the lumbosacral region is indicated by the dotted yellow lines. The central axis of the asymmetric beamlets is indicated by the solid blue line. The limits of the three pairs of beamlets in the cervicothoracic region are indicated by the pairs of dotted blue lines.

View larger version (106K): [in this window] [in a new window]   Figure 7. The uncompensated isodose distribution for the cranial fields, with the 110% isodose in yellow around the periphery of the skull, 105% isodose in orange covering most of the cranium and the 95% isodose in pale green.

View larger version (126K): [in this window] [in a new window]   Figure 8. The segmented cranial fields used to achieve a homogeneous dose distribution. One pair of segments closely follows the 110% isodose line and the second pair closely follows the shape of the 105% isodose line as shown in Figure 7.

View larger version (59K): [in this window] [in a new window]   Figure 9. A multiplanar reconstruction(MPR) demonstrating for a spinal field <45 cm the summated compensated cranial and spinal fields with the 100% isodose in green and the 105% in orange.