Craniospinal axis irradiation: an improved electron technique for irradiation of the spinal axis

Abstract

In this work we review the dosimetric features of craniospinal axis irradiation in the areas of matching cranial and spinal fields, with reference to the normal structures within the spinal field. The implications of the use of photon or electron modalities for the spinal port were evaluated. A novel method of matching the cranial photon and the spinal electron fields involving a computer-aided junction design is presented. The technique involves moving the photon beam in three steps to degrade its penumbra to match that of the electron field. Thermoluminescent dosimetry in a Rando phantom and computed tomography-based dose-volume histogram study for an illustrative paediatric case were used to compare the dose to normal structures within the spinal field. Our results show that the use of electrons for the spinal field leads to better sparing of deep seated normal structures. In the case of bone marrow, the use of a customized bolus for the spinal field results in an improved dose distribution, making electrons potentially superior to photons for radiobiological reasons.

A modified technique for craniospinal irradiation in children designed to reduce acute and late radiation toxicity

“…With modern treatment protocols many children will survive a childhood malignancy 9,10 . Therefore, the treating radiation oncologist must take care to minimize permanent radiation morbidity (late effects) while ensuring that acute and subacute toxicity are kept tolerable and disease control is not compromised.…”

Treatment planning of total marrow irradiation with intensity-modulated spot-scanning proton therapy

“…Three to four isocenters were used for treatment planning, which were separated by 24 cm in the cranial–caudal direction. The collimators were rotated by 90° to enable the use of asymmetric jaws, allowing for full-range travel of the MLC for intensity modulation following the previously reported methodology ( 15 , 18 , 19 , 22 ). Photon treatment fields use full arc rotations starting from 181° in the clockwise direction and 179° in the counterclockwise direction, with large fields of 30 × 40 cm 2 .…”

Dosimetric comparison of metastatic spinal photon treatment techniques

“…6 For radiation treatment of metastatic lesions, various modalities (i.e., 3D-conformal radiotherapy, intensity-modulated radiation therapy [IMRT], stereotactic body radiation therapy [SBRT], tomotherapy, CyberKnife) and radiation types as photon, electron, and protons are available. 5,[7][8][9][10][11][12][13][14][15][16][17] However, sometimes treatment options are limited due to the availability of resources or due to previous treatment being either at or close to the current site of disease. Spinal cord position is variable depending on body location 18 and hence treatment techniques need to be variable.…”

“…12,[21][22][23] Spinal treatments have also been attempted with electron beams; however, because of inhomogeneity correction and electron scatter at bone, such treatments are not universally accepted. 9,11,13,24 Moreover, even high-energy electron beams do not achieve a sufficient depth dose to be effective.…”