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Wt Radiograph 4P beam

V cut U, LFTih CH 0. POSsh cm 0. SUPih cm 0. S SO CK 04.

ANT SLD=6CM AR SE P=12 CM

Figure 11.5.2

Combined photon and electron treatment for diffuse skull metastases.The photon field can be seen around the periphery of the skull, including the skull base. This field is deeply penetrating. The electron fields (e") are in the middle, treating the lateral skull superficially. This allows radiation to the entire bony calvarium and skull base with relative sparing of the brain.

tron emission tomography (PET) scans can be fused with treatment planning computed tomography (CT) scans to aid in defining disease sites in challenging cases (Hevezi 2003; Krasin et al. 2004).

The radiation technique employed depends upon the site being treated, the planned dose, patient age, and whether there has been prior radiation. Most commonly, patients with high-risk disease receive a relatively low dose of 21 Gy to the primary site, often in the adrenal gland. Based on patterns of failure, it is important in these cases to cover the para-aortic lymph nodes (Wolden et al. 2000). CT planning is imperative to precisely delineate the target region as well as normal tissues including the kidneys and liver. Simple anterior and posterior beams, as demonstrated in Fig. 11.5.1, are often the best solution, but IMRT may be helpful if standard techniques would not provide adequate sparing of critical organs.

Bone metastases are also often best treated with simple opposed beams; however, more sophisticated approaches are needed when treating sites in the head and neck because of the complex anatomy and critical structures. For instance, IMRT may be useful for metastatic disease in the paranasal sinuses (Fig. 11.5.2). For high-risk patients with diffuse metastases throughout the calvarium, orbits, and skull base, we have employed a relative "brain-sparing" radiation technique that allows treatment of bones without full exposure of the brain in young children (Fig. 11.5.3). Photons are used to treat the outer skull, posterior orbits, and skull base. These fields are matched to low-energy electron beams to treat the lateral skull. Electron beams do not penetrate very deeply beyond the bone, and therefore much of the brain is spared (Hall 2000).

17 18 19 20 21 Gy

Figure 11.5.3

Intensity-modulated radiation therapy (IMRT plan) for a solitary but extensive skull metastasis. The percentage of the prescription radiation dose is represented by the colored"isodose"lines. This technique maximizes sparing of adjacent critical structures.

Radiation is also an important modality for palliation of patients with progressive neuroblastoma. It is extremely effective for relief of bone pain and neurologic deficits. The appropriate fractionation regimens for palliative therapy depend upon the site of treatment and anticipated survival of the patient. For a high-functioning child, 15 fractions of 2 Gy each may be used while for a patient with end-stage disease, a single fraction of 7 Gy may be considered. IMRT is very useful if a specific site requires a second course of salvage radiation therapy. Parenchymal brain metastases have become an increasing site of isolated failure in high-risk patients (see the present chapter). Investigators at MSKCC have found that even solitary brain metastases are associated with a very high rates of leptomeningeal dissemination, suggesting that prophylactic craniospinal radiation therapy may have clinical utility for patients who develop brain metastases (S.L. Wolden, personal communication).

Neuroblastoma is common in very young children, necessitating the frequent use of anesthesia for radiation treatments. In this case,propofol is safe and well tolerated, even for twice-daily treatments. With proper immobilization devices and input from parents and child-life specialists, some very young children can be coached to receive treatment without anesthesia; however, the precision of our current radiation techniques requires a great deal of cooperation and lack of motion.

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