This technique treats the entire craniospinal axis and frequently is utilized with a high rate of success in other malignant diseases of the craniospinal axis, such as medulloblastoma and central nervous system (CNS) germinoma. Because of the compartmental nature of leptomeningeal carcinomatosis, craniospinal irradiation is occasionally used in the treatment of this disease process. It involves a technically complex set-up of two opposed lateral brain fields and one or two posterior spine fields (depending on the patient's height) to treat the entire craniospinal axis homogeneously without one region receiving too high or too low of a dose. The following diagram demonstrates how a craniospinal set-up is often planned.6
The brain and spine photon fields are matched to each other via two general approaches: 1) gapping, and 2) divergence matching. Gapping involves either positioning of the beams so that the divergent edges intersect at a depth, or directly abutting the beams so they intersect at a zero depth. This technique is referred to as "gapping" since it results in a gap on the patient's skin. Divergence matching involves positioning the beams so that their respectively divergent field surfaces are parallel and adjacent to one another at the time of treatment.7
Different institutions use a variety of techniques. In one commonly employed technique, the patient lies prone on the treatment table or couch. The posterior spine field is set up to treat the entire thecal sac and the superior border of the spine field is demarcated on the patient's neck. The brain is treated with opposed lateral fields. These cranial fields are set up so that their inferior borders match the longitudinal divergence of the edge of the superior spine port. This is accomplished by rotating the treatment machine's collimator of the brain field. By rotating the treatment couch, the transverse superior edge of the spine field is made parallel to the inferior divergent edge of the brain port. The two angles of rotation of the collimator and the couch are given by the formulas:
0 (collimator) = tan"1 [spine length / 2 x SSD]
6 (couch) = tan"1 [brain length / 2 x SAD] This setup is demonstrated in the following diagram.8
The junction line between the cranial and spinal fields is moved down on the neck one centimeter on predetermined treatment days in order to minimize hot spots. The daily radiation fraction size is generally small (1.21.8 Gy) with the total dose dependent on the tumor type and tumor load.
Boosts are given to areas at highest risk for relapse, such as the primary site or regions with large tumor burden.
The median survival of patients with leptomeningeal carcinomatosis without treatment is four to six weeks.2 Outcomes from standard craniospinal radiation therapy for carcinomatous meningitis are generally poor, resulting in a median survival of only a few months; therefore, radiotherapy is surely not of primary value in providing a major survival benefit. However, in many clinical instances, it relieves symptoms, or halts rapid progression of neurologic symptoms such as cranial neuropathies. The latter constitutes the major benefit of radiotherapy and several review papers have summarized small single institutional experiences. In one of the more modern such series, Hermann, et al, evaluated the efficacy and feasibility of craniospinal irradiation with and without intrathecal chemotherapy, specifically as it pertains to symptom palliation and survival. Sixteen patients with leptomeningeal carcinomatosis (nine breast cancer, five lung cancer, one unknown primary and one renal cancer) received 36 Gy craniospinal radiotherapy (1.6-2 Gy/fraction), ten of whom also received two to eight cycles of intrathecal methotrexate at 15 mg/cycle. The overall median survival was 12 weeks; patients receiving craniospinal irradiation alone had a median survival of eight weeks, compared to 16 weeks for those patients receiving both methotrexate and craniospinal irradiation. The combined approach, although tested in only a small cohort, appeared more efficacious from a survival point-of-view. Over two-thirds of patients9 experienced regression of their neurological symptoms either during or within days after radiotherapy was completed, outlining its palliative efficacy. Particularly impressive was the observation that seven previously non-ambulatory patients regained ambulation, six had substantial pain reduction, and three patients experienced restitution of bladder and bowel continence. All of these functional domains: ambulation, sphincter control and pain, represent critically important elements in terms of quality-of-life improvement and justify the use of craniospinal irradiation, with or without intrathecal methotrexate in selected patients with leptomeningeal carcinomatosis. However, approximately one-third of patients developed grade 3 myelosuppression; dysphagia, mucositis and nausea were relatively common. These side effects may be controlled with appropriate medications and should not necessarily preclude the use of CSI.9
With the increasing use of intrathecal chemotherapy, the optimal role of radiotherapy is called into question. No randomized trials have addressed this issue directly; however, one randomized study of two different chemotherapy approaches supported the use of radiotherapy. A prospective randomized trial of intrathecal methotrexate (MTX) versus MTX plus cytosine arabinoside (Ara-C) found that concurrent radiotherapy to the CNS was associated with significantly better response (73% v 35%; P <0.05). Overall median survival for the whole group was eight weeks, but responders fared better than nonresponders (median survival, 18 v 7 weeks). Since radiation enhanced the response rate and responders lived longer, this trial indirectly supports the up-front use of radiotherapy with intrathecal methotrexate.10
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