Treatment of Leukemia

 

The natural history of the different types of acute leukemia before effective therapy was developed justified the designations of acute or chronic at that time. Therapeutic successes over the past 40 years have profoundly altered the natural history of some of these diseases, most notably acute leukemia in children. More than one half of children with acute leukemia, properly treated, are long-term survivors, free of all evidence of disease and no longer on therapy. A lesser degree of progress has occurred for adults with acute leukemia. Chronic leukemias have proved far more resistant to treatment, but recent results are encouraging.

 

Radiation therapy has a limited role in the care of patients with leukemia. Its use is confined to palliative treatment. The most common indications for irradiation are urgent ones, including irradiation of the base of the skull for cranial nerve abnormalities due to infiltration of the leptomeninges or involvement of the cauda equina with pain and weakness in the lower extremities. The nature of these leukemic infiltrates is such that imaging studies may be normal. In the presence of manifest leukemia and neurologic abnormalities, irradiation on clinical grounds alone is often palliative. Larger tumor infiltrations may be seen in patients with lymphocytic or myelocytic leukemias. Biopsies of the former may be interpreted as lymphomas, and those of the latter may be calledgranulocytic sarcomas (formerly called chloromas). Low total doses such as 20 to 25 Gy are usually sufficient for rapid palliation.

 

 

 

Hodgkin Lymphoma

Hodgkin lymphoma, also known as Hodgkin disease, is an unusual form of cancer in that the neoplastic cells (i.e., Reed-Sternberg cells) account for only a very small portion of the disease process; most of that process results from the wide range of inflammatory cells and fibrous bands that accompany the Reed-Sternberg cells. Hodgkin lymphoma arises mainly within the lymph nodes, and evidence is accumulating to suggest that most of the Reed-Sternberg cells are of B-cell origin. Considered uniformly fatal 50 years ago, Hodgkin lymphoma is now considered one of the most curable types of cancer. Areas of active research include understanding the pathogenesis of Hodgkin lymphoma at the molecular level and minimizing side effects from treatment while maintaining high cure rates. The remainder of this section on Hodgkin lymphoma consists of an overview of the disease, with emphasis on its management.

 

Radiation Therapy Techniques

 

 

Mantle Field Irradiation

In mantle field irradiation, the bilateral cervical, supraclavicular, infraclavicular, axillary, mediastinal, and hilar lymphatics are the target volumes (Fig. 34-5A). Simulations are usually performed with the patient supine with arms akimbo. This position has the advantage of easy reproducibility, although keeping the hands raised rather than at the waist would allow a bit more of the lung parenchyma to be spared through superolateral movement of the axillary lymphatics.The patient’s neck is slightly hyperextended so that the mouth block can also block the occipital head without compromising the coverage of the cervical lymphatics.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

FIGURE 34-5 

 

A, A typical initial mantle irradiation field for a patient with Hodgkin disease to be treated with radiation only. B, Dosimetry for para-aortic and spleen fields for the patient in A.

Equally weighted 6-MV opposed photon fields typically are used for mantle radiation. Lung blocks are shaped superolaterally for adequate coverage of the axillary and infraclavicular lymphatics. Medially, the lung blocks should allow margins adequate to cover the mediastinum and bilateral hila. The inferolateral border of the lung blocks is determined by the lateral-most point of the sixth rib. The inferior border of the mantle fields is placed immediately above the highest point of excursion of the left hemidiaphragm on expiration, unless this placement compromises tumor coverage in the lower mediastinum. If the inferior border is lower than this, field matching with the para-aortic and spleen fields may take place in the spleen, which is undesirable. The left ventricle of the heart is shielded throughout the treatment unless this shielding would compromise tumor coverage. After 25.2 Gy, the inferior field border is raised superiorly to about two vertebral bodies below the carina to shield additional heart volume, unless this movement would compromise tumor coverage.140 An anterior larynx block is placed over the true vocal cords after 19.8 Gy unless it compromises tumor coverage.

 

 

Para-Aortic and Spleen Field Irradiation

Expanding the radiation field to include the para-aortic nodes and spleen (see Fig. 34-5B) usually involves the use of equally weighted 18-MV opposed photon fields. The superior border of these fields is matched with the inferior border of the mantle fields. The inferior border is usually at the L4-L5 interspace, which would allow coverage of the entire para-aortic lymphatics. The margin left around the spleen should be sufficient to allow splenic excursion with breathing.

 

 

Involved-Field Irradiation

The term involved fields usually implies treatment of the tumor volumes that were present before chemotherapy, with some additional margins. The exact extent of the fields depends on the location of the initial disease, the extent of residual disease after chemotherapy, and the exposure to adjacent organs such as kidneys, heart, and salivary glands. The advantages of higher dose and larger target volume must be balanced against the additional morbidity associated with this technique.