Treatment Approach for Children and Adolescents with Hodgkin Lymphoma
A linear accelerator with a beam energy of 6 mV is desirable because of its penetration, well-defined edge, and homogeneity throughout an irregular treatment field. Excellent immobilization techniques are necessary for young children to ensure accuracy and reproducibility. Treatment of involved supradiaphragmatic fields or a mantle field requires precision because of the distribution of lymph nodes and the critical adjacent normal tissues. These fields can be simulated with the arms up over the head or with arms down and hands on the hips. The former position pulls the axillary lymph nodes away from the lungs, allowing greater lung shielding; however, the axillary lymph nodes then move into the vicinity of the humeral heads, which should be blocked in growing children. Thus, the position chosen involves weighing concerns about lymph nodes, lung, and humeral heads. Attempts should be made to exclude or position breast tissue under the lung/axillary blocking. When the decision is made to include some or all of a critical organ (such as liver, kidney, or heart) in the radiation field, then normal tissue constraints are critical depending on chemotherapy used and patient age. For example, the possible indications for whole heart irradiation (10-15 Gy) are pericardial involvement, as suggested by a large pericardial effusion or frank pericardial invasion with tumor. Whole lung irradiation (10-15 Gy), with partial transmission blocks, are a consideration in the setting of overt pulmonary nodules. For example, the Society for Paediatric Oncology and Haematology (GPOH) HD-95 trial administered ipsilateral whole lung radiation therapy to patients who had not achieved a complete response in the lungs to the first two cycles of chemotherapy.
Role of LD-IFRT in childhood and adolescent Hodgkin lymphoma
Evaluating late effects associated with treatment for Hodgkin lymphoma is difficult. Because late effects may take 10 years to 30 years or more to become clinically apparent, it is often the case that a regimen associated with a given late effect is no longer utilized by the time the late effect becomes apparent. The type and incidence of late effects associated with modern combination chemotherapy and LD-IFRT regimens are unknown.
Because all children and adolescents with Hodgkin lymphoma receive chemotherapy, a question commanding significant attention is whether patients who achieve an initial CR to chemotherapy require any radiation therapy. Conversely, the judicious use of LD-IFRT may permit a reduction in the intensity or duration of chemotherapy.
In most pediatric cancers, salvage rates for patients who fail initial therapy are very poor, but this is not the case for patients with pediatric Hodgkin lymphoma who relapse after initial treatment. Studies comparing combination chemotherapy with or without radiation therapy for adults with advanced-stage Hodgkin lymphoma showed that the EFS was higher for patients who received initial chemotherapy and radiation therapy. OS, however was no different for patients whose initial therapy was chemotherapy alone. Many of the salvage regimens utilized included intensive chemotherapy followed by peripheral blood stem cell transplant. Thus it is not clear whether EFS or OS should be the appropriate endpoint for a trial comparing chemotherapy with or without radiation. In addition, there is an inherent assumption made in a trial comparing chemotherapy alone versus chemotherapy and radiation that the effect of radiation on EFS will be uniform across all patient subgroups. It is not clear how histology, presence of bulk disease, presence of symptoms, or other variables affect the efficacy of postchemotherapy radiation.