New ILROG Guidelines for Pediatric Hodgkin's Lymphoma

Alexander M. Castellino, PhD

March 11, 2015

New guidelines on how to integrate imaging information into the definition of radiation volume in children with Hodgkin's lymphoma have been issued by the International Lymphoma Radiation Oncology Group (ILROG).

The guidelines appear in the March–April issue of Practical Radiation Oncology.

The guidelines were prompted by recent advances in imaging technology; contrast enhanced CT and fluorodeoxyglucose (FDG)-PET have led to improvements in staging and in the evaluation of treatment response.

In children with Hodgkin's lymphoma, treatment is more effective when 3-dimension imaging results are considered during the planning of radiation therapy (RT) and the calculation of the RT volume to be administered, said David C. Hodgson, MD, associate professor in the Department of Radiation Oncology at the University of Toronto, and radiation oncologist at Princess Margaret Hospital/University Health Network in Toronto. In addition, the radiation dose delivered to normal tissue is lower, decreasing the late adverse effects of therapy, he told Medscape Medical News.

Previous guidelines defining radiation fields for lymphoma were developed in the 1990s. "Since then, there have been advances in imaging technologies and the ability to plan and deliver radiation therapy," Dr Hodgson explained.

The new guidelines do not address how to select patients for RT, he reported.

"More accurate ways of delivering radiation therapy and more detailed patient selection criteria have made a significant change in our ability to customize treatment for many cancer patients," Dr Hodgson said in a press release issued by the American Society for Radiation Oncology (ASTRO).

Principles of Target-Volume Planning and Involved-Site RT

CT and FDG-PET scans before chemotherapy are critical in the calculation of RT volume because they indicate the extent of tissue involvement.

"Imaging studies of the neck and thorax should be performed to assess the extent of cervical and mediastinal disease," Dr Hodgson and his colleagues write. This is particularly helpful when the involvement of these sites in children with Hodgkin's lymphoma is challenging; FDG-PET is a very useful staging tool, they add.

When planning RT, it is important to determine the gross tumor volume that needs to be radiated. This volume is determined from prechemotherapy imaging. Postchemotherapy imaging provides information on sites that remain abnormal. Gross tumor volumes should be considered when defining the "volume we need to treat" or when planning the volume of RT to deliver in children, they note.

"Clinical target volume for radiation will take into account the shrinkage that occurred with chemotherapy," Dr Hodgson told Medscape Medical News. All this impinges on the concept of involved-site RT.

The concept of involved-site RT was developed to identify and target nodal tissue involved and to spare uninvolved nodes and vascular structures not involved in the clinical target volume.

Historically, planning was based on the equivalent of doing chest x-rays (i.e., 2-D imaging). With 3-D imaging, it is possible to shape RT volume to avoid normal tissue, he explained.

"Delineation of [clinical target volume] requires consideration of the expected routes of disease spread, and the quality of pretreatment imaging," the authors report.

They discuss how, when planning RT volume, it is important to determine internal target volume, which takes into account variations in shape and motion in each patient, and the need for immobilization procedures.

In addition, they note that a boost in radiation dose might be appropriate in cases of bulky residual disease or when responses are poor.

The team provides guidance on available information about the effects of radiation effects on, for example, the breast, soft tissue, and skeletal system, which require particular attention in children.

The Need for Guidelines in Children With Hodgkin's Lymphoma

In the past, children and adults with Hodgkin's lymphoma received similar treatment with chemotherapy and RT. Curative doses of radiation were targeted to all potentially involved nodal tissue; however, morbidity and mortality were significant.

In children in particular, impairment in musculoskeletal and soft tissue development were noted. The new guidelines were issued with the intent to reduce these morbidities in growing children, the authors explain.

Contrast-enhanced CT and FDG-PET made it possible to localize involved disease sites. The use of 3-D CT-based RT planning, the technical information available on organ motion and target localization, and the ability to quantify and modify radiation doses to target and normal tissue, make the guidelines imperative.

What the Guidelines Achieve

These guidelines have "the potential to reduce the radiation therapy breast dose by about 80% and the heart dose by about 65% for an adolescent girl with Hodgkin's lymphoma," Dr Hodgson said in the ASTRO press release.

This shift to treatment planning tailored to an individual patient's disease will optimize risk/benefit considerations for patients and reduce the likelihood that they will suffer late effects from RT, he explained.

These guidelines will be used in an upcoming Children's Oncology Group Study of involved-site RT for patients with high-risk Hodgkin's lymphoma, he added.

The authors have disclosed no relevant financial relationships.

Pract Radiat Oncol. 2015;5:85-92. Abstract

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