Radiotherapy of Follicular Lymphoma: Updated Role and New Rules

Radiation is established as one of the most powerful, highly effective treatments for non-Hodgkin lymphoma (NHL). Unfortunately, in recent years the medical oncology community has improperly underutilized radiotherapy (RT) in the management of NHL. Replacing RT with longer chemotherapy and/or immunotherapy may not necessarily be a good alternative approach and may lead to suboptimal outcome and more toxicity, particularly in patients with localized disease. Some misconceptions regarding the use of RT emanated from the ways RT has been utilized in the past-as a single therapy and in high doses and large fields. Major developments in imaging technology, radiation planning concepts, and RT precision and delivery have been revolutionized RT for NHL over the past two decades. Modern proper administration should result with very minimal acute or late side effects. Some of the controversial issues of the use of RT borrowed from Hodgkin lymphoma, such as risk of secondary tumors, are irrelevant to patients with NHL but cause unnecessary patient and physician scare. Many lymphoma types are notoriously sensitive to RT, especially the indolent types. When localized, like in most marginal zone lymphoma (MZL) and almost a third of follicular lymphomas (FL), RT is potentially curative, even with low dose and small volumes. In more aggressive lymphomas, RT often is an effective consolidation after chemotherapy in complete or even incomplete responders. It also is an important component of salvage and palliation. In older patients, RT is particularly valuable, because chemotherapy tolerance and salvage options may be limited. The International Lymphoma Radiation Oncology Group (ILROG) developed and published modern guidelines for using RT in NHL, including FL. The guidelines emphasize the new concept of RT field: involved site radiotherapy (ISRT). These modern ILROG principles and several relevant studies that looked into the proper integration of RT in the management of NHL patients are the focus of this manuscript.