Malignant lymphoma can be simply divided into Hodgkin’s lymphoma (HL) and non-Hodgkin’s lymphoma (NHL), both of which can be subdivided into many subtypes based on their immune cell origin and histopathological morphology, biological behavior and treatment prognosis. Radiotherapy plays a very important role in the treatment of malignant lymphomas, with more than half of patients requiring radiotherapy involvement. The role of radiotherapy in the treatment of Hodgkin’s lymphoma In 1994, the International Lymphoma Study Group regrouped HL into two categories based on morphologic, phenotypic, genotypic and clinical features: nodular lymphocyte-predominant Hodgkin’s lymphoma (NLPHL) and classic Hodgkin’s lymphoma (CHL), which in turn includes nodular sclerosis, mixed-cell, lymphocyte-reduced and lymphocyte-rich Hodgkin’s The latter includes nodular sclerosis, mixed cell, lymphocytic reduction and lymphocyte rich Hodgkin’s lymphoma (LRCHL), which was recognized by WHO in 1999. Hodgkin’s lymphoma (HL) originates from lymphoid hematopoietic tissue and is one of the malignancies with better treatment and higher cure rates. With the advancement of radiation technology and chemotherapeutic drugs, especially the application of integrated chemotherapy and radiotherapy, not only the cure rate is ensured, but also the complications and sequelae of treatment are greatly reduced. In recent decades, the role of radiation therapy in the treatment of Hodgkin’s lymphoma has changed considerably. In the 1960s and 1970s, expanded field irradiation was effective in curing most early and intermediate stage HL. In the last decade, chemotherapy plus involved field irradiation has become the mainstay of treatment for stage I-II HL, and for patients with stage III and IV post-chemotherapy, involved field irradiation is used for large masses or residual lesions. The latter is divided into the hoe field (para-aortic and spleen) and pelvic field, and sub-total lymph node irradiation refers to the hoe field plus the bucket field. Involved field (IF) refers to an irradiated field that includes only the lymphatic area where the tumor is clinically invasive. Expanded field irradiation is an effective treatment for early stage HL, but the combination of chemotherapy and radiotherapy has gradually become the standard of care for stage I-II HL, while patients with advanced HL who do not achieve complete remission after chemotherapy or who have large masses before chemotherapy need to receive radiation therapy. Therefore, involved field irradiation has become an important treatment for all stages of HL. The definition of involved field, the extent of irradiation and the dose of irradiation vary widely among different oncologic radiotherapy centers. Most units apply the Ann Arbor staging principles of lymph node invasion area illustration to define and determine the involved field area and irradiation range. The dose of radiotherapy is generally controlled at about 30 Gy, and there is a trend to further reduce the dose. The role of radiotherapy in the treatment of patients with advanced disease is still debated. There are mainly the following 3 aspects: (i) adjuvant radiotherapy after CR by chemotherapy; (ii) as a part of comprehensive treatment; (iii) radiotherapy after partial remission by chemotherapy. In patients with residual lesions after chemotherapy or large masses before chemotherapy for advanced HL, radiotherapy improves survival; without large masses or chemotherapy CR, there is no evidence that radiotherapy improves survival. Recent Meta-analyses have shown that the benefit of radiotherapy in advanced patients is related to the number of chemotherapy cycles, and that the benefit of radiotherapy may be diminished if chemotherapy is overdone. It is worth emphasizing that irradiation of bones, muscles and soft tissues during childhood can affect their growth and development with adverse effects. Unilateral neck irradiation can lead to unilateral soft tissue and skeletal dysplasia, asymmetric growth and malformation of the neck in children. Therefore, in children with HL cervical lymph node invasion, the involved fields should be irradiated bilaterally instead of performing unilateral neck irradiation. 2. The role of radiotherapy in the treatment of non-Hodgkin’s lymphoma With the widespread use of the new REAL/WHO pathologic classification of malignant lymphoma and advances in chemotherapy, the status of radiotherapy in the treatment of non-Hodgkin’s lymphoma (NHL) has changed considerably. First, radiotherapy remains the primary treatment for certain early stage low-grade malignant/inert lymphomas or early stage lymphomas with good prognosis, such as stage I/II grade I/II follicular lymphoma, stage I/II small lymphocytic lymphoma, early stage cutaneous follicular center cell lymphoma, cutaneous mycosis fungoides, stage IE cutaneous large cell mesenchymal lymphoma and stage IE-IIE extra-nodal (gastric, parotid, thyroid, etc.) mucosa-associated lymphoma, etc. Secondly, some aggressive lymphomas are resistant to chemotherapy, and radiotherapy is the main or radical treatment for them. The combination of chemotherapy and radiotherapy remains the standard of care for early stage diffuse large B-cell lymphoma. In contrast, chemotherapy is the mainstay of treatment for highly malignant NHL of any stage, such as T-lymphoblast lymphoma, and radiotherapy only plays a palliative role or reduces the local recurrence rate, with no effect on survival. Radiation therapy alone: Follicular lymphoma is highly sensitive to radiation therapy. Whether expanded field irradiation or whole lymph node irradiation is superior to involved irradiation remains an unresolved clinical question. Treatment principles are, based on current clinical research evidence, the following treatment strategies for grade I/II follicular lymphoma: Stage I/II: (i) early stage can be cured and treatment should not be delayed. (ii) Radiotherapy alone, with irradiation of the involved field or expanded field. ③There is still no positive evidence that chemotherapy added to radiotherapy can improve overall survival. Stage III/IV: ①Palliative treatment, not curable. (ii) Oral benzodiazepine is effective, with a clinical remission rate of 65%. (iii) Combination chemotherapy improved the complete remission rate but not the overall survival rate. ④The combination of chemotherapy and melphalan improved the remission rate and survival. ⑤ IFN maintenance therapy significantly improved disease-free survival, but not overall survival. ⑥High-dose chemotherapy plus bone marrow transplantation may be beneficial in patients younger than 60 years of age. Treatment of stage I/II follicular lymphoma grade I/II can be done with radiotherapy alone (expanded field irradiation) or combination therapy. Treatment of advanced follicular lymphoma is based on chemotherapy, mostly with CHOP regimens, and more aggressive chemotherapy regimens have not improved the survival of follicular lymphoma. The principles of treatment for grade III follicular lymphoma are the same as those for diffuse large B-cell lymphoma, with stage I/II being treated primarily with combination therapy, followed by 3-4 cycles of CHOP regimens followed by irradiation of the involved fields. The most common site of MALT lymphoma is the gastrointestinal tract, accounting for 45% to 56% of all MALT lymphomas. Other more common non-gastrointestinal sites include the lung, eye and conjunctiva, skin, thyroid, and breast. According to recent publications, 66%-74% of patients have stage I/II MALT lymphoma, and about 11%-23% have concurrent multisite MALT lymphoma, sometimes metastasizing to distant lymph nodes and other hematologic systems such as bone marrow, liver or spleen, while peripheral lymph node metastasis is rare. The median age is 60 years, and it is more common in women. Radiation therapy is the most important treatment for stage I/II extranodal MALT lymphoma, achieving very good outcomes while preserving organ function. In recent bulk literature, the 5-year survival rate for early-stage extranodal MALT lymphoma with radiotherapy alone is over 95% and the disease-free survival rate is 77%. The prognosis of gastric and thyroid MALT lymphoma is better than that of other extra-nodal MALT lymphomas, and gastric NHL is sensitive to radiotherapy. Because radiotherapy is a non-invasive treatment that preserves gastric function and improves the quality of survival, radiotherapy with or without chemotherapy is gradually becoming one of the main treatments for stage I/II gastric NHL to preserve gastric function. The 5-year survival rate and disease-free survival rate of radiotherapy for stage IE/IIE gastric MALT lymphoma are over 90% and 80%, respectively. Indications for radiotherapy include the following: stage IE, stage IIE or higher with t(11; 18)(q21; q21) translocation or transformation, and highly malignant gastric MALT lymphoma (diffuse large B-cell lymphoma) that is ineffective with anti-infective therapy or HP-negative. Comprehensive treatment of early-stage non-Hodgkin’s lymphoma: The treatment of early-stage non-Hodgkin’s lymphoma has undergone a series of changes. Half a century ago, due to the lack of effective chemotherapeutic agents, early stage NHL was often treated with radiation therapy alone. In the last decade or so, the rapid development of chemotherapeutic agents and the understanding of the biological line of NHL have led to the widespread use of chemotherapy and have effectively improved the survival rate of NHL patients. In recent years, clinicians have realized that radiation therapy still plays a very important role in the treatment of early NHL, especially the local control rate of radiation therapy is significantly better than that of chemotherapy. Chemotherapy, as a systemic therapy, can control distant organ metastases and invasion. The combination of chemotherapy and radiotherapy can control both local recurrence and distant metastases. Another important aim of combination therapy is to reduce the toxicity of treatment. Combination therapy improves the efficacy of early stage moderate to highly malignant NHL, and it is important to consider reducing the chemotherapy cycle when combination therapy is applied. Radiotherapy uses irradiation of the involved field rather than expanded field irradiation. In cases where complete remission is achieved with chemotherapy, the dose of radiation therapy should be reduced. In some patients, such as those who are old or refuse chemotherapy, expanded field irradiation alone may be administered. The rationale and advantage of combination therapy is that systemic chemotherapy is effective in controlling subclinical metastases to distant organs, while radiotherapy is effective in controlling local recurrence. Radiotherapy followed by chemotherapy was mostly used in early randomized controlled studies. Thereafter, Yamayu recognized that occult distant metastases were the main cause of treatment failure in NHL, and the combination therapy soon shifted to chemotherapy followed by radiotherapy. Starting in the late 1980s, a combination treatment regimen of chemotherapy plus irradiation of the involved fields gradually replaced radiotherapy alone as the standard of care for moderately to highly malignant or aggressive NHL. Several randomized studies have demonstrated that combination therapy significantly improves patient survival and/or disease-free survival when compared with radiotherapy alone or chemotherapy alone. Combination therapy with chemotherapy followed by radiotherapy has been widely accepted as the standard of care for adults with stage I/II B-cell-derived intermediate to highly malignant NHL, particularly diffuse large B-cell lymphoma. The 5-10 year overall and disease-free survival rates after combination therapy for stage I/II diffuse large cell lymphoma are 63% ~85%. In contrast, radiation therapy uses irradiation of the involved field to reduce the risk of a second primary tumor and to reduce toxic side effects.