Application of Stereotactic Body Radiotherapy (SBRT) Bridging to Allogeneic Hematopoietic Stem Cell Transplantation in Adult Hematological Malignance Patients with Extramedullary Lesions. This study aims to improve transplantation outcomes with extramedullary lesions. The investigators aim to study the Post-Transplantation Evaluation of Disease-Free Survival, Overall Survival, Treatment-Related Mortality, Cumulative Recurrence Rate, Post-Transplantation Complications, and Safety Data.

Inclusion Criteria:

Subjects who meet all of the following criteria are eligible for enrollment in this study:

• Age between 18 and 60 years.
• A confirmed diagnosis of a hematologic malignancy, including but not limited to Acute Myeloid Leukemia (AML), Acute Lymphoblastic Leukemia (ALL), Chronic Myeloid Leukemia (CML), Myelodysplastic Syndromes (MDS), Non-Hodgkin Lymphoma (NHL), Hodgkin Lymphoma (HL), and Multiple Myeloma (MM).
• Diagnosis of extramedullary disease/lesions confirmed by one of the following: pathological biopsy, cytology, or at least one imaging modality (including PET-CT, contrast-enhanced CT, or contrast-enhanced MRI).
• Presence of a suitable donor and scheduled to undergo allogeneic hematopoietic stem cell transplantation (allo-HSCT).
• Karnofsky Performance Status (KPS) score > 60% or Eastern Cooperative Oncology Group Performance Status (ECOG PS) score of 0 to 2.
• Has not participated in any other clinical trial involving cell-based or immunotherapies for the treatment of the primary disease.
• The subject voluntarily agrees to participate in the study, demonstrates good compliance, and is willing to cooperate with follow-up procedures.
• A signed informed consent form must be obtained prior to the initiation of any study-related procedures. For subjects aged 18 years or older, consent is to be provided by the subject or their immediate family member. If, in the physician's judgment, obtaining consent directly from the subject is not in the patient's best interest regarding their medical condition, the informed consent form may be signed by the legal guardian or an immediate family member of the patient

Exclusion Criteria:

• Previous history of one or more autologous or allogeneic stem cell transplants prior to enrollment.
• Uncontrolled infection at the time of enrollment, or requirement for mechanical ventilatory assistance, or hemodynamic instability.
• Severe organ dysfunction, including but not limited to hepatic or renal impairment, and heart failure.
• Evidence of active HIV replication; positive HCV antibody and detectable HCV-RNA within 90 days prior to enrollment; or positive HBsAg. Known seropositivity for HIV or active hepatitis C virus.
• Presence of psychiatric disorders or any other condition that, in the investigator's opinion, would compromise the subject's ability to cooperate with study treatment and monitoring requirements.
• Inability or unwillingness to provide written informed consent.
• Any other condition or circumstance that, in the judgment of the investigator, may pose a risk to the subject or prevent the subject from meeting or fulfilling the study requirements.