Total Body Irradiation (TBI)

Introduction

Total Body Irradiation, usually shortened to TBI, is a form of radiation therapy in which the entire body receives a carefully measured dose of radiation. Unlike most radiation treatments, which target a single tumour or area, TBI treats the body as a whole. It is almost always given as one step in a larger treatment plan — most commonly the preparation before a bone marrow transplant or stem cell transplant.

If you or your child has been told that TBI will be part of upcoming treatment, you are likely already meeting with a transplant team, a haematologist, and a radiation oncologist. This article is written for that moment. It explains what TBI is, why it is given, how the sessions are planned and delivered, what side effects to expect in the short and long term, and how follow-up care continues for years afterwards.

TBI is a demanding treatment, and understanding it in advance can make the experience feel more manageable. Decisions about whether TBI is the right conditioning approach, and at what dose, are made by your transplant team based on the disease being treated, age, overall health, and the type of transplant planned.

What Is Total Body Irradiation?

Total Body Irradiation is the use of external beam radiation to deliver a uniform dose to the whole body. The radiation comes from a machine called a linear accelerator, the same kind of machine used for many other forms of radiotherapy. The difference is in how the patient is positioned, the distance from the machine, the shielding used to protect certain organs, and the dose given.

• To suppress the immune system enough that the body will not reject the donor cells
• To create space in the bone marrow for the new donor cells to settle and grow
• To destroy any remaining cancer cells, including those that may be hiding in places where chemotherapy reaches less effectively, such as the brain, spinal cord, or testes

Most conditioning regimens combine high-dose chemotherapy with or without TBI. Whether TBI is added, and at what dose, depends on the disease being treated and the type of transplant. The terms myeloablative (high-dose) and reduced-intensity conditioning describe how strong the regimen is overall.

How TBI Works

Radiation damages the DNA inside cells. Cells that are dividing quickly — such as bone marrow cells, immune cells, and many cancer cells — are the most sensitive. By delivering a controlled dose of radiation across the entire body, TBI:

• Empties the bone marrow of existing cells, including diseased ones, so the donor cells have room to grow.
• Wipes out the patient’s immune system, which would otherwise recognise the donor cells as foreign and attack them. This lowers the risk of graft rejection.
• Reaches sanctuary sites — areas of the body where chemotherapy drugs penetrate less well. The central nervous system and the testes are the most important examples in leukaemia.

Because the goal is to treat the whole body, TBI uses different techniques from the focused, high-precision beams used for solid tumours. Shielding may be placed over the lungs, kidneys, or other organs to limit damage to tissues that are particularly sensitive to radiation. The lungs in particular are protected because radiation pneumonitis — inflammation of the lungs — is a serious risk.

Who Receives Total Body Irradiation?

TBI is used mainly for people undergoing an allogeneic stem cell transplant — a transplant using donor cells — though it is also used in some autologous transplants (where the patient’s own previously collected stem cells are returned). The diseases most commonly treated with conditioning regimens that include TBI are:

• Acute lymphoblastic leukaemia (ALL), particularly in children and young adults. TBI-based conditioning has long been a standard approach in this disease, and current evidence continues to support it for many patients.
• Acute myeloid leukaemia (AML) in selected cases, although chemotherapy-only conditioning is also widely used.
• Chronic myeloid leukaemia (CML) in patients proceeding to transplant.
• Myelodysplastic syndromes (MDS).
• Some lymphomas, including certain non-Hodgkin lymphomas, in selected cases.
• Multiple myeloma in selected protocols, although chemotherapy-only conditioning is more common.
• Severe aplastic anaemia and other bone marrow failure conditions, where lower doses of TBI may be used to allow donor cells to take hold without giving high-dose chemotherapy.
• Certain inherited conditions in children, such as some immunodeficiencies and metabolic disorders, when stem cell transplant is needed.

Whether TBI is included in the conditioning regimen depends on several factors: the specific disease and its risk features, prior treatment, age, organ function (particularly heart, lungs, kidneys, and liver), and the type of donor. Children and young adults often tolerate TBI better than older adults, which influences when it is offered.

Types of TBI

TBI is not a single fixed treatment. The dose, the schedule, and the technique can vary considerably depending on the disease and the goal.

High-dose (myeloablative) TBI

This is the most intensive form. A total dose of around 12 to 13.2 Gy (Gray, the unit of radiation dose) is typically given in multiple smaller doses over three or four days. Splitting the dose into smaller sessions, called fractionation, allows healthy tissue to recover between sessions and reduces the risk of long-term side effects compared with a single large dose. Hyperfractionated schedules — two sessions per day — are common.

High-dose TBI is used when the goal is to wipe out the bone marrow completely and treat aggressive disease. It is most often combined with high-dose chemotherapy such as cyclophosphamide or etoposide.

Reduced-intensity and non-myeloablative TBI

Lower doses of TBI, sometimes as low as 2 Gy in a single session, are used in reduced-intensity conditioning. The goal here is not to destroy the bone marrow but to suppress the immune system enough to let donor cells take hold. This approach is often used in older adults or in people whose organs cannot safely tolerate full-dose conditioning.

Total marrow irradiation and total marrow and lymphoid irradiation

Newer techniques, sometimes called total marrow irradiation (TMI) or total marrow and lymphoid irradiation (TMLI), use advanced radiation planning to focus radiation on the bone marrow and lymph nodes while sparing other organs. These techniques use image-guided and intensity-modulated radiation therapy. They are not available at every centre but are part of ongoing research and are increasingly used in specialised transplant programmes.

Where TBI Fits in the Transplant Pathway

1. Workup and assessment. Heart, lung, kidney, and liver function are tested, along with blood counts, infection screening, dental check, and fertility counselling. A central line is placed for delivering drugs and taking blood.
2. Donor identification (for allogeneic transplants) or stem cell collection (for autologous transplants).
3. Conditioning regimen. This is where TBI fits, given alongside or after high-dose chemotherapy, typically over several days in the inpatient or day-care setting.
4. Stem cell infusion (“day 0”). The donor cells, or the patient’s own cells, are given through the central line. It looks similar to a blood transfusion.
5. Engraftment phase. Over the next two to four weeks, the new cells travel to the bone marrow and begin to produce blood cells. During this time blood counts are very low and the risk of infection and bleeding is high.
6. Early recovery. Usually around 30 to 100 days after transplant, with close monitoring for graft-versus-host disease (in allogeneic transplants), infections, and organ toxicity.
7. Long-term follow-up. Continues for years, watching for late effects of conditioning, including effects of TBI.

Knowing where TBI fits helps explain why side effects, recovery, and follow-up are best understood in the context of the whole transplant, not in isolation.

Preparing for TBI

Before TBI begins, the radiation oncology team performs a planning session, sometimes called a simulation. This involves:

• Detailed measurements of body dimensions to plan the radiation field
• CT scans used to design lung shields and confirm anatomy
• Practising the treatment position to make sure it can be held comfortably for the duration of each session
• Marking the skin with small permanent or temporary marks to align the body for each treatment

The position used depends on the equipment at the centre. Some patients lie on a bed at an extended distance from the radiation machine, others stand or sit on a specially designed chair, and some lie on a moving couch that translates the body through the beam. In every case the position is chosen so that the radiation reaches the whole body as uniformly as possible.

Before the conditioning regimen starts, you will also have:

• A central venous catheter placed (if not already in place) for fluids, medicines, blood transfusions, and the eventual stem cell infusion
• Conversations about fertility. TBI almost always causes permanent infertility in both men and women, and counselling about sperm, egg, or embryo preservation is offered before treatment begins where time allows.
• Dental review to treat any infections that could become serious once the immune system is suppressed
• Vaccination review (although live vaccines are avoided)
• A conversation about the conditioning regimen as a whole — the chemotherapy drugs, the TBI schedule, and what to expect each day

Fertility preservation is a particularly important conversation. For children, options may include ovarian or testicular tissue cryopreservation. For adults, sperm banking, egg freezing, or embryo freezing may be possible. The transplant team can usually arrange referral to a fertility specialist before conditioning starts.

What Happens During TBI

A typical course of high-dose TBI is delivered over three to four days, with one or two sessions per day. Each session lasts anywhere from 20 minutes to over an hour, depending on the technique used.

During each session you will be in the treatment room alone, but the radiation therapists watch and speak to you through a camera and microphone throughout. The machine itself is silent for most of the session; you will hear a humming when the beam is on. You do not feel the radiation as it is delivered. There is no pain during treatment.

Some patients describe a metallic taste in the mouth during sessions. Mild nausea may begin during or shortly after the first session. Anti-nausea medication is given before each session to help with this.

Children, especially younger children, may need sedation or general anaesthesia to lie still for the duration of each session. The anaesthetic team works closely with the radiation team in these cases.

Side effects of TBI overlap with those of the chemotherapy given alongside it. They are usually divided into early effects, which begin during conditioning and in the weeks after transplant, and late effects, which can appear months or years later.

Early side effects

The most common early effects include:

• Nausea and vomiting, often starting during the first day of TBI. Anti-nausea medications are given before and after each session.
• Tiredness, which builds through the conditioning week and is usually most pronounced in the days after transplant.
• Loss of appetite and altered taste. Many patients find that food tastes strange or unappealing for some weeks. Nutritional support, including feeding through the central line if needed, helps maintain weight.
• Mouth and gut soreness (mucositis), where the lining of the mouth and digestive tract becomes inflamed. This can be very painful and may require strong pain relief and intravenous nutrition.
• Diarrhoea, related to mucositis in the gut.
• Hair loss, usually complete and starting around two weeks after conditioning. Hair generally regrows in the months after transplant, though the texture or colour may change.
• Skin changes, including redness, dryness, and itchiness, similar to a sunburn.
• Parotid gland swelling, causing painful, swollen glands near the jaw, often in the first day or two.
• Low blood counts, which combined with chemotherapy lead to anaemia, bleeding risk, and a very high risk of infection. Patients are usually nursed in a protected environment with strict infection control until the new cells engraft.

The transplant team manages these effects with anti-nausea medications, pain relief, mouth care, blood transfusions, antibiotics, antifungals, antivirals, and intensive nursing care. Most early side effects ease over the weeks following transplant.

Effects in the first months

• Radiation pneumonitis — inflammation of the lungs — can develop in the months after TBI. Symptoms include cough, breathlessness, and sometimes fever. Treatment usually involves steroids.
• Veno-occlusive disease (VOD), also called sinusoidal obstruction syndrome, is a serious complication where small blood vessels in the liver become blocked. It can cause weight gain, abdominal pain, and jaundice. Both chemotherapy and TBI contribute to the risk.
• Graft-versus-host disease (GVHD) in allogeneic transplants, where donor immune cells attack the patient’s tissues. This is not caused by TBI itself but is a major part of the post-transplant landscape.
• Infections, both common and unusual, are a constant concern for many months as the new immune system slowly matures.

Late side effects

Long-term effects of TBI are an important reason why follow-up continues for many years. They include:

• Infertility. Most patients who receive high-dose TBI become permanently infertile. Reduced-intensity regimens carry lower but still significant risk.
• Cataracts. Clouding of the lens of the eye is common several years after TBI and may need surgical treatment.
• Thyroid dysfunction. The thyroid gland is sensitive to radiation. An underactive thyroid is common and is treated with daily hormone replacement.
• Other hormone changes, including effects on the pituitary gland, growth hormone production (particularly important in children), and sex hormones.
• Lung scarring. Some patients develop long-term reduction in lung function.
• Kidney damage. Reduced kidney function can develop slowly over years.
• Heart disease. Risk of long-term heart problems is increased, particularly when combined with certain chemotherapy drugs.
• Bone effects, including reduced bone density and, in children, effects on growth and skeletal development.
• Second cancers. Years after TBI, the risk of new cancers, including skin cancers and some solid tumours, is higher than in the general population.
• Cognitive and developmental effects in children treated at young ages, particularly affecting learning, attention, and memory.

These late effects are an important part of why long-term follow-up clinics exist for transplant survivors. Screening allows problems to be picked up and treated early.

Response and Monitoring

Because TBI is part of a conditioning regimen, response is not measured as a separate outcome for the radiation itself. What is monitored is the success of the whole transplant: whether the donor cells engraft, whether the original disease is controlled, and how the body recovers.

During the weeks after transplant, the team watches:

• Blood counts, to detect engraftment when new white cells, red cells, and platelets start to appear
• Tests for graft-versus-host disease and infections
• Liver, kidney, and lung function
• Disease markers, depending on the original illness

In the months and years after transplant, follow-up shifts to long-term effects. Regular checks usually include:

• Eye examinations to detect cataracts
• Thyroid function blood tests
• Heart and lung function tests
• Bone density scans
• Skin examination for new lesions
• Hormone and growth assessments in children
• Vaccination updates, since transplant patients lose previous immunity and need a re-vaccination programme

Long-term follow-up after transplant with TBI is generally lifelong. The schedule becomes less intense over time but does not stop.

Combining TBI with Other Treatments

TBI is almost always given alongside chemotherapy. Common partner drugs include cyclophosphamide, etoposide, fludarabine, and others, chosen based on the disease and the regimen. The combination is designed so that the two modalities work together — chemotherapy reaches some cells better, TBI reaches others, and together they prepare the body for the new cells.

In addition to conditioning, TBI sits within a wider treatment plan that may have included:

• Several previous lines of chemotherapy
• Targeted therapies (for example tyrosine kinase inhibitors in some leukaemias)
• Immunotherapy (for example CAR-T cells in some leukaemias and lymphomas)
• Earlier radiation to specific sites such as the brain

Because TBI affects organs that may already have been stressed by previous treatment, your transplant team carefully weighs the cumulative risk to the heart, lungs, kidneys, and other organs when deciding whether to include TBI and at what dose.

Some centres now use chemotherapy-only conditioning instead of TBI for certain diseases, particularly in adults. Others use reduced-intensity TBI as a less toxic alternative. The choice depends on the disease, age, organ function, and the experience of the transplant centre.

TBI in Children

TBI is a particularly important treatment in paediatric stem cell transplant, especially for acute lymphoblastic leukaemia. Recent international research has supported the use of TBI-based conditioning in many children with ALL undergoing transplant, in preference to chemotherapy-only conditioning, while accepting the burden of late effects.

The practical experience of TBI for a child differs from that of an adult in several ways:

• Sedation or anaesthesia is usually needed for younger children to keep them still during each session.
• Play preparation by child life or play therapy specialists can help older children understand the procedure and reduce anxiety.
• Parents are usually present in the lead-up to each session and waiting at the end of it, although they cannot be in the treatment room while the radiation is being given.
• Schooling is interrupted for many months. Hospital school services, where available, help maintain learning during the long inpatient stay.

• Growth. TBI can reduce final adult height, both by direct effects on the skeleton and through effects on growth hormone. Some children are offered growth hormone treatment after transplant.
• Puberty and fertility. Most children who receive high-dose TBI will not go through puberty without hormone treatment and will not be able to have biological children naturally. Hormone replacement helps puberty progress at an appropriate age.
• Thyroid function. Hypothyroidism is common and needs lifelong replacement.
• Learning and cognition. Younger age at TBI is associated with greater risk of difficulties with attention, processing speed, and memory. Educational support is an important part of long-term care.
• Dental development can be affected in young children, including changes in tooth shape and enamel.
• Second cancers become a long-term concern, with risk continuing throughout adult life.

Long-term follow-up clinics for children who have had transplant are organised around tracking these issues year by year, with input from endocrinology, cardiology, ophthalmology, dentistry, psychology, and education specialists as needed.

Living During and After Treatment

The conditioning week and the first weeks after transplant are usually spent in hospital. After discharge, recovery continues for many months. The first 100 days are often the most demanding, with frequent clinic visits, blood tests, transfusions, infection precautions, and medication changes.

Practical things that help during this period:

• A care partner. Most transplant programmes require a dedicated adult caregiver to be available, particularly in the early outpatient phase.
• Infection precautions. The transplant team gives detailed guidance on food, water, crowds, animals, and gardening during the period of low immunity.
• Nutrition. Mouth soreness, taste changes, and poor appetite can persist for weeks. Small frequent meals and dietitian support help.
• Skin care. Skin remains sensitive to sun for many years, and lifelong sun protection is important because of the higher risk of skin cancer.
• Activity. Gentle, gradually increasing activity supports recovery. Energy levels often take many months to return.
• Emotional and psychological support. The intensity of the treatment, the isolation of the early recovery period, and the awareness of long-term effects often have a significant emotional impact. Counselling, peer support, and family support are valuable parts of recovery.

Returning to work, school, or normal social life happens gradually. For many adults, a return to work is possible at six to twelve months after transplant, often part-time at first. For children, return to school is staged with input from the school and the medical team.

Frequently Asked Questions

Will I be radioactive after TBI?

No. TBI uses external beam radiation, which passes through the body but does not stay in it. You are not radioactive after treatment and there is no risk to family members, children, or pets from being near you.

Will I feel the radiation during the session?

Most patients do not feel the radiation itself. Some describe a metallic taste in the mouth or mild warmth on the skin. Side effects like nausea may begin during or shortly after the session.

How is TBI different from radiation for a tumour?

Radiation for a tumour aims to deliver a high dose to one specific area while protecting the rest of the body. TBI aims to deliver a uniform dose to the entire body, with shielding only for particularly sensitive organs such as the lungs. The planning, positioning, and dose are different.

Why is TBI given over several days instead of all at once?

Will I lose my hair?

Yes. Hair loss is expected from both TBI and the chemotherapy given with it. Hair generally begins to grow back a few months after transplant, although its texture, colour, or thickness may be different.

Will TBI affect my ability to have children?

High-dose TBI causes permanent infertility in most patients, both male and female. Reduced-intensity TBI carries a lower but still significant risk. Fertility preservation options — such as sperm, egg, embryo, or ovarian/testicular tissue freezing — are discussed before conditioning begins where time allows.

Can TBI be used more than once?

Repeating high-dose TBI in the same patient is rarely possible because the body cannot safely tolerate a second full course. In some situations a small additional radiation dose to a specific area may be considered later, but a second whole-body TBI is unusual.

What is the difference between TBI and total marrow irradiation?

Standard TBI delivers radiation to the entire body. Total marrow irradiation (TMI) and total marrow and lymphoid irradiation (TMLI) use more advanced techniques to focus radiation on the bone marrow and lymph nodes while sparing other organs. These techniques aim to reduce side effects and are increasingly used in specialised transplant programmes.

How long does recovery take?

The early hospital recovery typically takes three to six weeks. The first 100 days after transplant involve very close monitoring and gradual recovery. Most patients feel substantially better by six to twelve months, although energy levels, immune recovery, and some side effects can take a year or more to settle. Long-term follow-up continues indefinitely.

Can my child go to school during recovery?

Not in the early months. Children usually need to stay away from school during the period of low immunity and high infection risk. The transplant team gives specific guidance on when school can resume, often staged and starting with reduced hours.

What follow-up will be needed years later?

Long-term follow-up after TBI includes regular checks of thyroid function, eyes, heart, lungs, kidneys, bones, and skin, along with hormone and growth monitoring in children. Vaccinations are usually restarted on a planned schedule, and screening for second cancers continues lifelong.

Conclusion

Total Body Irradiation is a powerful and carefully designed treatment used to prepare the body for a stem cell or bone marrow transplant. It works alongside chemotherapy to suppress the immune system, clear remaining disease, and make space for new donor cells. The treatment itself is short — usually three or four days — but its effects, both early and long-term, are significant and shape the recovery and follow-up that come afterwards.

Decisions about whether TBI is included in conditioning, at what dose, and using which technique are made by the transplant team in light of the disease, age, organ function, and goals of treatment. Understanding what TBI is, why it is being recommended, and what to expect can help you and your family prepare for the weeks of conditioning and the long period of recovery that follows. The questions to ask your transplant and radiation oncology teams — about the regimen, the side effects, fertility, and long-term follow-up — are an important part of that preparation.