Last reviewed by Dr. Dharmender Malik on 13 May 2026 · this article reflects the published evidence and current clinical practice at FMRI Gurugram.
Introduction
Neuroblastoma is the most common extracranial solid tumour of childhood, accounting for around 7 to 10 percent of paediatric cancers. It arises from primitive cells of the sympathetic nervous system — most commonly in the adrenal gland, but also along the sympathetic chain from neck to pelvis. The disease has a wide range of behaviours: some children with low-risk disease are cured with minimal treatment, while children with high-risk disease face a difficult and prolonged treatment journey.
For children with high-risk and relapsed neuroblastoma, Iodine-131 metaiodobenzylguanidine (I-131 MIBG) therapy is one of the longest-established targeted radioligand therapies in clinical use. The same MIBG molecule that produces a diagnostic scan, when labelled with the therapeutic isotope I-131 instead of the diagnostic isotope I-123, delivers a treatment dose of radiation directly to the tumour. This guide is written for parents, families, and referring physicians who want to understand what the therapy is and what the treatment journey looks like.
How I-131 MIBG works
MIBG is a small molecule that mimics noradrenaline. Cells of the sympathetic nervous system — including neuroblastoma cells in most patients — actively take MIBG up via the noradrenaline transporter. When MIBG is labelled with Iodine-131, this uptake brings a beta-emitting radioisotope inside the cancer cell, where it delivers its therapeutic radiation locally.
The same biology that lets a diagnostic I-123 MIBG scan light up neuroblastoma deposits is what makes the therapy work. Children whose neuroblastoma takes up MIBG on the diagnostic scan (about 90 percent of cases) are candidates for the therapy; the small proportion whose tumours are MIBG-negative are not, because the targeting mechanism is absent. This is theranostic logic applied to one of the oldest theranostic agents.
When I-131 MIBG is used
I-131 MIBG is most commonly used in two settings: as part of multimodality treatment for high-risk neuroblastoma (typically in consolidation or as part of induction), and as salvage therapy for relapsed or refractory neuroblastoma after standard treatment. The decision to include MIBG is made by the paediatric oncology team, often in international tumour-board discussion, and depends on disease pattern, MIBG uptake on diagnostic scan, prior treatments, and overall clinical context.
The therapy is not a stand-alone treatment for neuroblastoma. It is one element within a comprehensive treatment plan that may include chemotherapy, surgery, autologous stem cell transplant, external-beam radiotherapy, anti-GD2 immunotherapy, and supportive care. The role of I-131 MIBG within this plan is specific and time-bound.
Pre-treatment preparation
Preparation for I-131 MIBG therapy involves several steps. The child needs thyroid blockade — potassium iodide started a few days before the therapy and continued for several weeks afterwards — to prevent uptake of free radioactive iodine by the thyroid gland. Several medications that interfere with MIBG uptake (some antihypertensives, some antidepressants, and some decongestants) need to be stopped well in advance, on a list provided by the nuclear medicine team.
Baseline assessments include kidney function, full blood count, thyroid function, and an updated diagnostic MIBG scan to confirm uptake. Stem cell rescue may need to be planned where high-dose MIBG therapy could compromise marrow reserve. The full preparation usually takes one to two weeks before the treatment date.
The treatment procedure
The therapy is delivered as an intravenous infusion of I-131 MIBG over typically two to four hours, in a shielded inpatient room designed for radioactive isotope administration. The child stays in this isolation room for typically three to seven days afterwards, until radiation levels measured externally fall below the limit that allows discharge. During this stay, contact with visitors is restricted and structured by radiation safety protocols — siblings and pregnant family members cannot enter the room; one designated parent or carer at a time can enter with appropriate distancing and time limits.
This isolation period is the most difficult part of the journey for many families. We work hard to make it as bearable as possible: every isolation room is set up with the child's familiar toys, books, and devices; play therapy is provided where the radiation protocol allows; parents are supported with information, comfort, and updates throughout. The medical and nursing team monitors the child closely and is available at any moment.
Side effects and recovery
The main short-term side effects are bone marrow suppression (reductions in blood counts) and transient nausea. Marrow suppression typically reaches its lowest point about three to six weeks after the therapy and then recovers; in some children, stem cell rescue is planned in advance to support this recovery. Late effects include hypothyroidism (which is why thyroid blockade is given carefully) and, in a small proportion of children, secondary cancers many years later — a recognised risk that is weighed against the benefits of treating an otherwise refractory disease.
Follow-up scans (typically a diagnostic MIBG scan and other imaging) are scheduled at intervals to assess response. The full benefit of the therapy may not be apparent for several weeks after administration, because the treatment effect continues over time as the tumour cells die.
Where I-131 MIBG fits in the care journey
I-131 MIBG therapy is delivered as part of a comprehensive paediatric neuroblastoma programme that brings together paediatric oncology, surgery, radiology, nuclear medicine, paediatric intensive care, child-life services, and family support. At FMRI Gurugram, we deliver I-131 MIBG therapy in shielded isolation rooms designed for paediatric patients, with a multidisciplinary team supporting the child and family throughout the inpatient stay and the post-treatment follow-up period.
If your child has been diagnosed with high-risk or relapsed neuroblastoma and the team has raised the possibility of I-131 MIBG therapy, the most useful preparation is to bring all imaging (especially the most recent MIBG scan), recent bloodwork, the complete treatment history, and a written list of every medication your child is taking. With that information, an individualised plan can be discussed in detail. We will also walk you through the practical reality of the inpatient stay so that nothing about the experience comes as a surprise.
For patients & referring clinicians
Frequently asked questions
Q01
What is I-131 MIBG therapy?
I-131 MIBG therapy is a targeted radioligand treatment in which the molecule metaiodobenzylguanidine (MIBG) is labelled with the therapeutic isotope Iodine-131 and given as an intravenous infusion. The labelled MIBG is taken up by neuroblastoma cells via the noradrenaline transporter, and the I-131 then delivers beta radiation locally to the tumour cells. The therapy has been used clinically for several decades and remains an important option for high-risk and relapsed neuroblastoma.
Q02
Who qualifies for I-131 MIBG therapy?
The main eligibility requirements are: a diagnosis of neuroblastoma, demonstrated MIBG uptake on a recent diagnostic I-123 MIBG scan (or PET-CT equivalent), adequate kidney and bone marrow function (or planned stem cell support), and a clinical context — typically high-risk disease in consolidation or relapsed/refractory disease — where the therapy fits within the overall plan. The decision is made by the paediatric oncology team in multidisciplinary review.
Q03
How long does the treatment take?
The intravenous infusion itself takes typically two to four hours. The child then stays in a shielded isolation room for typically three to seven days while external radiation levels fall to the limit that allows discharge. The full course of I-131 MIBG may involve one or two cycles separated by several weeks, depending on the protocol and the child's response. Follow-up scans and clinic visits continue for many months afterwards.
Q04
What is the isolation period like?
The isolation period is the part of the journey families find most difficult. Your child stays in a shielded inpatient room with restricted visitor access. Pregnant family members and young siblings cannot enter. One designated parent or carer at a time can be with the child, with structured time and distance limits set by radiation safety. The room is set up with familiar toys, books, and devices; play therapy and child-life support are provided where the protocol allows. The nursing team is in constant contact. Families are supported with information, comfort, and updates throughout.
Q05
What are the side effects?
The main short-term side effects are bone marrow suppression (typically reaching its lowest point three to six weeks after therapy) and transient nausea. Hypothyroidism is a late risk and is mitigated by thyroid blockade with potassium iodide started before therapy and continued afterwards. A small risk of secondary cancers many years later exists and is weighed against the benefit of treating an otherwise refractory disease. Side effects are managed closely by the paediatric oncology and nuclear medicine team.
Q06
How is the family supported?
Family support is built into the care pathway. Before therapy: detailed counselling about what the inpatient stay involves, practical preparation for daily life around the isolation period, and a clear explanation of radiation safety. During therapy: a designated nurse and child-life or play-therapy support, plus open communication with the medical team. After therapy: clear discharge instructions about ongoing thyroid blockade, household precautions for the first few weeks, follow-up scan scheduling, and access to the paediatric oncology team for any concerns. The Indian paediatric oncology community also has parent-support networks that many families find valuable.
Q07
How effective is the therapy?
Effectiveness depends heavily on the clinical context. In relapsed/refractory neuroblastoma, response rates of approximately 30 to 40 percent are reported in published series, with some children achieving meaningful and durable disease control. In consolidation of high-risk disease, MIBG therapy contributes to overall outcomes as one element within a multimodality plan rather than as a stand-alone metric. The realistic conversation about expected benefit is one we have with families in detail before treatment starts.
Citations & references
Matthay KK, Yanik G, Messina J, et al. Phase II study on the effect of disease sites, age, and prior therapy on response to iodine-131-metaiodobenzylguanidine therapy in refractory neuroblastoma.
J Clin Oncol. 2007;25(9):1054-1060.
ReferenceDuBois SG, Granger MM, Groshen S, et al. Randomized Phase II Trial of MIBG Versus MIBG, Vincristine, and Irinotecan Versus MIBG and Vorinostat for Patients With Relapsed or Refractory Neuroblastoma.
J Clin Oncol. 2021;39(31):3506-3514.
Reference
About the Author
Dr. Ishita B. Sen
MBBS · MD (Nuclear Medicine) · DNB · Post-doctoral Fellowship, Memorial Sloan Kettering Cancer Center, New York
Director and Chief of Nuclear Medicine at Fortis Memorial Research Institute. Co-founder of Theranostic Physicians Private Limited (TPPL). Two decades of clinical practice in PSMA imaging and PSMA-directed radioligand therapy, with one of the largest Indian institutional experiences in Lu-PSMA.