Radiation treatment for childhood lymphoma and leukemiaMedical editor Alexander Fosså MD
Oslo University Hospital
GeneralRadiation therapy for children with malignant lymphomas is usually limited to childhood Hodgkin's lymphoma. Radiation treatment is not used to treat non-Hodgkin lymphoma. Some acute childhood leukemia patients may require radiation to the brain or the brain in combination with the entire CNS axis. Total body irradiation may also be used for patients with leukemia as part of a stem cell transplantation.
There are detailed treatment protocols for radiation therapy for malignant lymphomas and leukemia. Radiation therapy is almost always given after, or in combination with chemotherapy. The protocols give clear guidelines for use of radiation therapy and information on what anatomical areas are suitable for radiation, as well as volumes and margins to the tumor area. Appropriate image diagnostics, dosage planning, radiation dosages and limits are also found in the protocols.
For Hodgkin's lymphoma, treatment is given according to the GPOH-HD-95 protocol. A new European protocol (EuroNet-PHL-C1) started in 2008 emphasizes reducing the use of radiation treatment in this patient group.
Radiation therapy is an effective treatment form and can improve the chance of long-term disease-free survival of Hodgkin's lymphoma patients. In some leukemia and non-Hodgkin lymphomas, radiation therapy to the brain or CNS axis may be part of the treatment for metastases to the central nervous system or be important in preventing metastases to that area. The risk for delayed damage in the child after radiation therapy (particularly growth disturbances, damage to radiated organs, or radiation-induced cancer) limits the use of radiation therapy to cases where it is absolutely necessary.
Radiation therapy is given at the University Hospital.
Very young children will require general anesthesia to complete the dosage planning and the necessary treatments (fractions). The dosage fraction (daily radiation dose) is most often in the range of 1.8–2 Gy and the total dose of radiation for Hodgkin's lymphoma is in the area of 20–35 Gy. The dosage depends on the size of the remaining lymphoma after chemotherapy and what organs are radiated. For total brain radiation or CNS axis, the total dose is in the area of 12-24 Gy. The dosages are significantly lower and the risk for delayed injury is much lower than after radiation therapy for most solid and CNS tumors in children.
Curative radiation therapy
Radiation therapy can be given as a part in the curative treatment plan for:
Hodgkin's lymphoma after chemotherapy according to protocol
Certain cases of acute leukemia according to protocol
Rare cases of non-Hodgkin lymphoma according to protocol or individual assessment
Palliative radiation therapy
- All patients with a local problem associated with growth of lymphoma or leukemia should be assessed for palliative radiation therapy. The plan general follows the same guidelines as the curative treatment plan with individual changes.
|Target volume definitions from ICRU
(International Commission on Radiation Units and Measurements)
GTV (= Gross Tumor Volume)
Palpable or visible/demonstrative area of malignant growth. Detected lymph nodes are described as GTV-N, other metastases with GTV-M.
CTV (= Clinical Target Volume)
Clinical target volume
Tissue volume which contains GTV and/or subclinical microscopic malignant disease.
ITV (= Internal Target Volume)
Volume containing CTV and one inner margin taking into account inner movements and revisions of CTV.
This is the volume that should receive the optimal radiation dose.
PTV (= Planning Target Volume)
Geometric volume containing ITV and one setup margin taking into account assumed variations for patient movements, variations in patient arrangement, and field tuning.
Planning contour: Beams-Eye-View projection of PTV.
IM (Inner margin) and SM (Set-up margin)
IM and SM cannot be summed linearly. The total margin must be given specifically for different tumor localizations.
Before the first treatment is given, the child must go through multiple steps in the planning process.
Consultation with the child and parents/guardian
The parents/guardian must be informed about the indication, planning, and implementation of the treatment. It is also very important to discuss the side effects on a short and long-term basis in relation to radiation therapy and necessary follow-up care.
The extent of preliminary examinations depends on which areas will be radiated, doses given, and circumstances for the patient. Some examples are:
- Survey of the function of healthy organs that will receive a relevant dose of radiation and therefore be susceptible to short-term and/or long-term damage (lungs, kidneys, heart, eyes etc.)
- Ovariopexy (operation to elevate and fix the ovaries to the abdominal wall) to protect the ovaries before irradiation toward the pelvis
- Dental check up and possibly treatment if irradiating to the teeth/jaw region
Small children will usually not be able to complete fixation, simulation, or treatment without general anesthesia.
In order for the child to maintain the same position for each treatment, the part of the body to be irradiated must be fixed with the help of special equipment that is adapted for each patient.
Examples may be:
- A mask over the head and neck/shoulders if irradiating the head/neck region
- A modeled form of polystyrene (VaccFix) to fix the trunk in a position to irradiate the CNS axis
- Splints, pillows, etc. to hold the arms and legs in defined positions
- Special markings (lead thread) to mark incisions, visible findings, etc.
- Equipment for shielding the testicles or ovaries
Image-taking and simulation
CT images are usually taken of the child in the treatment position on a CT machine dedicated for this. The CT images form the basis for planning the treatment. This is a step-wise process that occurs without the patient present during the waiting period between the CT and the first treatment. The process usually takes 7-10 days.
- The CT images are used for 3-dimensional tracing of the target volume to be irradiated.
- Risk organs are defined and drawn.
- The field layout and calculation of dosage to target volume and risk organs are defined.
- The treatment plan must be approved after taking into consideration the amount of radiation and tolerance of healthy organs.
- The patient must usually be present for drawing of treatment fields on the skin with the help of X-ray on the simulation machine. The simulation machine is built identical to the treatment apparatus.
The treatment is given as daily small doses (fractions) of usually short duration. The treatment is usually carried out on an outpatient basis.
General anesthesia is usually necessary for each treatment in small children.
Treatment is usually only given on weekdays (Monday-Friday) with breaks on weekends.
Fractionation of the total dosage can vary greatly depending on the condition of the patient. If is very important to be well acquainted with the treatment protocol.
- Hodgkin's lymphoma – after chemotherapy 1.8 Gy x 11 (x 16–17 to larger remaining lesions after chemotherapy) according to protocol.
- Acute lymphoblastic leukemia – total brain or neural axis 2 Gy x 6–12 according to protocol.
- Rare cases of non-Hodgkin lymphoma after individual assessment
- Palliative treatment after individual assessment.
The child will receive supportive care from the radiation department during treatment. For many, a close dialogue with the pediatrician will be necessary during radiation therapy.
Acute reactions occurring during and a short time after treatment, depend on the region irradiated, how large the area is, and dose. In children with lymphoma, acute reactions are most often mild and temporary. Details should be explained by the treating physician. Information can also be found in the respective treatment protocols for lymphoma in adults.
Injury to healthy organs can be delayed for a few years, to more than 20-30 years. Delayed injury is an important factor in small children, and should be an important topic of discussion with the parents during the planning of therapy.
Despite doses for Hodgkin's lymphoma being lower today than before, and assumption that the risk of delayed damage therefore is less, adequate information should still be provided.
Follow-up care should take into account the risk for late effects. This will be central in follow-up care after 3-5 years, when the risk for recurrence decreases. Which elements the follow-up care should consist of depend on which region is irradiated, the dose to risk organs, and the age of the child during treatment. Details should be discussed with the treating doctor. Information can also be found in the respective treatment protocols for lymphoma in adults.