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WHY CHILDREN
WITH CANCER
NEED PROTECTION

Information about commonly used treatments:

CHEMOTHERAPY

RADIATION

INVESTIGATING TREATMENTS
WITH MEDLINE


WHAT IS RADIATION THERAPY?

Radiation therapy usually comprises the administration of x-rays or gamma rays. X-rays are generated by machines such as linear accelerators. Gamma rays are produced by radioactive isotopes such as cobalt-60, cesium-137, or radium-226.

Childhood cancers are radiated similarly to adult cancers and a “Radiation Prescription” is written that includes: the site being treated, number of beams, number of fractions, dose per fraction, number of fractions per day and total dose. A “Radiation Boost” is the extra dose of radiation that is usually administered to a small specific area where the tumor is or was located.


BODY'S TOLERANCE FOR RADIATION

Different tissues tolerate different amounts of radiation. The table below lists the tissue tolerance of some organs and structures in the body. Radiation dosage is measured in a unit called a “Gray,” abbreviated Gy. One Gray equals one hundred Centi-Gray (cGy). One cGy is equivalent to one rad.

Tissue
Dose (cGy)
Complications
Brain
6,000
Necrosis
Spinal cord
4,500
Myelitis
Heart
4,500
Pericarditis,
myocardial damage
Intestine
4,500
Stenosis, perforation
Liver
3,000
Hepatitis,
hepatic vein thrombosis
Lung
2,000
Pneumuonitis, fibrosis
Kidney
2,000
Nephropathy, renal failure
Bone marrow
250
Aplasia
Ovary
200
Sterilization
Testes
100
Sterilization

The normal tissue tolerance is defined as the dose at which no more than 5% of patients will have the stated complication within 5 years. Source: Anthony S. Fauci et al., Harrison’s principles of internal medicine 525-526 (14TH ed. 1998).

Using dental x-rays as a comparison, 6,000 Gy of brain radiation is equivalent to approximately 60,000 to 100,000 consecutive dental x-rays.

RADIATION RISKS

As the excerpts below suggest, radiation therapy can be:

  • Toxic;
  • Mutagenic (causing mutations in DNA);
  • Carcinogenic;
  • Teratogenic (producing defects in offspring);
  • Cause necrosis (death of tissue);
  • And lead to significant deficits.

Therefore, oncologists should communicate appropriate information to patients (or their parents) when discussing risks and benefits of various treatment options that incorporate radiation therapy.


RADIATION IS TOXIC, MUTAGENIC, CARCINOGENIC AND TERATOGENIC

According to a leading medical treatise:

“Radiation therapy is associated with both acute toxicity and long-term sequelae…long term sequelae …(may) occur many months or years after the completion of therapy…” In addition, “Radiation therapy is known to be mutagenic, carcinogenic, and teratogenic and is associated with an increased risk of developing both secondary leukemias and solid tumors.”
- Source: Anthony S. Fauci et al., Harrison’s principles of internal medicine 525-526 (14TH ed. 1998).

There are many demonstrations of these assertions in the medical literature. For example in discussing thyroid cancer after radiotherapy, one doctor from the Radiation Epidemiology Branch of the National Cancer Institute has written:

“Because of the extreme sensitivity of the thyroid gland in children, there is a risk of radiation-induced thyroid cancer even when the thyroid gland is outside of the irradiated field. Increased incidence of thyroid cancer has been noted following radiotherapy for childhood Hodgkin disease, non-Hodgkin lymphoma, neuroblastoma, Wilms tumor, acute lymphocytic leukemia and tumors of the central nervous system. Radiation-induced tumors begin to appear 5-10 years after irradiation and excess risk persists for decades, perhaps for the remainder of life.”
- Source: P.D. Inskip, Thyroid cancer after radiotherapy for childhood cancer, MED PEDIATR ONCOL 2001 May;36(5):568-73


RADIATION CAN LEAD TO SEVERE DEFICITS

According to a recent report from the National Cancer Institute:

“Functional deficits in patients after radiotherapy (for brain cancer) are probably more common than is currently reported. These deficits include mental retardation in patients irradiated as infants, learning disabilities in older pediatric patients, and memory or cognitive deficits in adults. Whole-brain radiotherapy for metastatic disease can result in a range of neurocognitive outcomes, ranging from little or no deficit to full-blown dementia. The factors contributing to the development of neurocognitive deficits are poorly understood. These deficits have severe effects on quality of life for patients and their families.”
- Source: Brain Tumor Progress Review Group, Radiation Biology, Co-chairs: Dennis Shrieve, M.D., Ph.D., and Philip J. Tofilon, Ph.D. National Cancer Institute, July 1, 2001


RADIATION CAN LEAD TO RADIATION NECROSIS

Radiation can also lead to necrosis. Necrosis is defined as the death of tissue. For example, according to two doctors:

“Radiation necrosis (from brain radiation) can occur as soon as a few months or as long as decades after treatment. It generally occurs 6 months to 2 years after radiation therapy…Radiation necrosis can be fatal. It also can cause problems associated with a mass lesion, such as seizures, focal deficits, increased intracranial pressure, and herniation syndromes…Occurrence (of radiation necrosis) generally is related to total radiation doses and fractionation size…Patients who have received a total dose of 5500 cGy have a 3-5% occurrence of radiation necrosis. Fractionation daily dose exceeding 200 cGy also increases risk. Other predisposing factors include the following: other vasculopathic risk factors (e.g. diabetes mellitus, hypercholesterolemia); and intravenous chemotherapy.”
- Source: Robert Wilson, D.O. and Anna Janss, M.D., eMedicine Journal, November 16 2001, Volume 2, Number 11.



CHEMOTHERAPY PLUS RADIATION CAN ALSO LEAD TO NECROSIS

When chemotherapy and radiation are used together the result can also be necrosis. There are a number of cases in the medical literature that demonstrate this possibility. Below is one example from the treatment of a child with a pediatric brain tumor.

“A three year old girl received (radiation and chemotherapy for a recurrence)… After two months of chemotherapy, central nervous system toxicity progressed rapidly from ataxia to paraplegia to quadriplegia to central respiratory failure. Radiographic scans and autopsy material revealed brain stem necrosis.”
- Source: Watterson J, et al., "Fatal brain stem necrosis after standard posterior fossa raidation and aggressive chemotherapy for metastic medulloblastoma." Cancer 1993 Jun 15; 71(12): 4111-7.

 

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