Pediatric Oncology Nursing

Chapter 9
Radiation Therapy (S. 195-196)

Joan M. O’Brien · Deborah Tomlinson

Radiotherapy has had a role in malignancies for the last century. X-rays were discovered by Von Roentgen in 1895 and were used diagnostically.The element radium was isolated by Marie and Pierre Curie in 1898. The first therapeutic report of a patient cures by radiation therapy was in 1899. However it has a diminishing role in childhood malignancies due to more effective chemotherapy regimens and the recognition of late effects of radiation treatment. Children will often be assessed on an individual level regarding the need of radiotherapy. However it is still required for around 20% of children and young people with cancer. Focus in radiation therapy (XRT) has been on methods of delivery that will minimize injury to normal tissues, to try to avoid long-term negative sequalae.

9.1 Principles of treatment

Radiotherapy causes damage to cells in a localised area. Ionising radiation both causes and treats cancer. Damage is caused by breaking strands of DNA, either double or single strands. This inhibits cell division. It may harm normal cells in the area they pass through or in the area around tumor. Radiation treatment has three main roles in the treatment of childhood and young person:

- Radical: Treatment with curative intent
- Adjuvant: "Added on" treatment
- Palliative: Treatment aimed at symptom control

Radiation is frequently used as part of a bone marrow ablative regimen. At times radiation may be used to ameliorate side effects from tumors that are threaten life or organ function, to quickly reduce the size of a mass that is impinging on the airway, or to relieve pressure on the spinal cord to decrease or prevent paralysis. Palliative radiotherapy is given to relieve pain in progressive or metastatic disease. It provides shrinkage of tumor to relieve pain and/or obstructions interfering with quality of life. The dose is monitored to ensure minimal toxicities.

9.2 Description of treatment

All radiation emits radiant energy, either in waves and particle form.

- Electrons are electromagnetic and produced from a linear accelerator. They can provide treatment to super.cial tumors and have increased absorption to bone.(X-rays are electromagnetic radiation that is produced extranuclearly, electrons are accelerated to high energy and then stopped abruptly at a tungsten target (Farah and Weichselbaum 1994)).
- Gamma rays are electromagnetic radiation produced intranuclearly from a radioactive source. They provide local and wide-.eld radiation, and are skin sparing. Gamma rays require lead or concrete to absorb them.
- Protons are high energy atoms, emitted from a machine, for the treatment of tumours needing speci.c dose localization. They are delivered by stereotaxis (a form of radiation that delivers the beam in an extremely precise manner).

9.2.1 Cell radiosensitivity

Factors that contribute to cell radiosensitivity include:
- Phase of cell cycle that cell is in: Studies have shown that cells are most radiosensitive in the M and G2 phases and most resistant in late S phase (Farah and Weichselbaum 1994). Between dose fractions, cells may move through the cell cycle to more sensitive phases. This process is called “reassortment”. This allows for a greater cell kill.