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Complications of Radiotherapy

  1. Radiotherapy is not free of side-effects. It is usual to see some percentage of radiation complications if treated in curative intent; hence it is called “radiation accompaniment” or radiation morbidities.
  2. The incidence of systemic symptoms of radiotherapy depends upon the field size, fraction size and the total dose of radiation. Radiation injury to the cells can induce change in rapidly dividing cells (early reacting tissues) and slowly dividing cells (late reacting tissues). The rapidly dividing cells are usually present in mucosa and hematopoietic cells those have greater potentiality to regenerate and repair after a given radiation damage called sub-lethal radiation damage.
  3. However, stable cells like kidney, and brain cannot regenerate after a given radiation damage and the effects of radiation damage are permanent. The change in the early reacting tissues is seen during or immediately after radiotherapy, whereas the late effects are seen 6 moths to years following radiotherapy.
  4. The common acute reactions are radiation sickness, mucositis and sore throat, diarrhoea, cystitis, vomiting and fall in blood counts. The late-effects of radiation appear 6 months to years following radiotherapy. If the radiation treatment dose exceeds a particular threshold dose, the latter induce permanent damage due to fibrosis.
  5. The common late effects are rectal bleeding, hematuria, osteoradionecrosis, radiation nephritis, square pneumonia etc.
  6. Growth retardation is a significant problem in pediatrics age group of patients who receive radiotherapy to the axial skeletons (skull and spine). The decrease in the sitting height up to 20% at 10 year is noted among patients who received radiotherapy to their axial skeleton.
  7. Similarly pediatric leukemia patients received prior cranial irradiation prophylaxis show signs of 10-20% decrease in the IQ level compared to controls. Facial asymmetry, chest deformity, aplasia of breast and endocrinological alterations are a few morbidities encountered after radiotherapy.
  8. The late side effects are sometimes proportionate to the dose (non-stochastic effect, e.g. cataract) or irrespective of dose (stochastic e.g. second cancer).Q
  9. The commonest neoplasm induced by radiation is development of osteosarcoma in retinoblastoma patients received radiotherapy in the past and leukemia in total axial nodal irradiation for Hodgkin’s lymphoma.Q

A fleck of calcium in a normal-sized globe of a child younger than 6 years is characteristic of retinoblastoma until proven otherwise.Q

Radionuclide Energy Half life Medical uses
Radium-226            0.83 mv 1625 years For brachytherapy but not used now a days
Cobalt-60               1.25 mv 5.4 years Teletherapy & brachytherapy
Caesium-137 0.666 mv 30 years Teletherapy & brachytherapy
Iridium-192                           0.380mv                72 days                  Brachytherapy only
Iodine-125                              0.030mv 60 days Brachytherapy
Iodine-131                            0.61 mv 8 days Unsealed radioiodine for thyroid cancer rx
Gold-198 0.412mv 2.7 days Brachytherapy
Strontium-90 2.24mv 3 0 years For shield (mould) in eye tumors
Phosphorous -32 1.71mv 14 days Intraperitonial

Guide to the Relative Radiosensitivity
of Normal Tissue

  1. Radiosensitive
    1. Lymphocytes Bone marrow Gonads              
    2. Embryonic tissue
  2. Moderately sensitive
    1. Skin, Small blood vessels Lens of the eye Growing tissues Lung tissue Salivary glands
  3. Moderately resistant
    1. Skin             
    2. Thyroid gland               
    3. Nerve cells
  4. RadioresistantQ
    1. Muscle         
    2. Bone            
    3. Connective tissue
    4. Mature red­ blood corpuscles

Guide to the Relative Radiosensitivity of TumoursQ

Highly Radiosensitive Moderately Radiosensitive Relatively Resistant Highly Resistant
Small Cell Lung Cancer Squamous Cell Carcinoma Of Lung Melanoma
Myeloma Breast Cancer Rcc Osteosarcoma
Seminoma Basal Cell Carcinoma Rectal Carcinoma Pancreatic Ca
Dysgerminoma Medulloblastoma Bladder Carcinoma  
Ewing’s Sarcoma Teratoma Sift Tissue Sarcoma  
Wilm’s Tumor Ovarian Cancer Cervical Cancer  

Extra Edge:

  1. Radiation therapy is a component of curative therapy for a number of diseases, including breast cancer, Hodgkin's disease, head and neck cancer, prostate cancer, and gynecologic cancers.
  2. Radiation therapy can also palliate disease symptoms in a variety of settings: relief of bone pain from metastatic disease, control of brain metastases, reversal of spinal cord compression and superior vena caval obstruction, shrinkage of painful masses, and opening of threatened airways.
  3. Radiation therapy can prevent the development of leptomeningeal disease and brain metastases in acute leukemia and lung cancer.
Facts to remember:
  1. Dividing part of cells are most sensitive to RT
  2. Non dividing cells are relatively resistant
  3. Hypoxic cells are relatively resistant
  4. Phase of cells cycle that is most sensitive to radiation: G2M> <M
  5. Phase of cell cycle in which radiation exposure leads to chromosomal aberration:G1
  6. Phase of cell cycle in which radiation exposure leads to chromatid aberration : G2

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