• Radiotherapy

    by  • 27/05/2013 • Oncology

     

    1. Uses ionizing radiation to produce free radicals which damage DNA
    2. Normal cells are better at repairing this damage than cancer cells – so are able to recover before next dose (or fraction) of treatment.
    3. Approaches:
      1. o Radical treatment: given with curative intent, total doses range from 40-70Gy in 15-35 daily fractions. Some regimens involve giving several smaller fractions a day with a gap of 6-8h. Combined chemoradiation is used in some sites, eg. anus and oesophagus.
      2. o Palliation: aims to relieve symptoms. Doses are 8—30Gy, given in 1, 2, 5, 10 fractions. Bone pain, haemoptysis, cough, dyspnoea, and bleeding are helped in >50%.
    1. Reactions to RT
      1. o Early reactions:
      2. Tiredness: common after radical treatments
      3. Skin reactions: erythemadry desquamationulceration. Various forms of skin reaction. Tx: moisturisers.
      4. Mucositis: avoid smoking, alcohol, spicy foods. Tx: antiseptic mouthwash, aspirin gargle, if oral thrush – nystatin (1ml swill and swallow every 6h) +/- fluconazole 50mg/24h PO
      5. N&V: occurs when stomach, liver, or brain treated. Tx: metoclopramide 10-20mg/8h PO, or domperidone 10-20mg/8h PO, if unsuccessful try ondansetron 4-8mh/8h PO/IV
      6. Diarrhoea: after abdo/pelvic RT. Tx loperamide.
      7. Dysphagia: follows thoracic RT
      8. Cystitis: after pelvic RT. Tx: NSAIDs, diclofenac
      9. Bone marrow suppression: more commonly after CT, unless a very large area is irradiated
      10. o Late reactions:
      11. CNS: somnolence (tx steroids), spinal cord myelopathy, brachial plexopathy, reduced IQ in children irradiated
      12. Lung: pneumonitis (tx prednisolone 40mg OD)
      13. GI: xerostomia = reduced saliva (tx pilocarpine 5mg/8h OD, or artificial saliva), benign strictures of oesophagus or bowel (tx dilatation), fistulae (tx surgery), radiation proctitis (occurs after prostate RT)
      14. GU: urinary frequency due to small fibrosed bladder, infertility due to pelvic irradiation, vaginal stenosis and dyspareunia, erectile dysfunction
      15. Others: panhypopituitarism (following RT of pit fossa), hypothyroidism (after neck treatments – such as for Hodgkin’s lymphoma), secondary cancers can appear – usually ~10 years later. Risk of cataracts.

     

    Tumour markers:

    1. PSA = Prostate Specific Antigen (elevated in prostate carcinoma, BPH, prostatitis)
    2. Prostatic acid phosphatase = prostate carcinoma
    3. CEA = CarcinoEmbryonic Antigen (produced by 70% of CRC, pancreatic, gastric, and breast cancers. Very non-specific)!
    4. Alpha-fetoprotein = normally made by foetus (can be elevated in hepatocellular carcinomas, nonseminomatous germ cell tumours of the testis e.g. yolk sac tumour)
    5. Beta-HCG = Hydratiform moles, Choriocarcinomas, Gestational trophoblastic tumours
    6. CA-125 = ovarian, malignant epithelial tumours
    7. S-100 = melanoma, neural tumours, astrocytomas
    8. Alkaline phosphatase = bony mets, obstructive biliary disease, Paget’s disease of the bone
    9. Bombesin = neuroblastoma, lung, gastric cancer
    10. TRAP (tartrate-resistant acid phosphatase) = hairy cell leukaemia (a B-cell neoplasm). TRAP the HAIRY animal
    1. CA-19-9 = pancreatic adenocarcinoma
    2. CA-15-3 = breast cancer
    3. LDH = testicular cancer

     

    Key tumour suppressor genes:

    Loss of function cancer; both alleles must be lost for expression of disease

    1. Rb (C13q) = retinoblastoma, osteosarcoma
    2. BRCA1 (C17q) = breast and ovarian cancer
    3. BRCA2 (C13q) = breast only
    4. p53 (C17p) = most human cancers, Li-Fraumeni syndrome
    5. p16 (C9p) = melanoma
    6. APC (C5q) = CRC (associated with familial adenomatous polyposis = 1001000s of small polyps in large intestine. Initially benignmalignantCRC)
    7. WT1 (C11p) = Wilm’s tumour (cancer of kidneys in children)
    8. NF1 (C17q) = neurofibromatosis type 1
    9. NF2 (C22q) = neurofibromatosis 2 (type 2 = C22)
    10. DPC (C18q) = pancreatic cancer (DPC = Deleted in Pancreatic Cancer)
    11. DCC (C18q) = colon cancer (DCC = Deleted in Colon Cancer)  
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