Updated: 3/26/2017

Radiation Therapy

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Introduction
  • Two mechanisms of action
    • production of free radicals
    • direct genetic damage
Indications
  • Indications of external beam irradiation
    • definitive control (primary malignant bone tumors)
      • Ewing sarcoma/primative neuroectodermal tumor
      • primary lymphoma of bone 
      • hemangioendothelioma
      • solitary plasmacytoma of bone 
    • adjuvant to surgical excision
      • soft tissue sarcomas 
        • may be given pre or post-operatively as adjuvant to surgical excision
        • no difference exists in overall survival and the timing of radiation
    • palliative care and impending fracture fixation
      • metastatic bone disease 
        • needed after fixation of impending/pathologic fractures to reduce overall tumor burden
        • prostate tumors are very radiosensitive
        • breast cancer is 70% sensitive, 30% resistant
        • GI and renal tumors are not radiosensitive
Technique
  • 1 rad = 1 centiGray
  • Typical dose is 180-200 cGy/day
    • radiation is given in "fractions" as radiotherapy is cumulative
    • the total dose of therapy is the summation of all the separate fractions given during treatment
  • Total dose
    • < 45 Gray: usually leads to uncomplicated tissue healing
    • 45 - 55 Gray: tissue usually heals but with problems
    • > 60 Gray: tissue will likely not he
Preoperative vs. Postoperative
 
 
Preoperative RT (neoadjuvant)
Postoperative RT (adjuvant)
Wound complications More wound complications (up to 40%) Less wound complications (<20%)
Edema, fibrosis, joint stiffness Less (<15%) More edema, fibrosis, joint stiffness (>20%) (usually temporary)
Radiation field Smaller field Larger field
Pseudocapsule Allows formation of pseudocapsule to facilitate close-margin resection No pseudocapsule advantage
Tumor shrinkage Helps shrink tumor prior to surgery No tumor shrinkag advantage
Local recurrence Lower local recurrence rates Higher local recurrence rates
 
Complications 
  • Soft tissue complications
    • early effects
      • delayed wound healing
      • infection
      • desquamation
    • late effects
      • fibrosis
      • joint stiffness
      • secondary sarcoma (below)
      • fractures (below)
  • Post-radiation sarcoma
    • defined by the development of a sarcoma in a region previously radiated for malignancy
    • incidence is ~13%
      • more frequent in patients with prior chemotherapy
    • overal patient prognosis is very poor
  • Post-radiation fractures   
    • approximately 25% incidence following soft tissue sarcoma resection and external beam irradiation
      • risk factors for post radiation fracture
        • radiation dose ≥ 59Gy
        • weight bearing bones esp. femur
        • female
        • volume of bone receiving it
        • anterior femoral compartment resection
        • age
        • periosteal stripping
          • some advocate prophylactic fixation if periosteal stripping is performed
        • osteoporosis 
 

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Questions (3)

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(OBQ10.182) A 63-year-old female sustains a subtrochanteric femoral fracture after a fall in her home. Five years ago she underwent resection of a left thigh leiomyosarcoma with adjuvant radiotherapy. Which of the following is not a known risk factor for development of pathologic fracture post radiotherapy? Review Topic

QID: 3275
1

Female

14%

(232/1648)

2

Age

3%

(57/1648)

3

Dose of radiotherapy

5%

(76/1648)

4

Periosteal resection during sarcoma removal

19%

(307/1648)

5

Method of radiotherapy administration

59%

(971/1648)

L 2

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