Updated: 6/18/2021

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 unlikely to heal
  • Preoperative vs. Postoperative
    • Preoperative vs. Postoperative Radiation
      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 shrinkage 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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(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?

QID: 3275
1

Female

15%

(356/2360)

2

Age

4%

(85/2360)

3

Dose of radiotherapy

6%

(133/2360)

4

Periosteal resection during sarcoma removal

18%

(429/2360)

5

Method of radiotherapy administration

57%

(1345/2360)

L 3 D

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