Radiation Therapy in Gynecologic Malignancies

RT Fundamentals - Ray Basics & Bio

• Radiation Types:
  • Photons (X-rays, γ-rays): Low LET, common.
  • Particles (electrons, protons): Variable LET.
• Key Terms:
  • Linear Energy Transfer (LET): Energy/unit path; ↑LET = ↑damage.
  • Relative Biological Effectiveness (RBE): Biological damage vs reference radiation.
• Radiobiology's 4 R's:
  • Repair (sublethal DNA damage)
  • Redistribution (cells to sensitive cycle phases)
  • Repopulation (normal & tumor cells)
  • Reoxygenation (hypoxic tumor cells, ↑sensitivity)

⭐ Hypoxic cells: 2.5-3x more radioresistant than oxic cells.

Brachytherapy - Close Combat Radiation

• Delivers radiation directly to/near tumor, sparing normal tissues.
• Types:
  • Low Dose Rate (LDR): Continuous, ~0.4-2 Gy/hr.
  • High Dose Rate (HDR): Short bursts, >12 Gy/hr; common now.
  • Pulsed Dose Rate (PDR): Pulses simulate LDR.
• Isotopes: $^{137}$Cs (LDR), $^{192}$Ir (HDR), $^{60}$Co, $^{125}$I.
• Indications: Cervical (boost after EBRT), endometrial, vaginal cancers.

⭐ HDR brachytherapy for cervical cancer often targets Point A (2 cm superior to external os, 2 cm lateral to cervical canal) to ~80-85 Gy total EQD2 (External Beam + Brachytherapy).

EBRT Techniques - Beaming from Afar

• External Beam Radiotherapy (EBRT) uses external radiation sources to target malignancies, complementing brachytherapy.
• Key Techniques:
  • 3D-CRT (3D Conformal RT): Shapes radiation beams to match the planning target volume (PTV).
  • IMRT (Intensity-Modulated RT): Advanced; modulates beam intensity for superior conformity and sparing of organs at risk (OARs).
  • VMAT (Volumetric Modulated Arc Therapy): IMRT delivered in continuous rotational arcs, often improving treatment speed.
• Planning: Involves CT simulation for precise target volume delineation (GTV, CTV, PTV).
• Typical Pelvic EBRT Dose: 45-50 Gy in 1.8-2 Gy per fraction over 5-6 weeks.

⭐ IMRT significantly reduces acute and late gastrointestinal and genitourinary toxicities compared to 3D-CRT in gynecologic cancers by better sparing the bladder and rectum. 📌 Intensity Modulation Reduces Toxicity (IMRT).

RT for Gynae Cancers - Site-Specific Strategies

• Cervical Cancer:

  • Early (FIGO IA-IIA1): Surgery primary. Adjuvant RT for high-risk (LVSI, +margins, nodes).
  • Locally Advanced (FIGO IB2-IVA): Definitive Concurrent ChemoRT (CCRT).
    • EBRT: 45-50 Gy + Brachytherapy (BT).
    • Chemo: Weekly Cisplatin 40 mg/m².
  • Flowchart:

• Endometrial Cancer:

  • Adjuvant RT post-surgery for high-risk:
    • Vaginal Brachytherapy (VBT) for vaginal cuff recurrence prevention.
    • EBRT for nodal/extensive disease (e.g., Grade 3, deep invasion, LVSI, Stage II/III).

• Vulvar/Vaginal Cancer:

  • Vulvar: Adjuvant RT for +margins, +nodes. Primary RT for unresectable.
  • Vaginal: Primary RT (EBRT + BT) often curative.

⭐ Point A in cervical cancer brachytherapy is defined as 2 cm superior to the cervical os and 2 cm lateral to the uterine canal; it's a critical dose prescription point.

RT Complications & Care - Damage Control

• Acute (During/Post-RT < 90 days):
  • Skin: Erythema, dry/moist desquamation
  • Mucosal: Cystitis, proctitis, vaginitis (pain, discharge, bleeding)
  • GI: Nausea, vomiting, diarrhea
  • Hematologic: Myelosuppression (esp. with chemo-RT)
• Late (Months-Years > 90 days):
  • Fibrosis & Stenosis: Vaginal, rectal, ureteral
  • Chronic: Proctitis, cystitis, enteropathy (malabsorption, obstruction)
  • Fistulae (VVF, RVF), lymphedema, telangiectasias
  • Ovarian failure, bone necrosis/fractures, secondary malignancies
• Management:
  • Acute: Symptomatic (hydration, anti-emetics, anti-diarrheals, topical agents)
  • Late: Vaginal dilators, pelvic floor PT, hyperbaric oxygen, surgical correction for fistulae/obstruction.

    ⭐ Vaginal stenosis is a common late effect of pelvic RT; counsel patients on regular use of vaginal dilators post-treatment to maintain patency and sexual function.

High‑Yield Points - ⚡ Biggest Takeaways

• Cervical cancer: Brachytherapy (LDR/HDR) is crucial with EBRT. Point A (2cm lateral, 2cm superior to os) is key.
• Endometrial cancer: Adjuvant vaginal brachytherapy for high-intermediate risk; EBRT for advanced disease.
• Ovarian cancer: Generally radioresistant; radiation is mainly palliative.
• Vulvar/Vaginal cancers: EBRT +/- brachytherapy, often with chemosensitization, for advanced stages.
• IMRT/VMAT spares organs, reducing acute toxicities like cystitis and proctitis.
• Chronic effects: Vaginal stenosis, fibrosis, fistulae formation possible after treatment for gynecologic malignancies with radiation therapy.