Cervix Brachytherapy

Fletcher Suit

  • Fletcher Suit afterloading applicator (Tandem and ovoids, (T/O)) using Cs137 (22mm or 25mm in length) gives a pear shaped distribution that delivers high dose to the cervix, paracervical tissue but reduced dose to the rectum and bladder (shielding in Ovoids (also called culpostats)).
  • Descendent of Manchester System

Manchester system

Summary

  • Prescribe dose based on placing a perfect implant:

Calculation Points

  • Pt A: 2cm superior to fornix, 2cm lateral to tandem (medial parametria).
    • 1953 revision of Manchester system: Pt A calculated from external os or flange.
  • Pt B: at the level of Pt A, 5 cm lateral to midline of patient (lateral parametria/ pelvic sidewall).
  • Pt P: at the level of point A, just medial to pelvic sidewall.
  • Rectal Pt: 0.5 cm posterior to packing at mid-point of ovoid.
  • Bladder Pt: posterior-most point of Foley bulb filled with 7cc CystoConray.

MDAH System

  • MDAH system a la Patricia Eifel: Milligram-hour to points in the pelvis (mg-hr = mg radium equivalent of material x number of hours of the implant). Example: 6 ources (10mgRaEq each) x 30 hours = 3000 mg-hr.
  • For cGy the typical dose rate is 40-60cGy/hr. Total cGy to point A is approximately 80% of total dose and point B is 10%.
  • Point organ tolerance: rectum (70Gy), Bladder (75Gy), upper vagina (140), and lower vagina (120). The cervix can tolerate ~200 Gy without necrosis.

Technique

Ovoid Choice

  • To optimize dose at depth and minimize the vaginal mucosa, use the largest ovoids possible.

Ovoid Loading

  • Mini — 1.5cm, load with 10 mgRaEq, mucosal dose 100 cGy/hr.
  • Small — 2.0cm (no cap), load with 15 mgRaEq, mucosal dose 90 cGy/hr.
  • Medium — 2.5cm (small caps), load with 20 mgRaEq, , mucosal dose 80 cGy/hr.
  • Large — 3.0cm, (large caps), load with 25(rarely) mgRaEq, mucosal dose 75 cGy/hr.
  • Most mini’s do not have shielding ant and post (for bladder and rectum) although the one’s at UF do have shielding.

Ovoid Geometry

  • Avoid excessive separation between the ovoids because can have a cold spot at cervix.

Tandem Choice

  • 4 curvatures
    • use more curved tandems for larger cavities
  • Longest tandem to be placed to optimize parametria dose.
    • but < 8cm to avoid increased small bowel and sigmoid doses.

Tandem Loading

  • amount of radium in tandem should be greater than in ovoids
  • examples
    • 15 10 10
    • 15 10 10 10
    • 15 10
  • The distal source should be positioned so that there is an optimum pear shaped distribution with no hot spot on adjacent critical structures. The typical placement is the end of the distal source is a few mm beyond the cervical os.

Tandem Geometry

  • The tandem should be between the bladder and the sacrum to avoid over dosing the rectum, so use a curved tandem.
  • Axis of the tandem should be between the ovoids on AP film and bisect them in lateral films.
  • The flange should be flush against the cervical os.

Packing

  • Carefully pack the anterior and posterior vagina, especially under the ovoids to avoid a hot spot on the rectum.
  • ICRU 38 guidelines: Dose specified in terms of 1) total reference air kerma in uGy at 1 meter 2) describe the reference volume to be included in the reference isodose volume 3) calculated dose to specific points (bladder, rectum, vagina)

Complications

  • Uterine perforation
  • detected during CT planning or Ultra sound if we were suspicious.
  • Remove the tandem and reposition.
  • There is no contraindication to continuing or to bringing the patient back the next day/week.

Indications for Interstial Implants

(i) bulky parametrial extension;
(ii) bulky primary disease;
(iii) extensive paravaginal or distal vaginal involvement;
(iv) narrow vagina or poor geometry not accommodating an ovoid (colpostat);
(v) loss of endocervical canal not allowing a tandem placement;
(vi) prior radiation therapy to implanted area (recurrent or residual disease);
(vii) post hysterectomy recurrences;
(viii) cut through hysterectomy; and
(ix) cervical stump presentation.

  • 1 cm spacing between needles
  • Ir-192 after loading

ICRU #38 Definition

ICRU1
ICRU2

RT compare to Surgery

. Advantages to RT:

  • Tolerated by a wide range of patients
  • Avoid mortality risk during treatment
  • Less bladder dysfunction
  • Less dependent on precise staging

1. Morbidity: The cervix can tolerate 200Gy without necrosis. Severe complications include cystitis, proctitis, enteritis, SBO. Also can have fistula and stenosis.

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