Radiation Oncology/Cervix/Brachytherapy

Radiation Oncology/Cervix/TOC

Intracavitary brachytherapy

Three systems:

• Paris system
• Stockholm system
• Manchester system

Also see:

• Madison system (see below)

Manchester system

• Point A dose definitions:

  Allegedly, Point A corresponds to the paracervical triangle in the medial edge of the broad ligament where the uterine vessels cross the ureter

  • Original definition: draw a line connecting the superior aspects of the vaginal ovoids and measuring 2 cm superior along the tandem and then 2 cm perpendicular to this. (weakness: failure of localization radiographs to show the surface of the ovoids' caps)
  • Revised definition #1: 2 cm above the external cervical os and 2 cm lateral to midline
  • Revised definition #2 (1953, Tod & Meredith): 2 cm above the distal end of the lowest source in the tandem and 2 cm lateral to the tandem
  • Common variation: use flange at cervical os

• Point B - 5 cm lateral from the midline at the same level as Point A

The Manchester applicators consisted of a rubber tandem and two ellipsoid "ovoids" with diameters 2, 2.5, and 3 cm. No shielding in ovoids, so needed generous packing anteriorly and posteriorly. Used radium. Used 17.5, 20, and 22.5 mg Ra for the small, medium, and large ovoids, respectively.

Designed such that:

• Point A dose rate was approximately 0.53 Gy/hr for all allowed applicator loadings
• Vaginal contribution to Point A was limited to 40% of the total dose
• The rectal dose should be 80% or less of the Point A dose

Prescribed 80 Gy to point A in two applications, total of 144 hours, in the absence of external beam.

Weakness: wide variation in Point A in respect to the ovoids. Point A often occurs in a high-gradient region of the isodose distribution. Therefore, minor differences in position can result in large differences in dose.

References:

• No PMID - M. Tod and W. Meredith, A dosage system for use in the treatment of cancer of the uterine cervix. Br J Radiol 11 (1938), pp. 809–824.
• Revised (1953) - PMID 13042092 — "M. Tod and W. Meredith, Treatment of cancer of the cervix uteri—a revised “Manchester method.”. Br J Radiol 26 (1953), pp. 252–257.

Fletcher applicator

Derives from the Manchester system. Added internal shielding in the colpostats. Afterloading ability. Colpostat has 2 cm diameter that can be increased to 2.5 or 3 cm by the addition of plastic caps. Minicolpostats are 1.6 cm and have a flat inner surface and have no shielding. Use 15, 20, and 25 mg Ra for small, medium, and large colpostats; use 10 for the minis. Tandems are available in three curvatures. Flange on the tandem avoids slippage past the cervical os, and a keel helps keep it from rotating. A yoke attaches the tandem and colpostats to maintain proper position. Loading of the tandem is 20 - 10 - 10 mgRaEq with Cs-137.

Plastic Fletcher applicators are available to be compatible with CT simulation or MRI.

Good Insertion Characteristics

• AP View
  • Tandem midline, unrotated
  • Tandem midway between colpostats
  • Keel (flange) in close proximity to gold seed markers
  • Colpostats high in the fornices along cervix
• Lateral View
  • Tandem bisects the colpostat
  • Sufficient anterior and posterior packing
  • Foley balloon firmly tugged down

American Brachytherapy Society (ABS)

Recommend prescribing to Point H - Draw a line connecting the mid-dwell positions of the ovoids and find the point this line intersects the tandem. Follow 2 cm superior (along the tandem) plus the radius of the ovoids, then 2 cm perpendicular to the tandem. Note: This is basically 2 cm above the top of the ovoids.

European Society for Therapeutic Radiation Oncology (ESTRO)

• ESTRO
  • 2006 PMID 16403584 -- "Recommendations from gynaecological (GYN) GEC ESTRO working group (II): concepts and terms in 3D image-based treatment planning in cervix cancer brachytherapy-3D dose volume parameters and aspects of 3D image-based anatomy, radiation physics, radiobiology." (Potter R, Radiother Oncol. 2006 Jan;78(1):67-77. Epub 2006 Jan 5.)
    • Recommendations for 3D dose-volume parameters
  • 2005 PMID 15763303 -- "Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group (I): concepts and terms in 3D image based 3D treatment planning in cervix cancer brachytherapy with emphasis on MRI assessment of GTV and CTV." (Haie-Meder C, Radiother Oncol. 2005 Mar;74(3):235-45.)
    • Specification of image-guided GTV and CTV

Dose prescriptions

EBRT + HDR:

• Point A - LDR equivalent of 80-85 Gy (early stage disease, nonbulky Stage I-II) or 85-90 Gy (advanced stage, Stage IIIB or > 4 cm).
• Pelvic Sidewall - LDR equivalent of 50-55 Gy (early stage) or 55-60 Gy (advanced stage)

HDR

See ABS recommendations

Suggested doses in combination with EBRT (from ABS - PMID 10924990, see below):

EBRT dose	# HDR fractions	HDR dose/fx
20	6	7.5
20	7	6.5
20	8	6.0
45	5	6.0
45	6	5.4

The Madison system (University of Wisconsin):

• PMID 1526873, 1992 — "High dose rate intracavitary brachytherapy for carcinoma of the cervix: the Madison system: I. Clinical and radiobiological considerations." Stitt JA et al. Int J Radiat Oncol Biol Phys. 1992;24(2):335-48.
• PMID 1526874, 1992 — "High dose rate intracavitary brachytherapy for carcinoma of the cervix: the Madison system: II. Procedural and physical considerations." Thomadsen BR et al. Int J Radiat Oncol Biol Phys. 1992;24(2):349-57.

HDR - LDR equivalent doses

HDR dose	LDR equivalent
6 Gy x 4	32 Gy
6 Gy x 5	40 Gy

• Taiwan (1996) - PMID 8631555 — "Determination of the appropriate fraction number and size of the HDR brachytherapy for cervical cancer." Liu WS et al. Gynecol Oncol. 1996 Feb;60(2):295-300.

• Detroit (1991) - PMID 1938550 — "Comparison of high and low dose rate remote afterloading for cervix cancer and the importance of fractionation." Orton CG et al. Int J Radiat Oncol Biol Phys. 1991 Nov;21(6):1425-34.
  • Analysis of 17,000 cervix cancer pts in 56 institutions using HDR.
  • Conversion of dose from LDR to HDR, use dose factor of 0.54.

Linear-quadratic equation

BED for HDR and LDR:

• HDR: $\text{BED}=N*d(1+\frac{d}{\alpha /\beta })$
• LDR: $\text{BED}=N*R*t[1+\frac{2R}{\mu *(\alpha /\beta )}*(1-\frac{1-e^{-\mu t}}{\mu *t})]$

(from ABS, PMID 10924990)
Problem: What dose/fraction of HDR delivered in six fractions will be equivalent in terms of tumor control to 60 Gy delivered to Point A at 0.55 Gy h−1?

Solution: Assume α/β (tumor) = 10 Gy, μ (tumor) = 0.46 h−1.

Then: BED (LDR) = 60[1 + (2 × 0.55)/(0.46 × 10)] = 74.3

Equating this to the BED for 6 HDR fractions with dose/fraction d gives:

74.3 = 6d(1 + d/10)

Solving this quadratic equation for d gives: d = 7.20 Gy.

Conclusion: 6 fractions of 7.20 Gy with HDR is equivalent in terms of tumor control to 60 Gy delivered at 0.55 Gy h−1.

Other references:

• PMID 10661360 (2000) — "A simple method of obtaining equivalent doses for use in HDR brachytherapy." Nag S et al. Int J Radiat Oncol Biol Phys. 2000 Jan 15;46(2):507-13.

Comparison of HDR and LDR

• India, 1994 (1986-89) - PMID 8276647 — "Low dose rate vs. high dose rate brachytherapy in the treatment of carcinoma of the uterine cervix: a clinical trial." Patel FD et al. Int J Radiat Oncol Biol Phys. 1994 Jan 15;28(2):335-41.
  • 482 pts. Randomized two groups (Group I - early stage, brachy only. Group II - EBRT + BT) to HDR vs LDR.
  • 5-yr LC 79.7% (LDR) vs 75.8% (HDR). OS: Stage I - 73% vs 78%, Stage II - 62% and 64%, Stage III - 50% and 43. Rectal complications lower for LDR (19.9% vs 6.4%)

Dose limits

Points specified in ICRU Report 38

• Please see the ICRU report page on more detail about definitions
• Bladder point - on the surface of a Foley balloon filled with 7 cc of contrast; located at center of balloon on AP film, posterior surface of the balloon on a line through midballoon on lateral film
• Rectum point - 0.5 cm posterior to the posterior vaginal wall at the level of the bisection of the T&O. May also use barium + air contrast in rectum
• Vaginal mucosa - at surface of ovoids
• Pelvic sidewall, and external, common, and para-aortic LN points should be reported according to ICRU defintions

Keep dose to rectum and bladder points below 80% of dose to Point H (ABS recommendation). Or, maximum dose to rectum, 75 Gy (avg dose 68 Gy); bladder, 80 Gy (avg 70 Gy); vagina, 120-140 (avg 125 Gy).

Acute complications

• PMID 10725629 (1960-1992) - "Perioperative and postoperative complications of intracavitary radiation for FIGO stage I-III carcinoma of the cervix." Jhingran A et al. Int J Radiat Oncol Biol Phys. 2000; 46 (5):1177-83
  • Retrospective. 7662 intracavitary procedures in 4043 patients for FIGO I-III cervical CA
  • 2.8% uterine perforation rate, 14% have fever >101 C during at least 1 admission, 0.1% fatal thromboembolism rate. Perforation did not affect DSS in stage I, II, but did lead to worse prognosis in stage III.

Late complications

• PMID 7635768, 1995 (1960-89) — "Time course and incidence of late complications in patients treated with radiation therapy for FIGO stage IB carcinoma of the uterine cervix." Eifel PJ et al. Int J Radiat Oncol Biol Phys. 1995 Jul 30;32(5):1289-300.
  • Retrospective. 1784 pts, FIGO stage IB. Grade 3 or higher complications occurred in 7.7% at 3 yrs and 9.3% at 10 yrs. After 10 yrs, 0.34% per year, so at 20 yrs, 14.4% risk. Risk of rectal complications was the greatest, more than urinary complications.
  • Conclusion: low risk of major complications using brachytherapy.

Guidelines

Keep total duration (of EBRT + implants) to < 8 weeks. For HDR, this necessitates beginning brachytherapy while EBRT is ongoing. Usually give an HDR treatment once per week, not giving EBRT on that day.

ABS recommendations

• LDR (2002) - PMID 11777620 — "The American Brachytherapy Society recommendations for low-dose-rate brachytherapy for carcinoma of the cervix." Nag S et al. Int J Radiat Oncol Biol Phys. 2002 Jan 1;52(1):33-48.
• HDR (2000) - PMID 10924990 — "The American Brachytherapy Society recommendations for high-dose-rate brachytherapy for carcinoma of the cervix." Nag S et al. Int J Radiat Oncol Biol Phys. 2000 Aug 1;48(1):201-11.

Miscellaneous

• Patterns of care study (2005, 1996-99) - PMID 16099599 — "Patterns of brachytherapy practice for patients with carcinoma of the cervix (1996-1999): a patterns of care study." Erickson B et al. Int J Radiat Oncol Biol Phys. 2005 Nov 15;63(4):1083-92.

External links

• [PDF] (2005) — LDR Intracavitary Brachytherapy Applicators - John Horton, MDACC
  • Really nice presentation. Many pictures of applicators, dosimetry, etc.