RAD 540: Brachytherapy Lecture 7 - GYN Intracavitary Brachytherapy
The wall of the uterus is divided into what three layer?
(1) Outer Serosal Layer (perimetrium) (2) The Middle Myometrium (12-15mm of muscle with blood vessels and nerves) (3) The Endometrium (outermost layer that lines the uterine cavity)
Gynecological (GYN) Cancers refer to the 5 major types of cancer that affect the female reproductive system and Include:
(1) Uterine Cervix/Cervical (2) Uterine Corupus/Endometrial (3) Ovarian (4) Vulvar (5) Vaginal
According to the Manchester system, the point A dose contribution from the ovoids is limited to ______; the remaining _____ is given from the tandem.
(A) 1/3 (B) 2/3
Vaginal Cylinders Treat with _______________ Dwell Positions in __________ steps.
(A) 10-13 (B) 2-5 mm (5 mm for Varian)
The Dose per Fraction used for Vaginal Cylinder Treatments has Varied from ______________ Gy over _________ fractions, typically separated by 1-2 Weeks Depending on Stage and EBRT use.
(A) 3.5 to 7 Gy (B) 2 to 7
The Cervix measures approximately ______________ cm and is predominantly a _________________ organ.
(A) 3x3 (B) Fibrous
The rectal reference point for T&O tx is found with a lateral x-ray, drawing an AP/PA line through the lower end of the tandem, the point is located _____mm behind the posterior vaginal wall; receives ~____ point A dose
(A) 5 (B) 1/2
Point P is located ______________ to the Patient's Midline and Corresponds to the Location of the ______________________.
(A) 6 cm Lateral (B) Pelvic Lymph Nodes
For LDR application using Cs-137 (derived from clinical data with Ra-226), a total of ______________________ are loaded with a _____________ vaginal to intrauterine loading.
(A) 80mg RaEq (B) 1:1 ****IE: 40mgRaEq to the tandem 2-1-1 and 40mgRaEq to the ovoids****
Specifying the total radiation exposure (mg-hrs or IRAK) used for an implant can help to convey information concerning:
(A) Applicator Geometry (B) Loading (C) Volume of Tissue Irradiated (D) Information Concerning Point A
Regarding Good Implant Geometry for Ovoids, the Implant Should:
(A) Be Located Inferior to the Foley Bulb and at the Level of the Femoral Heads (B) Be Superimposed w.r.t. Lateral View
Regarding Good Implant Geometry for Tandems, the Implant Should:
(A) Be Positioned Roughly Midway Between the Sacral Promontory & Symphysis Pubis (B) Bisect the Ovoids (C) Not be Rotated
The Manchester System results in a linear relationship between ___________ to point A and the total _____________ of the implant.
(A) Dose (B) Time
Activating dwells through the ovoids for HDR can increase _____________________________________ and potentially __________________________.
(A) High Dose Region out of Applicator Caps (B) Damage Normal Tissue/Cause a Fistula ∙ Go 0.5cm superior and start marking at ½ spacing, leaving 1cm every 3 dwell positions until out of tandem ∙ Do a better job at implanting or start marking at the maximum attainable distal dwell position and stop 0.5cm from the ovoid surface
On a lateral x-ray, an AP/PA line is drawn through the balloon, and the bladder reference point is placed on this line at the _______________ surface of the balloon; receives ~____ point A dose.
(A) Posterior (B) 1/2
Other important dose specification points defined by the ICRU 38 (in addition to Points A and B) Include:
(A) Rectal Dose Point (B) Bladder Dose Point
Examples of HDR Dwell Time Calculations (¹⁹²Ir Source): (A) Use 3.5U for today's source strength, 256mgRaEq-hr per ovoid, 3 dwell positions per ovoid, and calculate the dwell time in each ovoid. (B) There are 3 dwells in the first 2 segments, positions 1-3, 5-7, and 1 dwell in the 3rd segment (positions 9-11( due to shorter tandem placement than standard. Find the dwell times for standard loading for each position.
(A) Standard → Modern Dwell Position td = mg-hr/Sk ∙ Nd ∙ Cir Cir = 0.3844 mg-hr/U-s (1) 256 mg-hr/ 3.5 U ∙ 3 ∙ 0.3844 mg-hr/U-s (2) td = 63.4299 seconds (A.2) Modern Dwell Position Dose rate @ point A = 65 cGy/min 10 Ci = Activity 700 cGy @ point A 50 days Past 10 Ci date T 1/2 ¹⁹² Ir = 73.8 days (1) Final DR = Initial DR ∙ 0.5^ti/T 1/2 (half-life) (2) 65 ∙ 0.5^50 days/73.8 days (3) 40.6925 cGy/min (4) 700cGy/40.6925 cGy/min (5) 6.74 minutes (B) (2:1:1 loading) → 200, 100, 100 Segment One (1-3) td closed system (1) td = 200/3.5 ∙ 3 ∙ 0.3844 = 49.6 seconds Segment Two (5-7) (1) td = 100/3.5 ∙ 3 ∙ 0.3844 = 24.8 seconds Segment Three (single source → 9 position) (1) 33 (1/3 of 100)/3.5 ∙ 1 ∙ 0.3844 = 24.8 seconds
Dose Distributions for Vaginal Cylinders are optimized to Deliver the Prescribed Dose at Either the ______________________ or at ____________________________. Depending on Whether the Vaginal Mucosa or Entire Lining is to be Treated.
(A) Surface of the Cylinder (LDR) (B) 0.5 cm Depth from the Surface (HDR)
The Vaginal Wall is composed of what Three Layers:
(A) The Inner Vaginal Mucosa (B) Muscularis (C) Adventitia
The Cervix is Divided into:
(A) Upper/Supervaginal Portion ∙ Endocervical Canal ∙ Vaginal Portion Projecting in the Vaginal Vault (B) Central, Rounded Vaginal Region ∙ Cervical Os Extending Inward to the Internal Os (C) The Endocervical and Endometrial Canals
Intracavitary Delivery Methods for Brachytherapy for Gynecologic Cancer Include?
(A) Vaginal Cylinder: ∙ Vaginal Cancer (lower or upper vagina) ∙ Vaginal Cuff, Post-op Endometrial → Target: Lining of the Vagina or Cuff (B) Tandem and Ovoid/Tandem and Ring ∙ Cervical Cancer ∙ Pre-operative Endometrial → Target: Cervix Gross Tumor, Possible Extensions to Lining of Uterus (C) Ring Applicators ∙ Stop uncontrolled Cervical Bleeding in Advanced Cases (high doses in short fractions)
What are Some Potential Adverse Side Effects of Vaginal Cylinder Treatments?
(A) Vaginal Telangiectasia (dilated blood vessels) (B) Vaginal Stenosis (narrowing) (C) Sexual Dysfunction
The Manchester system is designed to ensure that point A dose rate remains fixed at _________________ for LDR implementation with variations under ______________% regardless of applicator size.
(A) ~60cGy/hr (B) 15
The vagina mucosa dose used as a tissue constrain for MIR LDR T&O tx is ______Gy total with EBRT + brachy.
150
The vaginal surface typically receives ~______% of point A dose for T&O treatment.
150
The standard T&O applicator (MIR System) loading is based on ____ cm ovoids.
2
Vaginal Cylinders are Commonly Available in What Diameters?
2 - 4.5 cm
What type of loading has shown to provide the most appropriate pear-shaped dose distribution, maintaining the dose rate to point A while minimizing rectal dose?
2-1-1
The two vaginal ovoids are typically ____cm spaced apart.
4
"Dumbbell" Loaded Sources can have Dwell Times > ____x the Dwell Time as the Mid-cylinder Sources, as well as Activity being ____x the Activity as the Middle Source.
5, 3
The intrauterine tandem is typically ___ cm long.
6
The Mallinckrodt MIR LDR loading designed to achieve a relatively constant dose rate of _____ cGy/hr to point A, independent of implant size/geometry.
65
The High Dose Escalation Close to the Source in Brachytherapy is Similar to What Other Delivery Method?
Ablative Therapy Models (SABR) used in Stereotactic Treatments
The ring in the T&R applicator uses the surface of the ______________ as the prescription point.
Applicator
Gynecologic cancers with clinically and radiologically well-defined margins with low risk of regional and metastatic spread are typically the most suitable for brachytherapy in what form?
As a Single Treatment Modality
point ___ is defined as 5 cm along the mid-line at the same level as point A (2 cm from top of ovoid).
B
As Tandem Length Increases (Distance Increases), so in turn, does the Dose to Point _______ for the Same Dose to Point ________.
B; A
Current 3D Planning for GYN Brachytherapy Utilizes What Imaging?
CT or MR Imaging Dependent on the Patient and Facility → MRI provides exceptional soft tissue contrast for targets and OARs (not as common in depts)
The _______________________________ system was developed in 1938 and remains the basis for loading rules in modern T&O treatments.
Classical Manchester
What is Another Name for Ovoids?
Colpostats
Dose Distributions around applicators for a ring prescription to the surface of the applicator for selected dwell positions are:
Computed and Spreadsheets Generated to Determine the Dwell Weight
Ring replaces ovoids but can limit _____________ due to fixed ring diameter.
Depth Dose
Fletcher-Suit-Delco applicators contain _______________________ in the ovoids.
Directional Shielding (reduce dose, are radiopaque creating artifacts on imaging)
What is used to obtain the bladder reference point for T&O tx, how much contrast volume?
Foley Catheter, 7 cc → The balloon is filled and pulled down to bring the balloon against the urethra
Brachytherapy differs significantly from EBRT due to its:
Heterogenous Dose Distributions with Isolated Areas Receiving 200% of the Dose and Sharp Dose Fall-off.
The use of brachytherapy for the management of endometrial carcinoma was first described by _______________________, prior to the routine use of hysterectomy for uterine cancers.
Heyman in 1935
Brachytherapy is much more important when it is integrated with EBRT to deliver:
Highly Localized Boost Doses → EBRT is used to treat the larger area of possible microscopic and nodal spread with brachytherapy used to boost areas of gross macroscopic or microscopic residual disease (ensuring that high doses are achieved within GTV while keeping normal tissues below tolerance)
For cervical tumors larger than 5 cm, ____________ ____________ are used with a ring applicator.
Interstitial Needles
_______________ Diameter Ovoids Increase Dose to Point A for Same RSD.
Larger
What System system Was the First to use an applicator and loading rules specifically designed to define target/tissue tolerances area based on dose to point A?
Manchester System
Point A dose is a linear function of duration and not of ______________.
Mg-hrs
How are HDR Vaginal Cylinder Doses Calculated?
Most Often, Using a TG-43 Based Canned or Template Plan → improves turn-around time of patients
What is the benefit of Vaginal Cylinder Treatment in Post-op Endometrial Carcinoma Cases?
Much Fewer Acute GI Toxicities than EBRT
Vaginal Cylinder Dose Distributions have Isodose Lines more ____________ to the Cylinder when they are "Dumbbell" Loaded vs Uniform Loaded (vs oval IDLs).
Parallel (End sources are typically longer dwells than middle)
point B represents the location of what anatomy? typically is _____ the dose of point A
Pelvic Obturator Nodes, 1/3 (relatively symmetric)
RSD Stands for:
Rad Surface Dose (cGy/mgRaEq-hr)
What GYN applicator (used at WashU) to treat uncontrolled cervical bleeding (typically late stage advanced tumors)?
Ring (alone)
In a Canned or Template Vaginal Cylinder Plan, for a given Prescription, the mghr or IRAK will be the ___________ between fractions.
Same
Historically, what Radiopaque Markers were Placed at the Vaginal Apex to Verify Applicator Position. Ensuring the Vaginal Cylinder Made Adequate Contact with the Vaginal Apex on Radiographic Film or CT Scans Used for Treatment Planning?
Seeds or Surgical Clips → As CTs get better, this is less common
The __________________________ RSD is used as tolerance dose in the MIR GYN implant system
Single Ovoid
The Total Treatment Time for a HDR Vaginal Cylinder Treatment is Inversely Proportional to the:
Source Strength (Rx dose/(A/A0))
The Individual Dwell Times for a Vaginal Cylinder will Produce Desired Linear Dose Distributions as _____________ but depends on cylinder diameter.
Surface of Cylinder
_____ or _____ applicators are typically used for cervical tumors < 5 cm.
T&O or T&R ∙ The applicator is placed in an operating suite with patient in the lithotomy position ∙ The cervix is dilated and a uterine tandem is placed (under anesthesia) ∙ The largest ovoids that reasonably fit in the vaginal fornices are used to increase depth dose
The standard Target mgRaeq-hrs Rx based on the "standard loading" MIR T&O loading technique Consisted of the following:
Tandem 20mg-10mg-10mg & Ovoids 20mg-20mg (2:1:1:2:2)
Typical application of T&R uses ________________for ring loading to simulate ovoid distribution, heavily weighting laterally.
Template Style Plan
point A is defined as 2 cm lateral to what?
The Center of the Uterine Canal
What Portion of a Vaginal Cylinder Varies by Manufacturer and Design of the Applicator?
The Most Distal Source Position ∙ 4 mm for Varian ∙ 5 mm for Nucletron
The Steep Gradients in Brachytherapy are a Consequence of:
The Proximity of the Source and the Inverse Square Law
The total Ovoid RSD is equal to:
The Whole Pelvis External beam dosage to vaginal mucosa + single ovoid RSD of implant 1 + single ovoid RSD of implant 2
The uterus and the cervix have a rich lymphatic network that drains into:
The paracervical lymph nodes go to the external and hypogastric lymph nodes, and the pelvic lymphatics go into the common iliac and the paraaortic lymph nodes. ∙ Lymphatics from the fundus pass laterally along the ovarian vessels into the para-aortic lymph nodes
Why Should the Longest Tandem Possible Be Used in a T&O Treatment?
To Allow Greater Plan Flexibility and Increase Dose at Depth
Why is it Necessary to Always Use the Largest Ovoids that fit Comfortably?
To Ensure Good Dose to Target Without Becoming Limited by Vaginal Mucosa Dose Tolerance
During a Vaginal Cylinder Treatment, why Should the Largest Applicator that Fits Comfortably be Used?
To Increase the Dose at Depth While Sparing the Vaginal Mucosa and Decreasing the Likelihood of Long-term Pain
point A is defined as 2 cm superior to what?
Top of Ovoid (also known as the mucous membrane of the lateral vaginal fornices in the plane of the uterus)
Today, the standard of care for Operable Endometrial Cancer is:
Total Abdominal Hysterectomy with Bilateral SalpingoOophorectomy (TAH-BSO) → removal of the uterus and the cervix through an abdominal incision
T/F: Manchester and Fletcher Systems Utilize Similar Loading Rules.
True → results in a constant Point A dose rate for all applicator loadings - 52 cGy/hr
How is LDR Vaginal Cylinder Radiation Surface Dose (RSD) in cGy/hr per mgRaEq Calculated?
Using Long and Away Tables
How are RSD LDR Calculations Performed?
Using Long/Away Tables
The main artery supplying the uterus is the ___________________________.
Uterine Artery
Point A represents where what 2 anatomy cross each other?
Uterine Vessels and Ureter (Corresponds to Medial Edge of Broad Ligament)
The ______________ is a hollow, pear-shaped muscular organ in the pelvis between the bladder and the rectum. It is divided into the ____________________________, ___________________, and the __________________________.
Uterus (A) Fundus (superior aspect) (B) Body (corpus) (C) Uterine Cervix
The ______________________ is a fibromuscular tube that extends from the cervix down to the vestibule between the vaginal mucosa and the cervix, which are termed the anterior, posterior, and lateral fornices.
Vagina
What is the Post-op RT Procedure for Endometrial Cancer?
Vaginal Cylinder→ The superior two thirds of the vagina (3-5cm) a.k.a Vaginal Cuff is treated typically with a single central catheter.
What was used in the Manchester/Fletcher T&O Systems to Decrease Rectum and Bladder Dose and Ensure Tandem and Ovoids are Securely Fixed in place by pushing the rectum and bladder away from applicators?
Vaginal Packing → 1 mm packing decreases rectum dose from 18% (single ovoid) and 6-7% (tandems)
What applicators can be used to treat the entire uterus (uterine serosa) for inoperable endometrial cancer patients?
Y-shaped applicators, Multiple tandems, or Simon-Heyman Capsules → via a combination of EBRT and BT when available
What are the limitations of specifying point A dose rate?
Yields no clear info regarding applicator geometry, loading, or volume of tissue irradiated
What are the limitations of specifying the volume of tissue receiving a specific dose?
Yields no clear information concerning point A, loading, or applicator geometry
For Fixed Point A Prescriptions:
∙ Constant Treatment Times for All Loadings ∙ Mg-hr Vary by 30-70% ∙ Reference Dose Tx Volume Varies by Factor of 2.5
For Fixed mg-hr Prescriptions:
∙ Patient A Dose Varies by Loading ∙ Treatment Time Varies by Loading ∙ Similar V60Gy, Independent of Geometry/Loading
