Brachytherapy in Carcinoma Cervix

Applicators in Gynaecological Brachytherapy

17.1 Applicators for Cervix Interstitial Brachytherapy

Venezia Applicator (Fig. 17.1):

• Recently launched by Elekta.
• Applicator can be used for intracavitary, interstitial, and intravaginal brachytherapy in cervical cancers.
• Can be used for cervix, vulva, urethra, prostate, and rectal interstitial brachytherapy; hence, termed a universal template.
• Adds a unique insertion tool to place needles at exact depths, allowing better preplanning.
• Angled needles can cover up to 7 cm of parametrium.
• Inner table is sutured to the perineum with stay sutures.
• Consists of two lunar-shaped ovoids that form a ring when clicked together.
• Features an integrated cervical stopper.
• Has a one-click system for easy assembly.
• Available in 22, 26, and 30 mm sizes.
• Cylinder caps allow treatment of the vaginal wall.
• Ovoid holes allow parallel and oblique needles to reach the parametrium.
• Includes perineal templates for reaching vaginal extensions.

17.1.1 MUPIT (Fig. 17.2):

• Martinez Universal Perineal Interstitial Template.
• Features a fixing screw for the cylinder or circular insert.
• Includes an inner template, circular insert, cylinder, and outer template.
• Has an MR-compatible insertion tool to guide the depth of needle placement.
• Space for TRUS probe.
• The angle between parallel and angled needles is 13 degrees.
• Slots for needles and a screw to fix the outer and inner plate.
• Slot for obdurator or rectal catheter based on the positioning of the template.
• Outer plate to fix with the inner plate to prevent displacement of needles.
• Assembled MUPIT showing obdurator, needles, inner and outer template.
• A hole in the obdurator is used for placing a tandem if the cervical os is negotiable.
• Fixing screw.
• Circular insert if vaginal stenosis is present and the obdurator cannot be placed.
• Template is made of plastic material and needs to be handled with care due to the risk of bending or cracking.

17.1.2 Applicators in Cervix Intracavitary Brachytherapy

• Modified Fletcher-Suit applicator (Fig. 17.3):
  • Commonly used ICRT applicator.
  • Ovoids of various sizes are available to fit properly in the vagina.
  • The flange has an adjustable lock for different intrauterine lengths.
  • Only CT compatible.
• MR compatible intracavitary applicator (Fig. 17.4a):
  • The MR-compatible applicator is thicker in size, making placement difficult in stenosis of the cervical OS (requires more dilatation) and vagina.
  • Can be used in CT-based reconstruction as well.
• Utrecht CT/MR interstitial applicator:
  • Uses Ovoids as a template for interstitial needles
• Rotterdam Cervix applicator
  • Made of titanium
  • Has insertion tool to guide depth of needle placement
• Fletcher Williamson Cervix applicator
  • Has in built rectal and bladder shield
  • Additions for treating vaginal extensions
  • Fixed geometry applicator. Easily inserted if smit sleeve is in situ
• Henschke Cervix applicator
  • Made of titanium
• Vienna ring applicator (Fig. 17.4b):
  • It has 2 locks placed at fixed distances, making placement difficult in a short vagina.
  • The angle of the ring is also fixed.
  • Only parallel needles can be placed, and so the lateral throw into the parametrium is less.

Other applicators (Fig. 17.5).

17.2 Intracavitary Brachytherapy (ICRT) in Cervix

Patient Selection

• All patients undergoing external beam radiotherapy for carcinoma cervix should be evaluated for intracavitary brachytherapy.
• Examination of the supraclavicular fossa, inguinal region, and per speculum/vaginum needs to be done to ascertain the extent of the disease.
• Patients may be taken for applicator placement under mild sedation and analgesia or under spinal anaesthesia.
• Spinal anesthesia is preferred for three reasons:
  1. Pelvic muscle relaxation, leading to better maneuverability and easier placement of applicators.
  2. Good analgesia during applicator placement and treatment, leading to more patient compliance for subsequent sessions.
  3. Minimal voluntary movement of lower limbs decreases the risk of displacement of applicators.
• Risks of spinal anesthesia specific to carcinoma cervix patients:
  1. Prolonged immobilization may lead to a higher risk of deep vein thrombosis (cancer being thrombophilic).
  2. Full analgesia may make it difficult to detect vaginal tears and uterine perforations early during the procedure.

17.2.1 Tumour Specific Criteria for Patient Selection of ICRT

1. No vaginal stenosis.
2. Os negotiable.
3. Tumour size <4 cm (i.e., <2 cm on either side of os) at the time of ICRT.
4. No or minimal parametria extension at the time of ICRT.
5. No involvement of lower vagina.
6. No adjacent organ involvement.

17.2.2 Patient Specific Criteria for Patient Selection of ICRT

1. Normal hemogram and prothrombin time.
2. Patient can be placed in lithotomy position or at least with lower limb abducted and externally rotated >30 degrees.

17.2.3 Procedure

1. Patient placed in lithotomy position after anesthesia/analgesia.
2. Cleaning of perineum done.
3. Two-way Foley catheter placed in the bladder, and 7 mL of diluted (2 mL contrast and 5 mL water) contrast placed in bulb.
4. Draping of perineum done.
5. Transrectal ultrasound (TRUS) is used (Fig. 17.1) to identify:
   • Uterine position (retroverted versus anteverted).
   • Presence or absence of pyometra.
   • Approximate length of uterus.
6. Uterine sound placed through os to confirm the length of uterus.
7. Hegar dilator used to dilate cervical os for placement of tandem.
8. Tandem of appropriate length placed such that it reaches the uterine fundus.
9. TRUS used to confirm placement within the uterus.
10. Ovoids or ring of largest possible size placed in the vagina at the level of the flange.
11. The applicator locks are placed.
12. Initial posterior packing behind the ovoids or ring to decrease rectal dose, followed by anterior packing to decrease bladder dose.

17.2.4 Contouring for MR Guided Brachytherapy

1. Pre-RT MR imaging is ideal for imaging of the primary cervical disease. Evaluation of the vagina can be optimized by inserting vaginal contrast, such as gel.
2. Information on clinical examination is also helpful in addition to MRI.
3. A pelvic surface improves the resolution of the MR imaging.
4. The ideal time for MR imaging for BT contouring is while the BT applicators are in situ.
5. GEC-ESTRO recommends MRI imaging for BT in 3 T2WI planes [fat saturation is not required]-axial, coronal, and sagittal.
6. Advantage of T2 images: even with treatment, the tumor shows intermediate to high signal intensity.
7. Enlarged pelvic lymph nodes could be a sign of disease. Some of the lymph nodes after EBRT undergo cystic necrosis and may have the appearance with multiple cysts [similar to the ovary].

17.3 Interstitial Brachytherapy (Carcinoma Cervix)

17.3.1 Patient Selection and Indications

1. Vaginal stenosis present.
2. Os not negotiable.
3. Tumour size > 4 cm (i.e., >2 cm on either side of os) at the time of brachytherapy.
4. Parametria extension at the time of brachytherapy.
5. Involvement of lower vagina present.
6. Adjacent organ involvement present at baseline.
7. Normal hemogram and prothrombin time.