Cervical Cancer: Brachytherapy Techniques – Flashcards
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Most common applicator for intracavitary brachy
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Fletcher-Suit intrauterine tandem and ovoids or tandem and ring
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Proper position of flange
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Flush against cervical surface
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Proper position of tandem
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Should bisect angle of colpostats,unrotated,midline
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Proper position of colpostats
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Hi in fornices along cervix
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Flange position represents
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Cervical os
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Where are marker seeds placed
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1cm above position of flange
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What positions are marker seeds
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2, 5, 8, 11 o'clock positions or just one for depth
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What holds positions of tandem of ovoids
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Proper packing
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Improper packing does what
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Increases doses to rectum/bladder but rectal shield part of nucleotron applicator may reduce the need for packing
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Insertion techniques for intracavitary applicators
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US and fluoroscopic guidance
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Advantage of Smit sleeve
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May facilitate applicator placement;+risk of perf
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Point A
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2cm cephalad from cerv os, 2 cm lat to uterine canal We prescribe to this point
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What does point A represent
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Med parametrium/lat cervix (ureter/uterine art cross)
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Point B
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5 cm lat to center of pelvis at same level as point A
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What does point B represent
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Obturator nodes/lat parametrium
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Point B receives what% of Point A dose
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1/3 to 1/4
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What does point C represent
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Pelvic sidewall dose
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Point C receives what% of Point A dose
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1/5
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Point P
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most lateral point of bony pelvic sidewall
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What does point P represent
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Minimal dose to ext iliac nodes
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Point H
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2 cm above ovoid level, 2 cm lat line bisecting ovoids
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Significance of point H
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recommended rx point by ABS
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Bladder point
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post surface foley on lat film/middle of foley on AP
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Rectal point
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5mm behind vag wall@last intrauterin tandem source
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Vaginal point
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lat edge of ovoid on AP/mid-ovoid on lat
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Historically point A used for
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Tolerance dose
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Now point A is used for
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Prescription point
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Dose for stage IB-IIA cervical CA
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80-85 Gy to point A (85 Gy more accepted) We use 7Gy x 4 after 45Gy/25fx but can use 6Gy x 5fx
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Dose for more advanced stage disease
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85-95 Gy to point A (assuming EBRT to 50.4/28fx)
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Problem w/ prescribing to point A
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empirical point (does not reflect tumor dose)
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ICRU recommendation instead of rx to point A
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determine tissue volume in 60 Gy isodose sur
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American working group developed system
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Prescribe to 3 separate CTVs
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High risk CTV
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GTV prior to xrt + entire cervix (80-90 Gy)
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Intermediate risk CTV
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Hi risk CTV + 0.5-1.5 cm margin (60 Gy)
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Low risk CTV
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Tumor volume covered by ext beam
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Onset of brachytherapy at what time point
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No later than week 6 Can be given during EBRT, but avoid chemo day
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Total duration of xrt should be no more than
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<8 wks, as there is benefit to shortening the treatment interval - local control and survival is affected by 1% a day, (Perez, IJRBOP, 1995; Girinsky, IJROBP 1993) from RTOG 90-01
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Tandem/ring has what dose distribution
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Narrow dose distribution, cover ant/post lip of cvx
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Tandem/ovoid has what dose distribution
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Pear shaped, covers upper vagina
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Tandem/cylinder has what dose distribution
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Narrow distribution, tx entire vagina, <5mm
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Interstitial implant has what dose distribution
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Covers distal vagina >5mm
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Mini-ovoids
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Unshielded This applicator was designed for the patient with a narrow vault. The medial area of the ovoid is flattened to accommodate a very small anatomy.
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Advantage of tandem/ring
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Reproducible geometry; easy to insert
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When is tandem/ring used
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When vaginal fornices absent/asymmetric
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When is interstitial implant used
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Vag narrowing, absent fornices, vag extension
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When is tandem/cylinder used
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Need interstitial implant but not available
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Disadvantage of tandem/cylinder
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Lower parametrial doses,higher bladder/rectal doses
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For deep or thick vaginal involvement consider this brachy tehcnique
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Interstitial
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What kind of gauze should be used for cervical cancer brachy packing
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Triple-sulfate soaked gauze for LDR and KJ-Jelly for HDR
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What should the brachy implant look like during anterior plain film evaluation:
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ant film: tandem bisects ovoids and tandem not rotated; phlange close to cervical marker seeds: ovoids high in fornices <1cm from marker seeds with 0.5-1cm spacing between them.
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What should the brachy implant look like during lateral plain film evaluation:
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tandem bisects ovoids and is midway between sacrum and bladder, at least 3 cm from asacral promontory;, sufficient andterior and posterior packing, foley balloon firmly pulled down.
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Dose constraint for HDR to bladder and rectum?
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<70% of point A dose
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Dose constrain for LDR to bladder and rectum?
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limit rectal point to <70Gy and bladder point to <75Gy
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What are the constraints for the vagina for brachy?
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Upper vaginal mucosa <120Gy Midvaginal mucosa <80-90G Lower vaginal mucosa <60-70Gy
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What dose can cause fibrosis and stenosis of the vaginal canal?
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50+ Gy
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What dose should the uterus be limited to ?
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<100Gy
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What dose should the ureters be limited to?
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<75Gy
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What dose should the femoral heads be limited to?
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<50Gy
