Challenging Cases in Cervical Cancer: Parametrial
BoostingBeth Erickson, MD, FACR, FASTRO
Medical College Wisconsin
Disclosure
• Chart Rounds participant
• No COI
Learning Objectives
• Discuss the challenges of boosting the parametria
• Discuss external beam strategies for boosting the parametria
• Discuss brachytherapy strategies for boosting the parametria
• 42 y/o pt with a 10 mo. history of increasing pelvic pain and difficult BMs with weight loss.
• Endoscopy and pelvic exam negative initially.
• Eventual discovery of a 6 cm posterior lip cervical cancer involving the right uterosacral ligament and compressing the rectum
• Biopsy + for poorly diff adenocarcinoma.
• Stage IIIB
• Pelvic external beam‐45 Gy, 4 field 3D conformal and weekly Cis‐P
• Transperineal interstitial implant‐22 needles and tandem; 5 HDR fx of 450 cGy periphery/540 cGy core(~75Gy/83 Gy LDR equivalent)
• Parametrial boosting‐3.6 Gy split pelvis and 10.8 Gy to right pelvic sidewall
Repeat MR after 45 Gy
• Pt had resolution of presenting symptoms with negative 3 mo.PET
• Rectal bleeding 9 months later
• Endoscopy‐angiodysplasias of the rectum‐argon plasma coagulation(APC) X 3 and carafate enemas
• Rare bleeding at 24 mo.• Patient NED at 24 mo.
Parametrial/Paracervical Tissue • Fat and loose
connective tissue and smooth muscle around the uterus and cervix− Contains blood vessels and lymph nodes
− 30% of pts with localized disease will have pathologic involvement
− Disease may extend from the primary or be discontinuous and throughout the parametria
Netter F. Atlas of Human Anatomy 4th Ed
Good et al Brachytherapy 11(2012):77‐79.
Lim et al IJROBP, 2010
The Traditional Approach
External Beam Doses for Cervical Cancer
Whole pelvis 4500 cGy
Split pelvis (midline block) 5040 cGy
Parametrial boosts 5400‐5940 cGy
The clinical challenge: How do you reach the parametria?
–3D conformal boost with MLB ?
– IMRT boost?– Interstitial brachytherapy boost?
Good et al Brachytherapy 11(2012):77‐79.
3D Conformal Midline Blocks
Intended to avoid regions of excessive dose adjacent to the implant, but deliver adequate dose to tumor‐bearing regions outside of implant
3D Conformal Midline Blocks
• Parametrial boosts traditionally done with AP‐PA fields with a MLB
1) standardized rectangular or
2) customized to an ICBT isodose line.
– Used by major centers for years
– No additional investment in software or equipment
– Time honored
“It is current standard practice not to consider the radiation dose to the bladder and rectum from the parametrial boosts because these organs are blocked by the
midline shield”
Ting, Radiology 209:825‐830, 1998
Problems with Midline Blocks: Blocking too Little
• Portions of the bladder and rectosigmoid are not under the midline block and will get both the brachytherapy doses and WP and PM doses.
4 cm midline block
Fenkell et al IJROBP (2011)79:1572‐1579
Problems with Midline blocksBlocking too Little
‐ The packed applicator may move cephalad towards the rectosigmoid during the implant
‐ The upper rectum and rectosigmoid may extend above the midline block after the implant
‐ The upper rectum and rectosigmoid are not always midline
Rectosigmoid ComplicationsHuang Gyn Onc (2000)79:406‐410
NPMB= 40‐45 Gy; LPMB=50‐54 Gy; HPMB= > 54 Gy
Problems with Midline Blocks:Blocking too Little
Ext beamWP
D2cc Bladder
D2cc Rectum
D2cc Sigmoid
45.0 Gy 83.8 57.5 71.450.4 Gy 85.9 59.6 73.555.8 Gy 88.0 61.7 75.659.4 Gy 89.4 63.1 77.0
The Challenge of Uterosacral ligament Involvement
Safer to avoid early in treatment if
uterosacral ligament involvement
May want to consider oblique
boosts with uterosacral ligament
involvement
Midline Blocks
Chao; IJROBP 40:1998
Outcomes with Parametrial Boosts
No consensus as to indications,
optimal technique, or dose of PMB
Typically for bulky IIB and IIIB
patients
PMB range: 5‐20 Gy after 40‐50
Gy WP
Total dose 60‐62 Gy (range 50‐70
Gy) Perez; Cancer 51:1983
Perez IJROBP 41(2):307‐317,1998)
(Viswanathan IJROBP 2011)
Some correlation with local control and PMB dose( < 50 Gy) but higher doses only associated with increased complications
Technical Challenges Integrating Brachytherapy and External Beam
Most external beam and brachytherapy treatment planning systems cannot integrate to add external beam and brachytherapy
doses together
Lack of a True cumulative dose to Tumor and OAR
IMRT Parametrial Boosting• Concurrent SIB offers
accelerated fractionation to bulky disease and standard fractionation to microscopic disease
• Does not require isodosematching or adding two IMRT plans
• How do you separate the parametrial disease from the central cervical disease?
• Easier to do for nodes!
• Sequential IMRT boost takes disease regression into account with decreased boost volume
• Not always a visible parametrial GTV after external beam but there may still be palpable retraction towards a sidewall
Good et al Brachytherapy 11(2012):77‐79.
Integration of External Beam and Brachytherapy
To improve outcomes in patients with cervical
cancer, the external beam doses and techniques must be scrutinized and controlled just as carefully
as the brachytherapydoses and techniques
Parametrial Dose from Brachytherapy
• D90 > 85 Gy (80‐90 Gy); D90> 87 Gybulky tumors
• Dose escalation for large tumors with interstitial needles added to the ring
Dose specification:
HR CTV
• Rectum < 70‐75 Gy• Sigmoid < 70‐75 Gy• Bladder < 90 Gy
Dose volume constraints for OAR: (D2cc)
Parametrial Boost with BrachytherapyIntracavitary/interstitial Applicators
Intracavitary/Interstitial Tandem and Ring, Tandem and ovoids• 60% of tumors can be covered with IC and the remaining require IC‐interstitial
• Only 5% require template‐based interstitial
10‐20% of total dwell time comes from the needles and the remainder from IC T/R Tanderup et al Rad Onc 94:173‐180,2010
Image‐Guided Adaptive Parametrial Boost
• Supplement brachytherapy boost with a high‐precision, high‐gradient stereotactic hypo‐fractionated IMRT boost to the under‐dosed part of the HR CTV.
• IMRT boost is planned and delivered with the brachytherapy applicator in place
• Requires integration of external beam and brachytherapy TP systems
Assenholt et al Acta Oncol 2008;47:1337‐1343Tanderup et al Radiother Oncol 2010; 96: S427‐S428.
Image‐Guided Adaptive Parametrial Boost
Assenholt et al Acta oncologica 2008:47:1337‐1343
Interstitial techniques
• Template‐based approaches are indicated for bulky disease after external beam
• Can selectively implant one or both parametria
• Can implant medial and some of the lateral parametria
• May not cover uterosacralligaments well or lateral parametrial disease
How do you do your parametrialboosts?
1. Midline block/3D conformal2. IMRT3. SBRT4. Tandem and ring/ovoids with needles5. Transperineal interstitial implant
Questions?