Challenging Cases in Cervical Cancer: Parametrial Boosting Beth 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 Endoscopyangiodysplasias 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 4 th 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 tumorbearing 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 blocks Blocking too Little Huang Gyn Onc (2000)79:406 410 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 Complications NPMB= 40 45 Gy; LPMB=50 54 Gy; HPMB= > 54 Gy
Problems with Midline Blocks: Blocking too Little Ext beam WP D2cc Bladder D2cc Rectum D2cc Sigmoid 45.0 Gy 83.8 57.5 71.4 50.4 Gy 85.9 59.6 73.5 55.8 Gy 88.0 61.7 75.6 59.4 Gy 89.4 63.1 77.0
The Challenge of Uterosacral ligament Involvement Safer to avoid early in treatment if uterosacral ligament involvement Midline Blocks Chao; IJROBP 40:1998 May want to consider oblique boosts with uterosacral ligament involvement
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 (Viswanathan IJROBP 2011) Perez IJROBP 41(2):307 317,1998) 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 isodose matching 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 brachytherapy doses and techniques
Parametrial Dose from Brachytherapy Dose specification: HR CTV D90 >85 Gy (80 90 Gy); D90> 87 Gy bulky tumors Dose escalation for large tumors with interstitial needles added to the ring Dose volume constraints for OAR: (D2cc) Rectum < 70 75 Gy Sigmoid < 70 75 Gy Bladder < 90 Gy
Parametrial Boost with Brachytherapy Intracavitary/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 templatebased 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 hypofractionated 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 1343 Tanderup 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 uterosacral ligaments well or lateral parametrial disease
How do you do your parametrial boosts? 1. Midline block/3d conformal 2. IMRT 3. SBRT 4. Tandem and ring/ovoids with needles 5. Transperineal interstitial implant
Questions?