Online

WCB 2021 - Online

Session Item

Thursday
May 06
09:00 - 10:15
Image guided BT and Outcome for Cervical Cancer: Update from different regions
0025
Symposium
09:36 - 09:54
Cervical Cancer Brachytherapy at Washington University: 1920-2020
Perry Grigsby, USA
SP-0005

Abstract

Cervical Cancer Brachytherapy at Washington University: 1920-2020
Authors: Perry Grigsby(Mallinckrodt Institute of Radiology, Radiation Oncology/Nuclear Medicine/Obstetrics & Gynecology, St. Louis, USA)
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Abstract Text

The use of intracavitary Radium to treat cervical cancer began at Washington University in 1920.  Then, as today, the treating physicians understood that there were two targets: the primary cervix tumor and the lymph nodes.  Imaging of the implants was nonexistent.  It was observed clinically that Radium could cure the primary cervix tumor but not the lymph node metastases.  2-D imaging of brachytherapy implants and the use of kilovoltage external irradiation to the lymph nodes was performed beginning in the 1930s.  The hallmark of cervical cancer treatment at Washington University was to apply as much dose as possible to the cervix (within tolerance) with brachytherapy and to limit the use of 200-500 kVp external irradiation using small fields to the lymph nodes only.  The results of this treatment were mixed.  The primary cervix tumor was cured in a very high percentage of cases but control of lymph node metastases by kilovoltage and orthovoltage irradiation was dismal.  In 1954 Washington University installed a 24 MeV Allis-Chalmers Betatron.  The use of 24 MeV x-rays allowed the pelvic lymph nodes to be successfully treated and cured without the skin toxicity of lower energy x-rays.  Two critical clinical decisions were made at that time.  First, given that the primary cervix tumor control rates were high with the use of Radium, then, the cervix would continue to be treated with very high doses of Radium while the lymph nodes were targeted with 24 MeV x-rays and the primary central tumor would be blocked out of the 24 MeV external irradiation fields with a midline rectangular block.  Secondly, brachytherapy and external irradiation would be given concurrently.  This treatment paradigm of initiating treatment with brachytherapy, limiting external irradiation to the primary cervix tumor, and concurrent external irradiation and brachytherapy was continued.  The only alteration was the replacement of the midline rectangular block with a midline stepwedge block whose steps conformed to the falloff of the intracavitary radioisotope application.  Intracavitary applicator imaging was routinely performed with orthogonal 2-D radiographs.  There was no imaging of the primary tumor.

  Computerized 2-D brachytherapy dose distributions were developed at Washington University in 1964 and were then routinely used.  Efforts at computerized tomography (CT) for 3-D brachytherapy imaging and dosimetry were begun in the mid- to late-1990’s, however, the major limitation to routine adoption was the metallic artifact from the tungsten-shielded Fletcher-Suit intracavitary applicators.  Our efforts toward 3-D image guided brachytherapy then focused on the use of FDG-PET imaging.  Using the Fletcher-Suit applicators, we successfully imaged the applicator in the patient’s tumor by using PET.  The FDG isotope was placed in small tubes inside the applicator as a “dummy”.  The patient was then injected with FDG and subsequently imaged.  This allowed us to visualize brachytherapy source positions within the metabolic tumor volume and calculate 3-D dose distributions.  PET brachytherapy was continued with the goals of understanding 3-D dose distributions to OARs, tumor coverage, and metabolic response of the tumor to treatment.  PET brachytherapy is a novel research tool but is not feasible for routine clinical use.  During the period of the early 2000’s, several other technological advances occurred.  CT and MR compatible intracavitary applicators and 3-D brachytherapy treatment planning systems became available.  LDR brachytherapy was replaced by HDR brachytherapy. IMRT and volumetric arc therapy are now routinely used for external irradiation.  The challenges during this transition were then to re-think and understand OAR toxicity limits and appropriate tumor dose prescriptive criteria.  Much data collected over the past 20 years have increased our understanding of these issues. 

Today at Washington University, we administer external irradiation with IMRT and continue to limit the external irradiation dose to the primary cervix tumor while delivering high doses of brachytherapy given once weekly during external irradiation.  We use MR-guided brachytherapy for six weekly fractions during the 6-week course of external irradiation.  OARs and GTVs (as defined by DWI imaging) are contoured and doses calculated and summed with the external irradiation on each of the 6 brachytherapy fractions.  A real-time DoseTracker® updates with each radiation fraction and predicts total cumulative doses as treatment progresses.  D2cc OAR doses are used to limit toxicity and Dmean doses are used as the GTV prescriptive dose.  Examples of treated cases and toxicity and tumor control rates will be presented.