S69Abstracts / Brachytherapy 9 (2010) S23eS102

In 7 out of 15 patients, the shape of the uterus and/or position of the tandemcaused one or more OARs to receive a higher dose from MMeBx than fromstandard 192Ir HDR in the region most proximal to the tandem. In 5 out of 7of these patients, this region constituted less than 10% of the total organvolume.Conclusions: ‘‘Mixed modality’’ 192Ir and 50 kV eBx tandem and ovoidtreatment of cervical cancer is capable of providing equivalent targetcoverage to the cervix, uterus and paracervical areas as traditional 192IrHDR, while significantly reducing overall dose to the bladder, rectum,colon and small intestine.

PD29

Customized Planning for Cervix Cancer Patients Receiving HDR

Brachytherapy Concurrently with External Beam Radiation

Therapy

Susan L. Richardson, Ph.D., Jacqueline Esthappan, Ph.D., Perry W.

Grigsby, M.D. Radiation Oncology, Washington University School of

Medicine, St. Louis, MO.

Purpose: A number of investigators have reported on the use of customizedplanning versus a single standard plan for high-dose-rate (HDR)brachytherapy treatment of cervix cancer, where the customized plans aregenerated by minimizing dose to the organs at risk e.g., bladder, rectum,bowel. Here, we present an alternative customized planning techniquethat adapts the brachytherapy dose to the changing tumor size, i.e.,applicator geometry, throughout treatment.Materials and Methods: Forty cervix cancer patients were treated withexternal beam radiation therapy (EBRT), typically 50.4 Gy at 1.8 Gy

fractions, and 6 fractions of HDR brachytherapy, at 5.5 - 6.5 Gy perfraction, delivered once a week during the course of EBRT. Tandem andovoids were used for brachytherapy treatments where tandem insertiondepths and ovoid diameters were based on the tumor size at time ofbrachytherapy treatment. The applicator source loading configurations(dwell times and positions) used for treatment were determined usinglow-dose-rate (LDR)-based loading rules designed to maintain a constantdose to point A. A retrospective review of the brachytherapy portion oftreatment was done to assess the variation in applicator geometry, i.e.,ovoid size and tandem length, and in the corresponding integral referenceair kerma (IRAK) over the course of treatment.Results: The ovoids decreased in size for 25 of the 40 patients. In 7 patients,it changed more than once (for example from 2.5 cm to 2.0 cm to 1.6 cmdiameter). In 6 patients, ovoids could not be inserted by the last fraction.A change in tandem loading (dropping or adding of at least 1 dwellposition) occurred in 32 patients, while in 10 patients the tandem haddropped more than 3 dwells on at least one fraction. In Figure 1, theIRAK delivered for each fraction was normalized to the prescribed IRAK,corresponding to a standard loading geometry, i.e., 6 cm length tandemand 2 cm diameter ovoids. In most patients, the average, normalizedIRAK decreased over the course of treatment, largely due to thedecreasing ovoid loading. The ratio of the average, normalized IRAKs forfraction 6 to fraction 1 was 0.88. For the ovoid IRAK alone, thecorresponding ratio was 0.70.

Conclusions: Use of a standard plan for all fractions of HDR brachytherapywas found to be inappropriate for a number of our cervix cancer patientswho receive the brachytherapy concurrently with EBRT because of tumorshrinkage over the course of treatment. For these patients, the tumorresponse led to a change in applicator geometry, requiring the generationof an applicator-specific customized plan for each treatment. Furthermore,by adapting the dose to the changing tumor size, doses to bladder andrectum were maintained at acceptable levels although no specificoptimization was done with respect to these OARs.

PD30

A Novel Method for Tumor Delineation on Sagittal MRI Sequences

for Image-Guided Brachytherapy

Jeffrey D. Radawski, M.D.1, Zhibin Huang, Ph.D.1, Jian Z. Wang, Ph.D.1,

William T.C. Yuh, M.D., M.S.E.E.2, Nina A. Mayr, M.D.1 1Radiation

Medicine, Ohio State University, Columbus, OH; 2Radiology, Ohio State

University, Columbus, OH.

Purpose: Image-guided brachytherapy (IGBT), a novel concept of MRI-based target delineation and dose prescription, has shown promise inimproving precision of brachytherapy and outcome in cervical cancer.However, precise delineation of the tumor on the MRI remainschallenging. While the topology and configuration of cervical tumors is