108 Abstracts / Brachytherapy 7 (2008) 91e194

Conclusions: There is an increase of ipsilateral lung exposure with wedgecompensation and brachytherapy techniques. For all the other endpointPBSI dramatically reduces the body exposure to scatter radiation. Wedgecompensation should be avoided and replaced by modern technique ofbreast XRT.

OR45 Presentation Time: 10:40 AM

Theoretical and benchtop study of a novel means of skin sparing

by sculpting dose with the Xoft Axxent source

Steve Axelrod, Ph.D. Office of Advanced Technology and Science, Xoft,

Inc., Fremont, CA.

Purpose: HDR balloon brachytherapy has become a commonplace methodof treating post-lumpectomy early stage breast cancer. The Xoft Axxentsystem is unique in that the source is a miniature x-ray tube rather thana radioactive seed. The source operates with a hardened 50 kVp spectrum.Although it provides similar depth-dose characteristics to Ir-192 over thetreatment volume, the lower energy makes it much easier to fully orpartially shield the source, and enables shaping the dose distribution bymeans of strategically placed and shaped partial attenuators, or ‘‘shadowdots.’’Generally, attenuating x-ray beams hardens them, so depth-dosecharacteristics will be different behind the attenuators than elsewhere.However materials such as silver or molybdenum, with K-edge absorptionenergies in the mid range of the x-ray spectrum, make possible selectableattenuation without substantially changing depth-dose.Methods and Materials: Benchtop measurements and computersimulations were used to demonstrate that it is possible to reduce dose bya selectable amount over a definable region outward from the source.Sample shadow dots were placed on the catheter of the Xoft source, anddose was measured in scans over azimuthal and polar angles, at differentdepths in a water phantom. Computer studies using models of the sourcedistribution and attenuation properties of the shadow dots were used toconstruct full 3D volumetric data.Results: Measured data show reduced dose behind shadow dots consistentwith predictions of absorption calculations. The physical extent of theshadowing is controllable by choice of physical dimensions of the dot(s).In stepping mode the situation is more complex due to effects when thedwell point is off-axis from the dot, but such effects are manageable viadot size and dwell point spacing.Conclusions: It is feasible to sculpt source output so as to reduce the dose tosensitive structures such as skin, accommodating situations where skinspacing is below normally accepted limits. This concept is promising forretaining the option of brachytherapy for breast cancer cases with smallballoon-to-skin spacing.

GYNE ORAL PRESENTATION SESSION 2

(endometrial/image guided)

Monday May 5, 2008

3:00 PMe4:10 PM

OR46 Presentation Time: 3:00 PM

Are we hitting the target and if not, can we safely alter the pear?

Tracy Kelly, M.D., Jason Rownd, M.S., Beth Erickson, M.D. Radiation

Oncology, Medical College of Wisconsin, Milwaukee, WI.

Purpose: CT-based dosimetry for each HDR fraction has been used atMCW since 2004 for cervical cancer patients receiving brachytherapy todefine and limit dose to normal tissues. An MRI at fraction 1 has beenobtained to define tumor volume using the GEC ESTRO guidelines.Using CT-based plans we reviewed how well we met the GEC ESTROguidelines on the MRI scans. In those patients in whom a D90 of 85 Gywas not met, we used an MRI plan with simple modifications to assessthe ramifications on the adjacent normal organs of altering the dosedistribution to cover the HR CTV.

Methods and Materials: A review of the implications of using exclusiveCT-based dosimetry to limit normal organ doses but without knowledgeof coverage of the GTV and the HR CTV was performed on 27 patientstreated from 2004e2007. For the CT-based plans, the goal was to limitthe normal organ doses to !80% of the point A dose by assessing andaltering the isodose distributions on the anatomy without knowledge oftumor volume coverage. For those patients in whom the D90 was !85 Gy,a standard MRI plan based on the original CT plan was generated andmodified in regions of suboptimal HR CTV coverage using graphicaloptimization. The implications for the normal tissues were assessed usingthe GEC ESTRO normal tissue constraints of D2cc !75 Gy and 90 Gyfor rectosigmoid and bladder.Results: In 17/27 patients (63%), the CT plan met the goal of D90 of 85 Gywith 1 patient exceeding the normal tissue constraints. In 10/27(37%) theCT plan revealed a D90 !85 Gy. Using the MRI plan, graphicaloptimization was performed and the normal tissue constraints compared.The D2cc of these 10 patients before graphical optimization using just theCT-based plan was an average of 56 Gy for rectum, 66 Gy for sigmoid,and 73 Gy for bladder. With the MRI-based graphical optimization plan,these same average D2cc doses were 81 Gy, 99 Gy and 115 Gy.Conclusions: CT-based planning was successful in covering the HR CTVin 63% of our patients and in limiting the normal tissues constraints.Though CT-based dosimetry is very helpful in understanding and alteringthe dose to the normal tissues, the lack of soft tissue resolution does notallow for assessment of the tumor volume coverage and the implicationsof changing the dose distribution to limit normal organ doses. Asa result, in 37% of our patients, the D90 was !85 Gy. MRI is pivotal inrevealing the HR CTV and the need for changes in the dose distributionto enhance coverage of the GTV and HR CTV. Graphical optimizationcan enhance target volume coverage but must be combined with carefuladjustments in dose to the normal organs or excessive doses will bedelivered.

OR47 Presentation Time: 3:10 PM

Outcomes following surgery and adjuvant radiation in stage II

endometrial adenocarcinoma

George M. Cannon, M.D.1 Theron C. Casper, B.S.2 Soren M. Bentzen,

Ph.D.1 Kristin A. Bradley, M.D.1 1Human Oncology, University of

Wisconsin, Madison, WI; 2Statistics, University of Wisconsin, Madison, WI.

Purpose: The primary purpose of this study is to evaluate locoregionalcontrol and disease-free (DFS) and overall survival (OS) in patientstreated with surgery and adjuvant radiation for Stage II adenocarcinomaof the endometrium. Secondary goals include identification of prognosticfactors and the comparison of toxicity profiles after high-dose-rate vaginalcuff intracavitary brachytherapy (IC) alone or combined with pelvicexternal beam radiation therapy (EXT).Methods and Materials: Between January 1991 and December 2006, 71pts with FIGO Stage II adenocarcinoma of the endometrium (23 StageIIA and 48 Stage IIB) received adjuvant radiation at the University ofWisconsin. Fifty patients were treated with EXT and IC, twenty with ICalone, and one with EXT alone. Surgical approaches included abdominalhysterectomy alone (23 pts), abdominal hysterectomy with lymph nodesampling (20 pts), and abdominal hysterectomy with pelvic andparaaortic lymph node dissection (28 pts).Results: At a mean followup of 5.1 years (range, 0.5e16.8 years), 5-yearOS and DFS were both 82%. Of 71 patients, nine recurred and eight diedof their disease. Factors associated with an increased risk for recurrenceincluded depth of myometrial invasion (p 5 0.005) and lymphovascularinvasion (p 5 0.02), and a strong trend towards significance for highergrade (p 5 0.051). Extent of surgery, type of radiation, and stage werenot significant. Receiving EXT correlated to an increased depth ofmyometrial invasion (p 5 0.007), higher grade (p 5 0.003), and lessextensive surgery (p 5 0.01). Of the recurrences, three were initially localalone and six were distant recurrences alone. Two patients recurredlocally within the pelvis after EXT. The third patient received IC alonewith a subsequent pelvic lymph node recurrence. The three patients withlocal recurrences had undergone incomplete lymphadenectomy. Acute