29 Variations of the intracavitary applicator geometry during multiple hdr brachytherapy insertions and its influence on dose specification in carcinoma cervix

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VARIATIONSOFTHE INTRACAVITARY APPLICATOR GEOMETRy DURING MULTIPLE HDR BRACRYTHERAPY INSERTIONS AND ITS INFLUENCE ON DOSE SPECIFICATION IN CARCINOMA CERVIX NR.Datta', S.Kumar'. K.J.Maria Da.s', S.l-lalder'.C.MPandey'. S.,~yyagasi'. Depallments of Rediot~t'ppy" & Bioslalistic.s',Sanjay Gandhi Postgraduate lnsdmtc of Medical Scie:aces. Lucknow, India I n t r o d u c t i o n : This paper exanunes the variation in the applicator geometry, donng muldple high dose rate (HI)R) intracavihary brachytherapy (ICBT) insertions and it's impact on dose specaficafion parameters M a t e r i a l & M e t h o d s : A relrospecdve examination of the records of 20 consecutive patients of carcinoma cervix (F'IGO stages II A to IIIB) each of whom lind 4 ICBT applications at weekly lioervals following 50 Gy/ 5wks/ 25 fr of tdetho'apy (midiinc block after 40 Gy) was pcffomled ICBT applications were camcd out using a Ralsuon - 20 Bum t. which has semi fixed applicators consisting of a flexible PVC intrautcnne tandem (It rl') and a pmr of ovoids (OV) "lltc It rr and C)V ;tsscmhhcs nrc however lltUtu~dly free mid I|taloc coliform tO the Ih3ticltls ;utinoln) "l'h¢ al:l~li~tmr geometry was evaluated in terms of - ot angle, ~ angle. [Lfl length (ILr]'L). iot¢='ovdid (IOV), us to right ovoid fORT) and us to left ovoid (OLT) distances. All these were measured from 80 post insertion orthogonal radiographs. Since an avta-age dose of 6Gy was prescribed at point A for each application, the corresponding dos~ to right point A (ARD), left point A (ALE)) along with a re£erence volume of 6 Gy for ICRU height. ([RH). width (IRW). thickness (IRT) and volume (IRV) were also estimated as spctafied in ICRU 38. R e s u l t s : The variation in the spatial geometry of the applicator bexwco~ 4 applications for each of the 20 patients was studied using one way ANOVA. This showed a sigmficant variation in all the applicator factors between multiple insertions in a given patient - ,a angle (p=- 0.001). [5 angle (p=0.000). ]UTL (p=0.000). IOV (p = 0.000), ORT (F--0.000) and OLT (p=0.009). Although the average dose prcscnbed to point A w~s optimized to nearly 6 Gy. a variation in the ARD (p= 0.027), ALD doses ( p= 0.016). the 6 Gy envelope for IRH (p=0.000), IRW (p=0000), IRT (p--0.000) and IRV (p=0.001) was observed be[we~t the 4 applications. Step wise forward linear regression analysis idenufied the applicator factors which mflucnced the various dose spoc~ficaUon parameters - U'FLN for IRT; ORT, [3 angle and U'ILN for IRH; [OV and UTLN for IRW and [] mtgle alone I~,r the ARD. ALD and 6Gy IRV. C o n c l u s i o n s : The apphcator g~ometry dunng multiple HDR ICBT varies significantly in a given patient between muluphi insertions. This inJlucnce-s not only Ihc spatial rclanon of the prc.scnpUon volume for each insertion but also has in~pllcations for reporting [hc 60 Gy reference volumc as requircd by ]CRL{ 38

MRI AND CT IMAGING DURING PULSED DOSE RATE INTRACAVITARY BRACHYTHERAPY IN CARCINOMA OF THE CERVIX L. Thomas, A. Chemin, O. Lasbareilles, J. Palussi6re, M. Ducassou, J. Pigneux, G. Kantor. Institut BergoniE, Regional Cancer Center, Bordeaux, France

Purpose : The aim of this study was to evaluate the use of imaging in gynecological brachytherapy dose distribution and to show that the use of imaging could allow the utilization of different ways of optimization. Material and Methods :Betore clinical application and fusion software utilization (software Eval of Nucletron for CT fusion and a new fusion software for MR images), some studies have been necessary. Reference correlation points necessary for fusion have been determined on the applicator and visualized on CT and MR images. CT and MR geometrical distorsion has been studied. Protocols of CT and MR exams during brachytherapy with compatible applicators have been also decided. In three patients with carcinoma of the cervix slage T1 (2) and T2b (1), both CT and MRI were performed during brachytherapy using a CT/MR compatible applicator (modified). The computed dose distribution ol the treatment realized according to standard guidelines was displayed on CT and MR images by matching of correlation points. The dose distribution in relationship to the target volume and critical organs (bladder, rectum) was then evaluated qualitatively and quantitatively on CT and MRI (dose volume histograms only for CT). The same evaluation was then performed with optimized dose distribution. Results : The target volume could be delineated in CT and MR images (best visualization in MR images with special interest to the sagittal plane). The correlation points and the critical organs were good visualized. The evaluation has shown that in our three cases, the reference isodose didn't fully encompass the target volume in the 3D directions. Quantitatively the dose volume histograms have shown that the maximum rectum and bladder dose were superior to those computed on dosimetry according to ICRU 38 guidelines. The optimization of radioactive configuration and the use of optimization algorithms in relationship to the target volume visualized on imaging could allow case by case better coverage of the target. Conclusion : The use of imaging (CT and MRI) in gynecological brachytherapy allows a better knowledge of dose distribution (target volume and critical organs). Fusion of dose distribution to imaging is one step to get optimized and individualized brachytherapy treatment. Further evaluation is necessary.

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THE AMERICAN BRACHYTHERAPY GUIDELINES ON INTRAVASCULAR

SOCIETY CONSENSUS BRACHYTHERAPY

Subir Nag, lan Crocker, Vincent Massulo, Burton Speiser. Prabhakar Tripuraneni, Jeffrey Williamson. The American Brachytherapy Society, Reston, V A Introduction: Recent clinical studies indicate that intravascular irradiationcan substantiallyreduce the rote of restenosisfollowing angiographic pmcdurns. However, thereare no guidelinesavailable for opumal therapy. Methods: The members ofthe Inmavascular Subcommittee ofthe American Brachytherapy Society identified the indications, techniques, and resultsof intravascularbrachytherapy (IVB) based on the clinical experience of the members and on analysis of published reports. Results: There was consensus that IVB is a high risk procedure whose efficacy and long term toxicity is not well known. These procedures most be done as part of a controlled clinical trial. Patients at high risk for restenosis (restenofic lesions, diffuse lesions, long length, narrow arteries, diabetics, totally occluded ve4ssels) were considered good candidates for IVB Patients with prior irradiation to vessel site. children and pregnant women should be excluded from IVB. In addilon to the A A P M T G - 6 0 recommendation for dose reporting, the following data should be reported: the dose prescription point, the lesion length, target length, treaanent length, minimum luminal diameter, dose at minimal luminal radius, dose at maximal luminal radius and dose at 2 mm from the source center. It was felt that the minimum dose to the target tissue should be approximately 8 Gy and the maximum dose restricted to 30 Gy. Comprehensive procedures for quality assurance, radiation protection and emergencies should be in place before an IVB program is started. C o n c l u s i o n : IVB is a promising modality for the prevention o f restenosis. Guidelines have been developed to assist the intraventional brachytherapy team in developing protocols for the use of IVB. Long term outcome data with standard reporting system is needed to firmly establish the place of brachytherapy in the armumantarium against vascular restenosis.

C-f-BASED VIRTUAL, SLMULATION (CTVS) IN THE DESIGN AND OPTIMIZATION OF ENDOVASCULAR BKACHY'I'HEI~APY (EB) H Marslglia*, R Lazzari*, M Ghilezan", M.C. Leonardi*, B. Jereczk Fosse*, R Oreechia*. M G Brambilla °, F. Orsi 0, A. Banorelli c~. *Department of Radiation Onediogy, o Medical Physics Department, • P..adiologyDivismn - European Institute of Oncology Milan. Italy. o HemodynanucsSerwce, Monzino Cardiolog3' Centre Milan. Italy Purpose To evaluate the efficacy of CTVS in determining the target volume and its ralationship with the surrounding critical organs The virtual simulation equally permit a predictive dnsimeme study and allows te establish the proper position of the endovnscularcatheter (EC). The optimal position of the EC is in the center of the vascular lumen. If the catheter is not in a central position, the dose distribution is altered, carrying a risk of high dose irrudialion to the surrounding tissues. We report here the use of CTVS in a case of advanced restenosisof the Superior Veua Cava (SVC) in which the fibrous tissue occupied nearly all the character of the lumen, the only permeableportion being in contact with the ascending aorta. Materials and methods : An advancedSVC syndrome in a 37 years old man having a large, post-itffantmatory resteno~is which has been treated during the last 5 years by multiple catheter dilations and slent posinonning. On adntission, a helicoidal high definition CT showed the degree of o~mJction, iIs indirect expression with the pathological uptake of Ihe Azygos veto. arid Ihe proxilnthy of the aural wall (21nln) front the rentalnlng lulnen Basedon serial CT slices and with 3D reconstruction ",~ determined the theorelzcal optimal position of the EC that corresponded to the center of the fibrous cap A predictive 3D dnsimetry was considered as satist'aying, with the anrtal v'all recieving a minimal dose (30%). Using a femoraJ catheter coupled with a mini-drill, an artificial lumen was created and the EC was subsequently placed m the new lumen. We delivered 10 Gy (prescribed at 3ram) on 30 mm length using a Brachytherapy High Dose Rate Unit. There ,.=,'ereno vascular or medical complications during and aRer the procedure. Results : Within 2 weeks of the EB the SVC syndrome resolved. The patient had no evidence of increasedcentral venouspressure at a 3 month follow-up visit The CT showed that there was no more uptake of the A.zygos veto Conelnstons The use of CT based virtual simulation has been extremely usehil in the nmdelling of an "ideal" planmng, with the correct placement of the EC prior to the procedure. A predictive 3D doslmetry enabled us Io optimize the treatment delivery The integration od 3D dosmtetry with the CT-based vinual simulation will authorize a conformal approach improving the therapeuuc ratio and the safety of EB