We evaluated dose optimization for the treatment of cervical cancer using Buchler's high-dose-rate (HDR) remote-control-afterloading-system (RALS). When Buchler's system is used for intracavitary treatment, the irradiation times for the tandem and ovoid sources should be selected separately. The effects of variation of the tandem-to-ovoid dose ratio on the dose distribution are described.journal articl

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OGATA, Hitoshi

OHNISHI, Hiroshi

UCHIYAMA, Guio

English

University of Yamanashi Academic Repository

Yamanashi Med. J. 9(3), 91--95, }994Optimization ef Dose Distribution in Intracavitary TreatmeRt     of Cervical Cancer with Buchler's Afterloading System             Hitoshi. OGATA, Guio. UcKiyAMA, and Hiroshl OHNisHi           DePartment ofRadiology, Yamanashi Medical Universitpu School ofMedicineAbstract: We evaluated dose optimization for the treatment of cervical cancer using Buchler'shigh-dose-rate (HDR) remote-control-afterloading-system (RALS). When Buchler's system is usedfor intracavitary treatment, the irradiation times for the tandem and ovoid sources should beselected separately. The effects of variation of the tandem-to-ovoid dose ratio on the dosedistribution are descrlbed.Key words: Buchler's HDR-RALS, dose optimization             INTRODUCTION  In the treatment ef carcinoma of the uterinecervlx, lt ls not uncommon to encounterpatients who have never borne children orwi£h carcinoma which has deeply invaded thevaginal wall. The vaginal vaults in such pa-tients do Rot readily expand whelt it is attemp-ted to place oveid applicators as close to theuterine orifice as possible. We have eftenfouRd it necessary to irradiate patien£s withunsatisfactory position of ovoid applicators. Asthe distance of the ovoid sources frem thevaginal vaults increases, the irradiation timerequired for the dose from these sources isincreased. The patieitt's rec£al dose is in-creased as well (Fig. 1). This article describesan investigation ofa method of minimizing theincrement of the rectal dose in such a case inorder to optimize the dose distribution iniBtracavitary treatmeRt in individual patients.lHO Shimokato, Tamaho, Nakakoma-gun, Yama-ltashi 409-38, Japan.Received June 16, 1994Accepted October 12, 1994'A,lt'ANst,, sig e   5" "-    s ---- .- --- -. veN,eeetS,ANDE"1-OVOIDRATXO 3Gy/3GyO--A DIStl['ANCE ----------v-- 3 cftl                                  4 ciaFig. I. Illustration of the effect of placement of      the ovoid applicators 1 cm away from the      vaginal vault. The ovoid-to-A-point dls-      tance (O-A distance) is increased to 4 cm      instead of 3 cm. The 6 Gy isodose line in-      cluding the A-point extends inferiorly      (a}so sagitally and coronally) more than is      necessary. The rectal dose is therefore in-      creased.92 H. Ogata, G. Uchiyama, and H. OhnishiMETKoD  Buckler's afterloading system includes anIr-I92 sources with a tandem applicator andtwe Cs-137 sources with ovoid applicators (Fig.2). We usually draw a 6 Gy-Iine through theA-point (A-line) at every treatment.  In order to determine the extent of varia-tions, we reviewed reference X-ray films andmeasured the ovoid-te-A-point distance (O-Adistance) in 40 treatments. Most of the patientsunderweltt intracavitary irradiation 4 times in4 weeks (6 Gylfraction). The iRterpatient varia-tion and the treatment to £reatment intrapa-tient variation of O-A distance was then evalu-ated.  When Buchler's afterloading sys£em is }ised          rT"ANDEMnt   (A)Fig. 2.--- uterus ---OVOID----- vagma------ rectum                  (B)Diagrammatic representation of tandemand ovoid applicators.A) anterior view B) lateral viewfor the intracavitayy trea£ment of cervix caR-cer, the time necessary to obtain a certainirradiation dese at the A-point must beselected separately for the tandem source andfor the ovoid sources. Isodose patterns can bemodified by changing the relative contributionof the tandem source and to ovoid sources.Therefore, in the examinatioR of variations indose patterns, A-lines were drawn at varieusratio of tandem dose to ovoid dose at targetdelivery to the A-point of 6 Gy. A-lines withunsatisfactory ovoid applicator position werealso drawn to examiRe the limit of O-Adistance £hat could be corrected with thesimple procedure of varying the ratio oftandem dose to ovoid dese.REsuLT  Conciderable intertreatment variation of theisodose pattem was seen in censecutive 40treatments. Isodose curves iR treatments withshort and long O-A distaltce are illustrated inFig. 3. The evoid size was 2 cm diameter, andthe distance from the Cs-sources £o the topsurface of the ovoid was 1 cra. Therefore,when the ovoids were placed deep in both sidesof the vaginal portien of the uterus, the O-Adistance was very short. When the carcinomawas so large or the patient's vagina was sopoorly expandable that the ovoid applicatorAFig.     A A/- "" -･xA 2`IGy                                  t tN 1                                  l tN S                                 1' ti !1                                 - iA1             #le4824e // /./ Xx...L))'>N76Gy                               Ll 1                               iN Sr              lx    3 ts. -.. rT                               N .--.'-.-..-" 1                                st                           sl                           Nt             Nl                                  st           s-O-A 2.lcrn -"-"                                       O-A 2.1ctn                                   --u----- O-A 4crn3. Isodose curves in a treatment with short O-A distaRce of 2.1   cm (left) and with a rather long O-A distance of 4.0 cm (cen-   ter). On the right, the two sets of curves are superimposed to   show the effect on the rectal dose.'A4'82d1263O-A 4cmDose Optimization with Buchler's RALS 93(time)  15105Fig. 4.2,Or-2.5 2.5--3.0 3.0-･3.5 3.5--(cm)                     O-A distanceThe O-A distance measured on 40 refer-ence X-ray films varied from 2.0 to 4.3cm. The average distance was 2.8 cm. In40 percent of the treatments the distancewas more than 3 cm.O--Adiatance  (cm)    432iili ,r'FrXncould not be fixed deep eneugh, the O-Adistance was very long. The review of the 40reference X-ray films revea}ed that the O-Adistance varied frem 2.0 to 4.3 cm (Fig. 4), andFig. 5.                      (case)The interpatient variation of the averageO-A distance is ranged from 2.3 to 3.7.Intrapatient variation is indicated by thevertical line on each column. ORe patient(left column) showed only O.2 cm treat-ment variatioR, while aRother (6th col-umn from the left) showed 2.0 cm varia-tion. The average intrapatient variationwas O.8 cm.the average distance was 2.8 cm. In 40 percentofthe treatments, the distance was more than 3cm. Interpatieltt variation in the mean O-A1iil' ;illl "jtt /vi,L Nx'x..-.!'"x...-.  SS N  (A)  t --`t . .. - --      "7' Nlxi XX'       'ix         t'N         N, X,         ii          ,Ns          X, N,           'x Nl        - 'f Jtt         i-'  tt  B lt't4.sXll -~ NN  s.(B). . elN-       s".        N)lr.     . ,;I     : /f----'V'// / 7i-------!7/   O-ADISTANCE3crn O-ADISTANCE                                     3cm ---TANDEM/OVOID RATSO                                   3.5cm -----   2G.Y!,:8Y :" ,.. -   5Gyl1Gy --mu                             TANDEMIOVOgD RATgO 412GyFig. 6. A) A-lines fbr 3 different tandem-ovoid dose combinations at fixed       O-AdistaRce(3cm)areshown.Theyare3Gy13Gy( ),4Gy12Gy       (-----), and 5GyllGy (---).       B) A-lines for 3 different O-A distances at fixed tandem-ovoid dose       combination(4Gy12Gy).Theyare4cm( ),3.5cm(-----),and3       cm (---).94 H. Ogata, G. Uchiyama, and H. Ohnishidistance was evaluated in IO coltsecutive pa-tients (Fig. 5), in whom £he distance rangedfrom 2.3 to S.7 cm. IntertreatmeRt variation ofthe O-.AL distaRce in individual patient was alsostttdied; Ilt one patient, the variation was 2.0crR, while in another it was only e.2 cm. Theaverage variation was O.8 cm. Variations oftheA-line for3 different tandem-ovoid dose com-binations at fixed O--A distance are shown inFigure 6-A. They show variation in widthabove and below the A-point. Variations of theA-line for 3 different ovoid positions at fixedtandem--ovoid dose are shown in Figure 6-B.They swell eu£ in the lower region below theA-point as the O-A distance increases.               DIscussloN  In conventional RALS systems, Co-60 areused for tandem aRd ovoid sources, whileBuchler's system in our department is equip-ped with two types ofsources, which are Ir-192and Cs-137. The activities of these sources areguite different, and the irradiation time shouldbe selected accordingly. Furthermore, as theIr-}92 source is rather recently developedsource, dose optimization for this system is stillunder development.  We used irradiation ef 3 Gy from thetandem source and 3 Gy from the ovoidsource$ for a total A-point dose of 6 Gy. If theovoid seurces were placed apart frora theuterinc orifice, the time necessary to irradiate 3Gy from ovoid sources had to be increased,resulting increse ofthe rec£al dose. Even underthis condition, by varying the tandem-ovoiddose ratio, we can reduce the rectai dose andkeep the A-peint line at almost the same targetzone. This procedure is effective when theovoid sources are placed not more than 1 cmfrom the uterine orifice. In one patient, theintertreatment variation of the O-A distancewas 2 cm.In such a case, it may be necessary toapply 3nother tandem-ovoid assemb}y pattemor to rearrange the applicators. However theaverage iRtra-patient variation in the O-Adistance variatioit was ra£her small. Therefore,in most patients, the dose distribution inindividual treatments could be well correctedby selecting the appropriate £aftdem-evoiddose ratio.  We are no£ certain whether the specificisodose pattern of 3 Gy/ 3 Gy we used is thebest pattern for basic treatment. Some authorshave suggested the use of isodose pattemssimilar to those in low dose-rate irradiation asManchester's method, which we fbrmerlyroutinely app}iediua3). The A-lines of thesepatterns reughly correspond to 4 Gy/ 2 Gypattern. However we are certain that the basicmethod of selecting the optimal dose distribu-tion fbr each patient and for each pattem ofcarcmoma lnvaslon ls a super!or treatmentrnethod. Buchler's afterloading system offersversatility in terms of producing many dosedistributien patterns using program diskswhich oscillate the tandem source in theapplicator. Furthermore, when we used va-rious dose combina£ions from the tandem andovoid sources, we were able not en}y to reducethe rectal dose in £he event of less than idealplacement of the ovoid applicator, but also toselect more suitable dose distrib}.itions fer eachtreatment (Fig. 7),  All of these patients showed complete remis-sion after the £reatment. Hewever the follow-up period has not been long enough toevaluate the late side effects, because late sideeffect of rectal iajuries needs several years tocome eut. We believe that decreasing the rectaldose by modifying the dese distribution is animportant procedure in avoiding rectal in-.. "    tanderp 5Gy tandern 3Gy    ovold IGy ovoid 3GyKg. 7. Examples ofselection ofdose djstribution      pattern according to tumor extension.Dose Optimization with Buchler's RALS 95juriesin the intracavitary irradiatioR ofcervicalcancer.  The dose distributiofl in each treatrnent callbe optimized by use of a computer system inwhich target coitfiguration is input en ananatomical image disp}ayed on a CRT, such asthat for MRI. After the applicators are fixedand the reference X-ray data input, the com-puter generates optimized information andthe final parameters necessary for irradiatien,such as the irradiation time for each applica-tor, or generates instructions regarding rear-rangement of the applicators.CONCLUSION  The use ofvarious taRdem-ovoid dose ratiosiR the intracavitary treatment of cervical carci-Roma using Buchler's af£erleading system wasexamined. By this way, we were able £o obtainthe optimal dose distribution for individualtreatments. Using this technique, we couldmodify the isodose curves to minimize increaseof the rectal dose produced by increase of thedistance of the ovoid applicaters from thevaginal vaults.REFERENCES1) O'ConnellD,JoslinCAF,HowardN,etal.The   Treatment of Uterine Carcinoma Using the   Cathetron. Part 1, Brit J Radiol l967; 4e:   882-887.2) TabushiK,ItohS,SakuraM,etal.:Automated   Calculatioxx ofOptimum Dose Distribution and   Irradiation Condition for Intracavitary Treat-   ment of Uterine Carcinoma. NippoR Acta   Radiol, }972; 32: 669---682.3) Sakata S, Sutoh S, Nakano M, et al.: A Consid-   eration of Distributions and Trea£ment Sche-   dules in }-Ilgh-Dose-Rate Intracavitary Ther-   apy of Carcinoma of the Uterine Cervix.   Nippon Acta Radiol l979; 39: 727-736.

<Original Article> Optimization of Dose Distribution in Intracavitary Treatment of Cervical Cancer with Buchler's Afterloading System

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<Original Article> Optimization of Dose Distribution in Intracavitary Treatment of Cervical Cancer with Buchler's Afterloading System

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