90 Linear-quadratic model: Aplication software

S23

90

a9

LINEAR-QIIADRATIC

MATHEMATlCALSIMllLATION OF BIOLOGICALL\’ EQlIl\‘ALENT DOSES FOR LDR-HDR

Centre of Oncolog>

h Slosarek. A .?JUSZ M Sklodowska-Cone Memorial Poland

Institute.

examples of the

are time

presented of repair

accelerated repopulation The calculations btologically

with the use of different of sublethal datnages attd

performed

equivalent

doses

show.

can

be

that

obtained

the for

came diflerem

parameters of cell hinetics changes during radiation treatmettt It also show. that during btologically eqmvaleat dose calculations for different radmtherapy schedules. ignorance of cell kmetics parameters

can lead to relevant

APLICATION

SOFTWARE

Victor J. Bourel. Isabel Rodriguez, Marcels de la Terre Braqui - Buenos Aires, Argentina

Ghwce

Based on the LQ model examples of btolotically equivalent doses LDR HDR and evtemal beams were calculated. The biologically equivalent doses for LDR were calculated by appending to the LQ model the corrector for the time of repair of radiation sublethal damages For radiation cominously delivered at a low dose rate the influence of sublethal damage repair time changes on hmlogically equivalent doses were analysed For fi-actionated treatment wth high dose rate the biologicall\ equivalent doses \rere calculated by addinig to the LQ model the formula of accelerated repopttlat8on For total biolo@call> equivalent dose calculation for combine LDR-HDR-Tele madiation parameters

MODEL:

et~ors

Introduction: Radiobxolog? finds m the linear-quadratic model the most appropiate tool to support radiotherapy m outhmng and comparing trcatmcnt schemes Smce the mcreasing complexit? of tbc model makes It lmposible its global deahng through tables. It has been developed a sofmarc that allow to compare fractlonatton schemes or to find cquivalcnt schemes even among different treabncmt modalities such us external radtothcrap?. LDR brach?therapy and HDR brachythcrapy. Material and Methods: This software has bwn developed m the window cm xomcnt wch makes It easy to use and lets it be run in simple 386 compatibles cqutptncnts or modem ones In this software has been incorporated all the cquatlons of the bnearquadratic model wch are no!\ nldcl! known and accepted due to thclr utiliQ Results and discussion: The Linear-Quadratr model adjust cell surwal curves more efficiently than earher models and its contmual evolutton has alloned for the effects such as the cell rcpainng during continuous prolonged Irradiation (LDR Brach!therapy). the dlffcrencc bctwcn the important in tumoral and normal tissue repau time (h@l> hrpcrfractlonatlon). the modrficatlon of the tumoral groxkth rate aficr weks of treatment. etc. to be mcorporated m their mathematical form No\\ada!s. man! dlffcrcnt authors keep on Improving the model mcorporatmg m It all the fcnomcna that arc mvolved in a radiation treatment Conclusion: The dcslgncd soft\xarc has proved to bc vev easy to use and cfflclent since It constdcrs all the radiobiological parameters of the different tissues (normal and tumoral) uwolved in the treatment so as to asscs not onI? the probablhty of tumoral control but also the morbrhty of the dlffercnt compared and designed schemes

91

92

HDR BRACHYTHERAPJ’ ANNEALING COUPIXD

OPTIhlI%ATIOS USING SIMULATED \\ ITH A GKADII-VT TECHNIQUE.

THE CALCULATION OF ISODOSE PARAMETERS FOR T&E’S APPLICATOR IN GYNECOLOGYCAL BRACHYfHERWY

D. Salhani’,

A. LI’ H.Yang

Physics’ Ottawa.

Several

L. Grmlard’.

and Radiation Oncology~.O~raua Ontario, CANADA.

algorithms

Dcpartmen~

Regional

Cancer

Cemrc.

to

optimize dose distrihutlons by determining the source po\itwn\ dwell time& to minimize user-defined objective functions. The

and

objective

functions and clinical

annealing

employed

arc constrained

prercquihites.

methodology

for HDR

01

Brachythcrapy

criptions

have been devclopcd

J. Oldel’.

(SA).

We pre5ent

applied

by physician

prc\-

a modified

\imul;wd

to achieve

optimal

dl\trihutions for homr climcal situtions. The SA 15 coupled wth a down-hill senplcx (gradient) tcchniquc to handle dew gradient more efficiently.

The gradlent

technique

This

computiry

methodology

tmx

a> 25% over

flexibility structures

with regard to a defined hyperdose \Icc\c. dorc outside the target volume. and dose homogcncity

the target compared

SA alone.

reduces

ah much

alhws

hy great IO crItical wthin

volume. Results from the aforcmcntioncd algorithm\ IO dlhtrlbutions generated usrnp the Nuclcrron

optimization algonthms’( regressional analy&). System. Breast. anal canal. and ncLwpharynfcnl are presented, comparing the three dohlmctrlc optimization methodology used for routine clinical

is at prcsertt application.

under

arc

and the Pari\ implani di\trlhution\ appronchc\ l‘hih

developmcm

and I\ not

Kernlkler G.. Asia) I.. Tunwl Tore G istanbul University Oncolog\

N.. Yalcm S D&I Institute.

istanbul.

R &bay

I.. Dincer M

TURKWE

The role of intracawtar) wraQation in the treatment of uterine cervix carcinoma is well established and over yars a number of different system for mtracavitary irraQation have been developed. The ICRU Report 38 recommends the use of reference volume doses and reference volumes for the reponmg of intracavitary gynecologic therap. The dimensions chosen as representatives of this volume are the overall height(hm). maximum wdth(l). maldmum lhickness(e). width(l’). and the thickness(e’) at the level of upper I13 of the uterine catheter. In this stady we presented the calculation of the isodose uarameters for T&E’s micator. which was developed at the Univ&sity of istanbulOnc&gy Institute. in gynecological brachytherapy. The radioactive source was LDR Ir”’ ;length of vagrnal sowces(v) was fixed and 2 cm.. the &stances hehxen vaginal sources were 2. 3 and 4 cm. In thirty-eight applications. the dimensions of isodoses produced by the computer were measarred and calculated with Bridier‘s (Inst Gustave Roussy) formulas. “hm. 1. I’. e’ dimension values” were found to be I” agreement with those achieved from computer calculations to within an absolute median error of about Zmm However. for the parameter “e” absolute median error was 9.28mm. therefore a new formula uils &veloped for the manual calculation of this parameter. The means of the dtmensions of i&w wth T&E‘s Awlicator were found to be hm 86.46~13.91mm. 1, 58:i6*5.53mm. I’. 32.78f4.67mm. e’ 38.63f5.55mm and e’: 32 5f40.66mm. In these applications the mean dose rate for the bladder was 22 8? 9 04 &y/h and 22 2Sti6.65 cGy/h for the rectum. The mean dose rate was 33.29+5.5&y/b for the reference isodose. 32.87fi.55 cGy% for nght pomt A and 311SfS.63 cG>ih for the left [so&se parameters of our applicator were swtable to treat cerw carcinoma convenientI? with brach>therap. On the other hand. manual calculauon of the is&se parameters was also possible.