14 CT Planning of HDR-implants in definitive irradiation of the breast

s25 14

13 CT-SCAN CANCER

BASED

BRACHYTHERAPY

PLANNING

FOR

HEAD

AND

CT PLANNlNG OF HDR - IMPLANTS IN DEFINITIVE

NECK

IRRADIATION OF THE BREAST

C.G.J.H. NiCl , I.K.K. Kolkman-Deurloo, Levendag, Dr. Daniel den Hoed Cancer The Netherlands.

P.C.M. Nowak, P.C. Clinic, Rotterdam,

SEEWALDD.H.,HA&EVERJ.. ZOIDL J.P., TRACK Ch., PUTZ E Institut of Radiation Oncology,

Sisters of Mercy Hospital, Linz, Austria. Relating the dose distribution of an implant to the target as well as to the surrounding normal tissues is not possible in an accurate way by interpreting (orthogonal) X-ray films. Dose prescription in brachytherapy is therefore mainly related to the implant (e.g. as in the Paris system for breast implants) or to the applicator (e.g. as in the Manchester system for cervical cancer). This warrants more or less uniformity in dose prescription; however, it remains difficult to draw conclusions regarding the adequacy of brachytherapy in terms of the obtained target dose and the dose delivered to normal tissues. This is in sheer contrast to external beam radiation where first a target is defined on CT scan, the dose distribution is "shaped" by and. subsequently, the use of a treatment planning computer in order to obtain maximal target irradiation with minimal irradiation of surrounding normal tissue. We therefore developped a non-invasive external localization frame to be used in tumors located in the brain or in the head and neck region in order to match the (orthogonal) X-ray films with a CT-scan visualization of the target and the surrounding critical structures. This method results in a planning procedure of the dose distribution which is (as in external beam therapy) target related. Due to the possibility of optimizition in pulsed dose rate as well as in high dose rate brachytherapy, an optimal dose distribution can be achieved within the geometrical limits of the implant. The procedure also allows for an accurate evaluation of the dose in surrourding critical structures. Furthermore new criteria can be developped to evaluate the quality of an implant. A high dose rate application with a nasopharyngeal mould is worked out as an example.

Conservative surgery and following radiation therapy has become a standard treatment in the management of early breast cancer. The use of a boost irradiation in the area of the primary tumour seems to be promising in decreasing the local recurrence rates. Since 1984 more than 500 patients with carcinoma of the breast have been treated with radiation therapy. Most of the patients have received a boost dose by interstitial HDR Iridium 192 therapy. There are some reports about localization techniques of the boost volume for external irradiation. Less has been reported about the target volume localization of HDR interstitial implants of the breast. Therefore we have improved the method of the interstitial

implantation

by CT planning under

anesthesia. The implant is planned in the simulator room by localizing the radiopaque clips of the tumor bed, the projection of the clips to the skin is determined. Then the implantation is done in the afterloading room. A device for patient transportation

between Iridium unit,

simulator and CT has been constructed. The implanted needles and the clips are visualized by means of CT-scan and the target volume can be defined and documented This method improves the accuracy of targetlocalization.

Therefore the treated volume can be adapted

and

minimized, resulting in less side effects and may contribute to maximize local control.

15 A QUALITY ASSURANCE PROGRAM AFTERLOADING SYSTEMS.

FOR HDR - REMOTE

G.F. Stuecklschweiger, H. Leitner, E. Poier, B. Zurl, B. Pakisch, A. Ha&l. Department of Radiology, Division of Radiotherapy, Gnu, Austria. The recent application to high dose rate afterloading demonstmtes the extreme importance to perform adequate quality control checks. At the Division of Radiotherapy

in Graz an Ir-192 HDR micro-

selectron

remote

machine

calibration

is carried out when the source is changed every three

afterloading

is

installed.

A

full

months. A set of quality control checks and tests should be made at that time or on either a daily, weekly or monthly basis.

16 SOME PHYSICAL AND TECHNICAL ASPECTS OF SELEC TRON LDR/MDR QIJALITY ASSURANCE.

The daily checks include the radiation warning light, emergency stop and a control operation

of the device.

Also we check the

inhibition of the exposure of the source if the treatment room doors are open. Once a week we check the timer by comparison with an independent reproducibility

timer (accuracy

and linearity).

The accuracy

and

of the source positioning will be checked 3-monthly

If a new source is installed we measure the air lcerma in air and water in a special calibration phantom too. The mean ratio of the

by autoradiography

relationship measurements

between

for all applicators

the air

kerma

used in our division.

rates

derived

and those of the test certificate

from

our

is 1.034 (range:

0.944 - 1.076). Once a year a wipe test is carried out additionally.

Matache, Gh. Central Military Hospital, Bucharest - Romania Selectron LDR/MDR with 40 mCi spherical Caesium-137 sources was installed in Central Military Hospital from Bucharest in 1993. Initially a formal acceptance test was undertaken to evaluate the safety, mechanical and electronic features of the system. Verification of the Caesium-137 sources activities was made at that time, and the autoradiograph technique was used to test the programmed source/spacers sequencing also. It tested the radiographic system for reconstruction and the treatment planning system. A program was established for Periodic tests, the method to be used and the frequency. The paper contains the results of the first acceptance test, our own Quality Assurance Program, related to our present facilities.