6th European ALARA Network Workshop Madrid, oct. 23rd 2002 Radiation Protection in the commissioning and in the use of a IORT-dedicated mobile linac Giampiero Tosi - Mario Ciocca Department of Medical Physics European Institute of Oncology Milano - Italy

WHAT IS MEANT BY INTRA-OPERATIVE RADIOTHERAPY? IORT By intra-operative radiotherapy (IORT) is meant a radiotherapeutical treatment performed in the course of a surgical intervention, with administration of a single dose

WHICH TYPE OF EQUIPMENT CAN BE USED TO PERFORM IORT-TREATMENTS? CONVENTIONAL LINAC (electron beams: 4 - 15 MeV) CONVENTIONAL LINAC INSTALLED IN A “DEDICATED” BUNKER MOBILE “DEDICATED” LINACS (electron beams: 4-15 MeV) AFTER-REMOTE-LOADING BRACHYTHERAPY UNITS (HDR - 192Ir) ORTHOVOLTAGE X-RAY EQUIPMENT (140 - 250 kV)

THE THREE CHOICES 1 2 3 PATIENT IN GENERAL ANAESTHESIA CONVENTIONAL BUNKER 1 “DEDICATED” BUNKER LINAC + O.R. 2 RADIATION SOURCE CONVENTIONAL OPERATING ROOM 3

ADVANTAGES / DISADVANTAGES OF THE THREE CHOICES 1 - OPTIMUM QUALITY OF THE IORT, BUT - RISKS FOR THE PATIENT (INFECTION - EXTENSION OF THE TIME LENGTH OF ANAESTHESIA) - EXTREMELY LOW THROUGHPUT 2 - OPTIMUM OVERALL QUALITY, BUT - LOW THROUGHPUT - EXTREMELY HIGH COSTS 3 - THE BEST COMPROMISE (VERY GOOD QUALITY OF OF THE IORT), BUT - RADIATION PROTECTION PROBLEMS

NOVAC 7* is a IORT-dedicated mobile linear accelerator of electrons It can be employed directly in a “conventional” O.R. It can be easily moved and blocked inside the O.R. It can produce pulsed electron beams (2 - 9 cGy/pulse) of 4 different nominal energies: 3, 5, 7, 9 MeV In order to employ such a linac in conditions of safety, both for the patients and for the staff, the following points must be taken into consideration: RADIATION SAFETY acceptance test for the evaluation of the real performances quality control program * Manufactured by Hitesys, Aprilia, It

MOBILITY The linac NOVAC 7 is mounted in a structure that can easily be moved inside the operating room and brought very slowly near the operating table; an arrow indicates the direction of the displacement

AZIMUTH ROTATION OF  45° AROUND A VERTICAL AXIS - 45° + 45°

DISPLACEMENT IN THE VERTICAL PLANE IN THE RANGE - 30° / +60° - 30° + 60°

INCLINATION OF THE RADIANTING HEAD IN THE RANGE  45° + 45° - 45°

ROTATION OF THE HEAD IN THE RANGE  45° - 45° + 45°

Available plane (0°) and bevelled (22.5° and 45°) applicators 0° 22.5° 45°

Actual energy of the beams evaluated on the basis of depth dose curve in water and on range-energy relationship:

Depth-dose curves measured in a water phantom with small diodes

STRAY RADIATION The linac produces a small amount of stray radiation,that can easily be shielded The main source of such radiation is the patient, who behaves as a “target” for the electron beam, that loses a small percentage of its energy (0.3 - 0.5%) as braking radiation

A sort of cloud of electrons is produced around the applicators; the mean energy of such electrons is very low, so that it is sufficient to use some mobile barriers, properly designed, to completely confine such radiation inside the operating room.

Both the intensity and the energy of the braking and scattered radiation produced by the patient’s tissues depend on the angle with respect to the axis of the electron beam. The intensity can be reduced to very low and safe values by means of a “beam stopper” (15 cm Pb) in the direction of the beam and by 3 mobile barriers of variable thickness of lead (0.51.5 cm) placed around the operating table 4.0 MeV X Rays 2.0 MeV X Rays 3.5 MeV X Rays 2.5 MeV X Rays 1.5 MeV X Rays

ANGULAR DEPENDENCE OF THE BRAKING RADIATION AND CORRESPONDING TVL IN Pb

THE MOBILE LINAC FORT IORT IN THE O.R. Mobile barrier Phantom Beam stopper

MOBILE BARRIER

Environmental dosimetry * : restricted areas during irradiation 15 : mobile barriers 35* 50* * : restricted areas during irradiation 50 O.R. Adjacent O.R. Beam stopper 10 25 50* Area 1.st floor below OR: 20 Novac7 30 80* 35 25 10 50 50 Control panel 5 25 10 Stray radiation outside the operating room (OR- 2.nd floor) (air kerma rates expressed in Gy/hour)

“RULES” OF RADIATION PROTECTION AND CLASSIFICATION OF THE AREAS AND OF THE PERSONNEL The O.R. is classified as controlled area only during the emission of the beam During the irradiation of the patient (that takes less tha 2 min) all the personnel (included the anaesthetist) leaves the O.R. During the first six months of activity, all the personnel was monitored with film-badges and TLD: nobody received an effective dose > 100 Sv Before starting the emission, a series of warnings is activated All the personnel, unless otherwise classified for other activities, is classified as not exposed worker

CONCLUSIONS - 1 Although the utilisation of Novac7 in clinical practice is still limited to a few Centres in Europe (high cost), the interest is increasing. Great emphasis to mobile dedicated facilities is given in the Report on QA in IORT in preparation by a Task Group of Italian Health Institute “Istituto Superiore di Sanità”. Based on our 2-year experience (more than 200 patients treated), Novac7 appears suitable for routine clinical use in terms of reliability and performance stability.

CONCLUSIONS - 2 Radiation protection: Novac7 can safely work in an existing OR, simply using a “beam stopper” and mobile barriers. Air kerma rates measured in the areas around and underlying the OR are compatible with a workload of about 400 treatments per year at 20 Gy/treatment, calibration and QA procedures included. All the personnell of the O.R (surgeons, anaesthetist, nurses etc.) can be classified as not exposed workers