Development of a hardware-software system for dynamic irradiation for the proton beam radiotherapy

Development of a hardware-software system for dynamic irradiation

for the proton beam radiotherapy.

A. Agapov

Medico-Technical Complex of DLNP, JINR

Abstract

The present technique of 3D conformal proton radiotherapy realized at the Medico-Technical Complex of JINR for irradiation of tumours seated in the vicinity of radiosensitive vitals provides great precision in dose delivery. But the actual proton treatments can not always be perfect in terms of the best possible dose distribution. One of the major limitations in the static proton irradiation technique using a range-modulation device such as a ridge filter or a propeller is that a fixed width of the spread-out Bragg peak (SOBP) has to cover the irregular 3D target volume. Therefore, it is usually inevitable for the fixed SOBP to extend to healthy tissues. A method of dynamic proton beam irradiation (or a layer-stacking method) was proposed to resolve this problem by producing a variable SOBP of the wide proton beam without requiring a drastic modification of the already existing beam delivery system.

In the layer-stacking method, a target volume is virtually divided into relatively thin layers in the depth direction. Each individual layer is irradiated with a common non-modified proton beam with the thin Bragg peak of the specific range and with the conformal profile of the beam.

In order to deliver the sequence of irradiations automatically as a dynamic method, the hardware-software system is under development at the Medico-Technical Complex. The system will consist of several devices such as the computer controlled range shifter and multileaf collimator. The range shifter will change the energy of the wide proton beam step-by-step and the multileaf collimator will change the aperture of the beam automatically according to the current energy.

The hardware-software system will provide an option for improved conformal radiotherapy without interfering with the existing technique and we expect the commissioning of the dynamic delivery system in the near future.

Development of 3D treatment planning system for conformal radiotherapy

Medico-Technical Complex of DLNP, JINR

Abstract

Introduction

The technique of three-dimensional conformal proton radiotherapy was realized in the Medico-Technical Complex (MTC) of the Joint Institute for Nuclear Research. Today this method is using for irradiation of deep seated tumors of different localizations. The 3D conformal proton therapy is impossible without precise computer planning. A treatment planning system (TPS) called “TPN” elaborated in the first hospital based proton therapy center in Loma-Linda, USA, is used for this purpose in the MTC. Unfortunately, this program cannot be modified for new techniques of irradiation. So, the new version of TPS is under development now.

Methods and results

The simple patient database was developed for the program. This database is necessary for optimal storage of data and for administration. Program works with a list of treating patients. Each patient has an individual directory that holds its data such as CT images and tissue region descriptions. Each patient may have a number of alternative treatment plans (prescriptions) for comparative evaluation.

Input data for the program is the data obtained from an X-ray computer tomograph. This data are presented in program as a three-dimensional array. CT images are displayed in full 512 x 512-pixel resolution.

The program includes developed graphical editor which allows one to draw anatomical structures on axial slices. Graphical editor has the following functions: 1) automatically closing contour; 2) correction of intersections; 3) editing of drawing structure; 4) calculation of an external contour; 5) constructing sections of drawing structures in sagittal and coronal planes.

Each treatment plan contains one or more sub-plans (treatment prescriptions). Prescriptions divide the plan into one or more beam groups such as a sub-plan for appli­cation of a treatment boost. A prescription specifies the dose and fractionation schedule, the location of a point where all beams assigned to the prescription isocenter. After a physician (or a planner) sets the angle of irradiation, the program automatically calculates beam’s-eye-view projection of a selected structure. Then the program calculates and draws a contour of a proton beam collimator. This contour may be edited manually by user.

Conclusions

For today the program is working in the test mode. Recently a pencil beam algorithm for calculation of the proton beam 3D dose distribution elaborated in our group was incorporated into the program. Now this algorithm passes the optimization process. Another algorithm for visualization of calculated data on tomograms is under development. Also an extended user interface is creating for the program.

Verification of Patient Positioning in Proton Therapy Based on Digital X-ray Images

K. N. Shipulin

Medico-Technical Complex of DLNP, JINR

Abstract

Purpose

To conduct the verification of the target position relative to the proton beam, a digital X-ray imaging apparatus by Konica Minolta Company has been installed at the Medico–Technical Complex of the JINR. This method is applied instead of the old one based on the conventional X-ray films.

Methods

This method presents the superposition of the X-ray image which is taken by the X-ray tube and the digitizer immediately before the therapeutic irradiation, with a digital reconstructed radiogram (DRR) calculated from the slices of the X-ray computer tomography. The application of this new technique allowed us to short the time necessary for the preparation of the proton beam irradiation.

There are two stages to define the necessary correction of the patient position before irradiation. First one: the corresponding DRR of the patient is printed out before the beginning of treatment sessions. Then the DRR contours are drawn out on a transparent film (for example, the bonny structures of the skull) and the proton beam aperture as well. Also the target isocentre is marked at the DRR that defines the position of the beam axis relative to the patient on the transparent film.

Second one: the digital X-ray image is loaded and displayed on the screen immediately before the therapeutic irradiation. Then the transparent film of the DRR is put on the screen. The drawn contour on the transparent film is superimposed onto the X-ray image at the monitor (superposition for the bone structures of the skull).

After the superposition, the distance of misalignment is measured from the center cross of the digital X-ray image to the target isocentre of the transparent film. Then the position of the patient is corrected with a help of a therapeutic armchair driving gears and the proton irradiation is started.

Results

Production of the digital X-ray image by digitizer REGIUS170 of Konica Minolta Company takes 20 seconds. With the old method with the conventional X-ray films, the image was processed during 3 minutes.

The application of the developed program together with the digital X-ray imaging technique allowed us to reduce the verification time to one minute.

Therefore, we can increase approximately 1.5 times the number of patients treated at the Medico–Technical Complex.

Conclusions

The developed program is the first version. In this version the superposition process can’t be carried out without an operator. The next version of the program is creating now and it will have a function for the automatic superposition of the two images.