[Image guidance for the evaluation of setup accuracy]

[Partial delegation to radiation therapists of the control by cone beam CT of prostate positioning]

PURPOSE

Intensity modulated radiotherapy for prostate cancer involves daily monitoring of the positioning of the prostate, possible with cone beam CT (CBCT). It allows increased accuracy compared to readjustments but induces an increase in the time dedicated to these medical checks. The aim of the study was to evaluate the possibility of delegation of this task to the radiation therapists by comparing their readjustments to the doctors.

PATIENTS AND METHODS

Five consecutive patients treated with radiation for prostate cancer (76Gy) were analysed. All had a daily CBCT for position control. The movements of the prostate relative to the bony part, the positional variations of the prostate measured by the radiation therapists and the doctors and medical time required to analyse imagery (filling of the rectum and bladder and perform a recalibration) were measured.

RESULTS

One hundred seventy-six CBCT were analysed or 980 steps in the three axes. The movements of the prostate relative to bony part were respectively at least 5mm in 19%, 7% and 3% in the anterior-posterior, upper-lower and right-left axes. Changes readjustments between radiation therapists and doctors were in 95% of cases at the most 4mm in the anterior-posterior and upper-lower axis, and 3mm in the left-right axis. The time for medical use of the CBCT averaged 8min 40 [4 to 22min].

CONCLUSION

The daily readjustment on the prostate using CBCT may be delegated to radiation therapists with acceptable concordance of less than 4mm for 95% of measurements. An initial and ongoing training will ensure treatment safety.

[Interobserver variability study for daily cone beam computed tomography registration of prostate volumetric modulated arc therapy]

PURPOSE

This work evaluated the interobserver variability in cone beam computed tomography (CBCT) registration for prostate cancers treated with intensity-modulated radiotherapy.

MATERIAL AND METHODS

Twelve technologists realized 286 CBCT/CT registrations (bone registration followed by prostate to prostate registration). The registration results were compared to those obtained by two radiation oncologists (reference). Each technologist reported the shifts calculated by the software in all three axes. A statistical analysis allowed us to calculate the minimum threshold under which 95% of the observers found similar values. A variance analysis followed by the post hoc test were used to find differences in interobserver registration variability and determine whether any individual users performed registrations which differed significantly from those of the other users.

RESULTS

The registration differences compared to the reference in the three directions in terms of 95th percentile are: 2.1mm left-right, 3.5mm target-gun, 7.3mm anterior-posterior. In the posterior direction, 4% of the observers have found differences superior to 8mm, margin used in routine without the use of a daily CBCT. The variance test revealed a P-value <0.05 only for target-gun and for all observers there was no significant difference compared to the reference.

CONCLUSION

This study confirmed the interest of a 3D tissue registration for prostate treatments. The registration study showed a good interobserver reproducibility. This showed the importance of a daily CBCT/CT registration in prostate treatment with the possibility of a planning target volume margin reduction in the three directions. An evaluation of a partial delegation of registration to technologists should be done by the radiation oncologists.

[Evaluation and choice of imaging protocols on the Elekta XVI(®) kilovoltage cone-beam computed tomography imaging system]

PURPOSE

This work proposes an evaluation of the Elekta XVI(®) kilovoltage cone-beam computed tomography imaging system. The average dose delivered for each acquisition protocol proposed by default by the manufacturer was measured with several detectors and compared to theoretical dose values given by Elekta. At the same time, an evaluation of image quality for pelvic protocols correlated to dose measurements in homogeneous and heterogeneous mediums allowed to optimize the use of the XVI(®) system.

MATERIALS AND METHODS

The dose was measured for each acquisition protocol (varying filters, FOV and collimations) with four detectors (CT pencil ion chamber, 0.3 and 0.125 cm(3) cylindrical ion chambers, radiothermoluminescent dosimeters) in a CTDI phantom. The dose evaluation in a heterogeneous medium was performed in an experimental anthropomorphic phantom simulating a male pelvis. Image quality was assessed with a Catphan(®) 600 phantom.

RESULTS

The average dose measured in a homogeneous medium was about 17 mGy and 25 mGy per acquisition for Pelvis and Prostate protocols and about 17 mGy and 1 mGy for Lung and Head protocols. The study performed with different detectors showed that doses obtained were of the same order of magnitude (± 10 %) and agreed with those supplied by the manufacturer. The evaluation of image quality correlated to the average dose measured allowed to optimize the use of XVI(®) acquisition protocols. Measurement results in a heterogeneous medium showed a dose decrease by a factor 1.5 for bone and by a factor 2 for titanium.

CONCLUSION

The study showed that theoretical values proposed by the manufacturer could be used to estimate the average dose delivered to the patient by the kV-CBCT imaging system. The analysis of all the results led to the implementation of a procedure allowing to optimize and account for the dose delivered to the patient by the CBCT imaging system and to report it in the patient folder.

[Image-guided radiotherapy and partial delegation to radiotherapy technicians: Clermont-Ferrand experience]

The various image-guided radiotherapy techniques raise the question of how to achieve the control of patient positioning before irradiation session and sharing of tasks between radiation oncologists and radiotherapy technicians. We have put in place procedures and operating methods to make a partial delegation of tasks to radiotherapy technicians and secure the process in three situations: control by orthogonal kV imaging (kV-kV) of bony landmarks, control by kV-kV imaging of intraprostatic fiducial goldmarkers and control by cone beam CT (CBCT) imaging for prostate cancer. Significant medical overtime is required to control these three IGRT techniques. Because of their competence in imaging, these daily controls can be delegated to radiotherapy technicians. However, to secure the process, initial training and regular evaluation are essential. The analysis of the comparison of the use of kV/kV on bone structures allowed us to achieve a partial delegation of control to radiotherapy technicians. Controlling the positioning of the prostate through the use and automatic registration of fiducial goldmarkers allows better tracking of the prostate and can be easily delegated to radiotherapy technicians. The analysis of the use of daily cone beam CT for patients treated with intensity modulated irradiation is underway, and a comparison of practices between radiotherapy technicians and radiation oncologists is ongoing to know if a partial delegation of this control is possible.

[Task sharing with radiotherapy technicians in image-guided radiotherapy]

The development of accelerators with on-board imaging systems now allows better target volumes reset at the time of irradiation (image-guided radiotherapy [IGRT]). However, these technological advances in the control of repositioning led to a multiplication of tasks for each actor in radiotherapy and increase the time available for the treatment, whether for radiotherapy technicians or radiation oncologists. As there is currently no explicit regulatory framework governing the use of IGRT, some institutional experiments show that a transfer is possible between radiation oncologists and radiotherapy technicians for on-line verification of image positioning. Initial training for every technical and drafting procedures within institutions will improve audit quality by reducing interindividual variability.