[Image-guided and adaptive radiotherapy]

Prospective medical analysis of radiation therapist image repositioning during image-guided radiotherapy

PURPOSE

Radiation oncologists are responsible for deciding which day-to-day variations are acceptable or not in the treatment setup. However, properly qualified and trained radiation therapists might be capable to perform image registration. We evaluated in our centre the capability and accuracy of radiation therapists to validate positioning images in a prospective study.

METHODS AND PATIENTS

A total of 84 patients treated for prostate, head and neck, lung or breast cancer was prospectively and randomly included from July 2011 to July 2013 in radiotherapy unit of our institution. For each patient, three positioning images were randomly analysed. Two radiation oncologists analysed all positioning images and shifts decided by the radiation therapists in an independent and blinded way. The radiation oncologists had to decide whether to validate or not this shift and give a corresponding additional shift, if any. A theoretical disagreement rate less than 5% between radiation therapists and radiation oncologists was planned.

RESULTS

A total of 240 images were analysed (head and neck: 15.0%; prostate: 14.2%; breast: 55.0%; lung: 15.8%). The global disagreement between radiation oncologists and radiation therapists for all the images analysed was 2.5% 95% confidence interval (95% CI) [1.0-5.0], corresponding to six images out of 240. A 100% agreement was reached for prostate and lung images, a 97.2% agreement for head and neck images and a 96.2% agreement for breast images.

CONCLUSIONS

The radiation therapist validation for repositioning images seemed accurate for image-guided radiotherapy in our institution. Periodic evaluation and in-house training are warranted when routine delegation of image registration to radiation therapists is considered.

[Intraprostatic calcifications as natural fiducial markers in image-guided radiotherapy for prostate cancer]

PURPOSE

To establish whether intraprostatic calcifications can serve as natural fiducials for image-guided radiotherapy (IGRT), replacing the implantation of intraprostatic fiducial markers.

PATIENTS AND METHODS

Patients with prostate cancer, having intraprostatic calcifications visible on CT scan were selected and underwent intensity-modulated radiotherapy/3D conformal radiotherapy with IGRT in the department of radiotherapy of Henri-Mondor Hospital. All cone-beam computed tomographies (CBCT) were repositioned on intraprostatic calcifications. For each acquired image, displacements of intraprostatic calcifications were calculated with reference to position on planning CT in three directions: lateral, longitudinal and vertical.

RESULTS

Between 2011 and 2013, nine patients had 183 CBCT. For each image, three displacements and space coordinates were calculated using a single reference (intraprostatic calcification). Mean lateral, longitudinal and vertical movements were 0.26±5.7 mm, -1±4.6 mm and 0.42±3.5 mm, respectively.

CONCLUSION

Studies exploring prostatic movements with fiducial markers as reference and ours with natural fiducials yield similar results. Our data confirm previous studies that have suggested that intraprostatic calcifications can be used as natural fiducials with potential reduction of iatrogenic risks and costs associated with the implantation of fiducial markers.

The potential role of magnetic resonance spectroscopy in image-guided radiotherapy

Magnetic resonance spectroscopy (MRS) is a non-invasive technique to detect metabolites within the normal and tumoral tissues. The ability of MRS to diagnose areas of high metabolic activity linked to tumor cell proliferation is particularly useful for radiotherapy treatment planning because of better gross tumor volume (GTV) delineation. The GTV may be targeted with higher radiation dose, potentially improving local control without excessive irradiation to the normal adjacent tissues. Prostate cancer and glioblastoma multiforme (GBM) are two tumor models that are associated with a heterogeneous tumor distribution. Preliminary studies suggest that the integration of MRS into radiotherapy planning for these tumors is feasible and safe. Image-guided radiotherapy (IGRT) by virtue of daily tumor imaging and steep dose gradient may allow for tumor dose escalation with the simultaneous integrated boost technique (SIB) and potentially decrease the complications rates in patients with GBM and prostate cancers.

[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.

[Results of definitive radiotherapy for squamous cell carcinomas of the larynx patients with subglottic extension]

BACKGROUND

Squamous cell carcinoma of larynx with subglottic extension is a rare location described to carry a poor prognosis. The aim of this study was to analyze outcomes and feasibility of definitive radiotherapy in patients with squamous cell carcinoma.

PATIENTS AND METHODS

Between 1998 and 2012, 56 patients with squamous cell carcinoma were treated at our institution and included in the analysis. Patients received definitive radiotherapy/chemoradiotherapy alone (63%) or after induction chemotherapy (37%) at our institute.

RESULTS

The 5-year actuarial overall survival, progression-free survival and specific survival were 64% (CI 95%: 48-90), 45% (CI 95%: 28-61), 88% (CI 95%: 78-98), respectively, with median follow-up of 74 months. The 5-year locoregional control was 69% (CI 95%: 56-83) and the 5-year distant control was 95% (CI 95%: 89-100). There was no difference in overall survival and locoregional control according to front-line treatments or between primary subglottic cancer and glotto-supraglottic cancers with subglottic extension. In the multivariate analysis, performance status of at least 1 and positive N stage were the only predictors for overall survival (hazard ratio [HR] [CI 95%]: 6.5 [1.3-34; P=0.03] and 11 [1.6-75; P=0.02], respectively). No difference of locoregional control was observed according to the first received therapy. The univariate analysis retrieved that T3-T4 patients had a lower locoregional control (HR: 3.1; CI 95%: 1.1-9.2, P=0.04), but no prognostic factor was retrieved in the multivariate analysis. In patients receiving a larynx preservation protocol, 5-year larynx preservation rate was 88% (CI 95%: 78-98), and 58% in T3 patients. The 5-year larynx preservation rate was 91% (CI 95%: 79-100) and 83% (CI 95%: 66-100) for patients who received radiotherapy/chemoradiotherapy or induction chemotherapy as a front-line treatment, respectively.

CONCLUSION

This analysis suggests that the results for squamous cell carcinoma patients treated with radiotherapy/chemoradiotherapy are comparable to those obtained for other laryngeal tumors. This thus suggests the feasibility of laryngeal preservation protocols for infringement subglottic for selected cases. Further studies are needed to clarify these preliminary data.

[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.

[Image guidance for the evaluation of setup accuracy]

Information obtained by different methods of image-guided radiotherapy now allows us to reposition the target volume. This evolution causes a change in practice and positioning control. In order to control positioning errors, a systematic control during the first three to five sessions is required. Random repositioning errors and clinical target volume motions can be mastered only by performing a daily imaging. Finally, image-guided radiotherapy allows assessing anatomical changes occurring during treatment, and opens the field of adaptive radiotherapy.