Biomedical subjects

Cristina Garibaldi

Publications and source records attributed to Cristina Garibaldi.

7 recordsLinked to original sources

PubMed2006

Patient set-up verification by infrared optical localization and body surface sensing in breast radiation therapy.

BACKGROUND AND PURPOSE: The aim of the study was to investigate the clinical application of a technique for patient set-up verification in breast cancer radiotherapy, based on the 3D localization of a hybrid configuration of surface control points. MATERIALS AND METHODS: An infrared optical tracker provided the 3D position of two passive markers and 10 laser spots placed around and within the irradiation field on nine patients. A fast iterative constrained minimization procedure was applied to detect and compensate patient set-up errors, through the control points registration with reference data coming from treatment plan (markers reference position, CT-based surface model). RESULTS: The application of the corrective spatial transformation estimated by the registration procedure led to significant improvement of patient set-up. Median value of 3D errors affecting three additional verification markers within the irradiation field decreased from 5.7 to 3.5 mm. Errors variability (25-75%) decreased from 3.2 to 2.1 mm. Laser spots registration on the reference surface model was documented to contribute substantially to set-up errors compensation. CONCLUSIONS: Patient set-up verification through a hybrid set of control points and constrained surface minimization algorithm was confirmed to be feasible in clinical practice and to provide valuable information for the improvement of the quality of patient set-up, with minimal requirement of operator-dependant procedures. The technique combines conveniently the advantages of passive markers based methods and surface registration techniques, by featuring immediate and robust estimation of the set-up accuracy from a redundant dataset.

Breast Neoplasms↗

PubMed2006

Robust frameless stereotactic localization in extra-cranial radiotherapy.

In the field of extra-cranial radiotherapy, several inaccuracies can make the application of frameless stereotactic localization techniques error-prone. When optical tracking systems based on surface fiducials are used, inter- and intra-fractional uncertainties in marker three-dimensional (3D) detection may lead to inexact tumor position estimation, resulting in erroneous patient setup. This is due to the fact that external fiducials misdetection results in deformation effects that are poorly handled in a rigid-body approach. In this work, the performance of two frameless stereotactic localization algorithms for 3D tumor position reconstruction in extra-cranial radiotherapy has been specifically tested. Two strategies, unweighted versus weighted, for stereotactic tumor localization were examined by exploiting data coming from 46 patients treated for extra-cranial lesions. Measured isocenter displacements and rotations were combined to define isocentric procedures, featuring 6 degrees of freedom, for correcting patient alignment (isocentric positioning correction). The sensitivity of the algorithms to uncertainties in the 3D localization of fiducials was investigated by means of 184 numerical simulations. The performance of the implemented isocentric positioning correction was compared to conventional point-based registration. The isocentric positioning correction algorithm was tested on a clinical dataset of inter-fractional and intra-fractional setup errors, which was collected by means of an optical tracker on the same group of patients. The weighted strategy exhibited a lower sensitivity to fiducial localization errors in simulated misalignments than those of the unweighted strategy. Isocenter 3D displacements provided by the weighted strategy were consistently smaller than those featured by the unweighted strategy. The peak decrease in median and quartile values of isocenter 3D displacements were 1.4 and 2.7 mm, respectively. Concerning clinical data, the weighted strategy isocentric positioning correction provided the reduction of fiducial registration errors, featuring up to 61.7% decrease in median values (versus 46.8% for the unweighted strategy) of initial displacements. The weighted strategy proved high performance in minimizing the effects of fiducial localization errors, showing a great potential in improving patient setup. The clinical data analysis revealed that the application of a robust reconstruction algorithm may provide high-quality results in patient setup verification, by properly managing external fiducials localization errors.

Algorithms↗

PubMed2005

3D optoelectronic analysis of interfractional patient setup variability in frameless extracranial stereotactic radiotherapy.

PURPOSE: To investigate size and frequency of interfractional patient setup variability in hypofractionated stereotactic extracranial radiotherapy. METHODS AND MATERIALS: Infrared optical 3D tracking of surface markers was applied to quantify setup variability on 51 patients. Isocenter position repeatability was assessed by means of frameless anatomic calibration and was compared with portal image evaluation. Specific data analysis allowed for compensation of patients' breathing movements and for separation of the effects of operator-dependent misalignments and respiration-induced displacements. Effects of patient position (supine vs. prone) and treatment table configuration were investigated. RESULTS: Patient positioning assisted by the optical tracking device allowed reducing displacements of surface control points within the 3-mm range. Errors in isocenter localization were in the range of a few millimeters. This was in agreement with the portal image evaluation. Breathing motion introduced appreciable errors, which increased control points and isocenter 3D variability. This effect was significantly higher than those related to other investigated factors. CONCLUSIONS: The role of infrared optical tracking devices for patient positioning is assessed on a large patient population. Their use in the frame of high-precision radiotherapy is emphasized by the application of related methodologies for breathing phase detection and frameless isocenter localization.

Abdominal Neoplasms↗

PubMed2004

Dosimetric effects within target and organs at risk of interfractional patient mispositioning in left breast cancer radiotherapy.

PURPOSE: To investigate the effects of interfraction setup uncertainties on the dose distribution within the clinical target volume (CTV) and the organs at risk (OAR) of left-sided breast cancer patients undergoing external radiotherapy. METHODS AND MATERIALS: Interfractional setup errors were assessed by measuring surface control points displacements during 89 irradiation sessions in 4 patients, by means of opto-electronic localization. The measured position deviations were fed back to the treatment planning system for the evaluation of the corresponding dosimetric effects within CTV and OARs (lung, heart). RESULTS: Results revealed errors above 5 mm on some of the control points, but corresponding volumetric variations were on average below 2% for both the CTV within the 95-105% dose range and the OARs receiving more than 50% and 90% of the prescribed dose. A specific sensitivity to the setup errors was found as a function of the treatment plan design, leading to isolated cases exhibiting volumetric variations of CTV and OARs exceeding 2%. CONCLUSIONS: This study confirms the potential increase of treatment quality provided by the systematic patient position verification and highlights the role of opto-electronic position detection systems for the real-time check of patient setup errors and the evaluation of the corresponding dosimetric consequences, as a way to achieve consistent dose delivery.

Analysis of Variance↗

PubMed2003

In vivo dosimetry using radiochromic films during intraoperative electron beam radiation therapy in early-stage breast cancer.

BACKGROUND AND PURPOSE: To check the dose delivered to patients during intraoperative electron beam radiation therapy (IOERT) for early breast cancer and also to define appropriate action levels. PATIENTS AND METHODS: Between December 2000 and June 2001, 54 patients affected by early-stage breast cancer underwent exclusive IOERT to the tumour bed using a Novac7 mobile linac, after quadrantectomy. Electron beams (5, 7, 9 MeV) at high dose per pulse values (0.02-0.09 Gy/pulse) were used. The prescribed single dose was 21 Gy at the depth of 90% isodose (14-22 mm). In 35 cases, in vivo dosimetry was performed. The entrance dose was derived from the surface dose measured with thin and calibrated MD-55-2 radiochromic films, wrapped in sterile envelopes. Films were analysed 24-72 h after the irradiation using a charge-coupled-device imaging system. Field disturbance caused by the film envelope was negligible. RESULTS: The mean deviation between measured and expected doses was 1.8%, with one SD equal to 4.7%. Deviations larger than 7% were found in 23% of cases, never consecutively, not correlated with beam energy or field size and with no evidence of linac daily output variation or serious malfunctioning or human mistake. The estimated overall uncertainty of dose measurement was about 4%. In vivo dosimetry appeared both reliable and feasible. Two action levels, for unexplained observed deviations larger than 7 and 10%, were preliminary defined. CONCLUSIONS: Satisfactory agreement between measured and expected doses was found. The implementation of in vivo dosimetry in IOERT is suggested, particularly for patients enrolled in a clinical trial.

Breast Neoplasms↗

PubMed2003

Analysis of mandibular dose distribution in radiotherapy for oropharyngeal cancer: dosimetric and clinical results in 18 patients.

BACKGROUND AND PURPOSE: The relationship between the radiation dose and the risk of the osteoradionecrosis is well known. However, the dose to the mandible is not routinely assessed in the radiotherapy for head and neck cancer. The aim of our study was to analyze the mandibular dose distribution in the patients administered curative radiotherapy for squamous cell carcinoma of the oropharynx. Moreover, the clinical results have been analyzed. MATERIAL AND METHODS: We examined the clinical records and treatment plans in 18 patients treated with bifractionated radiotherapy for stage II-IV oropharyngeal cancer. In 17 patients, the total radiotherapy dose prescribed in the International Committee of Radiation Units and Measurements (ICRU) reference point was 74.4 Gy administered in 62 fractions (1.2 Gy twice daily with 6h interfraction interval) and one patient received a dose of 75.6 Gy. The whole dose to the mandibular-orophryngeal region was delivered with 6 MV photons. The mandible was contoured manually on computed tomographic scans and the point doses at the both mandibular condyles, ascending ramus, mental symphysis, molar and retromolar regions were assessed. Moreover, the cumulative dose-volume histograms (DHVs) were evaluated. The median follow-up period for alive patients is 30 months (range, 21-44+ months). RESULTS: Tumor remission was observed in 17 patients: in 11 cases, complete remission was achieved and in six cases, only partial remission was possible. One patient was lost to follow-up before the first response evaluation. The median survival for all patients is 22 months (range, 3-44+ months). Ten patients are alive and seven died. In six cases, the cause of death was head and neck tumor and in one died due to pancreatic cancer (second primary). No late bone post-radiation complication was seen. The highest radiotherapy doses were observed in the retromolar regions. The mean percentage doses at the right and left retromolar regions were 101.3+/-3.8% (range, 90.2-109.1%) and 101.7+/-2.5% (range, 95.2-105.8%), respectively. Lower doses were seen in ascending ramus (the mean percentage doses at right and left ascending ramus were 97.3+/-8.5% and 97.8+/-7.6%, respectively), the molar regions (the mean percentage doses at right and left molar regions were 86.0+/-13.5% and 88.1+/-12.9%, respectively), and at the mandibular condyles (the mean percentage doses at the right and left mandibular condyles were 72.6+/-18% and 77.0+/-16.5%, respectively). The volume of the mandible ranged from 60.1 to 110.1cm(3) (a mean of of 82.3 cm(3)). In all patients, the maximum dose absorbed in the mandible was higher than the dose prescribed in the ICRU point and the mean maximum dose absorbed in the mandible was 105.7+/-2.1% (range, 102.4-110.6%). The percentage of mandibular volume receiving a dose higher than prescribed was 28.6+/-14.9% (range 10.2-58.1%). The area underlying the DVH curve, the maximum mandibular doses and the retromolar doses did not appear to statistically depend on use of wedge or mandibular volume. CONCLUSIONS: Radiotherapy for oropharyngeal cancer is associated with high doses to the retromolar mandibular regions (the dose can be higher than prescribed in the ICRU reference point), ascending ramus and molar regions. Lower doses are absorbed at the condyles and mental symphysis. The single dose point (for example, the ICRU reference point) could be not used as a representative for the mandibular dose. In our small series of patients treated with hyperfractionated irradiation, these dose heterogeneities were not correlated to the patient- and treatment-related factors and are not related to the increased risk of late bone complications. The clinical relevance of mandibular dose distribution remains to be established in larger series of patients treated with conventionally and unconventionally fractionated irradiation.

Adult↗

PubMedDate not supplied

CT image fusion as a tool for measuring in 3D the setup errors during conformal radiotherapy for prostate cancer.

AIMS AND BACKGROUND: The importance of optimal daily patient positioning has been stressed in order to ensure treatment reproducibility and gain in accuracy and precision. We report our data on the 3D setup uncertainty during radiation therapy for prostate cancer using the CT image fusion technique. METHODS: Ten consecutive patients scheduled for radiation therapy for prostate cancer underwent 5 prone position CT scans using an individualized immobilization cast. These different setups were analyzed using the image fusion module of the ERGO 3D-Line Medical System (Milan, Italy) treatment planning system. The isocenter and the body marker displacements were measured. RESULTS: The 3D isocenter dislocations were quantified: systematic error was sigma(3D) = 3.9 mm, whereas random error was sigma(3D) = 1 mm. The mean of the minimum displacements was 0.2 +/- 1 mm showing that the immobilization device used allows an accurate setup to be obtained. Single direction errors were also measured showing systematic errors, sigma(AP), = 2.6 mm, sigma(LL) = 0.6 mm, SigmaSI = 3 mm in the anterior-posterior, latero-lateral, superior-inferior direction, respectively. Related random errors were sigma(AP), = 1 mm, sigma(LL) = 0.6 mm, sigma(SI) = 1.2 mm. In terms of accuracy, our uncertainties are similar to those reported in the literature. CONCLUSIONS: By applying the CT image fusion technique, a 3D study on setup accuracy was performed. We demonstrated that the use of an individualized immobilization system for prostate treatment is adequate to obtain good setup accuracy, as long as a high-quality positioning control method, such as the stereoscopic X-ray-based positioning system, is used.

Aged↗