Biomedical subjects

S Lavertu

Publications and source records attributed to S Lavertu.

3 recordsLinked to original sources

PubMed2006

Sphincter-preserving radiation therapy for rectal cancer: a simulation study using three-dimensional computerized technology.

BACKGROUND: The acquisition of detailed computerized tomography (CT) imaging at the time of simulation, along with three-dimensional (3D) treatment planning software has been integrated with radiation delivery hardware to create the modality known as 3D conformal radiotherapy (3DXRT). This approach provides, in theory, a means to selectively subtract the anal sphincter from the high-dose field of irradiation in patients with stage II and III adenocarcinomas of the mid-rectum scheduled for low anterior resection (LAR). HYPOTHESIS: Implementation of 3DXRT with sphincter blocking may be a feasible strategy to reduce the dose of radiation distributed to the anal canal without reduction in the dose distribution to the gross tumour volume (GTV) plus adequate margins. METHODS: Pretreatment simulation CT scans of 10 patients with rectal cancers located between 5 and 10 cm from the anal verge were retrieved from a computerized database. Radiation oncologists and colorectal surgeons defined the contours of the GTV and the anal sphincter, respectively, on successive CT scan slices. These contours provided the volumetric data required to quantify dose distribution and compute dose-volume histograms. The standard mode of pelvic irradiation planned with CT simulation was compared with a 'virtual CT simulation' approach, in which a sphincter block was added to the protocol. RESULTS: The mean distance of tumours from the anal verge was 6.3 cm. In the virtual simulation treatment plan, a 2-cm margin separated the sphincter block from the lower limit of the GTV. The mean volume of the anal sphincter was 16.1 +/- 3.5 cm(3). The dose distributed to the GTV in the real plan and in the virtual simulated block plan were 51.7 +/- 1.4 and 51.6 +/- 1.4 Gy respectively (P = 0.85). By comparison the mean dose distributed to the anal sphincter was dramatically reduced by using a sphincter block (33.2 +/- 12 Gy vs 6.4 +/- 4.1 Gy, P < 0.001). CONCLUSION: During a course of radiotherapy for most low- or mid-rectal cancers, the anal canal is included within the field of irradiation with a mean dose distribution to the sphincter of 33 Gy. Evaluation of 3DXRT with full sphincter block (mid-rectum) and partial sphincter block (distal rectum) is a feasible strategy to decrease the volume of anal sphincter carried to full dose without reduction in dose to the GTV. This approach, by minimizing treatment-induced damage to the anal sphincter, might improve functional outcome of LAR.

Anal Canal↗

PubMed2000

Observation study of electronic portal images for off-line verification.

PURPOSE: The goals of this study were to evaluate the use of electronic portal imaging device (EPID) paper images as off-line verification tools and to assess the feasibility of replacing portal films by EPID printed images. MATERIALS AND METHODS: Electronic portal images were acquired using a video-based imaging system. After contrast enhancement, these images were printed and compared to portal films when prescribed, and judged about their usefulness for off-line verification. A total of 2025 images were acquired from 322 fields on 137 patients. The images were shown to eight radiation oncologists and two senior residents in radiation oncology, each one of them judging fields relevant to his (her) daily practice. The questions asked were related to the choice of important anatomical structures and the visibility of such structures, the usefulness of the printed images, the comparison with portal films and the possible replacement of such films by paper images. RESULTS: Answers to the different questions were treated as quantitative scores. For the visibility question, means and standard deviations were calculated for each individual structure, then a global score was obtained for a given treatment site. Means and standard deviations were also computed for the comparison question. Proportions and confidence intervals were used for the other questions. The results show that EPID paper images are useful for some treatment sites such as breast, thorax, prostate, abdomen, pelvis (other than rectum) and axilla. The image quality remains insufficient for some other sites such as head and neck and spine. CONCLUSION: Although global anatomical landmarks scores are good, the usefulness score is not always as high because some essential anatomical structures scores must be taken into account. There is also a strong habit factor related to acceptance of EPID printed images as verification tools. As long as they see more and more images, radiation oncologists can more easily visualize anatomical structures and are less stringent when evaluating the efficiency of EPID paper images as off-line verification tools.

Electronics, Medical↗

PubMed1999

Local failure is responsible for the decrease in survival for patients with breast cancer treated with conservative surgery and postoperative radiotherapy.

PURPOSE: The aim of the present study was to evaluate the role of local failure (LF) in the survival of patients treated with lumpectomy and postoperative radiotherapy and to investigate whether LF is not only a marker for distant metastasis (DM) but also a cause. METHODS: Charts of patients treated with breast conservative surgery between 1969 and 1991 were reviewed retrospectively. There were 2,030 patients available for analysis. The median duration of follow-up was 6 years. A Cox regression multivariate analysis was performed using LF as a time-dependent covariate. RESULTS: Local control (LC) was 87% at 10 years. Local failure led to poorer survival at 10 years than local control (55% v 75%, P < .00). In a Cox model, local failure was a powerful predictor of mortality. The relative risk associated with LF was 3.6 for mortality and 5.1 for DM (P < .00). In patients with LF, the rate of DM peaked at 5 to 6 years, whereas it peaked at 2 years for patients with LC. The mean time between surgery and DM was 1,050 days for patients without LF and 1,650 days for patients with LF (P < .00). CONCLUSION: Our results show that local failure is associated with an increase in mortality. The difference in the time distribution of distant metastasis for LF and LC could imply distinct mechanisms of dissemination. Local failure should be considered not only as a marker of occult circulating distant metastases but also as a source for new distant metastases and subsequent mortality.

Actuarial Analysis↗