Source localization for template implants with particular reference to stepping-source afterloaders

A real-time image-guided intraoperative high-dose-rate brachytherapy system

PURPOSE

To develop a real-time, image-guided intraoperative high-dose-rate brachytherapy system.

METHODS AND MATERIALS

The surface applicator, a catheter array on a 1-mm-thick soft and semitransparent silicone rubber sheet, was directly sutured on the surgical bed. A three-dimensional video camera was then used to instantly capture images of the catheters and the surgical surface. Tracing the catheters on the images allowed us to automatically determine the dwell source positions. Dwell times in the dwell positions were optimized to minimize the dose variation and deviation from the treatment prescription. A dose-texture plot was created to quantify the dose distribution.

RESULTS

Treatment planning time was reduced from hours to a few minutes. Phantom tests have shown that the new source localization is accurate with sigma<1.5 mm. All hot spots and cold spots had been eliminated after the dwell-time optimization.

CONCLUSIONS

This real-time, image-guided planning system can provide optimal image-guided intraoperative high-dose-rate brachytherapy with geometric and dosimetric improvements and a short planning time.

Three-dimensional localisation based on projectional and tomographic image correlation: an application for digital tomosynthesis

Accurate three-dimensional tumor localisation in Radiotherapy, is critical to the treatment outcome, particularly when high dose gradients are present. A number of techniques have been proposed for the localisation of anatomical structures or markers. The present study proposes an approach to a concurrent maximisation of localisation accuracy and efficiency by correlation of tomographic and projectional images. The method introduces an element of direct verification and interactive optimisation of the process. Tomographic images are used for the identification of a point of interest. Its position is computed within the treatment co-ordinate system and verification of this position is achieved by obtaining the beam's eye view of the identified point on two projection radiographs. The key element of the approach is that all images used should be part of one single image data set. The implementation of this localisation method, as part of the functionality of a Digital Tomosynthesis prototype, has provided an integrated facility for localisation, of optimised accuracy and precision, while easy and efficient to use. The considerations are general and apply in principle to any imaging system that can augment tomographic images with projections.

CT-based software for 3-D localization and reconstruction in stepping source brachytherapy

This paper describes innovative software for catheter localization and three-dimensional (3-D) reconstruction in stepping source brachytherapy applications. Patient information is a set of computed tomography (CT) slices scanned during the implantation of brachytherapy catheters. Catheter geometry and patient anatomy are exported for use with dose calculation software modules. The errors produced by the system are also encouragingly low. Time saving was achieved, in terms of other traditional reconstruction techniques. Various automated procedures, 3-D graphics and a user-friendly GUI, have contributed to providing a powerful, comprehensive software tool, directly useable in the clinical practice.

A method for more efficient source localization of interstitial implants with biplane radiographs

The conventional method for source localization in an interstitial ribbon implant by means of biplane radiographs can be difficult, especially when a large number of seeds are involved. We present a new algorithm for more efficient source localization with the same conventional biplane radiographs. The method does not require a one-to-one source correspondence between two radiographs. The user needs only to digitize several points, following the shape of each ribbon from both films. The points that are digitized do not need to be the location of the seeds, and they do not have to correspond to the same points on both films. The algorithm uses the multidimensional minimization method to reconstruct the three-dimensional locus of the ribbon. The location of each seed is then determined by its pathlength relative to the corresponding starting point. We have used phantom experiments and clinical cases to test the reliability of the algorithm. The results show that the errors in the determination of seed locations are less than 2 mm, and the efficiency in source digitization for data entry can be increased by a factor up to 5.

Pulsed low dose rate brachytherapy for pelvic malignancies

PURPOSE

The pulsed low dose rate remote afterloading unit was designed to combine the radiation safety and isodose optimization advantages of high dose rate technology with the radiobiologic advantages of continuous low dose rate brachytherapy. This is the first report of a prospective clinical trial evaluating the relative incidence of acute toxicity and local control in patients with pelvic malignancies who underwent interstitial or intracavitary brachytherapy with the pulsed low dose rate remote afterloader.

METHODS AND MATERIALS

From 5/11/92-6/21/95, 65 patients underwent 77 brachytherapy procedures as part of their treatment regimen for pelvic malignancies. Using the pulsed low dose rate Selectron, equipped with a single cable-driven 0.3-1.0 Ci Ir192 source, target volume doses of 0.40-0.85 Gy per pulse were prescribed to deliver the clinically determined dose. Forty-five intracavitary and 32 interstitial procedures were performed. Fifty-four patients had primary and 11 recurrent disease. Patients were followed closely to assess incidence of Grade 3-5 acute and delayed toxicity, local control, and survival.

RESULTS

With a median follow-up of 16.1 months (range 1-29), 33 patients are NED, 10 alive with disease, 13 dead with disease, 4 dead of intercurrent disease, and 5 lost to follow-up. Local control was maintained until last follow-up or death in 48 cases, local failure occurred in 11, unknown in 5. Grade 3-5 acute toxicities (requiring medical or surgical intervention) occurred in 5 out of 77 procedures (6.5%), delayed complications in 10 patients (15% actuarial incidence at 2 years). In the 52 procedures performed for 42 patients with cervix cancer, the acute toxicity incidence was 5.8%, with a 14% 2-year actuarial incidence of delayed complications. Of 32 interstitial templates performed on 30 patients for pelvic malignancies, there were three incidences of acute toxicity and five delayed toxicities.

CONCLUSION

Using the parameters described for this initial clinical study in patients treated for pelvic malignancies, pulsed low dose rate brachytherapy shows no significant increase in acute toxicity above that seen with the standard continuous low dose rate approach. Using the isodose optimization possible with pulsed brachytherapy, local control is excellent in patients treated at initial presentation, although longer follow-up is required for full assessment of local control and late toxicity. Further trials will need to be carried out to determine if larger doses per pulse and shorter total treatment times have comparable therapeutic ratios.