PubMed Health⌕ Search

Biomedical subjects

B B Van Duyse

Publications and source records attributed to B B Van Duyse.

2 recordsLinked to original sources
PubMed1998

Conformal radiotherapy of Stage III non-small cell lung cancer: a class solution involving non-coplanar intensity-modulated beams.

PURPOSE: We developed a semiautomatic class solution to irradiate centrally located Stage III non-small cell lung cancer (NSCLC), involving a beam intensity modulation technique and optimization using a biophysical cost function. METHODS AND MATERIALS: Treatment for 10 patients with Stage III NSCLC was planned, using a conventional three- or four-beam three-dimensional (3D) technique and two techniques involving, respectively, seven (BIM1) and five (BIM2) noncoplanar beam incidences with intensity modulation. Two planning target volumes were defined: PTV1 included macroscopic tumor volume and PTV2 included macroscopic and microscopic disease. Beams were divided into beam parts (segments) and their outlines were defined during virtual simulation. Optimization using a biophysical cost function determined beam weights, segment weights, and wedge angles. Biological end points included tumor control probability of both target volumes (TCP1 and TCP2) and normal tissue complication probability (NTCP) of heart, lung, and spinal cord. The resulting uncomplicated local control probability (UCLP) was calculated. Physical end points included dose at PTV1 expressed as a dose minimum and dose maximum. Target-dose inhomogeneity was constrained in all plans. RESULTS: Concerning tumor evaluation, TCP1 was 74% (range 54-89%) for the 3D plan, 78.0% (range 62-94%) for BIM1, and 86.0% (range 59-93%) for BIM2. TCP1*TCP2 was, respectively, 67.0% (range 39-81%), 73.0% (range 56-94%), and 81.0% (range 54-93%). Minimum doses to PTV1 were 85, 80, and 88 Gy with the three respective techniques, while dose maxima were 89, 101, and 100 Gy. NTCPs of lung were 45.0% (range 11-75%) for 3D, 19.5% (range 8-59%) for BIM1, and 24.5% (range 3-61%) for BIM2. NTCPs of heart and spinal cord were comparable for all techniques. ULCPs were 37.0% (range 9-73%), 52.5% (range 22-86%), and 60.0% (range 20-85%), respectively. Applying physical limits to ensure clinical safety, minimum doses at PTV1 were recalculated. These were 72, 71, and 74 Gy for 3D, BIM1, and BIM2, respectively. CONCLUSION: The BIM2 plan is a candidate class solution for dose escalation studies in centrally located Stage III NSCLC.

Algorithms↗
PubMed1998

3D conformal intensity-modulated radiotherapy planning: interactive optimization by constrained matrix inversion.

BACKGROUND AND PURPOSE: This paper presents a method for interactive optimization of 3D conformal intensity-modulated radiotherapy plans employing a quadratic objective that also contains dose limitations in the organs at risk. This objective function is minimized by constrained matrix inversion (CMI) that follows the same approach as the gradient technique using matrix notation. MATERIALS AND METHODS: Sherouse's GRATIS radiotherapy design system is used to determine the outlines of the target volume and the organs at risk and to input beam segments which are given by the beam segmentation technique. This technique defines the beam incidences and the beam segmentation. The weights of the segments are then calculated using a quadratic objective function and CMI. The objective function to be minimized consists of two components based on the planning target volume (PTV) and the organ at risk (OAR) with an importance factor w associated with the OAR. RESULTS: Optimization is tested for concave targets in the head and neck region wrapping around the spinal cord. For a predefined w-value, segment weights are optimized within a few seconds on a DEC Alpha 3000. In practice, 5-10 w-values have to be tested, making optimization a less than 5 min procedure. This optimization procedure predicts the possibility of target dose escalation for a tumour in the lower neck to 120-150 Gy without exceeding the spinal cord tolerance, whereas human planners could not increase the dose above 65-80 Gy. CONCLUSIONS: Treatment plans optimized using a quadratic objective function and the CMI algorithm are superior to those which are generated by human planners. The optimization algorithm is very fast and allows interactive use. Quadratic optimization by CMI is routinely used by clinicians at the Division of Radiotherapy, U.Z.-Gent.

Equipment Design↗