[Assessment of movements of the different anatomic portions of the bladder, implications for image-guided radiation therapy for bladder cancer]. / Évaluation des mouvements des différentes portions anatomiques de la vessie, implications pour la radiothérapie guidée par l'image pour les cancers de vessie.

PURPOSE: To assess interfraction and intrafraction bladder wall movements in the different anatomic portions of the bladder. PATIENTS AND METHODS: Six patients were treated for prostate cancer with conformal irradiation. Daily online cone beam computed tomography was performed for repositioning and an additional one was performed following irradiation once weekly. Four craniocaudal levels were defined to calculate movements amplitudes compared to the scanner tracking: level 1 at the bladder neck, level 2 at mid-height of the bladder, level 3 at mid-height of the dome, level 4 at the apex in a distended bladder. Bladder height was also measured. RESULTS: On 198 daily cone beam computed tomographies, radial bladder right/left/anterior/posterior wall displacements at level 2 were 0.08 ± 0.24, 0.11 ± 0.33, 0.16 ± 0.45 and 0.14 ± 0.50 cm and at level 3 0.07 ± 0.78, 0.18 ± 0.98, 0.43 ± 0.94 and 0.04 ± 1.02 cm. Dome and neck displacements were 0.08 ± 1.41 cm and 0.08 ± 0.64 cm. Seventeen cone beam computed tomographies were done following irradiation. Radial bladder right/left/anterior/halfway up the trine wall displacements at level 2 before and after irradiation were 0.02±0.18, 0.01±0.30, 0.09 ± 0.32 and 0.22 ± 0.42 cm and at level 3 0.27 ± 0.60, 0.37 ± 1.15, 0.18 ± 0.87 and 0.54 ± 1.68 cm. CONCLUSION: Significant bladder wall displacements were observed on the anterior wall and upper portion of the bladder. Isotropic margins may not be sufficient to account for inter- and intrafraction bladder wall displacements at the latter levels. Tailored bladder anatomy-based anisotropic margins may be necessary to optimally spare the small intestine and to guaranty proper tumour coverage in case of bladder cancer. For upper bladder tumours, margins of over 2 cm would be necessary, which make them less adequate for external beam irradiation.

Development of a positron probe for localization and excision of brain tumours during surgery.

The survival outcome of patients suffering from gliomas is directly linked to the complete surgical resection of the tumour. To help the surgeons to delineate precisely the boundaries of the tumour, we developed an intraoperative positron probe with background noise rejection capability. The probe was designed to be directly coupled to the excision tool such that detection and removal of the radiolabelled tumours could be simultaneous. The device consists of two exchangeable detection heads composed of clear and plastic scintillating fibres. Each head is coupled to an optic fibre bundle that exports the scintillating light to a photodetection and processing electronic module placed outside the operative wound. The background rejection method is based on a real-time subtraction technique. The measured probe sensitivity for (18)F was 1.1 cps kBq(-1) ml(-1) for the small head and 3.4 cps kBq(-1) ml(-1) for the large head. The mean spatial resolution was 1.6 mm FWHM on the detector surface. The gamma-ray rejection efficiency measured by realistic brain phantom modelling of the surgical cavity was 99.4%. This phantom also demonstrated the ability of the probe to detect tumour discs as small as 5 mm in diameter (20 mg) for tumour-to-background ratios higher than 3:1 and with an acquisition time around 4 s at each scanning step. These results indicate that our detector could be a useful complement to existing techniques for the accurate excision of brain tumour tissue and more generally to improve the efficiency of radio-guided cancer surgery.