K. Keraudy

Conformal radiotherapy (CRT) planning for lung cancer: analysis of intrathoracic organ motion during extreme phases of breathing

PURPOSE Conformal radiotherapy beams are defined on the basis of static computed tomography acquisitions by taking into account setup errors and organ/tumor motion during breathing. In the absence of precise data, the size of the margins is estimated arbitrarily. The objective of this study was to evaluate the amplitude of maximum intrathoracic organ motion during breathing. METHODS AND MATERIALS Twenty patients treated for non-small-cell lung cancer were included in the study: 10 patients at the Institut Curie with a personalized alpha cradle immobilization and 10 patients at Tenon Hospital with just the Posirest device below their arms. Three computed tomography acquisitions were performed in the treatment position: the first during free breathing and the other two during deep breath-hold inspiration and expiration. For each acquisition, the displacements of the various intrathoracic structures were measured in three dimensions. RESULTS Patients from the two centers were comparable in terms of age, weight, height, tumor site, and stage. In the overall population, the greatest displacements were observed for the diaphragm, and the smallest displacements were observed for the lung apices and carina. The relative amplitude of motion was comparable between the two centers. The use of a personalized immobilization device reduced lateral thoracic movements (p < 0.02) and lung apex movements (p < 0.02). CONCLUSION Intrathoracic organ movements during extreme phases of breathing are considerable. Quantification of organ motion is necessary for definition of the safety margins. A personalized immobilization device appears to effectively reduce apical and lateral displacement.

A modified 60C teletherapy unit for total body irradiation

PURPOSE A modified teletherapy unit to achieve total body irradiation with a vertical beam in a conventional treatment room. METHODS AND MATERIALS A standard 60C teletherapy unit has been modified to achieve total body irradiation with a vertical beam in a conventional treatment room. Patients are treated in prone and supine positions. Removal of the adjustable collimator assembly of this standard machine provides a circular field of 196 cm in diameter at 167 cm from the source. Second, the machine has been elevated by about 50 cm on a metallic base to enlarge irradiation field to obtain 248 cm in diameter at 210 cm from the source, and to encompass tall patients under better conditions. A special lead conical beam flattening filter, 10-mm thick at the center, was designed to compensate the spatial inhomogeneity of the beam. An instantaneous dose rate of 6.10(-2) Gy/min is attained at the L4 level (midplane) in an average 20-cm thick patient with a source activity of 5099 RHM (air kerma rate of 44.8 Gy.h-1.m2). Between February 2, 1984 and December 27, 1990, 244 total body irradiations were performed either by single dose (n = 69, 10 Gy were given to midplane at L4 level in about 6 to 8 h, 8 Gy to the lungs), or by fractionated dose (n = 175, 12 Gy were given in 6 fractions over 3 consecutive days to midplane at L4 level, 9 Gy to the lungs). RESULTS The dose distribution is similar than the ones obtained by a linear accelerator with patients lying on their sides. CONCLUSION Patients were treated in a comfortable and highly reproductible position. Organ shielding was easily achievable. This could be a less expensive and reasonable alternative to linear accelerator.

Investigation of ROC analysis for inverse treatment planning evaluation

We have experienced the inverse planning system in stereotactic irradiation using the singular value decomposition SVD [1, 2]. These last years, we have implemented this inverse planning module for IMRT, starting by an experimental environment [3] and then a clinical one.

The influence of dose matrix and voxel dimensions for the dose calculation on inverse treatment planning for stereotactic radiosurgery

Brain tumours and arteriovenous malformations with simple elliptical or more complex shapes treated by stereotactic irradiation using converging beams of small dimensions (minibeams) could be regarded as candidates for precision conformai radiotherapy. In stereotactic radiosurgery, the development of new optimisation techniques are also crucial as in conventional radiotherapy. We propose as optimisation technique, the Singular Value Decomposition (SVD) [1–4]. The SVD analysis takes into account all the voxels of the 3D dose matrix for the calculation of the dose distribution and allows the measurement of the ill-conditioning of the stereotactic radiosurgery problem.