Analysis of head motion prior to and during proton beam therapy.

PURPOSE: We report on the use of a noninvasive patient motion monitoring system to evaluate the amount of head motion prior to and during proton radiation therapy sessions. METHODS AND MATERIALS: Two optical displacement sensors, placed close to the patient's head, were used for online monitoring of the head position, with submillimeter accuracy. Motion data, including the difference between start and end position (Dx) and the maximum displacement during the recorded session (Dx-max), were acquired for pretreatment sessions to analyze alignment radiographs, and for treatment sessions. We have recorded 102 pretreatment and 99 treatment sessions in 16 patients immobilized with a thermoplastic mask, and 44 pretreatment and 56 treatment sessions in 13 patients immobilized with vacuum-assisted dental fixation. To avoid incorrect data analysis due to replicate observations, only 1 pretreatment and 1 treatment session per patient were selected at random for statistical comparison of mean or median motion parameters in different subgroups. RESULTS: Both techniques showed similar immobilization efficiencies. The median Dx and Dx-max values were 0. 18 mm and 0.46 mm, respectively, for 16 treatment sessions with mask immobilization, and 0.22 mm and 0.50 mm, respectively, for 13 treatment sessions with dental immobilization. Motion parameters for pretreatment and treatment sessions were not statistically different. CONCLUSION: Online verification of patient's head motion is feasible and provides valuable data for confirmation of proper treatment delivery in individual patients, as well as for the evaluation of different immobilization methods.

Radiochromic film dosimetry for verification of dose distributions delivered with proton-beam radiosurgery.

In this work we studied the feasibility of radiochromic film for dosimetry verification of proton Bragg peak stereotactic radiosurgery with multiple beams. High-sensitivity MD-55 radiochromic film was calibrated for proton beam irradiation and the RIT 113 system was employed for film evaluation. Simulated stereotactic radiosurgery with a special phantom arrangement for film dosimetry was performed, following the same procedure as for a patient undergoing treatment. Five-beam irradiation was developed using a 3D treatment planning system. This plan was then delivered to the phantom in a one-day experiment. Planned and measured composite dose distributions were compared. Spatial accuracy of dose delivery to a region containing a simulated critical structure was evaluated for a single portal. Radiochromic film dosimetry validated the prescribed dose delivery within +/- 5%, one standard deviation, by comparing calculated doses with measured values. The alignment of apertures and boluses, as well as the alignment of the phantom with respect to the isocentre, was confirmed. Spatial accuracy of the method would have been able to detect possible misalignments greater than +/- 2 mm. We have demonstrated how radiochromic film dosimetry can be used to measure complex dose distributions in an irradiated phantom, thus enabling us to verify planned dose delivery of proton Bragg peak stereotactic radiosurgery with multiple beams. We assume that the dosimetric agreement between planned and measured dose distributions for the reported simulations will apply to patient treatments.

[Radiation dose in critical organs due to non-coplanar irradiation of the hypophysis]. / Strahlenbelastung von Risikoorganen durch nonkoplanare Bestrahlung der Hypophyse.

BACKGROUND: In order to estimate the somatic and genetic risk associated with a non-coplanar linac-based radiation technique of the pituitary gland, systematic secondary-dose measurements in a phantom and sample measurements of the dose near critical organs of patients were performed. PATIENTS AND METHODS: For measurements of the dose outside the primary radiation field an acrylic-PVC phantom was used which was irradiated with a single field (4 x 4 cm2). Eight patients with pituitary tumors were treated isocentrically with a combination of sagittal and transverse rotational arcs. To measure the dose in critical organs. LiF thermoluminescence dosimeters (TLD) in chip form were placed onto 1 eyelid, the skin over the thyroid, and the patient's clothes covering the region of breasts and ovaries of female patients and the testicles of male patients. Measurements were performed for all patients during 1 sagittal irradiation and for the majority of patients during 1 transverse irradiation. RESULTS: The phantom measurements demonstrated that the secondary dose measured on the patients surface can be considered as a good approximation for the dose in adjacent organs. The median dose in critical organs for sagittal irradiation was in the range of 25.8 mGy (eyes) to 1.9 mGy (testicles), and for transverse irradiation in the range of 23.3 mGy (eyes) to 1.3 mGy (testicles). The ratio of median organ doses for sagittal and transverse irradiation was 2.1 for the thyroid gland, 1.1 for the eyes, and 1.5 for the other organs. CONCLUSIONS: The dose in critical organs due to non-coplanar irradiation of the pituitary gland is only a small fraction of the dose delivered to the reference point of the planning target volume. The risk of a radiation-induced tumor and a genetic consequence associated with these small doses is generally less than 1% and 0.1%, respectively.

Computed tomography slice-by-slice target-volume delineation for stereotactic proton irradiation of large intracranial arteriovenous malformations: an iterative approach using angiography, computed tomography, and magnetic resonance imaging.

PURPOSE: Target-volume delineation for stereotactic irradiation is problematic for large and irregularly shaped arteriovenous malformations (AVMs). The purpose of this report is to quantify modifications in the target volume that result from iterative treatment planning that incorporates multimodality imaging data. METHODS AND MATERIALS: Stereotactic neuroimaging procedures were performed for 20 consecutive patients with AVM volumes > 10 cm3. Angiographically defined extrema were transformed into computed tomography (CT) space. The resulting target contours were then modified by a multidisciplinary treatment planning team after iterative review of angiographic, CT, and magnetic resonance imaging (MRI) data. Volumes of interest and dose-volume histograms for proton irradiation were calculated before and after iterative target delineation. RESULTS: Initial (angiographically defined) target volumes ranged from 15.3 to 96.1 cm3 (mean, 43.6 cm3). Final (iteratively defined) target volumes ranged from 10.7 to 114.0 cm3 (mean, 38.4 cm3). The volume of presumed normal tissue excluded by iterative planning ranged from 2.6 to 47.0 cm3 (mean, 15.5 cm3). Initially untargeted AVM, most commonly obscured by embolization material, was identified in all cases (range, 0.3 to 57.8 cm3; mean, 10.3 cm3). Corresponding dose-volume histograms demonstrated marked differences regarding lesion coverage and sparing of normal tissue structures. CONCLUSIONS: Iterative target-volume delineation resulted in significant modifications from initial, angiographically defined target volumes. Substantial amounts of apparently normal tissue were excluded from the final target, and additional abnormal vascular structures were identified for incorporation. We conclude that an iterative multimodality approach to target-volume delineation may improve the overall results for stereotactic irradiation of large and complex AVMs.