An anthropomorphic breathing phantom of the thorax for testing new motion mitigation techniques for pencil beam scanning proton therapy.

Motion-induced range changes and incorrectly placed dose spots strongly affect the quality of pencil-beam-scanned (PBS) proton therapy, especially in thoracic tumour sites, where density changes are large. Thus motion-mitigation techniques are necessary, which must be validated in a realistic patient-like geometry. We report on the development and characterisation of a dynamic, anthropomorphic, thorax phantom that can realistically mimic thoracic motions and anatomical features for verifications of proton and photon 4D treatments. The presented phantom is of an average thorax size, and consists of inflatable, deformable lungs surrounded by a skeleton and skin. A mobile 'tumour' is embedded in the lungs in which dosimetry devices (such as radiochromic films) can be inserted. Motion of the tumour and deformation of the thorax is controlled via a custom made pump system driving air into and out of the lungs. Comprehensive commissioning tests have been performed to evaluate the mechanical performance of the phantom, its visibility on CT and MR imaging and its feasibility for dosimetric validation of 4D proton treatments. The phantom performed well on both regular and irregular pre-programmed breathing curves, reaching peak-to-peak amplitudes in the tumour of <20 mm. Some hysteresis in the inflation versus deflation phases was seen. All materials were clearly visualised in CT scans, and all, except the bone and lung components, were MRI visible. Radiochromic film measurements in the phantom showed that imaging for repositioning was required (as for a patient treatment). Dosimetry was feasible with Gamma Index agreements (4%/4 mm) between film dose and planned dose >90% in the central planes of the target. The results of this study demonstrate that this anthropomorphic thorax phantom is suitable for imaging and dosimetric studies in a thoracic geometry closely-matched to lung cancer patients under realistic motion conditions.

Computed tomography of renal mass lesions.

The use of C.T. scanning is an extremely useful tool in the assessment and evaluation of renal mass lesions. This is a noninvasive procedure that offers precise anatomic detail that may on occasion alleviate the need for further angiographic examinations. The need for close clinical correlation is absolutely essential.

Tomography in expansile lesions of the nasal and paranasal sinuses.

Of 35 nasal and paranasal sinus masses examined by radiography and tomography, 22 malignant tumors showed purely destructive growth. Bone expansion was observed in 13 benign, and 2 slowly growing malignant masses. Pluridirectional tomography in carefully selected projections is often necessary to reveal expansile growth. The 13 expansile lesions, including mucocele, neurofibroma, dermoid, epidermoid, cementifying fibroma, angiofibroma, inverting papilloma, and cylindroma, are briefly described. Tomographic appearance alone did not characterize histopathologic entities. However, distinctions may be made between fibro-osseous and epithelial tumors, and between fast growing and slowly growing tumors.