A customizable, open-source Winston-Lutz system for multi-target, single isocentre radiotherapy.

Objective. To present and share an open-source system (phantom and software) for verifying the targeting accuracy of linac-based, single-isocenter, multi-target radiotherapy. This quality assurance test extends the traditional Winston-Lutz test, which considers a single target located at isocentre.Approach. Plans for a 3D-printed phantom are provided, which can be customized to accommodate various target (BB) positions. Given BB positions and gantry/collimator/couch combinations, the software generates multi-leaf collimator positions to facilitate multi-target Winston-Lutz (MTWL) plan creation. The software determines deviations between detected and expected BB positions on MV images resulting from MTWL plan delivery. BBs are located using a Hough circle detection algorithm, which is modified to favour the detection of circles: (1) having a reasonable size, (2) that are contained within the radiation field, and (3) having reasonable pixel intensities. Validation was performed in two ways: (1) using synthetic data with zero targeting errors and (2) by measuring real linac targeting errors and comparing against results obtained using a commercial system.Main results. Validation using the synthetic data yielded a mean (maximum) absolute discrepancy of 0.11 mm (0.21 mm), which is comparable to the synthetic phantom resolution (0.2 mm). The mean (maximum) absolute discrepancy compared to the commercial system is 0.13 mm (0.43 mm). These values are similar to results obtained with repeated deliveries of the same MTWL plan with the same phantom setup. Both validation tests yield reasonable results and are therefore considered successful. The MTWL test was performed independently by three physicists on two linacs to investigate repeatability, resulting in a mean (maximum) absolute discrepancy of 0.14 mm (0.51 mm) among the various attempts.Significance. Successful completion of this quality assurance test, using our customizable and open-source system, provides confidence that multi-target, single isocentre radiotherapy treatments can be delivered with sufficient geometric accuracy according to the chosen tolerance level.

Why patients return after refraction.

Although nonsurgical ophthalmologic practice depends on refraction, in recent years interest in this procedure has decreased. The ophthalmologist, however, must recognize that a well done refraction builds the patient's confidence and is the basis on which most surgical practices develop.

Intravitreal and intracameral cysticercosis.

A 49-year-old Mexican male presented with a free-floating cyst in the vitreous. The cyst was removed at the time of cataract surgery and on the first postoperative day a second cyst was found in the anterior chamber. The second cyst was excised by cryoextraction 6 weeks after the initial surgery, but the eye developed an inoperable retinal detachment and phthisis bulbi. Although the diagnosis of cysticercosis was made clinically, initially, the only laboratory evidence for parasitic infection was a peripheral blood eosinophilia. The patient later developed an enlarged liver which was consistent with parasitic infection based on a liver scan. The morphology and life cycle of the parasite is described as well as suggestions for surgical removal.

Helminthosporium corneal ulcers.

Two cases of fungal corneal ulcer caused by Helminthosporium are discussed. Dematiacious fungi are pigmented filamentary molds of which Helminthosporium is representative. Ulcers due to such dematiacious fungi seem to have a better prognosis than other types of fungal corneal ulcers. The importance of classifying fungal ulcers is emphasized. Therapy is considered for these keratomycoses.