Laser Light Trapping Phenomenon in a 3D Radiotherapy Polymer Gel Dosimeter

This paper aims to explain the phenomenon of laser light trapping (LLT) in a 3D polymer gel dosimeter. A VIC-T polymer gel dosimeter containing 17% N-vinylpyrrolidone, 8% N,N′-methylenebisacrylamide, 12% tert-butyl alcohol, 5% gelatine, 0.02% hydroquinone and 14 mM tetrakis(hydroxymethyl)phosphonium chloride was used in this study. It was exposed to green laser light with a wavelength of 532 nm. A film was recorded during the exposure. After exposure, Raman spectroscopy was used to study the reactions taking place inside the dosimeter. The obtained results were used to explain what the LLT phenomenon is, what are the consequences for the dosimeter in which such a phenomenon occurs, and what dosimeter components play an important role in the occurrence of LLT. In addition, the conditions under which 3D polymer gel dosimeters can be measured using optical computed tomography at short wavelengths of visible laser light are indicated.

Abstract 16206: An Atypical Presentation of Spontaneous Coronary Artery Dissection in a Young Male Patient

Background: Spontaneous coronary artery dissection (SCAD) is an important cause of myocardial infarction (MI) in women but rare in young healthy males. We report a case of a young male who presented with left hand tingling/numbness and was ultimately diagnosed with SCAD. Case Presentation: A 24-year-old male with history of asthma developed left hand tingling/numbness while playing basketball. This progressed to cold left upper extremity, prompting him to go to emergency room. Doppler ultrasound showed acute left brachial thrombus and emergent embolectomy of left brachial artery was done. Transesophageal echocardiogram, performed to investigate possible cardiac source of thrombus, showed normal ejection fraction, dyskinetic apex and biventricular thrombus (Figure 1A). Cardiac MRI revealed a large transmural MI in distribution of a wraparound left anterior descending artery (LAD) with associated regional akinesis of the left ventricular apex and an infarct in the right ventricular apex. Subsequent angiography revealed normal coronary arteries (Figure 1B) except a heterogenous linear filling defect in the apical LAD consistent with Type 1 SCAD (Figure 1C). No intervention was performed and the patient was treated conservatively. It was postulated that patient sustained an apical MI after SCAD of LAD, leading to formation of ventricular thrombi which then embolized to cause acute brachial artery thrombosis. Discussion: SCAD in young males is rare and can be a diagnostic challenge. Type 1 “pathognomic” angiographic finding in SCAD, is the classic appearance of multiple radiolucent lumens or arterial wall contrast staining. In case of inconclusive angiography, intravascular ultrasound or optical computed tomography can confirm diagnosis. Interventionalists should be familiar with angiographic appearance of SCAD as advanced imaging might not be available and in many cases, conservative management is preferred to percutaneous coronary intervention.

Review on the feasibility of using PRESAGE® dosimeter in various radiotherapy techniques

The emergence of advanced radiotherapy techniques, such as intensity-modulated radiotherapy (IMRT), brachytherapy, conformal radiotherapy, magnetic resonance-guided radiotherapy (MRgRT), stereotactic synchrotron radiotherapy (SSRT) and microbeam radiotherapy (MRT), has increased the importance of the verification of volumetric dose distribution. The verification of dose distribution is usually done by 2D films and 3D gel dosimeters, but PRESAGE® due to its affordability, reproducibility, precision, accuracy, unique dosimetric and physical properties is considered as an effective candidate in providing 3D dose data. PRESAGE® is insensitive to oxygen contamination, machinable and can be molded to a variety of shapes and sizes. It is absorbing rather than scattering light which facilitates high-accuracy readout by optical computed tomography (OP-CT). This review focuses on the feasibility of using PRESAGE® in various complicated radiotherapy techniques by comparing its measured doses with 2D films and treatment planning system (TPS) calculated doses.

Effects of collagen crosslinking on porcine and human tarsal plate

Background Floppy eyelid syndrome is a disorder in which the tarsal plate is easily distensible and is currently treated with conservative or surgical measures. Human tarsal plate contains type I collagen, which is crosslinked in corneal tissue as a treatment for keratoconus. We hypothesized that collagen crosslinking would similarly stiffen tarsal plate tissue and investigated this in porcine and human tarsal plate specimens. Methods Riboflavin-sensitized porcine and human tarsus samples were irradiated with ultraviolet-A light. Porcine experiments were analyzed with gross photographs, anterior segment optical computed tomography (AS-OCT) imaging, and tensile testing. A prospective study of human tarsus was performed on samples from patients undergoing wedge resection for floppy eyelid syndrome and was analyzed with AS-OCT and tensile testing. Results 73 porcine adnexa and 9 patients (16 eyelids) who underwent wedge excision were included in the study. Grossly, greater stiffness was observed in crosslinked porcine tissue. AS-OCT imaging in porcine tissue showed a distinct hyperreflective band in crosslinked specimens whose area and intensity increased with longer treatment time (P = 0.003); this band was also visible in crosslinked human specimens. Tensile testing was performed, but results were not statistically significant. Conclusions AS-OCT imaging, which has not been previously described for tarsal plate, showed a characteristic change in crosslinked porcine and human specimens. Tissue stiffness was increased grossly, but changes in tensile properties were not statistically significant. Further study is warranted to determine relevance as a potential treatment for floppy eyelid syndrome.