Monte Carlo study on beam hardening effect of physical wedges

Physical wedges are still widely used as beam modifiers in external beam radiotherapy. However the presence of them in the beam trace may cause beam hardening which may not be considered in many treatment planning systems. The aim of this study is to investigate the beam hardening effect generated by physical wedges via different beam quality indexes as photon spectrum, half value layer, mean energy and tissue-phantom ratio. The effect of physical wedges on the photon beam quality of a 6-18MV Varian 2100C/D accelerator was studied with the BEAMnrc Monte Carlo code. Good agreements were obtained between measured and calculated depth doses and beam profiles for open and wedged photon beams at both energies. It was noticed that for 6 MV photon beams, physical wedges have more significant effects on beam quality than for 18 MV. Also it was obtained that at 18 MV photon beam as the wedge angle increased, the effect of wedge on beam quality becomes reversed and beam softening occurred. According to these results, it is recommended that beam hardening and softening of physical wedges should be considered in treatment planning systems in order to increase the accuracy in dose delivery

[ case report of radial artery spasm during anesthesia]

One of the most important drawbacks of radial artery is its tendency toward spasm and one of the rare etiologies of that is recurrent blood sampling of the artery. Other causes are injection of drugs in artery in spite of vein, or using radial artery in cardiopulmonary bypass. Papaverine is a useful drug in vasospasm, but it must be used with special caution to avoid it's complications such as arrhythmia. The patient was a 72 year old man with intestinal gangrene and peritonitis whom was operated in Al-Zahra hospital in 2008. During Laparatomy surgery, because of severe acidosis, blood sampling was done 3 times for blood gas analysis. After being taken to the recovery ward, no radial pulse was detectable in the patient's right hand and severe cyanosis in the same hand was seen. After inserting the arterial catheter in brachial artery, treatment with Papaverine, indications of recovery were seen. Despite the rarity of radial artery spasm during anesthesia, it is very dangerous situation, and anesthesiologist must try to prohibit and be able to manage this problem and have suitable drugs in the operation room