İnterstisyel Foton Radyasyonunun Temel Prensipleri
Özet
İnterstisyel foton radyasyon tedavisi, özellikle çevre dokuların kan akımından kaynaklanan "heat-sink fenomeni" nedeniyle başarı oranı düşen ısı-bazlı ablatif yöntemlere (radyofrekans ve kriyoablasyon) güçlü bir alternatif sunmaktadır. Yalnızca çevre doku dansitesinden etkilenen bu yöntem, vasküler yapılara yakın hypervasküler alanlarda da etkinliğini korumaktadır. Temelde mikrovasküler oklüzyon ve radyoaktif mikropartikül implantasyonu ile brakiterapi gibi çalışan sistem, yüksek dozda radyasyonu serbest oksijen radikalleri ve direkt DNA hasarı yoluyla p53 bağımlı apoptoz oluşturarak hedef dokuya iletir. Tedavide lineer akseleratör (PRS), Gamma-knife ve Bragg iyonizasyon piki kullanan partikül-ışın olmak üzere üç farklı radyocerrahi metodu uygulanmaktadır. Bu yöntemlerin en büyük avantajı, hedef dışı dozdaki dik düşüş sayesinde çevre doku hasarını en aza indirmesidir. Klinik kullanımı günümüze kadar malign beyin tümörleri ve arteryovenöz malformasyonlarla sınırlı kalsa da yapılan hayvan deneyleri renal ablasyonda başarılı sonuçlar vermiş olup, özellikle opere edilemeyen hilusa yakın küçük renal kitlelerde yeni klinik çalışmalara ihtiyaç duyulmaktadır.
Interstitial photon radiation therapy offers a powerful alternative to heat-based ablative methods (radiofrequency and cryoablation), whose success rates decrease due to the "heat-sink phenomenon" caused by the blood flow of surrounding tissues. Affected only by the density of the surrounding tissue, this method maintains its efficacy even in hypervascular areas close to vascular structures. Working essentially like brachytherapy with microvascular occlusion and radioactive microparticle implantation, the system delivers high doses of radiation to the target tissue by creating p53-dependent apoptosis through free oxygen radicals and direct DNA damage. Three different radiosurgery methods are applied in therapy: linear accelerator (PRS), Gamma-knife, and particle-beam using the Bragg ionization peak. The greatest advantage of these methods is minimizing collateral damage to surrounding tissues thanks to a steep dose fall-off outside the target. Although its clinical use has been limited to malignant brain tumors and arteriovenous malformations to date, animal experiments have yielded successful results in renal ablation, and new clinical studies are needed especially for inoperable small renal masses located near the hilum.
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