Baş boyun fantom modelinde kontrast maddenin ve hava boşluklarının 3-boyutlu konformal radyoterapi planlamalarda doz dağılımına etkisi

Abstract

Çalışmada baş boyun kanserleri radyoterapisinde, kontrast maddenin ve hava boşluklarının konvansiyonel ve konformal tedavi planlarındaki doz dağılımına etkisi karşılaştırılarak araştırıldı. Akrilik PMMA malzemesinden baş boyun bölgesine benzer fantom tasarlandı. Su ve kontrastlı suyun koyulabileceği, hava etkisinin incelenebileceği silindir bir kap yapıldı. Simülasyon için plaka, kavite, sulu ve kontrastlı su karışımının bulunduğu dört çekim görüntüsünden alınan ROI ile HU verilerinin ortalamaları HU +125 kemik doku, su ve kontrastlı su ortalamaları sırasıyla 4.39 ile 27.18 HU olup sıvı ile uyumlu bulundu. Görüntülerde GTV, CTV ve PTV alanları konturlandı, her birinde konvansiyonel ve konformal olmak üzere 6 MV X ışını kullanılarak iki tedavi planı yapıldı. Toplam 200 cGy tek fraksiyonda, PTV'nin ortalama doz değerine ve %100'lük izodoza normalize edilerek hesaplandı. Plan sonuçları bağımsız gruplarda T testi ile hesaplanan p değeriyle analiz edildi. Plaka ve Kavite modellerinin konvansiyonel ve konformal plan karşılaştırmasında CTV dozu için p This comparative study was to investigate the radiotherapy of head and neck cancers by comparing the effects of the contrast agent and the air cavity on the patient dose in the conventional and conformal treatment plans. A phantom in the form of head/neck area has been designed with acrylic PMMA material. A cylindrical container was built in which the water and the contrast enhanced water could be placed in and the effect of air could be observed. For simulation the mean ROI and HU data gathered from the four images where slabs, cavity, water and contrast enhanced water were present was found to be HU 125 for cylindrical container wall, thus compatible with the bone tissue. Water and contrast enhanced water are compatible with the liquid as they were measured to be 4.39 and 27.18 HU respectively. In the images GTV, CTV and PTV areas were countered and for each one of them two treatment plans that are conformal and conventional were planned with 6 MV X-ray. A single dose of 200 cGy were calculated to PTV and normalized to 100%. Plan results were analyzed with p-values of the t-test calculated from independent groups. In the comparison of slab and cavity models for the conventional and conformal plans the p-value of the CTV dose was found to be significantly high (<0.05) in favour of the cavity plan. The result was attributed to be a consequence of the scattering in the cavity which might have increased CTV mean dose. In the conventional plans of slab and water models CTV dose and in the conformal plan GTV dose were found to be significant in favour of water. This might be resulting from the HU differences in between the slab, water and the wall of cylindrical container, but for daily applications it is not significant enough to make any difference. In the conventional and conformal plans of water and contrast no significant difference was determined for GTV and CTV. According to the results the use of contrast agent before the treatment plan in the increase of the dose, whereas the clinical effect can be neglected. If the cavities are not wide, the total dose is not clinically affected in a serious manner, but the normal tissue dose accumulation in the cavity walls should be taken into account.