BAŞ-BOYUN KANSERİ YOĞUNLUK AYARLI RADYOTERAPİSİNDE PAROTİS BEZİ HACMİ VE HEDEF HACİM İLİŞKİLERİNİN PAROTİS BEZİ DOZUNA ETKİSİ

Öz

Amaç Baş-boyun kanseri radyoterapisinde, parotis ve hedef hacim ilişkilerinin, parotisin alacağı radyasyon dozu üzerine etkisini araştırmaktır. Gereç ve Yöntem Baş-boyun bölgesi kanserleri tanısı ile küratif, definitif veya postoperatif adjuvan radyoterapi uygulanmış hastalardan rastgele 50 hasta seçildi. Konturlama sonrası her hastanın sağ ve sol parotislerinin ayrı ayrı kraniyo-kaudal uzunluğu (KKU), parotis hacmi (Vparotis), parotis ile kesişen planlanan hedef hacim (PTV) dozu, sağ ve sol parotisin ayrı ayrı PTV70 hedefi ile örtüşen KKU, parotis seviyesinde olan fakat parotis ile kesişmeyen maksimum PTV dozu ve parotisin PTV ile kesişen hacminin toplam parotis hacmine oranı kaydedildi. Ayrıca, parotis seviyesindeki kesitlerde PTV70 hacminin olup-olmadığı; var ise yerleşiminin tek taraflı mı veya bilateral olup-olmadığı kaydedildi. Yoğunluk ayarlı radyoterapi planlaması sonrası, doz-hacim histogramları kullanılarak ortalama parotis dozu (Dmean), 20 Gy ve üstü doz alan parotis hacmi oranı (V20) ve 30 Gy ve üstü doz alan parotis hacmi oranı (V30) değerleri ölçüldü. Ortalama parotis dozunun 26 Gy üstünde olmasına etki edebilecek faktörler lojistik regresyon analizi ile incelendi. Sınır değer belirleme amacıyla Receiver operating characteristics (ROC) eğrisi analizi kullanıldı. Bulgular Tüm parotislerin ortanca Dmean, V20 ve V30 değerleri sırasıyla, 26,55 Gy (14,74-66,78), %50,91 (26,53- 100) ve %32,21 (7,12-100) idi. Dmean>26Gy olan grupta, parotis hacmi istatistiksel olarak anlamlı yüksek bulundu (p=0,027). Dmean>26Gy olan grupta, parotisin PTV ile kesişen hacminin tüm parotise oranı belirgin yüksekti (%1,25 karşın %7,06, p<0,001). Çok değişkenli analiz sonucunda parotis hacmi ve PTV ile kesişen parotis hacminin oranının, parotis Dmean üzerinde istatistiksel olarak anlamlı etkili olduğu görüldü (her ikisi için de p<0,001). Dmean>26Gy olma ihtimalini en iyi gösterecek PTV ile kesişen parotis hacmi oranının sınır değerini tespit etmek için yapılan ROC analizi sonucunda, sınır değer %2,8 olarak bulundu. Sonuç Parotis ortalama dozunu 26 Gy altında tutmak adına, radyasyon onkoloğu konturlama aşamasında, PTV ile kesişen parotis hacmini %2,8 altında tutmaya çalışması faydalı olabilir.

Anahtar Kelimeler

• Baş-boyun kanseri
• parotis bezi
• yoğunluk ayarlı radyoterapi

THE EFFECT OF PAROTID GLAND VOLUME AND TARGET VOLUME RELATIONSHIPS ON PAROTID GLAND DOSE IN INTENSITY MODULATED RADIOTHERAPY OF HEAD AND NECK CANCER

Öz

Objective To investigate the effect of parotid and target volume relationships on the radiation dose to be received by the parotid in head and neck cancer radiotherapy. Material and Methods Fifty patients were randomly selected from the patients who underwent curative, definitive or postoperative adjuvant radiotherapy with the diagnosis of head and neck cancer. After contouring, the cranio-caudal length (CCL) of the right and left parotids, the parotid volume (Vparotis), the planning target volume (PTV) dose overlapping with the parotids, the CCL of the right and left parotid overlapping with the PTV 70 target, the maximum PTV dose at parotid level but not overlapping with parotids and the ratio of the parotid volume overlapping with PTV to the total parotid volume were recorded. In addition, it was recorded whether there was a PTV70 volume in the slices at parotid level and whether it was located unilaterally or bilaterally. After the intensity modulated radiation therapy planning, by using dose-volume histograms, mean parotid gland dose (Dmean), volume ratio of parotid gland that received 20 Gy and more doses (V20), and volume ratio of parotid gland that received 30 Gy and more doses (V30) were measured. The factors that may affect the mean parotid dose above 26 Gy were analyzed by logistic regression analysis. Receiver operating characteristics (ROC) curve analysis was used to determine the cut-off value. Results The median Dmean, V20 and V30 value of all parotid glands was 26.55 Gy (14.74-66.78), 50.91% (26.53- 100) and 32.21% (7.12-100), respectively. The parotid gland volume was found to be statistically significant higher in the group with Dmean>26Gy (p=0.027). In the group with Dmean>26Gy, the ratio of the volume of the parotid gland overlapping with the PTV to the entire parotid gland was significantly higher (1.25% vs. 7.06%, p<0.001). As a result of multivariate analysis, it was observed that the ratio of parotid gland volume and the volume of the parotid gland overlapping with the PTV had a statistically significant effect on the parotid Dmean (p<0.001 for both). As a result of the ROC analysis, the cut-off value for the parotid gland volume ratio overlapping with PTV that show the probability of Dmean>26Gy, was found to be 2.8%. Conclusion To keep the mean dose of the parotid gland below 26 Gy, radiation oncologist should pay attention to keep the volume ratio of the parotid gland overlapping with PTV below 2.8%.

Anahtar Kelimeler

• Head and neck cancer
• parotid gland
• intensity modulated radiation therapy

Kaynakça

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