THE EVALUATION OF DOSIMETRIC PARAMETERS FOR PELVIC INTENSITY RADIOTHERAPY AND SIMULTANE INTEGRATED BOOST TREATMENT PLANS IN PROSTAT CANCER

Öz

OBJECTIVE: The aim of this study is to compare two different Conformity Index (CI), Critical organ scoring index (COSI), Tumor control probability (TCP) and Normal Tissue complication probability (NTCP) calculations, and Dose Volüme Histogram (DVH) parameters of 3 different IMRT treatment techniques in prostate cancer patients who underwent pelvic radiotherapy and prostate simultane integre boost (SIB).
MATERIAL AND METHODS: In this study, a total of 20 plans with conformal radiotherapy (3DCRT) and different intensity modulated radiotherapy (IMRT) techniques were made in the treatment planning system for 5 prostate cancer patients who had been treated in our clinic. In the evaluation of plans; homogeneity index (HI), mean dose (Dmean), TCP and two different CI values were calculated for all planning target volumes (PTV). Also, DVH data, NTCP and COSI calculations for the rectum, bladder, small intestine and femoral head were found and evaluated. For normal tissue, the volume receiving half of the prescribed dose (V40Gy) and the volume receiving 90% (V72Gy) were evaluated.
RESULTS: The RTOGCI mean values for PTV2 and PTV3 were significantly closer to 1 with IMRT plans when compared to 3DCRT plan (P=0.007 and P=0.008, respectively). The PADDICKCI mean values for PTV1 and PTV2 revealed that 3DCRT plans were significantly worse than IMRT plans (P=0.011 and P=0.009, respectively). For the PTV1, according to the CI assessment, the 9IMRT plan was found to be the best, whereas the TCP assessment found the result in favor of the 7IMRT plan. The best plan for bladder and rectum was found 7IMRT. Although the small bowel volume of 195 cc was the best in 3DCRT, the results in the NTCP and COSI evaluation were in favor of 5IMRT. In addition, the lowest volume receiving half of the dose prescribed for normal tissue was found for 7IMRT in both DVH and COSI evaluation. (5.7% and 0.62, respectively).
CONCLUSIONS: In the study, the best technique for RTOGCIPTV1 was found to be 3DCRT, which leads to error in the evaluation. This shows that this index is incompatible with reality in multiple PTV definitions. Another index, PADDICKCI, takes into account the PTV and the organs at risk vicinity of the target. However, this index requires an additional equation in the evaluation of SIB plans. Therefore, we consider the use of TCP and NTCP radiobiological evaluation parameters as important tools for selecting the most applicable from multiple plans.

Anahtar Kelimeler

• Prostate Cancer, Radiotherapy, Treatment Planning

PROSTAT KANSERİNDE PELVİK YOĞUNLUK AYARLI RADYASYON TEDAVİSİ VE EŞ ZAMANLI EK DOZ TEDAVİ PLANLAMALARINDA DOZİMETRİK PARAMETRELERİN DEĞERLENDİRİLMESİ

Öz

AMAÇ: Çalışmada, pelvik radyoterapi ve prostata eşzamanlı ek doz (SIB) uygulanmış prostat kanserli hastalarda, konformal radyoterapi (3BKRT) çalışması temel alınarak, 3 farklı Yoğunluk Ayarlı Radyasyon Tedavisi (IMRT) tedavi tekniğine ait iki farklı Uygunluk indeksi (CI), Kritik Organ Skorlama İndeksi (COSI), Tümör Kontrol Olasılığı (TCP) ve Normal Dolu Komplikasyon Olasılığı (NTCP) hesaplamaları ile Doz Volüm Histogramları (DVH) parametrelerinin karşılaştırılması amaçlanmıştır.
GEREÇ VE YÖNTEM: Kliniğimizde tedavi görmüş 5 prostat kanserli hasta için tedavi planlama sisteminde 3BKRT ve farklı IMRT tekniklerinde toplam 20 plan yapılmıştır. Planların değerlendirilmesinde; tüm planlanan hedef hacimler (PTV) için Homojenite İndeksi (HI), Ortalama Doz (Dort), TCP ve iki farklı CI değeri hesaplanmıştır Rektum, mesane, ince barsak ve femur başı için DVH verileri, NTCP ve COSI hesaplamaları yapılmış ve değerlendirmeye alınmıştır. Normal doku için reçete edilen dozun yarısını alan hacim (V40Gy) ile %90’nı alan hacim (V72Gy) değerlendirilmiştir.
BULGULAR: PTV2 ve PTV3 için RTOGCI değerleri 3BKRT için IMRT teknikleri ile karşılaştırıldığında istatistiksel anlamlı olarak 1’e daha yakın bulunmuştur (sırasıyla, P = 0.007 ve P=0.008). PADDICKCI, PTV1 ve PTV2 ortalama değerleri, 3BKRT planlarının IMRT planlarından önemli ölçüde daha kötü olduğunu ortaya koydu (sırasıyla, P = 0.011 ve P=0.009). PTV1 için, CI değerlendirmesine göre 9IMRT planı daha iyi iken, TCP değerlendirmesinde sonuç 7IMRT planı lehine bulunmuştur. Mesane ve rektum için en iyi plan 7IMRT bulunmuştur. İnce barsak için 195 cc hacmin aldığı doz 3BKRT’de en az iyi iken, NTCP ve COSI değerlendirmesinde sonuç 5IMRT lehine bulunmuştur. Normal doku için reçete edilen dozun yarısını alan en düşük hacim hem DVH hem de COSI değerlendirmesinde 7IMRT için bulunmuştur (sırasıyla; %5.7 ve 0.62).
SONUÇ: Çalışmada, RTOGCIPTV1 için en iyi tekniğin 3BKRT olarak bulunması değerlendirmede hataya yol açmaktadır. Bu da çoklu PTV tanımlamalarında bu indeksin gerçekle bağdaşmadığını göstermektedir. Diğer bir indeks olan PADDICKCI, hem PTV hem de PTV yakınlarındaki organları dikkate alır. Fakat bu indeks, SIB planlarının değerlendirmesinde ayrıca bir denkleme gerek duymaktadır. Bu nedenle, TCP ve NTCP radyobiyolojik değerlendirme parametrelerini, birden fazla plan arasından uygulanabilir olanını seçmek için önemli araçlar olarak görüyor ve kullanılmasını öneriyoruz.

Anahtar Kelimeler

• Prostat Kanseri
• Radyoterapi
• Tedavi Planlama

Kaynakça

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