The verification of dose distributions in nasopharyngeal cancer patients who were treated by intensity modulated radiotherapy

I.ÖZET : Amaç: Bu çalışmada yoğunluk ayarlı radyoterapi (YART) tekniği kullanılarak tedavi edilen nazofarenks kanserlerinde oluşan doz dağılımının doğrulanması amaçlandı. Bunun için tedavi planlama sistemi (TPS)'ndeki dozimetrik sonuçlar Alderson Rando Fantomda (ARF), film dozimetre tekniği kullanılarak elde edilen rölatif dozimetrik ölçümlerle karşılaştırıldı. Gereç ve Yöntem: Tedavi planlaması için tedavi pozisyonunda (sırtüstü ve başaltı köpüğü ile) yatırılan ARF'dan Siemens Somatom marka bilgisayarlı tomografi (BT) aygıtı ile alınan görüntüler TPS'e aktarıldı. Nazofarenks kanseri için ICRU 50-62 nolu protokolde tanımlanan hedef hacim ve riskli organlar, bu fantomdan elde edilen tüm BT kesitlerinde ilgili hekim tarafından konturlanarak 3 boyutlu görüntüler oluşturuldu. TPS'de var olan bu verilerden yararlanılarak uygun YART planlaması yapıldı. Planlamalarda Oncentra Tedavi Planlama (OTP) sistemi kullanıldı. TPS'de seçilen referans 3 kesit için koordinat sistemi oluşturuldu ve her bir kesit için biri koordinat sisteminin merkezinde olmak üzere x ekseni üzerinde toplam 5 nokta belirlendi. Bu noktaların dozları kaydedildi. Bu referans kesit ve noktaların fantomdaki karşılığı bulundu. Planlama sonuçları Siemens marka Primus lineer hızlandırıcı aygıtına gönderildi ve ilgili referans kesitleri arasına Kodak EDR2 radyografi filmi yerleştirilen fantom 6 MV-X ışını ile ışınlandı. Işınlanan filmler yüksek yoğunluklu lazer tarayıcıda (FIPS plus) okutuldu ve Mephysto yazılımına aktarıldı. Her bir referans kesit için 30 fraksiyon boyunca referans x ekseni üzerinde alınan 5 farklı nokta için rölatif dozlara ait verilerinin ortalaması alınarak tablolar oluşturuldu. Bu ölçümler sonucu bulunan ortalama ölçüm verilerinin TPS verileri ile karşılaştırıldığı doz değişim grafikleri her bir referans kesit için çizdirildi Bulgular: Film dozimetri ile elde edilen nokta veriler, TPS verileri ile karşılaştırıldığında dozdaki değişimin (?D) -3.0% ile +2.5% aralığında olduğu gözlendi. Film dozimetrisine göre referans noktaların kendi aralarındaki günlük değişimi değerlendirildiğinde iseæ standart sapmanın 0.5 ile 1.1 aralığında olduğu gözlendi. Her bir kesite ait referans noktalardaki standart sapma ve ortalama ölçüm değerleri dikkate alındığında 30 fraksiyon boyunca okunan rölatif doz değerleri için ortalamadan maksimum uzaklık -3.2% olarak bulundu. Sonuç: Nazofarenks kanserinin tedavisinde, YART tekniği uygulanarak elde edilen TPS'deki doz dağılımının, film dozimetri yöntemi kullanılarak elde edilen rölatif ölçüm sonuçlarıyla karşılaştırıldığı bu çalışmada film sonuçları ile TPS verileri arasındaki doz değişimin kabul edilebilir aralıkta olduğu gözlendi. ARF kullanılarak yapılan bu çalışmada doku heterojenitesinin etkisi de dikkate alındı. Aynı zamanda Kodak EDR2 filmlerinin kullanılabilirliği gösterildi. Elde edilen verilere göre film ışınlamaları ile TPS'nde elde edilen doz profillerindeki değişim miktarları hem birbirleriyle hem de literatürdeki benzer çalışmaların sonuçlarıyla uyumlu bulundu. Planlanan doz dağılımı ile ölçülen doz dağılımı arasında anlamlı bir farklılık saptanmadı. Anahtar Sözcükler: Nazofarenks kanseri, Alderson rando fantom, YART, film dozimetri 2. SUMMARY: Purpose: In this study our aim is to find the verification of dose distribution in nasopharyngeal cancers treated with intensity modulated radiotherapy (IMRT) technique. Therefore the dosimetric results of the treatment planning system (TPS) were compared with the relative dosimetric measurements which were obtained by using the film dosimetry technique in Alderson Rando Phantom (ARP). Material and Methods: The computed tomography (CT) images of the scanned ARP, which were taken at a treatment position in a Siemens Somatom CT for treatment simulation, were transferred to TPS. The targeted volumes and organs at risk were contoured by the responsible physican according to ICRU 50-62 protocol for nasopharyngeal cancer and three dimensional images were formed. By using the necessary data in the TPS the IMRT treatment plan for nasopharyngeal cancer was performed. Oncentra treatment planning (OTP) system software was used for the treatment planning. A coordinate system was formed for the three reference slices chosen at the TPS and a sum of 5 points were determined, one for each reference slice, one at the centre of the system and the rest on the x axis. The doses at these points were recorded. The equivalent points and slices at the phantom were found. The results of the planning system were sent to the linear accelerator (Primus, Siemens) and the phantom with the necessary Kodak EDR2 films was than treated with 6 MV-X rays. The irradiated films were read at the high concentrated laser scanner (FIPS plus) and trasferred to Mephysto software. Tables were prepared for each referance slice and for the 5 different points on the referance x axis with the median data of the relative doses during 30 fractions. The dose difference graphics of the comparison between TPS data and the median measurement data of the slices were then made for each referance slice. Results: When the point data, obtained by film dosimetry, were compared with the TPS data, the difference at the dose level (?D) was observed between -3.0% and +2.5%. And when the daily difference between each referance point according to film dosimetry was evaluated, it was observed that the standart deviation was between 0.5 and 1.1. When median measurement values and the standart deviation at the referance points of each slice were taken into consideration, the maximum difference from the median was found as -3.2% for the relative dose values during 30 fractions. Conclusion: In this study when the dose distribution obtained at the TPS during the treatment of nasopharyngeal cancer with IMRT was compared with the relative measurement results obtained by the film dosimetry method, it was observed that the dose difference between the TPS data and the film dosimetry results were at a considerable interval. In this study the effect of tissue heterogenity was taken into consideration by using ARF. At the same time the applicability of the Kodak EDR2 films were shown. According to the results, it was also found that the difference values of the dose profiles obtained at the TPS and the film dosimetry were quite correlated either with each other or with the similar studies in the literature. There was not significant difference between the measured dose distrubition and planned dose distrubition. Key words: Nasopharyngeal cancer, IMRT, Alderson Rando phantom, film dosimetr

The Effect of Deep Inspiration Breath-Hold Technique on Right Coronary Artery, Heart, and Liver Doses in Right Breast Cancer Radiotherapy

Purpose/Objective(s): The deep inspiration breath-hold (DIBH) approach has been thoroughly researched with the aim of reducing radiation exposures to normal tissues in breast cancer patients. Although heart and lung toxicity are widely addressed in many literature, radiation associated liver toxicity and dose constraints for the right coronary artery (RCA)are no twell studied in relation to breast radiotherapy. Additionally, very few studies have investigated the relationship between doses to cardiac substructures. This study aimed to determine the effect of the DIBH technique on the right coronary artery (RCA) region, cardiac substructures, and liver dose in right breast cancer irradiation. Materials/Methods: Between January 2022 and December 2022, thirty-five right breast cancer patients who previously received breast-surgery underwent computed tomography (CT) simulation with both free-breathing (FB) and DIBH techniques. Patients were contoured by a radiation oncologist on the scans using the Treatment Planning System. For cardiac substructures, reference atlas contours were used for accurate delineation and to reduce interobserver variation. Each patient underwent two treatment plans for both the DIBH and FB datasets.The plan comprised the FB and DIBH techniques, and the doses to the cardiac substructures, ipsilateral lung, RCA region, and liver were compared using atwo-tailed paired t-test. Radiotherapy was delivered with a Linac with the prescription dose of 50Gy in 25 fractions. Results: ForbothFBandDIBHirradiationgroups, the mean radiation doses to the ipsilateral lung, heart, and RCA region in patients with FB and DIBH techniques were; 14.67Gy, 2.33Gy, 4.88Gy and 12.05Gy, 1.34Gy and 3.29Gy respectively. The mean radiation doses to the cardiac substructures; for the left ventricle, right ventricle, left atrium,and right atrium for the FB were 1.08Gy, 1.79Gy, 4.11Gy, and for DIBH, 0.49Gy, 1.49Gy, 0.95Gy, and 2.61Gy, respectively. For the DIBH group, the liver maximum dose (p&lt;0.01), right lung mean dose (p=0.001), heart maximum dose (p=0.009), RCA mean dose (p=0.020), RCA maximum dose(p=0.008), RCA V5 dose(p=0.035), right atrium maximum dose (p=0.009) and right ventricle mean dose (p=0.040) were significantly lower than in patients treated in the non-gated group. Conclusion: DIBH resulted in considerable displacement of the liver away from the high-dose target region, such that the volume of liver in the high dose region was reduced. Additionally, the use of the DIBH technique in right breast cancer irradiation effectively reduces the radiation doses to the cardiac substructures, such as the left ventricle, right ventricle, left atrium, right atrium, RCA region, and lungs. DIBH could lead to substantial sparing of these structures with the right breast cancer radiotherapy. Future prospective studies are required to determine whether improvements to dose-distribution will translate in to improved toxicity outcomes.</p