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High atomic number and density of dental implants leads to major problems at providing an accurate dose distribution in radiotherapy and contouring tumors and organs caused by the artifact in head and neck tumors. The limits and deficiencies of the algorithms using in the treatment planning systems can lead to large errors in dose calculation, and this may adversely affect the patient's treatment. In the present study, four commercial dental implants were used: pure titanium, titanium alloy (Ti‐6Al‐4V), amalgam, and crown. The effects of dental implants on dose distribution are determined with two methods: pencil beam convolution (PBC) algorithm and Monte Carlo code for 6 MV photon beam. The central axis depth doses were calculated on the phantom for a source–skin distance (SSD) of 100 cm and a 10×10 cm2 field using both of algorithms. The results of Monte Carlo method and Eclipse TPS were compared to each other and to those previously reported. In the present study, dose increases in tissue at a distance of 2 mm in front of the dental implants were seen due to the backscatter of electrons for dental implants at 6 MV using the Monte Carlo method. The Eclipse treatment planning system (TPS) couldn't precisely account for the backscatter radiation caused by the dental prostheses. TPS underestimated the back scatter dose and overestimated the dose after the dental implants. The large errors found for TPS in this study are due to the limits and deficiencies of the algorithms. The accuracy of the PBC algorithm of Eclipse TPS was evaluated in comparison to Monte Carlo calculations in consideration of the recommendations of the American Association of Physicists in Medicine Radiation Therapy Committee Task Group 65. From the comparisons of the TPS and Monte Carlo calculations, it is verified that the Monte Carlo simulation is a good approach to derive the dose distribution in heterogeneous media.PACS numbers: 87.55.K‐

Background/aim: To investigate the effect of positron emission tomography-computed tomography (PET/CT)-based contouring on dosimetric parameters in rectal cancer patients undergoing preoperative intensity-modulated radiation therapy (IMRT). Materials and methods:Preoperative radiation therapy plans with conformal radiotherapy (CRT) or IMRT were created and examined according to the CT-and PET/CT-based contouring of 20 rectal cancer patients, retrospectively. Results:The target volumes delineated with PET/CT were significantly larger than the volumes created by CT (P = 0.043). Dose delivered to 98% of the planning target volume was high in IMRT planning contouring with CT and PET/CT compared with CRT planning, but the difference was not statistically significant (P = 0.056). Percent volumes receiving 105% of dose and 110% of dose were low in IMRT planning when compared with CRT (P < 0.0001 and P = 0.044, respectively). The volumes receiving 45 Gy for the small intestine, femur heads, and bladder and the maximum dose received by the bladder were significantly lower in IMRT. Conclusion:We showed that the target volumes created with PET/CT are significantly larger than the target volumes created with CT and that IMRT provides lower radiation exposure to the tumor-free tissues compared to the CRT planning. The dosimetric results primarily favor IMRT planning in rectal cancer patients and consequently present the significant alteration in target volumes.

Purpose: To investigate high conformality on target coverage and the ability on creating strict lung dose limitation of intensitymodulated radiation therapy in malignant pleural mesothelioma. Patients and Methods: Twenty-four radiation therapy plannings were evaluated and compared with dosimetric outcomes of conformal radiation therapy and intensity-modulated radiation therapy. Hemithoracal radiation therapy was performed on 12 patients with a fraction of 1.8 Gy to a total dose of 50.4 Gy. All organs at risk were contoured. Radiotherapy plannings were differed according to the technique; conformal radiation therapy was planned with conventionally combined photon-electron fields, and intensity-modulated radiation therapy was planned with 7 to 9 radiation beam angles optimized in inverse planning. Strict dose-volume constraints were applied. Results: Intensity-modulated radiation therapy was statistically superior in target coverage and dose homogeneity (intensity-modulated radiation therapyplanning target volume 95 mean 100%; 3-dimensional conformal radiation therapy-planning target volume 95 mean 71.29%, P ¼ .0001; intensity-modulated radiation therapy-planning target volume 105 mean 11.14%; 3-dimensional conformal radiation therapy-planning target volume 105 mean 35.69%, P ¼ .001). The dosimetric results of the remaining lung was below the limitations on intensity-modulated radiation therapy planning data (intensity-modulated radiation therapy-lung mean dose mean 7.5 [range: 5.6%-8.5%]; intensity-modulated radiation therapy-lung V5 mean 55.55% [range: 47%-59.9%]; intensity-modulated radiation therapy-lung V20 mean 4.5% [range: 0.5%-9.5%]; intensity-modulated radiation therapy-lung V13 mean 13.43% [range: 4.2%-22.9%]). Conclusion: With a complex and large target volume of malignant pleural mesothelioma, intensitymodulated radiation therapy has the ability to deliver efficient tumoricidal radiation dose within the safe dose limits of the remaining lung tissue.

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Objective: In this study, the posterior and anterior axillary field dosimetries, where the target volume was determined on computerised tomography (CT), were compared in breast cancer irradiation. Materials and Methods: Twenty-six breast cancer patients were examined in this study. Target volumes were contoured by 2 physicians. The posterior field was established by traditional anatomical structures in the posterior axillary plan (PAP). The second anterior field was performed in the same gantry angle with Supraclacicular field (SCF) at the anterior axillary plan (AAP). V105 (volume receiving ≥105% prescribed dose), V80 ve V30 values, mean lung dose, V20 (lung volume receiving ≥20 Gy) value, maximum spinal cord dose, conformity index and monitor unit (MU) values were defined. Two independent groups were compared with Mann-Whitney U test, 2 dependent groups were compared with Wilcoxon's signed rank test. p<0.05 was considered as statistically significant. Results: Small hot-point areas defined as volumes receiving more than 105% of the prescribed dose and more conformal 90% isodose curves were established at AAP. Low-dose areas were wider at PAP. Mean V105 (70.8 to 52.8, p=0.005), V80 and V30 volumes (p=0.005 and p=0.009 respectively), mean lung dose (p=0.04) and V20 value (p=0.03) were statistically significantly lower at AAP. There was no difference between two groups as maximum spinal cord dose. Conformity index was significantly higher at AAP (0.023 to 0.025, p=0.005). Treatment time was found longer at PAP (242.3 MU, p=0.047). Conclusion: According to the anatomy of the Turkish patients, AAP was superior when compared to the traditional method. The CT based treatment planning with dose optimization and target volume determination must be the standard treatment of SCF and axillary lymph node. Different techniques should be studied comparatively in terms of dosimetric and clinical superiority. Key words: Breast cancer, lymphatic irradiation, new tecniques ÖZETAmaç: Çalışmada meme kanseri ışınlamasında geleneksel arka aksilla alanını içeren plan dozimetrisi, bilgisayarlı tomografide (BT) hedef hacmin belirlenerek yapıldığı ön aksilla alanını içeren plan dozimetrisi ile karşılaştırılmıştır. Yöntem ve Gereçler: Yirmi altı meme kanserli olgu çalışmaya seçilmiştir. Hedef hacimler 2 öğretim görevlisi tarafından konturlanmıştır. Arka aksilla planında geleneksel anatomik yapılar baz alınarak posterior alan oluşturulmuştur. Ön aksilla alanının bulunduğu planda supraklavikuler (SK) bölge ile aynı gantri açısında ikinci bir ön alan oluşturulmuştur. V105 (%105 ve üzerinde doz alan hacim), V80 ve V30 değerleri, akciğer ortalama dozu, akciğer V20 (20 Gy ve üzerinde doz alan hacim) değeri, maksimum spinal kord dozu, konformite indeksi ve monitör ünit (MU) değerleri belirlenmiştir. İki bağımsız grubun kıyaslanmasında Mann-Whitney U testi, 2 bağımlı grubun kıyaslamasında Wilcoxon's signed rank testi kullanılmıştır. p<0,05 değeri anlamlı olarak kabul edilmiştir. Bulgular: Ön aksilla planında daha küçük sıcak nokta alanla...

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