Background: Due to the complicated dose calculations, in volumetric modulated arc therapy (VMAT), treatment errors may occur with changes around the lesion due to changes in the patient volume. The head and neck contain many major organs at risks (OAR)s increasing the likelihood of volume changes in OARs due to the effects of radiotherapy. Materials and Methods: The dose distribution and effects according to the changes in patient volume were analyzed while maintaining the same beam and irradiation conditions as in the initial treatment plan. The volume was extracted to quantify the volume change by setting the region of interest (ROI) of a fan-shaped area formed tangentially to the planning target volume (PTV), with the spinal cord as the center in the transverse plane. Results: As the radiation treatment progressed, the head and neck volume changes accelerated. As the volume change increased, the target's low-dose distribution area, the incident dose to the spinal cord and parotid gland, and the incident dose to the target periphery increased. In particular, an increase in the target's cold spot and the incident dose to the parotid gland can cause late effects as well as insufficient treatment. Conclusion: The alteration in dose distribution can be anticipated by monitoring the shift in patient volume using the ROI extraction method outlined in this study.

Background: This study aims to compare retrospectively generated gated internal target volumes (ITVs) and to evaluate whether gated ITVs can reduce planned target volumes (PTVs) compared with standard ITV expansions. Materials and Methods: In this study, we retrospectively generated respiratory-gated ITVs and PTVs for our cohort of patients who underwent four-dimensional computed tomography for thoracic radiotherapy in our department between August 2018 and February 2019. We calculated the standard ITVs and two gated ITVs to analyze the volumetric reduction. Further, we considered a PTV reduction of >10% to be significant, and we analyzed the role of the localization and the size of the gross tumor volumes. Results: We included 38 patients with a median age of 70 years (mean = 68, SD ± 13, 4, range =43– 89), of whom 18 (47%) were females and 20 (52%) were males. The two gated PTVs (PTV 30%– 70% and PTV 80%– 20%) were significantly smaller than the standard PTVs (p-value < 0, 001 for both PTVs). Considering the volume of the gross target volume (GTV), we found a significant correlation between GTV30cc and ITV30%– 70% (chi-square analysis, p: 0, 006) and between GTV5cc and ITV80%– 20% (p: 0, 003). We also found a correlation between the localization of the target lesion (mediastinal/ central/peripheral lesion) for both the gated ITVs (p: 0, 030 for ITV 30%– 70% and p: 0, 018 for ITV 80%– 20%). Conclusion: Gated ITV plans could be useful for the sparing of normal tissues. Our results show that this approach could be useful for small lesions and for certain localizations (island tumors).

Background and purpose: Breast‑ conserving surgery followed by radiation therapy to the whole breast is now recognized as a standard strategy in patients with breast cancer. Recommended technique for radiotherapy is whole breast irradiation followed by boost to the tumor bed. This study aimed to compare the dosimetric parameters of electron and photon beams for boosting irradiation in post‑ lumpectomy patients of breast cancer. Materials and methods: This analytical study included 50 patients of post-lumpectomy breast cancer. Treatment Planning System (TPS) was used to compare the plans for electron beam and photon beam boost irradiation. The organs at risk (OAR) consist of heart, ipsilateral lung, and skin. Targetvolume coverage, Conformity Index (CI), Homogeneity Index (HI), and doses to OAR were compared. Results: Photon plans represented a considerably better CI and HI for the planning target volumes (PTV), compared to the electron beam plans. Regarding OAR sparing, the V1Gy and Dmean in heart and ipsilateral lung with photon beam were significantly higher than electron beam (P<0. 05). Conclusion: Dosimetric analysis revealed that CI index, HI index, and PTV coverage were significantly better in photon boost plans, while OAR dosimetry conveyed a significant reduction in ipsilateral lung and heart doses with electron beam plans.

Background: To introduce a simple glioblastoma (GBM) target delineation method based on peritumoral edema. Materials and Methods: A postoperative GBM patient was selected, the target volume was delineated using three methods, including the methods recommended by the Radiation Therapy Oncology Group (RTOG method), by the European Organization for Research and Treatment of Cancer (EORTC method) and by this study (New method), and radiotherapy plans were formulated by the same physicist. The dose distributions of each schedule were compared. Then, patients treated with the delineation method recommended in this study were retrospectively analyzed, and progression-free survival and overall survival were determined. Results: The distributions of the high-dose regions of the 3 plans were as follows: RTOG method > EORTC method > New method, as was the low-dose region. Thirty-three patients were included in this retrospective study, and the median progression-free survival (PFS) and overall survival (OS) were 12 and 25 months, respectively. Conclusions: Our study suggested that delineating the target volume for GBM radiotherapy based on peritumoral edema is a good choice.

Background: For the purpose of individual clinical target volume assessment in radiotherapy of prostate cancer, MRSI was used as a molecular imaging modality with MRI and CT images. Materials and Methods: The images of 20 prostate cancer patients were used in this study. The MR and MRSI images were registered with CT ones using non‐rigid registration technique. The CT based planning (BP), CT/MRI BP and CT/MRSI BP was performed for each patient. For plan evaluation, Dose Volume Histograms (DVHs) data were used. A paired sample T‐test was used for the analysis of the obtained data.Results: The percentage of variation of CTVMRI to CTVCT and PTVMRI to PTVCT were 12.83% and 8.97%, respectively. CTVMRSI and PTVMRSI were 21% and 27.41% more than their corresponding values of CT volumes. The mean percentage of variation in rectum volume that received 60% of the prescribe dose (V60R) in MRSI/CT BP relative to CT BP was 14.66%.Conclusion: The use of MRSI in detecting of prostate adenocarcinoma could provide some decisive information to determine optimum volume and safe margin for target definition to improve adaptive radiotherapy in prostate cancer.

Background: Radiotherapy is associated with a high risk of heart disease in patients with left-sided breast cancer. Previously, the entire heart was considered an organ at risk (OAR) during planning. Studies have shown that the effect of radiation therapy depends on the dose to specific heart substructures. However, the tolerance dose of the left anterior descending coronary artery (LAD), an important cardiac substructure, is yet to be determined. This study aims to verify the feasibility of reducing the LAD dose with appropriate dose-volume constraints for patients undergoing left whole-breast radiotherapy, without compromising the target dose coverage, using tomotherapy techniques.Method: This retrospective study generated tomohelical and tomodirect plans initially without considering the LAD as OAR in the treatment planning. To reduce the LAD dose, plans were regenerated by including the LAD as an OAR with appropriate dose constraints. The dose-volume histogram parameters of these plans were compared with those of the initial plans of the respective types.Results: Tomohelical plans showed a 4.4% reduction in maximum dose and a 3.8% reduction in V15 for LAD, while tomodirect plans registered a 3% reduction in V15, with the conformity index remaining constant. Based on the LAD dosimetric results, considering the LAD as an OAR is associated with lower LAD doses without compromising the target volume coverage.Conclusion: It is feasible to reduce the LAD dose without compromising target volume coverage or affecting other OAR doses in patients with left breast cancer, using tomotherapy techniques.

Introduction: To implement the newly introduced concept volume of Definite Target Volume (DTV) and compare the distribution and dose-escalation in the DTV and clinical plans. Material and Methods: We used seven samples of hepatocellular carcinoma (HCC) and three cervix tumour plans. DTV is determined through occupancy probability and margin contraction. This margin reduces the Clinical Target Volume (CTV) to obtain the DTV volume. DTV optimisation was achieved by giving the maximum dose to the target volume and limiting the organ at risk (OAR) by constraint. Results: The DTV volume is obtained with a range of 60. 8–, 913. 9 cc for HCC and 2. 4–, 22. 9 cc for the cervix tumour. In HCC, the average 𝐷, 𝑚, 𝑎, 𝑥,at DTV volume increased to 124. 98 ±,29. 02, whereas the average 𝐷, 𝑚, 𝑒, 𝑎, 𝑛,increased to 105. 36% ±,2. 66% for the Planning Target Volume-crop (PTV-crop). For cervix tumour cases, the highest dose on DTV volume reached 138. 49%, and the average 𝐷, 𝑚, 𝑎, 𝑥,at DTV volume increased to 116. 80% ±,13. 19%. In addition, the average 𝐷, 𝑚, 𝑒, 𝑎, 𝑛,increased to 101. 89% ±,5. 58% for the PTV-crop. A larger dose delivered at the DTV will be associated with an increase in OAR. The dose increase of OARHCC is 106. 93% ±,5. 57%, and OAR-cervix is 101. 18% ±,1. 87%. Conclusion: The larger margins generate smaller DTV volumes or vice versa. The dose to target DTV has increased considerably, but dose increases to PTV-crop and OAR are still within clinically acceptable levels.