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Showing 3 results for Dosimetric Parameters
B. Ghadimi, Dr. N. Jabbari, L. Karimkhani, K. Mostafanezhad, Volume 16, Issue 1 (1-2018)
Abstract
Background: Field-in-field (FIF) technique for treatment of breast cancer has become a widely performed method over the recent years. However, there was no study in the application of FIF technique in patients with breast cancer undergoing mastectomy and lumpectomy. This study is an attempt to compare dosimetric outcomes after applying the FIF technique in these patients. Materials and Methods: Twenty-four patients with right and left breast cancer participated in this study. The FIF planning technique was carried out for patients undergoing mastectomy and lumpectomy using the TiGRT treatment planning system (TPS). For the comparison purpose, we used two main indices, i.e. dose homogeneity index (HI) and conformity index (CI), the number of subfields, as well as mean, maximum, and minimum doses, doses received by 2% (D2) and 98% (D98) of the target volume, volumes received greater than 107% (V>107%) and less than 95% (V<95%) of the prescribed dose, doses to organs at risk (OARs), and total monitor units (MUs). Results: The results indicated that CI and HI are better in patients with right and left breast lumpectomy surgery (p<0.038 and p<0.047) relative to mastectomy patients (p<0.037 and p<0.029), respectively. Other parameters mentioned in Materials and Methods did not show any significant difference between the two groups of patients (p>0.05). Conclusion: The use of alternative subfields resulted in better dose distribution in target volume with the increase in breast volume. Moreover, to disappear the hot spot areas in isodose curves, it is essential to elevate the number of subfields.
Dr. H. Alipour, K. Hadad, R. Faghihi, Volume 17, Issue 3 (6-2019)
Abstract
Background: Due to the small size of the beamlets in IMRT (intensity modulated radiotherapy), physical penumbra is one of the important dosimetric parameters and small changes in the penumbra have a notable impact on the results. The physical penumbra width is defined as the lateral distance between two specified isodose curves at a specified depth of phantom. In this study, after demonstrating the inconsistency of conventional physical penumbra definition for non-uniform MLC (multileaf collimator) fields, two new dosimetric parameters proposed that are suitable for MLC fields. Materials and Methods: Physical penumbra evaluation was obtained using IAEA (international atomic energy agency) phase space data for a Varian IX and EGS (electron gamma shower)nrc Monte Carlo code package. These measurements have been performed in water phantom at an SSD of 100 cm and a depth of 5 cm. Results: With conventional definition, physical penumbra width for all MLC setups on right and left sides of isodose curves (parallel to X and Y axes) are not equal. With a novel beam penumbra parametrization, the effect of MLC setup is taken into consideration. Conclusion: The conventional definition of physical penumbra for non-uniform MLC setups is not comprehensive. For such cases, surface penumbra and uniformity index parameters are demonstrated to be more suitable and indicative of the field non-uniformity. It is also shown that for an idle treatment planning system, the uniformity index approaches unity.
S.m. Rezaeijo, Ph.d., B. Hashemi, B. Mofid, M. Bakhshandeh, A. Rostami, S.h. Molana, Volume 19, Issue 4 (10-2021)
Abstract
Background: Comparing three whole pelvic radiotherapy (WPRT) procedures as well as two local radiotherapy (LRT) procedures with each other for the treatment of prostate cancer patients using dosimetric parameters and radiobiological models: tumor control probability (TCP), normal tissue complication probability (NTCP), and equivalent uniform dose (EUD). Materials and Methods: Two groups of prostate cancer patients underwent WPRT (n=16) and LRT (n=16) procedures. In the WPRT group, the patients treated with two intensity modulated radiation therapy (IMRT+IMRT) procedures at two consecutive phases. Then, two other techniques including a three dimensional (3D) conformal radiation therapy (3DCRT) phase followed by an IMRT phase (3DCRT+IMRT) and also two consecutive 3DCRT procedures (3DCRT+3DCRT) were carried out on the patients' data. In the LRT group, the patients treated with just an IMRT technique. Then a 3DCRT technique was also performed on the patients' data. All the WPRT and LRT procedures compared with each other based on the dosimetric parameters and radiobiological models. Results: The mean of dosimetric parameters did not exceed the specified dose constraints for the bladder and femoral heads in the 3DCRT+ IMRT, and for the bladder in the 3DCRT technique. In the WPRT and LRT procedures, the TCP values for the prostate did not reveal any significant differences (P>0.05). The NTCP results in accordance with the dosimetric results for the organs at risk (OARs) showed a significant decrease in the IMRT+IMRT (WPRT) and the IMRT (LRT) techniques (P<0.05). However, the EUD results were dependent on the type of the procedure and OARs. Conclusion: For selecting the appropriate treatment technique for each prostate cancer patient, a compromise between the dosimetric and radiobiological evaluation of the WPRT and LRT procedures should be considered.
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