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Introduction: Treatment of pelvic bone metastases using a Halcyon machine, mostly presents some difficulties to plan, especially for big volumes because of the machine field size. The purpose of this study is to use two lateral isocenters in the treatment of pelvic bone metastases with the Halcyon machine, in order to overcome its limitations in treating large volumes. Material and Methods: We report a retrospective study of 8 patients who received radiotherapy for pelvic bone metastases, all treated by two different VMAT techniques. The first technique was performed by two longitudinal isocenters (LONI) and the second by two lateral isocenters (LATI) respecting the authorized distance longitudinally between two isocenters which must be less than 8 cm. For each isocenter, two opposite arcs are used for all treated patients. Results: The plans conformity index (CI) assessment shows no difference between the two used techniques for all the treated patients. Remarkable coverage of PTVs was obtained in lateral isocenter (LATI) with 96.2% compared to 94%.6% for LONI, as well as the maximum dose which was 109.4% for LATI versus 112.3% for LONI. However, the Conformation number (CN) that takes into account both healthy tissue and organ at risk protection was improved by 7.3% by using LATI. Conclusion: A very satisfactory result has been obtained in the treatment of pelvic bone metastases with LATI. With this technique, we can exceed the limits of the Halcyon machine and process larger volumes. [ABSTRACT FROM AUTHOR]

Introduction: Before starting optimization using the Volumetric Modulated Arc Therapy (VMAT) technique, the choice of the convenient aperture shape controller can be one of the most important factors that affect the plan quality. Material and Methods: Three different clinical cases were selected: head and neck cancer, pelvic cancer (prostate, cervix, and endometrium), and breast cancer treated with the VMAT technique. By keeping the same conditions, plans were reoptimized by varying aperture shape controllers (OFF, VERY LOW, LOW, MODERATE, HIGH, VERY HIGH). For plans evaluation, the homogeneity index (HI), conformity index (CI), target coverage (D98% and V98%), dose max (DMAX) and near max (D2%), treatment time delivery (MUs), and gamma index passing rate were analyzed. Results: All the studied localizations treated with the VMAT technique met clinical objectives. The VERY LOW technique achieved the best dose conformity for all localizations. A slight improvement in terms of PTV coverage and max dose is obtained in a VERY LOW technique for pelvic cancer. For breast cancer, almost the same results were obtained. However, for head and neck treatments, better results were observed with the HIGH and VERY HIGH techniques, where coverage and maximum dose improved by up to 6%. Conclusion: Changing the Strength of Aperture Shape Controller in VMAT optimization can affect dose calculation, especially in concave volumes such as Head and Neck. [ABSTRACT FROM AUTHOR]

Introduction: Patient repositioning in treatment radiotherapy is one of the main factors that increase error of target irradiation. However additional margin is necessary to consider the uncertainties created along and around X, Y and Z-axis. Material and Methods: Set-up and random errors were calculated in translational and rotational axis for a sample of 20 prostatic patients; using daily IGRT-CBCT method. The aim of this study was to determine the additional margin that should be added from clinical target volume (CTV) to prevent toxicity and increase the irradiation precision in radiotherapy. The van Hark formula (PTV margin =2.5S +0.7s) was used for all patients to perform PTV margin for prostatic localization. Results: The research performed for a sample of 20 consecutive patients. With respect to systematic error along the lateral axis, longitudinal and anterior-posterior was 2.32, 2.42 and 3.54 respectively. The Random error was 1.82, 2.19 and 1.76° along lateral axis, longitudinal and anterior-posterior respectively. The rotational systematic error was 1.49, 2.04 and 2.14° around lateral, longitudinal and anterior-posterior axis respectively. The Random error was 1.78, 1.75 and 1.63° around lateral, longitudinal and anterior-posterior axis respectively. The calculated safety margin to cover clinical target volume (CTV) taking the prostate variability into account measured 7.55, 8.08 and 10.79 mm for lateral, longitudinal and anterior posterior respectively and 7mm would be enough in the posterior side. Rotational set-up errors for almost 95% of patients were between -2° and 2°. Conclusion: The calculated safety margin in all direction was smaller than 1 cm except in anterior side that was 1 cm or more. [ABSTRACT FROM AUTHOR]