Purpose: IMRT (intensity modulated radiotherapy) verification techniques are reviewed together with investigations, demonstrating the intrinsic verification problems.

This study on patients with localized prostate cancer was set up to investigate valuable differences using flattened beam (FB) and flattening filter free (FFF) mode in the application of intensity‐modulated radiotherapy (IMRT) and volumetric‐modulated arc therapy (VMAT). For ten patients, four different plans were calculated with Oncentra planning system of Elekta, using Synergy machines: IMRT and VMAT, with and without flattening filter. Homogeneity and conformity indexes, dose to the organs at risk, and measurements of peripheral dose and dosimetric plan verification including record of the delivery times were analyzed and statistically evaluated. The indexes for homogeneity and conformity (CTV and PTV) are either advantageous or not significantly different for FFF compared to FB with one minor exception. Regarding the doses to the organs at risk and the measured peripheral dose, equivalent or lower doses were delivered for FFF than with FB. Furthermore, the delivery times were significantly shorter for FFF. VMAT compared to IMRT reveals benefits or at least equivalent values. VMAT‐FFF combines the most advantageous plan quality parameters with the shortest delivery times and reduced peripheral dose and is therefore recommended for the given equipment and cancer localization.

BackgroundSince December 2009 a new VMAT planning system tool is available in Oncentra® MasterPlan v3.3 (Nucletron B.V.). The purpose of this study was to work out standard parameters for the optimization of prostate cancer.MethodsFor ten patients with localized prostate cancer plans for simultaneous integrated boost were optimized, varying systematically the number of arcs, collimator angle, the maximum delivery time, and the gantry spacing. Homogeneity in clinical target volume, minimum dose in planning target volume, median dose in the organs at risk, maximum dose in the posterior part of the rectum, and number of monitor units were evaluated using student’s test for statistical analysis. Measurements were performed with a 2D-array, taking the delivery time, and compared to the calculation by the gamma method.ResultsPlans with collimator 45° were superior to plans with collimator 0°. Single arc resulted in higher minimum dose in the planning target volume, but also higher dose values to the organs at risk, requiring less monitor units per fraction dose than dual arc. Single arc needs a higher value (per arc) for the maximum delivery time parameter than dual arc, but as only one arc is needed, the measured delivery time was shorter and stayed below 2.5 min versus 3 to 5 min. Balancing plan quality, dosimetric results and calculation time, a gantry spacing of 4° led to optimal results.ConclusionA set of parameters has been found which can be used as standard for volumetric modulated arc therapy planning of prostate cancer.

IntroductionA sweeping beam technique for total body irradiation in standard treatment rooms and for standard linear accelerators (linacs) is introduced, which does not require any accessory attached to the linac. Lung shielding is facilitated to reduce the risk of pulmonary toxicity. Additionally, the applicability of a commercial radiotherapy planning system (RTPS) is examined.Material and MethodsThe patient is positioned on a low couch on the floor, the longitudinal axis of the body in the rotational plane of the linac. Eight arc fields and five additional fixed beams are applied to the patient in supine and prone position respectively. The dose distributions were measured in a solid water phantom and in an Alderson phantom. Diode detectors were calibrated for in-vivo dosimetry. The RTPS Oncentra was employed for calculations of the dose distribution.ResultsFor the cranial 120 cm the longitudinal dose profile in a slab phantom measured with ionization chamber varies between 94 and 107 % of the prescription dose. These values were confirmed by film measurements and RTPS calculations. The transmittance of the lung shields has been determined as a function of the thickness of the absorber material. Measurements in an Alderson phantom and in-vivo dosimetry of the first patients match the calculated dose.Discussion and conclusionA treatment technique with clinically good dose distributions has been introduced, which can be applied with each standard linac and in standard treatment rooms. Dose calculations were performed with a commercial RTPS and should enable individual dose optimization.

Background and Purpose: Intensity-modulated radiation therapy (IMRT) has shown its superiority to 3D conformal radiotherapy in the treatment of prostate cancer. Different optimisation algorithms are available: algorithms which first optimise the fluence followed by a sequencing (IM) and algorithms which involve the machine parameters directly in the optimisation process (DSS). The aim of this treatment planning study is to compare both of them regarding dose distribution and treatment time.Patients, Material and Methods: Ten consecutive patients with localized prostate cancer were enrolled for this planning study. The planning target volume (PTV) and the rectum volume, urinary bladder and femoral heads as organs at risk (OAR) were delineated. Average doses, the target dose homogeneity H, D 5 , D 95 , monitor units per fraction and the number of segments were evaluated. Results:While there is only a small difference in the mean doses at rectum and bladder, there is a significant advantage for the target dose homogeneity in the DSS-optimised plans compared to the IMoptimised ones. Differences in the monitor units (nearly 10% less for DSS) and the number of segments are also statistically significant and reduce the treatment time. Conclusion:Particularly with regard to the tumor control probability the better homogeneity of the DSS-optimised plans is more profitable. The shorter treatment time is an improvement regarding intrafractional organ motion. The DSS-optimiser results in a higher target dose homogeneity and, simultaneously, in a lower number of monitor units. Therefore it should be preferred for IMRT of prostate cancer.