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[en] In addition to an earlier developed 'compensator integrated modification technique', a method is derived which uses as basic principle the 'field integrated dose modification' (FIDM) without need for computer tomographic data. The method enables the radiotherapist to introduce one or more volumes within which doses can be delivered which are different from the one in the main irradiation volume. The steps of practical preparation and clinical application are described in detail. The radiobiological aspects of FIDM, especially those in case of acceleration and hyperfractionation, are elucidated by discussing three typical examples. 25 refs.; 5 figs
[en] The planning target volume (PTV) concept has been created within the context of external beam radiotherapy (EBRT). It would be ideal to have a similar approach in brachytherapy (BT) to compensate for uncertainties. However, the BT and EBRT dose distributions are profoundly different, and the role of a PTV concept in BT needs a distinct discussion. The EBRT PTV concept is based on expanding the dose distribution into a homogeneous plateau reaching beyond the CTV. According to basic BT physics, there are significant dose gradients around radioactive source positions, and it is impossible to create homogeneous dose plateaus. This means that PTV margins cannot be directly applied in BT. Application of PTV margins in lateral and anterior-posterior directions can even lead to a significant and overall dose escalation (∼8% per mm margin applied) for the individual patient and for the entire patient population. In the specific direction along the intrauterine tandem, safety margins can partly account for uncertainties, though. In conclusion, safety margins can only be partially applied in intracavitary BT, and it is not recommended to perform PTV delineation. The PTV seems not to be useful for dose reporting, and dose normalisation to PTV is strongly discouraged since it can lead to dose escalation.
[en] Optimum radiation therapy requires the most homogenous possible dose distribution within the target volume, with the steepest possible dose drop outside this volume. Distinctions are made according to the depth of the target volume, surface therapy, intermediate therapy and deep radiation therapy. In the case of surface therapy, an important role is played by the radiation quality, type of radiation and the distance between the radiation source and the skin surface. This therefore almost exclusively involves fixed-field therapy, whereby one differentiates between single field and multifield therapy. A further possibility is moving-field therapy which avoids dose peaks but considerably increases the relative depth dose. Extensive irradiation methods such as sectional, part-body or whole-body irradiation have been developed for general blood picture diseases, particularly for myeloic leukemia, where it is necessary to limit to low radiation doses due to the large target volume. Radiation therapy of haemoplastoses is hardly carried out in the form of extracorporeal blood irradiation, it however involves special requirements of personnel and technique. (MG)
[de]Eine optimale Strahlentherapie erfordert eine moeglichst homogene Dosisverteilung innerhalb des Zielvolumens mit einem moeglichst steilen Dosisabfall ausserhalb dieses Volumens. Man unterscheidet je nach Tiefenlage des Zielvolumens die Oberflaechentherapie, Halbtiefentherapie und Tiefentherapie. Bei der Oberflaechentherapie spielen Strahlenqualitaet, Strahlenart und Abstand der Strahlenquelle von der Hautoberflaeche eine entscheidende Rolle. Sie erfolgt fast ausschliesslich durch Stehfeldbestrahlung, wobei man Einzelfeld- und Mehrfelderbestrahlung unterscheidet. Eine weitere Moeglichkeit ist die Bewegungsbestrahlung, die Dosisspitzen vermeidet, darueber hinaus aber eine wesentlich staerkere Erhoehung der relativen Tiefendosis bewirkt. Bei generalisierten Erkrankungen des blutbildenden Systems, insbesondere bei der myeloischen Leukaemie, wurden ausgedehntere Bestrahlungsmethoden wie Abschnitts-, Teilkoerper- und Ganzkoerperbestrahlung entwickelt, wobei aufgrund des grossen Zielvolumens eine Beschraenkung auf niedrige Strahlendosen noetig ist. Eine Strahlentherapie von Haemoblastosen in Form der extracorporealen Blutbestrahlung wird selten durchgefuehrt, stellt aber auch besondere Anforderung an Personal und Technik. (MG)
[en] We investigate the gamma passing rate (GPR) consistency when applying different types of gamma analyses, linacs, and dosimeters for volumetric modulated arc therapy (VMAT). A total of 240 VMAT plans for various treatment sites, which were generated with Trilogy (140 plans) and TrueBeam STx (100 plans), were retrospectively selected. For each VMAT plan, planar dose distributions were measured with both MapCHECK2 and ArcCHECK dosimeters. During the planar dose distribution measurements, the actual multileaf collimator (MLC) positions, gantry angles, and delivered monitor units were recorded and compared to the values in the original VMAT plans to calculate mechanical errors. For each VMAT plan, both the global and local gamma analyses were performed with 3%/3 mm, 2%/2 mm, 2%/1 mm, 1%/2 mm, and 1%/1 mm. The Pearson correlation coefficients (r) were calculated 1) between the global and the local GPRs, 2) between GPRs with the MapCHECK2 and the ArcCHECK dosimeters, 3) and between GPRs and the mechanical errors during the VMAT delivery. For the MapCHECK2 measurements, strong correlations between the global and local GPRs were observed only with 1%/2 mm and 1%/1 mm (r > 0.8 with p < 0.001), while weak or no correlations were observed for the ArcCHECK measurement. Between the MapCHECK2 and ArcCHECK measurements, the global GPRs showed no correlations (all with p > 0.05), while the local GPRs showed moderate correlations only with 2%/1 mm and 1%/1 mm for TrueBeam STx (r > 0.5 with p < 0.001). Both the global and local GPRs always showed weak or no correlations with the MLC positional errors except for the GPRs of MapCHECK2 with 1%/2 mm and 1%/1 mm for TrueBeam STx and the GPR of ArcCHECK with 1%/2 mm for Trilogy (r < − 0.5 with p < 0.001). The GPRs varied according to the types of gamma analyses, dosimeters, and linacs. Therefore, each institution should carefully establish their own gamma analysis protocol by determining the type of gamma index analysis and the gamma criterion with their own linac and their own dosimeter.
[en] A simplified dose calculation method for mantle technique is described. In the routine treatment of lymphom as using this technique, the daily doses at the midpoints at five anatomical regions are different because the thicknesses are not equal. (Author)
[pt]Descreve-se um metodo simples e rapido de calculo de dose para a tecnica do manto. Na rotina de tratamento de linfomas, usando esta tecnica, as doses diarias nas diferentes regioes anatomicas do campo sao diferentes devido as espessuras nao serem iguais. (Autor)
[en] ICRU 50/62 provides a framework to facilitate the reporting of external beam radiotherapy treatments from different institutions. A predominant role is played by points that represent 'the PTV dose'. However, for new techniques like Intensity Modulated Radiotherapy (IMRT) - especially step and shoot IMRT - it is difficult to define a point whose dose can be called 'characteristic' of the PTV dose distribution. Therefore different volume based methods of reporting of the prescribed dose are in use worldwide. Several of them were compared regarding their usability for IMRT and compatibility with the ICRU Reference Point dose for conformal radiotherapy (CRT) in this study. The dose distributions of 45 arbitrarily chosen volumes treated by CRT plans and 57 volumes treated by IMRT plans were used for comparison. Some of the IMRT methods distinguish the planning target volume (PTV) and its central part PTV_x (PTV minus a margin region of × mm). The reporting of dose prescriptions based on mean and median doses together with the dose to 95% of the considered volume (D_9_5) were compared with each other and in respect of a prescription report with the aid of one or several possible ICRU Reference Points. The correlation between all methods was determined using the standard deviation of the ratio of all possible pairs of prescription reports. In addition the effects of boluses and the characteristics of simultaneous integrated boosts (SIB) were examined. Two types of methods result in a high degree of consistency with the hitherto valid ICRU dose reporting concept: the median dose of the PTV and the mean dose to the central part of the PTV (PTV_x). The latter is similar to the CTV, if no nested PTVs are used and no patient model surfaces are involved. A reporting of dose prescription using the CTV mean dose tends to overestimate the plateau doses of the lower dose plateaus of SIB plans. PTV_x provides the possibility to approach biological effects using the standard deviation of the dose within this volume. The authors advocate reporting the PTV median dose or preferably the mean dose of the central dose plateau PTV_x as a potential replacement or successor of the ICRU Reference Dose - both usable for CRT and IMRT
[en] In special cases of Total Body Irradiation(TBI), Half Body Irradiation(HBI), Non-Hodgkin's lymphoma, E-Wing's sarcoma, lymphosarcoma and neuroblastoma a large field can be used clinically. The dose distribution of a large field can use the measurement result which gets from dose distribution of a small field (standard SSD 100 cm, size of field under 40 x 40 cm2) in the substitution which always measures in practice and it will be able to calibrate. With only the method of simple calculation, it is difficult to know the dose and its uniformity of actual body region by various factor of scatter radiation. In this study, using Multidata Water Phantom from standard SSD 100 cm according to the size change of field, it measures the basic parameter (PDD,TMR,Output,Sc,Sp) From SSD 180 cm (phantom is to the bottom vertically) according to increasing of a field, it measures a basic parameter. From SSD 350 cm (phantom is to the surface of a wall, using small water phantom. which includes mylar capable of horizontal beam's measurement) it measured with the same method and compared with each other. In comparison with the standard dose data, parameter which measures between SSD 180 cm and 350 cm, it turned out there was little difference. The error range is not up to extent of the experimental error. In order to get the accurate data, it dose measures from anthropomorphous phantom or for this objective the dose measurement which is the possibility of getting the absolute value which uses the unlimited phantom that is devised especially is demanded. Additionally, it needs to consider ionization chamber use of small volume and stem effect of cable by a large field.
[en] Purpose: Volumetric modulated arc therapy (RapidArc) allows for fast delivery of stereotactic body radiotherapy (SBRT) delivery in stage I lung tumors. We compared dose distributions and delivery times between RapidArc and common delivery techniques in small tumors. Methods: In 18 patients who completed RapidArc SBRT for tumors measuring <70 cm3, new treatment plans were generated using non-coplanar 3D conformal fields (conf-SBRT) and dynamic conformal arc radiotherapy (DCA). For 9 patients with tumors adjacent to the chest wall, co-planar intensity-modulated radiotherapy (IMRT) plans were also generated. PTV dose coverage, organs at risk (OAR) doses and treatment delivery times were assessed. Results: RapidArc plans achieved a superior conformity index (CI) and lower V45Gy to chest wall (p < 0.05) compared to all other techniques. RapidArc led to a small increase in V5Gy to contralateral lung compared to conf-SBRT (4.4 ± 4% versus 1.2 ± 1.8%, p = 0.011). For other OAR, RapidArc and conf-SBRT plans were comparable, and both were superior to DCA plans. Delivery of a 7.5 Gy-fraction required 3.9 min (RapidArc), 11.6 min (conf-SBRT), and 12 min (IMRT). Conclusions: In stage I lung tumors measuring <70 cm3, RapidArc plans achieved both the highest dose conformity and shortest delivery times.
[en] Purpose: To examine the adequacy of the planning target volume (PTV) dose distribution as the worst-case representation of clinical target volume (CTV) dose distribution in prostate volumetric-modulated arc therapy (VMAT) plans. Methods: Ten intact prostate cancer cases treated by VMAT at our institution were randomly selected. Isocenter was shifted in the three cardinal directions by a displacement equal to the PTV expansion on the CTV (±3 mm) for a total of six shifted plans per original plan. Rotationally-perturbed plans were generated with a couch rotation of ±1° to simulate patient yaw. The eight perturbed dose distributions were recalculated in the treatment planning system using the same, fixed fluence map as the original plan. The voxel-wise worst-case CTV dose distribution was constructed from the minimum value per voxel from the eight perturbed doses. The resulting dose volume histograms (DVH) were evaluated for statistical correlation between the worst-case CTV and nominal PTV dose distributions based on D95% by Wilcoxon signed-rank test with significance level p ≤ 0.05. Results: Inspection demonstrates the PTV DVH in the nominal dose distribution is bounded by the CTV DVH in the worst-case dose distribution. Comparison of D95% for the two dose distributions by Wilcoxon signed-rank test gives p = 0.131. Therefore the null hypothesis cannot be rejected since the difference in median values is not statistically significant. Conclusion: The assumption that the nominal dose distribution for PTV represents the worst-case dose distribution for CTV appears valid for the ten plans under examination. Although the worst-case dose distribution is unphysical since the dose per voxel is chosen independently, it serves as a lower bound for the possible CTV coverage. Furthermore, this is consistent with the unphysical nature of the PTV. Minor discrepancies between the two dose distributions are expected since the dose cloud is not strictly static. Funding Support: NIH/NCI K25CA168984, Eagles Cancer Research Career Development, The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, Mayo ASU Seed Grant, and The Kemper Marley Foundation