Abstract: BACKGROUND AND PURPOSE: To evaluate the results in terms of dosimetric parameters and acute toxicity of two clinical studies (MARA-1 and MARA-2) on accelerated IMRT-based postoperative radiotherapy. These results are compared with historical control group (CG) of patients treated with "standard" 3D postoperative radiotherapy. MATERIALS AND METHODS: Prescribed dose to the breast was 50.4Gy in the CG, 40Gy in MARA-1 (low risk of local recurrence), and 50Gy in MARA-2 (medium-high risk of recurrence). The tumor bed total dose was 60.4Gy (sequential 10Gy electron boost), 44Gy (concomitant 4Gy boost), and 60Gy (concomitant 10Gy boost) in CG, MARA-1 and MARA-2 studies, respectively. Overall treatment time was of 32 fractions for CG (6.4weeks); 16 fractions for MARA-1 study (3.2weeks) and 25 fractions for MARA-2 study (5weeks). RESULTS: Three hundred and thirty two patients were included in the analysis. Dosimetric analysis showed D(max) and V(107%) reduction (p<0.001) and D(min) improvement (p<0.001) in the PTV in patients treated with IMRT. Grade 2 acute skin toxicity was 33.6%, 13.1%, and 45.1% in the CG, MARA-1, and MARA-2, respectively (p<0.001), and grade 3 acute skin toxicity was 3.1%, 1.0%, and 2.0%, respectively. Similarly, larger PTV and use of chemotherapy with anthracyclines and taxanes were associated with a greater acute toxicity. With a median follow-up of 31 months, no patients showed local or nodal relapse. CONCLUSIONS: A simplified step and shoot IMRT technique allowed better PTV coverage and reduced overall treatment time (CG, 6.6weeks; MARA-1, 3.2weeks; MARA-2, 5weeks) with acceptable short-term toxicity.

Abstract: INTRODUCTION: The breath-hold is one of the techniques to obtain the dose escalation for lung tumors. However, the change of the patient's breath pattern can influence the stability of the inhaled air volume, IAV, used in this work as a surrogate parameter to assure the tumor position reproducibility during dose delivery. MATERIALS AND METHOD: In this paper, an Elekta active breathing coordinator has been used for lung tumor irradiation. This device is not an absolute spirometer and the feasibility study here presented developed (i) the possibility to select a specific range epsilon of IAV values comfortable for the patient and (ii) the ability of a transit signal rate S(t), obtained by a small ion-chamber positioned on the portal image device, to supply in real time the in vivo isocenter dose reproducibility. Indeed, while the selection of the IAV range depends on the patient's ability to follow instructions for breath-hold, the S(t) monitoring can supply to the radiation therapist a surrogate of the tumor irradiation reproducibility. RESULTS: The detection of the S(t) in real time during breath-hold was used to determine the interfraction isocenter dose variations due to the reproducibility of the patient's breathing pattern. The agreement between the reconstructed and planned isocenter dose in breath-hold at the interfraction level was well within 1.5%, while in free breathing a disagreement up to 8% was observed. The standard deviation of the S(t) in breath-hold observed at the intrafraction level is a bit higher than the one obtained without the patient and this can be justified by the presence of a small residual tumor motion as heartbeat. CONCLUSION: The technique is simple and can be implemented for routine use in a busy clinic.

Abstract: BACKGROUND AND PURPOSE: Quality assurance procedures (QA) may reduce the risk of errors in radiotherapy. The aim of this study was to assess a QA program based on independent check (IC) procedures in patients undergoing 3D, intensity modulated (IMRT) and extracranial stereotactic (ESRT) radiotherapy. MATERIALS AND METHODS: IC for set-up (IC1) and for radiotherapy treatments (IC2) was tested on 622 patients over a year. Fifteen events/parameters and 17 parameters were verified by IC1 and IC2, respectively. A third evaluation check (IC3) was performed before treatment. Potential errors were classified based on their magnitude. Incidents involving only incorrect or incomplete documentation were segregated. Treatments were classified based on a complexity index (COMIX). RESULTS: With IC1, 75 documentation incidents and 31 potential errors were checked, and with IC2 111 documentation incidents and 6 potential errors were checked. During the study period 10 errors undetected by standard procedures (IC1, IC2) were detected by chance or by IC3. The incidence of errors and serious errors undetected by standard procedures was 1.6% and 0.6%, respectively. There was no higher incidence of errors undetected in patients undergoing IMRT or ESRT, while there was a higher incidence of errors undetected in more complex treatments (p < 0.001). CONCLUSIONS: Systematic QA procedures can reduce the risk of errors. The risk of errors undetected by standard procedures is not correlated with the treatment technological level (3D versus IMRT/ESRT).

Abstract: A method for the determination of the in vivo isocenter dose, D(iso), has been applied to the dynamic conformal are therapy (DCAT) for thoracic tumors. The method makes use of the transmitted signal, S(t,alpha), measured at different gantry angles, a, by a small ion chamber positioned on the electronic portal imaging device. The in vivo method is implemented by a set of correlation functions obtained by the ratios between the transmitted signal and the midplane dose in a solid phantom, irradiated by static fields. The in vivo dosimetry at the isocenter for the DCAT requires the convolution between the signals, S(t,alpha), and the dose reconstruction factors, C(alpha), that depend on the patient's anatomy and on its tissue inhomogeneities along the beam central axis in the a direction. The C(alpha) factors are obtained by processing the patient's computed tomography scan. The method was tested by taking measurements in a cylindrical phantom and in a Rando Alderson phantom. The results show that the difference between the convolution calculations and the phantom measurements is within +/-2%. The in vivo dosimetry of the stereotactic DCAT for six lung tumors, irradiated with three or four arcs, is reported. The isocenter dose up to 17 Gy per therapy fraction was delivered on alternating days for three fractions. The agreement obtained in this pilot study between the total in vivo dose D(iso) and the planned dose D(iso,TPS) at the isocenter is +/-4%. The method has been applied on the DCAT obtaining a more extensive monitoring of possible systematic errors, the effect of which can invalidate the current therapy which uses a few high-dose fractions.

Abstract: A 2D array (PTW, type 10024), equipped with 729 vented plane parallel ion-chambers, has been calibrated as a detector for the in vivo comparison between measured and predicted portal doses for head-neck tumors. The comparison of absolute portal doses measured to ones predicted by a commercial treatment planning system within the field of view of the CT scanner, can help the delivered dose verification during different treatment fractions, in particular when the patient's present weight loss. This paper reports the preliminary results of the comparison of the portal doses measured by a PTW 2D array during several radiotherapy fractions and the predicted portal doses for seven patients undergoing head-neck tumor radiotherapy. The gamma index analysis supplied an agreement of more than 95% of the dose-point P(gamma)>95% within acceptance criteria, in terms of dose difference, DeltaD(max), and distance-agreement, Deltad(max), equal to 5% and 4mm, respectively. After the third week, one patient showed a decrease of P(gamma) values due to the markedly reduced patient's thickness. Even if the spatial resolution of the 2D array was 1cm, there were two advantages in the use of this 2D array as a portal dose device for IMRT quality control. The first one was the use of a stable and efficient absolute dosimeter for in vivo verification, although its construction and behavior for other gantry angles need to be tested, and the second one was the time efficiency in verifying the correct dose delivery in several fractions of the therapy. This study presents acceptance criteria for the comparison of TPS-predicted portal dose images with in vivo 2D ion-chamber measurements for IMRT. In particular, portal dose measurements offer clues for additional studies as to which indicators can signal the need for replanning during treatment.

Abstract: This work reports a practical method for the determination of the in vivo breast middle dose value, D(m) on the beam central axis, using a signal S(t), obtained by a small thimble ion chamber positioned at the center of the electronic portal imaging device, and irradiated by the x-ray beam transmitted through the patient. The use of a stable ion chamber reduces many of the disadvantages associated with the use of diodes as their periodic recalibration and positioning is time consuming. The method makes use of a set of correlation functions obtained by the ratios S(t)/D(m), determined by irradiating cylindrical water phantoms with different diameters. The method proposed here is based on the determination of the water-equivalent thickness of the patient, along the beam central axis, by the treatment planning system that makes use of the electron densities obtained by a computed tomography scanner. The method has been applied for the breast in vivo dosimetry of ten patients treated with a manual intensity modulation with four asymmetric beams. In particular, two tangential rectangular fields were first delivered, thereafter a fraction of the dose (typically less than 10%) was delivered with two multi leaf-shaped beams which included only the mammarian tissue. Only the two rectangular fields were tested and for every checked field five measurements were carried out. Applying a continuous quality assurance program based on the tests of patient setup, machine settings and dose planning, the proposed method is able to verify agreements between the computed dose D(m,TPS) and the in vivo dose value D(m), within 4%.

Abstract: This work reports the results of the application of a practical method to determine the in vivo dose at the isocenter point, D(iso), of brain thorax and pelvic treatments using a transit signal S(t). The use of a stable detector for the measurement of the signal S(t) (obtained by the x-ray beam transmitted through the patient) reduces many of the disadvantages associated with the use of solid-state detectors positioned on the patient as their periodic recalibration, and their positioning is time consuming. The method makes use of a set of correlation functions, obtained by the ratio between S(t) and the mid-plane dose value, D(m), in standard water-equivalent phantoms, both determined along the beam central axis.The in vivo measurement of D(iso) required the determination of the water-equivalent thickness of the patient along the beam central axis by the treatment planning system that uses the electron densities supplied by calibrated Hounsfield numbers of the computed tomography scanner. This way it is, therefore, possible to compare D(iso) with the stated doses, D(iso,TPS), generally used by the treatment planning system for the determination of the monitor units.The method was applied in five Italian centers that used beams of 6 MV, 10 MV, 15 MV x-rays and (60)Co gamma-rays. In particular, in four centers small ion-chambers were positioned below the patient and used for the S(t) measurement. In only one center, the S(t) signals were obtained directly by the central pixels of an EPID (electronic portal imaging device) equipped with commercial software that enabled its use as a stable detector.In the four centers where an ion-chamber was positioned on the EPID, 60 pelvic treatments were followed for two fields, an anterior-posterior or a posterior-anterior irradiation and a lateral-lateral irradiation. Moreover, ten brain tumors were checked for a lateral-lateral irradiation, and five lung tumors carried out with three irradiations with different gantry angles were followed. One center used the EPID as a detector for the S(t) measurement and five pelvic treatments with six fields (many with oblique incidence) were followed. These last results are reported together with those obtained in the same center during a pilot study on ten pelvic treatments carried out by four orthogonal fields.The tolerance/action levels for every radiotherapy fraction were 4% and 5% for the brain (symmetric inhomogeneities) and thorax/pelvic (asymmetric inhomogeneities) irradiations, respectively. This way the variations between the total measured and prescribed doses at the isocenter point in five fractions were well within 2% for the brain treatment, and 4% for thorax/pelvic treatments. Only 4 out of 90 patients needed new replanning, 2 patients of which needed a new CT scan.

Abstract: The case is reported of a patient with locally recurrent carcinoma of the tongue treated with intensity-modulated radiotherapy (IMRT) (simultaneous integrated boost) plus concurrent chemotherapy, who during the third week of radiotherapy developed grade 3 mucositis.Treatment was interrupted for 10 days until significant resolution of the symptoms. At the time of treatment resumption the patient showed 8% weight loss, and in vivo portal dose verification revealed large discrepancies between the computed and measured doses. A new CT scan showed marked tumor shrinkage and modifications to the critical structures. The comparison between the original plan and the hybrid IMRT showed a minimal dose increase in the new target volumes and a marked dose increase in the organs at risk. This case confirms the need for a robust quality assurance program when using IMRT, the feasibility and efficacy of in vivo dosimetry to detect significant discrepancies between planned and delivered dose, and the need to combine IMRT with 4-dimensional radiotherapy, at least for head and neck cancer.

Abstract: A method for the in vivo determination of the isocenter dose, Diso, and mid-plane dose, Dm, using the transmitted signal St measured by 25 central pixels of an aSi-based EPID is here reported. The method has been applied to check the conformal radiotherapy of pelvic tumors and supplies accurate in vivo dosimetry avoiding many of the disadvantages associated with the use of two diode detectors (at the entrance and exit of the patient) as their periodic recalibration and their positioning. Irradiating water-equivalent phantoms of different thicknesses, a set of correlation functions F(w, l) were obtained by the ratio between St and Dm as a function of the phantom thickness, w, for a different field width, l. For the in vivo determination of Diso and Dm values, the water-equivalent thickness of the patients (along the beam central axis) was evaluated by means of the treatment planning system that uses CT scans calibrated in terms of the electron densities. The Diso and Dm values experimentally determined were compared with the stated doses D(iso,TPS) and D(m,TPS), determined by the treatment planning system for ten pelvic treatments. In particular, for each treatment four fields were checked in six fractions. In these conditions the agreement between the in vivo dosimetry and stated doses at the isocenter point were within 3%. Comparing the 480 dose values obtained in this work with those obtained for 30 patients tested with a similar method, which made use of a small ion-chamber positioned on the EPIDs to obtain the transmitted signal, a similar agreement was observed. The method here proposed is very practical and can be applied in every treatment fraction, supplying useful information about eventual patient dose variations due to the incorrect application of the quality assurance program based on the check of patient setup, machine setting, and calculations.

Abstract: A new 2D array Seven 29T model (PTW, Freiburg), equipped with 729 vented plane-parallel ion chambers, projected for pretreatment verification of radiotherapy plans, was used as a detector for the transmitted or portal dose measurements below a Rando phantom. The dosimetric qualities of the 2D array make it attractive for measuring transmitted dose maps from step-and-shoot intensity-modulated radiotherapy (IMRT). It is well known that for step-and-shoot IMRT beams that use a small number of monitor units (MUs) per sequence, the early and recent electronic portal imaging devices (EPIDs) present a different response at X-ray start-up that affects the accuracy of the measured transmitted dose. The comparison of portal doses measured to those calculated by a commercial treatment-planning system (TPS) can verify correct dose delivery during treatment. This direct validation was tested by irradiating a simulated head tumor in a Rando anthropomorphic phantom by step-and-shoot IMRT beams. The absolute transmitted doses on a plane orthogonal to the beam central axis below the phantom were measured by the 2D array calibrated in terms of dose to water and compared with the computed portal dose extracted by custom software. In a previous paper, the comparison between the IMRT portal doses, computed by a commercial TPS and measured by a linear array that supplied a 1 mm spatial dose resolution, was carried out. The gamma-index analysis supplied an agreement of more than 95% of the dose point with acceptance criteria, in terms of dose difference, DeltaDmax, and distance agreement, deltadmax, equal to 4% and 4 mm, respectively. In this paper, we verify the possible use of the PTW 2D array for measurements of the transmitted doses during several fractions of head and neck tumor radiotherapy. There are two advantages in the use of this 2D array as a portal dose device for the IMRT quality assurance program: first is the ability to perform absolute dose comparisons for hundreds of measurement positions to verify the correct dose delivery in several fractions of the therapy; second is the efficiency in time to detect these kinds of dose distributions within the field of view area of the CT scanner.

Abstract: As all methods for in-vivo dosimetry require special efforts many physicists are often discouraged in verifying the middle dose in a patient along the beam central axis. This work reports a practical method for the determination of the middle dose value, D(m), on the central beam axis, using a signal S(t), obtained by a small thimble ion-chamber positioned at the center of the electronic portal imaging device, and irradiated by the X-ray beam transmitted through the patient. The use of a stable ion-chamber reduces many of the disadvantages associated to the use of diodes as their periodic recalibration and time consuming positioning. The method makes use of a set of correlation functions obtained by the S(t) and D(m) ratios, determined by irradiating a water-equivalent phantom with 6 MV, 10 MV and 5 MV X-ray beams. Several tests were carried out in phantoms with asymmetric inhomogeneities. The method here proposed is based on the determination of the water-equivalent thickness of the patient, along the beam central axis, by the treatment planning system that makes use of the electron densities obtained by a computer tomography scanner, that works with calibrated Hounsfield numbers. This way, it is therefore possible to compare the dose, D(m, TPS), obtained by a treatment planning system, with the in-vivo dose D(m) value, both defined at density middle point (identified along the beam central axis, where the thick material, in terms of g cm(-2), above and below, is the same). The method has been applied for the in-vivo dosimetry of 30 patients, treated with conformed beams for pelvic tumor, checking: anterior-posterior or posterior-anterior irradiations and lateral-lateral irradiations. For every checked field at least five measurements were carried out. Applying a correct quality assurance program based on the tests of the patient set-up, machine settings and calculations, results showed that the method is able to verify agreements between the dose D(m,TPS) and the in-vivo dose value D(m), within 4% for 95% of the 240 measurements carried out in-vivo.

Abstract: In the last two decades there was a radical change in radiotherapy setup. The growing availability of CT equipment and console for computer-aided treatment planning setup enabled the use of advanced technologies as conformal 3D radiation therapy in most centers. In particular in 1987 virtual simulation was proposed for setup. During its use a number of application modalities appeared. Virtual simulation in some centers is applied alone while in others it is associated with conventional simulation. However, from numerous reports published in last years it seems that virtual simulation significantly improves treatment quality independently of radical or palliative intent and of the size of treated volumes (high doses to small volumes or wide shaped fields). Some studies stressed that virtual simulation could significantly shorten treatment planning times with consequent cost reduction. The use of virtual simulation evidenced associated problems and in particular setup limitations due to the CT gantry size, the need to up-date the conventional modalities of setup verification according to the new technologies and more generally to up-date quality assurance procedures in an advanced technological setting. Finally there was the self-evident need of a better knowledge of the anatomy on axial sections, of tumor spread routes in particular.