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Background & purpose Lean Six Sigma Methodology (LSSM) was introduced in industry to provide near-perfect services to large processes, by reducing improbable occurrence. LSSM has been applied to redesign the 2D-2D breast repositioning process (Lean) by the retrospective analysis of the database (Six Sigma). Materials & methods Breast patients with daily 2D-2D matching before RT were considered. The five DMAIC (define, measure, analyze, improve, and control) LSSM steps were applied. The process was retrospectively measured over 30 months (7/2014–12/2016) by querying the RT Record&Verify database. Two Lean instruments (Poka-Yoke and Visual Management) were considered for advancing the process. The new procedure was checked over 6 months (1–6/2017). Results 14,931 consecutive shifts from 1342 patients were analyzed. Only 0.8% of patients presented median shifts >1 cm. The major observed discrepancy was the monthly percentage of fractions with almost zero shifts (AZS = 13.2% ± 6.1%). Ishikawa fishbone diagram helped in defining the main discrepancy con-causes. Procedure harmonization involving a multidisciplinary team to increase confidence in matching procedure was defined. AZS was reduced to 4.8% ± 0.6%. Furthermore, distribution symmetry improvement (Skewness moved from 1.4 to 1.1) and outlier reduction, verified by Kurtosis diminution, demonstrated a better “normalization” of the procedure after the LSSM application. Conclusions LSSM was implemented in a RT department, allowing to redesign the breast repositioning matching procedure.

Volumetric modulated arc therapy (VMAT) for left breast treatments allows heart sparing without compromising PTV coverage. However, this technique may require highly complex plans. Deep Inspiration Breath Hold (DIBH) procedure increases the heart-to-breast distance, facilitating the dose sparing of the heart. The aim of the present work was to investigate if the cardiac-sparing benefits of the DIBH technique were achieved with lower plan modulation and complexity than Free Breathing (FB) treatments.Ten left side breast cases were considered by two centers with different treatment planning systems (TPS) and Linacs. VMAT plans were elaborated in FB and DIBH according to the same protocol. Plan complexity was evaluated by scoring several complexity indices. A new global score index accounting for both plan quality and dosimetric parameters was defined. Pre-treatment QA was performed for all VMAT plans using EPID and Epiqa software.DIBH-VMAT plans were associated with significant PTV coverage improvement and mean heart dose reduction (p 0.003), increasing the resulting global score index. All the evaluated complexity indices showed lower plan complexity for DIBH plans than FB ones, but only in few cases the results were statistically significant. All plans passed the gamma analysis with the selected criteria.The DIBH technique is superior to the FB technique when the heart needs further sparing, allowing a reduction of the doses to OARs with a slightly lower degree of plan complexity and without compromising plan deliverability. These benefits were achieved regardless of the technological scenarios adopted.

Purpose Radiotherapy with intensity modulation (IMRT and VMAT) implies the setup of adequate QA programs to guarantee safe treatments. Concerning this issue, amorphous silicon EPID technologies are particularly interesting due to their high spatial resolution, large area, stability, dynamic range, and real-time acquisition capabilities. In this context, the GLAaS [1] algorithm has proved capable to meet a variety of applications with a simple direct calibration process to convert raw measurements into absorbed-dose-to-water; nevertheless, GLAaS was never validate with a different technology apart from Varian-EPIDs. To test its feasibility out of single manufacture environment, GLAaS was applied to Elekta iViewGT images. Methods GLAaS accounts for pixel-by-pixel response changes in time differentiating on field and/or segment sizes and beam quality, i.e. primary or transmitted radiation (e.g. below MLC), basis. Dosimetric data from a 6 MV Elekta-Synergy were collected at dmax and SDD = 160 cm (EPID position), for primary and transmitted radiation to be correlated with iViewGT pixel reading (R). For open and modulated fields, comparison to TPS dose maps (Monaco-XVMonteCarlo) was assessed through profiles and gamma analysis. Results For a given beam, the response of iViewGT was confirmed to be linear (D(Gy) = m ∗ R + q), as already established for Varian EPIDs. Similarly, the variable slope response to primary radiation was modelled according to the following empirical algorithm: m pr ( OF ) = a · OF + b; OF ( EwwF ) = [ c + d · ln ( EwwF ) - 1 where EwwF is the equivalent field size of each segment based on IC data and OF is the EPID reading measured output factor. For transmitted radiation the relation mtr = k · mpr was adopted. Download : Download high-res image (325KB) Download : Download full-size image Conclusions The extension of GLAaS to iViewGT offers the opportunity to easily set-up flexible and reliable verification, also in highly demanding conditions as for SRS and SBRT treatments; the compatibility with different technologies could encourage multi-centers studies concerning treatment delivery and dose calculation problematics.

Purpose The concept of quality assurance in radiotherapy encompasses a comprehensive approach to all activities in the department. When hypo-fractionation regiment is adopted, the need of a continuous quality procedures updating is self-evident. At this aim, the Lean Six Sigma Methodology (LSSM) has been applied. LSSM was introduced in industry for providing near-perfect services to large processes, by reducing improbable occurrence. It consists of the synergetic adoption of two methods: (i) create a continuous process flow eliminating waste (Lean); (ii) reduce process variation (Six sigma). LSSM has been prospectively applied to breast patient repositioning. This is the first time the LSSM has been rigorously applied to a RT process. Methods Breast patients treated by hypo-fractionated RT in SIB delivered through VMAT technology with daily 2D-2D matching were considered. The five DMAIC (Define, Measure, Analyze, Improve, Control) LSSM steps were applied by an interdisciplinary team. The process was retrospective measured over 30 months (Jul2014–Dec2016) by querying the RT RecordV distribution symmetry improvement (Skewness moved from 1.4 to 1.1) and outlier eduction, verified by Kurtosis diminution, demonstrated better “normalization” of the procedure after the LSSM application. Conclusions LSSM was successfully applied in a RT department, allowing the breast repositioning matching procedure to be redesigned.

Purpose: Complex radiotherapy fields delivered using a tertiary multileaf collimator(MLC) often feature small open segments surrounded by large areas of the beam only shielded by the MLC. The aim of this study was to test the ability of two modern dose calculation algorithms to accurately calculate the dose in these fields which would be common, for example, in volumetric modulated arc treatment (VMAT) and study the impact of variations in dosimetric leaf gap (DLG), focal spot size, and MLC transmission in the beam models. Methods: Nine test fields with small fields (0.6–3 cm side length) surrounded by large MLC shielded areas (secondary collimator 12 × 12 cm2) were created using a 6 MV beam from a Varian Clinac iX linear accelerator with 120 leaf MLC. Measurements of output factors and profiles were performed using a diamond detector (PTW) and compared to two dose calculations algorithms anisotropic analytical algorithm [(AAA) and Acuros XB] implemented on a commercial radiotherapytreatment planning system (Varian Eclipse 10). Results: Both calculation algorithms predicted output factors within 1% for field sizes larger than 1 × 1 cm2. For smaller fields AAA tended to underestimate the dose. Profiles were predicted well for all fields except for problems of Acuros XB to model the secondary penumbra between MLC shielded fields and the secondary collimator. A focal spot size of 1 mm or less, DLG 1.4 mm and MLC transmission of 1.4% provided a generally good model for our experimental setup. Conclusions: AAA and Acuros XB were found to predict the dose under small MLC defined field segments well. While DLG and focal spot affect mostly the penumbra, the choice of correct MLC transmission will be essential to model treatments such as VMAT accurately.

Purpose : Flattening filter free (FFF) beams generated by medicallinear accelerators have recently started to be used in radiotherapy clinical practice. Such beams present fundamental differences with respect to the standard filter flattened (FF) beams, making the generally used dosimetric parameters and definitions not always viable. The present study will propose possible definitions and suggestions for some dosimetric parameters for use in quality assurance of FFF beams generated by medicallinacs in radiotherapy. Methods : The main characteristics of the photon beams have been analyzed using specific data generated by a Varian TrueBeam linac having both FFF and FF beams of 6 and 10 MV energy, respectively. Results : Definitions for dose profile parameters are suggested starting from the renormalization of the FFF with respect to the corresponding FF beam. From this point the flatness concept has been translated into one of “unflatness” and other definitions have been proposed, maintaining a strict parallelism between FFF and FF parameter concepts. Conclusions : Ideas for quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given here, keeping them similar to those used for standard FF beams. By following the suggestions in this report, the authors foresee that the introduction of FFF beams into a clinical radiotherapy environment will be as safe and well controlled as standard beam modalities using the existing guidelines.

To assess the clinical impact of the Acuros XB algorithm (implemented in the Varian Eclipse treatment-planning system) in non-small-cell lung cancer (NSCLC) cases.A CT dataset of 10 patients presenting with advanced NSCLC was selected and contoured for planning target volume, lungs, heart, and spinal cord. Plans were created for 6-MV and 15-MV beams using three-dimensional conformal therapy, intensity-modulated therapy, and volumetric modulated arc therapy with RapidArc. Calculations were performed with Acuros XB and the Anisotropic Analytical Algorithm. To distinguish between differences coming from the different heterogeneity management and those coming from the algorithm and its implementation, all the plans were recalculated assigning Hounsfield Unit (HU) = 0 (Water) to the CT dataset.Differences in dose distributions between the two algorithms calculated in Water were0.5%. This suggests that the differences in the real CT dataset can be ascribed mainly to the different heterogeneity management, which is proven to be more accurate in the Acuros XB calculations. The planning target dose difference was stratified between the target in soft tissue, where the mean dose was found to be lower for Acuros XB, with a range of 0.4% ± 0.6% (intensity-modulated therapy, 6 MV) to 1.7% ± 0.2% (three-dimensional conformal therapy, 6 MV), and the target in lung tissue, where the mean dose was higher for 6 MV (from 0.2% ± 0.2% to 1.2% ± 0.5%) and lower for 15 MV (from 0.5% ± 0.5% to 2.0% ± 0.9%). Mean doses to organs at risk presented differences up to 3% of the mean structure dose in the worst case. No particular or systematic differences were found related to the various modalities. Calculation time ratios between calculation time for Acuros XB and the Anisotropic Analytical Algorithm were 7 for three-dimensional conformal therapy, 5 for intensity-modulated therapy, and 0.2 for volumetric modulated arc therapy with RapidArc.The availability of Acuros XB could improve patient dose estimation, increasing the data consistency of clinical trials.

Purpose To evaluate the performance of a model-based optimisation process for volumetric modulated arc therapy, VMAT, applied to whole breast irradiation. Methods and Materials A set of 150 VMAT dose plans with simultaneous integrated boost were selected to train a model for the prediction of dose-volume constraints. The dosimetric validation was done on different groups of patients from three institutes for single (50 cases) and bilateral breast (20 cases). Results Quantitative improvements were observed between the model-based and the reference plans, particularly for heart dose. Of 460 analysed dose-volume objectives, 13% of the clinical plans failed to meet the constraints while the respective model-based plans succeeded. Only in 5 cases did the reference plans pass while the respective model-based failed the criteria. For the bilateral breast analysis, the model-based plans resulted in superior or equivalent dose distributions to the reference plans in 96% of the cases. Conclusions Plans optimised using a knowledge-based model to determine the dose-volume constraints showed dosimetric improvements when compared to earlier approved clinical plans. The model was applicable to patients from different centres for both single and bilateral breast irradiation. The data suggests that the dose-volume constraint optimisation can be effectively automated with the new engine and could encourage its application to clinical practice.

Purpose: To assess the accuracy against measurements of two photon dose calculation algorithms (Acuros XB and the Anisotropic Analytical algorithm AAA) for small fields usable in stereotactic treatments with particular focus on RapidArc. Methods: Acuros XB and AAA were configured for stereotactic use. Baseline accuracy was assessed on small jaw-collimated open fields for different values for the spot sizes parameter in the beam data: 0.0, 0.5, 1, and 2 mm. Data were calculated with a grid of 1 x 1 mm{sup 2}. Investigated fields were: 3 x 3, 2 x 2, 1 x 1, and 0.8 x 0.8 cm{sup 2} with a 6 MV photon beam generated from a Clinac2100iX (Varian, Palo Alto, CA). Profiles, PDD, and output factors were measured in water with a PTW diamond detector (detector size: 4 mm{sup 2}, thickness 0.4 mm) and compared to calculations. Four RapidArc test plans were optimized, calculated and delivered with jaw settings J3 x 3, J2 x 2, and J1 x 1 cm{sup 2}, the last was optimized twice to generate high (H) and low (L) modulation patterns. Each plan consisted of one partial arc (gantry 110 deg. to 250 deg.), and collimator 45 deg. Dose to isocenter was measuredmore » in a PTW Octavius phantom and compared to calculations. 2D measurements were performed by means of portal dosimetry with the GLAaS method developed at authors' institute. Analysis was performed with gamma pass-fail test with 3% dose difference and 2 mm distance to agreement thresholds. Results: Open square fields: penumbrae from open field profiles were in good agreement with diamond measurements for 1 mm spot size setting for Acuros XB, and between 0.5 and 1 mm for AAA. Maximum MU difference between calculations and measurements was 1.7% for Acuros XB (0.2% for fields greater than 1 x 1 cm{sup 2}) with 0.5 or 1 mm spot size. Agreement for AAA was within 0.7% (2.8%) for 0.5 (1 mm) spot size. RapidArc plans: doses were evaluated in a 4 mm diameter structure at isocenter and computed values differed from measurements by 0.0, -0.2, 5.5, and -3.4% for Acuros XB calculations (1 mm spot size), and of -0.1, 0.3, 6.7, and -1.2% for AAA, respectively for J3 x 3, J2 x 2, J1 x 1H, J1 x 1L RapidArc plans. Gamma Agreement Index from 2D dose analysis was higher than 95% for J3 x 3 and J2 x 2 plans, being around 80% for J1 x 1 maps. Sensitivity with respect to the dosimetric leaf gap and transmission factor MLC parameters was evaluated in the four RapidArc plans, showing the need to properly set the dosimetric leaf gap for accurate calculations. Conclusions: Acuros XB and AAA showed acceptable characteristics for stereotactic small fields if adequate tuning of configuration parameters is performed. Dose calculated for RapidArc stereotactic plans showed an acceptable agreement against point and 2D measurements. Both algorithms can therefore be considered safely applicable to stereotactic treatments.« less

Purpose: The RapidArc volumetric modulated arc therapy (VMAT) planning process is based on a core engine, the so-called progressive resolution optimizer (PRO). This is the optimization algorithm used to determine the combination of field shapes, segment weights (with dose rate and gantry speed variations), which best approximate the desired dose distribution in the inverse planning problem. A study was performed to assess the behavior of two versions of PRO. These two versions mostly differ in the way continuous variables describing the modulated arc are sampled into discrete control points, in the planning efficiency and in the presence of some new features. The analysis aimed to assess (i) plan quality, (ii) technical delivery aspects, (iii) agreement between delivery and calculations, and (iv) planning efficiency of the two versions. Methods: RapidArc plans were generated for four groups of patients (five patients each): anal canal, advanced lung, head and neck, and multiple brain metastases and were designed to test different levels of planning complexity and anatomical features. Plans from optimization with PRO2 (first generation of RapidArc optimizer) were compared against PRO3 (second generation of the algorithm). Additional plans were optimized with PRO3 using new features: the jaw tracking, the intermediate dose and the air cavity correction options. Results: Results showed that (i) plan quality was generally improved with PRO3 and, although not for all parameters, some of the scored indices showed a macroscopic improvement with PRO3. (ii) PRO3 optimization leads to simpler patterns of the dynamic parameters particularly for dose rate. (iii) No differences were observed between the two algorithms in terms of pretreatment quality assurance measurements and (iv) PRO3 optimization was generally faster, with a time reduction of a factor approximately 3.5 with respect to PRO2. Conclusions: These results indicate that PRO3 is either clinically beneficial or neutral in terms of dosimetric quality while it showed significant advantages in speed and technical aspects.

Purpose In breast radiotherapy with intensity modulation, it is a well established practice to extend the dose fluence outside the limit of the body contour to account for small changes in size and position of the target and the rest of the tissues due to respiration or to possible oedema. A simple approach is not applicable with RapidArc volumetric modulated are therapy not being based on a fixed field fluence delivery. In this study, a viable technical strategy to account for this need is presented. Methods RapidArc (RA) plans for six breast cancer patients (three right and three left cases), were optimized (PRO version III) on the original CT data set (0) and on an alternative CT (E) generated with an artificial expansion (and assignment of soft-tissue equivalent HU) of 10 mm of the body in the breast region and of the PTV contours toward the external direction. Final dose calculations for the two set of plans were performed on the same original CT data set O, normalizing the dose prescription (50 Gy) to the target mean. In this way, two treatment plans on the same CT set O for each patient were obtained: the no action plan (OO) and the alternative plan based on an expanded optimization (EO). Fixing MU, these two plans were then recomputed on the expanded CT data set and on an intermediate one (with expansion = 5 mm), to mimic, possible changes in size due to edema during treatment or residual displacements due to breathing not properly controlled. Aim of the study was to quantify the robustness of this planning strategy on dose distributions when either the OO or the EO strategies were adopted. For all the combinations, a DVH analysis of all involved structures is reported. Results I. The two optimization approaches gave comparable dose distributions on the original CT data set. II. When plans were evaluated on the expanded CTs (mimicking the presence of edema), the EO approach showed improved target coverage if compared to OO: on CT_10 mm, Dv = 98% [%]= 92.5 +/- 0.9 and 68.5 +/- 3.1, respectively, for EO and OO. Minor changes were registered in organs at risk sparing for both EO and OO. III. From dose distributions and DVHs, EO approach allowed to irradiate at near to prescription levels also the expanded fraction of the target: this would account also for residual intrafraction movements. Conclusions The proposed plan strategy could represent a robust approach to account for moderate changes in target or body volume during the course of breast radiotherapy and to account for residual intrafractional respiratory motion in volumetric modulated are therapy. The strategy, logistically simple to implement requiring only modifications to the standard planning workflow was routinely implemented at author's institute for treatment of breast patients with RapidArc.

A preclinical investigation was undertaken to explore a treatment technique for total marrow irradiation using RapidArc, a volumetric modulated arc technique.Computed tomography datasets of 5 patients were included. Plans with eight overlapping coaxial arcs were optimized for 6-MV photon beams. Dose prescription was 12 Gy in 2 Gy per fraction, normalized so that 100% isodose covered 85% of the planning target volume (PTV). The PTV consisted of the whole skeleton (including ribs and sternum), from the top of the skull to the medium distal third of the femurs. Planning objectives for organs at risk (OARs) were constrained to a median dose6 to 7 Gy. OARs included brain, eyes, oral cavity, parotids, thyroid, lungs, heart, kidneys, liver, spleen, stomach, abdominal cavity, bladder, rectum, and genitals. Pretreatment quality assurance consisted of portal dosimetry comparisons, scoring the delivery to calculation agreement with the gamma agreement index.The median total body volume in the study was 57 liters (range, 49-81 liters), for an average diameter of 47 cm (range, 46-53 cm) and a total length ranging from 95 to 112 cm. The median PTV volume was 6.8 liters (range, 5.8-10.8 liters). The mean dose to PTV was 109% (range, 107-112%). The global mean of median dose to all OARs was 4.9 Gy (range, 4.5-5.1 Gy over the 5 patients). The individual mean of median doses per organ ranged from 2.3 Gy (oral cavity) to 7.3 Gy (bowels cavity). Preclinical quality assurance resulted in a mean gamma agreement index of 94.3 ± 5.1%. The delivery time measured from quality assurance runs was 13 minutes.Sparing of normal tissues with adequate coverage of skeletal bones was shown to be feasible with RapidArc. Pretreatment quality assurance measurements confirmed the technical agreement between expected and actually delivered dose distributions, suggesting the possibility of incorporating this technique in the treatment options for patients.

Purpose To report the treatment of cranio-spinal irradiation (CSI) with volumetric modulated arc therapy (RapidArc) in adults and a child. Materials and methods Five patients from 5 institutions were treated with CSI using RapidArc technology. Patient age varied between 7 and 45years. The lengths of the planning target volumes (PTV) and dose prescriptions ranged from 54.6 to 78.4cm, and from 12 to 36Gy, respectively. Different arc arrangements were used, with two or three isocentres, from two to six modulated arcs, for patient positioned either in prone ( n =3) or supine position ( n =2). Doses to PTV, organs at risk and non-target tissue are reported for each of the five patients. Data concerning imaging strategy and pre-treatment quality assurance are also reported. Results The mean conformity index CI 95% was 1.05±0.05 (range: 1.00, 1.13). Mean doses to the lenses, lungs, heart, and kidneys were, respectively, 7.6±1.6, 6.6±3.0, 5.7±2.3, and 6.1±2.1Gy, keeping those value acceptably low. Mean non-target tissue dose was 21.0±3.8% (5.6±1.8Gy, range: 3.0–8.1Gy). All patients were successfully planned and treated with RapidArc. Conclusions RapidArc techniques achieved highly conformal treatment plans for 5 adults or paediatric patients. Beam-on time was short, and RapidArc plans were satisfactorily delivered to all presented patients.

Purpose: A study was carried out to evaluate the robustness and mutual interplay of two variables concurring to generate modulation patterns of the RapidArc (RapidArc) implementation of volumetric modulated arc therapy. Dose rate (DR) and gantry speed (GS) are free parameters optimized alongside field aperture shape by the RapidArc engine; however, they are limited by machine constraints and mutually compensate in order to deliver the proper MU/deg during the gantry rotation. Methods: Four test cases (one geometrical and three clinical) were selected and RapidArc plans were optimized using maximum allowed dose rates from 100 to 600 MU/min. The maximum gantry speed was fixed at 4.8 deg/s. Qualitative analysis of DR and GS patterns from these cases was summarized together with quantitative assessment of delivery parameters. Pretreatment quality assurance measurements and scoring of plan quality aimed to determine whether preferable initial conditions might be identified or the optimization engine might be invariant to those variables and capable of providing adequate plans independently from the limits applied. Results: The results of the study were: (i) High dynamic range in MU/deg is achievable across all dose rates by means of gantry speed modulation; (ii) there is a robust compensation mechanism between the twomore » variables; (iii) from a machine delivery point-of-view, slightly improved accuracy is achieved when lower DRs are applied; however, this does not have practical consequences since measurements and plan evaluation showed a lack of clinically relevant deviation; and (iv) reduced total treatment time is a major advantage of high DR. Conclusions: A trend toward improved plan quality for clinical cases was observed with high DR but cannot be generalized, due to the limited amount of cases investigated and the consequent limited significance of the observed differences. As a minimum benefit, the reduced total treatment time should be considered as well.« less

Purpose: In 2008, a national intensity modulated radiation therapy (IMRT) dosimetry intercomparison was carried out for all 23 radiation oncology institutions in Switzerland. It was the aim to check the treatment chain focused on the planning, dose calculation, and irradiation process. Methods: A thorax phantom with inhomogeneities was used, in which thermoluminescence dosimeter (TLD) and ionization chamber measurements were performed. Additionally, absolute dosimetry of the applied beams has been checked. Altogether, 30 plan-measurement combinations have been used in the comparison study. The results have been grouped according to dose calculation algorithms, classified as ``type a`` or ``type b,`` as proposed by Knoos et al. [``Comparison of dose calculation algorithms for treatment planning in external photon beam therapy for clinical situations,`` Phys. Med. Biol. 51, 5785-5807 (2006)]. Results: Absolute dosimetry check under standard conditions: The mean ratio between the dose derived from the single field measurement and the stated dose, calculated with the treatment planning system, was 1.007 +/- 0.010 for the ionization chamber and 1.002 +/- 0.014 (mean +/- standard deviation) for the TLD measurements. IMRT Plan Check: In the lung tissue of the planning target volume, a significantly better agreement between measurements (TLD, ionization chamber) and calculations is shown for type b algorithms than for type a (p > 0.001). In regions outside the lungs, the absolute differences between TLD measured and stated dose values, relative to the prescribed dose, vertical bar(D-m - D-s) / D-prescribed vertical bar, are 1.9 +/- 0.4% and 1.4 +/- 0.3%, respectively. These data show the same degree of accuracy between the two algorithm types if low-density medium is not present. Conclusions: The results demonstrate that the performed intercomparison is feasible and confirm the calculation accuracies of type a and type b algorithms in a water equivalent and low-density environment. It is now planned to offer the intercomparison on a regular basis to all Swiss institutions using IMRT techniques. (C) 2010 American Association of Physicists in Medicine. [DOT: 10.1118/1.3460795]

Radiosensitive neurogenic stem cells reside in the hippocampi, suggesting that avoidance of the hippocampi may be an important strategy to reduce potential radiation-related cognitive effects. Six patients treated for base of skull tumours were re-planned using co-planar helical fan beam arc therapy (tomotherapy) and co-planar and non-coplanar volumetric arc techniques (RapidArc). The hippocampi were contoured as avoidance structures with the specific goal of minimising the dose. Two gross target volume (GTV) to planning target volume (PTV) expansions (10 and 2 mm) were considered to evaluate the impact of margin selection on organ at risk (OAR) sparing. The dose prescription was 50 Gy to >95% of the PTV. Comparison of the hippocampus avoidance plans demonstrated the importance of non-coplanar delivery when the 10 mm margin was used. With the 2 mm margin, both co-planar and non-coplanar delivery provided similar degrees of sparing. A mean dose of 3–4 Gy and a V6Gy

A study was carried out to evaluate the possibility of delivering volumetric modulated arc therapy with the RapidArc technology under respiratory-gated conditions. The experiments were performed in the framework of a non-clinically released environment. Plans of six patients, all realized for a single arc, were used for the experiments. The Real-time Position Management (RPM) respiratory gating system from Varian was used to generate gate-open signals of different durations. Arcs were delivered applying the different gates creating sequences of beam-hold/beam-on during the dose delivery: the average number of interruptions for a single arc ranged from 0 to 45. Dose prescription was set to 2 Gy and different gate-open periods of 30, 15 and 5 s to keep gantry speed constant at maximum. 5 Gy and 15 Gy doses were then applied to gate-open signals of 5 and 8 s, respectively, to mimic the most challenging conditions of slow gantry rotation and high-frequency interruptions. The 5 and 15 Gy experiments represent dose conditions of clinical interest for stereotactic treatments. For each patient and gating condition, pre-treatment 2D verification measurements were performed using the PTW-729 array in conjunction with the Octavius phantom (PTW, Freiburg); measurements were performed on different days (one per patient, with the complete setup of phantom and detectors every time), while each gating experiment was repeated seven consecutive times for reproducibility (without a new setup of the measurement equipment). Measurements were compared with dose calculations in the treatment planning system (performed without any gating) to appraise the dosimetric impact of the presence of gating and the eventual dependence from the number of interruptions during a single arc. Analysis of machine-registered log files in terms of average deviations between actual and expected positions (from automatic measurements every 50 ms) resulted in mean Delta MU (monitor units)

A treatment planning study was performed to compare volumetric-modulated arc radiotherapy against conventional fixed field IMRT.CT datasets of 10 patients affected by carcinoma of the anal canal were included and five plans were generated for each case: fixed beam IMRT, single (RA1)- and double (RA2)-modulated arcs with the RapidArc technique. Dose prescription was set according to a simultaneous integrated boost strategy to 59.4 Gy to the primary tumour PTVI (at 1.8 Gy/fraction) and to 49.5 Gy to risk area including inguinal nodes, PTVII. Planning objectives for PTV were minimum dose95%, maximum dose107%; for organs at risk (OARs): bladder (mean45 Gy, D(2%)56 Gy, D(30%)35 Gy), femurs (D(2%)47 Gy), small bowel (mean30 Gy, D(2%)56 Gy). MU and delivery time scored treatment efficiency.All techniques fulfilled objectives on maximum dose. Some deviations were observed on minimum dose for PTV. Uniformity (D(5)-D(95)) on PTVI resulted 6.6+/-1.4% for IMRT and ranged from 5.7+/-0.3% to 8.1+/-0.8% for RA plans (+/-1 standard deviation). Conformity index (CI(95%)) was 1.3+/-0.1 (IMRT) and 1.4+/-0.1 (all RA techniques). Bladder: all techniques resulted equivalent above 40 Gy; V(30 Gy) approximately 57% for the double arcs, approximately 61% for RA1 and approximately 65% for IMRT. Femurs: maximum dose was of the order of 41-42 Gy for all RA plans and approximately 45 Gy for IMRT. Small bowel: all techniques respected planning objectives. The number of computed MU/fraction was 1531+/-206 (IMRT), 468+/-95 (RA1), and 545+/-80 (RA2) leading to differences in treatment time: 9.4+/-1.7 min for IMRT vs. 1.1+/-0.0 min for RA1 and 2.6+/-0.0 min for double arcs.RapidArc showed improvements in organs at risk and healthy tissue sparing with uncompromised target coverage when double arcs are applied. Optimal results were also achieved anyway with IMRT plans.

Background and purpose The potential benefits and limitations of the new RapidArc treatment concept compared to Helical Tomotherapy and fixed gantry intensity modulation techniques have been assessed at treatment planning level on 12 patients presenting with ‘benign' brain tumours. Materials and methods Plans for five acoustic neurinomas, five meningiomas and two pituitary adenomas were computed for an Helical Tomotherapy (HT) unit, for RapidArc delivery (RA) on a linac equipped with two types of MLC (RA_HD120 with the new High Definition MLC with 2.5mm leaf width at isocentre and RA_M120 with the standard Millennium with 5mm resolution) and for fixed beam IMRT with the High Definition MLC. Analysis was mostly performed on physical quantities derived from Dose–Volume Histograms (DVHs). Results Target coverage resulted basically equivalent among techniques. V 95% (in %) was higher than 99% for all techniques, minimum significant dose ( D 99% ) was 95.5±1.4 for IMRT, 96.2±1.4 and 97.0±1.2 for the RA_HD120 and RA_M120 approaches and 96.8±1.7 for HT, maximum significant dose ( D 1% , in %) was 102.2±0.8, 102.7±0.5, 102.4±0.5 and 103.0±1.1, respectively, standard deviation (in %) was 1.4±0.4, 1.3±0.3, 1.1±0.2 and 0.8±0.3, respectively. Conformity Index (CI 95% ) was 0.47±0.12, 0.46±0.12, 0.43±0.11 and 0.38±0.11, respectively. For organs at risk all techniques respected planning objectives. Concerning the healthy tissue: V 10Gy (in %) was 9.4±5.5, 9.9±6.1, 9.2±6.1 and 12.1±8.8, respectively. Integral dose measured on the healthy tissue was 7.5±3.3, 9.7±3.4, 8.7±3.4, 10.4±4.2 10 3 Gycm 3 , respectively. Conclusions For the class of tumours investigated in this report, HT and RA and IMRT proved to be adequate to properly treat patients. Further studies on more complex cases need to be investigated in order to assess the effectiveness of this new technique in a broader clinical perspective.

The GLAaS algorithm for pretreatment intensity modulation radiation therapy absolute dose verification based on the use of amorphous silicon detectors, as described in Nicolini et al. [G. Nicolini, A. Fogliata, E. Vanetti, A. Clivio, and L. Cozzi, Med. Phys. 33, 2839-2851 (2006)], was tested under a variety of experimental conditions to investigate its robustness, the possibility of using it in different clinics and its performance. GLAaS was therefore tested on a low-energy Varian Clinac (6 MV) equipped with an amorphous silicon Portal Vision PV-aS500 with electronic readout IAS2 and on a high-energy Clinac (6 and 15 MV) equipped with a PV-aS1000 and IAS3 electronics. Tests were performed for three calibration conditions: A: adding buildup on the top of the cassette such that SDD-SSD = d(max) and comparing measurements with corresponding doses computed at d(max), B: without adding any buildup on the top of the cassette and considering only the intrinsic water-equivalent thickness of the electronic portal imaging devices device (0.8 cm), and C: without adding any buildup on the top of the cassette but comparing measurements against doses computed at d(max). This procedure is similar to that usually applied when in vivo dosimetry is performed with solid state diodes without sufficient buildup material. Quantitatively, the gamma index (gamma), as described by Low et al. [D. A. Low, W. B. Harms, S. Mutic, and J. A. Purdy, Med. Phys. 25, 656-660 (1998)], was assessed. The gamma index was computed for a distance to agreement (DTA) of 3 mm. The dose difference deltaD was considered as 2%, 3%, and 4%. As a measure of the quality of results, the fraction of field area with gamma larger than 1 (%FA) was scored. Results over a set of 50 test samples (including fields from head and neck, breast, prostate, anal canal, and brain cases) and from the long-term routine usage, demonstrated the robustness and stability of GLAaS. In general, the mean values of %FA remain below 3% for deltaD equal or larger than 3%, while they are slightly larger for deltaD = 2% with %FA in the range from 3% to 8%. Since its introduction in routine practice, 1453 fields have been verified with GLAaS at the authors' institute (6 MV beam). Using a DTA of 3 mm and a deltaD of 4% the authors obtained %FA = 0.9 +/- 1.1 for the entire data set while, stratifying according to the dose calculation algorithm, they observed: %FA = 0.7 +/- 0.9 for fields computed with the analytical anisotropic algorithm and %FA = 2.4 +/- 1.3 for pencil-beam based fields with a statistically significant difference between the two groups. If data are stratified according to field splitting, they observed %FA = 0.8 +/- 1.0 for split fields and 1.0 +/- 1.2 for nonsplit fields without any significant difference.

A treatment planning study was performed to evaluate the performance of new radiotherapy techniques based on non-coplanar multiple fields or on dynamic conformal arcs for early stage breast treatments.CT datasets of 7 different patients that were deemed unsuitable for tangential beam treatment due to a large volume of lung in the treatment fields were used as input for the study. Standard tangential field plans and inversely modulated IMRT plans were used as benchmark to evaluate performances of conformal plans with 3 non-coplanar fields (3F-NC), with 2 short dynamic conformal arcs (2-Arc) or hybrid plans with one static conformal field and one dynamic conformal arc (P-Arc). All plans were designed to achieve the higher target coverage and minimum ipsilateral lung involvement depending on the planning technique with a key objective to avoid involvement of the contralateral breast. The following planning objectives were selected. For PTV: D(1%) (maximum significant dose) lower than 110% and D(99%) (minimum significant dose) higher than 90%. For the ipsilateral lung a mean dose lower than 15 Gy and/or a volume receiving more than 20 Gy lower than 22%. For contralateral breast, all techniques but IMRT were set to have no beam impinging this organ at risk, while for IMRT plans were further designed to keep the mean dose lower than 5 Gy and to minimise the volume receiving a dose higher than 70% of the prescribed dose.P-Arc resulted to be on average a better technique, as it provides a PTV dose distribution highly conformal (Conformity index 1.45), homogeneous (D(5%)-D(95%)=15.6%), with adequate coverage (V(90%)=96.4%) and a limited involvement of the ipsilateral lung (MLD approximately 9 Gy, V(5 Gy) approximately 36%, NTCP2%) when compared to four other treatment techniques. 3F-NC presented similar but slightly worse performances on target: Conformity index 1.57, D(5%)-D(95%)=18.1%, V(90%)=95.7%). 3F-NC on ipsilateral lung resulted as the P-Arc. The tangential approach, the 2-Arc or the IMRT techniques, resulted to be inferior to the previous in either conformality (tangentials), ipsilateral lung sparing (tangentials, 2-Arc and IMRT) and in contralateral or healthy tissue involvement (IMRT).For early stage breast cancer when high sparing of lung tissues is required and no involvement of contralateral breast is allowed, the P-Arc or the 3F-NC techniques might be recommended in terms of dosimetric expectations.

Background To evaluate the performance of a broad scope model-based optimisation process for volumetric modulated arc therapy applied to esophageal cancer. Methods and materials A set of 70 previously treated patients in two different institutions, were selected to train a model for the prediction of dose-volume constraints. The model was built with a broad-scope purpose, aiming to be effective for different dose prescriptions and tumour localisations. It was validated on three groups of patients from the same institution and from another clinic not providing patients for the training phase. Comparison of the automated plans was done against reference cases given by the clinically accepted plans. Results Quantitative improvements (statistically significant for the majority of the analysed dose-volume parameters) were observed between the benchmark and the test plans. Of 624 dose-volume objectives assessed for plan evaluation, in 21 cases (3.3 %) the reference plans failed to respect the constraints while the model-based plans succeeded. Only in 3 cases (

Background Machine Performance Check (MPC) is an application to verify geometry and beam performances of TrueBeam Linacs, through automated checks based on their kV-MV imaging systems. In this study, preliminary tests with MPC were analyzed using all photon beam energies of our TrueBeam, comparing whenever possible with external independent checks. Methods Data acquisition comprises a series of 39 images (12 with kV and 27 with MV detector) acquired at predefined positions without and with the IsoCal phantom in the beam, and with particular MLC pattern settings. MPC performs geometric and dosimetric checks. The geometric checks intend to test the treatment isocenter size and its coincidence with imaging devices, the positioning accuracy of the imaging systems, the collimator, the gantry, the jaws, the MLC leaves and the couch position. The dosimetric checks: refer to a reference MV image and give the beam output, uniformity and center change relative to the reference. MPC data were acquired during 10 repetitions on different consecutive days. Alternative independent checks were performed. Geometric: routine mechanical tests, Winston-Lutz test for treatment isocenter radius. Dosimetric: the 2D array StarCheck (PTW) was used just after the MPC data acquisition. Results Results were analyzed for 6, 10, 15 MV flattened, and 6, 10 MV FFF beams. Geometric checks: treatment isocenter was between 0.31 ± 0.01 mm and 0.42 ± 0.02 mm with MPC, compared to 0.27 ± 0.01 mm averaged on all energies with the Winston-Lutz test. Coincidence of kV and MV imaging isocenters was within 0.36 ± 0.0 and 0.43 ± 0.06 mm, respectively (0.4 ± 0.1 mm with external tests). Positioning accuracy of MLC was within 0.5 mm; accuracy of jaws was 0.04 ± 0.02, 0.10 ± 0.05, −1.01 ± 0.03, 0.92 ± 0.04 mm for X1, X2, Y1, Y2 jaws, respectively, with MPC. Dosimetric tests: the output stability relative to the baseline was in average 0.15 ± 0.07% for MPC to compare with 0.3 ± 0.2% with the independent measurement. Conclusions MPC proved to be a reliable, fast and easy to use method for checking the machine performances on both geometric and dosimetric aspects. Electronic supplementary material The online version of this article (doi:10.1186/s13014-015-0381-0) contains supplementary material, which is available to authorized users.

A new calibration algorithm (GLAaS) to derive absolute dose maps from images acquired with the Varian PV-aS500 electronic portal imager (based on amorphous silicon detectors) has been developed incorporating the dependence of detector response on primary and transmitted radiation and on field size. Detector calibration and algorithm validation were performed at different depths (10.0, 3.8, 1.5, and 0.8 cm) in solid water to investigate various application possibilities. Calibration data were obtained against ion chamber measurements. Validation experiments were performed on intensity-modulated fields and comparison was carried out against calculated dose maps as well as against film measurements. Split fields were acquired independently and PV-aS500 images were summed offline with the new algorithm allowing complex fields to be verified in conditions most closely resembling clinical conditions. Excellent results were obtained for the 3.8, 1.5, and 0.8 depths on a set of 34 modulated fields including both split and nonsplit fields. Applying the gamma index analysis (with distance to agreement and dose thresholds set to 3 mm and 4%, respectively), only 2.3% of the field area showed {gamma}>1 at 1.5 cm depth (8.1%, 3.1%, 2.7% at 10.0, 3.8, and 0.8 and 2.5% with films at 10 cm depth). Tests were also performedmore » to verify GLAaS at gantry angles different from 0 deg. . No statistical differences were obtained for the comparison between split and nonsplit fields and between different gantry angles. Highly significant statistical differences were obtained when comparing independent samples of 240 fields verified either with GLAaS or with film. Fields verified with GLAaS presented a mean area with {gamma}>1 of 2.1{+-}1.3% while for film this value was 3.9{+-}3.4% (p

A comparative study of different systems for proton-based radiotherapy was conducted. The Paul Scherrer Institute method for spot scanning was compared with the systems for passive scattering from the Helax-TMS and the Varian Eclipse. Twelve cases of “benign” brain tumors were considered (meningiomas, neurinomas, and hypophyseal adenomas). Organs at risk included chiasm, brainstem, eyes and optic nerves as well as the not otherwise specified healthy brain tissue in view of long-term toxicity. The results showed that high target coverage was achievable (V90 > 98% for all systems). Plans designed with the spot-scanning technique presented the minimum involvement of healthy tissue (e. g., the lowest maximum significant dose to healthy brain [25.6 Gy] or the lowest conformity index [CI95 = 1.3], between 38% and 46% lower than for the other techniques). In this study, no definitive indication of superiority of any technique can be drawn but spot scanning can better conform dose distributions and minimize the irradiation of healthy volumes at medium to low dose levels, a factor of interest when long life expectancy is considered.

In July 2005 a new algorithm was released by Varian Medical Systems for the Eclipse planning system and installed in our institute. It is the anisotropic analytical algorithm (AAA) for photon dose calculations, a convolution/superposition model for the first time implemented in a Varian planning system. It was therefore necessary to perform validation studies at different levels with a wide investigation approach. To validate the basic performances of the AAA, a detailed analysis of data computed by the AAA configuration algorithm was carried out and data were compared against measurements. To better appraise the performance of AAA and the capability of its configuration to tailor machine-specific characteristics, data obtained from the pencil beam convolution (PBC) algorithm implemented in Eclipse were also added in the comparison. Since the purpose of the paper is to address the basic performances of the AAA and of its configuration procedures, only data relative to measurements in water will be reported. Validation was carried out for three beams: 6 MV and 15 MV from a Clinac 2100C/D and 6 MV from a Clinac 6EX. Generally AAA calculations reproduced very well measured data, and small deviations were observed, on average, for all the quantities investigated for open and wedged fields. In particular, percentage depth-dose curves showed on average differences between calculation and measurement smaller than 1% or 1 mm, and computed profiles in the flattened region matched measurements with deviations smaller than 1% for all beams, field sizes, depths and wedges. Percentage differences in output factors were observed as small as 1% on average (with a range smaller than +/-2%) for all conditions. Additional tests were carried out for enhanced dynamic wedges with results comparable to previous results. The basic dosimetric validation of the AAA was therefore considered satisfactory.

Background and purpose To appraise the potential benefit of a conformal technique with non-coplanar fields to minimise lung irradiation in the radiation treatment of breast. Patients and methods A comparative study was carried out at planning level for six patients selected for their inadequate sparing of healthy lung tissue with the reference tangential technique. Plans were designed for the conventional tangential technique, for an alternative conformal approach with three beams and for the newly proposed technique with two non-coplanar beams. Results In average for the new technique compared to the reference, mean lung dose dropped from ∼16 to 10.5Gy, V 20Gy from 29.5 to 18.2% and the dose delivered to 1/3 (1/4) of the lung volume dropped from 28.5% (67.3%) to 8.7% (13.4%). For PTV, the volume receiving at least 90% of the prescribed dose resulted 97.4% for the new and 97.3% for the reference. Conformity index improved significantly from 2.58 for the reference to 1.84 for the new technique. Conclusions For a subgroup population of breast cancer patients, where conventional techniques failed to achieve high conformal avoidance, a treatment modality with non-coplanar beams was developed and clinically tested for six patients. It resulted dosimetrically adequate, particularly when the risk of toxicity is relevant.

Background and purpose To evaluate the performance of ten different treatment-planning systems when intensity modulated (IMRT) plans are designed for breast treatments that include the irradiation of the internal mammary chain. Patients and methods A dataset of five patients (CT images and volumes of interest) was distributed to design IMRT plans on the ten systems. To minimise biases, the same geometry and clinical planning aims were imposed on the individual plans. Results were analysed in terms of dose distributions and dose volume histograms. Results and conclusions For target coverage, the volume receiving more than 95% of the prescribed dose ranged from 77% (OTP) to 91% (Eclipse and Pinnacle), the volume receiving more than 107% ranged from 3.3% (Hyperion) to 23.2% (OTP). The mean dose to ipsilateral lung ranged from 13 Gy (Eclipse) to 18 Gy (OTP). The volume of the contralateral breast receiving more than 10 Gy ranged from 3% (Pinnacle) to 26% (Precise). The volume of heart receiving more than 20 Gy ranged from 7% (Eclipse) to 47% (Precise), the maximum significant dose to heart ranged from ∼27 Gy (XiO) to ∼49 Gy (Precise). The maximum significant dose to healthy tissue ranged from ∼51 Gy (Eclipse) to ∼62 Gy (OTP). It was also possible to show that the treatment geometry proposed here enables to minimise contralateral breast irradiation while keeping minimal ipsilateral lung (or heart) involvement and satisfactory target coverage.

Background and purpose: Aim of the study is the critical appraisal of the two delivery techniques for intensitymodulated treatments commonly known as dynamic and static step and shoot, in the framework of a sliding window multileaf sequencing method. Methods: The study was performed using the solution commercialised by Varian with the Eclipse treatment planning system (TPS) and the Clinac accelerator. For a set of intensity modulated fluences, the calculated dose maps and the dose delivered to films were compared for the static and dynamic modes to verify the capability of the TPS to accurately model both the delivery modes. For these investigations, the g concept of Low et al. [Low D, Harms W, Mutic S, Purdy J. A technique for the quantitative evaluation of dose distributions. Med Phys 1998;25: 656‐60] was applied demonstrating, in general, optimal modeling for both static and dynamic tests. Optimal and actual fluences, were analysed to ascertain the degree of the TPS accuracy in converting ‘ideal’ maps into realistic leaf motions. Results: Among the methods used, the Webb’s Modulation Index [Webb S. Use of a quantitative index of beam modulation to characterize dose conformality: illustration by a comparison of full beamlet IMRT, few-segment IMRT and conformal unmodulated radiotherapy. Phys Med Biol. 2003;48: 2051‐2062] proved to be useful. Also, dose volume histogram analysis was applied on deliverable plans using more clinical tools. Conclusion: The dynamic delivery method seems to offer a more reliable agreement with the optimal calculations and, clinically, a slightly superior performance in terms of target coverage. q 2005 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 75 (2005) 112–119.

A method for evaluating scattered dose contribution in portal images acquired under clinical conditions (phantom-device distance of 30 cm) is presented. This method is based on radiographic film and ionisation chamber measurements and is valid for homogenecus polystyrene phantoms and square fields of different size. The portal imaging device consisted of a radiographic film placed between slabs of polystyrene under full build-up conditions (1.5 cm for 6 MV beam and 3 cm for 18 MV and 1 cm of polystyrene backscatter material. First the primary dose image in the portal plane P(i,j) is obtained using a projection algorithm, then the scattered dose image S(i,j) is found by subtracting the primary dose image in the portal plane P(i,j) from the total dose image acqu red in the portal plane T(i,j). The ratio S(i,j)/T between the scattered dose distribution and the dose value measured on the bearn axis in the portal plane was found to be uniform within the radiation field for all the geometrical configuration of phantoms and fields studied. Under these conditions the mean value of the scatter fraction S/T evaluated within a ROI centred on the bearn axis accurately describes the scatter fraction distribution S(i,j)/T within the whole radiation field. S/T ranges from 7.4% to 31.1% in the 6 MV beam and from 8.9% to 30.8% in the 18 MV beam. Finally an analytical method to evaluate the ratio S/T has been developed from the experimental results. It comprises phantom, accelerator head and portal imaging device contributions and depends on field size and phantom thickness.

Since 2001, 50 breast cancer patients, for whom extensive lung/heart involvement was expected from the use of conventional tangential 2-field technique (2F) owing to complex anatomies, were irradiated using a 3-field conformal technique (3F). Dose plans were designed for both 3F and 2F and a dose volume histogram analysis on ipsilateral lung, heart, and target was conducted. The 3F technique allowed a significant reduction in ipsilateral lung irradiation: mean dose dropped from 16.0+/-3.8 (2F) to 12.0+/-2.7 Gy (3F) and V(45Gy) from 20.7+/-6.8 (2F) to 3.2+/-2.9% (3F). Similarly, in patients irradiated to the left breast, heart mean dose was reduced from 8.1 Gy (2F) to 6.8 Gy (3F) and D(15%) from 19.0 Gy to 14.0 Gy. All differences reached a high degree of significance. The target coverage was not clinically compromised since the slight reduction using 3F compared with 2F is limited to V(95%) while V(90%) difference, even if statistically significant, is small: 98.2+/-1.8% (3F) and 98.8+/-1.6 (2F). A preliminary report on clinical follow up is also included; with a mean follow up of 15.8 months, no pulmonary or cardiac complications were observed.

The use of intensity-modulated radiotherapy (IMRT) is now widely advocated for the treatment of head-and-neck cancers, to increase the therapeutic ratio of radiotherapy used as sole modality of treatment or in combination with chemotherapy. This report aims to summarize the technical and dosimetric factors to be taken into consideration to assess the respective advantages of the various high conformality treatments in radiotherapy, especially in the framework of quality assurance procedures.Twenty-six head-and-neck cancer patients were irradiated following a feasibility internal protocol with IMRT. Treatments were performed with either the static step-and-shoot (20) or the dynamic sliding window (6) techniques on a 6 MV Varian Clinac equipped with a multileaf collimator with 80 leaves. Dose plans were computed using commercial treatment planning systems: MDS-Nordion Helax-TMS for static cases and Varian Eclipse for dynamic cases. Dose plans were evaluated in terms of physical quantities based on dose-volume histograms and isodose distributions. Each IMRT plan was also compared to a reference 3D conformal therapy plan (3DCRT).Elective target volumes ranged from 530 to 1151 cm(3) with a mean of 780 +/- 141 cm(3). Boost volumes ranged from 248 to 832 cm(3) with a mean of 537 +/- 165 cm(3). Thirty-two dose plans were generated with static technique and 10 with dynamic. In the static mode, 6.8 +/- 3.4 fields were applied on average with 12.5 +/- 1.3 segments per field. In the static mode, 264 +/- 56 MU per Gy were erogated, whereas in the dynamic mode, 387 +/- 126 MU per Gy were erogated, to be compared to 147 +/- 20 computed for reference 3DCRT plans. For all target volumes in general, conformity was improved compared to 3DCRT (e.g. V(95) increased from 85% to 93% with p0.001, or equivalent uniform dose normalized to prescribed dose increased from 0.86 to 0.96 with p = 0.002). Irradiation of parotid glands or spinal cord improved, as well: For parotids, D(2/3V) reduced from 59 Gy to 41 Gy (p0.001). For spinal cord, D(max) reduced from about 40 Gy to about 30 Gy (p0.001).

The potential benefit of the simultaneous integrated boost (SIB) concept in proton therapy was investigated in a planning study. The proposed fractionation strategy consisted of a SIB treatment following a first phase of conventional fractionation to the elective volume (named SEQ/SIB). The novel method was compared to a conventional sequential fractionation and to a full SIB approach. Treatment plans were designed for five patients on the proton planning system developed for spot scanning at the Paul Scherrer Institute of Villigen (CH). Three to five beams were applied for all plans and fractionations. All effective dose distributions were corrected using biological models to take into account repopulation and time at repopulation onset. Corrected and uncorrected plans were compared on the basis of dosimetry criteria and dose-volume histograms. The results showed a dosimetric advantage for the SEQ/SIB approach in terms of target coverage, without significant disadvantages for risk structures and healthy tissue. Considering the high logistic impact and the limited availability of radiation facilities, the clinical exploitation of accelerated SIB treatment with protons appears promising.

Aim of this report was to summarise clinical experience in the field of pre-treatment dosimetric verification of intensity-modulated photon beams (IRMT). From May 2001 to July 2003, 50 patients were irradiated according to IMRT techniques with 6 MV photon beams produced by a Varian Clinac equipped with a 80 leaves multileaf collimator. Dose plans were computed using commercial treatment planning systems, Nucletron Helax-TMS for static cases and Varian Eclipse-Helios for dynamic cases. Pre-treatment dosimetric verification was carried out on a field-per-field basis measuring 2D absolute dose distributions in solid water at 10 cm depth using films or an electronic portal imaging device (EPID). Verification measurements were compared with expected dose maps, and differences were evaluated by means of both a point-to-point analysis and the Gamma Index. Irradiated target volumes (30 head and neck, 8 breast, 12 other patients) ranged from 111 to 2121 cm3 with a mean of 652 +/- 378 cm3. Twenty-nine dose plans were delivered with dynamic technique and 44 with static technique. On average, 5.9 +/- 1.3 fields were applied per plan, with 12.1 +/- 1.6 segments per field in the static mode. Averaging over the whole number of fields we obtained a mean difference (on a pixel-by-pixel basis and per 100 MU delivered) of -0.22 +/- 0.64 cGy between calculation and measurement, with a standard deviation of 1.93 +/- 0.65 cGy. The mean value for the Gamma Index evaluation was 0.47 +/- 0.10, with a mean standard deviation of 0.35 +/- 0.17. The fraction of pixels lying inside the field and showing a gamma index larger than 1 was 5.7% for the triplet Eclipse-film-dynamic delivery and 9.9% for the triplet Helax-TMS-EPID-static delivery. The employed IMRT treatments proved that this technique is feasible and dosimetrically accurate. Treatment verification stability and dosimetric analysis of treated plans are highly satisfactory and allow the safe introduction of this modality in the spectrum of techniques offered to a large class of patients.