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To quantify the dosimetric impact of contouring variability of axillary lymph nodes (L2, L3, L4) in breast cancer (BC) locoregional radiotherapy (RT).18 RT centres were asked to plan a locoregional treatment on their own planning target volume (single centre, SC-PTV) which was created by applying their institutional margins to the clinical target volume of the axillary nodes of three BC patients (P1, P2, P3) previously delineated (SC-CTV). The gold standard CTVs (GS-CTVs) of P1, P2 and P3 were developed by BC experts' consensus and validated with STAPLE algorithm. For each participating centre, the GS-PTV of each patient was created by applying the same margins as those used for the SC-CTV to SC-PTV expansion and replaced the SC-PTV in the treatment plan. Datasets were imported into MIM v6.1.7 [MIM Software Inc.], where dose-volume histograms (DVHs) were extracted and differences were analysed.17/18 centres used intensity-modulated RT (IMRT). The CTV to PTV margins ranged from 0 to 10 mm (median 5 mm). No correlation was observed between GS-CTV coverage by 95% isodose and GS-PTV margins width. Doses delivered to 98% (D98) and 95% (D95) of GS-CTVs were significantly lower than those delivered to the SC-CTVs. No significant difference between SC-CTV and GS-CTV was observed in maximum dose (D2), always under 110%. Mean dose ≥99% of the SC-CTVs and GS-CTVs was satisfied in 84% and 50%, respectively. In less than one half of plans, GS-CTV V95% was above 90%. Breaking down the GS-CTV into the three nodal levels (L2, L3 and L4), L4 had the lowest probability to be covered by the 95% isodose.Overall, GS-CTV resulted worse coverage, especially for L4. IMRT was largely used and CTV-to-PTV margins did not compensate for contouring issues. The results highlighted the need for delineation training and standardization.

Lancet Oncology, The - Sous presse. Epreuves corrigees par l'auteur. Disponible en ligne depuis le mercredi 11 aout 2021

In this review a summary of the published literature pertaining to the stereotactic body radiation therapy multiplanning comparison, data sharing strategies, and implementation of benchmark planning cases to improve the skills and knowledge of the participating centers was investigated. A total of 30 full-text articles were included. The studies were subdivided in 3 categories: multiplanning studies on dosimetric variability, planning harmonization before clinical trials, and technical and methodologic studies. The methodology used in the studies were critically analyzed to find common and original elements with the pros and cons. Multicenter planning studies have played a key role in improving treatment plan harmonization, treatment plan compliance, and even clinical practices. This review has highlighted that some fundamental steps should be taken to transform a simple treatment planning comparison study into a potential credentialing method for stereotactic body radiation therapy accreditation. In particular, prescription and general requirements should always be well defined; data analysis should be performed with independent dose volume histogram or dose calculations; quality score indices should be constructed; feedback and correction strategies should be provided; and a simple web-based collaboration platform should be used. The results reported clearly showed that a crowd-based replanning approach is a viable method for achieving harmonization and standardization of treatment planning among centers using different technologies.

This topical review focuses on the applications of artificial intelligence (AI) tools to stereotactic body radiation therapy (SBRT). The high dose per fraction and the limited number of fractions in SBRT require stricter accuracy than standard radiation therapy. The intent of this review is to describe the development and evaluate the possible benefit of AI tools integration into the radiation oncology workflow for SBRT automation. The selected papers were subdivided into four sections, representative of the whole radiotherapy process: ‘AI in SBRT target and organs at risk contouring’, ‘AI in SBRT planning’, ‘AI during the SBRT delivery’, and ‘AI for outcome prediction after SBRT’. Each section summarises the challenges, as well as limits and needs for improvement to achieve better integration of AI tools in the clinical workflow.

High-energy small electron beams generated by linear accelerators are used for radiotherapy of localized superficial tumors. The aim of the present study is to assess the dosimetric performance under small radiation therapy electron beams of the novel PTW microSilicon detector by comparison with commercially available dosimeters. Relative dose measurements of circular fields with 20, 30, 40 and 50 mm aperture diameters were performed for 4 to 12 MeV energy range of electron beams generated by an Elekta Synergy linac. Percentage depth dose, transverse profiles and output factors normalized to the 10 × 10 cm2 reference field were measured. All dosimetric data were collected in a PTW MP3 motorized water phantom at SSD of 100cm by using the novel PTW microSilicon detector. The PTW diode E and the PTW microDiamond were also used in all beam aperture for benchmarking. Data for the biggest field size were also measured by the PTW Advanced Markus ionization chamber.Measurements performed by the microSilicon are in good agreement with the reference values for all the tubular applicators and beam energies, within the stated uncertainties. This confirms the reliability of the microSilicon detector for relative dosimetry of small radiation therapy electron beams collimated by tubular applicators.

Purpose Stereotactic body radiation therapy (SBRT) for early stage solid tumors and metastases is increasing worldwide. In 2013, the Italian Association of Medical Physicists (AIFM) created a working group in order to standardize the SBRT dosimetric aspects (AIFM/SBRT-WG). The aim of this study was to investigate the current status of technology and quality assurance (QA) as regards SBRT in Italy. Clinical evaluation of SBRT was beyond the scope of the present study. Methods A pre-questionnaire was designed by three medical physicists expert in SBRT. It contained questions on 4 main aspects: technology, image-guidance solutions (IGRT), treatment planning system commissioning and QA. In early 2018, all the centers involved in the AIFM/SBRT-WG were invited to complete the online questionnaire. Results The survey was undertaken by 45 centres (83% of them involved in the AIFM/SBRT-WG). The most available delivery system was conventional linacs with VMAT modality; 6MV and 6MV-FFF were the most common energies; robotic couch was available in 56% of centers; CBCT/MVCT was the most used IGRT technique (58% of centers) and 40% of centers adopted respiratory management during treatment delivery. The smallest measured field size for lateral beam profiles was ≤1 × 1 cm2 in 79% of linac-based centers. Great heterogeneity in terms of protocols and guidelines for QA were found. A large number of centers (51%) felt the need to upgrade their dosimetric QA devices dedicated to SBRT. Conclusion This survey on SBRT is a starting point in standardizing the dosimetry of SBRT verification and to improve the QA procedure.

To evaluate, in a multi-institutional context, the role of Dose Volume Histogram (DVH) sharing in order to achieve higher plan quality, to harmonize prostate Stereotactic Body Radiation Therapy (SBRT) plans and to assess if the planner's experience in SBRT could lead to lower dose at organs at risk (OARs).During the first phase five patients enrolled for prostate SBRT were planned by multiple physicists according to common protocol. The prescription dose was 35 Gy in 5 fractions. Dosimetric parameters, modulation index (MIt), plan parameters, and planner experience level (EL) were statistically analyzed. During the second phase median DVHs from all centers were shared and physicists replanned one patient of the five, aiming at inter-planner harmonization and further OARs sparing. Data were summarized by Spearman-correlogram (p 0.05) and boxplots. The Kruskal-Wallis test was used to compare the re-plans to the original plans.Seventy-eight SBRT plans from 13 centers were evaluated. EL correlated with modulation of plan parameters and reduction of OARs doses, such as volume receiving 28 Gy of rectum (rectum-V28Gy), rectum-V32Gy, and bladder-V30Gy. The re-plans showed significant reduced variability in rectum-V28Gy and increased PTV dose homogeneity. No significant difference in plan complexity metrics and plan parameters between plans and re-plans were obtained.Planner's experience in prostate SBRT was correlated with dosimetric parameters. Sharing median DVHs reduced variability among centers whilst keeping the same level of plan complexity. SBRT planning skills can benefit from a replanning phase after sharing DVHs from multiple centers, improving plan quality and concordance among centers.

Purpose The complexity of the modern Stereotactic Body Radiation Therapy (SBRT) techniques requires comprehensive quality assurance programs, to ensure the right treatment to the patient. Dosimetry of small radiation fields is a challenge especially for radiotherapy centres starting to work on this issue. The matter to be discussed here concerns the need of detailed measurement procedures and cross checks to be paired to the usual recommendations on detectors and correction factors. Materials and Methods The presented work involved 24 Italian radiotheraphy centres, with the specific purpose to minimize systematic errors in output factor measurements over different radiotherapy centres. Using the unshielded silicon diode IBA Razor, reference curves for the relative signal ratio (RSR) as a function of beam size were created for each Linac family. Results With this study we have demonstrated consistency of small field dosimetry on all the centres involved, moreover all radiotherapy centres using Razor are allowed to compare measurements amongst each other and centres with values deviating more than 5% from the reference curve are advised to repeat their measurements. With this procedure, some critical issues were detected from two centres in RSR measurements, that, if implemented into the own treatment planning system, would induce an unwanted overdosage larger than 5%. Conclusions The proposed approach could allow one to envision high-skilled therapy centres providing support to those featuring minor experience and could represent an important strategy for the clinical implementation of emerging technologies at high quality levels. The methodology adopted exploits crowd knowledge methods which could be applied in others areas of radiation dosimetry.

Objectives: To determine interobserver variability in axillary nodal contouring in breast cancer (BC) radiotherapy (RT) by comparing the clinical target volume of participating single centres (SC-CTV) with a gold-standard CTV (GS-CTV). Methods: The GS-CTV of three patients (P1, P2, P3) with increasing complexity was created in DICOM format from the median contour of axillary CTVs drawn by BC experts, validated using the simultaneous truth and performance-level estimation and peer-reviewed. GS-CTVs were compared with the correspondent SC-CTVs drawn by radiation oncologists, using validated metrics and a total score (TS) integrating all of them. Results: Eighteen RT centres participated in the study. Comparative analyses revealed that, on average, the SC-CTVs were smaller than GS-CTV for P1 and P2 (by −29.25% and −27.83%, respectively) and larger for P3 (by +12.53%). The mean Jaccard index was greater for P1 and P2 compared to P3, but the overlap extent value was around 0.50 or less. Regarding nodal levels, L4 showed the highest concordance with the GS. In the intra-patient comparison, L2 and L3 achieved lower TS than L4. Nodal levels showed discrepancy with GS, which was not statistically significant for P1, and negligible for P2, while P3 had the worst agreement. DICE similarity coefficient did not exceed the minimum threshold for agreement of 0.70 in all the measurements. Conclusions: Substantial differences were observed between SC- and GS-CTV, especially for P3 with altered arm setup. L2 and L3 were the most critical levels. The study highlighted these key points to address. Advances in knowledge The present study compares, by means of validated geometric indexes, manual segmentations of axillary lymph nodes in breast cancer from different observers and different institutions made on radiotherapy planning CT images. Assessing such variability is of paramount importance, as geometric uncertainties might lead to incorrect dosimetry and compromise oncological outcome.

Purpose The influence of basic plan parameters such as slice thickness, grid resolution, algorithm type and field size on calculated small field output factors (OFs) was evaluated in a multicentric study. Methods and materials Three computational homogeneous water phantoms with slice thicknesses (ST) 1, 2 and 3 mm were shared among twenty-one centers to calculate OFs for 1x1, 2x2 and 3x3 cm2 field sizes (FSs) (normalized to 10x10 cm2 FS), with their own treatment planning system (TPS) and the energy clinically used for stereotactic body radiation therapy delivery. OFs were calculated for each combination of grid resolution (GR) (1, 2 and 3 mm) and ST and finally compared with the OFs measured for the TPS commissioning. A multivariate analysis was performed to test the effect of basic plan parameters on calculated OFs. Results A total of 509 data points were collected. Calculated OFs are slightly higher than measured ones. The multivariate analysis showed that Center, GR, algorithm type, and FS are predictive variables of the difference between calculated and measured OFs (p Conclusions Modern TPSs slightly overestimate the calculated small field OFs compared with measured ones. Grid resolution, algorithm, center number and field size influence the calculation of small field OFs.

PURPOSE To report how the adoption of a Lean Thinking mindset in the management of a national working group (WG) on the physics of stereotactic body radiation therapy (SBRT) contributed to achieve SBRT standardization objectives. METHODS Vision for the WG has been established as fragmentation reduction and process harmonization enhancement in SBRT for Italian centers. Two main research themes of the technical aspects of SBRT emerged as areas with major standardization improvement needs, small field dosimetry and SBRT planning comparisons, to be investigated through multi-institutional studies. The management of the WG leveraged on the Lean concept of fostering self-organization in a non-hierarchical environment. Four progressive involvement levels were defined for each study. No specific "scientific" pre-experience was required to propose and coordinate a project, just requiring a voluntary commitment. People engagement was measured in terms of number of published articles. The standardization goals have been conducted through a simplified "5S" (Sort, Set in Order, Shine, Standardize, and Sustain) methodology, first considering a phase of awareness (the first three "S"), then identifying and implementing standardization actions (the last two "S"). RESULTS Since the beginning, 157 medical physicists joined the AIFM/SBRT-WG. Twenty-four papers/reviews/letters have been published in the period 2014-2019 on major radiation oncology journals, authored by >100 physicists (>50% working in small hospitals). Six over 12 first authors worked in peripheral/small hospitals, with no prior publication as first author. These studies contributed to the awareness and standardization phases for both small-field dosimetry and planning. In particular, errors in small-field measurements in 8% of centers were detected thanks to a generalized output factor curve in function of the effective field size created by averaging data available from different Linacs. Furthermore, planner's experience in SBRT was correlated with dosimetric parameters in the awareness phase; while sharing median dose volume histograms (DVHs) reduced variability among centers while keeping the same level of plan complexity. Finally, all the dosimetric parameters statistically significant to the planner experience during the awareness phase, were no longer significantly different in the standardization phase. CONCLUSIONS The experience of our SBRT-WG has shown how a Lean Thinking mindset could foster the SBRT procedure standardization and spread the physics of SBRT knowledge, enhancing personal growth. Our expectation is to inspire other scientific societies that have to deal with fragmented contexts or pursue processes harmonization through Lean principles.

Purpose To perform a systematic review on the research on the application of artificial intelligence (AI) to imaging published in Italy and identify its fields of application, methods and results. Materials and Methods A Pubmed search was conducted using terms Artificial Intelligence, Machine Learning, Deep learning, imaging, and Italy as affiliation, excluding reviews and papers outside time interval 2015–2020. In a second phase, participants of the working group AI4MP on Artificial Intelligence of the Italian Association of Physics in Medicine (AIFM) searched for papers on AI in imaging. Results The Pubmed search produced 794 results. 168 studies were selected, of which 122 were from Pubmed search and 46 from the working group. The most used imaging modality was MRI (44%) followed by CT(12%) ad radiography/mammography (11%). The most common clinical indication were neurological diseases (29%) and diagnosis of cancer (25%). Classification was the most common task for AI (57%) followed by segmentation (16%). 65% of studies used machine learning and 35% used deep learning. We observed a rapid increase of research in Italy on artificial intelligence in the last 5 years, peaking at 155% from 2018 to 2019. Conclusions We are witnessing an unprecedented interest in AI applied to imaging in Italy, in a diversity of fields and imaging techniques. Further initiatives are needed to build common frameworks and databases, collaborations among different types of institutions, and guidelines for research on AI.

To investigate critical aspects and effectiveness of in vivo dosimetry (IVD) tests obtained by an electronic portal imaging device (EPID) in a multicenter and multisystem context. Eight centers with three commercial systems—SoftDiso (SD, Best Medical Italy, Chianciano, Italy), Dosimetry Check (DC, Math Resolution, LCC), and PerFRACTION (PF, Sun Nuclear Corporation, SNC, Melbourne, FL)—collected IVD results for a total of 2002 patients and 32,276 tests. Data are summarized for IVD software, radiotherapy technique, and anatomical site. Every center reported the number of patients and tests analyzed, and the percentage of tests outside of the tolerance level (OTL%). OTL% was categorized as being due to incorrect patient setup, incorrect use of immobilization devices, incorrect dose computation, anatomical variations, and unknown causes. The three systems use different approaches and customized alert indices, based on local protocols. For Volumetric Modulated Arc Therapy (VMAT) treatments OTL% mean values were up to 8.9% for SD, 18.0% for DC, and 16.0% for PF. Errors due to “anatomical variations” for head and neck were up to 9.0% for SD and DC and 8.0% for PF systems, while for abdomen and pelvis/prostate treatments were up to 9%, 17.0%, and 9.0% for SD, DC, and PF, respectively. The comparison among techniques gave 3% for Stereotactic Body Radiation Therapy, 7.0% (range 4.7–8.9%) for VMAT, 10.4% (range 7.0–12.2%) for Intensity Modulated Radiation Therapy, and 13.2% (range 8.8–21.0%) for 3D Conformal Radiation Therapy. The results obtained with different IVD software and among centers were consistent and showed an acceptable homogeneity. EPID IVD was effective in intercepting important errors.

Large uncertainties in output factor (OF) small fields dosimetry motivated multicentric studies. The focus of the study was the determination of the OFs, for different linacs and radiosurgery units, using new-generation detectors. Intercomparison studies between radiotherapy centers improved quality dosimetry practices. Results confirmed the effectiveness of the studies to uncover large systematic inaccuracies in small field dosimetry. Keywords: Multicentric studies, Small field dosimetry, Output factors

The aim of this study was to develop and apply an evaluation method for assessing the accuracy of a novel 3D EPID back-projection algorithm for in vivo dosimetry. The novel algorithm of Dosimetry Check (DC) 5.8 was evaluated. A slab phantom homogeneously filled, or with air and bone inserts, was used for fluence reconstruction of different squared fields. VMAT plans in different anatomical sites were delivered on an anthropomorphic phantom. Dose distributions were measured with radiochromic films. The 2D Gamma Agreement Index (GAI) between the DC and the film dose distributions (3%, 3 mm) was computed for assessing the accuracy of the algorithm. GAIs between films and TPS and between DC and TPS were also computed. The fluence reconstruction accuracy was within 2% for all squared fields in the three slabs’ configurations. The GAI between the DC and the film was 92.7% in the prostate, 92.9% in the lung, 96.6% in the head and the neck, and 94.6% in the brain. An evaluation method for assessing the accuracy of a novel EPID algorithm was developed. The DC algorithm was shown to be able to accurately reconstruct doses in all anatomic sites, including the lung. The methodology described in the present study can be applied to any EPID back-projection in vivo algorithm.

Purpose In modern radiation therapy accurate small fields dosimetry is a challenge and its standardization is fundamental to harmonize delivered dose in different institutions. This study presents a multicenter characterization of MLC-defined small field for Elekta and Varian linear accelerators. Measurements were performed using the Exradin W1 plastic scintillator detector. Materials and methods The project enrolled 24 Italian centers. Each center performed Tissue Phantom Ratio (TPR), in-plane and cross-plane dose profiles of 0.8 × 0.8 cm2 field, and Output Factor (OF) measurements for square field sizes ranging from 0.8 to 10 cm. Set-up conditions were 10 cm depth in water phantom at SSD 90 cm. Measurements were performed using two twin Exradin W1 plastic scintillator detectors (PSD) correcting for the Cerenkov effect as proposed by the manufacturer. Results Data analysis from 12 Varian and 12 Elekta centers was performed. Measurements of 7 centers were not included due to cable problems. TPR measurements showed standard deviations (SD) Conclusions High degree of consistency was registered for all the considered parameters. This work confirmed the importance of multicenter dosimetric intercomparison. W1 PSD could be considered as a good candidate for small field measurements.

Monte Carlo simulation was used to calculate correction factors for output factor (OF), percentage depth-dose (PDD), and off-axis ratio (OAR) measurements with the CyberKnife M6 System. These include the first such data for the InCise MLC. Simulated detectors include diodes, air-filled microchambers, a synthetic microdiamond detector, and point scintillator. Individual perturbation factors were also evaluated. OF corrections show similar trends to previous studies. With a 5 mm fixed collimator the diode correction to convert a measured OF to the corresponding point dose ratio varies between −6.1% and −3.5% for the diode models evaluated, while in a 7.6 mm × 7.7 mm MLC field these are −4.5% to −1.8%. The corresponding microchamber corrections are +9.9% to +10.7% and +3.5% to +4.0%. The microdiamond corrections have a maximum of −1.4% for the 7.5 mm and 10 mm collimators. The scintillator corrections are 15%, reducing to d max were

Purpose To analyze results from three years of in vivo transit EPID dosimetry of abdominal and pelvic stereotactic radiotherapy and to establish tolerance levels for routine clinical use. Material 80 stereotactic VMAT treatments (152 fractions) targeting the abdomen or pelvis were analyzed. In vivo 3D doses were reconstructed with an EPID commercial algorithm. Gamma Agreement Index (GAI) and DVH differences in Planning Target Volume (PTV) and Clinical Target Volume (CTV) were evaluated. Initial tolerance level was set to GAI > 85% in PTV. Fractions Over Tolerance Level (OTL) were deemed to be due to set-up errors, incorrect use of immobilization devices, 4D errors, transit EPID algorithm errors and unknown/unidentified errors. Statistical Process Control (SPC) was applied to determine local tolerance levels. Results Average GAI were (82.7 ± 20.9) % in PTV and (72.9 ± 29.7) % in CTV. 37.8% of fractions resulted OTL and were classified as: set-up errors (3.3%), incorrect use of immobilization devices (2.1%), 4D errors (2.1%), EPID transit algorithm errors (17.1%). OTL causes for the remaining 13.2% of fractions were not identified. The differences between PTV and CTV measured in vivo and calculated mean dose (average difference ± standard deviation) were (−3.3% ± 3.2%) and (−2.3% ± 3.0%). When tolerance levels based on SPC to PTV mean dose differences were applied, the percentage of OTL decreased to 7% and no EPID algorithm error occurred. One error was not identified. Conclusions The application of local tolerance levels to EPID in vivo dosimetry proved to be useful for detecting extra-lung SBRT treatment errors.

Stereotactic body radiation therapy (SBRT) has been recognized as a standard treatment option for many anatomical sites. Sophisticated radiation therapy techniques have been developed for carrying out these treatments and new quality assurance (QA) programs are therefore required to guarantee high geometrical and dosimetric accuracy. This paper focuses on recent advances on in-vivo measurements methods (IVM) for SBRT treatment. More specifically, all of the online QA methods for estimating the effective dose delivered to patients were compared. Determining the optimal IVM for performing SBRT treatments would reduce the risk of errors that could jeopardize treatment outcome. A total of 89 papers were included. The papers were subdivided into the following topics: point dosimeters (PD), transmission detectors (TD), log file analysis (LFA), electronic portal imaging device dosimetry (EPID), dose accumulation methods (DAM). The detectability capability of the main IVM detectors/devices were evaluated. All of the systems have some limitations: PD has no spatial data, EPID has limited sensitivity towards set-up errors and intra-fraction motion in some anatomical sites, TD is insensitive towards patient related errors, LFA is not an independent measure, DAMs are not always based on measures. In order to minimize errors in SBRT dose delivery, we recommend using synergic combinations of two or more of the systems described in our review: on-line tumor position and patient information should be combined with MLC position and linac output detection accuracy. In this way the effects of SBRT dose delivery errors will be reduced.

Purpose The aims of this study were: (i) to validate in a multi-site context the suitability of the IBA Razor silicon diode detector for CyberKnife relative dosimetry. (ii) to fit the multi-center experimental data into a function relating the field output factors to the effective field size (EFS). Methods and materials Ratio of detector readings in clinical and reference field (OFdet) and beam profiles were acquired on five CyberKnife units for fixed collimator diameters (range 5–60 mm), using both Razor and PTW 60017 diodes. Measured OFdet were corrected using published MonteCarlo correction factors to get field output factors Ω Qclin , Q m s r fclin , f m s r . Profiles were analyzed in terms of penumbra and EFS. Ω Qclin , Q m s r fclin , f m s r obtained in four centers were fitted as a function of EFS, while the data of the 5th center were used to validate the fitting curve. Results Differences between Razor and PTW60017 Ω Qclin , Q m s r fclin , f m s r were within 1.5% over all centers down to 7.5 mm aperture and within 3.5% for the 5 mm diameter. The fit showed a coefficient of determination R2 = 0.997. The mean deviation of measured points from the predictive curve was within 0.5%. Data of the 5th center showed a mean deviation of 0.4% from the curve, with maximum differences within 2.5% for the 7.5 mm aperture. Conclusions The results confirmed the suitability of Razor detector for CyberKnife dosimetry by comparison to the PTW 60017 diode which has been well characterized and is in widespread use. The proposed mathematical relation between Ω Qclin , Q m s r fclin , f m s r and EFS is a robust predictive model applicable to different CyberKnife systems and detectors.

Within the dosimetric characterization of particle beams, laterally-integrated depth-dose-distributions (IDDs) are measured and provided to the treatment planning system (TPS) for beam modeling or used as a benchmark for Monte Carlo (MC) simulations. The purpose of this work is the evaluation, in terms of ion recombination and polarity effect, of the dosimetric correction to be applied to proton and carbon ion curves as a function of linear energy transfer (LET). LET was calculated with a MC code for selected IDDs. Several regions of Bragg peak (BP) curve were investigated. The charge was measured with the plane-parallel BP-ionization chamber mounted in the Peakfinder as a field detector, by delivering a fixed number of particles at the maximum flux. The dose rate dependence was evaluated for different flux levels. The chamber was connected to an electrometer and exposed to un-scanned pencil beams. For each measurement the chamber was supplied with {±400, +200, +100} V. Recombination and polarity correction factors were then calculated as a function of depth and LET in water. Three energies representative of the clinical range were investigated for both particle types. The corrected IDDs (IDD k s) were then compared against MC. Recombination correction factors were LET and energy dependent, ranging from 1.000 to 1.040 (±0.5%) for carbon ions, while nearly negligible for protons. Moreover, no corrections need to be applied due to polarity effect being

Objectives: This multicentric study was carried out to investigate the impact of small field output factors (OFs) inaccuracies on the calculated dose in volumetric arctherapy (VMAT) radiosurgery brain plans. Methods: Nine centres, realised the same five VMAT plans with common planning rules and their specific clinical equipment Linac/treatment planning system commissioned with their OFs measured values (OFbaseline). In order to simulate OFs errors, two new OFs sets were generated for each centre by changing only the OFs values of the smallest field sizes (from 3.2 × 3.2 cm2 to 1 × 1 cm2) with well-defined amounts (positive and negative). Consequently, two virtual machines for each centre were recommissioned using the new OFs and the percentage dose differences ΔD (%) between the baseline plans and the same plans recalculated using the incremented (OFup) and decremented (OFdown) values were evaluated. The ΔD (%) were analysed in terms of planning target volume (PTV) coverage and organs at risk (OARs) sparing at selected dose/volume points. Results: The plans recalculated with OFdown sets resulted in higher variation of doses than baseline within 1.6 and 3.4% to PTVs and OARs respectively; while the plans with OFup sets resulted in lower variation within 1.3% to both PTVs and OARs. Our analysis highlights that OFs variations affect calculated dose depending on the algorithm and on the delivery mode (field jaw/MLC‐defined). The Monte Carlo (MC) algorithm resulted significantly more sensitive to OFs variations than all of the other algorithms. Conclusion: The aim of our study was to evaluate how small fields OFs inaccuracies can affect the dose calculation in VMAT brain radiosurgery treatments plans. It was observed that simulated OFs errors, return dosimetric calculation accuracies within the 3% between concurrent plans analysed in terms of percentage dose differences at selected dose/volume points of the PTV coverage and OARs sparing. Advances in knowledge: First multicentre study involving different Planning/Linacs about undetectable errors in commissioning output factor for small fields.

Purpose Small radiation fields (

Purpose A large-scale multi-institutional planning comparison on lung cancer SABR is presented with the aim of investigating possible criticism in carrying out retrospective multicentre data analysis from a dosimetric perspective. Methods Five CT series were sent to the participants. The dose prescription to PTV was 54 Gy in 3 fractions of 18 Gy. The plans were compared in terms of PTV-gEUD 2 (generalized Equivalent Uniform Dose equivalent to 2 Gy), mean dose to PTV, Homogeneity Index (PTV-HI), Conformity Index (PTV-CI) and Gradient Index (PTV-GI). We calculated the maximum dose for each OAR (organ at risk) considered as well as the MLD 2 (mean lung dose equivalent to 2 Gy). The data were stratified according to expertise and technology. Results Twenty-six centers equipped with Linacs, 3DCRT (4% – 1 center), static IMRT (8% – 2 centers), VMAT (76% – 20 centers), CyberKnife (4% – 1 center), and Tomotherapy (8% – 2 centers) collaborated. Significant PTV-gEUD 2 differences were observed (range: 105–161 Gy); mean-PTV dose, PTV-HI, PTV-CI, and PTV-GI were, respectively, 56.8 ± 3.4 Gy, 14.2 ± 10.1%, 0.70 ± 0.15, and 4.9 ± 1.9. Significant correlations for PTV-gEUD 2 versus PTV-HI, and MLD 2 versus PTV-GI, were observed. Conclusions The differences in terms of PTV-gEUD 2 may suggest the inclusion of PTV-gEUD 2 calculation for retrospective data inter-comparison.

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.

The dosimetric variability in spine stereotactic body radiation therapy (SBRT) planning was investigated in a large number of centres to identify crowd knowledge-based solutions.Two spinal cases were planned by 48 planners (38 centres). The required prescription dose (PD) was 3 × 10 Gy and the planning target volume (PTV) coverage request was: VIn all, 12.5% of plans did not meet the protocol requirements. After re-optimization, 98% of plans fulfilled the constraints, showing the positive impact of knowledge sharing. Statistical analysis showed a significant correlation (p 0.05) between the homogeneity index (HI) and PTV coverage for both cases, while the correlation between HI and spinal cord sparing was significant only for the single dorsal PTV case. Moreover, the multileaf collimator leaf thickness correlated with the spinal cord sparing. Planners using comparable delivery/planning system techniques produced different QI, highlighting the impact of the planner's skills in the optimization process.Both the technology and the planner's skills are fundamentally important in spine SBRT planning optimization. Knowledge sharing helped to follow the plan objectives.

Dosimetry check (DC) is a commercial software that allows reconstruction of 3D dose distributions using transit electronic portal imaging device (EPID) images. In this work, we evaluated the suitability of DC software for volumetric modulated arc therapy (VMAT) transit dosimetry. The volumetric gamma agreement index 3%/3 mm between twenty VMAT dose distributions reconstructed by DC and calculated with treatment planning system (TPS) were compared to those obtained using PTW OCTAVIUS®4D to assess DC accuracy in VMAT quality assurance (QA). The sensitivity of DC in detecting VMAT delivery and set-up errors and anatomical variations has been investigated by measuring the variation of the gamma agreement index before and after the introduction of specific errors in four VMAT plans related to different anatomical sites. The influence of dose computation algorithm in presence of density inhomogeneity was also assessed. The assessment of VMAT QA shows agreements with TPS maps comparable to OCTAVIUS® 4D (OCT) in homogeneous phantom (p

A systematic study of the PTW microDiamond (MD) output factors (OF) is reported, aimed at clarifying its response in small fields and investigating its suitability for small field reference dosimetry. Ten MDs were calibrated under 60Co irradiation. OF measurements were performed in 6 MV photon beams by a CyberKnife M6, a Varian DHX and an Elekta Synergy linacs. Two PTW silicon diodes E (Si-D) were used for comparison. The results obtained by the MDs were evaluated in terms of absorbed dose to water determination in reference conditions and OF measurements, and compared to the results reported in the recent literature. To this purpose, the Monte Carlo (MC) beam-quality correction factor, , was calculated for the MD, and the small field output correction factors, , were calculated for both the MD and the Si-D by two different research groups. An empirical function was also derived, providing output correction factors within 0.5% from the MC values calculated for all of the three linacs. A high reproducibility of the dosimetric properties was observed among the ten MDs. The experimental values are in agreement within 1% with the MC calculated ones. Output correction factors within +0.7% and -1.4% were obtained down to field sizes as narrow as 5 mm. The resulting MD and Si-D field factors are in agreement within 0.2% in the case of CyberKnife measurements and 1.6% in the other cases. This latter higher spread of the data was demonstrated to be due to a lower reproducibility of small beam sizes defined by jaws or multi leaf collimators. The results of the present study demonstrate the reproducibility of the MD response and provide a validation of the MC modelling of this device. In principle, accurate reference dosimetry is thus feasible by using the microDiamond dosimeter for field sizes down to 5 mm. © 2017 Institute of Physics and Engineering in Medicine.

Purpose Around 10 centers worldwide treat ocular tumors with proton therapy, all with dedicated eyelines. Our synchrotron-based facility is equipped with general-purpose fixed beamlines; proton and carbon ion treatments are delivered with pencil beam scanning modality (range in water 3 ÷ 32 cm). Recently, our proton beamline was adapted to treat also ocular diseases. The main dosimetric properties of this new eyeline are described in this work. Methods A 3 cm water-equivalent range shifter (RS) was placed along the beamline to reach shallower penetration depths. In order to achieve steep lateral dose gradients, the position of the RS and patient-specific collimator were simulated using MonteCarlo (MC) FLUKA code. Lateral dose profiles were measured with gafchromic EBT3 films to evaluate lateral penumbra width and dose homogeneity. Several beam scanning patterns were tested. Depth-dose distributions (DDDs) were measured with the Peakfinder system. To obtain uniform dose distributions (Spread-Out Bragg Peaks, SOBPs), the weights of each DDD were optimized simulating different targets. Absorbed doses were then measured in water with an advanced Markus chamber. Neutron dose at the contralateral eye was also evaluated with passive bubble dosimeters. Results MC simulations and experimental results showed that maximizing the distance between RS and collimator reduces the lateral dose penumbra of the collimated beam and increases field transversal dose homogeneity. Therefore, RS and patient-specific collimator were placed at about 98 cm (behind beam monitors) and 6 cm from the isocenter, respectively. The lateral penumbra (distal fall-off) ranged between 1.0 and 1.8 mm (1.0 and 1.6 mm). The measured SOBP doses were in very good agreement with MC simulations, as shown in Fig. 1. The mean neutron dose at the contralateral eye was 68.8 ± 10.2 μSv/Gy. Conclusions Our eyeline satisfied the requirements to treat ocular tumors. The first ocular patient was treated in August 2016. Around 60 patients have been treated so far.