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Gamma dose and thermal neutron fluence in a phantom exposed to an epithermal neutron beam for boron neutron capture therapy (BNCT) can be measured by means of a single thermoluminescence dosemeter (TLD-700). The method exploits the shape of the glow curve (GC) and requires the gamma-calibration GC (to obtain gamma dose) and the thermal-neutron-calibration GC (to obtain neutron fluence). The method is applicable for BNCT dosimetry in case of epithermal neutron beams from a reactor because, in most irradiation configurations, thermal neutrons give a not negligible contribution to the TLD-700 GC. The thermal neutron calibration is not simple, because of the impossibility of having thermal neutron fields without gamma contamination, but a calibration method is here proposed, strictly bound to the method itself of dose separation. [ABSTRACT FROM AUTHOR]

Purpose CT imaging in radiotherapy represents the standard for treatment planning. The calculation of dose distribution requires appropriate energy-dependent calibration curves to convert Hounsfield Units (HU) into electronic densities relative to water (rEDs). To obtain optimal image quality and reduce dose, it could be useful to modulate X-ray tube potential based on patient size, but in radiotherapy treatment planning this practice requires the use of several calibration curves. A novel algorithm (DirectDensity™, DD™ recently developed by Siemens Healthcare, uses CT projection data to reconstruct images directly proportional to rEDs, independently of kVp used, thus removing the need of different curves. The purpose of the study is to evaluate this algorithm for clinical use. Methods The CIRS Density Phantom with different tissue equivalent inserts was scanned at 70, 80, 100, 120 and 140 kVp with the new Siemens Confidence CT scanner. Images were reconstructed with the DD™ algorithm to assess the correspondence of rEDs obtained from imaging with those certified. Afterwards the images of 7 patients scanned at 120 kVp were reconstructed with standard filtered backprojection (FBP) and DD™ algorithm. Treatment plans were calculated on both FBP and DD™ images by using standard HU-rEDs curve and linear CTvalue-rEDs relationship respectively (Fig. 1). Dose differences were evaluated through γ -analysis (1 mm, 1%). Results The rEDs measured from images (by reversing the linear relationship between CTvalue and rED) in regions corresponding to phantom inserts were compared to certified rEDs: differences were reported in Table 1. Minimal dosimetric differences were found between treatment plans calculated on both FBP and DD™ images. DVHs showed differences in Dmean, D98, D2 and V95 for PTVs and OARs smaller than 1%. γ -analysis indicated negligible differences between dose distributions, with lowest passing rate at 97%. Conclusions This study proved the equivalence between DD™ and FBP, including the possibility to modulate kVp during CT acquisition, thus reducing patient dose without complicating treatment planning workflow. [ABSTRACT FROM AUTHOR]

Purpose The purpose of the AIFM Pediatric Commission is to contribute to a better knowledge of the medical physics aspects of paediatric applications. The Commission will focus mostly on the study of quality and safety aspects, supporting the contacts between scientific associations, institutions and stakeholders, and promoting communication and shared projects. Methods The Commission will address three entities: 1) Scientific societies and institutions, to help coordinate initiatives and create synergies in medical physics applications in paediatrics; 2) the AIFM members, for whom the Commission should be a "reference point" for issues that are specific of paediatric applications; 3) The stakeholders and the population. We are planning the initial following actions: – A public event on dosimetric data in paediatrics, to be organized in 2018 together with the paediatric groups of other professional and scientific societies; – A national survey to collect numbers and procedures for paediatric patients across Italy; – For the AIFM members: a. a dedicated page on the web site, to openly expose goals and results of the Commission. The page will also be a virtual conference room to discuss paediatric topics, and a repository of guidelines and literature in the field; b. a dedicated e-mail address has been defined: commissionepediatrica@fisicamedica.it ; c. the Commission being the AIFM reference for all paediatric topics in medical physics, will propose Working Groups (WGs) on this subject. Our WGs will follow the standard procedure of any AIFM WGs. It is desirable that any other new paediatric group is initially submitted to the Commission, which will express its opinion to the AIFM Management Commitee. – In order to understand what AIFM can offer to the stakeholders and to the "outside world", questions related to paediatrics and already submitted to the existing AIFM forum will be analysed. Results the results of the national survey will be presented (data collection is still ongoing); the architecture of the AIFM web page will be shown. Conclusions the congress will be an important moment to understand the members' needs and interest on this topic. [ABSTRACT FROM AUTHOR]

Purpose Investigate late radiation damages after focal radiotherapy (RT) for childhood brain cancer in terms of neurocognitive outcome. Methods 45 retrospective children (age at RT:median = 6.2 years, range 1.1–22.5, age at valuations:median = 11.1 years, range 4.4–25.9) who received focal RT at our Institution with at least 3-years follow-up without relapse, were recruited to undergo cognitive, neuropsychological and psychological testing. Planning CT images were retrieved and patients' brains were parceled in 116 regions of interest (ROIs) using the Tzourio-Mazoyer atlas [1] and a dedicated home-made, multimodal, highly deformable registration framework specifically developed for the study. Mean RT dose value was collected for each ROI. The pattern of association between the categorized cognitive tests scores and RT dose was assessed in each ROI through the Kruskal Wallis test. Subsequently, the preliminary threshold of RT dose (optimal cut-off value) discriminating patients with and without neurocognitive changes (impaired/non-impaired patients), was selected by using a Receiver Operating Characteristic curve (ROC). Results The statistical analysis allowed us to identify the ROIs where mean dose values and cognitive tests results were significantly related. For the 29 ROIs showing the most significant associations, preliminary threshold dose values related to a specific cognitive or neuropsychological damage were obtained, ranging from 3.5 to 29.8 Gy. As an example, Figure1 shows the distributions of dose values in the ROI "Frontal_ Sup_Orb_ R" for patients with impaired/non-impaired performances in a specific cognitive test (Processing Speed Index, WISC III). Conclusions The preliminary analysis of the retrospective children suggested that the main aim (identify brain structures highly susceptible to radiation damages and the respective radiation dose thresholds) is achievable, justifying a prospective study currently open to children enrollment. Partially funded by AIRC. [ABSTRACT FROM AUTHOR]

Purpose Development of NTCP models of late severe urinary symptoms after radical RT for prostate cancer (PCa). Methods Patients were enrolled in a prospective, multicentre, observational trial in 2010–2014 and treated with conventional (74–80 Gy at 1.8–2 Gy/fr) or moderately hypofractionated IMRT (65–75.2 Gy at 2.2–2.7 Gy/fr). Bladder dose-surface histograms were corrected to 2 Gy/fr equivalent doses (EQD2) and reduced to Equivalent Uniform Doses at varying α / β and n. Urethral stricture requiring urethrotomy and bleeding (assessed by the physicians) and late obstructive symptoms and incontinence (through ICIQ and IPSS questionnaires) were evaluated before RT, at its completion and every 6 months until 5 years of follow-up. Incidence of late obstructive symptoms was defined as an increase of ⩾10 points with respect to baseline in the IPSS, at least once between 6–36 months after RT; incidence of incontinence as the sum ICIQ3 + ICIQ4 > 5, with the same timing, in continent patients before RT (ICIQ3 + ICIQ4 = 0). Maximum likelihood estimation (MLE) was employed for calculating the best-fit NTCP parameters (EUD50 and k) of all symptoms. Results 319 patients were followed for ⩾36 months with at least 3 follow-up evaluations. 27/319 (23%) patients exhibited at least one severe late urinary symptom (details in Table). Bleeding, obstructive symptoms and incontinence showed greater incidence for hypofractionation and EQD2 > 78 Gy. The highest likelihood was obtained for very low n in all cases; low α / β was found for all the endpoints except stricture. Figure shows the best-fit NTCP parameters: incontinence and bleeding curves were steeper with rising EUD. Conclusions Incidence of late severe urinary symptoms in patients treated with IMRT for PCa was about 20%. Bladder seems to act as a serial organ and all the symptoms significantly depend on the prescribed dose. In addition, all the symptoms, except for stenosis, show a surprisingly important effect of hypofractionation. [ABSTRACT FROM AUTHOR]

MO Skins are MOSFET dosimeters designed and developed at the Centre for Medical Radiation Physics (University of Wollongong, Australia), optimized to measure the dose in steep dose gradients. In this work, their clinical application to rectal wall in vivo dosimetry (IVD) during gynecological and prostate high dose rate brachytherapy (HDR-BT) was studied. To evaluate the discrepancies between planned and measured doses to the rectal wall and to investigate the impact of the duration of the treatment planning procedure on these discrepancies. In gynecological HDR-BT, three MO Skins were assembled over a semi-flexible rectal probe and 51 IVD measurements were performed. In prostate HDR-BT, two MO Skins were assembled on the trans-rectal ultrasound probe and 36 IVD measurements were performed. The absolute differences ΔD between measured and calculated doses in the estimated dosimeters positions were quantified and a possible correlation with the treatment planning time was investigated. Grouping ΔD according to the time elapsed between imaging and treatment (i.e., group 1: ⩽90 min; group 2: >90 min), average ΔD for groups 1 and 2 were 5.1 ± 3.0% and 8.3 ± 6.2% for prostate and 3.8 ± 3.5% and 6.5 ± 4.3% for gynecology HDR-BT, respectively. Average ΔD were in both cases lower for group 1, demonstrating higher uncertainties of the calculated dose with higher treatment planning times (i.e., probability of morphological changes increases with time). MO Skin dosimeters coupled to rectal probes may be used for rectal IVD during gynecological/prostate HDR-BT. Planning time should be kept as low as possible to reduce uncertainties in calculated doses. none [ABSTRACT FROM AUTHOR]

A system (Calypso, Varian Medical Systems) based on the localization of electromagnetic transponders (ELM-TRNs) permanently implanted in the prostate allows real-time tracking during radiotherapy treatments. Development and validation of a dedicated software for ELM-TRNs signal analysis to quantify the amplitude of the intra-fraction prostate motion induced by patient's breathing, both in supine and prone position. For each treatment session, the software automatically identifies the breathing frequency on the power density spectrum of the recorded signal and creates a bandpass filter around this frequency. The obtained filter is then applied to selectively compute the breathing-induced harmonic excursion of the prostate around its nominal position. The software was validated with a moving phantom (QUASAR, Modus Medical Devices), provided with home-made inserts containing three ELM-TRNs. Harmonic motions along the three main directions were tracked at several known frequencies and amplitudes. The calculated frequencies and amplitudes were compared to the expected ones. The software was then applied to signals of patients who underwent radiotherapy treatments in supine or prone position. The software automatically computed the correct frequencies and amplitudes within a 0.6% and a 110 μm uncertainty, respectively, without any significant difference among the three main directions. The software was demonstrated to properly work on signals acquired both with supine and prone patients. A software to quantify prostate motion due to patient's breathing was successfully developed, in-phantom validated and applied to supine and prone patients, highlighting significant motion differences between the two setups. None. Work partially funded by AIRC-(IG-14300). [ABSTRACT FROM AUTHOR]