Patient specific quality assurance in SBRT: a systematic review of measurement-based methods.

This topical review focuses on Patient-Specific Quality Assurance (PSQA) approaches to stereotactic body radiation therapy (SBRT). SBRT requires stricter accuracy than standard radiation therapy due to the high dose per fraction and the limited number of fractions. The review considered various PSQA methods reported in 36 articles between 01/2010 and 07/2022 for SBRT treatment. In particular comparison among devices and devices designed for SBRT, sensitivity and resolution, verification methodology, gamma analysis were specifically considered. The review identified a list of essential data needed to reproduce the results in other clinics, highlighted the partial miss of data reported in scientific papers, and formulated recommendations for successful implementation of a PSQA protocol.

Clinical implementation of a log file-based machine and patient QA system for IMRT and VMAT treatment plans.

PURPOSE: To determine the error detection sensitivity of a commercial log file-based system (LINACWatch®, LW) for integration into clinical routine and to compare it with a measurement device (OCTAVIUS 4D, Oct4D) for IMRT and VMAT delivery QA. MATERIALS AND METHODS: 76 VMAT/IMRT plans (H&N, prostate, rectum and breast) preliminarily classified according to their Modulation Complexity Score (MCS) calculated by LW, were considered. Receiver Operating Characteristic (ROC) Curves were used to establish gamma criteria for LW. 12 plans (3 for each site) were intentionally modified in order to introduce delivery errors regarding MLC, jaws, collimator, gantry and MU (for a total set of 168 incorrect plans) and irradiated on Oct4D; the corresponding log files were analysed by LW. Each incorrect plan was compared to the error-free plan using γ-index analysis for MLC, jaws and MU errors investigation and Root-Mean-Square (RMS) values for gantry and collimator errors investigation. RESULTS: MCS ranges values were: 0.10-0.20 for H&N, 0.21-0.40 for prostate and rectum, 0.41-1.00 for breast. From ROC curves, the Gamma Passing Rate (GPR) thresholds were: 87%, 92%, 99% for H&N, prostate and rectum, and breast, respectively. The 1.5%/1.5 mm/local criteria were adopted for the γ-analysis. LW sensitivity in detecting the introduced errors was higher when compared to Oct4D: 48.5% vs 30.4% respectively. CONCLUSIONS: LW can be considered useful complement to phantom-based delivery QA of IMRT/VMAT plans. The MCS tool is effective in detecting over or under modulated plans prior to pre-treatment QA. However, rigorous and routinely machine QCs are recommended.

The influence of basic plan parameters on calculated small field output factors - A multicenter study.

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 < 0.001). As FS decreases, the spread in the difference between calculated and measured OFs became larger when increasing the GR. Monte Carlo and Analytical Anisotropic Algorithms, presented a dependence on GR (p < 0.01), while Collapsed Cone Convolution and Acuros did not. The effect of the ST was found to be negligible. 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.

The influence of small field output factors simulated uncertainties on the calculated dose in VMAT plans for brain metastases: a multicentre study.

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.

A randomized in vitro evaluation of transient and permanent cardiac implantable electronic device malfunctions following direct exposure up to 10 Gy.

BACKGROUND AND PURPOSE: High-dose 6­MV radiotherapy may cause cardiac implantable electronic devices (CIEDs) to malfunction. To assess CIED malfunctions resulting from direct exposure up to 10 Gy, 100 pacemakers (PMs) and 40 implantable cardioverter-defibrillators (ICDs) were evaluated. MATERIALS AND METHODS: CIEDs underwent baseline interrogation. In ICDs, antitachycardia therapies were disabled via the programmer while the detection windows were left enabled. A computed tomography (CT) scan was performed to build the corresponding treatment plan. CIEDs were "blinded" and randomized to receive single doses of either 2, 5, or, 10 Gy via a 6-MV linear accelerator (linac) in a water phantom. Twenty-two wireless telemetry-enabled CIEDs underwent a real-time session, and their function was recorded by the video camera in the bunker. The CIEDs were interrogated after exposure and once monthly for 6 months. RESULTS: During exposure, regardless of dose, 90.9% of the CIEDs recorded electromagnetic interference, with 6 ICDs (27.3%) reporting pacing inhibition and inappropriate arrhythmia detections. After exposure, a backup reset was observed in 1 PM (0.7% overall, 1% among PMs), while 7 PMs (5% overall, 7% among PMs) reported battery issues (overall immediate malfunction rate was 5.7%). During follow-up, 4 PMs (2.9% overall; 4% among PMs) and 1 ICD (0.7% overall; 2.5% among ICDs) reported abnormal battery depletion, and 1 PM (0.7% overall; 1% among PMs) reported a backup reset (overall late malfunction rate was 4.3%). CONCLUSION: Apart from transient electromagnetic interference, last-generation CIEDs withstood direct 6­MV exposure up to 10 Gy. Permanent battery or software errors occurred immediately or later only in less recent CIEDs.

COVID-19 and radiation oncology: the experience of a two-phase plan within a single institution in central Italy.

BACKGROUND: COVID-19 in Italy has led to the need to reorganize hospital protocols with a significant risk of interruption to cancer treatment programs. In this report, we will focus on a management model covering the two phases of the COVID-19 emergency, namely lockdown-phase I and post-lockdown-phase II. METHODS: The following steps were taken in the two phases: workload during visits and radiotherapy planning, use of dedicated routes, measures for triage areas, management of suspected and positive COVID-19 cases, personal protective equipment, hospital environments and intra-institutional meetings and tumor board management. Due to the guidelines set out by the Ministry of Health, oncological follow-up visits were interrupted during the lockdown-phase I; consequently, we set about contacting patients by telephone, with laboratory and instrumental exams being viewed via telematics. During the post-lockdown-phase II, the oncological follow-up clinic reopened, with two shifts operating daily. RESULTS: By comparing our radiotherapy activity from March 9 to May 4 2019 with the same period in 2020 during full phase I of the COVID-19 emergency, similar results were achieved. First radiotherapy visits, Simulation Computed Tomography and Linear Accelerator treatments amounted to 123, 137 and 151 in 2019 compared with 121, 135 and 170 in 2020 respectively. There were no cases of COVID-19 positivity recorded either in patients or in healthcare professionals, who were all negative to the swab tests performed. CONCLUSION: During both phases of the COVID-19 emergency, the planned model used in our own experience guaranteed both continuity in radiotherapy treatments whilst neither reducing workload nor interrupting treatment and, as such, it ensured the safety of cancer patients, hospital environments and staff.

Estimating dose delivery accuracy in stereotactic body radiation therapy: A review of in-vivo measurement methods.

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.

Effects of high-energy photon beam radiation therapy on Jarvik 2000 LVAD: in vitro evaluation.

PURPOSE: Left ventricular assist device (LVAD) is considered a standard care for patients with advanced heart failure. The aim of this work was to study in vitro the effects of direct exposure of the Jarvik 2000 LVAD to 10-MV photon beams. METHODS: Jarvik 2000 pump was immersed in a siliconized box filled with deionized water. A 30 × 30 × 15 cm RW3 slabs were added forth and back to the box. A treatment plan consisting of a single direct 10 × 10 cm2 field size beam was used to deliver 1000 MU at the center of the pump. During irradiation, the external Flow Maker controller and the lithium battery were positioned away from the beam. Pump parameter data (included voltage, current and frequency) were measured, recorded and analyzed for changes in pump function among baseline, pre-irradiation, during irradiation, post-irradiation and after 6 months. The whole session lasted 6 months. The Mann-Whitney U test was used to compare the repeated measurements. X-ray radiation attenuation was also studied. RESULTS: The parameters investigated remained stable over the 6 months; that is, no pump stops, alarms, events, operational changes or abnormalities during the discharge rate of the connected power sources, were encountered, confirmed by the Mann-Whitney U test applied to all sessions (p > 0.1). The measured X-ray attenuation differed from the calculated one by TPS by 34%. CONCLUSION: The Jarvik 2000 resulted stable under direct X-ray beam of 10-MV energy. Its strong attenuation, however, can affect dose deposition in the pump in TPS, and it must be taken into account.

Community approach for reducing small field measurement errors: Experience over 24 centres.

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 radiotherapy 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.

Small field output factors evaluation with a microDiamond detector over 30 Italian centers.

PURPOSE: The aim of the study was a multicenter evaluation of MLC&jaws-defined small field output factors (OF) for different linear accelerator manufacturers and for different beam energies using the latest synthetic single crystal diamond detector commercially available. The feasibility of providing an experimental OF data set, useful for on-site measurements validation, was also evaluated. METHODS: This work was performed in the framework of the Italian Association of Medical Physics (AIFM) SBRT working group. The project was subdivided in two phases: in the first phase each center measured OFs using their own routine detector for nominal field sizes ranging from 10×10cm2 to 0.6×0.6cm2. In the second phase, the measurements were repeated in all centers using the PTW 60019 microDiamond detector. RESULTS: The project enrolled 30 Italian centers. Micro-ion chambers and silicon diodes were used for OF measurements in 24 and 6 centers respectively. Gafchromic films and TLDs were used for very small field OFs in 3 and 1 centers. Regarding the measurements performed with the user's detectors, OF standard deviations (SD) for field sizes down to 2×2cm2 were in all cases <2.7%. In the second phase, a reduction of around 50% of the SD was obtained using the microDiamond detector. CONCLUSIONS: The measured values presented in this multicenter study provide a consistent dataset for OFs that could be a useful tool for improving dosimetric procedures in centers. The microDiamond data present a small variation among the centers confirming that this detector can contribute to improve overall accuracy in radiotherapy.

Technical solutions to reduce mediastinal irradiation in young patients undergoing treatment for lymphomas: Preliminary experience.

This study aims at optimizing treatment planning in young patients affected by lymphoma (Stage II to III) by using an inclined board (IB) that allows reducing doses to the organs at risk. We evaluated 19 young patients affected by stage I to III lymphomas, referred to our Department for consolidation radiotherapy (RT) treatment on the mediastinum. Patients underwent 2 planning computed tomography (CT) scans performed in different positions: flat standard position and inclined position. A direct comparison between the different treatment plans was carried out analyzing dosimetric parameters obtained from dose-volume histograms generated for each plan. Comparison was performed to evaluate the sparing obtained on breast and heart. Dosimetric evaluation was performed for the following organs at risk (OARs): mammary glands, lungs, and heart. A statistically significant advantage was reported for V5, V20, and V30 for the breast when using the inclined board. A similar result was obtained for V5 and V10 on the heart. No advantage was observed in lung doses. The use of a simple device, such as an inclined board, allows the optimization of treatment plan, especially in young female patients, by ensuring a significant reduction of the dose delivered to breast and heart.

Predicting genitourinary toxicity in three-dimensional conformal radiotherapy for localized prostate cancer: A dose-volume parameters analysis of the bladder.

PURPOSE: In prostate cancer radiotherapy, the relationship between genitourinary (GU) toxicity and clinical-dosimetric parameters is debated. We report our analysis of the parameters associated with GU toxicity. MATERIALS AND METHODS: Eighty-six consecutive patients treated with conformal radiotherapy for localized prostate cancer were retrospectively analyzed; the bladder was delineated both as "whole bladder" (WB: Defined in its entirety as a solid organ) and "inferior bladder" (IB: Corresponding to the distal part of the bladder). GU toxicity and dose-volume parameters were correlated using the point biserial correlation coefficient. The normal tissue complication probability (NTCP) cut-off volume model was fitted to toxicity data; univariate analysis between GU toxicity and clinical parameters was done. RESULTS: Acute GU toxicity was correlated to doses higher than 80 Gy (P < 0.05) while late GU was correlated to doses higher than 77 Gy for WB and from 77.5 Gy for IB. The NTCP cut-off volume model identified for both WB and IB a bladder volume of 6 cc receiving a dose ≥77 Gy corresponding to a 50% probability of GU toxicity. At univariate analysis, acute GU toxicity was correlated with smoke (P < 0.001). CONCLUSION: Bladder maximal doses quantified as hotspots show a correlation to GU toxicity.

Lung stereotactic ablative body radiotherapy: A large scale multi-institutional planning comparison for interpreting results of multi-institutional studies.

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 54Gy in 3 fractions of 18Gy. The plans were compared in terms of PTV-gEUD2 (generalized Equivalent Uniform Dose equivalent to 2Gy), 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 MLD2 (mean lung dose equivalent to 2Gy). 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-gEUD2 differences were observed (range: 105-161Gy); mean-PTV dose, PTV-HI, PTV-CI, and PTV-GI were, respectively, 56.8±3.4Gy, 14.2±10.1%, 0.70±0.15, and 4.9±1.9. Significant correlations for PTV-gEUD2 versus PTV-HI, and MLD2 versus PTV-GI, were observed. CONCLUSIONS: The differences in terms of PTV-gEUD2 may suggest the inclusion of PTV-gEUD2 calculation for retrospective data inter-comparison.

Multicenter evaluation of a synthetic single-crystal diamond detector for CyberKnife small field size output factors.

PURPOSE: The aim of the present work was to evaluate small field size output factors (OFs) using the latest diamond detector commercially available, PTW-60019 microDiamond, over different CyberKnife systems. OFs were measured also by silicon detectors routinely used by each center, considered as reference. METHODS: Five Italian CyberKnife centers performed OFs measurements for field sizes ranging from 5 to 60mm, defined by fixed circular collimators (5 centers) and by Iris(™) variable aperture collimator (4 centers). Setup conditions were: 80cm source to detector distance, and 1.5cm depth in water. To speed up measurements two diamond detectors were used and their equivalence was evaluated. MonteCarlo (MC) correction factors for silicon detectors were used for comparing the OF measurements. RESULTS: Considering OFs values averaged over all centers, diamond data resulted lower than uncorrected silicon diode ones. The agreement between diamond and MC corrected silicon values was within 0.6% for all fixed circular collimators. Relative differences between microDiamond and MC corrected silicon diodes data for Iris(™) collimator were lower than 1.0% for all apertures in the totality of centers. The two microDiamond detectors showed similar characteristics, in agreement with the technical specifications. CONCLUSIONS: Excellent agreement between microDiamond and MC corrected silicon diode detectors OFs was obtained for both collimation systems fixed cones and Iris(™), demonstrating the microDiamond could be a suitable detector for CyberKnife commissioning and routine checks. These results obtained in five centers suggest that for CyberKnife systems microDiamond can be used without corrections even at the smallest field size.

Comparison between small radiation therapy electron beams collimated by Cerrobend and tubular applicators.

The purpose of this study was to compare the dosimetric properties of small field electron beams shaped by circular Cerrobend blocks and stainless steel tubular applicators. Percentage depth dose curves, beam profiles, and output factors of small-size circular fields from 2 to 5 cm diameter, obtained either by tubular applicators and Cerrobend blocks, were measured for 6, 10, and 15 MeV electron beam energies. All measurements were performed using a PTW microDiamond 60019 premarket prototype. An overall similar behavior between the two collimating systems can be observed in terms of PDD and beam profiles. However, Cerrobend collimators produce a higher bremsstrahlung background under irradiation with high-energy electrons. In such irradiation condition, larger output factors are observed for tubular applicators. Similar dosimetric properties are observed using circular Cerrobend blocks and stainless steel tubular applicators at lower beam energies. However, Cerrobend collimators allow the delivery of specific beam shapes, conformed to the target area. On the other hand, in high-energy irradiation conditions, tubular applicators produce a lower bremsstrahlung contribution, leading to lower doses outside the target volume. In addition, the higher output factors observed at high energies for tubular applicators lead to reduced treatment times.

Standard or hypofractionated radiotherapy in the postoperative treatment of breast cancer: a retrospective analysis of acute skin toxicity and dose inhomogeneities.

BACKGROUND: To identify predictive factors of radiation-induced skin toxicity in breast cancer patients by the analysis of dosimetric and clinical factors. METHODS: 339 patients treated between January 2007 and December 2010 are included in the present analysis. Whole breast irradiation was delivered with Conventional Fractionation (CF) (50 Gy, 2.0/day, 25 fractions) and moderate Hypofractionated Schedule (HS) (44 Gy, 2.75 Gy/day, 16 fractions) followed by tumour bed boost. The impact of patient clinical features, systemic treatments and, in particular, dose inhomogeneities on the occurrence of different levels of skin reaction has been retrospectively evaluated. RESULTS: G2 and G3 acute skin toxicity were 42% and 13% in CF patients and 30% and 7.5% in HS patients respectively. The retrieval and revaluation of 200 treatment plans showed a strong correlation between areas close to the skin surface, with inhomogeneities >107% of the prescribed dose, and the desquamation areas as described in the clinical records. CONCLUSIONS: In our experience dose inhomogeneity underneath G2 - G3 skin reactions seems to be the most important predictor for acute skin damage and in these patients more complex treatment techniques should be considered to avoid skin damage. Genetic polymorphisms too have to be investigated as possible promising candidates for predicting acute skin reactions.

Characterization of a cable-free system based on p-type MOSFET detectors for "in vivo" entrance skin dose measurements in interventional radiology.

PURPOSE: During radiological interventional procedures (RIP) the skin of a patient under examination may undergo a prolonged x-ray exposure, receiving a dose as high as 5 Gy in a single session. This paper describes the use of the OneDose(TM) cable-free system based on p-type MOSFET detectors to determine the entrance skin dose (ESD) at selected points during RIP. METHODS: At first, some dosimetric characteristics of the detector, such as reproducibility, linearity, and fading, have been investigated using a C-arc as a source of radiation. The reference setting (RS) was: 80 kV energy, 40 cm × 40 cm field of view (FOV), current-time product of 50 mAs and source to skin distance (SSD) of 50 cm. A calibrated PMX III solid state detector was used as the reference detector and Gafchromic(®) films have been used as an independent dosimetric system to test the entire procedure. A calibration factor for the RS and correction factors as functions of tube voltage and FOV size have been determined. RESULTS: Reproducibility ranged from 4% at low doses (around 10 cGy as measured by the reference detector) to about 1% for high doses (around 2 Gy). The system response was found to be linear with respect to both dose measured with the PMX III and tube voltage. The fading test has shown that the maximum deviation from the optimal reading conditions (3 min after a single irradiation) was 9.1% corresponding to four irradiations in one hour read 3 min after the last exposure. The calibration factor in the RS has shown that the system response at the kV energy range is about four times larger than in the MV energy range. A fifth order and fourth order polynomial functions were found to provide correction factors for tube voltage and FOV size, respectively, in measurement settings different than the RS. ESDs measured with the system after applying the proper correction factors agreed within one standard deviation (SD) with the corresponding ESDs measured with the reference detector. The ESDs measured with Gafchromic(®) films were in agreement within one SD compared to the ESDs measured using the OneDose(TM) system, as well. The global uncertainty associated to the OneDose(TM) system established in our experiments, ranged from 7% to 10%, depending on the duration of the RIP due to fading. These values are much lower than the uncertainty commonly accepted for general diagnostic practices (20%) and of about the same size of the uncertainty recommended for practices with high risk of deterministic side effects (7%). CONCLUSIONS: The OneDose(TM) system has shown a high sensitivity in the kV energy range and has been found capable of measuring the entrance skin dose in RIP.

Is the in vivo dosimetry with the OneDosePlusTM system able to detect intra-fraction motion? A retrospective analysis of in vivo data from breast and prostate patients.

BACKGROUND: The OneDosePlusTM system, based on MOSFET solid-state radiation detectors and a handheld dosimetry reader, has been used to evaluate intra-fraction movements of patients with breast and prostate cancer. METHODS: An Action Threshold (AT), defined as the maximum acceptable discrepancy between measured dose and dose calculated with the Treatment Planning System (TPS) (for each field) has been determined from phantom data. To investigate the sensitivity of the system to direction of the patient movements, fixed displacements have been simulated in phantom. The AT has been used as an indicator to establish if patients move during a treatment session, after having verified the set-up with 2D and/or 3D images. Phantom tests have been performed matching different linear accelerators and two TPSs (TPS1 and TPS2). RESULTS: The ATs have been found to be very similar (5.0% for TPS1 and 4.5% for TPS2). From statistical data analysis, the system has been found not sensitive enough to reveal displacements smaller than 1 cm (within two standard deviations). The ATs applied to in vivo treatments showed that among the twenty five patients treated for breast cancer, only four of them moved during each measurement session. Splitting data into medial and lateral field, two patients have been found to move during all these sessions; the others, instead, moved only in the second part of the treatment. Patients with prostate cancer have behaved better than patients with breast cancer. Only two out of twenty five moved in each measurement session. CONCLUSIONS: The method described in the paper, easily implemented in the clinical practice, combines all the advantages of in vivo procedures using the OneDosePlusTM system with the possibility of detecting intra-fraction patient movements.