Neutron activation of activation targets in neutron beams with interruptions is studied. A simple and robust formalism for determining the number of activated atoms in neutron activation measurement despite beam interruptions is derived. Two simplified methods for correcting for the decay of produced nuclei in the activation target during beam interruptions are obtained and equations for using them are presented. The error of the simplifications done in the correction methods is quantified for Mn and Au activation targets and typical BNCT quality assurance measurement conditions. Upper limits on the duration of interruptions are established for keeping the impact of the simplifications on the total measurement uncertainty small when resuming irradiation after beam breaks. With these corrections methods and respecting the obtained upper limits on total pause duration, quality assurance neutron activation measurements in BNCT can be accomplished even if the neutron beam contains pauses, thus saving time from resetting the experimental setup each time an interruption occurs.

BACKGROUND AND PURPOSE:The prognosis of recurrent head and neck (HN) cancer is poor. High response rates have been achieved with boron neutron capture therapy (BNCT) in the treatment of locally recurrent HN cancer. Radiation-induced oral mucositis (OM) is a common adverse effect of BNCT. We evaluated the factors associated with severe OM in patients treated with BNCT. Patient/material and methods: Ninety two patients with locally recurrent inoperable HN cancer were treated with nuclear reactor-based BNCT in 1-2 fractions. The association between grade 3 OM, patient clinical parameters and maximum weighted oral mucosa dose was evaluated. Mucosal dose was calculated using the skin nitrogen concentration of 4.2%. A sigmoidal normal tissue complication probability (NTCP) model was created by dividing patients into four equal sized groups based on increasing dose levels. RESULTS:Grade 3 OM was observed in 42% of patients after the first BNCT treatment. The prevalence of OM increased with higher maximum oral mucosa doses. From the NTCP curve, we estimated the dose corresponding to a 50% probability (D50) for grade 3 OM to be 13.5 Gy(W). Older age was the only patient- related factor significantly associated with increased grade 3 OM risk. INTERPRETATION:Higher maximum oral mucosa doses increased the risk of grade 3 OM. Older age was the only other factor related to severe OM.

Background and purpose: Boron neutron capture therapy (BNCT) is targeted radiation therapy enabling cellular-level cancer treatment. With epithermal neutrons, the dose maximum typically occurs ~2 cm deep in tissue, challenging superficial tumor control. As in external beam radiation therapy, surface dose can be increased using a bolus. However, in BNCT, tissue equivalency is complex and strongly dependent on elemental composition. This study examined a paraffin wax bolus’s effect on the epithermal neutron beam in accelerator-based BNCT (AB-BNCT) and evaluated agreement between treatment planning system (TPS) calculations and measurements. Materials and methods: Beam characterization used the neutron activation method with gold and manganese foils. Due to its high cross-section for thermal neutrons, manganese activation serves as a surrogate for boron dose estimation. Irradiations were conducted in a 3D water tank and in a head-shaped phantom with 5 and 10 mm boluses. Dose calculation utilized the newly commissioned RayStation TPS with a Monte Carlo-based engine built on the GEANT4 toolkit. Results: Calculated and measured results agree within 5% accuracy in significant dose region (>50% dose). Near the surface and at greater depths, agreement remains within 10%. The bolus shifts the activation depth curve toward the surface by 4–13 mm depending on its thickness. Manganese surface activation increases from 30% without a bolus to ~70% and ~ 90% with 5 and 10 mm boluses, respectively. Interpretation: Paraffin wax effectively moderates neutron energy, making it a suitable bolus material for AB-BNCT treatments requiring increased surface dose.

Imaging parameters, frequencies and resulting patient organ doses in treatments of prostate cancer were assessed in Finnish radiotherapy centres. Based on a questionnaire to the clinics, Monte Carlo method was used to estimate organ doses in International Commission on Radiological Protection standard phantom for prostate, bladder, rectum and femoral head. The results show that doses from cone beam computed tomography imaging have reduced compared to earlier studies and are between 3.6 and 34.5 mGy per image for the above-mentioned organs and for normal sized patients. There still is room for further optimization of the patient exposure, as many centres use the default imaging parameters, and the length of the imaged region may not be optimal for the purpose.

Boron neutron capture therapy (BNCT) is a biologically targeted radiotherapy modality that utilizes a neutron beam. Ionization chambers are used in neutron beam dosimetry which is part of the commissioning process and periodic quality assurance. Ionization chambers used in BNCT are a bit larger in size compared to conventional external beam radiotherapy counterparts and a fixed horizontal beam direction poses its challenges among other considerations. Because of this, more flexible ionization chamber positioning would be preferred even in a large water phantom. In this work, we explain the effects and uncertainties that depend on chamber orientation. We compared depth dose curves measured with Exradin T2 and M2 ion chambers with two radiation sources, 6X photon and epithermal neutron beam, and in two orientations; one where the ionization chamber rod was positioned in perpendicular and the other where it was positioned in parallel orientation compared to the beam central axis. The perpendicular orientation is the reference orientation used in calibration. However, the parallel orientation allowed us to measure depth dose closer to the surface and the measurements had smaller systematic uncertainties because of a more straightforward alignment process. We can convert the data between the two different orientations with two simple correction parameters; correction factor which adjusted amplitude (k) and shift which adjusted the change of the effective point position in depth direction (Δ). All correction factor results were within 1.000±0.015 and all shift results were smaller or the same order of magnitude compared to the positioning accuracy, 0.05mm - 0.5mm. Even without the usage of corrections, the measurements were already almost in agreement. Because of this, we would recommend taking into consideration 2% additional uncertainty if measurements are performed in parallel orientation and no such correction parameters are used.

Background and purpose:Metallic hip prostheses cause substantial artefacts in both computed tomography (CT) and magnetic resonance (MR) images used in radiotherapy treatment planning (RTP) for prostate cancer patients. The aim of this study was to evaluate the dose calculation accuracy of a synthetic CT (sCT) generation workflow and the improvement in implant visibility using metal artefact reduction sequences. Materials and methods:The study included 23 patients with prostate cancer who had hip prostheses, of which 10 patients had bilateral hip implants. An in-house protocol was applied to create sCT images for dose calculation comparison. The study compared prostheses volumes and resulting avoidance sectors against planning target volume (PTV) dose uniformity and organs at risk (OAR) sparing. Results:Median PTV dose difference between sCT and CT-based dose calculation among all patients was 0.1 % (-0.4 to 0.4%) (median(range)). Bladder and rectum differences (V50Gy) were 0.2 % (-0.3 to 1.1%) and 0.1 % (-0.9 to 0.5%). The median 3D local gamma pass rate for partial arc cases using a Dixon MR sequence was Γ20%2mm/2% = 99.9%. For the bilateral full arc cases, using a metal artefact reconstruction sequence, the pass rate was Γ20%2mm/2% = 99.0%. Conclusions:An in-house protocol for generating sCT images for dose calculation provided clinically feasible dose calculation accuracy for prostate cancer patients with hip implants. PTV median dose difference for uni- and bilateral patients with avoidance sectors remained <0.4%. The Outphase images enhanced implant visibility resulting in smaller avoidance sectors, better OAR sparing, and improved PTV uniformity.

Locally advanced oesophageal cancer can be treated with definitive chemoradiation (dCRT) or with neoadjuvant chemoradiation followed by surgery (nCRT + S), but treatment modality choice is not always clear. The aim of this study was to investigate the factors associated with the choice of treatment modality in locally advanced oesophageal cancer. This was a retrospective cohort study of 149 patients treated with dCRT(n = 85) or nCRT + S (n = 64) for oesophageal cancer in Helsinki University Hospital in 2008–2018. Logistic regression was used to analyse factors associated with choice of treatment modality and to compare dosimetric factors with postoperative complications. Multivariate analyses identified factors associated with survival. Surgery was performed after chemoradiation as planned on 64/91 patients (70

Background and purpose:Radiotherapy (RT) treatment planning is as a standard based on a computed tomography (CT) scan obtained at the planning stage (pCT), while most of the decisions whether to treat by RT are based on diagnostic CT scans (dCT). Bone metastases (BM) are the most common palliative RT target. The objective of this study was to investigate if a palliative RT treatment plan of BMs could be made based on a dCT with sufficient accuracy and safety, without sacrificing any treatment quality.Materials and methods:A retrospective study with 60 BMs of 8 anatomical sites was performed. RT planning was performed using intensity-modulated radiation therapy/volumetric modulated arc therapy techniques in dCT and transferred to pCT. The dose of clinical target volumes (CTVs), D(CTVV95%, V50%), were compared between plans for dCT and pCT. Patient setup was investigated in cone-beam CT scans.Results:The differences of D(CTVV95%, V50%) between dCT and pCT plans were the lowest in the pelvis (1.0%, 1.1%), lumbar spine (0.6%, 0.7%) and thoracic spine (0.7%, 2.1%), while the differences were higher in cervical spine (3.7%, 1.9%), long bones (2.3%, 0.8%), and costae (1.6%, 1.4%). The patient set-up was acceptable for 100% of the pelvic and lumbar, for 92% of thoracic spine cases, and for <80% of cases in other sites.Conclusion:This study showed the feasibility of using dCT images in palliative RT planning of BMs in thoracic, lumbar spine and pelvic sites, indicating the potential suitability of this strategy for clinical use.

Boron neutron capture therapy (BNCT) is a unique type of radiation therapy that enables biological targeting of cancer at the cellular level. BNCT has been used to treat cancer with a two-step proc...

AbstractBackground and purposeA novel method of retrospective liver modeling was developed based on four‐dimensional magnetic resonance (4D‐MR) images. The 4D‐MR images will be utilized in generation of the subject‐specific deformable liver model to be used in radiotherapy planning (RTP). The purpose of this study was to test and validate the developed 4D‐magnetic resonance imaging (MRI) method with extensive phantom tests. We also aimed to build a motion model with image registration methods from liver simulating phantom images.Materials and methodsA deformable phantom was constructed by combining deformable tissue‐equivalent material and a programmable 4D CIRS‐platform. The phantom was imaged in 1.5 T MRI scanner with T2‐weighted 4D SSFSE and T1‐weighted Ax dual‐echo Dixon SPGR sequences, and in computed tomography (CT). In addition, geometric distortion of the 4D sequence was measured with a GRADE phantom. The motion model was developed; the phases of the 4D‐MRI were used as surrogate data, and displacement vector fields (DVF's) were used as a motion measurement. The motion model and the developed 4D‐MRI method were evaluated and validated with extensive tests.ResultThe 4D‐MRI method enabled an accuracy of 2 mm using our deformable phantom compared to the 4D‐CT. Results showed a mean accuracy of <2 mm between coordinates and DVF's measured from the 4D images. Three‐dimensional geometric accuracy results with the GRADE phantom were: 0.9‐mm mean and 2.5 mm maximum distortion within a 100 mm distance, and 2.2 mm mean, 5.2 mm maximum distortion within a 150 mm distance from the isocenter.ConclusionsThe 4D‐MRI method was validated with phantom tests as a necessary step before patient studies. The subject‐specific motion model was generated and will be utilized in the generation of the deformable liver model of patients to be used in RTP.

The authors review the results of 249 patients treated with boron neutron capture therapy (BNCT) at the Helsinki University Hospital, Helsinki, Finland, from May 1999 to January 2012 with neutrons obtained from a nuclear reactor source (FiR 1) and using l-boronophenylalanine-fructose (l-BPA-F) as the boron delivery agent. They also describe a new hospital BNCT facility that hosts a proton accelerator-based neutron source for BNCT. Most of the patients treated with nuclear reactor-derived neutrons had either inoperable, locally recurrent head and neck cancer or malignant glioma. In general, l-BPA-F-mediated BNCT was relatively well tolerated with adverse events usually similar to those of conventional radiotherapy. Twenty-eight (96.6%) out of the evaluable 29 patients with head and neck cancer and treated within a clinical trial either responded to BNCT or had tumor growth stabilization for at least 5 months, suggesting efficacy of BNCT in the treatment of this patient population. The new accelerator-based BNCT facility houses a nuBeam neutron source that consists of an electrostatic Cockcroft-Walton-type proton accelerator and a lithium target that converts the proton beam to neutrons. The proton beam energy is 2.6 MeV operating with a current of 30 mA. Treatment planning is based on Monte Carlo simulation and the RayStation treatment planning system. Patient positioning is performed with a 6-axis robotic image-guided system, and in-room imaging is done with a rail-mounted computed tomography scanner. Under normal circumstances, the personnel can enter the treatment room almost immediately after shutting down the proton beam, which improves the unit capacity. ClinicalTrials.gov ID: NCT00114790.

We analyzed treatment, outcome, and risk factors for skin necrosis of 60 patients aged >= 65 years treated for a pretibial hematoma in the province of Kymenlaakso, Finland, between 2015 and 2019. Reviewing patients' medical records revealed two cohorts with distinct trajectories in outcome. By comparing the cohorts, we were able to discover factors associated with the prognosis for generating skin necrosis and the need for operative treatment. Thirty-five (58.3%) patients healed without any management, and 25 (41.7%) patients were treated with hematoma evacuation, mostly for having generated skin necrosis (72%). Among operatively treated patients' descriptions, such as "parchment skin" and "poor skin quality" were observed frequently (80%) in the medical records. This pathology, dermatoporosis, was statistically significant (p<0.00 01) among patients with a complicated outcome of a pretibial hematoma. In addition to dermatoporosis, patients with hematoma evacuation were more fragile having a higher Charlson comorbidity index (p = 0.005), a greater need for a walking aid (p = 0.0002), and overall compromised independency (p = 0.033). Hospitalization and rehabilitation were prolonged in the operatively treated cohort, 6.4 days vs. 2 days, respectively. We recorded a delay in the diagnosis and hematoma evacuation (mean 6, range 0-51 days). In addition, six (10%) patients were misdiagnosed for having erysipelas or deep vein thrombosis indicating that pretibial hematomas are not recognized. Skin quality should be documented, and prompt surgical hematoma evacuation should be executed in fragile patients with dermatoporosis. This could prevent skin necrosis and the further need of wound care or surgical care, long hospitalization, and rehabilitation periods. (c) 2022 The Author(s). Published by Elsevier Ltd on behalf of British Association of Plastic, Reconstructive and Aesthetic Surgeons.

Background and Purpose: Magnetic resonance imaging is increasingly used in radiotherapy planning; yet, the performance of the utilized scanners is rarely regulated by any authority. The aim of this study was to determine the geometric accuracy of several magnetic resonance imaging scanners used for radiotherapy planning, and to establish acceptance criteria for such scanners. Materials and Methods: The geometric accuracy of five different scanners was measured with three sequences using a commercial large-field-of-view phantom. The distortion magnitudes were determined in spherical volumes around the scanner isocenter and in cylindrical volumes along scanner z-axis. The repeatability of the measurements was determined on a single scanner with two quality assurance sequences with three single-setup and seven repeated-setup measurements. Results: For all scanners and sequences except one, the mean and median distortion magnitude was <1 mm and <2 mm in spherical volumes with diameters of 400 mm and 500 mm, respectively. For all sequences maximum distortion was <2 mm in spherical volume with diameter of 300 mm. The mean standard deviation of marker-bymarker distortion magnitudes over repeated acquisitions was <= 0.6 mm with both tested sequences. Conclusions: All tested scanners were geometrically accurate for their current use in radiotherapy planning. The acceptance criteria of geometric accuracy for regulatory inspections of a supervising authority could be set according to these results.

In this retrospective cohort study, we analysed treatment and outcomes among ≥65-year-old patients who experienced a traumatic pretibial laceration in the province of Kymenlaakso, Finland, between 2015 and 2019. We reviewed computerised medical records for 116 patients with a pretibial laceration, 107 of whom we analysed in further detail. Patients were traced from injury to healing, including rehabilitation periods in health care centres. As expected, the majority of patients were elderly women (67%). Most lacerations were superficial and small, explaining why treatment was mostly conservative. Only 11 (9.48%) patients were treated operatively with surgical debridement or a split-thickness skin graft. The number of overall complications in wounds was high, with a complication rate of 30.2%. Most complications were local wound infections. We found that wound healing took more than 3 months in 32% of patients. Thorough patient tracing revealed numerous follow-up visits and long rehabilitative hospitalisation periods, indicating a significant decline in patient independence and the excessive use of resources. Successful wound healing was eventually observed in 89.66% patients. Furthermore, no terminology regarding pretibial lacerations was found in patient records. This study indicates that pretibial lacerations remain poorly recognised and understood in Finland.

This population‐based study aimed to examine the incidence, patterns and results of multimodal management of metastatic colorectal cancer.

AbstractPurpose of our research was to develop a four‐dimensional (4D) magnetic resonance imaging (MRI) method of liver. Requirements of the method were to create a clinical procedure with acceptable imaging time and sufficient temporal and spatial accuracy. The method should produce useful planning image sets for stereotactic body radiation therapy delivery both during breath‐hold and in free breathing. The purpose of the method was to improve the localization of liver metastasis. The method was validated with phantom tests. Imaging parameters were optimized to create a 4D dataset compressed to one respiratory cycle of the whole liver with clinically reasonable level of image contrast and artifacts. Five healthy volunteers were imaged with T2‐weighted SSFSE research sequence. The respiratory surrogate signal was observed by the linear navigator interleaved with the anatomical liver images. The navigator was set on head‐feet — direction on the superior surface of the liver to detect the edge of diaphragm. The navigator signal and 2D liver image data were retrospectively processed with a self‐developed MATLAB algorithm. A deformable phantom for 4D imaging tests was constructed by combining deformable tissue‐equivalent material and a commercial programmable motor unit of the 4D phantom with a clinically relevant range of deformation patterns. 4D Computed Tomography images were used as reference to validate the MRI protocol. The best compromise of reasonable accuracy and imaging time was found with 2D T2‐weighted SSFSE imaging sequence using parameters: TR = 500–550 ms, images/slices = 20, slice thickness = 3 mm. Then, image processing with number of respiratory phases = 8 constructed accurate 4D images of liver. We have developed the 4D‐MRI method visualizing liver motions three‐dimensionally in one representative respiratory cycle. From phantom tests it was found that the spatial agreement to 4D‐CT is within 2 mm that is considered sufficient for clinical applications.