Autosegmentation based on different-sized training datasets of consistently-curated volumes and impact on rectal contours in prostate cancer radiation therapy.

Background and purpose: Autosegmentation techniques are emerging as time-saving means for radiation therapy (RT) contouring, but the understanding of their performance on different datasets is limited. The aim of this study was to determine agreement between rectal volumes by an existing autosegmentation algorithm and manually-delineated rectal volumes in prostate cancer RT. We also investigated contour quality by different-sized training datasets and consistently-curated volumes for retrained versions of this same algorithm. Materials and methods: Single-institutional data from 624 prostate cancer patients treated to 50-70 Gy were used. Manually-delineated clinical rectal volumes (clinical) and consistently-curated volumes recontoured to one anatomical guideline (reference) were compared to autocontoured volumes by a commercial autosegmentation tool based on deep-learning (v1; n = 891, multiple-institutional data) and retrained versions using subsets of the curated volumes (v32/64/128/256; n = 32/64/128/256). Evaluations included dose-volume histogram metrics, Dice similarity coefficients, and Hausdorff distances; differences between groups were quantified using parametric or non-parametric hypothesis testing. Results: Volumes by v1-256 (76-78 cm3) were larger than reference (75 cm3) and clinical (76 cm3). Mean doses by v1-256 (24.2-25.2 Gy) were closer to reference (24.2 Gy) than to clinical (23.8 Gy). Maximum doses were similar for all volumes (65.7-66.0 Gy). Dice for v1-256 and reference (0.87-0.89) were higher than for v1-256 and clinical (0.86-0.87) with corresponding Hausdorff comparisons including reference smaller than comparisons including clinical (5-6 mm vs. 7-8 mm). Conclusion: Using small single-institutional RT datasets with consistently-defined rectal volumes when training autosegmentation algorithms created contours of similar quality as the same algorithm trained on large multi-institutional datasets.

Properties of IBA Razor Nano Chamber in small-field radiation therapy using 6 MV FF, 6 MV FFF, and 10 MV FFF photon beams.

BACKGROUND: Small megavoltage photon fields are increasingly used in modern radiotherapy techniques such as stereotactic radiotherapy. Therefore, it is important to study the reliability of dosimetry in the small-field conditions. The IBA Razor Nano Chamber (Nano chamber) ionization chamber is particularly intended for small-field measurements. In this work, properties of the Nano chamber were studied with both measurements and Monte Carlo (MC) simulations. MATERIAL AND METHODS: The measurements and MC simulations were performed with 6 MV, 6 MV FFF and 10 MV FFF photon beams from the Varian TrueBeam linear accelerator. The source-to-surface distance was fixed at 100 cm. The measurements and MC simulations included profiles, percentage depth doses (PDD), and output factors (OF) in square jaw-collimated fields. The MC simulations were performed with the EGSnrc software system in a large water phantom. RESULTS: The measured profiles and PDDs obtained with the Nano chamber were compared against IBA Razor Diode, PTW microDiamond and the PTW Semiflex ionization chamber. These results indicate that the Nano chamber is a high-resolution detector and thus suitable for small field profile measurements down to field sizes 2 × 2 cm2 and appropriate for the PDD measurements. The field output correction factors kQclin, Qmsrfclin, fmsr and field OFs ΩQclin, Qmsrfclin, fmsr were determined according to TRS-483 protocol In the 6 MV FF and FFF beams, the determined correction factors kQclin, Qmsrfclin, fmsr were within 1.2% for the field sizes of 1 × 1 cm2-3 × 3 cm2 and the experimental and MC defined field output factors ΩQclin,Qmsrfclin,fmsr showed good agreement. CONCLUSION: The Nano chamber with its small cavity volume is a potential detector for the small-field dosimetry. In this study, the properties of this detector were characterized with measurements and MC simulations. The determined correction factors kQclin, Qmsrfclin, fmsr are novel results for the NC in the TrueBeam fields.

Dose-area product ratio in external small-beam radiotherapy: beam shape, size and energy dependencies in clinical photon beams.

In small-field radiotherapy (RT), a significant challenge is to define the amount of radiation dose absorbed in the patient where the quality of the beam has to be measured with high accuracy. The properties of a proposed new beam quality specifier, namely the dose-area-product ratio at 20 and 10 cm depths in water or DAPR20,10, were studied to yield more information on its feasibility over the conventional quality specifier tissue-phantom ratio or TPR20,10. The DAPR20,10may be measured with a large-area ionization chamber (LAC) instead of small volume chambers or semi-conductors where detector, beam and water phantom positioning and beam perturbations introduce uncertainties. The effects of beam shape, size and energy on the DAPR20,10were studied and it was shown that the DAPR20,10increases with increasing beam energy similarly to TPR20,10but in contrast exhibits a small beam size and shape dependence. The beam profile outside the beam limiting devices has been shown to have a large contribution to the DAPR20,10. There is potential in large area chambers to be used in DAPR measurement and its use in dosimetry of small-beam RT for beam quality measurements.

A Deep Learning-Based Automated CT Segmentation of Prostate Cancer Anatomy for Radiation Therapy Planning-A Retrospective Multicenter Study.

A commercial deep learning (DL)-based automated segmentation tool (AST) for computed tomography (CT) is evaluated for accuracy and efficiency gain within prostate cancer patients. Thirty patients from six clinics were reviewed with manual- (MC), automated- (AC) and automated and edited (AEC) contouring methods. In the AEC group, created contours (prostate, seminal vesicles, bladder, rectum, femoral heads and penile bulb) were edited, whereas the MC group included empty datasets for MC. In one clinic, lymph node CTV delineations were evaluated for interobserver variability. Compared to MC, the mean time saved using the AST was 12 min for the whole data set (46%) and 12 min for the lymph node CTV (60%), respectively. The delineation consistency between MC and AEC groups according to the Dice similarity coefficient (DSC) improved from 0.78 to 0.94 for the whole data set and from 0.76 to 0.91 for the lymph nodes. The mean DSCs between MC and AC for all six clinics were 0.82 for prostate, 0.72 for seminal vesicles, 0.93 for bladder, 0.84 for rectum, 0.69 for femoral heads and 0.51 for penile bulb. This study proves that using a general DL-based AST for CT images saves time and improves consistency.

Commissioning of the MultiRad 350 cell and small animal x-ray irradiation system.

PURPOSE: The main objective of this study was to commission a commercial x-ray irradiation system to be used for cell and small animal studies. MATERIALS AND METHODS: Evaluated characteristics of an x-ray irradiator included dose linearity and dose repeatability with respect to time, x-ray beam profiles, light field to irradiation field agreement and absolute radiation dose. Radiochromic films, ionization chambers and radiophotoluminescence dosimeters were used for dosimetry and the maximum settings of the irradiator were applied. RESULTS: The dose was linear with time using several voltage settings and the dose repeatability with time was within 5% beyond 15 s of irradiation time. The x-ray beam profiles were acceptable, flatness being less than 4%. The light field to irradiation field agreement appeared to have a maximum difference of 0.5 cm; the irradiation field being closer to the irradiator's door than the light field. CONCLUSIONS: The MultiRad 350 x-ray irradiation system can be used in a safe and controlled manner for irradiating cells and small animals. However, the user should be careful to verify the filter position prior the irradiation.

Measurement and properties of the dose-area product ratio in external small-beam radiotherapy.

In small-beam radiation therapy (RT) the measurement of the beam quality parameter, i.e. the tissue-phantom ratio or TPR20,10, using a conventional point detector is a challenge. To obtain reliable results, one has to consider potential sources of error, including volume averaging and adjustment of the point detector into the narrow beam. To overcome these challenges, a different type of beam quality parameter in small beams was studied, namely the dose-area product ratio, or DAPR20,10. With this method, the measurement of a dose-area product (DAP) using a large-area plane-parallel chamber (LAC) eliminates the uncertainties in detector positioning and volume averaging that are present when using a point detector. In this study, the properties of the DAPR20,10 of a cone-collimated 6 MV photon beam were investigated using Monte Carlo (MC) calculations and the obtained values were compared to measurements obtained using two LAC detectors, PTW Type 34073 and PTW Type 34070. In addition, the possibility of determining the DAP using EBT3 film and a Razor diode detector was studied. The determination of the DAPR20,10 value was found to be feasible in external small-beam radiotherapy using cone-collimated beams with diameters from 4-40 mm, based on the results of the two LACs, the MC calculations and the Razor diode. The measurements indicated a constant DAPR20,10 value for fields 20-40 mm in diameter, with a maximum relative change of 0.6%, but an increase of 7.0% for fields from 20-4 mm in diameter for the PTW Type 34070 chamber. Simulations and measurements showed an increase of DAPR20,10 with increasing LAC size or dose integral area for the studied 4-40 mm cone-collimated 6 MV photon beams. This has the consequence that there should be a reference to the size of the used LAC active area or the DAP integration area with the reported DAPR20,10 value.

Radiation surveillance using an unmanned aerial vehicle.

Radiation surveillance equipment was mounted in a small unmanned aerial vehicle. The equipment consists of a commercial CsI detector for count rate measurement and a specially designed sampling unit for airborne radioactive particles. Field and flight tests were performed for the CsI detector in the area where (137)Cs fallout from the Chernobyl accident is 23-45 kBq m(-2). A 3-GBq (137)Cs point source could be detected at the altitude of 50 m using a flight speed of 70 km h(-1) and data acquisition interval of 1s. Respective response for (192)Ir point source is 1 GBq. During the flight, the detector reacts fast to ambient external dose rate rise of 0.1 microSv h(-1), which gives for the activity concentration of (131)I less than 1 kB qm(-3). Operation of the sampler equipped with different type of filters was investigated using wind-tunnel experiments and field tests with the aid of radon progeny. Air flow rate through the sampler is 0.2-0.7 m(3)h(-1) at a flight speed of 70 km h(-1) depending on the filter type in question. The tests showed that the sampler is able to collect airborne radioactive particles. Minimum detectable concentration for transuranium nuclides, such as (239)Pu, is of the order of 0.2 Bq m(-3) or less when alpha spectrometry with no radiochemical sample processing is used for activity determination immediately after the flight. When a gamma-ray spectrometer is used, minimum detectable concentrations for several fission products such as (137)Cs and (131)I are of the order of 1 Bq m(-3).