The feasibility of CT simulation-free adaptive radiation therapy.

BACKGROUND: Novel on-board CBCT allows for improved image quality and Hounsfield unit accuracy. When coupled with online adaptive tools, this may have potential to allow for simulation and treatment to be completed in a single on-table session. PURPOSE: To study the feasibility of a high-efficiency radiotherapy treatment workflow without the use of a separate session for simulation imaging. The dosimetric accuracy, overall efficiency, and technical feasibility were used to evaluate the clinical potential of CT simulation-free adaptive radiotherapy. METHODS: Varian's Ethos adaptive radiotherapy treatment platform was upgraded with a novel CBCT system, HyperSight which reports image quality and Hounsfield unit accuracy specifications comparable to standard fan-beam CT. Using in-house developed MATLAB software, CBCT images were imported into the system and used for planning. Two test cases were completed on anthropomorphic phantoms equipped with small volume ion chambers (cross-calibrated to an ADCL traceable dose standard) to evaluate the feasibility and accuracy of the workflows. A simulated palliative spine treatment was planned with 8 Gy in one fraction, and an intact prostate treatment was planned with 60 Gy in 20 fractions. The CBCTs were acquired using HyperSight with default thorax and pelvis imaging protocols and reconstructed using an iterative algorithm with scatter removal, iCBCT Acuros. CBCTs were used for contouring and planning, and treatment was delivered via an online adaptive workflow. In addition, an external dosimetry audit was completed using only on-board CBCT imaging in an end-to-end head and neck phantom irradiation. RESULTS: An extended-field CBCT acquisition can be acquired in 12 s, in addition to the time for longitudinal table shifts, and reconstructed in approximately 1 min. The superior-inferior extent for the CBCT planning images was 38.2 cm, which captured the full extent of relevant anatomy. The contouring and treatment planning for the spine and prostate were completed in 30 and 18 min, respectively. The dosimetric agreement between ion chamber measurements and the treatment plan was within a range of -1.4 to 1.6%, and a mean and standard deviation of 0.41 ± 1.16%. All metrics used in the external audit met the passing criteria, and the dosimetric comparison between fan-beam and CBCT techniques had a gamma passing rate of 99.0% with a criteria of 2%/2 mm. CONCLUSION: Using an in-house workflow, CT simulation-free radiation therapy was shown to be feasible with acceptable workflow efficiency and dosimetric accuracy. This approach may be particularly applicable for urgent palliative treatments. With the availability of software to enable this workflow, and the continued advancement of on-treatment adaptation, single-visit radiation therapy may replace current practice for some clinical indications.

Describing a Process for Creating a Patient Visible Quality Educational Display to Increase Patient Engagement in Radiation Oncology Throughout the Canadian Maritimes Provinces.

Here, we report the process for creating a patient visible quality educational display to highlight the collaborative quality working practices of Radiation Oncology clinicians and staff in the main Radiotherapy Centers throughout three Canadian provinces. These processes are often not visible to patients yet they speak directly to the standards of care delivered at these centers. The Canadian Partnership for Quality Radiotherapy (CPQR) Quality Assurance Guidelines for Canadian Radiation Treatment Programs guided this process. The display slides created were approved by the local Radiation Oncology departmental leadership for each participating medical center as well as patient focus groups and revised with feedback from both perspectives. Of 27 patients/families who evaluated the resulting educational patient display, 70% expressed high engagement in the information presented, and 81% felt the display will be of interest to patients receiving radiotherapy treatment. Patients/families surveyed reported that the displayed content made them feel more informed and more comfortable with their treatments. Survey data from this project indicates that increasing transparency and deepening patient education about the quality working practices behind radiotherapy treatments has the potential to empower patients receiving radiotherapy and increase their confidence in the care they are receiving.

Energy-dependent OAR sparing and dose conformity for total marrow irradiation of obese patients.

PURPOSE: To investigate the effect on target coverage and organs at risk sparing by using 10 versus 6 MV for VMAT total marrow irradiation of obese patients. METHODS AND MATERIALS: Twenty-six total marrow irradiation, TMI, treatment plans delivered between December 2014 and June 2017 were reviewed and 10 were chosen for replanning based on patient characteristics and plan metrics. Beam geometry and isocenter placement were conserved, energy was changed from 6 to 10 MV and plans were reoptimized. Resulting dose distributions were compared to original plans to evaluate any potential advantage of choosing one energy over the other. RESULTS: Target coverage and total monitor units were consistent between the 6 and 10 MV plans when averaged over all ten patients. Improvement in the conformity index (-11.0%, P = 0.009) when using 10 MV was statistically significant compared to the 6 MV plans. Volumes of normal tissue receiving 50%, 75%, and 90% Rx all decreased for the 10 MV plans compared to the original 6 MV plans. The mean dose to individual OARs decreased significantly for all investigated structures except for the lenses, oral cavity, and genitalia. The largest decreases in Dmean were found for the rectum (22.4%, P = 0.004) and bladder (18.1%, P = 0.005). The three highest priorities for sparing during plan optimization (lungs, liver, and heart), showed decreases of 7.6%, 16.1%, and 13.0%. CONCLUSIONS: Use of a higher energy 10 MV beam provided similar dose to target while achieving increased OAR and normal tissue sparing for the patients reviewed in this study.

Novel Technology Allowing Cone Beam Computed Tomography in 6 Seconds: A Patient Study of Comparative Image Quality.

PURPOSE: The goal of this study was to evaluate the image quality provided by a novel cone beam computed tomography (CBCT) platform (HyperSight, Varian Medical Systems), a platform with enhanced reconstruction algorithms as well as rapid acquisition times. Image quality was compared with both status quo CBCT for image guidance, and to fan beam CT (FBCT) acquired on a CT simulator (CTsim). METHODS AND MATERIALS: In a clinical study, 30 individuals were recruited for whom either deep inspiration (DIBH) or deep exhalation breath hold (DEBH) was used during imaging and radiation treatment of tumors involving liver, lung, breast, abdomen, chest wall, and pancreatic sites. All subjects were imaged during breath hold with CBCT on a standard image guidance platform (TrueBeam 2.7, Varian Medical Systems) and FBCT CT (CTsim, GE Optima). HyperSight imaging with both breath hold (HSBH) and free breathing (HSFB) was performed in a single session. The 4 image sets thus acquired were registered and compared using metrics quantifying artifact index, image nonuniformity, contrast, contrast-to-noise ratio, and difference of Hounsfield unit (HU) from CTsim. RESULTS: HSBH provided less severe artifacts compared with both HSFB and TrueBeam. The severity of artifacts in HSBH images was similar to that in CTsim images, with statistically similar artifact index values. CTsim provided the best image uniformity; however, HSBH provided improved uniformity compared with both HSFB and TrueBeam. CTsim demonstrated elevated contrast compared with HyperSight imaging, but both HSBH and HSFB imaging showed superior contrast-to-noise ratio characteristics compared with TrueBeam. The median HU difference of HSBH from CTsim was within 1 HU for muscle/fat tissue, 12 HU for bone, and 14 HU for lung. CONCLUSIONS: The HyperSight system provides 6-second CBCT acquisition with image artifacts that are significantly reduced compared with TrueBeam and comparable to those in CTsim FBCT imaging. HyperSight breath hold imaging was of higher quality compared with free breathing imaging on the same system. The median HU value in HyperSight breath hold imaging is within 15 HU of that in CTsim imaging for muscle, fat, bone, and lung tissue types, indicating the utility of image data for direct dose calculation in adaptive workflows.

Considerations for intensity modulated total body or total marrow and lymphoid irradiation.

We compiled a sampling of the treatment techniques of intensity-modulated total body irradiation, total marrow irradiation and total marrow and lymphoid irradiation utilized by several centers across North America and Europe. This manuscript does not serve as a consensus guideline, but rather is meant to serve as a convenient reference for centers that are considering starting an intensity-modulated program.

Improving image quality and reducing dose with 2.5 MV diamond target volume-of-interest cone beam CT imaging.

PURPOSE: Over the past decades, continuous efforts have been made to improve megavoltage (MV) image quality versus dose characteristics, including the implementation of low atomic number (Z) targets in MV beamlines and the development of more efficient detectors. Recently, a diamond target beam within a commercial radiotherapy treatment platform demonstrated improved planar contrast-to-noise-ratio (CNR) per unit dose using a novel 2.5 MV sintered diamond target beam, which enabled image acquisition on the order of mGy. The present work assesses cone beam CT (CBCT) image quality characteristics for the novel 2.5 MV diamond target beam and the effects of volume-of-interest (VOI) collimation on the image quality and imaging dose distribution. METHODS: A sintered diamond target was incorporated into the target arm of the linear accelerator, replacing the 2.5 MV commercial copper imaging target. CBCT image quality was evaluated against the commercial imaging beam with regard to spatial resolution and CNR versus dose. In addition to full-field acquisitions, we investigated VOI techniques that collimate the imaging beam to preselected anatomy, to determine potential image quality improvements and dose sparing capacity. Using an anthropomorphic phantom, VOI regions were defined to encompass the maxillary and ethmoid sinuses and ranged in dimension from 3 cm to 4.85 cm equivalent radius. The MLC was fit to each VOI structure throughout a full CBCT arc and the corresponding MLC sequences were produced as XML scripts for acquisition. Calibrated radiochromic film was used in phantom to measure cumulative axial dose distributions during each CBCT acquisition. RESULTS: In full-field CBCT, the 2.5 MV diamond target beam demonstrated improved CNR versus dose compared to the commercial imaging beam, by factors of up to 1.7. The calculated modulation transfer function (MTF) displayed an increase of nearly 30% in f50 for the 2.5 MV diamond target beam compared to the commercial beam. Using VOI techniques, CNR increased monotonically as a function of equivalent radius at the bone-tissue interface. At the bone-sinus interface, the CNR for the full-field case was slightly decreased compared to the largest VOI case. Imaging dose in the anteroposterior direction increased with increasing VOI equivalent radius. CONCLUSION: The novel 2.5 MV sintered diamond target beam presents a simple modification to the commercial imaging beam which provides improved image quality in full-field CBCT and the potential for simultaneous dose sparing and CNR improvement at high-contrast interfaces using VOI acquisition techniques.

4D dose-position verification in radiation therapy using the RADPOS system in a deformable lung phantom.

PURPOSE: A novel 4D in vivo dosimetry system (RADPOS), in conjunction with a deformable lung phantom, has been evaluated as a potential quality assurance tool for 4D radiotherapy. METHODS: RADPOS detectors, which consist of a MOSFET dosimeter combined with an electromagnetic positioning probe, were placed inside the deformable lung phantom. One detector was positioned directly inside a tumor embedded in the lung phantom and another was positioned inside the lung portion of the phantom, outside the tumor. CT scans were taken with the phantom at three breathing phases, and for each phase, the detector position inside the phantom was read with the RADPOS software and compared to the position as determined from the CT data. These values were also compared to RADPOS measurements taken with the phantom on the couch of a Varian Clinac 6EX linac. The deformable phantom and the RADPOS system were also used in two radiation delivery scenarios: (1) A simulation of a free-breathing delivery and (2) a simulation of an adaptive treatment. RESULTS: Compared to CT imaging, the RADPOS positional accuracy was found to be better than 2.5 mm. The radial displacement measurements taken in the CT and linac rooms agreed to within an average of (0.7 +/- 0.3) mm. Hence, the system can provide relative displacement measurements in the treatment room, consistent with measurements made in the CT room. For the free-breathing delivery, the total dose reported by RADPOS agreed to within 4% and 5% of the treatment planning doses in the tumor and the lung portion of the phantom, respectively. The RADPOS-measured dose values for the adaptive delivery were within 1.5% of the treatment plan values, which was well within the estimated experimental uncertainties. CONCLUSIONS: This work has shown that the deformable lung phantom-RADPOS system can be an efficient quality assurance tool for 4D radiation therapy.

Design and evaluation of 3D printable patient-specific applicators for gynecologic HDR brachytherapy.

PURPOSE: The purpose of this study is to improve dose distribution and organ-at-risk sparing during gynecologic HDR brachytherapy with patient-specific applicators. The majority of applicators used today are generic in design and do not allow for dose modulation for patient-specific shaping of dose distributions. Their performance might be adjusted with commercially available wedge shields; however, this provides dose modulation in the orthogonal plane only and does not allow for variation along the length of the applicator. Generic applicators are available only in standard sizes and geometries, and provide suboptimal patient fit with limited dose modulation. METHODS: In this paper we use Monte Carlo modeling for comprehensive characterization of radiologic properties of various 3D printable biocompatible and sterilizable materials with comparison to water. Based on these results, we choose the optimal set of materials for a patient-specific applicator. We develop a novel method to design the patient-specific applicator without incurring a significant increase in treatment time or changes to clinical workflow. Finally, using an example of two selected vaginal cancers, we compare the performance of patient-specific and water-equivalent applicators in terms of target coverage and rectum sparing. RESULTS: In the energy range from 1 MeV to 4 MeV, all materials have similar attenuation coefficients. In the range from ~2 keV to 1 MeV and above 4 MeV, tungsten-polylactic acid composite (WPLA) was seen to have the highest attenuation coefficient. The dose distribution of the water-equivalent applicator was found to be symmetric about its central axis. At the same time patient-specific shielded applicators exhibit well-modulated dose distributions. Their isodose lines are seen to spread radially into the patient, while merging close to the applicator surface, where WPLA shielding has been applied. CONCLUSIONS: The patient-specific cylinders provide comparable dose to the target, while offering advanced healthy tissue sparing, not achievable with the generic design.

Investigation of planar image quality for a novel 2.5 MV diamond target beam from a radiotherapy linear accelerator.

BACKGROUND AND PURPOSE: A commercial 2.5 MV beam has been clinically available for beam's-eye-view imaging in radiotherapy, offering improved contrast-to-noise ratio (CNR) compared to therapeutic beams, due to the softer spectrum. Previous research suggested that imaging performance could be improved using a low-Z diamond target to reduce the self-absorption of diagnostic energy photons. The aim of this study was to 1) investigate the feasibility of two 2.5 MV diamond target beamline configurations and 2) characterize the dosimetry and planar image quality of these novel low-Z beams. MATERIALS AND METHODS: The commercial 2.5 MV beam was modified by replacing the copper target with sintered diamond. Two beamlines were investigated: a carousel-mounted diamond target beamline and a 'conventional' beamline, with the diamond target in the target arm. Planar image quality was assessed in terms of spatial resolution and CNR. RESULTS: Due to image artifacts, image quality could not be assessed for the carousel-mounted low-Z target beam. The 'conventional' 2.5 MV low-Z beam quality was softer by 2.7% compared to the commercial imaging beam, resulting in improved CNR by factors of up to 1.3 and 1.7 in thin and thick phantoms, respectively. In regard to spatial resolution, the 'conventional' 2.5 MV low-Z beam slightly outperformed the commercial imaging beam. CONCLUSION: With a simple modification to the 2.5 MV commercial beamline, we produced an improved energy spectrum for imaging. This 2.5 MV diamond target beam proved to be an advantageous alternative to the commercial target configuration, offering both superior resolution and CNR.

Surface Dosimetry of Patients Undergoing Total Body Irradiation: A Retrospective Analysis for Quality Assurance.

Total body irradiation (TBI) is used prior to bone marrow transplantation as part of the conditioning regimen in selected patients. A linear accelerator-based technique was used at our treatment centre between June, 2004 and August, 2015. Patients were treated supine with extended source-to-surface distance (SSD) lateral fields, and prescription dose was 12 Gy delivered in six fractions, two fractions per day. Dose was prescribed to midplane at the level of the umbilicus and monitor units were calculated manually based on measured beam data. Dose variation within 10% of the prescribed midplane dose is considered acceptable for TBI treatment. This was achieved in our clinic by using compensators to account for missing tissue in the head and neck and lower leg regions. Lung attenuators were routinely used to correct for internal inhomogeneity, which resulted from low density lung tissue. The purpose of this study was to determine whether dose variation was within acceptable limits for these patients as part of a quality assurance process. Following chart review, 129 patients who received six-fraction TBI from 2004 to 2015 were included in this study. Patients receiving single fraction treatment were excluded. Metal oxide semiconductor field effect transistors (MOSFET) dosimetry was used to measure surface dose at four or five locations during patients' first fraction of TBI. Dosimetry was repeated during the second fraction for any site with variation greater than 10%. Statistical analysis was carried out on patient data, diagnosis and dosimetry measurements. Of the 129 patients who met the inclusion criteria, 50 were diagnosed with acute myelogenous leukemia, 30 with acute lymphoblastic leukemia and 11 with chronic myelogenous leukemia. The rest of the patients were diagnosed with lymphoma or myelodysplastic syndromes. The mean percent variation in dosimetry measurements taken at the specific locations ranged between 3.5% and 8.3%. The highest variation was found in measurements performed on the cheek. A high percentage of all dosimetry readings (85.5%) was within the acceptable range of +10% from the expected value. The highest number of individual readings taken at a specific location that fell outside this range were found at the cheek. We conclude that the linear accelerator delivered TBI at our centre meets the acceptable limits of dose variation over an 11-year period.

Individualized Dose-Escalation of HDR Prostate Brachytherapy Implant to Decrease Required External Beam Radiation Dose: A Retrospective Feasibility Study.

PURPOSE: High-dose-rate brachytherapy (HDR-BT) is commonly combined with external beam radiation therapy (EBRT) for the treatment of localized prostate cancer. Escalating the HDR-BT dose as far as organ-at-risk (OAR) constraints allow, on a personalized basis, would allow for a reduction in EBRT dose while achieving similar total biologic equivalence. The primary objective of this study was to determine the dosimetric feasibility of escalating the HDR-BT dose from 15 Gy to 16 or 17 Gy while continuing to meet OAR constraints from the original 15 Gy plan on an individualized basis. METHODS AND MATERIALS: A total of 53 consecutive HDR-BT plans were retrospectively assessed to determine what percentage of plans could be reoptimized to deliver a dose of 16 Gy or 17 Gy, while meeting defined 15-Gy OAR constraints. Factors independently associated with dose escalation were examined. RESULTS: Thirty-nine plans (74%) and 2 plans (4%) were successfully escalated to a dose of 16 Gy and 17 Gy, respectively. Rectum V80 and urethra Dmax were independently predictive of the ability to dose escalate to 16 Gy. CONCLUSIONS: Individualized HDR-BT dose escalation beyond 15 Gy without compromising OAR constraints is dosimetrically feasible. This approach could allow for a corresponding reduction of EBRT fractions (ie, from 15 to 12 fractions) and would be beneficial in terms of resource savings for departments, convenience for patients, and potentially better tolerance of treatment with the expected reduction in biologically equivalent doses to OARs. A clinical trial is being developed to investigate the efficacy and tolerance of personalized HDR-BT/EBRT dose fractionation for localized intracapsular prostate cancer.

MOSFET detectors in quality assurance of tomotherapy treatments.

BACKGROUND AND PURPOSE: The purpose of this work was to characterize metal oxide semiconductor field-effect transistors (MOSFETs) in a 6 MV conventional linac and investigate their use for quality assurance of radiotherapy treatments with a tomotherapy Hi-Art unit. MATERIALS AND METHODS: High sensitivity and standard sensitivity MOSFETs were first calibrated and then tested for reproducibility, field size dependence, and accuracy of measuring surface dose in a 6 MV beam as well as in a tomotherapy Hi-Art unit. In vivo measurements were performed on both a RANDO phantom and several head and neck cancer patients treated with tomotherapy and compared to TLD measurements and treatment plan doses to evaluate the performance of MOSFETs in a high gradient radiation field. RESULTS: The average calibration factor found was 0.345+/-2.5%cGy/mV for the high sensitivity MOSFETs tested and 0.901+/-2.4%cGy/mV for the standard sensitivity MOSFETs. MOSFET measured surface doses had an average agreement with ion chamber measurements of 1.55% for the high sensitivity MOSFET and 5.23% for the standard sensitivity MOSFET when averaged over all trials and field sizes tested. No significant dependence on field size was found for the standard sensitivity MOSFETs, however a maximum difference of 5.34% was found for the high sensitivity MOSFET calibration factors in the field sizes tested. Measurements made with MOSFETS on head and neck patients treated on a tomotherapy Hi-Art unit had an average agreement of (3.26+/-0.03)% with TLD measurements, however the average of the absolute difference between the MOSFET measurements and the treatment plan skin doses was (12.2+/-7.5)%. The MOSFET measured patient skin doses also had good reproducibility, with inter-fraction deviations ranging from 1.4% to 6.6%. Similar results were found from trials using a RANDO phantom. CONCLUSIONS: The MOSFETs performed well when used in the tomotherapy Hi-Art unit and did not increase the overall treatment set-up time when used for patient measurements. It was found that MOSFETs are suitable detectors for surface dose measurements in both conventional beam and tomotherapy treatments and they can provide valuable skin dose information in areas where the treatment planning system may not be accurate.

Real-time measurement of urethral dose and position during permanent seed implantation for prostate brachytherapy.

PURPOSE: The in vivo dosimetry tool, RADPOS, has been modified to include a metal oxide-silicon semiconductor field effect transistor (MOSFET) array with an electromagnetic positioning sensor. This allows dose monitoring at five points rather than just at single dose point as in the other versions of the device. The detector has been used in a clinical trial, which is the first to measure both urethral dose and internal motion concurrently during permanent seed implantation for prostate brachytherapy using a single probe. METHODS AND MATERIALS: The RADPOS detector was secured inside a Foley catheter inside the patient's urethra. Spatial coordinates of the RADPOS detector were read every 0.5s, and the timing of events such as needle insertion was noted. The MOSFET readings were taken over two 10-min periods; once all seeds had been implanted both before and after the transrectal ultrasound (TRUS), the probe was removed. Measurements were completed for 16 patients. RESULTS: Maximum integral dose in the prostatic urethral ranged from 89 to 195Gy, and dose varied from -66% to 36% depending on the rectal probe position. The change in position of the RADPOS sensor owing to the removal of the TRUS probe ranged from 1.4 to 9.7mm. CONCLUSIONS: The modified RADPOS detector with MOSFET array is able to provide real-time dose information, which can be used to monitor dose rates while implantation is performed and to estimate the total integrated dose. Changes in position including those owing to the TRUS probe can be significant and should be quantified to evaluate the influence on dose distributions.

Clinical use of a novel in vivo 4D monitoring system for simultaneous patient motion and dose measurements.

PURPOSE: A new 4D in vivo dosimetry tool, RADPOS, has been used on lung cancer patients to evaluate the feasibility of using the detectors to characterize variations in patient breathing patterns as well as to monitor daily variations in dose. METHODS AND MATERIALS: The RADPOS system combines a MOSFET dosimeter with an electromagnetic positioning sensor for simultaneous measurement of real-time dose and spatial coordinates. Three RADPOS sensors were placed on patients' chest and abdomen during a 4DCT and daily treatments. A fourth detector was also placed on the couch as reference. Position data were collected in real-time and total dose was read at the end of each fraction. RESULTS: Significant deviations in surface motion have been found between the day of 4DCT and treatment fractions in 9 of 10 patients. Variations in daily dose ranged from 2.5 to 13.7 cGy (2.8-14.0%) and results agreed with treatment plan values for all but three points. CONCLUSIONS: Changes in breathing motion have been found that emphasize a need for continued position monitoring. RADPOS measurements can be used to monitor such variations as well as to measure surface dose without any disruption to the treatment schedule or discomfort to patients.