Tomotherapy: a new concept for the delivery of dynamic conformal radiotherapy

Surface-guided tomotherapy improves positioning and reduces treatment time: A retrospective analysis of 16 835 treatment fractions

PURPOSE

In this study, we have quantified the setup deviation and time gain when using fast surface scanning for daily setup/positioning with weekly megavoltage computed tomography (MVCT) and compared it to daily MVCT.

METHODS

A total of 16 835 treatment fractions were analyzed, treated, and positioned using our TomoTherapy HD (Accuray Inc., Madison, USA) installed with a Sentinel optical surface scanning system (C-RAD Positioning AB, Uppsala, Sweden). Patients were positioned using in-room lasers, surface scanning and MVCT for the first three fractions. For the remaining fractions, in-room laser was used for setup followed by daily surface scanning with MVCT once weekly. The three-dimensional (3D) setup correction for surface scanning was evaluated from the registration between MVCT and the planning CT. The setup correction vector for the in-room lasers was assessed from the surface scanning and the MVCT to planning CT registration. The imaging time was evaluated as the time from imaging start to beam-on.

RESULTS

We analyzed 894 TomoTherapy treatment plans from 2012 to 2018. Of all the treatment fractions performed with surface scanning, 90 % of the residual errors were within 2.3 mm for CNS (N = 284), 2.9 mm for H&N (N = 254), 8.7 mm for thorax (N = 144) and 10.9 for abdomen (N = 134) patients. The difference in residual error between surface scanning and positioning with in-room lasers was significant (P < 0.005) for all sites. The imaging time was assessed as total imaging time per treatment plan, modality, and treatment site and found that surface scanning significantly reduced patient on-couch time compared to MVCT for all treatment sites (P < 0.005).

CONCLUSIONS

The results indicate that daily surface scanning with weekly MVCT can be used with the current target margins for H&N, CNS, and thorax, with reduced imaging time.

Advances in Hybrid Fabrication toward Hierarchical Tissue Constructs

The diversity of manufacturing processes used to fabricate 3D implants, scaffolds, and tissue constructs is continuously increasing. This growing number of different applicable fabrication technologies include electrospinning, melt electrowriting, volumetric-, extrusion-, and laser-based bioprinting, the Kenzan method, and magnetic and acoustic levitational bioassembly, to name a few. Each of these fabrication technologies feature specific advantages and limitations, so that a combination of different approaches opens new and otherwise unreachable opportunities for the fabrication of hierarchical cell-material constructs. Ongoing challenges such as vascularization, limited volume, and repeatability of tissue constructs at the resolution required to mimic natural tissue is most likely greater than what one manufacturing technology can overcome. Therefore, the combination of at least two different manufacturing technologies is seen as a clear and necessary emerging trend, especially within biofabrication. This hybrid approach allows more complex mechanics and discrete biomimetic structures to address mechanotransduction and chemotactic/haptotactic cues. Pioneering milestone papers in hybrid fabrication for biomedical purposes are presented and recent trends toward future manufacturing platforms are analyzed.

Intensity-modulated radiation therapy for multiple targets with tomotherapy using multiple sets of static ports from different angles

BACKGROUND

To treat multiple targets separated in the craniocaudal direction within a short time, we invented a new technique using multiple static-port tomotherapy with the dynamic-jaw mode and named it the pseudo-DJDC (pDJDC) technique. We compared the pDJDC plans and helical tomotherapy plans using the dynamic-jaw mode (HDJ) for multiple targets. In the pDJDC plans, we used a beam set with 2-7 ports to the targets at the same level in the craniocaudal direction, and employed another beam set for other targets using different port angles (9-12 angles in total).

METHODS

In seven patients, two plans using the pDJDC and HDJ techniques were compared. For multiple targets (n = 2-6), 20-60 Gy in 2- to 7.5-Gy fractions were prescribed for the planning target volumes at D50%. The conformity index, uniformity index (D5%/D95%), dose distribution in the lung, and treatment time were evaluated.

RESULTS

The median conformity index of all seven patients was 3.0 for the pDJDC plans and 2.4 for the HDJ plans (P = 0.031). The median uniformity indices of the planning target volume (n = 25) for the two plans were 1.048 and 1.057, respectively (P = 0.10). For five patients with thoracic targets, the median mean lung doses were 2.6 Gy and 2.4 Gy, respectively (P = 0.63). The median V5Gy and V20Gy of the lungs in the five patients were 11.8% and 8.5% (P = 0.63), and 1.6% and 2.1% (P = 0.31), respectively. The pDJDC plans reduced the treatment time by 48% compared to the HDJ plans (median: 462 and 884 sec, respectively, P = 0.031).

CONCLUSION

The pDJDC technique allows treatment of multiple targets in almost half the time of the HDJ technique. The pDJDC plans were comparable to the HDJ plans in dose distribution, although the conformity index deteriorated.

Comparison of Different Combinations of Irradiation Mode and Jaw Width in Helical Tomotherapy for Nasopharyngeal Carcinoma

Purpose: To aid in the selection of a suitable combination of irradiation mode and jaw width in helical tomotherapy (HT) for the treatment of nasopharyngeal carcinoma (NPC).

Materials and Methods: Twenty patients with NPC who underwent radiotherapy were retrospectively selected. Four plans using a jaw width of 2.5 or 5-cm in dynamic jaw (DJ) or fix jaw (FJ) modes for irradiation were designed (2.5DJ, 2.5FJ, 5.0DJ, and 5.0FJ). The dose parameters of planning target volume (PTV) and organs at risk (OARs) of the plans were compared and analyzed, as well as the beam on time (BOT) and monitor unit (MU). The plans in each group were ranked by scoring the doses received by the OARs and the superity was assessed in combination with the planned BOT and MU.

Results: The prescribed dose coverage of PTV met the clinical requirements for all plans in the four groups. The groups using a 2.5-cm jaw width or a DJ mode provided better protection to most OARs, particularly for those at the longitudinal edges of the PTV (P < 0.05). The 2.5DJ group had the best ranking for OAR-dose, followed by the 2.5FJ and 5.0DJ groups with a same score. The BOT and MU of the groups using a 5.0-cm jaw width reduced nearly 45% comparing to those of the 2.5-cm jaw groups.

Conclusion: 2.5DJ has the best dose distribution, while 5.0DJ has satisfactory dose distribution and less BOT and MU that related to the leakage dose. Both 2.5DJ or 5DJ were recommended for HT treatment plan for NPC based on the center workload.

Fast Statistical Iterative Reconstruction for Mega-voltage Computed Tomography

Statistical iterative reconstruction is expected to improve the image quality of computed tomography (CT). However, one of the challenges of iterative reconstruction is its large computational cost. The purpose of this review is to summarize a fast iterative reconstruction algorithm by optimizing reconstruction parameters. Megavolt projection data was acquired from a TomoTherapy system and reconstructed using in-house statistical iterative reconstruction algorithm. Total variation was used as the regularization term and the weight of the regularization term was determined by evaluating signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and visual assessment of spatial resolution using Gammex and Cheese phantoms. Gradient decent with an adaptive convergence parameter, ordered subset expectation maximization (OSEM), and CPU/GPU parallelization were applied in order to accelerate the present reconstruction algorithm. The SNR and CNR of the iterative reconstruction were several times better than that of filtered back projection (FBP). The GPU parallelization code combined with the OSEM algorithm reconstructed an image several hundred times faster than a CPU calculation. With 500 iterations, which provided good convergence, our method produced a 512 × 512 pixel image within a few seconds. The image quality of the present algorithm was much better than that of FBP for patient data. J. Med. Invest. 67 : 30-39, February, 2020.

Technology-driven research for radiotherapy innovation

Technology has a pivotal role in the continuous development of radiotherapy. The long road toward modern ‘high‐tech’ radiation oncology has been studded with discoveries and technological innovations that resulted from the interaction of various disciplines. In the last decades, a dramatic technology‐driven revolution has hugely improved the capability of accurately and safely delivering complex‐shaped dose distributions. This has contributed to many clinical improvements, such as the successful management of lung cancer and oligometastatic disease through stereotactic body radiotherapy. Technology‐driven research is an active and lively field with promising potential in several domains, including image guidance, adaptive radiotherapy, integration of artificial intelligence, heavy‐particle therapy, and ‘flash’ ultra‐high dose‐rate radiotherapy. The evolution toward personalized Oncology will deeply influence technology‐driven research, aiming to integrate predictive models and omics analyses into fast and efficient solutions to deliver the best treatment for each single patient. Personalized radiation oncology will need affordable technological solutions for middle‐/low‐income countries, as these are expected to experience the highest increase of cancer incidence and mortality. Moreover, technology solutions for automation of commissioning, quality assurance, safety tests, image segmentation, and plan optimization will be required. Although a large fraction of cancer patients receive radiotherapy, this is certainly not reflected in the worldwide budget for radiotherapy research. Differently from the pharmaceutical companies‐driven research, resources for research in radiotherapy are highly limited to equipment vendors, who can, in turn, initiate a limited number of collaborations with academic research centers. Thus, enhancement of investments in technology‐driven radiotherapy research via public funds, national governments, and the European Union would have a crucial societal impact. It would allow for radiotherapy to further strengthen its role as a highly effective and cost‐efficient cancer treatment modality, and it could facilitate a rapid and equalitarian large‐scale transfer of technology to clinic, with direct impact on patient care.

Development of an Immobilization Device for Total Marrow Irradiation

PURPOSE

A body frame dedicated to total marrow (lymph node) irradiation (TMI/TMLI) could minimize patient motion during the potentially extended beam-on time with this technique. We present the development of a dedicated immobilization system for TMI/TMLI using volumetric modulated arc therapy.

METHODS AND MATERIALS

Since 2010, 59 adult patients were treated with TMI/TMLI using a multi-isocenter volumetric modulated arc therapy technique. Two computed tomographies (CTs) were required (1 head-first supine and 1 feet-first supine) to cover the whole volume. For the first 10 patients, 2 standard commercial frames with personalized masks (with/without personalized vacuum cushion for the lower extremities) were used without specific interfixation (frame A). For the next 49 patients a homemade 3-frame immobilization system was adopted (frame B), where each frame was interlocked with the next one and thermoplastic masks used to fix the patient. The effectiveness of the 2 immobilization systems was assessed by offline/online matching between daily cone beam CT of each isocenter and the simulation CTs.

RESULTS

Mean offline shifts for frame A were 3 to 12 mm in anterior-posterior, 2 to 5 mm in cranilal-caudal, and 2 to 6 mm in left-right directions. Larger shifts were found for feet-first supine series (shifts up to 23 mm). In frame B, mean offline shifts were 1 to 4 mm in anterior-posterior, 1 to 4 mm in cranial-caudal, and 1 to 4 mm in left-right directions. Mean online adjustments were -1 ± 4 mm in anterior-posterior, 0 ± 2 mm in cranial-caudal, and 0 ± 4 mm in left-right directions.

CONCLUSIONS

The patient positioning shifts for TMI/TMLI irradiation were mitigated by a homemade immobilization system and the use of individualized masks.

Proton therapy delivery: what is needed in the next ten years?

Proton radiation therapy has been used clinically since 1952, and major advancements in the last 10 years have helped establish protons as a major clinical modality in the cancer-fighting arsenal. Technologies will always evolve, but enough major breakthroughs have been accomplished over the past 10 years to allow for a major revolution in proton therapy. This paper summarizes the major technology advancements with respect to beam delivery that are now ready for mass implementation in the proton therapy space and encourages vendors to bring these to market to benefit the cancer population worldwide. We state why these technologies are essential and ready for implementation, and we discuss how future systems should be designed to accommodate their required features.

Treatment planning comparison of volumetric modulated arc therapy employing a dual-layer stacked multi-leaf collimator and helical tomotherapy for cervix uteri

Purpose

To ascertain the dosimetric performance of a new delivery system (the Halcyon system, H) equipped with dual-layer stacked multi-leaf collimator (MLC) for risk-adapted targets in cervix uteri cancer patients compared to another ring-based system in clinical operation (Helical Tomotherapy, HT).

Methods

Twenty patients were retrospectively included in a treatment planning study (10 with positive lymph nodes and 10 without). The dose prescription (45Gy to the primary tumour volume and a simultaneously integrated boost up to 55Gy for the positive patients) and the clinical planning objectives were defined consistently as recommended by an ongoing multicentric clinical trial. Halcyon plans were optimised for the volumetric modulated arc therapy. The plan comparison was performed employing the quantitative analysis of the dose-volume histograms.

Results

The coverage of the primary and nodal target volumes was comparable for both techniques and both subsets of patients. The primary planning target volume (PTV) receiving at least 95% of the prescription isodose ranged from 97.2 ± 1.1% (node-negative) to 99.1 ± 1.2% (node-positive) for H and from 96.5 ± 1.9% (node-negative) to 98.3 ± 0.9% (node-positive) for HT. The uncertainty is expressed at one standard deviation from the cohort of patient per each group. For the nodal clinical target volumes, the dose received by 98% of the planning target volume ranged 55.5 ± 0.1 to 56.0 ± 0.8Gy for H and HT, respectively. The only significant and potentially relevant differences were observed for the bowels. In this case, V_40Gy resulted 226.3 ± 35.9 and 186.9 ± 115.9 cm³ for the node-positive and node-negative patients respectively for Halcyon. The corresponding findings for HT were: 258.9 ± 60.5 and 224.9 ± 102.2 cm³. On the contrary, V_15Gy resulted 1279.7 ± 296.5 and 1557.2 ± 359.9 cm³ for HT and H respectively for node-positive and 1010.8 ± 320.9 versus 1203.8 ± 332.8 cm³ for node-negative.

Conclusion

This retrospective treatment planning study, based on the dose constraints derived from the Embrace II study protocol, suggested the essential equivalence between Halcyon based and Helical Tomotherapy based plans for the intensity-modulated rotational treatment of cervix uteri cancer. Different levels of sparing were observed for the bowels with H better protecting in the high-dose region and HT in the mid-low dose regions. The clinical impact of these differences should be further addressed.

Lateral head flexion as a noncoplanar solution for ring gantry stereotactic radiosurgery

PURPOSE

Ring gantry radiotherapy devices are often limited to deliver beams in the axial plane, severely limiting beam entrance angles and rendering noncoplanar beam delivery impossible. However, a ring gantry geometry greatly simplifies delivery machines and increases the efficiency of treatment with the potential to decrease the overall costs of radiotherapy. This study explores the use of lateral head flexion in order to increase beam entrance angles and extend the available solid angle space for a ring gantry stereotactic radiosurgery (SRS) application.

MATERIALS AND METHODS

A 1.5 T magnetic resonance imaging scanner was used to scan seven healthy volunteers at three different head positions: a neutral position, a left lateral flexion position and a right lateral flexion position. The lateral flexion scans were co-registered to the neutral head position scan using rigid registration and extracting the rotational transformation. The head pitch, roll, and yaw were computed for each registration to evaluate the natural range of motion for all volunteers. A ring gantry plan geometry was used to generate two sets of single fraction SRS plans (21 Gy): one coplanar set for head neutral scans, and a three-arc plan set using the head neutral and lateral head flexion scans. The conformity index (CI), intermediate dose fall-off (R50), low dose spillage (R10), and gradient measure (GM) were used to evaluate both sets of plans. The treatment plans were generated for a ring-gantry linear accelerator (linac) (Varian Halcyon 2.0) as well as radiosurgery linac (Varian Edge) for comparison.

RESULTS

The average pitch, yaw, and roll for the lateral head flexion scans were 4.1° ± 4.7°, 16.9° ± 3.7°, and 2.5° ± 4.9° for the right flexion and 4.9° ± 4.3°, 14.0° ± 3.7° and 2.8° ± 5.4° for left flexion. When comparing the head flexion technique with a fully coplanar geometry, the ring gantry plans showed an average improvement in CI of 7.3% (1.46 ± 0.25 vs 1.36 ± 0.28), a decrease of 13% in R50 (5.46 ± 1.14 vs 4.78 ± 1.12), a decrease of 32% in R10 (85.7 ± 20.3 vs 58.2 ± 15.1), and a decrease of 7.8% in GM (0.53 ± 0.05 vs 0.49 ± 0.04). The Edge plans showed an average improvement in CI of 3.0% (1.49 ± 0.26 vs 1.45 ± 0.25), a decrease of 6.8% in R50 (5.19 ± 1.03 vs 4.82 ± 0.83), a decrease of 29% in R10 (84.1 ± 16.3 vs 59.9 ± 12.5), and a decrease of 5.0% in GM (0.50 ± 0.04 vs 0.47 ± 0.03).

CONCLUSION

Lateral head flexion was shown to increase beam entrance angles considerably improving plan conformity and normal tissue sparing in this pilot study of seven sets of plans. Rigid registrations demonstrated each lateral flexion to be analogous to a 15° couch kick. The head flexion technique outlined here was shown to be a feasible solution for SRS treatments being delivered on ring gantry devices.

A survey on the current clinical application and practice of helical tomotherapy in mainland China

Aim:

To assess helical tomotherapy (TOMO) current clinical application and practice in mainland China.

Materials and methods:

Data were collected for all TOMO units clinically operational in mainland China by 30 April 2016, including (a) the distribution of installation and staffing levels; (b) types of cancers treated; (c) utilisation efficiency; (d) quality assurance; (e) maintenance; (f) optional features; and (g) satisfaction levels. The data were collected as a census and analysed qualitatively and quantitatively.

Results:

As of 30 April 2016, 23 TOMO units were used clinically by 22 hospitals in mainland China. In the same period, 22,558 cancer patients were treated. For TOMO units with more than a year of clinical utilisation, a median of 378 cases were treated annually per machine. The median daily operation was 10·5 hours, and treatment headcount was 38·3 patients. The median service outage rate was 2·6%, and the most common cause was malfunction of the multi-leaf collimator. In terms of overall satisfaction levels, 3 hospitals were very satisfied, 16 were satisfied and 3 considered their satisfaction level as average.

Findings:

The overall operation of TOMO is good, but there are some problems due to running at full capacity, lack of clinical efficacy research and insufficient quality assurance regulations.

Characterization of dynamic collimation mechanisms for helical CT scans with direct measurements

Dynamic collimation is an important dose reduction mechanism for helical CT scans, especially for modern wide-beam scanner models. Its implementation and efficacy need to be studied to optimize CT scan protocols and to reduce unnecessary patient dose. The purpose of this study is to evaluate dynamic beam collimation for modern wide-beam CT scanners with direct measurements and to estimate the efficacy for dose reduction. By using a linear-array solid state detector, primary x-ray beam coverage was measured for four CT scanner models: GE Revolution CT, Siemens Somatom Force, Philips iQon, and GE LightSpeed VCT. Supported independently from patient table, the detector remained stationary at the isocenter during helical scans. Data lines were recorded every 0.24 ms throughout one entire helical scan, with a spatial resolution of 0.8 mm along the craniocaudal direction. The measurements were repeated for various scan parameters related to dynamic collimation, including beam collimation width, pitch, rotation time, and scan length. The recorded beam coverage area was used as a surrogate to total primary dose, to model different dynamic collimation mechanisms. The directly measured total radiation range was compared to table travel distance and nominal scan length which equals to the ratio between DLP and CTDIvol. Equations to calculate the percentage dose reduction with dynamic collimation were derived for different mechanisms. Three different dynamic collimation mechanisms were revealed and related linear model parameters were reported for different helical scan parameters. The nominal scan length used to calculate DLP was shown to vary for different dynamic collimation mechanisms. For typical head and abdomen scans with nominal scan lengths of 17.5 cm and 25 cm, percentage dose reduction from dynamic collimation ranged from 2% to 32%. In conclusion, with direct measurements of primary x-ray beam coverage, dynamic collimation mechanisms and related dose reduction effects were characterized for four modern wide-beam CT scanners.

Intensity-modulated radiation therapy using TomoDirect for postoperative radiation of left-sided breast cancer including lymph node area: comparison with TomoHelical and three-dimensional conformal radiation therapy

Intensity-modulated radiation therapy (IMRT) delivers an excellent dose distribution compared with conventional three-dimensional conformal radiation therapy (3D-CRT) for postoperative radiation including the lymph nodes in breast cancer patients. The TomoTherapy system, developed exclusively for IMRT, has two treatment modes: TomoDirect (TD) with a fixed gantry angle for beam delivery, and TomoHelical (TH) with rotational beam delivery. We compared the characteristics of TD with TH and 3D-CRT plans in the breast cancer patients. Ten consecutive women with left breast cancer received postoperative radiation therapy using TD including the chest wall/residual breast tissue and level II-III axial and supraclavicular lymph node area. Fifty percent of the planning target volume (PTV) was covered with at least 50 Gy in 25 fractions. TD, TH and 3D-CRT plans were created for each patient, with the same dosimetric constraints. TD and TH showed better dose distribution to the PTV than 3D-CRT. TD and 3D-CRT markedly suppressed low-dose spread to the lung compared with TH. Total lung V5 and V10 were significantly lower, while V20 was significantly higher in the TD and 3D-CRT plans. The mean total lung, heart and contralateral breast doses were significantly lower using TD compared with the other plans. Compared with 3D-CRT and TH, TD can provide better target dose distribution with optimal normal-organ sparing for postoperative radiation therapy including the chest wall/residual breast tissue and lymph node area in breast cancer patients. TD is thus a useful treatment modality in these patients.

Total marrow irradiation for hematopoietic malignancies using volumetric modulated arc therapy: A review of treatment planning studies

Total Marrow Irradiation (TMI) has been introduced in the management of hematopoietic malignancies with the aim of reducing toxicities induced by total body irradiation. TMI is one of the most challenging planning and delivery techniques of radiotherapy, as the whole skeleton should be irradiated, while sparing nearby organs at risk (OARs). Target volumes of 7–10 k cm³ and healthy tissue volumes of 50–90 k cm³ should be considered and inverse treatment planning is needed. This review focused on aspects of TMI delivery using volumetric modulated arc therapy (VMAT). In particular, multiple arcs from isocenters with different positions are required for VMAT-TMI as the cranial-caudal lengths of patients are much larger than the jaw aperture. Therefore, many field junctions between arcs with different isocenters should be managed. This review covered, in particular, feasibility studies for managing multiple isocenters, optimization of plan parameters, plan optimization of the lower extremities, robustness of field junctions and dosimetric plan verification of VMAT-TMI. This review demonstrated the possibility of VMAT in delivering TMI with multi-arcs and multi-isocenters. Care should be paid in the patient repositioning, with particular attention to the cranial-caudal direction.

Technological evolution of radiation treatment: Implications for clinical applications

The contemporary approach to the management of a cancer patient requires an "ab initio" involvement of different medical domains in order to correctly design an individual patient's pathway toward cure. With new therapeutic tools in every medical field developing faster than ever before the patient care outcomes can be achieved if all surgical, drug, and radiation options are considered in the design of the appropriate therapeutic strategy for a given patient. Radiation therapy (RT) is a clinical discipline in which experts from different fields continuously interact in order to manage the multistep process of the radiation treatment. RT is found to be an appropriate intervention for diverse indications in about 50% of cancer patients during the course of their disease. Technologies are essential in dealing with the complexity of RT treatments and for driving the increasingly sophisticated RT approaches becoming available for the treatment of Cancer. High conformal techniques, namely intensity modulated or volumetric modulated arc techniques, ablative techniques (Stereotactic Radiotherapy and Stereotactic Radiosurgery), particle therapy (proton or carbon ion therapy) allow for success in treating irregularly shaped or critically located targets and for the sharpness of the dose fall-off outside the target. The advanced on-board imaging, including real-time position management systems, makes possible image-guided radiation treatment that results in substantial margin reduction and, in select cases, implementation of an adaptive approach. The therapeutic gains of modern RT are also due in part to the enhanced anticancer activity obtained by coadministering RT with chemotherapy, targeted molecules, and currently immune checkpoints inhibitors. These main clinically relevant steps forward in Radiation Oncology represent a change of gear in the field that may have a profound impact on the management of cancer patients.

Analyzation of the local confidence limits for IMRT and VMAT based on AAPM TG119 report

The aim of this study was to generate a local confidence limit (CL) for intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques for Clinac IX linear accelerator using the American Association of Physicists in Medicine (AAPM) Task Group (TG119) protocol. The results were compared with the published studies to test the capability and quality of the VMAT technique in our clinic. We used TG119 cases to create plans for IMRT and VMAT in Eclipse Treatment Planning System for Clinac IX using 6 MV and 10 MV photons. Two preliminary and 5 clinical test cases were created based on the dose prescriptions and planning objectives provided by TG119. Verification plans were created in a planning slab phantom, 2D matrix dosimetry system (MatriXX) with multicube phantom and a volumetric phantom (Delta⁴). Radiation absorption doses to high-dose points in the planning target volume region and low-dose points in avoidance structures were measured with a 0.125 cc semiflex thimble ionization chamber (PTW). The measured and planned doses were normalized with respect to their prescription doses and intercompared with each other. The gamma analysis was carried out for MatriXX and Delta⁴ adopting the acceptance criteria of 3% dose difference and 3 mm distance to agreement with 10% threshold dose, respectively. The local CLs with the bench mark set by TG119 were obtained for point, composite planar and field-by-field measurements for IMRT and VMAT with different energies. In this study, the CLs for the high-dose regions of IMRT with 6 MV and 10 MV were 0.025 and 0.014, respectively. For VMAT, they were 0.032 and 0.018. The counterpart CL was 0.045 in TG119. And in organs at risk region, the CLs of IMRT with 6 MV and 10 MV beam were 0.022 and 0.019, respectively, with the counterpart CL indicated by TG119 was 0.047. For VMAT with 6 MV and 10 MV photon beams, the CLs were measured 0.030 and 0.027 with Delta⁴, respectively. The CLs of the maximum gamma passing for all values were 2.0 in 6 MV VMAT plan, which however recommended in TG119 was 12.4. The data presented here showed all the CLs in our clinic meet the criteria of TG119 report well. All these local CLs reached the goals mentioned in AAPM TG119, which indicated that the local clinic had commissioned IMRT and VMAT techniques with adequate accuracy. Prior to the clinical application practice, it is essential to verify with the TG119 test cases for IMRT and VMAT, which allows us to better understand the basic capability of VMAT technology.

Fast, Low-Dose Megavoltage-Topogram Localization on TomoTherapy: Initial Clinical Experience With Mesothelioma Patients

PURPOSE

This study aimed to evaluate the potential of megavoltage-topogram (MV-topogram)-based alignment as an alternative to megavoltage computed tomography (MVCT) in reducing setup time and imaging dose for patients with malignant pleural mesothelioma who are receiving TomoTherapy.

METHODS AND MATERIALS

Twelve patients were enrolled in an ongoing institutional review board approved clinical trial at our institute. Patients were set up with a clinical protocol using red lasers. Anteroposterior (AP) and lateral (LAT) MV-topograms were acquired using gantry angles of 0°/90° with a 1 mm collimator opening, all multileaf collimator leaves open, a couch speed of 4 cm/s, and a 12.5-second scanning time. Routine MVCT scans were performed immediately afterward. The MV-topograms were reconstructed and enhanced using contrast-limited adaptive histogram equalization. Anteroposterior and LAT kilovoltage digital reconstructed topogram images were reconstructed based on TomoTherapy geometry from computed tomography simulation scans. Registrations between MV-topograms and kilovoltage-digital reconstructed topogram images were performed manually, and patients' daily shifts were recorded. Results were compared against the corresponding daily MVCT shifts. MV-topogram and MVCT doses were measured and recorded using an ion chamber on a cheese phantom with depths between 1 and 14 cm, as well as the times required to acquire the 2 image modalities.

RESULTS

The mean and standard deviation of shift discrepancies between MV-topogram and MVCT were 0.74 ± 2.08, -0.09 ± 4.46, and 0.45 ± 3.57 mm in the LAT, longitudinal, and vertical directions, respectively. The MVCT imaging doses measured were 14.74 to 26.92 times higher than the MV-topogram doses, depending on depth. On average, MV-topograms with a mean scan length of 50 cm achieved a 5-fold image acquisition time savings over MVCT, with a mean scan length of 38 cm.

CONCLUSIONS

MV-topograms has the potential to provide alignment performance equivalent to that of MVCT for patients with mesothelioma, with a significant reduction in imaging dose and acquisition time.

Fluence-weighted average subfield size in helical TomoTherapy

INTRODUCTION

Helical TomoTherapy allows a highly conformal dose distribution to complex target geometries with a good protection of organs at risk. However, the small field sizes associated with this method are a possible source of dosimetrical uncertainties. The IAEA has published detector-specific field output correction factors for static fields of the TomoTherapy in the TRS483. This work investigates the average subfield size of helical TomoTherapy plans.

MATERIAL AND METHODS

A new parameter for helical TomoTherapy was defined - the fluence-weighted average subfield size. The subfield sizes were extracted from the leaf-opening time sinograms in the RT-plan files for 30 clinical prostate and head and neck plans and were put in relation to Delat4 Phantom+ measurement results. Additionally the influence of planning parameters on the subfield size was studied by varying the modulation factor, number of iterations and pitch in the dose optimization and calculation for three different clinical indications H&N, prostate and rectum cancer. Selected plans were dosimetrically verified by Delta4 measurements to examine the reliability in dependence of the average subfield size. Furthermore, the impact of the planning parameters on a) the dose distribution, with regard to the planning target volume and regions at risks, and b) machine characteristics such as delivery time, actual modulation factor and leaf-opening times were evaluated.

RESULTS

The average equivalent square subfield lengths (s¯_eq) of the two investigated indications did not differ significantly - prostate plans: 2.75±0.14cm and H&N plans: 2.70±0.16cm, both with a jaw width of 2.5cm. No correlation between field size and measured dose deviation was detected. The number of iterations and the modulation factor have a considerable influence on the average subfield size. The higher the planned modulation factor and the more iterations are used during optimization, the smaller is the subfield size. In our pilot study plans were calculated with field sizes s¯_eq between 4.2cm and 1.7cm, with a jaw width of 2.5cm. Again, the measurement results of Delta4 showed no significant deviation from the doses calculated by the TomoTherapy planning system for the whole range of subfield sizes, and no significant correlation between field sizes and dose deviations was found. As expected, the clinical dose distribution improved with increasing modulation factor and an increasing number of iterations. The compromise between an improved dose distribution and smaller s¯_eq was shown.

CONCLUSION

In this work, a method was presented to determine the average subfield size for helical TomoTherapy plans. The response of the Delta4 did not show any dependence on field size in the range of the field sizes covered by the studied plans. The influence of the subfield sizes on other dosimetry systems remains to be investigated.

Single-arc VMAT optimization for dual-layer MLC

Dual-layer multi-leaf collimator (DLMLC) has recently attracted renewed interest due to its good balance among resolution, low leakage, and high fabricability. However, existing progressive sampling based volumetric modulated arc therapy (VMAT) algorithm is ineffective for DLMLC, requiring more arcs to achieve dosimetry comparable to VMAT plans with higher resolution single-layer MLC (SLMLC). In this study, we develop a novel single-arc VMAT optimization framework to take advantage of the unique DLMLC characteristics fully. Direct aperture optimization (DAO) for single-arc DLMLC VMAT was formulated as a least square dose fidelity objective, along with an anisotropic total variation term to regulate the fluence smoothness and a single segment term for forming simple apertures. The DAO was solved through alternating optimization approach. The DLMLC deliverability constraint and the MLC leaf speed constraint were formulated as the optimization constraints and solved using a graph optimization algorithm. Feasibility of the proposed framework was tested on a brain, a lung, and a prostate cancer patient. The framework was further adapted for a simultaneous integrated boost (SIB) case. The single-arc DLMLC-10 mm (leaf width) plan was compared against single-arc SLMLC VMAT plans including SLMLC-5mm, SLMLC-10mm, and SLMLC with 10 mm leaf width and 5 mm leaf step size (SLMLC-10mm-5mm). Compared with the SLMLC-10mm plan and the SLMLC-10mm-5mm plan, with the same target coverage, the DLMLC-10 mm plan reduced R50 by 30.7% and 10.0%, the average max OAR dose by 5.79% and 3.7% of the prescription dose, and the average mean OAR dose by 4.18% and 2.1% of the prescription dose, respectively. The plan quality is comparable to that of the SLMLC-5mm plan. The novel single-arc VMAT optimization framework for DLMLC utilizes two MLC layers to improve the effective modulation resolution and afford more sophisticated modulation. Consequently, DLMLC VMAT achieves superior dosimetry to SLMLC VMAT with the same leaf width.

Patient organ doses from megavoltage computed tomography delivery with a helical tomotherapy unit using a general treatment planning system

The purpose of this study was to quantify actual patient organ doses from megavoltage computed tomography (MVCT) using an MVCT beam model of a helical tomotherapy unit in a general treatment planning system (TPS). Dosimetric parameters (percentage depth dose, lateral beam profile, and longitudinal beam profile) of the MVCT beam were measured using Gafchromic EBT3 films (ISP Corporation, Wayne, NJ, USA) and used for beam modeling in a Pinnacle3 TPS (Philips, Amsterdam, Netherlands); this TPS is widely used with linear accelerators. The created beam model was adjusted and validated by assessing point doses in a cylindrical phantom in static and helical beam plans with fine, normal and coarse pitches. Maximum doses delivered to important organs from MVCT delivery for five clinical cases were calculated using the created beam model. The difference (average ± one standard deviation for all evaluation points) between calculated and measured doses was -0.69 ± 1.20% in the static beam plan. In the helical beam plan, the differences were 1.83 ± 2.65%, 1.35 ± 5.94% and -0.66 ± 8.48% for fine, normal and coarse pitches, respectively. The average maximum additional dose to important organs from MVCT in clinical cases was 0.82% of the prescribed dose. In conclusion, we investigated a method for quantifying patient organ dose from MVCT delivery on helical tomotherapy using an MVCT beam model in a general TPS. This technique enables estimation of the patient-specific organ dose from MVCT delivery, without the need for additional equipment.

A Helical tomotherapy as a robust low-dose treatment alternative for total skin irradiation

Mycosis fungoides is a disease with manifestation of the skin that has traditionally been treated with electron therapy. In this paper, we present a method of treating the entire skin with megavoltage photons using helical tomotherapy (HT), verified through a phantom study and clinical dosimetric data from our first two treated patients. A whole body phantom was fitted with a wetsuit as bolus, and scanned with computer tomography. We accounted for variations in daily setup using virtual bolus in the treatment plan optimization. Positioning robustness was tested by moving the phantom, and recalculating the dose at different positions. Patient treatments were verified with in vivo film dosimetry and dose reconstruction from daily imaging. Reconstruction of the actual delivered dose to the patients showed similar target dose as the robustness test of the phantom shifted 10 mm in all directions, indicating an appropriate approximation of the anticipated setup variation. In vivo film measurements agreed well with the calculated dose confirming the choice of both virtual and physical bolus parameters. Despite the complexity of the treatment, HT was shown to be a robust and feasible technique for total skin irradiation. We believe that this technique can provide a viable option for Tomotherapy centers without electron beam capability.

Radiation Shielding for Helical Tomotherapy Vault Design

Purpose:

The purpose of the present study is to carry out radiation shielding calculations to find out adequate thicknesses of protective barriers such as walls and ceiling based on minimum space required to house helical tomotherapy unit. This study also aim to derive expression for use factor and estimation of patient workload for tomotherapy facility for optimizing radiation shielding requirements.

Materials and Methods:

The basic definitions and formulae given in NCRP/IAEA reports were referred and modified for tomotherapy machine to calculate optimized shielding thicknesses requirements. Workload is estimated based on observations of patient treatments on tomotherapy machine and analysis of their treatment plan data. A mathematical expression is derived for calculating use factor in terms of beam divergence angle at source corresponding to field length, angle of source rotation about isocenter, and distance of primary barrier from isocenter. Radiation shielding requirement of protective barriers such as walls and ceiling of helical tomotherapy vault is calculated based on minimum room dimensions as specified by the manufacturer, permissible dose limit (s), and values of optimizing parameters such as workload, use factor etc. for tomotherapy machine.

Results:

Using derived mathematical expression for use factor in this study, it was found that value of use factor varies with distance of primary barrier from isocenter and its value was found to be 0.093 for given minimum room dimensions. Radiation shielding requirements for protective barriers (walls/ceiling, etc.) were arrived and reported in this paper.

Conclusions:

A typical helical tomotherapy vault design is proposed based on the calculated shielding thicknesses of protective barriers. Further, it is also concluded that tomotherapy machine can be installed in a vault designed for 6 MV conventional linear accelerator with minor modification.

A deep learning method for prediction of three-dimensional dose distribution of helical tomotherapy

PURPOSE

To develop a deep learning method for prediction of three-dimensional (3D) voxel-by-voxel dose distributions of helical tomotherapy (HT).

METHODS

Using previously treated HT plans as training data, a deep learning model named U-ResNet-D was trained to predict a 3D dose distribution. First, the contoured structures and dose volumes were converted from plan database to 3D matrix with a program based on a developed visualization toolkit (VTK), then transferred to U-ResNet-D for correlating anatomical features and dose distributions at voxel-level. One hundred and ninety nasopharyngeal cancer (NPC) patients treated by HT with multiple planning target volumes (PTVs) in different prescription patterns were studied. The model was typically trained from scratch with weights randomly initialized rather than using transfer-learning method, and used to predict new patient's 3D dose distributions. The predictive accuracy was evaluated with three methods: (a) The dose difference at the position r, δ(r, r) = D_c (r) - D_p (r), was calculated for each voxel. The mean (μ_δ(r,r) ) and standard deviation (σ_δ(r,r) ) of δ(r, r) were calculated to assess the prediction bias and precision; (b) The mean absolute differences of dosimetric indexes (DIs) including maximum and mean dose, homogeneity index, conformity index, and dose spillage for PTVs and organ at risks (OARs) were calculated and statistically analyzed with the paired-samples t test; (c) Dice similarity coefficients (DSC) between predicted and clinical isodose volumes were calculated.

RESULTS

The U-ResNet-D model predicted 3D dose distribution accurately. For twenty tested patients, the prediction bias ranged from -2.0% to 2.3% and prediction error varied from 1.5% to 4.5% (relative to prescription) for 3D dose differences. The mean absolute dose differences for PTVs and OARs are within 2.0% and 4.2%, and nearly all the DIs for PTVs and OARs had no significant differences. The averaged DSC ranged from 0.95 to 1 for different isodose volumes.

CONCLUSIONS

The study developed a new deep learning method for 3D voxel-by-voxel dose prediction, and shown to be able to produce accurately dose predictions for nasopharyngeal patients treated by HT. The predicted 3D dose map can be useful for improving radiotherapy planning design, ensuring plan quality and consistency, making clinical technique comparison, and guiding automatic treatment planning.

A convex optimization approach to radiation treatment planning with dose constraints

We present a method for handling dose constraints as part of a convex programming framework for inverse treatment planning. Our method uniformly handles mean dose, maximum dose, minimum dose, and dose-volume (i.e., percentile) constraints as part of a convex formulation. Since dose-volume constraints are non-convex, we replace them with a convex restriction. This restriction is, by definition, conservative; to mitigate its impact on the clinical objectives, we develop a two-pass planning algorithm that allows each dose-volume constraint to be met exactly on a second pass by the solver if its corresponding restriction is feasible on the first pass. In another variant, we add slack variables to each dose constraint to prevent the problem from becoming infeasible when the user specifies an incompatible set of constraints or when the constraints are made infeasible by our restriction. Finally, we introduce ConRad, a Python-embedded open-source software package for convex radiation treatment planning. ConRad implements the methods described above and allows users to construct and plan cases through a simple interface.

Long-term outcome of hypofractionated intensity-modulated radiotherapy using TomoTherapy for localized prostate cancer: A retrospective study

BACKGROUND

Recently, the clinical outcome of prostate cancer treated by hypofractionated radiation therapy has been reported. However, there are few reports from Japan. In Hidaka Hospital, hypofractionated intensity-modulated radiotherapy (HIMRT) for prostate cancer was initiated in 2007. The purpose of this study is to analyze the long-term outcome.

METHODS

Ninety-two patients with localized prostate cancer treated with HIMRT at Hidaka Hospital between 2007 and 2009 were retrospectively analyzed. HIMRT was delivered using TomoTherapy. The prescription dose was 66 Gy at 95% of the PTV in 22 fractions performed 3 days a week over 7 weeks in all patients. The overall survival rate, biochemical relapse-free rate, and acute and late toxicities were evaluated.

RESULTS

The median follow-up duration was 78 (range 14-100) months. The median age at the start of the HIMRT was 72 (range 46-84) years. The disease characteristics were as follows: stage T1c, 45; T2a, 20; T2b, 5; T2c, 1; T3a, 13; T3b, 6; T4, 2; Gleason score 6, 13; 7, 44; 8, 20; 9, 15; 10, 0; pretreatment PSA ≤10 ng/mL, 42; 10 to ≤20, 27; and >20, 23. According to the D'Amico classification system, 10, 37, and 45 patients were classified as low-risk, intermediate-risk, and high-risk. The overall survival rate, the cause-specific survival rate, and the biochemical relapse-free rate at 5 years was 94.7%, 100% and 98.9%, respectively. Severe acute toxicity (grade 3 or more) was not observed. The late urinary toxicity was 52.2% in grade 0, 28.3% in grade 1, 19.6% in grade 2, and 2.2% in grade 3. The late rectal toxicity was 78.3% in grade 0, 7.6% in grade 1, 9.8% in grade 2, and 4.3% in grade 3.

CONCLUSIONS

The present study demonstrated that HIMRT using TomoTherapy for prostate cancer has a favorable outcome with tolerable toxicity.

Blurring the lines for better visualisation

On-treatment imaging in radiotherapy has evolved over the last 60 years, bringing with it changes in the roles of radiographers, radiologists and oncologists. The ability to acquire and interpret high quality images (2D kilovoltage and megavoltage imaging and 3D CT and cone-beam CT) for radiotherapy planning and delivery requires therapy radiographers to have skills and knowledge that overlap with those of diagnostic radiographers. With the implementation of MRI-guided radiotherapy, treatment radiographers and clinical oncologists are exploring new territory, requiring truly collaborative working practices with their radiology partners. This short communication introduces the first images acquired using the hybrid MR Linac at our institution.

Clinical outcomes and dosimetric study of hypofractionated Helical TomoTherapy in breast cancer patients

We present a single center’s experience of treatment outcomes and dosimetric parameters for breast cancer patients treated with hypofractionated Helical TomoTherapy (HT). This is a retrospective study of one hundred and thirty-six patients with invasive breast cancer treated between March 2012 and October 2016. Dosimetric parameters and 3-year loco-regional failure free survival (LRFFS) were analyzed. Dose to ipsilateral lung, heart and contralateral breast as well as acute and late toxicities were recorded. The median follow-up time is 45 months (range: 5–83). Two patients had loco-regional failure. The 3-year LRFFS was 99%. Acute grade 1 and 2 skin toxicities occurred in 95% and 1%, respectively. Coverage of the target volumes was achieved with the mean ± standard deviation (SD) of homogeneity and conformity index being 0.1 ± 0.04, and 0.8 ± 0.07, respectively. Dose to ipsilateral lung, contralateral breast, and heart was also within the limited constraints regardless of the complexity of target volumes. Only two percent of patients experienced late grade 2 skin toxicity. No late grade 2 subcutaneous tissue toxicity was found. Nine percent of patients developed late grade 1 lung toxicity. Hypofractionated radiotherapy using Helical TomoTherapy in breast irradiation provides excellent 3-year LRFFS and minimal acute and late toxicities. A careful, longer follow-up of healthy tissue effects to lung, heart, and contralateral breast is warranted.

The Feasibility Study of Megavoltage Computed Tomographic (MVCT) Image for Texture Feature Analysis

Purpose: To determine whether radiomics texture features can be reproducibly obtained from megavoltage computed tomographic (MVCT) images acquired by Helical TomoTherapy (HT) with different imaging conditions.

Methods: For each of the 195 textures enrolled, the mean intrapatient difference, which is considered to be the benchmark for reproducibility, was calculated from the MVCT images of 22 patients with early-stage non-small-cell lung cancer. Test–retest MVCT images of an in-house designed phantom were acquired to determine the concordance correlation coefficient (CCC) for these 195 texture features. Features with high reproducibility (CCC > 0.9) in the phantom test–retest set were investigated for sensitivities to different imaging protocols, scatter levels, and motion frequencies using a wood phantom and in-vitro animal tissues.

Results: Of the 195 features, 165 (85%) features had CCC > 0.9. For the wood phantom, 124 features were reproducible in two kinds of scatter materials, and further investigations were performed on these features. For animal tissues, 108 features passed the criteria for reproducibility when one layer of scatter was covered, while 106 and 108 features of in-vitro liver and bone passed with two layers of scatter, respectively. Considering the effect of differing acquisition pitch (AcP), 97 features extracted from wood passed, while 103 and 59 features extracted from in-vitro liver and bone passed, respectively. Different reconstruction intervals (RI) had a small effect on the stability of the feature value. When AcP and RI were held consistent without motion, all 124 features calculated from wood passed, and a majority (122 of 124) of the features passed when imaging with a “fine” AcP with different RIs. However, only 55 and 40 features passed with motion frequencies of 20 and 25 beats per minute, respectively.

Conclusion: Motion frequency has a significant impact on MVCT texture features, and features from MVCT were more reproducibility in different scatter conditions than those from CBCT. Considering the effects of AcP and RI, the scanning protocols should be kept consistent when MVCT images are used for feature analysis. Some radiomics features from HT MVCT images are reproducible and could be used for creating clinical prediction models in the future.

Current state and future applications of radiological image guidance for particle therapy

In this review paper, we first give a short overview of radiological image guidance in photon radiotherapy, placing emphasis on the fact that linac based radiotherapy has outpaced particle therapy in the adoption of volumetric image guidance. While cone beam computed tomography (CBCT) has been an established technique in linac treatment rooms for almost two decades, the widespread adoption of volumetric image guidance in particle therapy, whether by means of CBCT or in-room CT imaging, is recent. This lag may be attributable to the bespoke nature and lower number of particle therapy installations, as well as the differences in geometry between those installations and linac treatment rooms. In addition, for particle therapy the so called shift invariance of the dose distribution rarely applies. An overview of the different volumetric image guidance solutions found at modern particle therapy facilities is provided, covering gantry, nozzle, C-arm, and couch-mounted CBCT as well different in-room CT configurations. A summary of the use of in-room volumetric imaging data beyond anatomy-based positioning is also presented as well as the necessary corrections to CBCT images for accurate water equivalent thickness calculation. Finally, the use of non-ionizing imaging modalities is discussed.

Current State of Image Guidance in Radiation Oncology: Implications for PTV Margin Expansion and Adaptive Therapy

Image guidance technology has evolved and seen widespread application in the past several decades. Advancements in the diagnostic imaging field have found new applications in radiation oncology and promoted the development of therapeutic devices with advanced imaging capabilities. A recent example is the development of linear accelerators that offer magnetic resonance imaging for real-time imaging and online adaptive planning. Volumetric imaging, in particular, offers more precise localization of soft tissue targets and critical organs which reduces setup uncertainty and permit the use of smaller setup margins. We present a review of the status of current imaging modalities available for radiation oncology and its impact on target margins and use for adaptive therapy.

H*(10) due to scattered radiation on the cancer-patient bodies treated with Tomotherapy

The ambient dose equivalent has been measured on the walls of a bunker with a 6 MV TomoLINAC, which was designed to have a conventional 18 MV LINAC. The ambient dose equivalent is due to scattered photons on patient bodies during cancer treatment. Measurements were carried out with thermoluminescent dosimeters that were fixed, at the isocentre plane, on the primary and secondary barriers, the maze, and on the TomoLINAC surface. Measurements were repeated three times, in each time dosimeters were on place during seven working days, where approximately 50 patients were treated per day. Ambient dose equivalent at each location was normalized to the total dose applied during the measuring time. The primary and secondary concrete barriers are thick enough to reduce the dose to safe values.

Clinical implementation of Dosimetry Check™ for TomoTherapy® delivery quality assurance

Purpose

The delivery quality assurance (DQA) of intensity‐modulated radiotherapy (IMRT) plans is a prerequisite for ensuring patient treatments. This work investigated the clinical usefulness of a new DQA system, Dosimetry Check™(DC), on TomoTherapy^®‐based helical IMRT plans.

Methods

The DQA was performed for 15 different TomoTherapy^®‐based clinical treatment plans. In Tomotherapy^® machines, the couch position was set to a height of 400 mm and the treatment plans were delivered using QA‐Treatment mode. For each treatment plan, the plan data and measured beam fluence were transferred to a DC‐installed computer. Then, DC reconstructed the three‐dimensional (3D) dose distribution to the CT images of the patient. The reconstructed dose distribution was compared with that of the original plan in terms of absolute dose, two‐dimensional (2D) planes and 3D volume. The DQA results were compared with those performed by a conventional method using the cheese phantom with ion chamber and radiochromic film.

Results

For 14 out of the 15 treatment plans, the absolute dose difference between the measurement and calculation was less than 3% and the gamma pass rate with the 3%/3 mm gamma evaluation criteria was greater than 95% for both DQA methods. The P‐value calculated using Wilcoxon signed‐rank test was 0.256, which implies no statistically significance in determining the absolute dose difference between the two methods. For one treatment plan generated using the 5.0 cm field width, the absolute dose difference was greater than 3% and the gamma pass rate was less than 95% with DC, while the DQA result with the cheese phantom method passed our TomoTherapy^® DQA tolerance.

Conclusion

We have clinically implemented DC for the DQA of TomoTherapy^®‐based helical IMRT treatment plans. DC carried out the accurate DQA results as performed with the conventional cheese phantom method. This new DQA system provided more information in verifying the dose delivery to patients, while simplifying the DQA process.

Milestones in stereotactic radiosurgery for the central nervous system

INTRODUCTION

Since Lars Leksell developed the first stereotactic radiosurgery (SRS) device in 1951, there has been growth in the technologies available and clinical indications for SRS. This expansion has been reflected in the medical literature, which is built upon key articles and institutions that have significantly impacted SRS applications. Our aim was to identify these prominent works and provide an educational tool for training and further inquiry.

METHOD

A list of search phrases relating to central nervous system applications of stereotactic radiosurgery was compiled. A topic search was performed using PubMed and Scopus databases. The journal, year of publication, authors, treatment technology, clinical subject, study design and level of evidence for each article were documented. Influence was proposed by citation count and rate.

RESULTS

Our search identified a total of 10,211 articles with the top 10 publications overall on the study of SRS spanning 443-1313 total citations. Four articles reported on randomized controlled trials, all of which evaluated intracranial metastases. The most prominent subtopics included SRS for arteriovenous malformation, glioblastoma, and acoustic neuroma. Greatest representation by treatment modality included Gamma Knife, LINAC, and TomoTherapy.

CONCLUSIONS

This systematic reporting of the influential literature on SRS for intracranial and spinal pathologies underscores the technology's rapid and wide reaching clinical applications. Moreover the findings provide an academic guide to future health practitioners and engineers in their study of SRS for neurosurgery.

Interfacility variation in treatment planning parameters in tomotherapy: field width, pitch, and modulation factor

Several studies have reported changes in dose distribution and delivery time based on the value of specific planning parameters [field width (FW), pitch, and modulation factor (MF)] in tomotherapy. However, the variation in the parameters between different facilities is unknown. The purpose of this study was to determine standard values of the above parameters for cases of head and neck cancer (HNC) and prostate cancer (PC) in Japan. In this survey, a web-based questionnaire was sent to 48 facilities performing radiation therapy with tomotherapy in March 2016. The deadline for data submission was April 2016. In the questionnaire, the values of the planning parameters usually used were requested and 23 responses were received, representing a response rate of 48% (23/48). The FW selected was 2.5 cm in most facilities, and facilities with a tomoEDGE license used dynamic FW rather than fixed FW. Facilities changed the pitch based on FW, dose per fraction, or target offset more frequently in HNC than in PC. In contrast, >50% of the facilities used the magic number proposed by Kissick et al. Median preset MFs (range, min to max) in HNC and PC were 2.4 (1.8-2.8) and 2.0 (1.8-3.0), respectively, and MF values showed large variations between the facilities. Our results are likely to be useful to several facilities designing treatment plans in tomotherapy.

Advances in Treatment with Intensity-Modulated Conformal Radiotherapy

The modern practice of radiotherapy centres on the development of conformai radiotherapy, techniques to ensure the high-dose volume is tightly wrapped around the diseased tissue and excluded as far as possible from adjacent normal structures. The development of conformai radiotherapy is a chain of processes involving treatment planning, development of new methods to deliver radiation, verification of the accuracy of radiation delivery and improvement of biological outcome. This is an enormous field of activity. This invited review paper summarises some of the main elements of progress towards implementing intensity-modulated conformai radiotherapy. This is the newest and most exciting development and, when achieved clinically, will lead to a quantum leap in tumour control probability with a fixed level of normal tissue damage.

Image guidance in proton therapy for lung cancer

Proton therapy is a promising but challenging treatment modality for the management of lung cancer. The technical challenges are due to respiratory motion, low dose tolerance of adjacent normal tissue and tissue density heterogeneity. Different imaging modalities are applied at various steps of lung proton therapy to provide information on target definition, target motion, proton range, patient setup and treatment outcome assessment. Imaging data is used to guide treatment design, treatment delivery, and treatment adaptation to ensure the treatment goal is achieved. This review article will summarize and compare various imaging techniques that can be used in every step of lung proton therapy to address these challenges.

Intensity-modulated radiation therapy: a review with a physics perspective

Intensity-modulated radiation therapy (IMRT) has been considered the most successful development in radiation oncology since the introduction of computed tomography into treatment planning that enabled three-dimensional conformal radiotherapy in 1980s. More than three decades have passed since the concept of inverse planning was first introduced in 1982, and IMRT has become the most important and common modality in radiation therapy. This review will present developments in inverse IMRT treatment planning and IMRT delivery using multileaf collimators, along with the associated key concepts. Other relevant issues and future perspectives are also presented.

Image guidance doses delivered during radiotherapy: Quantification, management, and reduction: Report of the AAPM Therapy Physics Committee Task Group 180

BACKGROUND

With radiotherapy having entered the era of image guidance, or image-guided radiation therapy (IGRT), imaging procedures are routinely performed for patient positioning and target localization. The imaging dose delivered may result in excessive dose to sensitive organs and potentially increase the chance of secondary cancers and, therefore, needs to be managed.

AIMS

This task group was charged with: a) providing an overview on imaging dose, including megavoltage electronic portal imaging (MV EPI), kilovoltage digital radiography (kV DR), Tomotherapy MV-CT, megavoltage cone-beam CT (MV-CBCT) and kilovoltage cone-beam CT (kV-CBCT), and b) providing general guidelines for commissioning dose calculation methods and managing imaging dose to patients.

MATERIALS & METHODS

We briefly review the dose to radiotherapy (RT) patients resulting from different image guidance procedures and list typical organ doses resulting from MV and kV image acquisition procedures.

RESULTS

We provide recommendations for managing the imaging dose, including different methods for its calculation, and techniques for reducing it. The recommended threshold beyond which imaging dose should be considered in the treatment planning process is 5% of the therapeutic target dose.

DISCUSSION

Although the imaging dose resulting from current kV acquisition procedures is generally below this threshold, the ALARA principle should always be applied in practice. Medical physicists should make radiation oncologists aware of the imaging doses delivered to patients under their care.

CONCLUSION

Balancing ALARA with the requirement for effective target localization requires that imaging dose be managed based on the consideration of weighing risks and benefits to the patient.

3D treatment planning on helical tomotherapy delivery system

The helical tomotherapy is a technologically advanced radiation dose delivery system designed to perform intensity-modulated radiation therapy (IMRT). It is mechanistically unique, based on a small 6-MV linear accelerator mounted on a ring gantry that rotates around the patient while the patient moves through a bore, ultimately yielding a helical path of radiation dose delivery. The helical pattern of dose delivery differentiated tomotherapy from other contemporary radiation therapy systems at the time of its inception. The accompanying 3-dimensional (3D) treatment planning system has been developed to solely support this specific type of dose delivery system. The treatment planning system has 2 modules identified as TomoHelical and TomoDirect to perform IMRT and conformal radiation therapy, respectively. The focus of this work within the scope of this special issue on 3D treatment planning systems is to assess the use of planning tools to generate treatment plans for helical tomotherapy. Clinical examples are used throughout to demonstrate the quality and differences of various clinical scenarios planned with tomotherapy.

Theory, simulation and experiments for precise deflection control of radiotherapy electron beams

Conventional radiotherapy is mainly applied by linear accelerators. Although linear accelerators provide dual (electron/photon) radiation beam modalities, both of them are intrinsically produced by a megavoltage electron current. Modern radiotherapy treatment techniques are based on suitable devices inserted or attached to conventional linear accelerators. Thus, precise control of delivered beam becomes a main key issue. This work presents an integral description of electron beam deflection control as required for novel radiotherapy technique based on convergent photon beam production. Theoretical and Monte Carlo approaches were initially used for designing and optimizing device´s components. Then, dedicated instrumentation was developed for experimental verification of electron beam deflection due to the designed magnets. Both Monte Carlo simulations and experimental results support the reliability of electrodynamics models used to predict megavoltage electron beam control.

Selection of external beam radiotherapy approaches for precise and accurate cancer treatment

Physically precise external-beam radiotherapy (EBRT) technologies may not translate to the best outcome in individual patients. On the other hand, clinical considerations alone are often insufficient to guide the selection of a specific EBRT approach in patients. We examine the ways in which to compare different EBRT approaches based on physical, biological and clinical considerations, and how they can be enhanced with the addition of biophysical models and machine-learning strategies. The process of selecting an EBRT modality is expected to improve in tandem with knowledge-based treatment planning.