Reduction of organ motion effects in IMRT and conformal 3D radiation delivery by using gating and tracking techniques

Feasibility assessment of inspiration breath-hold motion management for tumor tracking during cone-beam computed tomography for setup and radiotherapy in Veterinary Medicine: A pilot study

Radiotherapy (RT) for lung or liver tumors can be challenging due to respiration-induced organ motion (RIOM). There are some methodological solutions to minimize RIOM. We explored a new approach to evaluate the feasibility and reproducibility of RIOM during RT with five total client-owned tumor-bearing animals using a remote-triggered breath-hold ventilator under general anesthesia during image acquisition and RT. There was one stereotactic body radiotherapy, one conventionally fractionated definitive intent, and three conventionally fractionated palliative intent RT cases. Based on repeated cone beam CT, there were no treatment table shifts required prior to initiating beam on. No clinically significant complications such as hypotension occurred during anesthesia. This technique appeared to be safe in this group of patients and was easily clinically implemented and highly reproducible. More complete follow-up data and larger studies are needed to evaluate clinical outcomes with this breath-hold ventilator technique in veterinary RT.

Thoracic Proton Minibeam Radiation Therapy: Tissue Preservation and Survival Advantage Over Conventional Proton Therapy

PURPOSE

Proton minibeam radiation therapy (pMBRT) is an innovative radiation therapy approach that highly modulates the spatial dimension of the dose delivery using narrow, parallel, and submillimetric proton beamlets. pMBRT has proven its remarkable healthy tissue preservation in the brain and skin. This study assesses the potential advantages of pMBRT for thoracic irradiations compared with conventional radiation therapy in terms of normal tissue toxicity. The challenge here was the influence of respiratory motion on the typical peak and valley dose patterns of pMBRT and its potential biologic effect.

METHODS AND MATERIALS

The whole thorax of naïve C57BL/6 mice received one fraction of high dose (18 Gy) pMBRT or conventional proton therapy (CPT) without any respiratory control. The development of radiation-induced pulmonary fibrosis was longitudinally monitored using cone beam computed tomography. Anatomopathologic analysis was carried out at 9 months postirradiation and focused on the reaction of the lungs' parenchyma and the response of cell types involved in the development of radiation-induced fibrosis and lung regeneration as alveolar type II epithelial cells, club cells, and macrophages.

RESULTS

pMBRT has milder effects on survival, skin reactions, and lung fibrosis compared with CPT. The pMBRT-induced lung changes were more regional and less severe, with evidence of potential reactive proliferation of alveolar type II epithelial cells and less extensive depletion of club cells and macrophage invasion than the more damaging effects observed in CPT.

CONCLUSIONS

pMBRT appears suitable to treat moving targets, holding a significant ability to preserve healthy lung tissue, even without respiratory control or precise targeting.

Injectable Fiducial Marker for Image-Guided Radiation Therapy Based on Gold Nanoparticles and a Body Temperature-Activated Gel-Forming System

Injectable fiducial markers are crucial in image-guided radiation therapy (IGRT) due to their minimally invasive operations and improved patient compliance. This study presents the development of a ready-to-use injectable fiducial marker utilizing alginate stabilized-gold nanoparticles (alg-Au NPs) and a body temperature-activated in situ gel-forming system. Gram-scale alg-Au NPs were prepared in an hour by a green microwave-induced plasma-in-liquid process (MWPLP). Sodium alginate was introduced in this process to avoid aggregation between Au NPs, which ensured their stability and injectability. The gelation behavior of alginate with divalent cations and a temperature-dependent release of calcium source (glucono-delta-lactone (GDL) and CaCO3) served as the foundation of the body temperature-activated in situ gel-forming system. The injectable fiducial marker GDL/CaCO3/alg-Au NPs could maintain a liquid state at a low temperature for a higher injectability. After injection, on the other hand, Ca2+ would be released due to the body temperature-activated hydrolysis of GDL and the subsequent reaction with CaCO3, which would initiate the gelation of alginate. The injectable fiducial marker can be therefore delivered via injection and form gel at target site to avoid marker movement or Au NPs leakage after injection. Rheological measurements demonstrate the stability and gelation behavior of GDL/CaCO3/alg-Au NPs at different temperatures. Furthermore, the injectability and imaging ability of GDL/CaCO3/alg-Au NPs were also examined. In summary, ready-to-use injectable fiducial marker GDL/CaCO3/alg-Au NPs were developed via a green and facile method for IGRT.

Real-time marker-less tumor tracking with TOF PET: in silico feasibility study

Purpose. Although positron emission tomography (PET) can provide a functional image of static tumors for RT guidance, it’s conventionally very challenging for PET to track a moving tumor in real-time with a multiple frame/s sampling rate. In this study, we developed a novel method to enable PET based three-dimension (3D) real-time marker-less tumor tracking (RMTT) and demonstrated its feasibility with a simulation study. Methods. For each line-of-response (LOR) acquired, its positron-electron annihilation position is calculated based on the time difference between the two gamma interactions detected by the TOF PET detectors. The accumulation of these annihilation positions from data acquired within a single sampling frame forms a coarsely measured 3D distribution of positron-emitter radiotracer uptakes of the lung tumor and other organs and tissues (background). With clinically relevant tumor size and sufficient differential radiotracer uptake concentrations between the tumor and background, the high-uptake tumor can be differentiated from the surrounding low-uptake background in the measured distribution of radiotracer uptakes. With a volume-of-interest (VOI) that closely encloses the tumor, the count-weighted centroid of the annihilation positions within the VOI can be calculated as the tumor position. All these data processes can be conducted online. The feasibility of the new method was investigated with a simulated cardiac-torso digital phantom and stationary dual-panel TOF PET detectors to track a 28 mm diameter lung tumor with a 4:1 tumor-to-background 18FDG activity concentration ratio. Results. The initial study shows TOF PET based RMTT can achieve <2.0 mm tumor tracking accuracy with 5 frame s−1 sampling rate under the simulated conditions. In comparison, using reconstructed PET images to track a similar size tumor would require >30 s acquisition time to achieve the same tracking accuracy. Conclusion. With the demonstrated feasibility, the new method may enable TOF PET based RMTT for practical RT applications.

A transit portal dosimetry method for respiratory gating quality assurance with a dynamic 3D printed tumor phantom

BACKGROUNDS

Respiratory gating is one of the motion management techniques that is used to deliver radiation dose to a tumor at a specific position under free breathing. However, due to the dynamic feedback process of this approach, regular equipment quality assurance (QA) and patient-specific QA checks need to be performed. This work proposes a new QA methodology using electronic portal imaging detector (EPID) to determine the target localization accuracy of phase gating.

METHODS

QA tools comprising 3D printed spherical tumor phantoms, programmable stages, and an EPID detector are characterized and assembled. Algorithms for predicting portal dose (PD) through moving phantoms are developed and verified using gamma analysis for two spherical tumor phantoms (2 cm and 4 cm), two different 6 MV volumetric modulated arc therapy plans, and two different gating windows (30%-70% and 40%-60%). Comparison between the two gating windows is then performed using the Wilcoxon signed-rank test. An optimizer routine, which is used to determine the optimal window, based on maximal gamma passing rate (GPR), was applied to an actual breathing curve and breathing plan. This was done to ascertain if our method yielded a similar result with the actual gating window.

RESULTS

High GPRs of more than 97% and 91% were observed when comparing the predicted PD with the measured PD in moving phantom at 2 mm/2% and 1 mm/1% levels, respectively. Analysis of gamma heatmaps shows an excellent agreement with the tumor phantom. The GPR of 40%-60% PD was significantly lower than that of the 30%-70% PD at the 1 mm/1% level (p = 0.0064). At the 2 mm/2% level, no significant differences were observed. The optimizer routine could accurately predict the center of the gating window to within a 10% range.

CONCLUSION

We have successfully performed and verified a new method for QA with the use of a moving phantom with EPID for phase gating with real-time position management.

Preparation of Biopex-Supported Gold Nanoparticles as Potential Fiducial Markers for Image-Guided Radiation Therapy

Image-guided radiation therapy (IGRT) has emerged as a promising technique for cancer treatment to improve radiation precision and accuracy, thereby reducing the treatment toxicity and optimizing therapeutic efficacy. In IGRT, fiducial markers are required to be inserted near the tumor to get the spatial information of the tumor. Currently used metal fiducial markers with large sizes would be highly invasive; therefore, it is critical to develop minimally invasive alternatives to these markers. In this work, an injectable marker based on Biopex-supported Au NPs with adequate radio-opacity for X-ray visualization was developed. Biopex can function as a substrate for the growth of Au NPs and avoid excessive reaction-induced aggregation and precipitation. The self-curing property of Biopex prevents the leakage and elimination of isolated Au NPs, enabling long-term X-ray observation and radiotherapy. The effect of Biopex amount, gold precursor concentration, and reaction time were evaluated. The visibility of samples prepared by the optimized formula was also examined. The developed Biopex-Au NPs could be injected through a 21 G needle and exhibit great visibility in the X-ray visualization test, showing great potential as a fiducial marker for image-guided radiation therapy.

Baseline drift vector of multiple points on body surface using a near-infrared camera

The purpose of this study was to extract the three-dimensional (3D) vector of the baseline drift baseline drift vector (BDV) of the specific points on the body surface and to demonstrate the importance of the 3D tracking of the body surface. Our system consisted of a near-infrared camera (NIC: Kinect V2) and software that recognized and tracked blue stickers as markers. We acquired 3D coordinates of 30 markers stuck on the body surface for 30 min for eight healthy volunteers and developed a simple technique to extract the BDV. The BDV on the sternum, rib, and abdomen was extracted from the measured data. BDV per min. was analyzed to estimate the frequency to exceed a given tolerance. Also, the correlation among BDVs for multiple body sites was analyzed. The longitudinal baseline drift was observed in the BDV of healthy volunteers. Among the eight volunteers, the maximum probability that the BDV per min. exceeded the tolerance of 1 mm and 2 mm was 30% and 15%, respectively. The correlation among BDVs of multiple body sites suggested a potential feasibility to distinguish the translational movement of the whole area and the respiratory movement. In conclusion, we constructed the 3D tracking system of multiple points on the body surface using a noninvasive NIC at a low cost and established the method to extract the BDV. The existence of the longitudinal baseline drift showed the importance of the 3D tracking in the body surface.

Correlation of Optical Surface Respiratory Motion Signal and Internal Lung and Liver Tumor Motion: A Retrospective Single-Center Observational Study

Purpose: Surface-guided radiation therapy (SGRT) application has limitations. This study aimed to explore the relationship between patient characteristics and their external/internal correlation to qualitatively assess the external/internal correlation in a particular patient. Methods: Liver and lung cancer patients treated with radiotherapy in our institution were retrospectively analyzed. The external/internal correlation were calculated with Spearman correlation coefficient (SCC) and SCC after support vector regression (SVR) fitting (SCC_svr). The relationship between the external/internal correlation and magnitudes of motion of the tumor and external marker (A_i, A_e), tumor volume V_t, patient age, gender, and tumor location were explored. Results: The external/internal motions of liver and lung cancer patients were strongly correlated in the S-I direction, with mean SCC_svr values of 0.913 and 0.813. The correlation coefficients between the external/internal correlations and the patients’ characteristics (A_i, A_e, V_t, and age) were all smaller than 0.5; A_i, A_e and liver tumor volumes were positively correlated with the strength of the external/internal correlation, while lung tumor volumes and patient age were negative. The external/internal correlations in males and females were roughly equal, and the external/internal correlations in patients with peripheral lung cancers were stronger than those in patients with central lung cancers. Conclusion: The external/internal correlation shows great individual differences. The effects of A_i, A_e, V_t, and age are weakly to moderately correlated. Our results suggest the necessity of individualized assessment of patient's external/internal motion correlation prior to the application of SGRT technique for breath motion monitoring.

Radiotherapy for primary lung cancer

Herein are presented the recommendations from the Société française de radiothérapie oncologique regarding indications and modalities of lung cancer radiotherapy. The recommendations for delineation of the target volumes and organs at risk are detailed.

External irradiation treatment process

The purpose of this article is to describe the external irradiation process and updated recommendations of the French society for radiation oncology for patient follow-up.

Real-time liver tracking algorithm based on LSTM and SVR networks for use in surface-guided radiation therapy

Background

Surface-guided radiation therapy can be used to continuously monitor a patient’s surface motions during radiotherapy by a non-irradiating, noninvasive optical surface imaging technique. In this study, machine learning methods were applied to predict external respiratory motion signals and predict internal liver motion in this therapeutic context.

Methods

Seven groups of interrelated external/internal respiratory liver motion samples lasting from 5 to 6 min collected simultaneously were used as a dataset, D_v. Long short-term memory (LSTM) and support vector regression (SVR) networks were then used to establish external respiratory signal prediction models (LSTMpred/SVRpred) and external/internal respiratory motion correlation models (LSTMcorr/SVRcorr). These external prediction and external/internal correlation models were then combined into an integrated model. Finally, the LSTMcorr model was used to perform five groups of model updating experiments to confirm the necessity of continuously updating the external/internal correlation model. The root-mean-square error (RMSE), mean absolute error (MAE), and maximum absolute error (MAX_AE) were used to evaluate the performance of each model.

Results

The models established using the LSTM neural network performed better than those established using the SVR network in the tasks of predicting external respiratory signals for latency-compensation (RMSE < 0.5 mm at a latency of 450 ms) and predicting internal liver motion using external signals (RMSE < 0.6 mm). The prediction errors of the integrated model (RMSE ≤ 1.0 mm) were slightly higher than those of the external prediction and external/internal correlation models. The RMSE/MAE of the fifth model update was approximately ten times smaller than that of the first model update.

Conclusions

The LSTM networks outperform SVR networks at predicting external respiratory signals and internal liver motion because of LSTM’s strong ability to deal with time-dependencies. The LSTM-based integrated model performs well at predicting liver motion from external respiratory signals with system latencies of up to 450 ms. It is necessary to update the external/internal correlation model continuously.

[Lung cancer and pulmonary metastasis treated by stereotactic radiosurgery: Evaluation of the relevance of realisation of 3 4D CT by the RPM technique]

PURPOSE

Stereotactic lung radiosurgery has been carried out in the team at the Georges-François-Leclerc centre (CGFL) in Dijon since 2008 on a Truebeam® accelerator (Varian®) with the RPM technique.

MATERIALS AND METHODS

Fifty patients with primary T1-T2 stage lung cancer (n=30) or lung metastasis (n=20) were included in the study. Since 2014, 3 successive 4D scanners on D1, D2 and D3, have been produced in order to ensure the reproducibility of ITV (Internet Target Volume). The 3 ITVs are contoured (ITV 1, 2 and 3) from the MIP (Maximum Intensity Projection) of each of the 3 scanners. A global ITV is created from the ITV volumes of the 3 scanners (MIP 2 and 3 merged with MIP 1). A CBCT (Cone Beam Computerised Tomography) is performed at the start of each irradiation session to position the patient. The study consisted in analysing the relevance of the realisation of 3 different scanners before dosimetry to define the ITV and in comparing the volumes contoured on the different CBCT to the ITV to make sure that the tumour volume is well included in the ITV during the sessions.

RESULTS

There is a strong correlation between the different ITVs 1, 2, 3 and global, as well as between the volumes obtained on the different CBCTs. The correlation coefficient between the different ITVs and the volumes contoured on CBCT was high for upper lobar lesions. In terms of tolerance, the FEV1 (Maximum volume expired during the first second) did not seem to be a significant factor influencing the correlation between the ITV and the volumes bypassed on CBCT.

CONCLUSION

Performing a single 4D planification CT is sufficient to consider stereotactic lung irradiation, regardless of the location of the lung lesions. The correlation coefficient between ITV and CBCT was high for upper lobar lesions.

Couch and multileaf collimator tracking: A clinical feasibility study for pancreas and liver treatment

PURPOSE

Real-time tumor tracking through active correction by the multileaf collimator or treatment couch offers a promising strategy to mitigate delivery uncertainty due to intrafractional tumor motion. This study evaluated the performance of MLC and couch tracking using the prototype iTools Tracking system in TrueBeam Developer Mode and the application for abdominal cancer treatments.

METHODS

Experiments were carried out using a phantom with embedded Calypso transponders and a motion simulation platform. Geometric evaluations were performed using a circular conformal field with sinusoidal traces and pancreatic tumor motion traces. Geometric tracking accuracy was retrospectively calculated by comparing the compensational MLC or couch motion extracted from machine log files to the target motion reconstructed from real-time MV and kV images. Dosimetric tracking accuracy was measured with radiochromic films using clinical abdominal VMAT plans and pancreatic tumor traces.

RESULTS

Geometrically, the root-mean-square errors for MLC tracking were 0.5 and 1.8 mm parallel and perpendicular to leaf travel direction, respectively. Couch tracking, in contrast, showed an average of 0.8 mm or less geometric error in all directions. Dosimetrically, both MLC and couch tracking reduced motion-induced local dose errors compared to no tracking. Evaluated with five pancreatic tumor motion traces, the average 2%/2 mm global gamma pass rate of eight clinical abdominal VMAT plans was 67.4% (range: 26.4%-92.7%) without tracking, which was improved to 86.0% (range: 67.9%-95.6%) with MLC tracking, and 98.1% (range: 94.9%-100.0%) with couch tracking. In 16 out of 40 deliveries with different plans and motion traces, MLC tracking did not achieve clinically acceptable dosimetric accuracy with 3%/3mm gamma pass rate below 95%.

CONCLUSIONS

This study demonstrated the capability of MLC and couch tracking to reduce motion-induced dose errors in abdominal cases using a prototype tracking system. Clinically significant dose errors were observed with MLC tracking for certain plans which could be attributed to the inferior MLC tracking accuracy in the direction perpendicular to leaf travel, as well as the interplay between motion tracking and plan delivery for highly modulated plans. Couch tracking outperformed MLC tracking with consistently high dosimetric accuracy in all plans evaluated, indicating its clinical potential in the treatment of abdominal cancers.

Feasibility study for marker-based VMAT plan optimization toward tumor tracking

This work investigates the incorporation of fiducial marker‐based visibility parameters into the optimization of volumetric modulated arc therapy (VMAT) plans. We propose that via this incorporation, one may produce treatment plans that aid real‐time tumor tracking approaches employing exit imaging of the therapeutic beam (e.g., via EPID), in addition to satisfying purely dosimetric requirements. We investigated the feasibility of this approach for a thorax and prostate site using optimization software (MonArc). For a thorax phantom and a lung patient, three fiducial markers were inserted around the tumor and VMAT plans were created with two partial arcs and prescription dose of 48 Gy (4 fractions). For a prostate patient with three markers in the prostate organ, a VMAT plan was created with two partial arcs and prescription dose 72.8 Gy (28 fractions). We modified MonArc to include marker‐based visibility constraints (“hard”and “soft”). A hard constraint (HC) imposes full visibility for all markers, while a soft constraint (SC) penalizes visibility for specific markers in the beams‐eye‐view. Dose distributions from constrained plans (HC and SC) were compared to the reference nonconstrained (NC) plan using metrics including conformity index (CI), homogeneity index (HI), gradient measure (GM), and dose to 95% of planning target volume (PTV) and organs at risk (OARs). The NC plan produced the best target conformity and the least doses to the OARs for the entire dataset, followed by the SC and HC plans. Using SC plans provided acceptable dosimetric tolerances for both the target and OARs. However, OAR doses may be increased or decreased based on the constrained marker location and number of trackable markers. In conclusion, we demonstrate that visibility constraints can be incorporated into the optimization together with dosimetric objectives to produce treatment plans satisfying both objectives. This approach should ensure greater clinical success when applying real‐time tracking algorithms, using VMAT delivery.

[Stereotactic pulmonary radiotherapy: Which machine?]

Stereotactic radiotherapy represents a fundamental change in the practice of radiotherapy of lung cancers. Despite the great heterogeneity of sites, techniques, and doses, most studies found a high local control rate, around 70 to 90% at 2 years, and reduced toxicity, around 5% of grade 3 at 2 years. Stereotactic radiotherapy can be realized either by a dedicated accelerator (CyberKnife^®) or by a conventional accelerator associated with specific systems. The two modalities deliver a very precise irradiation whose very good results published to date are similar. Some technical characteristics specific to each type of linear accelerator could guide the choice according to the target volume treated.

Predicting tumour motion during the whole radiotherapy treatment: a systematic approach for thoracic and abdominal lesions based on real time MR

INTRODUCTION

Aim of this study was to investigate the ability of pre-treatment four dimensional computed tomography (4DCT) to capture respiratory-motion observed in thoracic and abdominal lesions during treatment. Treatment motion was acquired using full-treatment cine-MR acquisitions. Results of this analysis were compared to the ability of 30 seconds (s) cine Magnetic Resonance (MR) to estimate the same parameters.

METHODS

A 4DCT and 30 s cine-MR (ViewRay, USA) were acquired on the simulation day for 7 thoracic and 13 abdominal lesions. Mean amplitude, intra- and inter-fraction amplitude variability, and baseline drift were extracted from the full treatment data acquired by 2D cine-MR, and correlated to the motion on pre-treatment 30 s cine-MR and 4DCT. Using the full treatment data, safety margins on the ITV, necessary to account for all motion variability from 4DCT observed during treatment, were calculated. Mean treatment amplitudes were 2 ± 1 mm and 5 ± 3 mm in the anteroposterior (AP) and craniocaudal (CC) direction, respectively. Differences between mean amplitude during treatment and amplitude on 4DCT or during 30 s cine-MR were not significant, but 30 s cine-MR was more accurate than 4DCT. Intra-fraction amplitude variability was positively correlated with both 30 s cine-MR and 4DCT amplitude. Inter-fraction amplitude variability was minimal.

RESULTS

Mean baseline drift over all fractions and patients equalled 1 ± 1 mm in both CC and AP direction, but drifts per fraction up to 16 mm (CC) and 12 mm (AP) were observed. Margins necessary on the ITV ranged from 0 to 8 mm in CC and 0 to 5 mm in AP direction. Neither amplitude on 4DCT nor during 30 s cine MR is correlated to the magnitude of drift or the necessary margins in both directions.

CONCLUSION

Lesions moving with small amplitude show limited amplitude variability throughout treatment, making passive motion management strategies seem adequate. However, other variations such as baseline drifts and shifts still cause significant geometrical uncertainty, favouring real-time monitoring and an active approach for all lesions influenced by respiratory motion.

Advanced radiation techniques for locally advanced non-small cell lung cancer: intensity-modulated radiation therapy and proton therapy

Radiation therapy (RT) represents an integral part of a multimodality treatment plan in the definitive, preoperative and postoperative management of non-small cell lung cancer (NSCLC). Technological advances in RT have enabled a shift from two-dimensional radiotherapy to more conformal techniques. Three-dimensional conformal radiotherapy (3DCRT), the current minimum technological standard for treating NSCLC, allows for more accurate delineation of tumor burden by using computed tomography-based treatment planning instead of two-dimensional radiographs. Intensity-modulated RT (IMRT) and proton therapy represent advancements over 3DCRT that aim to improve the conformity of RT and provide the possibility for dose escalation to the tumor by minimizing radiation dose to organs at risk. Both techniques likely confer benefits to certain anatomic subgroups of NSCLC requiring RT. This article reviews pertinent studies evaluating the use of IMRT and proton therapy in locally advanced NSCLC, and outlines challenges, indications for use, and areas for future research.

Daily CT guidance improves target coverage during definitive radiation therapy for gastric MALT lymphoma

PURPOSE

Radiation therapy (RT) for gastric mucosa-associated lymphoid tissue (MALT) lymphoma is challenging because of variation in the stomach's position, size, and shape. We investigated the interfractional changes in stomach location, consequent dosimetric effects, and impact of daily computed tomography image guidance RT (CT-IGRT).

METHODS AND MATERIALS

Twelve patients treated for gastric MALT lymphoma with intensity modulated radiation therapy, using a breath-hold technique and restriction of oral intake, were studied retrospectively. The planning target volume (PTV) comprised a 0.5 to 1.0 cm expansion of the stomach. The prescription dose was 30 Gy in 15 to 20 fractions. CT-IGRT was performed daily using CT-on-Rails. Dosimetry was calculated on 229 daily CT images after bony versus CT-based soft tissue alignment, and doses delivered to the target and adjacent structures were compared with the treatment plan. Target coverage was expressed as the percent of the clinical target volume (CTV) and PTV receiving ≥95% of the prescribed dose (V95%).

RESULTS

The average change in stomach volume was -12.4% (range, -47.6% to 38.6%). The average shift required for target coverage was 1.0 cm (maximum, 2.2 cm). With CT-based alignment to the stomach, the average V95% was 98.5% for CTV and 94.9% for PTV; with bony alignment, these values were 94.5% and 90.4%, respectively (P < .01 for CTV and PTV). With bony alignment, the PTV V95% was ≤90% in 4 patients (33%) over the course of treatment and was as low as 72.5% for 1 fraction. The kidney position varied with respect to the stomach and bony anatomy. Consequently, the dose to the left kidney was higher based on daily CT scans than on planning scans. Dose to other organs at risk did not vary significantly.

CONCLUSIONS

Substantial interfractional variation in stomach volume was observed, despite treatment with breath-hold and restriction of oral intake. Daily CT-IGRT improved target coverage, enabling excellent coverage despite the use of small PTV margins.

Internal mammary lymph nodes radiotherapy of breast cancer in the era of individualized medicine

Inclusion internal mammary lymph nodes as a part of regional nodal irradiation have a potential to reduce local recurrence, distant recurrence, and improve survival in breast cancer. However, the increased risk of cardiac toxicity and lungs injure associated with internal mammary lymph nodes irradiation has drew more and more attention. Estimating risk of metastasis in internal mammary lymph nodes based on axillary lymph nodes metastasis status is not always reliable: low-risk do not always mean negative in internal mammary lymph nodes and high-risk do not always indicate positive in internal mammary lymph nodes. Inaccurate prediction of in internal mammary lymph nodes metastasis might lead to over- or under-treatment of in internal mammary lymph node. Internal mammary sentinel lymph node biopsy is a minimally invasive technique which has a high potential to accurately evaluate the metastasis status in in internal mammary lymph nodes and improve accuracy of nodal staging. This technique might be a useful tool to guide individualized internal mammary lymph nodes irradiation.

Technical Note: A novel quality assurance test to identify gantry angle inaccuracies in respiratory-gated VMAT treatments

PURPOSE

During respiratory-gated volumetric-modulated arc therapy (VMAT), the radiation beam is turned off each time the target exits the gating window. At the same time, the gantry slows, stops, and rewinds before the beam is turned back on. A quality assurance (QA) test was developed to detect inaccuracies in the gantry angle position between beam-off and beam-on events during respiratory-gated VMAT.

METHODS

Strips of Gafchromic™ EBT3 film were taped to the surface of a Capthan^® 504 phantom mounted at isocenter. A homogeneous dose was delivered to the films through a 2 cm × 10 cm slit in the jaws using a respiratory-gated VMAT arc without the multileaf collimator. A periodic breathing cycle was used. Errors in gated delivery ranging from 0.5 to 5° were simulated by delivering nongated arcs with the same field size with over- and underlapping sections of 0.5-5°. The simulated errors were used to define QA levels to analyze the gated delivery.

RESULTS

The QA test was capable of detecting errors as small as 0.5°. The test was delivered to three Varian TrueBeam™ linacs, and no gantry angle inaccuracies greater than or equal to 0.5° were detected on any of the films.

CONCLUSIONS

A QA test capable of detecting gantry angle inaccuracies at beam-off and subsequent beam-on as small as 0.5° was developed and implemented for Varian TrueBeam™ linacs.

Intensity-modulated radiotherapy for hepatocellular carcinoma: dosimetric and clinical results

Since the introduction of 3-dimensional conformal radiotherapy (3DCRT), new radiotherapy techniques have expanded the indication of radiotherapy for the treatment of hepatocellular carcinoma (HCC), from the hitherto palliative to a now curative-intent purpose. Intensity-modulated radiotherapy (IMRT), currently the most advanced radiotherapy technique, is considered an attractive option for the treatment of HCC, and is more widely applied because it can deliver a higher dose to the tumor than 3DCRT while sparing surrounding normal organs. However, the advantages and potential disadvantages of IMRT for treating HCC have not been fully established. This article deals with three different IMRT techniques, including static IMRT and volumetric modulated arc therapy using conventional multileaf collimator (MLC) mounted linear accelerators, and helical IMRT using binary MLC mounted helical tomotherapy machine. We review dosimetric and clinical studies for these IMRT techniques for the treatment of HCC.

Predictors of chest wall toxicity after stereotactic ablative radiotherapy using real-time tumor tracking for lung tumors

Background

To evaluate the incidence of chest wall toxicity after lung stereotactic ablative radiotherapy (SABR) and identify risk factors for the development of rib fracture.

Methods

Thirty-nine patients with 49 lesions underwent SABR for primary or metastatic lung tumors using Cyberknife® with tumor tracking systems. Patient characteristics, treatment factors and variables obtained from dose-volume histograms (DVHs) were analyzed to find the association with chest wall toxicity. Four-dimensional (4D) dose calculations were done to investigate the effect of respiratory motion on dose to the ribs.

Results

After follow-up of median 26.7 months (range: 8.4 – 80.0), 8 patients (20.5%) experienced rib fractures and among these patients, three (37.5%) had chest wall pain at 2–3 months after SABR. Median time to rib fracture was 13.4 months (range: 8.0 – 38.5) and the 2-year actuarial risk of rib fracture was 12.2%. Dose to the 4.6 cc of the ribs (D_4.6cc) and rib volume received 160 Gy or more (V₁₆₀) were significant predictor for rib fracture. No significant differences between three-dimensional (3D) and 4D dose calculations were found.

Conclusions

Parameters from DVH are useful in predicting the risk of chest wall toxicity after SABR for lung tumors. Efforts should be made to reduce the risk of the rib fracture after lung SABR.

Pathogenesis and Prevention of Radiation-induced Myocardial Fibrosis

Radiation therapy is one of the most important methods for the treatment of malignant tumors. However, in radiotherapy for thoracic tumors such as breast cancer, lung cancer, esophageal cancer, and mediastinal lymphoma, the heart, located in the mediastinum, is inevitably affected by the irradiation, leading to pericardial disease, myocardial fibrosis, coronary artery disease, valvular lesions, and cardiac conduction system injury, which are considered radiation-induced heart diseases. Delayed cardiac injury especially myocardial fibrosis is more prominent, and its incidence is as high as 20–80%. Myocardial fibrosis is the final stage of radiation-induced heart diseases, and it increases the stiffness of the myocardium and decreases myocardial systolic and diastolic function, resulting in myocardial electrical physiological disorder, arrhythmia, incomplete heart function, or even sudden death. This article reviews the pathogenesis and prevention of radiation-induced myocardial fibrosis for providing references for the prevention and treatment of radiation-induced myocardial fibrosis.

Are fiducial markers useful surrogates when using respiratory gating to reduce motion of gastroesophageal junction tumors?

BACKGROUND

Radiation therapy (RT) is an integral component of the management of gastroesophageal junction (GEJ) tumors. We evaluated the use of implanted radiopaque fiducials as tumor surrogates to allow for more focal delivery of RT to these mobile tumors when using respiratory gating (RG) to reduce motion.

MATERIAL AND METHODS

We analyzed four-dimensional computed tomography scans of 20 GEJ patients treated with RG and assessed correlation between tumor and implanted fiducial motion over the whole respiratory cycle and within a clinically realistic gate around end-exhalation. We evaluated fiducial motion concordance in 11 patients with multiple fiducials.

RESULTS

Gating reduced anterior-posterior (AP) and superior-inferior (SI) mean tumor and fiducial motions by over 50%. Fiducials and primary tumor motions were moderately correlated: R(2) for AP and SI linear fits to the entire group were 0.54 and 0.68, respectively, but the correlation had strong inter-patient variation. For all patients with multiple fiducials, relative in-gate displacements were below 3 mm; results were similar for eight of 11 patients over the whole cycle.

CONCLUSION

Implanted fiducial and gross tumor volume (GTV) motions correlate well but the correlation is patient-specific and may be dependent on the location of the fiducials with respect to the GTV.

Respiratory gated radiotherapy-pretreatment patient specific quality assurance

Organ motions during inter-fraction and intra-fraction radiotherapy introduce errors in dose delivery, irradiating excess of normal tissue, and missing target volume. Lung and heart involuntary motions cause above inaccuracies and gated dose delivery try to overcome above effects. Present work attempts a novel method to verify dynamic dose delivery using a four-dimensional (4D) phantom. Three patients with mobile target are coached to maintain regular and reproducible breathing pattern. Appropriate intensity projection image set generated from 4D-computed tomography (4D-CT) is used for target delineation. Intensity modulated radiotherapy plans were generated on selected phase using CT simulator (Siemens AG, Germany) in conjunction with “Real-time position management” (Varian, USA) to acquire 4D-CT images. Verification plans were generated for both ion chamber and Gafchromic (EBT) film image sets. Gated verification plans were delivered on the phantom moving with patient respiratory pattern. We developed a MATLAB-based software to generate maximum intensity projection, minimum intensity projections, and average intensity projections, also a program to convert patient breathing pattern to phantom compatible format. Dynamic thorax quality assurance (QA) phantom (Computerized Imaging Reference Systems type) is used to perform the patient specific QA, which holds an ion chamber and film to measure delivered radiation intensity. Exposed EBT films are analyzed and compared with treatment planning system calculated dose. The ion chamber measured dose shows good agreement with planned dose within ± 0.5% (0.203 ± 0.57%). Gamma value evaluated from EBT film shows passing rates 92–99% (96.63 ± 3.84%) for 3% dose and 3 mm distance criteria. Respiratory gated treatment delivery accuracy is found to be within clinically acceptable level.

Intensity-modulated radiotherapy for lung cancer: current status and future developments

Radiotherapy plays an important role in the management of lung cancer, with over 50% of patients receiving this modality at some point during their treatment. Intensity-modulated radiotherapy (IMRT) is a technique that adds fluence modulation to beam shaping, which improves radiotherapy dose conformity around the tumor and spares surrounding normal structures. Treatment with IMRT is becoming more widely available for the treatment of lung cancer, despite the paucity of high level evidence supporting the routine use of this more resource intense and complex technique. In this review article, we have summarized data from planning and clinical studies, discussed challenges in implementing IMRT, and made recommendations on the minimum requirements for safe delivery of IMRT.

Injectable Colloidal Gold for Use in Intrafractional 2D Image-Guided Radiation Therapy

In the western world, approximately 50% of all cancer patients receive radiotherapy alone or in combination with surgery or chemotherapy. Image-guided radiotherapy (IGRT) has in recent years been introduced to enhance precision of the delivery of radiation dose to tumor tissue. Fiducial markers are often inserted inside the tumor to improve IGRT precision and to enable monitoring of the tumor position during radiation therapy. In the present article, a liquid fiducial tissue marker is presented, which can be injected into tumor tissue using thin and flexible needles. The liquid fiducial has high radio-opacity, which allows for marker-based image guidance in 2D and 3D X-ray imaging during radiation therapy. This is achieved by surface-engineering gold nanoparticles to be highly compatible with a carbohydrate-based gelation matrix. The new fiducial marker is investigated in mice where they are highly biocompatible and stable after implantation. To investigate the clinical potential, a study is conducted in a canine cancer patient with spontaneous developed solid tumor in which the marker is successfully injected and used to align and image-guide radiation treatment of the canine patient. It is concluded that the new fiducial marker has highly interesting properties that warrant investigations in cancer patients.

The cardiac dose-sparing benefits of deep inspiration breath-hold in left breast irradiation: a systematic review

Introduction

Despite technical advancements in breast radiation therapy, cardiac structures are still subject to significant levels of irradiation. As the use of adjuvant radiation therapy after breast-conserving surgery continues to improve survival for early breast cancer patients, the associated radiation-induced cardiac toxicities become increasingly relevant. Our primary aim was to evaluate the cardiac-sparing benefits of the deep inspiration breath-hold (DIBH) technique.

Methods

An electronic literature search of the PubMed database from 1966 to July 2014 was used to identify articles published in English relating to the dosimetric benefits of DIBH. Studies comparing the mean heart dose of DIBH and free breathing treatment plans for left breast cancer patients were eligible to be included in the review. Studies evaluating the reproducibility and stability of the DIBH technique were also reviewed.

Results

Ten studies provided data on the benefits of DIBH during left breast irradiation. From these studies, DIBH reduced the mean heart dose by up to 3.4 Gy when compared to a free breathing approach. Four studies reported that the DIBH technique was stable and reproducible on a daily basis. According to current estimates of the excess cardiac toxicity associated with radiation therapy, a 3.4 Gy reduction in mean heart dose is equivalent to a 13.6% reduction in the projected increase in risk of heart disease.

Conclusion

DIBH is a reproducible and stable technique for left breast irradiation showing significant promise in reducing the late cardiac toxicities associated with radiation therapy.

Motion management in gastrointestinal cancers

The presence of tumor and organ motions complicates the planning and delivery of radiotherapy for gastrointestinal cancers. Without proper accounting of the movements, target volume could be under-dosed and the nearby normal critical organs could be over-dosed. This situation is further exacerbated by the close proximity of abdominal tumors to many normal organs at risk (OARs). A number of strategies have been developed to deal with tumor and organ motions in radiotherapy. This article presents a review of the techniques used in the evaluation, quantification, and management of tumor and organ motions for radiotherapy of gastrointestinal cancers.

Investigating the potential impact of four-dimensional computed tomography (4DCT) on toxicity, outcomes and dose escalation for radical lung cancer radiotherapy

AIMS

To investigate the potential dosimetric and clinical benefits predicted by using four-dimensional computed tomography (4DCT) compared with 3DCT in the planning of radical radiotherapy for non-small cell lung cancer.

MATERIALS AND METHODS

Twenty patients were planned using free breathing 4DCT then retrospectively delineated on three-dimensional helical scan sets (3DCT). Beam arrangement and total dose (55 Gy in 20 fractions) were matched for 3D and 4D plans. Plans were compared for differences in planning target volume (PTV) geometrics and normal tissue complication probability (NTCP) for organs at risk using dose volume histograms. Tumour control probability and NTCP were modelled using the Lyman-Kutcher-Burman (LKB) model. This was compared with a predictive clinical algorithm (Maastro), which is based on patient characteristics, including: age, performance status, smoking history, lung function, tumour staging and concomitant chemotherapy, to predict survival and toxicity outcomes. Potential therapeutic gains were investigated by applying isotoxic dose escalation to both plans using constraints for mean lung dose (18 Gy), oesophageal maximum (70 Gy) and spinal cord maximum (48 Gy).

RESULTS

4DCT based plans had lower PTV volumes, a lower dose to organs at risk and lower predicted NTCP rates on LKB modelling (P < 0.006). The clinical algorithm showed no difference for predicted 2-year survival and dyspnoea rates between the groups, but did predict for lower oesophageal toxicity with 4DCT plans (P = 0.001). There was no correlation between LKB modelling and the clinical algorithm for lung toxicity or survival. Dose escalation was possible in 15/20 cases, with a mean increase in dose by a factor of 1.19 (10.45 Gy) using 4DCT compared with 3DCT plans.

CONCLUSIONS

4DCT can theoretically improve therapeutic ratio and dose escalation based on dosimetric parameters and mathematical modelling. However, when individual characteristics are incorporated, this gain may be less evident in terms of survival and dyspnoea rates. 4DCT allows potential for isotoxic dose escalation, which may lead to improved local control and better overall survival.

Radiation oncology: a primer for medical students

Radiation oncology requires a complex understanding of cancer biology, radiation physics, and clinical care. This paper equips the medical student to understand the fundamentals of radiation oncology, first with an introduction to cancer treatment and the use of radiation therapy. Considerations during radiation oncology consultations are discussed extensively with an emphasis on how to formulate an assessment and plan including which treatment modality to use. The treatment planning aspects of radiation oncology are then discussed with a brief introduction to how radiation works, followed by a detailed explanation of the nuances of simulation, including different imaging modalities, immobilization, and accounting for motion. The medical student is then instructed on how to participate in contouring, plan generation and evaluation, and the delivery of radiation on the machine. Lastly, potential adverse effects of radiation are discussed with a particular focus on the on-treatment patient.

Present and future innovations in radiation oncology

The purpose of this article is to provide a review of innovations in radiation oncology that have been recently adopted as well as those that are likely to be adopted in the near future. Physics and engineering innovations, including image-guidance technologies and charged particle therapy, are discussed. Biologic innovations, including novel radiation sensitizers, functional imaging for use in treatment planning, and altered fractionation, are also discussed.

Respiratory Gating for Radiotherapy: Main Technical Aspects and Clinical Benefits

Respiratory-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast, and liver tumors. An increased conformality of irradiation fields leading to decreased complication rates of organs at risk is expected. Five main strategies are used to reduce respiratory motion effects: integration of respiratory movements into treatment planning, forced shallow breathing with abdominal compression, breath-hold techniques, respiratory gating techniques, and tracking techniques. Measurements of respiratory movements can be performed either in a representative sample of the general population, or directly on the patient before irradiation. Reduction of breathing motion can be achieved by using either abdominal compression, breath-hold techniques, or respiratory gating techniques. Abdominal compression can be used to reduce diaphragmatic excursions. Breath-hold can be achieved with active techniques, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily breath-holds. Respiratory gating techniques use external devices to predict the phase of the breathing cycle while the patient breathes freely. Another approach is tumor-tracking technique, which consists of a real-time localization of a constantly moving tumor. This work describes these different strategies and gives an overview of the literature.

[Gated radiotherapy in breast cancer]

Postoperative radiotherapy is a cornerstone of the local treatment in breast cancer. It has been proved with high level of evidence that it decreases local relapse and improves survival of patients. However, radiotherapy comes with healthy tissue toxicity, heart and lung in particular. With constant improvement of radiation techniques, several methods have been developed to decrease the dose to the heart and the lungs. Sometimes, respiratory maneuvers can help, due to patient's anatomy: the radiotherapy is gated with patient's breath. The Deep Inspiration Breath Hold technique is the most popular and there are several ways to perform it. This note will describe the different systems with published data in order to help the radiation oncologist in the daily practice.

A novel four-dimensional radiotherapy planning strategy from a tumor-tracking beam's eye view

To investigate the feasibility of four-dimensional radiotherapy (4DRT) planning from a tumor-tracking beam's eye view (ttBEV) with reliable gross tumor volume (GTV) delineation, realistic normal tissue representation, high planning accuracy and low clinical workload, we propose and validate a novel 4D conformal planning strategy based on a synthesized 3.5D computed tomographic (3.5DCT) image with a motion-compensated tumor. To recreate patient anatomy from a ttBEV in the moving tumor coordinate system for 4DRT planning (or 4D planning), the centers of delineated GTVs in all phase CT images of 4DCT were aligned, and then the aligned CTs were averaged to produce a new 3.5DCT image. This GTV-motion-compensated CT contains a motionless target (with motion artifacts minimized) and motion-blurred normal tissues (with a realistic temporal density average). Semi-automatic threshold-based segmentation of the tumor, lung and body was applied, while manual delineation was used for other organs at risk (OARs). To validate this 3.5DCT-based 4D planning strategy, five patients with peripheral lung lesions of small size (<5 cm(3)) and large motion range (1.2-3.5 cm) were retrospectively studied for stereotactic body radiotherapy (SBRT) using 3D conformal radiotherapy planning tools. The 3.5DCT-based 4D plan (3.5DCT plan) with 9-10 conformal beams was compared with the 4DCT-based 4D plan (4DCT plan). The 4DCT plan was derived from multiple 3D plans based on all phase CT images, each of which used the same conformal beam configuration but with an isocenter shift to aim at the moving tumor and a minor beam aperture and weighting adjustment to maintain plan conformality. The dose-volume histogram (DVH) of the 4DCT plan was created with two methods: one is an integrated DVH (iDVH(4D)), which is defined as the temporal average of all 3D-phase-plan DVHs, and the other (DVH(4D)) is based on the dose distribution in a reference phase CT image by dose warping from all phase plans using the displacement vector field (DVF) from a free-form deformable image registration (DIR). The DVH(3.5D) (for the 3.5DCT plan) was compared with both iDVH(4D) and DVH(4D). To quantify the DVH difference between the 3.5DCT plan and the 4DCT plan, two methods were used: relative difference (%) of the areas underneath the DVH curves and the volumes receiving more than 20% (V20) and 50% (V50) of prescribed dose of these 4D plans. The volume of the delineated GTV from different phase CTs varied dramatically from 24% to 112% among the five patients, whereas the GTV from 3.5DCT deviated from the averaged GTV in 4DCT by only -6%±6%. For planning tumor volume (PTV) coverage, the difference between the DVH(3.5D) and iDVH(4D) was negligible (<1% area), whereas the DVH(3.5D) and DVH(4D) were quite different, due to DIR uncertainty (∼2 mm), which propagates to PTV dose coverage with a pronounced uncertainty for small tumors (0.3-4.0 cm(3)) in stereotactic plans with sharp dose falloff around PTV. For OARs, such as the lung, heart, cord and esophagus, the three DVH curves (DVH(3.5D), DVH(4D) and iDVH(4D)) were found to be almost identical for the same patients, especially in high-dose regions. For the tumor-containing lung, the relative difference of the areas underneath the DVH curves was found to be small (5.3% area on average), of which 65% resulted from the low-dose region (D < 20%). The averaged V20 difference between the two 4D plans was 1.2% ± 0.8%. For the mean lung dose (MLD), the 3.5DCT plan differed from the 4DCT plan by -1.1%±1.3%. GTV-motion-compensated CT (3.5DCT) produces an accurate and reliable GTV delineation, which is close to the mean GTV from 4DCT. The 3.5DCT plan is equivalent to the 4DCT plan with <1% dose difference to the PTV and negligible dose difference in OARs. The 3.5DCT approach simplifies 4D planning and provides accurate dose calculation without a substantial increase of clinical workload for motion-tracking delivery to treat small peripheral lung tumors with large motion.

[Difficulties encountered and solutions found when implementing stereotactic radiotherapy of non-small cell lung cancer]

The aim of this paper is to describe the difficulties encountered when implementing stereotactic radiotherapy of non-small cell lung cancer (T1-T2, N0, M0) using a voluntary breath-hold technique. From 25/03/2010 to 22/02/2011, eight patients with a non-small cell lung cancer were selected for treatment. CT images were obtained with the patient maintaining breath-hold using a spirometer. Treatment was delivered when the patient maintains this level of breath-hold. Treatment was performed with a 4 MV and 10 MV photon beams from a linear accelerator Varian 2100CS, equipped with a 120 leaves collimator. 60 Gy or 48 Gy were delivered, in four sessions, to the 80% isodose. The planning target volume (PTV) was defined by adding a 5mm margin to the internal target volume (ITV), the ITV corresponding to the gross tumour volume (GTV) plus a 3mm margin. CTV is considered equal to GTV. The non-understanding of the gating technique, the great number of beams and the limited breath-hold times led to the failure of some treatments. It can be explained by some patients insufficient respiratory abilities and the low dose rate of one of the beams used for treatment, thus forcing some radiation fields to be delivered in two or three times. Implementing such a technique can be limited by the patients' physical abilities and the materials used. Some solutions were found: a training phase more intense with a coaching of the breath-hold technique more precise, or the use of an abdominal compression device.