Image-guided Radiotherapy Techniques Research Articles

Intensity-Modulated Radiation Therapy for Early-Stage Squamous Cell Carcinoma of the Glottic Larynx: A Systematic Review and Meta-Analysis

Early-stage squamous cell carcinoma of the glottic larynx is commonly treated with 2-dimensional or 3-dimensional conventional radiation therapy (CRT). Despite its use in other head and neck cancers, intensity-modulated radiation therapy (IMRT) remains controversial in this patient population. A systematic review was performed by querying 3 databases (Pubmed, Embase, Web of Science) for articles published between December 1, 2000 and September 2, 2022. Included studies reported outcomes in at least 10 patients treated with IMRT for early-stage glottic cancer. Data were extracted and reported following PRISMA standards. Pooled outcomes were estimated using random-effects models. Primary outcome was the rate of local failure (LF) following IMRT. Secondary outcomes included rates of regional failure (RF) following IMRT and rates of LF and RF following CRT. A total of 15 studies (14 retrospective, 1 prospective) consisting of 2083 patients were identified. IMRT was used in 873 patients (64% T1, 28% T2). Multiple treatment (partial larynx, single vocal cord carotid sparing) and image-guided radiation therapy techniques were used. The pooled crude rate of LF was 7.6% (95% confidence inverval [CI], 3.6%-11.5%) and actuarial LF rates at 3 and 5 years were 6.3% (95% CI, 2.2%-10.3%) and 9.0% (95% CI, 4.4%-13.5%), respectively. The pooled crude rate of RF after IMRT was 1.5% (95% CI, 0.5%-2.5%). On metaregression analysis, increased rate of LF was significantly associated with T2 disease (P < .001) and grade 2 to 3 histology (P < .001). Treatment with CRT was reported in 738 patients (76% T1, 22% T2). Among the studies reporting outcomes of both modalities, there was no significant difference in LF (log odds ratio; P=.12) or RF (log odds ratio; P=.58) between IMRT or CRT. In patients with early-stage glottic cancer, retrospective data suggests local and regional control are similar for patients treated with IMRT and CRT. Additional prospective studies with uniform methods of volume delineation and image guidance are needed to confirm the efficacy of IMRT.

Role of gastrointestinal ultrasound in image-guided radiation therapy: A review

Radiation therapy is one of the main modalities for cancer treatment. New radiotherapy techniques provide conformal radiation dose distribution and need higher accuracy in treatment delivery. Internal organ motions and displacements between and within the radiotherapy treatment fraction affect and weaken the reproducibility of delivering the planned irradiation to the target position. Image-guided radiation therapy (IGRT) can be used as a critical technology to improve patient positioning accuracy and reduce uncertainties in tumor target definition during treatment delivery. Ultrasound, a non-invasive imaging technique, is one of the important modalities in IGRT for accurate pre-treatment patient positioning and fiducial marker placement. The current study purposed to summarize recent advancements in ultrasound applications, techniques, and possible use in radiotherapy for cancers located in the abdomen and pelvic regions. We hope to give the readers a comprehensive understanding of the emerging clinical ultrasound-based IGRT applications and techniques.

Introduce a rotational robust optimization framework for spot-scanning proton arc (SPArc) therapy

Objective. Proton dosimetric uncertainties resulting from the patient’s daily setup errors in rotational directions exist even with advanced image-guided radiotherapy techniques. Thus, we developed a new rotational robust optimization SPArc algorithm (SPArcrot) to mitigate the dosimetric impact of the rotational setup error in Raystation ver. 6.02 (RaySearch Laboratory AB, Stockholm, Sweden). Approach. The initial planning CT was rotated ±5° simulating the worst-case setup error in the roll direction. The SPArcrot uses a multi-CT robust optimization framework by taking into account of such rotational setup errors. Five cases representing different disease sites were evaluated. Both SPArcoriginal and SPArcrot plans were generated using the same translational robust optimized parameters. To quantitatively investigate the mitigation effect from the rotational setup errors, all plans were recalculated using a series of pseudo-CT with rotational setup error (±1°/±2°/±3°/±5°). Dosimetric metrics such as D98% of CTV, and 3D gamma analysis were used to assess the dose distribution changes in the target and OARs. Main results. The magnitudes of dosimetric changes in the targets due to rotational setup error were significantly reduced by the SPArcrot compared to SPArc in all cases. The uncertainties of the max dose to the OARs, such as brainstem, spinal cord and esophagus were significantly reduced using SPArcrot. The uncertainties of the mean dose to the OARs such as liver and oral cavity, parotid were comparable between the two planning techniques. The gamma passing rate (3%/3 mm) was significantly improved for CTV of all tumor sites through SPArcrot. Significance. Rotational setup error is one of the major issues which could lead to significant dose perturbations. SPArcrot planning approach can consider such rotational error from patient setup or gantry rotation error by effectively mitigating the dose uncertainties to the target and in the adjunct series OARs.

Ultra-Hypo Fractionated Prostate IGRT with HDR Brachytherapy Boost as Compared to a Moderate-Hypo Fractionated Approach: Patient Reported Outcomes (PRO's) of a Phase Two Study Interim Analysis

<h3>Purpose/Objective(s)</h3> To report and compare PROs of an HDR brachytherapy (BB) combined to an ultra-hypo fractionated (UHF) prostate radiation therapy regimen as opposed to a moderate hypo fractionated (MHF). <h3>Materials/Methods</h3> This interim analysis of a prospective mono-centric phase 2 study includes 75 prostate cancer patients, mostly intermediate risk, recruited between July 2015 and September 2021. Using an image guided radiation therapy technique (IGRT), 25 Gy in 5 fractions plus 15 Gy HDR BB were delivered to the experimental arm (Exp). The control groups consisted of contemporary patients treated with IGRT and HDR BB (15 Gy) with 36 Gy in 12 fractions (Ctrl; n=119). IGRT treatment time is reported. Patient reported outcomes were collected using the International Prostate Symptom Score (IPSS) questionnaire at baseline and at each follow-up visits. A comparative linear mixed model analysis was performed on log transformed IPSS values. Expanded prostate cancer index composite-26 (EPIC-26) was also reported and compared between groups with a mixed model analysis. Biochemical relapse-free survival (BRFS) is reported. <h3>Results</h3> The 2 groups were similar with no statistical differences regarding: the median age (68 years), stage (T1C), Gleason scores (7), PSA (<10) and risk grouping (favorable intermediate). Median follow-up was 8 and 49 months respectively for Exp & Ctrl. The mixed model analysis showed that mean IPSS scores diverge with a significant difference in favor of Exp at 6, 12 and 24 months. Analysis of EPIC-26 data showed no differences throughout follow-up between Exp and Ctrl in all domains. To the patient's convenience, UHF median treatment was delivered in 7 days as compared to 17 days for MHF. Considering a short follow-up in the Exp group, its BRFS was 100% compared to 94.6 for Ctrl and these differences are not significative. <h3>Conclusion</h3> At the interim analysis, IPSS PROs for UHF treatment scheme with HDR BB seems to be significantly better tolerated at multiple FU time point compared to the control. However, there was no significant differences between groups reported with the EPIC-26. UHF treatment shorten treatment span by 10 days and given the short FU, seemingly provides similar BRFS. Therefore, we will pursue accrual to our phase 2 study.

Technical Radiotherapy Advances – The Role of Magnetic Resonance Imaging-Guided Radiation in the Delivery of Hypofractionation

Safe delivery of hypofractionated radiotherapy requires high levels of accuracy due to the high doses of radiation delivered per fraction. Magnetic resonance guided radiotherapy (MRgRT) represents a new treatment paradigm which allows improved visualisation of targets and organs at risk, alongside the capability to adapt the treatment plan in real time prior to treatment delivery. There are challenges to delivering hypofractionated radiotherapy with conventional image-guided radiotherapy (IGRT) techniques and MRgRT may help to improve accuracy in radiation delivery in a number of clinical and anatomical scenarios.Specifically, there is an emerging role of MRgRT in delivering stereotactic body radiotherapy (SBRT) for locally advanced pancreatic cancer (LAPC) due to the superior soft tissue contrast provided by Magnetic Resonance Imaging combined with the ability to accommodate variation in anatomical appearances during treatment delivery. Reported data on the use of MRgRT in LAPC and it's role in enabling dose escalation are discussed in this article.There are further potential benefits to the use of MRgRT, for example the use of functional imaging during treatment delivery and generation of synthetic computed tomography, which have previously been impractical or unachievable. The overall aim of this article is to demonstrate the utility of MRgRT in facilitating safe delivery of hypofractionated radiotherapy and to highlight ways in which it may help to overcome challenges posed by current IGRT techniques.

Artificial intelligence in image-guided radiotherapy: a review of treatment target localization.

Modern conformal beam delivery techniques require image-guidance to ensure the prescribed dose to be delivered as planned. Recent advances in artificial intelligence (AI) have greatly augmented our ability to accurately localize the treatment target while sparing the normal tissues. In this paper, we review the applications of AI-based algorithms in image-guided radiotherapy (IGRT), and discuss the indications of these applications to the future of clinical practice of radiotherapy. The benefits, limitations and some important trends in research and development of the AI-based IGRT techniques are also discussed. AI-based IGRT techniques have the potential to monitor tumor motion, reduce treatment uncertainty and improve treatment precision. Particularly, these techniques also allow more healthy tissue to be spared while keeping tumor coverage the same or even better.

Advanced Radiotherapy Techniques for Mediastinal Lymphomas: Results from an Italian Survey

Background: Multiple methods have been implemented to limit the impact of radiotherapy on patients affected by mediastinal lymphoma, including breathing control techniques, image-guided radiotherapy (IGRT) and intensity-modulated radiotherapy (IMRT), although the actual diffusion of such techniques is unclear. No surveys have been published to date evaluating the techniques adopted at different centers. Methods: A survey with a dedicated questionnaire was submitted to 195 Italian radiotherapy centers, assessing items regarding the characteristics of the center and clinical practice in the treatment of mediastinal lymphomas. Results: A total of 43 centers (22%) responded, the majority of which were university hospitals (37.2%) or cancer care centers (27.9%). In 95.4% of the centers, IMRT was used in the clinical practice, and the most frequently employed techniques were VMAT (48.8% of centers) and non-rotational IMRT (31.7%). Comparison of multiple plans was performed by 66.7% of the responding centers. Dose constraints for organs at risk were consistently prescribed. IGRT techniques were adopted by 93% of the centers, while breathing control or gating techniques were routinely used by only 25.6% of the centers. A necessity to standardize OAR constraints and define guidelines was perceived by almost all participants. Conclusions: Modern radiotherapy techniques are widely used in the Italian centers, although with heterogeneous characteristics.

Outcomes of patients with nasopharyngeal carcinoma treated with intensity-modulated radiotherapy.

Nasopharyngeal cancer shows a good response to intensity-modulated radiotherapy. However, there is no clear evidence for the benefits of routine use of image-guided radiotherapy. The purpose of this study was to perform a retrospective investigation of the treatment outcomes, treatment-related complications and prognostic factors for nasopharyngeal cancer treated with intensity-modulated radiotherapy and image-guided radiotherapy techniques. Retrospective analysis was performed on 326 consecutive nasopharyngeal cancer patients treated between 2004 and 2015. Potentially significant patient-related and treatment-related variables were analyzed. Radiation-related complications were recorded. The 5-year overall survival and disease-free survival rates of these patients were 77.9% and 70.5%, respectively. Age, AJCC (American Joint Committee on Cancer) stage, retropharyngeal lymphadenopathy, treatment interruption and body mass index were independent prognostic factors for overall survival. Age, AJCC stage, retropharyngeal lymphadenopathy, image-guided radiotherapy and body mass index were independent prognostic factors for disease-free survival. In conclusion, intensity-modulated radiotherapy significantly improves the treatment outcomes of nasopharyngeal cancer. With the aid of image-guided radiotherapy, the advantage of intensity-modulated radiotherapy might be further amplified.

Hypofractionated Radiation Therapy to the Prostate Bed With Intensity-Modulated Radiation Therapy (IMRT): A Phase 2 Trial

Postoperative radiation therapy (RT) is a common therapy used for patients with prostate cancer. Although clinical trials have established the safety and efficacy of hypofractionation as a primary therapy, there are limited data in a postoperative setting. We conducted a prospective trial to evaluate the safety and feasibility of postoperative hypofractionated RT to the prostate bed. In this phase 2 trial, patients submitted to radical prostatectomy were treated with hypofractionated RT to the prostate bed (adjuvant or salvage). The prescribed dose was 51 Gy in 15 fractions (3.4 Gy per fraction), using intensity modulated and image guided radiation therapy techniques. The primary endpoint was the rate of acute genitourinary (GU) grade ≥2 toxicity. Secondary endpoints included acute gastrointestinal (GI) and late GU/GI toxicities, biochemical failure-free survival (BFFS), metastasis-free survival, cancer-specific survival, overall survival, and health-related quality of life. Of 64 enrolled patients, 61 received radiation therapy (57 salvage and 4 adjuvant radiation therapy). After a median follow-up of 16 months, 11.5% of patients experienced acute grade ≥2 GU symptoms and 13.1% experienced acute grade ≥2 GI symptoms. The late grade ≥2 GU toxicity rate was 8.2%, and 1 patient (1.6%) developed both acute and late grade 3 GU toxicity. The late grade ≥2 GI toxicity rate was 11.5%, and no grade 3 GI adverse events were reported. The short follow-up limits our ability to perform a robust oncologic endpoint assessment; however, the 2-year BFFS, use of subsequent salvage therapy, and the development of metastasis were 95.1%, 0%, and 0%, respectively. Hypofractionated RT to the prostate bed in 15 treatments was safe, with an acceptable GU and GI toxicity profile. Further study in large, randomized trials is warranted.

The contribution of surgical clips for optimizing highly-conformal image-guided flank irradiation in pediatric renal tumors: A single center experience

Background and aimsTwo-opposing photon beams are considered standard of care for flank irradiation in pediatric patients with renal tumors. Nowadays, Image-Guided Radiotherapy (IGRT) techniques allow high-precision dose delivery to complex flank target volumes taking into account postoperative organ shifts and tumor bed motion. This study examines the contribution of a lateral and superior surgical clip on flank target volume delineation intended for IGRT. MethodsBetween 01-2015 and 09-2019, 30/162 newly-diagnosed pediatric patients with renal tumors, lateral/superior surgical clips (n = 30/30) and available 4D-CT-scans (n = 27/30), underwent postoperative flank irradiation. The lateral and superior clip, as respective markers for the lateral tumor extension and intrafraction motion, were analyzed. The positive and negative values depict the lateral/dorsal/cranial or the medial/ventral/caudal direction, respectively. Planning target volumes (PTV) were generated based on lateral clips (PTVlatclip), superior clips with 4D-CT technology (PTVsupclip), and both clips combined (PTVcombined), and compared to an approach without clips (PTVnoclip). ResultsIndicated by clips, the mean lateral tumor bed extension along the posterior wall was 74° (range: 50°–93°), while mean intrafraction motion was +1.2 mm (range: −1.8/+4.8 mm), +0.6 mm (range: +0.6/+4.9 mm), −0.3 mm (range: −3.8/+0.7 mm) in craniocaudal, ventrodorsal, mediolateral direction, respectively. The median PTVnoclip (556 mL) was statistically different from the median PTVlatclip (454 mL, p = <0.01), median PTVsupclip (373 mL, p = <0.01) and median PTVcombined (348 mL p = <0.01). ConclusionIn pediatric patients with renal tumors, surgical clips at the lateral and superior border of the tumor bed can optimize flank target volume delineation and, consequently, reduce the normal tissue volume receiving high-dose irradiation when IGRT techniques are applied.

Management Perspective on How to Plan and Deliver Image-guided Radiotherapy – Experience of the Oxford Cancer Centre Over the Past 10 Years

It is well established within the radiotherapy community that image-guided radiotherapy (IGRT) is in a perpetual state of evolution and requires a multi-professional approach to ensure early adoption of new equipment and IGRT techniques and that processes are implemented rapidly and successfully within radiotherapy departments. We aim to use the example of the development of IGRT over a 10-year period, in a single centre, to highlight the different aspects involved in planning IGRT delivery.

A six-degree-of-freedom robotic motion system for quality assurance of real-time image-guided radiotherapy

In this study we develop and characterise a six degree-of-freedom (6 DoF) robotic motion system for quality assurance of real-time image-guided radiotherapy techniques. The system consists of a commercially available robotic arm, an acrylic phantom with embedded Calypso markers, a custom base plate to mount the robot to the treatment couch, and control software implementing the appropriate sequence of transformations to reproduce measured tumour motion traces. The robotic motion system was evaluated in terms of the set-up and motion trace repeatability, static localization accuracy and dynamic localization accuracy. Four prostate, two liver and three lung motion traces, representing a range of tumor motion trajectories recorded in real patient treatments, were executed using the robotic motion system and compared with motion measurements from the clinical Calypso motion tracking system. System set-up and motion trace repeatability was better than 0.5 deg and 0.3 mm for rotation and translation, respectively. The static localization accuracy of the robotic motion system in the LR, SI and AP directions was 0.09 mm, 0.08 mm and 0.02 mm for translations, respectively, and 0.2°, 0.06° and 0.06° for rotations, respectively. The dynamic localization accuracy of the robotic motion system was <0.2 mm and <0.6° for translations and rotations, respectively. Thus, we have demonstrated the ability to accurately mimic rigid-body tumor motion using a robotically controlled phantom to provide precise geometric QA for advanced radiotherapy delivery approaches.

Complementary Relation Between the Improvement of Dose Delivery Technique and PTV Margin Reduction in Dose-Escalated Radiation Therapy for Prostate Cancer

PurposeThe purpose of this study is to demonstrate quantitatively the complementary relationship between the introduction of intensity modulated radiation therapy (IMRT) and planning target volume (PTV) margin reduction with an image guided technique in reducing the risk of rectal toxicity in dose-escalating prostate radiation therapy. Methods and MaterialsThree-dimensional conformal radiation therapy (CRT) and IMRT plans were generated for 10 patients with prostate cancer based on 2 PTV margin protocols (10/8 mm and 6/5 mm) and 2 dose prescriptions (70 Gy and 78 Gy). The normal tissue complication probability (NTCP) for each of the 8 scenarios was calculated using the Lyman-Kutcher-Burman model to estimate the risk of rectal and bladder late toxicity. The conformity and homogeneity indices of PTVs were calculated for each plan. ResultsThe IMRT plans showed superiority in conformity and inferiority in homogeneity over 3-dimensional CRT plans. The rectal NTCPs were increased 3.5 to 4.1 times when the prescribed total dose was changed from 70 Gy to 78 Gy and the dose delivery and the image guided radiation therapy techniques remained unchanged. PTV margin reduction was shown to reduce the value of rectal NTCP significantly. Overall, implementing the IMRT technique alone could reduce the NTCP values only by 2.1% to 7.3% from those of 3-dimensional CRT. The introduction of both IMRT and PTV margin reduction was found to be necessary for rectal NTCP to remain <5% in the dose escalation from 70 to 78 Gy. ConclusionsThe complementary relationship between the introduction of IMRT and PTV margin reduction was proven. We found that both approaches need to be implemented to safely deliver a curative dose in dose-escalating prostate radiation therapy.

The Potential Value of MRI in External-Beam Radiotherapy for Cervical Cancer

The reference standard treatment for cervical cancer is concurrent chemoradiotherapy followed by magnetic resonance imaging (MRI)-guided brachytherapy. Improvements in brachytherapy have increased local control rates, but late toxicity remains high with rates of 11% grade ≥3. The primary clinical target volume (CTV) for external-beam radiotherapy includes the cervix and uterus, which can show significant inter-fraction motion. This means that generous margins are required to cover the primary CTV, increasing the radiation dose to organs at risk and, therefore, toxicity. A number of image-guided radiotherapy techniques (IGRT) have been developed, but motion can be random and difficult to predict prior to treatment. In light of the development of integrated MRI linear accelerators, this review discusses the potential value of MRI in external-beam radiotherapy. Current solutions for managing pelvic organ motion are reviewed, including the potential for online adaptive radiotherapy. The impacts of the use of MRI in tumour delineation and in the delivery of stereotactic ablative body radiotherapy (SABR) are highlighted. The potential role and challenges of using multi parametric MRI to guide radiotherapy are also discussed.

An end-to-end postal audit test to examine the coincidence between the imaging isocenter and treatment beam isocenter of the IGRT linac system for Japan Clinical Oncology Group (JCOG) clinical trials

PurposeThe aim of this study was to develop an end-to-end postal audit test to examine the coincidence between the imaging isocenter and treatment beam isocenter of the image guided radiotherapy (IGRT) linac system for Japan Clinical Oncology Group (JCOG) trials, as a part of IGRT credentialing of institutions participating in JCOG trials. MethodsWe developed an end-to-end postal audit test to verify radiation positional errors associated with IGRT techniques. This test is intended for simulating a clinical IGRT flow and uses a static cubic phantom measuring 15 × 15 × 15 cm3 and weighing approximately 3.4 kg. The phantom has four gold fiducial markers and a spherical dummy target for setup, with known shift values from the phantom center. Two pairs of Gafchromic RTQA2 films were inserted 5 mm from the phantom’s anterior-posterior and right-left surfaces. Radiation positional errors at the isocenter were determined by analyzing the center of the radiation field on the films and the known shift values of the dummy target. The test was performed on 47 IGRT devices at 35 institutions. ResultsRadiation positional errors were within acceptance levels (1 mm/1°) for 42 IGRT devices (89.4%) in the first check. Median time to complete IGRT credentialing was 11.5 days. This audit method was applicable for any radiotherapy machine with an IGRT device. ConclusionsA postal audit test to verify radiation positional errors for JCOG trials was successfully developed. In the postal audit, all but one institution passed this credentialing item within two trials.

La radiothérapie externe guidée par l’imagerie dans le cancer de la prostate ; comment, quand et pourquoi ?

Novel techniques of prostate cancer radiotherapy require increased precision, which is allowed by Image Guided Radiation Therapy (IGRT), using fiducial markers and orthogonal radiographs, cone beam computed tomography, magnetic resonance imaging, ultrasound, and/or transponders. IGRT may reduce the toxicity of radiation therapy, but there is no clear recommendation on the best IGRT technique and how often it should be applied.

Image-guided radiotherapy for prostate cancer.

Intensity-modulated radiotherapy (IMRT) has become the standard radiotherapy technology utilized for the treatment of prostate cancer, as it permits the delivery of highly conformal radiation dose distributions. Image-guided radiotherapy (IGRT) is an essential companion to IMRT that allows the treatment team to account for daily changes in target anatomy and positioning. In the present review, we will discuss the different sources of geometric uncertainty and review the rationale behind using IGRT in the treatment of prostate cancer. We will then describe commonly employed IGRT techniques and review their benefits and drawbacks. Additionally, we will review the evidence suggesting a potential clinical benefit to utilizing IGRT.

The need for, and implementation of, image guidance in radiation therapy.

The introduction of image guidance in radiation therapy and its subsequent innovations have revolutionised the delivery of cancer treatment. Modern imaging systems can supplement and often replace the historical practice of relying on external landmarks and laser alignment systems. Rather than depending on markings on the patient's skin, image-guided radiation therapy (IGRT), using techniques such as computed tomography (CT), cone beam CT, MV on-board imaging (OBI), and kV OBI, allows the patient to be positioned based on the internal anatomy. These advances in technology have enabled more accurate delivery of radiation doses to anatomically complex and temporally changing tumour volumes, while simultaneously sparing surrounding healthy tissues. While these imaging modalities provide excellent bony anatomy image quality, magnetic resonance imaging (MRI) surpasses them in soft tissue image contrast for better visualisation and tracking of soft tissue tumours with no additional radiation dose to the patient. However, the introduction of MRI into a radiotherapy facility has a number of complications, including the influence of the magnetic field on the dose deposition, as well as the effects it can have on dosimetry systems. The development and introduction of these new IGRT techniques will be reviewed, and the benefits and disadvantages of each will be described.

Monitoring Tumor Lung Irradiation With Megavoltage Patient-Scattered Radiation: A Full System Simulation Study

We analyze by simulation a fully-3-D, low-dose imaging system aiming at assisting external-beam radiotherapy, either for on-board patient imaging, or for real-time radiotherapy monitoring. The system consists in detecting megavoltage patient-scattered radiation that is emitted at right angles with respect to the beam axis. Since photon scattering in the patient occurs with higher intensity in tissues of higher density, a multislice photon detection system positioned perpendicularly to the beam axis yields a signal correlated with patient morphology, including the tumor. We thus report on GEANT4 simulations carried out with an anthropomorphic phantom in order to analyze the capability of the system to detect pertinent and clinically relevant scenarios, e.g., lung tumor deviation and tumor regression/progression. The signal distribution obtained with a realistic full system (including the multislice collimator, the scintillator crystals, and the charge electronic readout mode) show a very high visual agreement both with the simulated, prescribed dose, and with the tumor location/size, as well as with the phantom structures. The capability of this system to obtain morphological images without X-ray source rotation potentially allows to highly reduce dose in healthy tissues and organs at risk in respect to other existing image-guided radiation therapy techniques, thus complementing them.

Post-Prostatectomy Image-Guided Radiotherapy: The Invisible Target Concept.

In the era of intensity-modulated radiation therapy, image-guided radiotherapy (IGRT) appears crucial to control dose delivery and to promote dose escalation while allowing healthy tissue sparing. The place of IGRT following radical prostatectomy is poorly described in the literature. This review aims to highlight some key points on the different IGRT techniques applicable to prostatic bed radiotherapy. Furthermore, methods used to evaluate target motion and to reduce planning target volume margins will also be explored.