Internal Organ Motion Research Articles

Francis Sibson (1814–1876): The Unsung Hero of Modern Surgery and Anesthesia

Francis Sibson (1814-1876) was a British physician and anatomist widely regarded as a true pioneer of the medical profession. He overcame a tragic and difficult childhood to become an avid educator at several medical schools and dedicated his life to research. For modern scientists, he is most remembered for describing Sibson's fascia, his experimental use of curare in the treatment of hydrophobia and tetanus, and his detailed description of the positions and movements of internal organs. He died on September 7, 1876 at the age of 62 from complications of an aortic aneurysm.

Quality assurance for image‐guided radiation therapy utilizing CT‐based technologies: A report of the AAPM TG‐179

Commercial CT-based image-guided radiotherapy (IGRT) systems allow widespread management of geometric variations in patient setup and internal organ motion. This document provides consensus recommendations for quality assurance protocols that ensure patient safety and patient treatment fidelity for such systems. The AAPM TG-179 reviews clinical implementation and quality assurance aspects for commercially available CT-based IGRT, each with their unique capabilities and underlying physics. The systems described are kilovolt and megavolt cone-beam CT, fan-beam MVCT, and CT-on-rails. A summary of the literature describing current clinical usage is also provided. This report proposes a generic quality assurance program for CT-based IGRT systems in an effort to provide a vendor-independent program for clinical users. Published data from long-term, repeated quality control tests form the basis of the proposed test frequencies and tolerances. A program for quality control of CT-based image-guidance systems has been produced, with focus on geometry, image quality, image dose, system operation, and safety. Agreement and clarification with respect to reports from the AAPM TG-101, TG-104, TG-142, and TG-148 has been addressed.

4D CT image acquisition errors in SBRT of liver identified using correlation

In the AAPM Report 80,( 1 ) the imaging modality of 4D CT and respiration‐correlated CT was declared a “promising solution for obtaining high‐quality CT data in the presence of respiratory motion”. To gather anatomically correct data over time, the existence of correlation between the internal organ movement and an external surrogate has to be assumed. For the in‐house evaluation of such correlation, we retrospectively analyzed 21 four‐dimensional computer tomography (4D CT) scans of five patients, out of which the artifacts experienced in three patients are shown here. To provide context and a baseline for the analysis of patient motion, a real‐tissue liver phantom was used with a solid water block and liver tissue. The superior–inferior motion of fiducials in phantom and patients was correlated to the recorded anterior–posterior motion of an external surrogate marker on the chest. The use of a solid water block yielded a measurable correlation coefficient of 0.98 or better using a sinusoidal animation pattern. With sinusoidally‐animated liver tissue, the minimum correlation observed was 0.96. Comparing this to retrospective patient data, we found three cases of a change in the correlation coefficient, or simply a low correlation. The source of this low correlation was investigated by careful examination of the breathing traces and the CT‐phase assignments used to reconstruct the datasets. Consequences of nonregular breathing are elaborated on. We demonstrate the impact of wrong phase assignments and missing image information in the 4D CT phase sampling processes. We also show how daily patient‐based correlation analysis can indicate changes in breathing traces, which can be significant enough to decrease, or completely eliminate, previously existing correlation.PACS numbers: 87.57.‐s, 87.57.Q‐, 87.57.cp, 87.57.N‐, 87.55.Qr

Technology with High-Speed Movies to Analyze the Movement of Internal Organs in Medaka

Technology with High-Speed Movies to Analyze the Movement of Internal Organs in Medaka

4D radiation therapy for prostate cancer

To further improve the clinical outcome and cost-effectiveness of radiation therapy for prostate patient, dose escalation and hypofractionated treatments are being implemented. Reducing the treatment margin is an essential way to satisfy the requirements for increased doses to the target volume and decreased doses to nearby critical structures, which depends on the patient setup error and internal organ motion effects. New image-guided localisation technologies and 4-dimensional (4D) treatment can improve the setup accuracy and significantly reduce effects of the time-dependent motion. This article discusses the effects of intrafractional motion of prostate and the technologies to perform 4D radiation therapy treatments.

First Clinical Release of an Online, Adaptive, Aperture-Based Image-Guided Radiotherapy Strategy in Intensity-Modulated Radiotherapy to Correct for Inter- and Intrafractional Rotations of the Prostate

We developed and evaluated a correction strategy for prostate rotations using direct adaptation of segments in intensity-modulated radiotherapy (IMRT). Implanted fiducials (four gold markers) were used to determine interfractional translations, rotations, and dilations of the prostate. We used hybrid imaging: The markers were automatically detected in two pretreatment planar X-ray projections; their actual position in three-dimensional space was reconstructed from these images at first. The structure set comprising prostate, seminal vesicles, and adjacent rectum wall was transformed accordingly in 6 degrees of freedom. Shapes of IMRT segments were geometrically adapted in a class solution forward-planning approach, derived within seconds on-site and treated immediately. Intrafractional movements were followed in MV electronic portal images captured on the fly. In 31 of 39 patients, for 833 of 1013 fractions (supine, flat couch, knee support, comfortably full bladder, empty rectum, no intraprostatic marker migrations >2 mm of more than one marker), the online aperture adaptation allowed safe reduction of margins clinical target volume-planning target volume (prostate) down to 5 mm when only interfractional corrections were applied: Dominant L-R rotations were found to be 5.3° (mean of means), standard deviation of means ±4.9°, maximum at 30.7°. Three-dimensional vector translations relative to skin markings were 9.3 ± 4.4 mm (maximum, 23.6 mm). Intrafractional movements in 7.7 ± 1.5 min (maximum, 15.1 min) between kV imaging and last beam's electronic portal images showed further L-R rotations of 2.5° ± 2.3° (maximum, 26.9°), and three-dimensional vector translations of 3.0 ±3.7 mm (maximum, 10.2 mm). Addressing intrafractional errors could further reduce margins to 3 mm. We demonstrated the clinical feasibility of an online adaptive image-guided, intensity-modulated prostate protocol on a standard linear accelerator to correct 6 degrees of freedom of internal organ motion, allowing safe and straightforward implementation of margin reduction and dose escalation.

Four‐dimensional magnetic resonance imaging (4D‐MRI) using image‐based respiratory surrogate: A feasibility study

Four-dimensional computed tomography (4D-CT) has been widely used in radiation therapy to assess patient-specific breathing motion for determining individual safety margins. However, it has two major drawbacks: low soft-tissue contrast and an excessive imaging dose to the patient. This research aimed to develop a clinically feasible four-dimensional magnetic resonance imaging (4D-MRI) technique to overcome these limitations. The proposed 4D-MRI technique was achieved by continuously acquiring axial images throughout the breathing cycle using fast 2D cine-MR imaging, and then retrospectively sorting the images by respiratory phase. The key component of the technique was the use of body area (BA) of the axial MR images as an internal respiratory surrogate to extract the breathing signal. The validation of the BA surrogate was performed using 4D-CT images of 12 cancer patients by comparing the respiratory phases determined using the BA method to those determined clinically using the Real-time position management (RPM) system. The feasibility of the 4D-MRI technique was tested on a dynamic motion phantom, the 4D extended Cardiac Torso (XCAT) digital phantom, and two healthy human subjects. Respiratory phases determined from the BA matched closely to those determined from the RPM: mean (± SD) difference in phase: -3.9% (± 6.4%); mean (± SD) absolute difference in phase: 10.40% (± 3.3%); mean (± SD) correlation coefficient: 0.93 (± 0.04). In the motion phantom study, 4D-MRI clearly showed the sinusoidal motion of the phantom; image artifacts observed were minimal to none. Motion trajectories measured from 4D-MRI and 2D cine-MRI (used as a reference) matched excellently: the mean (± SD) absolute difference in motion amplitude: -0.3 (± 0.5) mm. In the 4D-XCAT phantom study, the simulated "4D-MRI" images showed good consistency with the original 4D-XCAT phantom images. The motion trajectory of the hypothesized "tumor" matched excellently between the two, with a mean (± SD) absolute difference in motion amplitude of 0.5 (± 0.4) mm. 4D-MRI was able to reveal the respiratory motion of internal organs in both human subjects; superior-inferior (SI) maximum motion of the left kidney of Subject #1 and the diaphragm of Subject #2 measured from 4D-MRI was 0.88 and 1.32 cm, respectively. Preliminary results of our study demonstrated the feasibility of a novel retrospective 4D-MRI technique that uses body area as a respiratory surrogate.

Technological advances in radiotherapy for cervical cancer

To discuss the important technological advances that have taken place in the planning and delivery of both external beam radiotherapy and brachytherapy for patients with locally advanced cervical cancer, and the implications for improved clinical outcomes. Technological advances in external beam radiation treatment and brachytherapy for patients with cervical cancer allow more precise targeting of tumour and relative sparing of surrounding normal organs and tissues. Early evidence is emerging to indicate that these advances will translate into improvements in tumour control and reduced side effects. However, there are patient, tumour and treatment-related factors that can detract from these benefits. Foremost among these is complex, unpredictable and sometimes dramatic internal tumour and normal organ motion during treatment. The focus of current research and clinical development is on tracking internal anatomic change in individual patients and adapting treatment plans as required to assure that optimal tumour coverage and normal tissue sparing is maintained at all times. The success of this approach will depend on clear definitions of target volumes, high resolution daily soft tissue imaging, and new software tools for rapid contouring, treatment planning and quality assurance. Radiation treatment of locally advanced cervical cancer is evolving rapidly, driven by advances in technology, towards more individualized patient care that has the potential to substantially improve clinical outcomes.

SU‐E‐T‐838: Inverse‐Planned Multi‐Beam Intensity‐Modulated Radiation Therapy versus Three‐Dimensional Conformal Radiotherapy for Left Breast Cancer Patients after Mastectomy

Purpose: The purpose of this study was to compare dose distribution and normal tissue sparing in the treatment of left chest wall, as well as supraclavicular nodes (SCV), and, in one case, internal mammary nodes (IMN) for patients undergoing post mastectomy radiation using three‐dimensional conformal radiotherapy (3D‐CRT) vs. multi‐beam intensity‐modulated radiotherapy (IMRT). Methods: To date, a total of five patients were randomly selected for comparison. All the planning target volumes (PTV) were contoured according to the Breast Cancer Atlas for the Radiation Therapy Planning from Radiation Therapy Oncology Group (RTOG). A dose of 5040cGy was prescribed in 28 fractions to each PTV. Two plans were evaluated for each patient, one with beam split tangents and an additional supraclavicular field for 3D‐CRT, and the other one with five inverse‐planned IMRT beams. To obtain the desired skin dose, bolus was used every other day. Dose comparison metrics included: PTV homogeneity index (HI) and conformity index (CI), V30 and V5, and mean and maximum doses to normal tissue structures, such as heart, left lung, right lung, contralateral chest wall, and V20 to both lungs. Results: Compared to a conventional 3D‐CRT plan, the five‐field IMRT significantly improved PTV HI and CI, and marginally reduced heart and left lung maximum doses without compromising PTV coverage, but at the same time increased contralateral chest wall and lung dose, and heart V5. Conclusions: Five‐field IMRT plan provides far superior target volume coverage and comparable heart V30 and lung V20 to a conventional plan, while increasing low dose to contralateral side. The use of five beams —instead of 9 or 11, as recommended by other studies‐ reduces the treatment time and, consequently, possible setup and internal organ motion errors. Further clinical studies are needed to determine whether IMRT improves tumor control or reduces acute or late toxicities when compared to 3D‐CRT.

TH-A(SAM)-BRC-01: Physics and Dosimetry of SBRT

SBRT is a novel cancer treatment strategy where ultra-high doses per fraction are used, generally in the range of 6 to 20 Gy per fraction, in a hypofractionated regimen of 5 or fewer fractions. Such high doses per treatment were inconceivable in the past because of concerns about radiation-induced injury to normal tissue if large volumes of OARs were irradiated to high doses. However, with recent technical advancements in highly-conformal treatment planning, image-guided radiotherapy, and delivery technologies, it has become possible to deliver safely very large fractional doses of radiation to lesions in the lung, liver, spine, and prostate. Since SBRT involves technically sophisticated patient repositioning and treatment delivery procedure, it is not uncommon for a treatment to last 40 minutes. Clinicians are usually concerned of a possible compromise in treatment efficacy for individual fractions that require long treatment time because of tumor intra-fraction motion and patient involuntary movement during radiation delivery, as well as a theoretical risk of intra-fractional radiation damage repair within tumor cells in the context of prolonged fractional delivery time. In this session, methods for effective, optimal and accurate planning, and efficiency and robustness in the delivery of SBRT, including QA, will be presented so that these concerns are minimized. Furthermore, the technical challenges associated with the clinical implementation of SBRT will be discussed, thereby allowing the wide application of SBRT using current treatment planning and delivery technologies (fixed-field 3DCRT/IMRT, dynamic arcs, rotational IMRT). The specific objectives of the session are to: 1. Describe secure and comfortable immobilization techniques to minimize patient movement, techniques accounting for internal organ motion, and accurate patient repositioning methods using online imaging 2. Discuss treatment planning methods to ensure coverage of tumor volume within high dose regions with very rapid fall-off to surrounding OARs, including the use of Monte Carlo algorithms 3. Describe quality assurance and verification techniques for fixed-field (3DCRT, IMRT) and rotational (static/dynamic arcs, VMAT/Rapid Arc/Tomo) delivery, usually characterized by many small beam segments, and the assessment of target conformity coverage, and high dose “spillage” region

SU-E-T-504: Development of An Offline Based Internal Organ Motion Verification System during Treatment Using Sequential Cine EPID Images

Purpose: We developed an offline based organ motion verification system using cine EPID images and evaluated its accuracy and availability through phantom study. Methods: The system was designed for import of cine EPID images, which are obtained sequentially during treatment through a DICOM format and reconstructed into a live image. For verification of organ motion, a pattern matching algorithm using an internal surrogate was employed in the self-developed analysis software. For the system performance test, we developed a linear motion phantom, which consists of a human body shaped phantom with a fake tumor in the lung and linear motion cart with control software. The phantom was operated with a motion of 2 cm at 4 sec per cycle and cine EPID images were obtained at a rate of 3.3 frames/sec with 1024 × 768 pixel counts in a linear accelerator (10 MVX). Organ motion of the target was tracked using self-developed analysis software and compared with data from the RPM system (Varian, USA). For quantitative analysis, we analyzed correlation between two data sets in terms of average cycle, amplitude, and pattern (root mean square, RSM) of motion. Results: Averages for the cycle of motion from cine EPID and RPM system were 3.95±0.02 and 3.98±0.11 sec, respectively, and showed good agreement on real value (4 sec). Average of the amplitude of motion tracked by our system (1.71 ±0.02 cm) showed a slightly different value, compared with the actual value (2 cm), due to time resolution for image acquisition. The value of the RMS from the cine EPID image (0.379) grew slightly, by 3.8%, compared with data from the RPM (0.365). Conclusions: Our system showed good representation of its motion in a preliminary phantom study. The system can be implemented for clinical purposes, which include organ motion verification and its feedback for accurate dose delivery to the moving target.

196 speaker A CRITICAL OVERVIEW OF ARC THERAPY TECHNIQUES

The methodology for precision radiotherapy remains appropriate target volume delineation and treatment planning followed by reliable and accurate dose delivery over the entire course of radiotherapy. It is well recognised that one of the limitations for precision radiotherapy whether it is delivered by conformal or intensity modulated external beam radiotherapy is the presence of internal organ and target motion. This lecture will focus mainly on external beam therapies rather than on brachytherapy but accurate definition of implanted volumes is also a crucial element of quality brachytherapy. Amongst the recent strategic developments to account for temporal spatial variations noted during radiotherapy delivery is the use of adaptive therapy. The adaptive strategy uses repeated cross sectional imaging to determine the magnitude of systematic and random components of target variability for the individual patient. This imaging process often involves several feedback loops that may be either on-line or off-line to reduce the spatial positional uncertainty inherent in the initial radiotherapy treatment planning scan. Once the magnitude of the temporal spatial variations is quantified, the modifications to the treatment plan can be initiated and implemented. This process will still require verification and may need further optimisation where appropriate. Initially proposed and utilised in prostate radiotherapy, it was reported to significantly reduce the mean systematic error from 4 mm to 0.5 mm. It has since been investigated for other tumour subsites such as bladder, cervical as well as liver and other deformable target sites. In bladder radiotherapy where the target organ is the bladder, there can be substantial variation in both the position and size of the organ of up t. there is good evidence to define individual patterns of bladder filling reliably. Using this information, it is possible to predict the size of the bladder at the time of irradiation subsequent to the use of daily volumetric imaging on the LINAC. This strategy termed predictive organ localisation (POLO) has been tested and can be implemented clinically using a library of predefined plans based on the a-priori knowledge of the deformed bladder. Further refinement on this strategy Adaptive-POLO (APOLO) uses a wider range of library plans for daily on-line adaptive therapy. This has been implemented in routine clinical practice and can be utilised within a standard radiotherapy treatment slot. There will need to be education and training needs for radiotherapy staff. Other important issues include resource allocation. The potential clinical benefits for these adaptive strategies will need to be fully assessed in clinical trials to quantify the magnitude of benefit for our patients.

Radiosensibilité, radiocurabilité et réparation

Improvements in accuracy stand as the heart of the success of today's radiotherapy. The dose may be delivered with a sub millimetric accuracy, may also conform to complex shapes, or track external and internal organ motions. In parallel, we may increase the tumour's radiocurability by modulating the biological effects generated by ionizing radiation into the patient. It was precisely the topic of the 2009′ Lucien-Mallet prize organized by the French Society for Radiation Oncology (SFRO) and the Centre Antoine-Béclère under the auspices of the Fondation de France. In this review we will precisely describe the integrated molecular response to ionizing radiations. Starting from early observations, we are going to introduce the concept of cellular radiosensitivity as the global response of the irradiated cell. We will then focus into the cell and especially its nucleus. We will describe here the most complex and deleterious radio-induced damages. In the next chapter, we will dissect the molecular pathway that aims to detect and repair the previous lesions. The last part of the review will finally deal with the diagnostic, prognostic and therapeutic impacts emerging from the alliance between clinical and molecular radiobiology.

Sensitivity of postplanning target and OAR coverage estimates to dosimetric margin distribution sampling parameters

A dosimetric margin (DM) is the margin in a specified direction between a structure and a specified isodose surface, corresponding to a prescription or tolerance dose. The dosimetric margin distribution (DMD) is the distribution of DMs over all directions. Given a geometric uncertainty model, representing inter- or intrafraction setup uncertainties or internal organ motion, the DMD can be used to calculate coverage Q, which is the probability that a realized target or organ-at-risk (OAR) dose metric D, exceeds the corresponding prescription or tolerance dose. Postplanning coverage evaluation quantifies the percentage of uncertainties for which target and OAR structures meet their intended dose constraints. The goal of the present work is to evaluate coverage probabilities for 28 prostate treatment plans to determine DMD sampling parameters that ensure adequate accuracy for postplanning coverage estimates. Normally distributed interfraction setup uncertainties were applied to 28 plans for localized prostate cancer, with prescribed dose of 79.2 Gy and 10 mm clinical target volume to planning target volume (CTV-to-PTV) margins. Using angular or isotropic sampling techniques, dosimetric margins were determined for the CTV, bladder and rectum, assuming shift invariance of the dose distribution. For angular sampling, DMDs were sampled at fixed angular intervals w (e.g., w = 1 degree, 2 degrees, 5 degrees, 10 degrees, 20 degrees). Isotropic samples were uniformly distributed on the unit sphere resulting in variable angular increments, but were calculated for the same number of sampling directions as angular DMDs, and accordingly characterized by the effective angular increment omega eff. In each direction, the DM was calculated by moving the structure in radial steps of size delta (=0.1, 0.2, 0.5, 1 mm) until the specified isodose was crossed. Coverage estimation accuracy deltaQ was quantified as a function of the sampling parameters omega or omega eff and delta. The accuracy of coverage estimates depends on angular and radial DMD sampling parameters omega or omega eff and delta, as well as the employed sampling technique. Target deltaQ/ < l% and OAR /deltaQ/ < 3% can be achieved with sampling parameters omega or omega eef = 20 degrees, delta =1 mm. Better accuracy (target /deltaQ < 0.5% and OAR /deltaQ < approximately 1%) can be achieved with omega or omega eff = 10 degrees, delta = 0.5 mm. As the number of sampling points decreases, the isotropic sampling method maintains better accuracy than fixed angular sampling. Coverage estimates for post-planning evaluation are essential since coverage values of targets and OARs often differ from the values implied by the static margin-based plans. Finer sampling of the DMD enables more accurate assessment of the effect of geometric uncertainties on coverage estimates prior to treatment. DMD sampling with omega or omega eff = 10 degrees and delta = 0.5 mm should be adequate for planning purposes.

Megavoltage cone beam computed tomography: Commissioning and evaluation of patient dose

The improvement in conformal radiotherapy techniques enables us to achieve steep dose gradients around the target which allows the delivery of higher doses to a tumor volume while maintaining the sparing of surrounding normal tissue. One of the reasons for this improvement was the implementation of intensity-modulated radio therapy (IMRT) by using linear accelerators fitted with multi-leaf collimator (MLC), Tomo therapy and Rapid arc. In this situation, verification of patient set-up and evaluation of internal organ motion just prior to radiation delivery become important. To this end, several volumetric image-guided techniques have been developed for patient localization, such as Siemens OPTIVUE/MVCB and MVision megavoltage cone beam CT (MV-CBCT) system. Quality assurance for MV-CBCT is important to insure that the performance of the Electronic portal image device (EPID) and MV-CBCT is suitable for the required treatment accuracy. In this work, the commissioning and clinical implementation of the OPTIVUE/MVCB system was presented. The geometry and gain calibration procedures for the system were described. The image quality characteristics of the OPTIVUE/MVCB system were measured and assessed qualitatively and quantitatively, including the image noise and uniformity, low-contrast resolution, and spatial resolution. The image reconstruction and registration software were evaluated. Dose at isocenter from CBCT and the EPID were evaluated using ionization chamber and thermo-luminescent dosimeters; then compared with that calculated by the treatment planning system (TPS- XiO 4.4). The results showed that there are no offsets greater than 1 mm in the flat panel alignment in the lateral and longitudinal direction over 18 months of the study. The image quality tests showed that the image noise and uniformity were within the acceptable range, and that a 2 cm large object with 1% electron density contrast can be detected with the OPTIVUE/MVCB system with 5 monitor units (MU) protocol. The registration software was accurate within 2 mm in the anterior-posterior, left-right, and superior-inferior directions. The additional dose to the patient from MV-CBCT study set with 5 MU at the isocenter of the treatment plan was 5 cGy. For Electronic portal image device (EPID) verification using two orthogonal images with 2 MU per image the additional dose to the patient was 3.8 cGy. These measured dose values were matched with that calculated by the TPS-XiO, where the calculated doses were 5.2 cGy and 3.9 cGy for MVCT and EPID respectively.

Trimodality treatment for bladder cancer: does modern radiotherapy improve the end results?

With the advancement in endoscopic surgery, radiation treatment planning and execution, as well as the use of new chemotherapeutic regimens, bladder conservation has evolved into a competing alternative to radical cystectomy. Trimodality treatment has the great advantage of preserving a normally functioning urinary bladder. Despite the absence of direct randomized trials comparing both modalities, trimodality treatment comprising maximal transuretheral resection of bladder tumors followed by different regimens of combined radiochemotherapy achieved comparable results to radical cystectomy in many trials. Those who did not achieve complete remission after induction radiochemotherapy were salvaged by radical cystectomy. Improving the radiotherapeutic window is a challenging issue. In radiotherapy for bladder cancer, uncertainties include set-up errors, patient movement, internal organ movement and volume changes due to bladder filling (both inter- and intrafraction). The advancement in treatment verification procedures in modern radiotherapy and the use of fiducial markers reduces set-up errors, while adaptive radiotherapy could decrease the unnecessary irradiation of normal tissues by tracking bladder volume changes. In addition, new radiotherapeutic techniques, such as intensity-modulated radiotherapy and volume-modulated radiotherapy, permit dose escalation to the target without increasing the dose to the surrounding normal tissues.

The Emerging Use of IMRT for Treatment of Cervical Cancer

Radiation therapy plays an important role in both the definitive and adjuvant treatment of patients with cervical cancer. However, although radiation therapy is effective in controlling tumor growth, associated acute and chronic adverse effects are well known. Intensity-modulated radiation therapy (IMRT) is increasingly being used to treat cervical cancer and has the potential to improve the therapeutic ratio because of its ability to escalate dose to cancer targets while sparing adjacent healthy tissue. Multiple dosimetric studies were initially performed, establishing the conceptual feasibility of IMRT in patients with cervical cancer. Subsequent early reported series of patients treated with IMRT showed dosimetric and clinical benefits, with reduction in acute gastrointestinal and hematologic toxicity compared with historic controls, particularly in the posthysterectomy setting. Consensus is evolving regarding the use of IMRT in treating cervical cancer, particularly in the posthysterectomy setting, and for dose escalation to para-aortic nodes and bulky sidewall disease. Target delineation in the context of internal organ motion and tumor shrinkage during a course of fractionated external-beam radiotherapy remains an area of active investigation. IMRT in treating cervical cancer in the setting of an intact uterus remains in its nascent stage and should be used judiciously only within clinical trials. Although not a routine substitute for brachytherapy, it may be considered as a boost for highly selected patients who are not brachytherapy candidates.

Investigation of a Dynamical kV Aperture together with Combined MV-kV Dose Planning for Implementing Real-time 3D MV-kV Prostate Motion Tracking

In prostate cancer cases, there is no strong correlation between internal organ motion and externally visible motion, so optimal application of IGRT requires internal tracking techniques. Real-time 3D prostate tracking based on combined MV-kV imaging is an attractive solution since it uses the built-in hardware of modern LINACs equipped with OBI and EPID. However, continuous kV imaging throughout the treatment can lead to excess diagnostic dose exposure to the patient. To manage kV exposure, this work investigates the incorporation of the delivered kV tracking dose at the treatment planning stage through combined MV-kV beam modeling and conformal kV beam aperture shaping.

Clinical Application of Image-guided Radiotherapy in Bladder and Prostate Cancer

Advances in radiotherapy planning reduced the volumes of irradiated normal tissue and allowed safe dose escalation in prostate cancer. Image-guided radiotherapy solutions to prostate and bladder cancer offer further improvements. The initial process is understanding the causes and extent of internal organ motion, followed by development of equipment and protocols to minimise geographical miss. Further refinements may allow margin reduction and further dose escalation. This paper reviews these issues for bladder and prostate cancer.

Position Verification for the Prostate: Effect on Rectal Wall Dose

To evaluate the effect of gold marker (GM)-based position correction on the cumulative dose in the anorectal wall compared with traditional bony anatomy (BA)-based correction, taking into account changes in anorectal shape and position. A total of 20 consecutive prostate cancer patients, treated with curative external beam radiotherapy, were included. Four fiducial GMs were implanted in the prostate. Positioning was verified according to the shift in BA and GMs on daily electronic portal images. Position corrections were determined using on- and off-line position verification protocols according to the position of the GMs (GM-on and GM-off) and BA (BA-off). For all patients, intensity-modulated radiotherapy plans were made for the GM (8-mm planning target volume margin) and BA (10-mm planning target volume margin) protocols. The dose distribution was recomputed on 11 repeat computed tomography scans to estimate the accumulated dose to the prostate and anorectal wall while considering internal organ motion. The dose that is at least received by 99% of the prostate was, on average, acceptable for all protocols. The individual patient data showed the best coverage for both GM protocols, with >95% of the prescribed dose for all patients. The anorectal wall dose was significantly lower for the GM protocols. The dose that is at least received by 30% of the rectal wall was, on average, 54.6 Gy for GM-on, 54.1 Gy for GM-off, and 58.9 Gy for BA-off (p <.001). Position verification with GM and reduced planning target volume margins yielded adequate treatment of the prostate and a lower rectal wall dose, even when accounting for independent movement of the prostate and anorectal wall.