Variation In Radiotherapy Research Articles

A CARDIAC MOTION MODEL TO EVALUATE INTRA-FRACTION DOSIMETRIC VARIATIONS IN RADIOTHERAPY TREATMENTS

Purpose: A cardiac cycle model was implemented to simulate cardiac motion during radiotherapy to evaluate the intra-fraction dosimetric impact on cardiac sub-structures comparing different planning techniques. Methods: Cardiac sub-structures were automatically contoured in 10 CTs acquired in deep inspiration breath hold (DIBH) by using a recently developed hierarchical-clustering atlas-based algorithm. A deformable image registration algorithm was used to simulate the cardiac motion cycle based on volume variations available in the literature. Two synthetic CTs were created and contoured simulating contraction and expansion during the cardiac cycle. Ninety radiotherapy plans were calculated using three radiotherapy paradigms: tangential fields planned as Linac-3D-CRT with a steep linear dose gradient toward the heart-modulated therapy with an intermediately steep concave gradient of intermediate-to-high doses toward the heart, planned as Linac-VMAT; modulated therapy with a steep concave gradient of intermediate-to-high doses toward the heart, planned as helical tomotherapy. Python scripts were developed for autocontouring, automatic creation of synthetic CTs and data extraction. Results: Comparison between paradigms shows that different constraints (maximal gradient toward heart/lung versus maximal sparing of contralateral breast/axilla) do not necessarily result in preferred or reduced heart sparing, but this depends more on individual anatomy. A planning paradigm with an intermediate-steepness dose gradient showed the best robustness against intra-fraction organ motion. Conclusions: Patient-specific organ motion models may reduce differences between planned and delivered RT and may thus help to refine dose–volume–toxicity models for cardiac sub-structures and, as a consequence, clinical constraints. Automatized plan recalculation on synthetic image sets might be used for robustness optimization and evaluation.

A probabilistic deep learning model of inter-fraction anatomical variations in radiotherapy

Objective. In radiotherapy, the internal movement of organs between treatment sessions causes errors in the final radiation dose delivery. To assess the need for adaptation, motion models can be used to simulate dominant motion patterns and assess anatomical robustness before delivery. Traditionally, such models are based on principal component analysis (PCA) and are either patient-specific (requiring several scans per patient) or population-based, applying the same set of deformations to all patients. We present a hybrid approach which, based on population data, allows to predict patient-specific inter-fraction variations for an individual patient. Approach. We propose a deep learning probabilistic framework that generates deformation vector fields warping a patient's planning computed tomography (CT) into possible patient-specific anatomies. This daily anatomy model (DAM) uses few random variables capturing groups of correlated movements. Given a new planning CT, DAM estimates the joint distribution over the variables, with each sample from the distribution corresponding to a different deformation. We train our model using dataset of 312 CT pairs with prostate, bladder, and rectum delineations from 38 prostate cancer patients. For 2 additional patients (22 CTs), we compute the contour overlap between real and generated images, and compare the sampled and ‘ground truth’ distributions of volume and center of mass changes. Results. With a DICE score of 0.86 ± 0.05 and a distance between prostate contours of 1.09 ± 0.93 mm, DAM matches and improves upon previously published PCA-based models, using as few as 8 latent variables. The overlap between distributions further indicates that DAM’s sampled movements match the range and frequency of clinically observed daily changes on repeat CTs. Significance. Conditioned only on planning CT values and organ contours of a new patient without any pre-processing, DAM can accurately deformations seen during following treatment sessions, enabling anatomically robust treatment planning and robustness evaluation against inter-fraction anatomical changes.

A Simulation Study of Tolerance of Breathing Amplitude Variations in Radiotherapy of Lung Cancer Using 4DCT and Time-Resolved 4DMRI.

As patient breathing irregularities can introduce a large uncertainty in targeting the internal tumor volume (ITV) of lung cancer patients, and thereby affect treatment quality, this study evaluates dose tolerance of tumor motion amplitude variations in ITV-based volumetric modulated arc therapy (VMAT). A motion-incorporated planning technique was employed to simulate treatment delivery of 10 lung cancer patients' clinical VMAT plans using original and three scaling-up (by 0.5, 1.0, and 2.0 cm) motion waveforms from single-breath four-dimensional computed tomography (4DCT) and multi-breath time-resolved 4D magnetic resonance imaging (TR-4DMRI). The planning tumor volume (PTV = ITV + 5 mm margin) dose coverage (PTV D95%) was evaluated. The repeated waveforms were used to move the isocenter in sync with the clinical leaf motion and gantry rotation. The continuous VMAT arcs were broken down into many static beam fields at the control points (2°-interval) and the composite plan represented the motion-incorporated VMAT plan. Eight motion-incorporated plans per patient were simulated and the plan with the native 4DCT waveform was used as a control. The first (D95% ≤ 95%) and second (D95% ≤ 90%) plan breaching points due to motion amplitude increase were identified and analyzed. The PTV D95% in the motion-incorporated plans was 99.4 ± 1.0% using 4DCT, closely agreeing with the corresponding ITV-based VMAT plan (PTV D95% = 100%). Tumor motion irregularities were observed in TR-4DMRI and triggered D95% ≤ 95% in one case. For small tumors, 4 mm extra motion triggered D95% ≤ 95%, and 6-8 mm triggered D95% ≤ 90%. For large tumors, 14 mm and 21 mm extra motions triggered the first and second breaching points, respectively. This study has demonstrated that PTV D95% breaching points may occur for small tumors during treatment delivery. Clinically, it is important to monitor and avoid systematic motion increase, including baseline drift, and large random motion spikes through threshold-based beam gating.

Synthetic CT in assessment of anatomical and dosimetric variations in radiotherapy - procedure validation

Abstract Introduction: One of many procedures to control the quality of radiotherapy is daily imaging of the patient’s anatomy. The CBCT (Cone Beam Computed Tomography) plays an important role in patient positioning, and dose delivery monitoring. Nowadays, CBCT is a baseline for the calculation of fraction and total dose. Thus, it provides the potential for more comprehensive monitoring of the delivered dose and adaptive radiotherapy. However, due to the poor quality and the presence of numerous artifacts, the replacement of the CBCT image with the corrected one is desired for dose calculation. The aim of the study was to validate a method for generating a synthetic CT image based on deformable image registration. Material and methods: A Head & Torso Freepoint phantom, model 002H9K (Computerized Imaging Reference Systems, Norfolk, USA) with inserts was imaged with CT (Computed Tomography). Then, contouring and treatment plan were created in Eclipse (Varian Medical Systems, Palo Alto, CA, USA) treatment planning system. The phantom was scanned again with the CBCT. The planning CT was registered and deformed to the CBCT, resulting in a synthetic CT in Velocity software (Varian Medical Systems, Palo Alto, CA, USA). The dose distribution was recalculated based on the created CT image. Results: Differences in structure volumes and dose statistics calculated both on CT and synthetic CT were evaluated. Discrepancies between the original and delivered plan from 0.0 to 2.5% were obtained. Dose comparison was performed on the DVH (Dose-Volume Histogram) for all delineated inserts. Conclusions: Our findings suggest the potential utility of deformable registration and synthetic CT for providing dose reconstruction. This study reports on the limitation of the procedure related to the limited length of the CBCT volume and deformable fusion inaccuracies.

Coping with interfraction time trends in tumor setup.

PurposeInterfraction tumor setup variations in radiotherapy are often reduced with image guidance procedures. Clinical target volume (CTV)–planning target volume (PTV) margins are then used to deal with residual errors. We have investigated characterization of setup errors in patient populations with explicit modelling of occurring interfraction time trends.MethodsThe core of a “trendline characterization” of observed setup errors in a population is a distribution of trendlines, each obtained by fitting a straight line through a patient's daily setup errors. Random errors are defined as daily deviations from the trendline. Monte Carlo simulations were performed to predict the impact of offline setup correction protocols on residual setup errors in patient populations with time trends. A novel CTV‐PTV margin recipe was derived that assumes that systematic underdosing of tumor edges in multiple consecutive fractions, as caused by trend motion, should preferentially be avoided. Similar to the well‐known approach by van Herk et al. for conventional error characterization (no explicit modelling of trends), only a predefined percentage of patients (generally 10%) was allowed to have nonrandom (systematic + trend) setup errors outside the margin. Additionally, a method was proposed to avoid erroneous results in Monte Carlo simulations with setup errors, related to decoupling of error sources in characterizations. The investigations were based on a database of daily measured setup errors in 835 prostate cancer patients that were treated with 39 fractions, and on Monte Carlo–generated patient populations with time trends.ResultsWith conventional characterization of setup errors in patient populations with time trends, predicted standard deviations of residual systematic errors (Σres) after application of an offline correction protocol could be underestimated by more than 50%, potentially resulting in application of too small margins. With the new trendline characterization this was avoided. With the novel CTV‐PTV margin recipe with an allowed 10% of patients having nonrandom errors outside the margin, the observed percentage was 10.0% ± 0.2%. When using conventional characterization of errors and the van Herk margin recipe, on average 58.0% ± 24.3% of patients had errors outside the margin, while 10% was prescribed. For populations with no time trends, the novel recipe simplifies to the generally applied M=2.5Σ+0.7σ formula proposed by van Herk et al.ConclusionsIn populations with time trends in setup errors, the use of trendline characterizations in Monte Carlo simulations for establishment of residual errors after a setup correction protocol can avoid application of erroneous margins. The novel margin recipe can be used to accurately control the percentage of patients with nonrandom errors outside the margin. In case of daily image guidance of patients with multiple targets with differential motion, the recipe can be used to establish margins for the targets that are not the primary target for the image guidance (e.g., nodal regions). Probabilistic planning might be improved by using trendline characterization for modelling of setup errors. Population analyses of interfraction setup errors need to take into account potential time trends.

123O - Variation in radiotherapy after breast conserving surgery in patients aged 75 years or older between hospitals is not reflected in the locoregional recurrence risk

123O - Variation in radiotherapy after breast conserving surgery in patients aged 75 years or older between hospitals is not reflected in the locoregional recurrence risk

Sociodemographic variation in the use of chemotherapy and radiotherapy in patients with stage IV lung, oesophageal, stomach and pancreatic cancer: evidence from population-based data in England during 2013\u20132014

BackgroundSociodemographic inequalities in cancer treatment have been generally described, but there is little evidence regarding patients with advanced cancer. Understanding variation in the management of these patients may provide insights into likely mechanisms leading to inequalities in survival.MethodsWe identified 50,232 patients with stage IV lung, oesophageal, pancreatic and stomach cancer from the English national cancer registry. A generalised linear model with a Poisson error structure was used to explore variation in radiotherapy and chemotherapy within 6 months from diagnosis by age, sex, deprivation, ethnicity, cancer site, comorbidity and, additionally, performance status.ResultsThere was substantial variation by cancer site, large gradients by age, and non-trivial associations with comorbidity and deprivation. After full adjustment, more deprived patients were consistently least likely to be treated with chemotherapy alone or chemotherapy and radiotherapy combined compared with less deprived patients with equally advanced disease stage (treatment rate ratio: 0.82 95% CI (0.78, 0.87) for CT, 0.78 95% CI (0.71, 0.85) for CTRT p < 0.0001).ConclusionsThere was marked variation in the management of patients with stage IV cancer. Routinely collected data could be used for surveillance across all cancers to help reduce treatment variation and optimise outcomes among patients with advanced cancer.

Dosimetric Impact of Bladder Volume Variation in Radiotherapy for Prostate Cancer – A Pilot Study.

Dosimetric Impact of Bladder Volume Variation in Radiotherapy for Prostate Cancer – A Pilot Study.

Determination of subcellular compartment sizes for estimating dose variations in radiotherapy.

The variation in specific energy absorbed to different cell compartments caused by variations in size and chemical composition is poorly investigated in radiotherapy. The aim of this study was to develop an algorithm to derive cell and cell nuclei size distributions from 2D histology samples, and build 3D cellular geometries to provide Monte Carlo (MC)-based dose calculation engines with a morphologically relevant input geometry. Stained and unstained regions of the histology samples are segmented using a Gaussian mixture model, and individual cell nuclei are identified via thresholding. Delaunay triangulation is applied to determine the distribution of distances between the centroids of nearest neighbour cells. A pouring simulation is used to build a 3D virtual tissue sample, with cell radii randomised according to the cell size distribution determined from the histology samples. A slice with the same thickness as the histology sample is cut through the 3D data and characterised in the same way as the measured histology. The comparison between this virtual slice and the measured histology is used to adjust the initial cell size distribution into the pouring simulation. This iterative approach of a pouring simulation with adjustments guided by comparison is continued until an input cell size distribution is found that yields a distribution in the sliced geometry that agrees with the measured histology samples. The thus obtained morphologically realistic 3D cellular geometry can be used as input to MC-based dose calculation programs for studies of dose response due to variations in morphology and size of tumour/healthy tissue cells/nuclei, and extracellular material.

Comparison study of portable bladder scanner versus cone‐beam CT scan for measuring bladder volumes in post‐prostatectomy patients undergoing radiotherapy

In post-prostatectomy radiotherapy to the prostatic bed, consistent bladder volume is essential to maintain the position of treatment target volume. We assessed the differences between bladder volume readings from a portable bladder scanner (BS-V) and those obtained from planning CT (CT-V) or cone-beam CT (CBCT-V). Interfraction bladder volume variation was also determined. BS-V was recorded before and after planning CT or CBCT. The percentage differences between the readings using the two imaging modalities, standard deviations and 95% confidence intervals were determined. Data were analysed for the whole patient cohort and separately for the older BladderScan™ BVI3000 and newer BVI9400 model. Interfraction bladder volume variation was determined from the percentage difference between the CT-V and CBCT-V. Treatment duration, incorporating the time needed for BS and CBCT, was recorded. Fourteen patients were enrolled, producing 133 data sets for analysis. BS-V was taken using the BVI9400 in four patients (43 data sets). The mean BS-V was 253.2 mL, and the mean CT-V or CBCT-V was 199 cm(3). The mean percentage difference between the two modalities was 19.7% (SD 42.2; 95%CI 12.4 to 26.9). The BVI9400 model produced more consistent readings, with a mean percentage difference of -6.2% (SD 27.8; 95% CI -14.7 to -2.4%). The mean percentage difference between CT-V and CBCT-V was 31.3% (range -48% to 199.4%). Treatment duration from time of first BS reading to CBCT was, on average, 12 min (range 6-27). The BS produces bladder volume readings of an average 19.7% difference from CT-V or CBCT-V and can potentially be used to screen for large interfraction bladder volume variations in radiotherapy to prostatic bed. The observed interfraction bladder volume variation suggests the need to improve bladder volume consistency. Incorporating the BS into practice is feasible.

SU-E-T-579: Dosimetric Benefits of Online Adaptive Replanning for Post-Operative Radiation Therapy of Prostate Bed.

To demonstrate the dosimetric benefits of using an online adaptive replanning scheme to address interfractional variations in radiotherapy of prostate bed. We have previously developed an online adaptive replanning tool (RealART, Prowess Inc.) aiming to address interfractional variations including organ deformation and rotation. Using this tool, we analyzed a total of 102 daily pre-treatment CTs acquired using an in-room CT (CTVision, Siemens) for 10 patients treated with post-operative IMRT of prostate bed. The PTV was assumed to be the volume enclosed by the 95% prescription isodose surface generated for the conventional four field box. On each daily CT set, contours of the PTV, rectum and bladder were generated by populating the planning contours using an auto-segmentation tool based on deformable registration (ABAS, Elekta) with manual editing. Four plans were generated and compared: (1) IGRT (repositioning) plan by copying the original plan with aligning the anterior rectal wall from the daily CT to that of the planning CT, (2) IGRT plan by copying the original plan with aligning the surgical clips, (3) online adaptive plan by tailoring the original plan to conform to the anatomy of the day, and (4) a new plan re- optimized based on the daily anatomy. The adaptive and re- optimization plans are in general superior than the two repositioning plans in terms of both target coverage and critical structure sparing. For example, the averages of dose volume quantities for all daily CTs are: rectum V45Gy 55.7±18.0% (one standard deviation), 57.3±17.5%, 48.2±11.8%, 42.5±9.6%; rectum V60Gy 31.8±20.3%, 34.0±16.6%, 22.6±9.7%, 16.5±7.4%; bladder V45Gy 30.0±11.9%, 39.5±24.2%, 37.6±16.8%, 36.5±16.2%; bladder V60Gy 17.4±9.2%, 25.4±18.1%, 24.7±12.7%, 23.9±12.0%; PTV V100 81.9±16.6%, 88.7±7.9%, 92.9±4.6%, and 94.6±2.4% for the above (1)-(4) plans, respectively. The online adaptive replanning scheme is effective to account for interfractional variations in post-operative radiotherapy of prostate bed. This work is supported partially by MCW Cancer Center Fotsch Foundation.

Setup Variations in Radiotherapy of Anal Cancer: Advantages of Target Volume Reduction Using Image-Guided Radiation Treatment

To define setup variations in the radiation treatment (RT) of anal cancer and to report the advantages of image-guided RT (IGRT) in terms of reduction of target volume and treatment-related side effects. Twelve consecutive patients with anal cancer treated by combined chemoradiation by use of helical tomotherapy from March 2007 to November 2008 were selected. With patients immobilized and positioned in place, megavoltage computed tomography (MVCT) scans were performed before each treatment and were automatically registered to planning CT scans. Patients were shifted per the registration data and treated. A total of 365 MVCT scans were analyzed. The primary site received a median dose of 55 Gy. To evaluate the potential dosimetric advantage(s) of IGRT, cases were replanned according to Radiation Therapy Oncology Group 0529, with and without adding recommended setup variations from the current study. Significant setup variations were observed throughout the course of RT. The standard deviations for systematic setup correction in the anterior-posterior (AP), lateral, and superior-inferior (SI) directions and roll rotation were 1.1, 3.6, and 3.2 mm, and 0.3°, respectively. The average random setup variations were 3.8, 5.5, and 2.9 mm, and 0.5°, respectively. Without daily IGRT, margins of 4.9, 11.1, and 8.5 mm in the AP, lateral, and SI directions would have been needed to ensure that the planning target volume (PTV) received ≥95% of the prescribed dose. Conversely, daily IGRT required no extra margins on PTV and resulted in a significant reduction of V15 and V45 of intestine and V10 of pelvic bone marrow. Favorable toxicities were observed, except for acute hematologic toxicity. Daily MVCT scans before each treatment can effectively detect setup variations and thereby reduce PTV margins in the treatment of anal cancer. The use of concurrent chemotherapy and IGRT provided favorable toxicities, except for acute hematologic toxicity.

Target volume delineation variation in radiotherapy for early stage rectal cancer in the Netherlands

PurposeThe aim of this study was to measure and improve the quality of target volume delineation by means of national consensus on target volume definition in early-stage rectal cancer. Methods and materialsThe CTV’s for eight patients were delineated by 11 radiation oncologists in 10 institutes according to local guidelines (phase 1). After observer variation analysis a workshop was organized to establish delineation guidelines and a digital atlas, with which the same observers re-delineated the dataset (phase 2). Variation in volume, most caudal and cranial slice and local surface distance variation were analyzed. ResultsThe average delineated CTV volume decreased from 620 to 460cc (p<0.001) in phase 2. Variation in the caudal CTV border was reduced significantly from 1.8 to 1.2cm SD (p=0.01), while it remained 0.7cm SD for the cranial border. The local surface distance variation (cm SD) reduced from 1.02 to 0.74 for anterior, 0.63 to 0.54 for lateral, 0.33 to 0.25 for posterior and 1.22 to 0.46 for the sphincter region, respectively. ConclusionsThe large variation in target volume delineation could significantly be reduced by use of consensus guidelines and a digital delineation atlas. Despite the significant reduction there is still a need for further improvement.

Population-Based Study of Trends and Variations in Radiotherapy as Part of Primary Treatment of Cancer in the Southern Netherlands Between 1988 and 2006, With an Emphasis on Breast and Rectal Cancer

To explore current variations in the use of primary radiotherapy (RT) in a region with two RT departments with adjacent referral areas, one in the eastern and one in the western sector of the southern region of the Netherlands. We calculated the proportion of 147,588 patients with newly diagnosed cancer between 1988 and 2006 in the southern Netherlands who received primary RT. Especially for breast and rectal cancer patients we studied primary RT use according to stage (breast cancer) and age and separately for the eastern and western sectors. The number of patients with new diagnoses receiving primary RT increased from 1,668 patients in 1988 to 2,971 patients in 2006, with the proportion of the overall patients receiving RT remaining more or less unchanged (+/-30%). However, only 20% of elderly patients (75+ years) received primary RT. Over time, more patients with prostate and rectal cancer, fewer patients with lung and bladder cancer or Hodgkin's lymphoma, and, recently, more patients with cervical or endometrial cancer received RT. The proportion of patients with most other tumor types treated with RT remained more or less unchanged. The total RT rate was slightly higher for patients in the eastern sector. Of particular note, patients with breast or rectal cancer in the eastern sector were significantly more likely to receive primary RT than were their counterparts in the western sector (odds ratio = 1.4, 95% confidence interval =1.4-1.5, and odds ratio = 1.4, 95% confidence interval = 1.3-1.6, respectively). Although the number of RT-treated patients increased substantially during 1988 to 2006, the proportion remained essentially unchanged. In addition, large variations were found in referral rates for RT, especially in later years, between the eastern and the western sectors of the region.

WE-B-BRB-01: Patient Motion Modeling and Treatment Adaptation

Patient anatomical variation during the radiotherapy course can be described using a stochastic process. In this process, spatial position of each subvolume in patient organs of interest during the treatment course is represented using a random vector with an intrinsic probability distribution function (pdf). Two main parameters, the mean and the standard deviation, of the pdf have been historically used to characterize patient anatomical variation, the systematic and random variations, during the radiation treatment. It has been demonstrated that treatment dose distribution in an organ of interest can be evaluated using these two parameters alone, without the full knowledge of organ motion distribution. The approximation is, however, dependent on the size of the motion as well as the number of treatment fractions. It is straightforward to estimate these two parameters if patient anatomical variation process is stationary. In this case, the two parameters are constants or time-invariance during the treatment course. However, the estimation will be relatively difficult if patient anatomical variation process is non-stationary. Patient anatomical variation in radiotherapy can be managed using multiple or 4D image guided or feedback treatment techniques. Among them, adaptive approach is the most effective methodology in utilizing the 4D feedback information. Image guided adaptive radiation therapy is a closed loop treatment process which is designed to include the individual treatment information, such as organ dose that has been delivered and/or could be delivered in future, in the treatment evaluation and planning optimization. To include delivered organ dose in the planning optimization, deformable image registration is necessary. On the other hand, the measured organ variations are used to estimate what may happen in the future treatment. The patient specific information is, then, included in 4D adaptive planning modification or optimization. Based on a pre-determined control strategy, adaptive planning modification can be performed either offline with signal or multiple modifications, or online. However, selection of control strategy is quite complicated not only depending up on the nature of patient variation process, imaging sampling and estimation methodology, but also the clinical load and practical issues. The lecture will provide an overview of the model and description of patient anatomical variation process during the radiotherapy. In addition, effect of the variation on treatment dose, and options of control strategy will be discussed. Educational Objectives: 1. Understand the characteristics and dynamic model for patient anatomical variation during the course of radiotherapy. 2. Understand the effects of patient anatomical variation on treatment dose. 3. Understand the options and potentials of control strategy for image guided adaptive radiotherapy.

Setup Variations in Radiotherapy of Esophageal Cancer: Evaluation by Daily Megavoltage Computed Tomographic Localization

To use pretreatment megavoltage computed tomography (MVCT) scans to evaluate setup variations in anterior-posterior (AP), lateral, and superior-inferior (SI) directions and rotational variations, including pitch, roll, and yaw, for esophageal cancer patients treated with helical tomotherapy. Ten patients with locally advanced esophageal cancer treated by combined chemoradiation using helical tomotherapy were selected. After patients were positioned using their skin tattoos/marks, MVCT scans were performed before every treatment and automatically registered to planning kilovoltage CT scans according to bony landmarks. Image registration data were used to adjust patient setups before treatment. A total of 250 MVCT scans were analyzed. Correlations between setup variations and body habitus, including height, weight, relative weight change, body surface area, and patient age, were evaluated. The standard deviations for systematic setup corrections in AP, lateral, and SI directions and pitch, roll, and yaw rotations were 1.5, 3.7, and 4.8 mm and 0.5 degrees, 1.2 degrees, and 0.8 degrees, respectively. The appropriate averages of random setup variations in AP, lateral, and SI directions and pitch, roll, and yaw rotations were 2.9, 5.2, and 4.4 mm, and 1.0 degrees, 1.2 degrees, and 1.1 degrees, respectively. Setup variations were stable throughout the entire course of radiotherapy in all three translational and three rotational displacements, with little change in magnitude. No significant correlations were found between setup variations and body habitus variables. Daily MVCT scans before each treatment can effectively detect setup errors and thereby reduce planning target volume (PTV) margins. This will reduce radiation dose to critical organs and may translate into lower treatment-related toxicities.

MO‐D‐ValA‐02: Patient Motion Modeling &amp; Treatment Adaptation

Patient anatomical variation during the radiotherapy course can be modeled using a stochastic process. In this process, spatial position of each subvolume in patient organs of interest is defined as a random vector described using a probability distribution function (pdf). Two main parameters, the mean and the standard deviation, of the pdf have been historically used to characterize patient anatomical variation during the radiation treatment. It has been demonstrated that treatment dose distribution in an organ of interest can be evaluated approximately using these two parameters alone, without the full knowledge of organ motion distribution. The approximation is, however, dependent on the scale of the standard deviation as well as the number of treatment delivery fractions. It is straightforward to estimate these two parameters if patient anatomical variation process is stationary. In this case, the two parameters are constants or time‐invariance during the treatment course. However, the estimation will be relatively difficult if patient anatomical variation process is non‐stationary.Patient anatomical variation in radiotherapy can be systematically managed using image feedback adaptive treatment technique. The fundamental difference between adaptive treatment technique and other image‐guided techniques is the use of patient‐specific treatment information. Adaptive technique intends to use all patient‐specific dose information ‐ including what has been delivered in the previous treatments, what can be delivered at the present treatment, and what would be delivered in future treatments ‐ in the design of treatment plan. Therefore, treatment plan designed in adaptive radiotherapy is called 4D adaptive plan, which is in principle a treatment control law to manage treatment process. Mathematically, treatment control law is a spatial mapping from the parameter space of patient variation to the parameter space of treatment delivery control, which can be determined including the patient variation in the planning optimization or inverse planning. The objectives in adaptive planning optimization are constructed based on a selection of control strategies that could be either the online or the offline with one control action, multiple actions or continue actions. Selection of control strategy and number of control actions is, of course, dependent on the nature of patient variation process as well as the estimation uncertainties, and has to be determined considering also the clinical practice.The lecture will provide an overview of the models and characteristics of patient anatomical variation process during the radiotherapy, the 4D dose summation methodology and the strategies of adaptive treatment process.Educational Objectives:1. Understand the characteristics and dynamic model for patient anatomical variation during the course of radiotherapy.2. Understand the model and methodology of 4D dose summation.3. Understand the options of control strategy for image guided adaptive radiation treatment.

Prophylactic cranial irradiation for preventing brain metastases in patients undergoing radical treatment for non-small cell lung cancer.

In non-small cell lung cancer (NSCLC), there is a relatively high incidence of brain metastases following radical treatment. At present, the role of prophylactic cranial irradiation (PCI) in this group of patients is not clear. To investigate whether PCI has a role in the management of patients with NSCLC treated with radical intent. The electronic databases MEDLINE, EMBASE and Cancerlit, along with handsearching of journals, relevant books, and review articles used to identify potentially eligible trials. Randomised controlled trials (RCTs) comparing PCI with no PCI in NSCLC patients treated with radical intent. Four RCTs were reviewed. Due to the small patient numbers, and variations in radiotherapy (RT) dose, no meta-analysis was attempted. PCI may reduce the incidence of brain metastases, but there is no evidence of a survival benefit. There is no evidence that any regimen is superior, and the effect of PCI on quality of life (QOL) is not known. There is insufficient evidence to support the use of PCI in clinical practice. Where possible, patients should be offered entry into a clinical trial.

Chemotherapy as predictor of compliance

Patient compliance with the increasingly complex adjuvant therapy protocols has always been of concern, particularly in the head and neck cancer population. The Head and Neck Intergroup recently concluded a phase III prospective randomized trial testing the addition of three courses of cisplatinum containing combination chemotherapy to standard treatment defined as surgery and postoperative radiotherapy for advanced stage III and IV squamous cell carcinoma. The chemotherapy was administered following the surgery prior to the postoperative radiotherapy. Variation from protocol is ranked retrospectively as minor acceptable, major acceptable, and major unacceptable. The incidence of major unacceptable variation from the protocol for radiotherapy immediately following the surgery was 15% vs. 19% in the population that completed all three courses of the chemotherapy (P < 0.10). However, for those patients that completed less than the three courses of chemotherapy, the incidence of major unacceptable variation in radiotherapy was 33% (P < 0.001). This observation was controlled for site, stage, performance status, age, sex, surgical margins and experience of participating institution. We conclude that compliance with a multicourse adjuvant chemotherapy regimen is predictive of subsequent compliance to radiotherapy in the head and neck cancer population.