Building a New Model of Care for Rapid Breast Radiotherapy Treatment Planning: Evaluation of the Advanced Practice Radiation Therapist in Cavity Delineation.

AIMS: Breast radiotherapy treatment is commonly managed by a multidisciplinary team to ensure optimal delivery of care. We sought a new model of care whereby a clinical specialist radiation therapist (CSRT) delineates the cavity target for whole breast radiotherapy treatment planning and the radiation oncologist validates the contour during final plan review. This study evaluated the radiation oncologist's acceptance of these contours and identified characteristics of cavities suitable for CSRT-directed contouring. MATERIALS AND METHODS: Following specialised breast oncology education and training by the radiation oncologist, the CSRT prospectively delineated cavities in 30 tangential breast radiotherapy cases and consulted the radiation oncologist in 'complex' cases but directed 'non-complex' cases for treatment planning. Changes to CSRT contours were evaluated using the conformity index. Breast density, time since surgery and cavity location, size and visualisation score [CVS: range 1 (no visible cavity) to 5 (homogenous cavity)] were captured. RESULTS: Of the 30 CSRT delineated cavities contours, the CSRT directed 20 (66.7%) cases for planning without radiation oncology review; 19 were accepted (without changes) by the radiation oncologist upon final plan review and one was changed by the radiation oncologist (conformity index = 0.93) for boost treatment and did not affect the tangential treatment plan. Ten (33.3%) cases, all CVS ≤ 3, were reviewed with the radiation oncologist before planning (conformity index = 0.88 ± 0.12). CVS was inversely correlated with breast density and cavity size (P < 0.01). CONCLUSIONS: The CSRT delineated cavities appropriate for clinical radiotherapy treatment planning in women with well-visualised cavities, whereas 'complex' cases with dense breast parenchyma, CVS ≤ 3, and/or cases needing boost radiotherapy treatment required review with the radiation oncologist before planning.

Robust PET-guided intensity-modulated radiation therapy.

PURPOSE: Functional image guided intensity-modulated radiation therapy has the potential to improve cancer treatment quality by basing treatment parameters such as heterogeneous dose distributions information derived from imaging. However, such heterogeneous dose distributions are subject to imaging uncertainty. In this paper, the authors develop a robust optimization model to design plans that are desensitized to imaging uncertainty. METHODS: Starting from the pretreatment fluorodeoxyglucose-positron emission tomography scans, the authors use the raw voxel standard uptake values (SUVs) as input into a series of intermediate functions to transform the SUV into a desired dose. The calculated desired doses were used as an input into a robust optimization model to generate beamlet intensities. For each voxel, the authors assume that the true SUV cannot be observed but instead resides in an interval centered on the nominal (i.e., observed) SUV. Then the authors evaluated the nominal and robust solutions through a simulation study. The simulation considered the effect of the true SUV being different from the nominal SUV on the quality of the treatment plan. Treatment plans were compared on the metrics of objective function value and tumor control probability (TCP). RESULTS: Computational results demonstrate the potential for improvements in tumor control probability and deviation from the desired dose distribution compared to a nonrobust model while maintaining acceptable tissue dose. CONCLUSIONS: Robust optimization can help design treatment plans that are more stable in the presence of image value uncertainties.

Metabolic syndrome-related hepatocellular carcinoma treated by volumetric modulated arc therapy.

Hepatocellular carcinoma (hcc) is a leading cause of cancer mortality, and its incidence is increasing in developed countries. Risk factors include cirrhosis from viral hepatitis or alcohol abuse. Metabolic syndrome is a newly recognized, but important, risk factor that is likely contributing to the increased incidence of hcc. Surgery is the therapy of choice for hcc, but local therapies are often contraindicated, usually because of advanced disease or comorbid conditions such as cardiac disease (which is associated with metabolic syndrome). Current radiation therapy techniques such as stereotactic body radiotherapy allow for treatment plans that highly conform to the target and provide excellent sparing of normal structures. Radiation therapy is emerging as a viable option in patients not eligible for surgery or other locoregional therapies. Here, we report a case of a large hcc presenting in a patient with metabolic syndrome without significant alcohol history or biochemical liver dysfunction. The patient was not a candidate for locoregional therapies because of cardiac and renal comorbidities typical of patients experiencing the long-term sequelae of metabolic syndrome. Treatment using an arc-based volumetric-modulated arc therapy technique allowed for the highest dose of radiation to be delivered to the tumour while the peripheral radiation dose was minimized. A complete local response was confirmed by computed tomography imaging 21 months after treatment completion.

The Canadian Association of Radiation Oncology scope of practice guidelines for lung, liver and spine stereotactic body radiotherapy.

AIMS: The Canadian Association of Radiation Oncology-Stereotactic Body Radiotherapy (CARO-SBRT) Task Force was established in 2010. The aim was to define the scope of practice guidelines for the profession to ensure safe practice specific for the most common sites of lung, liver and spine SBRT. MATERIALS AND METHODS: A group of Canadian SBRT experts were charged by our national radiation oncology organisation (CARO) to define the basic principles and technologies for SBRT practice, to propose the minimum technological requirements for safe practice with a focus on simulation and image guidance and to outline procedural considerations for radiation oncology departments to consider when establishing an SBRT programme. RESULTS: We recognised that SBRT should be considered as a specific programme within a radiation department, and we provide a definition of SBRT according to a Canadian consensus. We outlined the basic requirements for safe simulation as they pertain to spine, lung and liver tumours, and the fundamentals of image guidance. The roles of the radiation oncologist, medical physicist and dosimetrist have been detailed such that we strongly recommend the development of SBRT-specific teams. Quality assurance is a key programmatic aspect for safe SBRT practice, and we outline the basic principles of appropriate quality assurance specific to SBRT. CONCLUSION: This CARO scope of practice guideline for SBRT is specific to liver, lung and spine tumours. The task force recommendations are designed to assist departments in establishing safe and robust SBRT programmes.

TU-G-BRB-04: A Robust-CVaR Optimization Approach to Left-Sided Breast IMRT.

PURPOSE: To test the feasibility of a cardiac sparing IMRT planning approach for patients with left-sided breast cancer using a robust optimization model. METHODS: A robust optimization model was developed for breast IMRT. The concept of conditional-value-at-risk (CVaR) was used in the robust framework to guarantee that the clinical dose volume criteria for targets and organs at risk hold under uncertainty in the patient's breathing pattern. Clinical treatment methods for breast cancer (inhale breath-hold with active breathing control (ABC) or free breathing) were simulated via optimization models. A 4DCT patient dataset with target and organs at risk on each breathing phase was used to simulate a clinical case with a total of 20% increase in lung volume from exhale to inhale over 5 phases. The results of the proposed robust model were compared with those of the current clinical models. RESULTS: Compared to the conventional IMRT method for breast cancer (with free breathing), the proposed robust-CVaR model resulted in a 14.6% reduction in mean heart dose without compromising the target coverage and dose homogeneity. The clinical dose-volume limits for the heart as well as the clinical target volume were met in robust results. The robust method resulted in 23.9% improvement in the maximum dose to 25cc of the heart volume. The robust results showed very low variability among the quality of planning and realized treatments. CONCLUSIONS: Using CVaR limits in a robust optimization framework can help improve the quality of IMRT treatments. The robust-CVaR can generate a high quality treatment plans, but is delivered during free breathing and does not require patient compliance with an external device. The quality of robust treatment remains the same under irregular breathing. Explicitly including metrics for lung and bigger motion amplitudes in the robust optimization method may further improve the results.

Early metabolic response evaluation after stereotactic radiotherapy for lung cancer: pilot experience with 18F-fluorodeoxyglucose positron emission tomography-computed tomography.

The early response of lung tumours to stereotactic radiotherapy was prospectively evaluated with 18F-fluorodeoxyglucose positron emission tomography-computed tomography. Three months after treatment, the maximum standardised uptake value and the tumour diameter fell by 64 and 30%, respectively. This imaging strategy therefore remains under ongoing evaluation with the aim of identifying predictive and prognostic factors.

Implementation and characterization of a 320-slice volumetric CT scanner for simulation in radiation oncology.

PURPOSE: Effective target definition and broad employment of treatment response assessment with dynamic contrast-enhanced CT in radiation oncology requires increased speed and coverage for use within a single bolus injection. To this end, a novel volumetric CT scanner (Aquilion One, Toshiba, Tochigi Pref., Japan) has been installed at the Princess Margaret Hospital for implementation into routine CT simulation. This technology offers great advantages for anatomical and functional imaging in both scan speed and coverage. The aim of this work is to investigate the system's imaging performance and quality as well as CT quantification accuracy which is important for radiotherapy dose calculations. METHODS: The 320-slice CT scanner uses a 160 mm wide-area (2D) solid-state detector design which provides the possibility to acquire a volumetric axial length of 160 mm without moving the CT couch. This is referred to as "volume" and can be scanned with a rotation speed of 0.35-3 s. The scanner can also be used as a 64-slice CT scanner and perform conventional (axial) and helical acquisitions with collimation ranges of 1-32 and 16-32 mm, respectively. Commissioning was performed according to AAPM Reports TG 66 and 39 for both helical and volumetric imaging. Defrise and other cone-beam image analysis tests were performed. RESULTS: Overall, the imaging spatial resolution and geometric efficiency (GE) were found to be very good (>10 lp/mm, <1 mm spatial integrity and GE160 mm=85%) and within the AAPM guidelines as well as IEC recommendations. Although there is evidence of some cone-beam artifacts when scanning the Defrise phantom, image quality was found to be good and sufficient for treatment planning (soft tissue noise <10 HU). Measurements of CT number stability and contrast-to-noise values across the volume indicate clinically acceptable scan accuracy even at the field edge. CONCLUSIONS: Initial experience with this exciting new technology confirms its accuracy for routine CT simulation within radiation oncology and allows for future investigations into specialized dynamic volumetric imaging applications.

Poster - Thurs Eve-22: Image guided radiation therapy for lung cancer.

OBJECTIVE: To determine the geometric accuracy of conventional and stereotactic lung radiotherapy using cone-beam CT image guidance, and assess the efficacy of these image-guided radiation therapy (IGRT) processes. MATERIALS AND METHODS: IGRT was first used for our stereotactic lung program, where high geometric accuracy is required to deliver high doses in few fractions. The initial positional accuracy for 47 patients was assessed by registering daily CBCT to the planning CT; the patient position was corrected when the CBCT indicated discrepancies > ± 3 mm in any direction. For 19 of these patients, a second CBCT was acquired to assess the residual error. IGRT was also used to assess the initial and residual errors for lung cancer patients treated conventionally with (14 pts; 584 CBCT) and without (25 pts; 1032 CBCT) a remote-controlled treatment couch. Systematic (Σ) and random (σ) positional errors were assessed for these three groups. RESULTS: For stereotactic lung patients, Σ and σ ranged between 4.1 and 6.1 mm. IGRT reduces these errors to 1.2-1.9 mm, raising the proportion of patients within ± 3 mm from 16% to 82%. For conventional lung cancer patients, Σ and σ ranged between 1.4 and 3.8 mm, and IGRT raises the proportion of patients within ± 3 mm from 27% to 67%, with the remote-controlled couch further improving this proportion to 84%. CONCLUSION: IGRT clearly confirms the high geometric accuracy required for stereotactic lung patients. This new paradigm has been transported to patients with locally-advanced lung cancer, with similar accuracy.

CT imaging of angiogenesis.

Tumor angiogenesis has significant implications in the diagnosis and treatment of various solid tumors. With the advent of fast, multi-slice CT scanners, CT imaging techniques capable of qualitative and quantitative analysis of tumor angiogenesis have been the subject of extensive investigation in the past 2 decades. The fundamental bases for CT imaging of angiogenesis are both the transport by blood flow of intravenously administered iodinated contrast material to tissue and the exchange by diffusion of these contrast molecules between the intravascular space and the extravascular interstitial space. With current fast CT scanners both tissue and vascular enhancement can be measured and traced over time at small time intervals to allow detailed modeling of the distribution of contrast agent in tissue. Both compartmental and distributed parameter models for contrast transport and exchange have been developed to quantify from the CT data the following angiogenesis related parameters: tissue blood flow, blood volume, mean transit time, contrast arrival time, capillary permeability surface area product and hepatic arterial fraction in case of the liver. This review addresses the following aspects of CT imaging of angiogenesis: 1) basic concepts related to the understanding of both compartmental and distributed parameter models; 2) comparison between both types of models; 3) practical issues with respect to the measurement of the arterial input function, which is required for the solution of both types of models; and, 4) illustration of the application of a distributed parameter model, the Johnson and Wilson model, in a number of experimental studies.

The use of CT perfusion to monitor the effect of hypocapnia during laser thermal therapy in a rabbit model.

One of the limiting factors in the thermal therapy of tumours is the dissipation of heat by blood flow. The current study investigates the use of hyperventilation (hypocapnia) to decrease tumour blood flow during laser thermal therapy. Rabbits with implanted VX2 thigh tumours were treated using a diode laser (805 nm) as the heating source. One group of rabbits (n = 8) was treated with the new hypocapnia protocol and another group (n = 8) with the conventional (normocapnia) protocol. The mean tumour volume and blood flow were the same for the two groups prior to treatment. The laser power temporal profile (3.0-1.5 W) and the duration of treatment (60 min) were also the same for both treatment protocols. Blood flow maps were calculated from a series of contrast-enhanced CT images. The average change in thermal lesion area at 60 min post-laser thermal therapy from pre-treatment normalized to the pre-treatment tumour area was significantly different between the two treatment protocols: 0.52+/-0.13 (hypocapnia) vs 0.33+/-0.12 (normocapnia) (p < 0.001). Similarly, the average fractional decrease in global tumour blood flow 60 min post-treatment from pre-treatment was also significantly different between the two protocols: 0.64+/-0.10 (hypocapnia) vs 0.41+/-0.14 (normocapnia) (p < 0.001). The hypocapnia protocol produced larger thermal lesion area and greater decrease in tumour blood flow post-treatment than the normocapnia protocol. These results support the further investigation of the use of hypocapnia to increase the therapeutic effect of laser thermal therapy.

Functional CT imaging of angiogenesis in rabbit VX2 soft-tissue tumour.

Functional parameters such as blood flow (BF), microvessel permeability surface area product (PS), blood volume (BV) and mean transit time (MTT) are physiological markers related to the changes associated with angiogenesis. In the current study we present a functional CT technique for the simultaneous measurement of these four functional parameters and the display of each parameter as a functional image over an entire tissue slice. New Zealand White rabbits with implanted VX2 thigh tumours were scanned using CT with contrast media injection. The ex vivo method of radioactive microspheres was used to evaluate the accuracy of BF measurements with the functional CT technique. There was a significant linear correlation (R = 0.96) between regional CT and microsphere-measured BF values, with a slope not significantly different from unity (0.98 +/- 0.02, P < 0.0001). The precision of our CT technique was determined by the repeated scanning under steady-state conditions. The precision of CT-measured BF, PS. BV and MTT was 14%, 18%, 20% and 24%, respectively. In conclusion, BF can be measured accurately and BF, PS, BV and MTT reproducibly using our functional CT technique. Functional CT can be readily incorporated into existing imaging protocols to assess tumour angiogenesis.

Dynamic contrast enhanced CT measurement of blood flow during interstitial laser photocoagulation: comparison with an Arrhenius damage model.

One effect of heating during interstitial laser photocoagulation (ILP) is to directly destroy the tumour vasculature resulting in a loss of viable blood supply. Therefore, blood flow measured during and after treatment can be a useful indicator of tissue thermal damage. In this study, the effect of ILP treatment on rabbit thigh tumours was investigated by measuring blood flow changes using dynamic contrast enhanced computed tomography (CT). The CT measured changes in blood flow of treated tumour tissue were fitted to an Arrhenius model assuming first order rate kinetics. Our results show that changes in blood flow of tumour tissue distant from surrounding normal tissue are well described by an Arrhenius model. By contrast, the temperature profile of tumour tissue adjacent to normal tissue must be modified to account for heat dissipation by the latter. Finally, the Arrhenius parameters derived in the study are similar to those derived by heating tumour tissue to a lower temperature (<47 degrees C) than the current study. In conclusion, CT can be used to monitor blood flow changes during ILP and these measurements are related to the thermal damage predicted by the Arrhenius model.