Pattern of failure after helical tomotherapy in head and neck cancer.

BACKGROUND AND PURPOSE: Helical tomotherapy (HT, Hi-Art TomoTherapy(®)) is a recently developed radiation device delivering highly conformal dose with a rotational gantry resulting in more uniform target doses and better avoidance of organs at risk. Treatment failure patterns in head and neck cancer (HNC) patients treated with HT were analyzed. PATIENTS AND METHODS: 63 patients with a biopsy-proven HNC were treated with HT. In patients with locoregional failure, the volume of failure (Vf) was contoured and co-registered with the initial planning computed tomography scan. With the use of dose-volume histogram (DVH) analysis, the Vf was classified as "in-field" (InF), "marginal" (MF) or "outside-field" (OutF), if ≥ 95%, 20-94%, and < 20% of Vf, respectively, were within the 95% isodose. RESULTS: Median follow-up time was 25 months (95% confidence interval 19.4-28 months). 2-year overall survival, disease-free survival, and locoregional control were 66%, 54%, and 77%, respectively. 13 patients developed a locoregional failure (four local, eight regional, and one local and regional). After DVH analysis, there were ten InF and two MF recurrences as well as one OutF recurrence. CONCLUSION: Target delineation and coverage were adequate. The majority of locoregional failures were InF, i.e., in the high-dose region. Future work on dose escalation to the highest risk regions is recommended.

Assessment of rectal distention in radiotherapy of prostate cancer using daily megavoltage CT image guidance.

PURPOSE: Assessment of rectal distention in a group of patients who are not receiving daily rectum emptying procedures during a course of prostate cancer radiotherapy to investigate which patients could benefit from daily rectum emptying. METHODS AND MATERIALS: Eighteen patients underwent daily megavoltage CT (MVCT) scanning with positioning based on bony anatomy. Emptying the rectum was only performed before planning CT and not during the actual treatment. The rectal average cross-sectional area (CSA) was determined on the MVCTs. The relative CSA (CSA(rel)) was defined as CSA on MVCT / CSA on planning CT. Additional prostate soft tissue matching was performed to verify the influence of rectal distention on prostate motion. RESULTS: Two distinct subgroups could be defined a posteriori. One group had a limited and stable rectal distention with a CSA (mean+/-SD) of 6.6+/-2.1cm(2), in contrast with a second group with large and variable rectal filling with a CSA of 9.5+/-3.7cm(2) (p<0.01). Mean anterior-posterior prostate displacement was 0.4+/-2.4 mm in the stable group versus -2.4+/-6.1 mm in the unstable group (p<0.01). A mean CSA(rel) of 1.35 of the first 3 days as cut-off value allowed for a correct a priori classification of 90% and 85% of the patients from groups 1 and 2, respectively. CONCLUSION: Based on a few measurements of the CSA by daily MVCT imaging at the first days of treatment, rectum emptying may be omitted in part of the patients.

Helical tomotherapy with simultaneous integrated boost for high-risk and lymph node-positive prostate cancer: early report on acute and late toxicity.

The use of whole pelvic radiotherapy (WPRT) for high-risk and lymph node-positive prostate cancer (PC) remains controversial. The purpose of this study was to evaluate the acute toxicity associated with helical tomotherapy in the treatment of high-risk and lymph node-positive prostate cancer. To do so, twenty-eight patients were treated to a dose of 54 Gy in daily fractions of 1.8 Gy to the pelvic lymph node area, while the prostate and the seminal vesicles received a simultaneous integrated boost (SIB) to a dose of 70.5 Gy. A SIB to a dose of 60 Gy was delivered to the involved lymph node region(s) in 8 patients with pelvic lymph node metastases. All patients received concurrent hormonal treatment. The incidence of grade 2 and 3 acute gastrointestinal (GI) toxicity was 7% and 0% respectively. Grade 2 and 3 acute genito-urinary (GU) side effects were observed in 14% and 4% of the patients respectively. No grade 4 side effects occurred. No increased toxicity was observed in the 8 lymph node-positive patients receiving a simultaneous pelvic nodal dose escalation. In conclusion, WPRT with a SIB to the prostate and seminal vesicles by helical tomotherapy resulted in a favourable toxicity profile. Pelvic nodal dose escalation in node-positive patients is feasible without increasing toxicity.

A diagnostic tool for basic daily quality assurance of a Tomotherapy Hi*Art machine.

To investigate and evaluate the use of an in-house developed diagnostic software tool using the imaging detector data for a quick daily quality assurance check of the output (dose) and lateral profile (cone) of a tomotherapy Hi*Art system. The Hi*Art treatment system is a radiation therapy machine for delivering intensity modulated radiation therapy (IMRT) in a helical fashion with an integrated CT scanner used for improved patient positioning before treatment. Since the system was developed specifically for IMRT, flat fields can be obtained by modulating the beam and therefore the flattening filter could be omitted. Because of this, the field has a cone-like profile in both lateral and transversal directions. Patients are treated in a helical fashion with a tight pitch and a constant gantry rotation speed, while modulation is performed by a binary MLC. Consequently dose output per time-unit (dose rate) as well as the shape of the cone-profile are very important for correct patient treatment and should be closely monitored. However, using the company-provided initial tools and conventional dosimetry, this can be a time consuming daily procedure. The aim of this work is to develop a fast, automated method of quality assurance based on the detector signal. A software tool called "tomocheck" running on the operation station has been developed to evaluate the output (dose rate) and the lateral cone profile (energy) of the Hi*Art system, comparing actual output and cone profile with a reference (previously approved against ionization chamber measurements). This is done by using the data of the 640 on-board detector array that are directly retrieved and processed after a specific QA procedure. The detector file consists of the CT detector data and the three monitoring dose chamber readings over a time period of 200 sec. To evaluate the method, the system was benchmarked against ionization chamber measurements and classical IMRT QA methods. Action levels (final status "NOT ACCEPTED") for dose ratio as well as the cone ratio are set to +/- 2%. The QA tool was introduced for daily QA in May 2007. For the following 24 months, a total of 931 morning checks was made on both tomotherapy machines. In 42 cases the check status was "NOT ACCEPTED". In 34 cases the dose ratio (DR) was out of tolerance. The corrected cone ratio (CCR) was outside of specification tolerance in 8 cases. The tomocheck data was related to the ionization chamber measurements for the IMRT plan indicating a close relationship between the CCR and the off-axis measurements. Average dose ratio against the mean value of the on- and off-axis IC measurement indicates that this parameter is a good interpretation of the dose output. This tool makes it possible to perform an easy-to-use and fast basic daily quality assurance check featuring an output as well as an energy evaluation. Ideally this tool should offer also the combined dosimetry check of jaw width, couch speed, leaf latency, output, leaf/gantry synchrony, and lasers. This will be investigated in the future.

Phase II study of preoperative helical tomotherapy for rectal cancer.

PURPOSE: To explore the efficacy and toxicity profile of helical tomotherapy in the preoperative treatment of patients with rectal cancer. PATIENTS AND METHODS: Twenty-four patients with T3/T4 rectal cancer were included in this nonrandomized noncontrolled study. A dose of 46 Gy in daily fractions of 2 Gy was delivered to the presacral space and perineum if an abdominoperineal resection was deemed necessary. This dose was increased by a simultaneous integrated boost to 55.2 Gy when the circumferential resection margin was less than 2 mm on magnetic resonance imaging. Acute toxicity was evaluated weekly. Metabolic response was determined in the fifth week after the end of radiotherapy by means of fluorodeoxyglucose-positron emission tomography scan. A metabolic response was defined as a decrease in maximal standardized uptake value of more than 36%. RESULTS: The mean volume of small bowel receiving more than 15 Gy and mean bladder dose were 227 ml and 20.8 Gy in the no-boost group and 141 ml and 21.5 Gy in the boost group. Only 1 patient developed Grade 3 enteritis. No other Grade 3 or 4 toxicities were observed. Two patients developed an anastomotic leak within 30 days after surgery. The metabolic response rate was 45% in the no-boost group compared with 77% in the boost group. All except 1 patient underwent an R0 resection. CONCLUSIONS: Helical tomotherapy may decrease gastrointestinal toxicity in the preoperative radiotherapy of patients with rectal cancer. A simultaneous integrated radiation boost seems to result in a high metabolic response rate without excessive toxicity.

Assessment of intrafractional movement and internal motion in radiotherapy of rectal cancer using megavoltage computed tomography.

PURPOSE: The aim of this study was to provide estimates of setup and internal margins of patients treated for rectal carcinoma using helical tomotherapy and to assess possible margin adaptations. Using helical tomotherapy, highly conformal dose distributions can be created, and the integrated megavoltage computed tomography (MVCT) modality allows very precise daily patient positioning. In clinical protocols, however, margins originating from traditional setup procedures are still being applied. This work investigates whether this modality can aid in redefining treatment margins. METHODS AND MATERIALS: Ten patients who were treated with tomotherapy underwent MVCT scanning before and after 10 treatments. Using automatic registration the necessary setup margin was investigated by means of bony landmarks. Internal margins were assessed by delineating and describing the mesorectal movement. RESULTS: Based on bony landmarks, movement of patients during treatments was limited to 2.45 mm, 1.99 mm, and 1.09 mm in the lateral, longitudinal, and vertical direction, respectively. Systematic errors were limited to <1 mm. Measured movement of the mesorectal space was -1.6 mm (+/- 4.2 mm) and 0.1 mm (+/- 4.0 mm) for left and right lateral direction. In the antero-posterior direction, mean shifts were -2 mm (+/- 6.8 mm) and -0.4 mm (+/- 3.8 mm). Mean shifts in the cranio-caudal direction were respectively -3.2 mm (+/- 5.6 mm) and -3.2 mm (+/- 6.8 mm). CONCLUSIONS: The use of the integrated MVCT on the tomotherapy system can minimize the setup margin for rectal cancer, and can also be used to adequately describe the internal margin allowing for direct treatment margin adaptation.

TomoTherapy: implications on daily workload and scheduling patients.

PURPOSE: The aim of the study was to measure the mean duration of treatments and to investigate the occasional events, with extreme influence on treatment time. PATIENTS AND METHODS: Time measurements were performed from the start of patient treatments (n=72) and one year later (n=27) on TomoTherapy. The time interval of the different procedures during treatment was measured. The cause of extra long treatment time was examined. All patients received a MV-CT scan prior to treatment. RESULTS: The mean overall total treatment time per localization ranged from 21.3 to 27.4 min. In 4.1% of the total population extreme long time measurements have been observed, interruptions due to equipment malfunction being the main cause (57.5%). Comparison between time measurements performed after clinical implementation and time measurements performed one year later to examine the learning curve, showed no differences. CONCLUSION: Treating a patient on TomoTherapy takes approximately 25 min, yielding 19 patients to be treated within 8 h. However, occasional treatment interruptions and variations in time of irradiation have a certain impact on daily patient scheduling for treatment, and influences the workload from day-to-day.

Assessment of secondary patient motion induced by automated couch movement during on-line 6 dimensional repositioning in prostate cancer treatment.

BACKGROUND AND PURPOSE: The purpose of this study is to assess retrospectively secondary patient motion induced by 6D patient setup correction. MATERIALS AND METHODS: For 104 patients, treated with Novalis, 6D setup correction prior to treatment was performed by ExacTrac5.0/NovalisBody in combination with the Robotic Tilt Module mounted underneath the Exact Couch top. This 6D correction might induce additional setup errors due to patient reaction against the rotations. To evaluate induced secondary motion, the 6D setup correction is verified and evaluated with respect to the tolerance limits. RESULTS: The majority of measured secondary motions are found within the tolerance limits. Detected secondary motions are mostly found in longitudinal shifts and lateral rotations, and mainly found in only 1 dimension during the same verification. The verifications indicate that the patient population can be divided into a group that hardly moves and a group that moves throughout all 6D setup corrections. The patient's behavior can be predicted by the evaluation of the first five fractions as none of the patients demonstrate a learning curve during the treatment. CONCLUSIONS: 6D setup correction does not induce secondary motion for the majority of the patients and can therefore be applied for all treatment indications.

An assessment of the use of skin flashes in helical tomotherapy using phantom and in-vivo dosimetry.

BACKGROUND AND PURPOSE: In helical tomotherapy the nature of the optimizing and planning systems allows the delivery of dose on the skin using a build-up compensating technique (skin flash). However, positioning errors or changes in the patient's contour can influence the correct dosage in these regions. This work studies the behavior of skin-flash regions using phantom and in-vivo dosimetry. MATERIALS AND METHODS: The dosimetric accuracy of the tomotherapy planning system in skin-flash regions is checked using film and TLD on phantom. Positioning errors are induced and the effect on the skin dose is investigated. Further a volume decrease is simulated using bolus material and the results are compared. RESULTS: Results show that the tomotherapy planning system calculates dose on skin regions within 2 SD using TLD measurements. Film measurements show drops of dose of 2.8% and 26% for, respectively, a 5mm and 10mm mispositioning of the phantom towards air and a dose increase of 9% for a 5mm shift towards tissue. These measurements are confirmed by TLD measurements. A simulated volume reduction shows a similar behavior with a 2.6% and 19.4% drop in dose, measured with TLDs. CONCLUSION: The tomotherapy system allows adequate planning and delivery of dose using skin flashes. However, exact positioning is crucial to deliver the dose at the exact location.

Treating patients with Dynamic Wave Arc: First clinical experience.

BACKGROUND AND PURPOSE: Dynamic Wave Arc (DWA) is a system-specific noncoplanar arc technique that combines synchronized gantry-ring rotation with D-MLC optimization. This paper presents the clinical workflow, quality assurance program, and reports the geometric and dosimetric results of the first patient cohort treated with DWA. METHODS AND MATERIALS: The RayStation TPS was clinically integrated on the Vero SBRT platform for DWA treatments. The first 15 patients treated with DWA represent a broad range of treatment sites: breast boost, prostate, lung SBRT and bone metastases, which allowed us to explore the potentials and assess the limitations of the current DWA site-specific template solution. For the DWA verification a variety of QA equipment was used, from 3D diode array to an anthropomorphic end-to-end phantom. The geometric accuracy of each arc was verified with an independent orthogonal fluoroscopy method. RESULTS: The average beam-on delivery time was 3min, ranging from 1.22min to 8.82min. All patient QAs passed our institutional clinical criteria of gamma index. For both EBT3 film and Delta4 measurements, DWA planned versus delivered dose distributions presented an average agreement above 97%. An overall mean gantry-ring geometric deviation of -0.03°±0.46° and 0.18°±0.26° was obtained, respectively. CONCLUSION: For the first time, DWA has been translated into the clinic and used to treat various treatment sides. DWA has been successfully added to the noncoplanar rotational IMRT techniques arsenal, allowing additional flexibility in dose shaping while preserving dosimetrically robust delivery.

Setup accuracy of stereoscopic X-ray positioning with automated correction for rotational errors in patients treated with conformal arc radiotherapy for prostate cancer.

We evaluated setup accuracy of NovalisBody stereoscopic X-ray positioning with automated correction for rotational errors with the Robotics Tilt Module in patients treated with conformal arc radiotherapy for prostate cancer. The correction of rotational errors was shown to reduce random and systematic errors in all directions. (NovalisBody and Robotics Tilt Module are products of BrainLAB A.G., Heimstetten, Germany).

Importing measured field fluences into the treatment planning system to validate a breathing synchronized DMLC-IMRT irradiation technique.

BACKGROUND AND PURPOSE: Recalculating dose distributions using measured IMRT fluence fields imported into the treatment planning system (TPS) to evaluate the technical feasibility of a prototype developed for breathing synchronized irradiation. PATIENTS AND METHODS: DMLC-IMRT fluence patterns acquired on radiographic film, generated by the linac in non-gated and gated mode, have been imported into the TPS. The effect of dose blurring and possible interplay between organ motion and leaf motion, and the efficacy of a breathing synchronized irradiation technique (an adapted version of a commercially available image-guidance system: NOVALIS BODY/ExacTrac4.0, BrainLAB AG) have been evaluated using radiographic film mounted to a simple phantom simulating a breathing pattern of 16 cycles per minute and covering a distance of 4 cm to obtain the resulting fluence maps. Two situations have been investigated to illustrate this principle: (a) a tumor located close to the diaphragm to assess the influence of organ motion on the dose to the target volume as well as to the gastro-intestinal tract that presents a high risk at intersecting with the beam during the breathing cycle. (b) A mediastinal lesion requiring complicated fluence patterns. RESULTS: Importing measured fluence maps yielded highly disturbed reconstructed dose distributions in case of the non-gated delivery with the phantom in motion (both orthogonal and parallel to the leaf direction), whereas the measurements from the static (film fixed in space) and the gated delivery showed good agreement with the original theoretical dose distribution. These findings have been confirmed by the dose-volume histograms, corresponding tumor control probabilities, conformity index and dose heterogeneity values. The normal tissue complication probabilities investigated in this study seem to be affected to a lesser degree, which concurs with the observation that the motion effects result in a dose spread in the direction of motion. The applied breathing synchronization technique introduced an increased treatment time with a factor 3-4. CONCLUSIONS: The use of measured fluence fields, delivered by the linac in non-gated and gated mode, as imported fluence maps for the treatment planning system is an interesting quality assurance tool and revealed the dramatic impact of dose blurring and interplay between DMLC-IMRT dose delivery and organ motion, as well as the potential of breathing synchronization to resolve this issue. The possible advantage of breathing synchronized irradiation is compromised with an increased treatment time.

Six dimensional analysis with daily stereoscopic x-ray imaging of intrafraction patient motion in head and neck treatments using five points fixation masks.

The safety margins used to define the Planning Target Volume (PTV) should reflect the accuracy of the target localization during treatment that comprises both the reproducibility of the patient positioning and the positional uncertainty of the target, so both the inter- and intrafraction motion of the target. Our first aim in this study was to determine the intrafraction motion of patients immobilized with a five-point thermoplastic mask for head and neck treatments. The five-point masks have the advantage that the patient's shoulders as well as the cranial part of the patient's head is covered with the thermoplastic material that improves the overall immobilization of the head and neck region of the patient. Thirteen patients were consecutively assigned to use a five-point thermoplastic mask. The patients were positioned by tracking of infrared markers (IR) fixed to the immobilization device and stereoscopic x-ray images were used for daily on-line setup verification. Repositioning was carried out prior to treatment as needed; rotations were not corrected. Movements during treatment were monitored by real-time IR tracking. Intrafraction motion and rotation was supplementary assessed by a six-degree-of-freedom (6-D) fusion of x-ray images, taken before and after all 385 treatments, with DRR images generated from the planning CT data. The latter evaluates the movement of the patient within the thermoplastic mask independent from the mask movement, where IR tracking evaluates the movement of the mask caused by patient movement in the mask. These two movements are not necessarily equal to each other. The maximum intrafraction movement detected by IR tracking showed a shift [mean (SD; range)] of -0.1(0.7; 6.0), 0.1(0.6; 3.6), -0.2(0.8;5.5) mm in the vertical, longitudinal, and lateral direction, respectively, and rotations of 0.0(0.2; 1.6), 0.0(0.2; 1.7) and 0.2(0.2; 2.4) degrees about the vertical, longitudinal, and lateral axis, respectively. The standard deviations and ranges found with the 6-D fusion demonstrate intrafraction patient displacements of -0.5(1.2; 7.4), 0.3(0.7; 5.3), 0.0(0.7; 5.7) mm in the vertical, longitudinal, and lateral direction, respectively, and rotations of -0.1(0.6; 4.1), 0.1(0.7; 8.3) and -0.2(0.8; 8.2) degrees about the vertical, longitudinal, and lateral axis, respectively. The 6-D fusions are considerably larger (p < 0.05) than detected by IR tracking. This indicates that the external marker tracking underestimates the magnitude of the actual intrafraction motion and rotation of the patient. The intrafraction motion detected for the patients immobilized with a conventional thermoplastic mask was relatively large. The feasibility to reduce this intrafraction movement by the application of alternative five-point thermoplastic mask types was evaluated as a second aim of this study. The preliminary results showed a clear reduction in the range, being an indication for the random movements, of both the intrafraction shift and rotation for both alternative mask types. The 6-D fusion is found a useful tool for a fast evaluation of the actual patient's intrafraction shift and rotation and shows the latter is not negligible and needs to be taken into account additional to the initial setup accuracy when determining the PTV margin.

Quality Assurance of a 50-kV Radiotherapy Unit Using EBT3 GafChromic Film: A Feasibility Study.

PURPOSE: Radiochromic EBT3 film is gaining acceptance as a valuable dosimetry system for high-energy photon beams. The advantages of these films over other dosimetry systems are low spectral sensitivity and high spatial resolution. The aim of this study was to validate EBT3 film as a dosimeter for machine and treatment quality assurance (QA) of a 50-kV radiotherapy unit. METHODS AND MATERIALS: Absolute and relative doses were acquired using EBT3 GafChromic films and compared to a parallel-plate ionization chamber (IC), the standard IC for low-energy X-rays. EBT3 was also used to evaluate beam profiles and output factors. Two films above each other, mimicking the clinical situation of a dosimeter on top of the skin, were simultaneously irradiated to evaluate EBT3 as in vivo dosimeter. All films were irradiated for 3 minutes, which corresponds with a surface dose of 3.25 ± 0.07 Gy. RESULTS: A fifth-order polynomial function was found to be the best fit for the calibration curves. Good agreement between IC and EBT3 was found for absolute (0.92% for green and red color channels) and relative (1.2% and 1.0% for green and red color channels, respectively) dosimetry. Output factors for IC and EBT3 were comparable within 2.04% and 1.02% for the green and red color channels, respectively. Flatness and symmetry at the surface were within 2%. By applying film as in vivo dosimeter, an absorption of 4.70% needs to be taken into account with respect to the surface dose. CONCLUSION: EBT3 GafChromic film is a feasible and valuable QA and dosimetry tool for a 50-kV radiotherapy unit. EBT3 can be used for absolute and relative dosimetry, measurement of output factors and beam profiles. In vivo patient-specific QA can also be performed if one corrects for the dose absorption of the film.

Geometric Verification of Dynamic Wave Arc Delivery With the Vero System Using Orthogonal X-ray Fluoroscopic Imaging.

PURPOSE: The purpose of this study was to define an independent verification method based on on-board orthogonal fluoroscopy to determine the geometric accuracy of synchronized gantry-ring (G/R) rotations during dynamic wave arc (DWA) delivery available on the Vero system. METHODS AND MATERIALS: A verification method for DWA was developed to calculate O-ring-gantry (G/R) positional information from ball-bearing positions retrieved from fluoroscopic images of a cubic phantom acquired during DWA delivery. Different noncoplanar trajectories were generated in order to investigate the influence of path complexity on delivery accuracy. The G/R positions detected from the fluoroscopy images (DetPositions) were benchmarked against the G/R angulations retrieved from the control points (CP) of the DWA RT plan and the DWA log files recorded by the treatment console during DWA delivery (LogActed). The G/R rotational accuracy was quantified as the mean absolute deviation ± standard deviation. The maximum G/R absolute deviation was calculated as the maximum 3-dimensional distance between the CP and the closest DetPositions. RESULTS: In the CP versus DetPositions comparison, an overall mean G/R deviation of 0.13°/0.16° ± 0.16°/0.16° was obtained, with a maximum G/R deviation of 0.6°/0.2°. For the LogActed versus DetPositions evaluation, the overall mean deviation was 0.08°/0.15° ± 0.10°/0.10° with a maximum G/R of 0.3°/0.4°. The largest decoupled deviations registered for gantry and ring were 0.6° and 0.4° respectively. No directional dependence was observed between clockwise and counterclockwise rotations. Doubling the dose resulted in a double number of detected points around each CP, and an angular deviation reduction in all cases. CONCLUSIONS: An independent geometric quality assurance approach was developed for DWA delivery verification and was successfully applied on diverse trajectories. Results showed that the Vero system is capable of following complex G/R trajectories with maximum deviations during DWA below 0.6°.

Feasibility of markerless tumor tracking by sequential dual-energy fluoroscopy on a clinical tumor tracking system.

A novel approach to dual-energy imaging for markerless tumor tracking was proposed consisting of sequential dual-energy fluoroscopy, omitting the need for fast-switching kV generators. The implementation of this approach on a clinical tumor tracking system and its efficacy is shown feasible through optimization of the imaging parameters.

Multi-institutional feasibility study of a fast patient localization method in total marrow irradiation with helical tomotherapy: a global health initiative by the international consortium of total marrow irradiation.

PURPOSE: To develop, characterize, and implement a fast patient localization method for total marrow irradiation. METHODS AND MATERIALS: Topographic images were acquired using megavoltage computed tomography (MVCT) detector data by delivering static orthogonal beams while the couch traversed through the gantry. Geometric and detector response corrections were performed to generate a megavoltage topogram (MVtopo). We also generated kilovoltage topograms (kVtopo) from the projection data of 3-dimensional CT images to reproduce the same geometry as helical tomotherapy. The MVtopo imaging dose and the optimal image acquisition parameters were investigated. A multi-institutional phantom study was performed to verify the image registration uncertainty. Forty-five MVtopo images were acquired and analyzed with in-house image registration software. RESULTS: The smallest jaw size (front and backup jaws of 0) provided the best image contrast and longitudinal resolution. Couch velocity did not affect the image quality or geometric accuracy. The MVtopo dose was less than the MVCT dose. The image registration uncertainty from the multi-institutional study was within 2.8 mm. In patient localization, the differences in calculated couch shift between the registration with MVtopo-kVtopo and MVCT-kVCT images in lateral, cranial-caudal, and vertical directions were 2.2 ± 1.7 mm, 2.6 ± 1.4 mm, and 2.7 ± 1.1 mm, respectively. The imaging time in MVtopo acquisition at the couch speed of 3 cm/s was <1 minute, compared with ≥15 minutes in MVCT for all patients. CONCLUSION: Whole-body MVtopo imaging could be an effective alternative to time-consuming MVCT for total marrow irradiation patient localization.

Impact of inadequate respiratory motion management in SBRT for oligometastatic colorectal cancer.

PURPOSE: Stereotactic body radiotherapy (SBRT) in oligometastatic colorectal cancer (CRC) resulted in a disappointing 1-year local control rate of 54% in our experience. We aimed to determine the root cause(s). METHODS: 47 oligometastatic CRC patients were treated with SBRT by helical tomotherapy to a dose of 40 or 50Gy in 10 fractions, without specific respiratory motion management and PTV-margins of 10-10-12mm in all patients. The local recurrences (LRs) were delineated on diagnostic PET-CT scans and co-registered with initial planning CTs. LRs were classified as in-field or marginal with respect to the initial dose distribution, and predictors for LR were determined. RESULTS: Out of 105 irradiated metastases, LR modeling yielded 15 in-field and 15 marginal failures. Metastases in moving organs (liver and lung) exhibited a local control of 53% at 1-year (95% confidence interval (CI): 38-67%), compared to 79% for lymph nodes (95% CI: 32-95%). The first group exhibited a sixfold increased risk compared to the latter on multivariate analysis (p=0.01). CONCLUSIONS: The nature and locations of LR indicated that dose prescription and methodology were both inadequate for liver and lung metastases. This study demonstrates the need for individual respiratory motion management and a biological effective dose of >75Gy.

Dosimetric comparison of different treatment modalities for stereotactic radiosurgery of arteriovenous malformations and acoustic neuromas.

PURPOSE: We investigated the influence of beam modulation on treatment planning by comparing four available stereotactic radiosurgery (SRS) modalities: Gamma-Knife-Perfexion, Novalis-Tx Dynamic-Conformal-Arc (DCA) and Dynamic-Multileaf-Collimation-Intensity-Modulated-radiotherapy (DMLC-IMRT), and Cyberknife. MATERIAL AND METHODS: Patients with arteriovenous malformation (n = 10) or acoustic neuromas (n = 5) were planned with different treatment modalities. Paddick conformity index (CI), dose heterogeneity (DH), gradient index (GI) and beam-on time were used as dosimetric indices. RESULTS: Gamma-Knife-Perfexion can achieve high degree of conformity (CI = 0.77 ± 0.04) with limited low-doses (GI = 2.59 ± 0.10) surrounding the inhomogeneous dose distribution (D(H) = 0.84 ± 0.05) at the cost of treatment time (68.1 min ± 27.5). Novalis-Tx-DCA improved this inhomogeneity (D(H) = 0.30 ± 0.03) and treatment time (16.8 min ± 2.2) at the cost of conformity (CI = 0.66 ± 0.04) and Novalis-TX-DMLC-IMRT improved the DCA CI (CI = 0.68 ± 0.04) and inhomogeneity (D(H) = 0.18 ± 0.05) at the cost of low-doses (GI = 3.94 ± 0.92) and treatment time (21.7 min ± 3.4) (p<0.01). Cyberknife achieved comparable conformity (CI = 0.77 ± 0.06) at the cost of low-doses (GI = 3.48 ± 0.47) surrounding the homogeneous (D(H) = 0.22 ± 0.02) dose distribution and treatment time (28.4min±8.1) (p<0.01). CONCLUSIONS: Gamma-Knife-Perfexion will comply with all SRS constraints (high conformity while minimizing low-dose spread). Multiple focal entries (Gamma-Knife-Perfexion and Cyberknife) will achieve better conformity than High-Definition-MLC of Novalis-Tx at the cost of treatment time. Non-isocentric beams (Cyberknife) or IMRT-beams (Novalis-Tx-DMLC-IMRT) will spread more low-dose than multiple isocenters (Gamma-Knife-Perfexion) or dynamic arcs (Novalis-Tx-DCA). Inverse planning and modulated fluences (Novalis-Tx-DMLC-IMRT and CyberKnife) will deliver the most homogeneous treatment. Furthermore, Linac-based systems (Novalis and Cyberknife) can perform image verification at the time of treatment delivery.

A complementary dual-modality verification for tumor tracking on a gimbaled linac system.

BACKGROUND AND PURPOSE: For dynamic tracking of moving tumors, robust intra-fraction verification was required, to assure that tumor motion was properly managed during the course of radiotherapy. A dual-modality verification system, consisting of an on-board orthogonal kV and planar MV imaging device, was validated and applied retrospectively to patient data. METHODS AND MATERIALS: Real-time tumor tracking (RTTT) was managed by applying PAN and TILT angular corrections to the therapeutic beam using a gimbaled linac. In this study, orthogonal X-ray imaging and MV EPID fluoroscopy was acquired simultaneously. The tracking beam position was derived from respectively real-time gimbals log files and the detected field outline on EPID. For both imaging modalities, the moving target was localized by detection of an implanted fiducial. The dual-modality tracking verification was validated against a high-precision optical camera in phantom experiments and applied to clinical tracking data from a liver and two lung cancer patients. RESULTS: Both verification modalities showed a high accuracy (<0.3mm) during validation on phantom. Marker detection on EPID was influenced by low image contrast. For the clinical cases, gimbaled tracking showed a 90th percentile error (E90) of 3.45 (liver), 2.44 (lung A) and 3.40 mm (lung B) based on EPID fluoroscopy and good agreement with XR-log file data by an E90 of 3.13, 1.92 and 3.33 mm, respectively, during beam on. CONCLUSION: Dual-modality verification was successfully implemented, offering the possibility of detailed reporting on RTTT performance.