6D image guidance for spinal non-invasive stereotactic body radiation therapy: Comparison between ExacTrac X-ray 6D with kilo-voltage cone-beam CT

Purpose

To investigate setup discrepancies measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for patients under treatments of stereotactic body radiation therapy (SBRT).

Materials and methods

In this work, phantom and patient studies were performed. In the phantom studies, an anthropomorphic phantom was placed with pre-defined positions, and imaged with ExacTrac X-ray 6D and CBCT to test the accuracy of the imaging systems. In the patient studies, 16 spinal SBRT patient cases were retrospectively analyzed. The patients were initially positioned in customized immobilization cradles and then aligned with ExacTrac X-ray 6D and CBCT. The setup discrepancies were computed and quantitatively analyzed.

Results

This study indicates modest discrepancies between ExacTrac X-ray 6D and CBCT with spinal SBRT. The phantom experiments showed that translational and rotational discrepancies in root-mean-square (RMS) between ExacTrac X-ray 6D and CBCT were, respectively, <1.0 mm and <1°. In the retrospective patient studies, translational and rotational discrepancies in RMS between ExacTrac X-ray 6D and CBCT were <2.0 mm and <1.5°.

Conclusions

ExacTrac X-ray 6D represents a potential alternative to CBCT; however, pre-caution should be taken when only ExacTrac X-ray 6D is used to guide SBRT with small setup margins.     

Comparative study of respiratory motion correction techniques in cone-beam computed tomography

Background and purpose

To validate the clinical usefulness of motion-compensated (MC) cone-beam (CB) computed tomography (CT) for image-guided radiotherapy (IGRT) in comparison to four-dimensional (4D) CBCT and three-dimensional (3D) CBCT.

Material and methods

Forty-eight stereotactic body radiation therapy (SBRT) patients were selected. Each patient had 5-12 long CB acquisitions (4 min) and 1-7 short CB acquisitions (1 min), with a total of 349 and 150 acquisitions, respectively. 3D, 4D and MC CBCT images of every acquisition were reconstructed. Image quality, tumor positioning accuracy and tumor motion amplitude were quantified.

Results

The mean image quality of long short acquisitions, measured using the correlation ratio with the planning CT, was 74%/70%, 67%/47% and 79%/74% for 3D, 4D and MC CBCT, respectively; both 4D and MC CBCT were corrected for respiratory motion artifacts but 4D CBCTs suffered from streak artifacts. Tumor positioning with MC CBCT was significantly closer to 4D CBCT than 3D CBCT (p < 0.0001). Detailed patient analysis showed that motion correction was not required for tumors with less than 1 cm motion amplitude.

Conclusions

4D and MC CBCT both allow accurate tumor position analysis under respiratory motion but 4D CBCT requires longer acquisition time than MC CBCT for adequate image quality. MC CBCT can therefore advantageously replace 4D CBCT in clinical protocols for patients with large motion to improve image quality and reduce acquisition time.     

Treatment delivery time optimization of respiratory gated radiation therapy by application of audio-visual feedback

Purpose

The feasibility to use visually guided voluntary breath-hold with and without audio assistance to reduce the total treatment time was evaluated.

Materials and methods

Patients referred for gated SBRT received hypofractionation schedules for lung or liver treatments. The patients were treated with the Novalis^® system (BrainLAB AG, Feldkirchen, Germany) and IGRT was performed with ExacTrac5.0/NovalisBody^® allowing gated irradiation. Video glasses, used for visual feedback to guide voluntary breath-hold, allowed additional audio assistance during treatment.The technique was applied for 25 patients of whom 9 were treated in free breathing, 7 had only visual feedback and another 9 had both audio and visual feedback.

Results

The delivery time of gated treatment during free breathing had an average value of 1.7 min/100 MU (SD 0.6 min/100 MU). The introduction of visual feedback reduced the average delivery time to 1.4 min/100 MU (SD 0.4 min/100 MU). The treatments with additional audio assistance indicated a significant reduction (p = 0.004) of the average delivery time to 0.9 min/100 MU (SD 0.2 min/100 MU).

Conclusion

The introduction of visually guided voluntary breath-hold with audio assistance led to treatment times for gated radiation therapy approaching conformal beam delivery times, which made gated treatments applicable in conventional treatment time slots.     

Image quality and stability of image-guided radiotherapy (IGRT) devices: A comparative study

Introduction

Our aim was to implement standards for quality assurance of IGRT devices used in our department and to compare their performances with that of a CT simulator.

Materials and methods

We investigated image quality parameters for three devices over a period of 16 months. A multislice CT was used as a benchmark and results related to noise, spatial resolution, low contrast visibility (LCV) and uniformity were compared with a cone beam CT (CBCT) at a linac and simulator.

Results

All devices performed well in terms of LCV and, in fact, exceeded vendor specifications. MTF was comparable between CT and linac CBCT. Integral nonuniformity was, on average, 0.002 for the CT and 0.006 for the linac CBCT. Uniformity, LCV and MTF varied depending on the protocols used for the linac CBCT. Contrast-to-noise ratio was an average of 51% higher for the CT than for the linac and simulator CBCT. No significant time trend was observed and tolerance limits were implemented.

Discussion

Reasonable differences in image quality between CT and CBCT were observed. Further research and development are necessary to increase image quality of commercially available CBCT devices in order for them to serve the needs for adaptive and/or online planning.     

ExacTrac X-ray 6 degree-of-freedom image-guidance for intracranial non-invasive stereotactic radiotherapy: Comparison with kilo-voltage cone-beam CT

Background and purpose

To compare the residual setup errors measured with ExacTrac X-ray 6 degree-of-freedom (6D) and cone-beam computed tomography (CBCT) for a head phantom and patients receiving intracranial non-invasive fractionated stereotactic radiotherapy (SRT).

Materials and methods

Setup data were collected on a Novalis Tx treatment unit for an anthropomorphic head phantom and 18 patients with intracranial tumors. Initial corrections were determined and corrected with the ExacTrac system only, and then the residual setup error was determined by means of three different procedures. These procedures included registrations of ExacTrac X-ray images with the corresponding digitally reconstructed radiographs (DRRs) using the ExacTrac 6D fusion, and registrations of CBCT images with the planning CT using both online 3D fusion and offline 6D fusion. The difference in residual setup errors between ExacTrac system and CBCT was computed. The impact of rotations on the difference was evaluated.

Results

A modest difference in residual setup errors was found between ExacTrac system and CBCT. The root-mean-square (RMS) of the differences observed for translations was typically <0.5 mm for phantom, and <1.5 mm for patients, respectively. The RMS of the differences for rotation(s) was however <0.2 degree for phantom, and <1.0 degree for patients, respectively. The impact of rotation on the setup difference was minor but not negligible.

Conclusions

This study indicates that there is a general agreement between ExacTrac system and CBCT.     

Mathematical estimation and in vivo dose measurement for cone-beam computed tomography on prostate cancer patients

Background and purpose

Cone-beam computed tomography (CBCT) increases the doses on normal tissues. Our study sought to develop a mathematical model that would provide an estimate of and verify in vivo rectal dose from CBCT in prostate cancer patients.

Materials and methods

Thermoluminescent dosimeters (TLDs) and Rando phantoms were used to measure doses to the pelvic region. We used an endorectal balloon to measure rectal doses for 10 prostate cancer patients who underwent radiotherapy and for whom we were able to acquire CBCT images. A solid water phantom and TLDs were used to correlate the rectal doses with body thickness/widths. A mathematical method was established to simulate the dose to which the patient is exposed during CBCT for the determined body parameters. The estimated doses were compared with the measured doses to determine the effectiveness of the model.

Results

The average measured rectal dose from CBCT was 2.8 ± 0.3 cGy. The mathematical method was able to predict the rectal dose, with the limits of agreement of −0.03 ± 0.18 cGy. The average difference between predictions and measurements was −1.1 ± 3.6%.

Conclusion

Our mathematical model was effective in estimating the exposed dose from CBCT.     

Applicator reconstruction in MRI 3D image-based dose planning of brachytherapy for cervical cancer

Background and purpose

To elaborate a method for applicator reconstruction for MRI-based brachytherapy for cervical cancer.

Materials and methods

Custom-made plastic catheters with a copper sulphate solution were made for insertion in the source channels of MR-CT compatible applicators: plastic and titanium tandem ring applicators, and titanium needles. The applicators were CT and MR scanned in a phantom for accurate 3D assessment of applicator visibility and geometry. A reconstruction method was developed and evaluated in 19 patient MR examinations with ring applicator (plastic: 14, titanium: 5). MR applicator reconstruction uncertainties related to inter-observer variation were evaluated.

Results

The catheters were visible in the plastic applicator on T1-weighted images in phantom and in 14/14 clinical applications. On T2-weighted images, the catheters appeared weaker but still visible in phantom and in 13/14 MR clinical applications. In the titanium applicator, the catheters could not be separated from the artifacts from the applicator itself. However, these artifacts could be used to localize both titanium ring applicator (5/5 clinical applications) and needles (6/6 clinical applications). Standard deviations of inter-observer differences were below 2 mm in all directions.

Conclusion

3D applicator reconstruction based on MR imaging could be performed for plastic and titanium applicators. Plastic applicators proved well to be suited for MRI-based reconstruction. For improved practicability of titanium applicator reconstruction, development of MR applicator markers is essential. Reconstruction of titanium applicator and needles at 1.5 T MR requires geometric evaluations in phantoms before using the applicator in patients.     

The use of palliative radiotherapy for bone metastasis

Background

The value of palliative radiotherapy (PRT) for bone metastases is well established, but little is known about its use in the general population.

Purpose

To describe the use of PRT for bone metastases in Ontario.

Materials and methods

This was a retrospective cohort study. Treatment records from all Ontario RT departments were linked to a population-based cancer registry to describe the use of PRT.

Results

12.2% of the 434,241 patients, who died of cancer in Ontario between 1984 and 2004, received at least one course of PRT for bone metastases in the last 2 years of life. The rate of use of PRT varied across the province (inter-county range, 8.2-18.6%). Older patients and residents of poorer areas were less likely to receive PRT (p < 0.0001). Patients diagnosed with cancer in a hospital with a radiotherapy facility and those who lived closer to a radiotherapy centre were more likely to receive PRT (p < 0.0001). Over the study period, the use of PRT decreased in breast cancer and myeloma, but increased in prostate cancer (p < 0.0001).

Conclusions

Access to PRT appears to be inequitable. More effort is required to make this useful treatment available to all those who would benefit from it.     

Does the planning dose-volume histogram represent treatment doses in image-guided prostate radiation therapy? Assessment with cone-beam computerised tomography scans

Purpose

To assess the accuracy of the initial CT plan dose-volume histograms (DVH’s) for prostate, rectum and bladder by comparison to delivered doses determined from cone beam CT (CBCT) scans acquired during image-guided treatment.

Materials and methods

Twelve prostate patients were treated using daily implanted fiducial guidance and following local protocol for bladder and rectal preparation. CBCT scans were acquired twice weekly and contoured for prostate, rectum and bladder. The planned beams were applied to all CBCT scans to determine the delivered doses. Prostate dose coverage was assessed by the proportion of the CTV fully encompassed by the 95% and 98% isodose lines. Rectal and bladder volumes receiving 40 Gy, 60 Gy and 70 Gy at treatment were compared to the initial plan, with significance determined using the one-sample t-test.

Results

Four patients showed marginally compromised CTV coverage by the 95% isodose at all CBCT plans. For nine patients the initial plan rectal DVH was significantly outside the range of the treatment DVH’s.

Conclusions

Dose coverage of the prostate was not achieved for all patients. Observed rectal and bladder doses were higher than predicted. The initial treatment plan cannot be assumed to represent accurate normal tissue doses.     

A novel method for megavoltage scatter correction in cone-beam CT acquired concurrent with rotational irradiation

Background and purpose

Acquisition of cone-beam CT (CBCT) concurrent with VMAT results in scatter of the megavoltage (MV) beam onto the kilovoltage (kV) detector deteriorating CBCT image quality. The aim of this paper is to develop a method to estimate and correct for MV scatter reaching the kV panel.

Material and methods

The correction method is based on an alternating pulse sequence such that the kV source is enabled in only every other frame. MV scatter, noise and artifacts in the kV-unexposed frames are separated based on their spatial and temporal frequency characteristics and subsequently subtracted from the exposed frames. The method was tested on a phantom and one lung cancer patient scanned on an Elekta Synergy system simultaneous with a 9 Gy VMAT delivery.

Results

Without correction, acquisition during VMAT leads to significant cupping and loss of bone contrast. The novel method removes the signal due to MV scatter. Compared to acquisition without MV beam, the reconstruction quality is identical except for some unavoidable noise due to the scattered MV radiation in the exposed frames. Correction is performed in-line with acquisition without introducing delays.

Conclusions

A novel, efficient and effective method was developed to correct for MV scatter in CBCT scans acquired concurrent with rotational radiotherapy.     

Treating intermediate-risk prostate cancer with hypofractionated external beam radiotherapy alone

Purpose

Intermediate-risk prostate cancer has been treated in many ways; the most effective treatment is uncertain. Hypofractionated external beam radiotherapy (HyRT) is a short and convenient alternative treatment. We report our results of HyRT in intermediate-risk patients.

Material and methods

Eighty two patients with intermediate-risk prostate cancer were treated with 3-dimensional conformal HyRT plans to the dose of 66 Gy/22 fractions prescribed at the isocenter without hormones. Intermediate-risk was defined as clinical stage T2b-T2c, or pre-treatment PSA between 10 and 20 ng/mL, or Gleason Score equal 7. The planning target volume consisted of the prostate plus a uniform 7 mm margin. Toxicity was prospectively graded by the Common Terminology Criteria version3. Biochemical relapse was defined as post-radiotherapy nadir PSA + 2 ng/mL.

Results

With a median follow-up of 51 months, 5-year actuarial biochemical recurrence free survival is 95.4%. At the last follow-up visit, grade ?2 late gastro-intestinal and genito-urinary toxicity rates were 2% and 7%, respectively. No patient ever developed grade 4 or 5 toxicity.

Conclusion

HyRT to a dose of 66 Gy in 22 fractions as a single treatment modality is convenient for patients and for the health care system and appears to provide similar results to other treatment choices.     

The accuracy of frameless stereotactic intracranial radiosurgery

Purpose

To determine the accuracy of frameless stereotactic radiosurgery using the BrainLAB ExacTrac system and robotic couch by measuring the individual contributions such as the accuracy of the imaging and couch correction system, the linkage between this system and the linac isocenter and the possible intrafraction motion of the patient in the frameless mask.

Materials and methods

An Alderson head phantom with hidden marker was randomly positioned 31 times. Automated 6D couch shifts were performed according to ExacTrac and the deviation with respect to the linac isocenter was measured using the hidden marker. ExacTrac-based set-up was performed for 46 patients undergoing hypofractionated stereotactic radiotherapy for 135 fractions, followed by verification X-rays. Forty-three of these patients received post-treatment X-ray verification for 79 fractions to determine the intrafraction motion.

Results

The hidden target test revealed a systematic error of 1.5 mm in one direction, which was corrected after replacement of the system calibration phantom. The accuracy of the ExacTrac positioning is approximately 0.3 mm in each direction, 1 standard deviation. The intrafraction motion was 0.35 ± 0.21 mm, maximum 1.15 mm.

Conclusion

Intrafraction motion in the BrainLAB frameless mask is very small. Users are strongly advised to perform an independent verification of the ExacTrac isocenter in order to avoid systematic deviations.     

Central thoracic lesions treated with hypofractionated stereotactic body radiotherapy

Purpose

To investigate the toxicity and outcome after moderately hypofractionated stereotactic body radiotherapy (SBRT) for central thoracic lesions.

Methods

Fifty-three patients undergoing 63 courses of SBRT for central thoracic lesions were retrospectively reviewed. Ninety-eight lesions received 30-63 Gy in 2.5-5.0 Gy fractions using the Novalis ExacTrac^® patient positioning platform.

Results

The 2-year lesion local control was 73%. Larger lesion volume was associated with poorer local control. The 2-year overall survival of patients with Stage I NSCLC, Stages II-III NSCLC and limited metastatic disease was 72%, 12% and 49%, respectively. There were four patient deaths from pulmonary causes, potentially grade 5 toxicities, though three had comorbid pulmonary conditions which may have contributed to the cause of death. One patient died from hemoptysis after undergoing two courses of SBRT to a mediastinal lesion. Most other deaths were attributable to metastatic progression.

Conclusions

Moderately hypofractionated SBRT to central thoracic lesions is effective with respect to local control and toxicity. Further dose escalation can provide an opportunity for better tumor control. Even with less aggressive dose fractionation, pulmonary deaths can occur, though it is difficult to ascertain the extent to which SBRT contributed to the death of patients with comorbid pulmonary conditions.     

Acquisition of MV-scatter-free kilovoltage CBCT images during RapidArc™ or VMAT

Purpose

To perform kilovoltage (kV) cone beam computed tomography (CBCT) imaging concomitant with the delivery of megavoltage (MV) RapidArc treatment, and demonstrate the feasibility of obtaining MV-scatter-free kV CBCT images.

Methods and materials

RapidArc/CBCT treatment and imaging plans are designed, and delivered on the Varian TrueBeam, using its Developer Mode. The plan contains 250 control points for MV-radiation delivery, each over an arc of 0.4-0.7^o. Interlaced between successive MV delivery control points are imaging control points, each over an arc of 0.7-1.1^o. During the 360^o gantry rotation for the RapidArc delivery, CBCT projections of a phantom are acquired at 11 frames per second. The kV projections with minimal MV-scatter are selected, based on gantry angle, and the CBCT_s image reconstructed. For comparison, a reference CBCT_r image is acquired in the normal way. In addition, to examine the effect of MV-scatter we acquire CBCT_c using the same treatment plan without the imaging control points, i.e. with continuous MV delivery during the 360^o rotation. Quantitative evaluation of image qualities is performed based on the concepts of CNR (contrast-to-noise ratio) and NSTD (normalized standard deviation).

Results

The different types of CBCT images were reconstructed, evaluated, and compared. Visual comparison indicates that the image quality of CBCT_s is similar to that of the reference CBCT_r, and that the quality of CBCT_c is significantly degraded by the MV-scatter. Quantitative evaluation of the image quality indicates that MV-scatter significantly decreases the CNR of CBCT (from ∼7 to ∼3.5 in one comparison). Similarly, MV-scatter significantly increases the inhomogeneity of image intensity, e.g. from ∼0.03 to ∼0.06 in one comparison.

Conclusion

We have developed a method to acquire MV-scatter-free kV CBCT images concomitant with the delivery of RapidArc treatment. Engineering development is necessary to improve the process, e.g. by synchronization of the MV and kV beams.     

Arsenic Trioxide in Recurrent Urothelial Cancer: A Cancer and Leukemia Group B Phase II Trial (CALGB 99903)

Background

Arsenic trioxide is highly active in patients with acute promyelocytic leukemia. There are also preclinical data to suggest that this drug might be active in nonhematopoietic malignancies, and transitional cell carcinoma cell lines are particularly sensitive to this agent.

Patients and Methods

Twelve evaluable patients with metastatic urothelial cancer were treated with arsenic trioxide in a phase II trial conducted by the Cancer and Leukemia Group B. Eligible patients were required to have measurable urothelial cancer and a maximum of 1 previous chemotherapy regimen. Arsenic trioxide was given at a dose of 0.3 mg/kg daily for 5 days every 28 days.

Results

No major responses were observed; 4 patients achieved stable disease. The median survival was 6.5 months (95% CI, 3.9-13.4 months). The most commonly observed toxicities included fatigue and malaise, anemia, nausea, emesis, and constipation.

Conclusion

Arsenic trioxide at this dose and schedule does not have significant activity in previously treated urothelial cancer and has substantial toxicity in this patient population.     

Target volume shape variation during hypo-fractionated preoperative irradiation of rectal cancer patients

Purpose

To quantify the day-to-day target volume shape variation in rectal-cancer patients treated with preoperative 5 × 5 Gy radiotherapy.

Materials and methods

For 27 patients a prone position plan-CT (pCT) and five daily pre-treatment cone-beam-CT (CBCT) scans were acquired. A sub-region of the CTV (MesoRect, anus up to the cranial end of the mesorectal-fascia) was delineated on all scans. The MesoRect deformation was quantified by the distance between pCT- and CBCT-delineations and was stored in surface-maps. Finally, the influence of bladder and rectum filling on MesoRect deformation was evaluated. Data were analyzed for male and female patients separately.

Results

A large range of systematic and random deformations, 1-7 mm (1SD), on different areas of the MesoRect were found. The maximum deformations were located at the upper-anterior-side of the MesoRect. For females the errors were up to 3 mm larger than for males. Small correlations, r² ? 0.4, were found with changes in bladder volume. Larger correlations, r² ? 0.7, were found for rectal volume in a distinctive area in the upper-half of the MesoRect.

Conclusions

Substantial and heterogeneous deformations of the MesoRect were found. Therefore different PTV margins in positions along the cranio-caudal axis, in the anterior-posterior direction. Margins should also be larger for female patients compared to male patients.     

Direct reconstruction of the Vienna applicator on MR images

Purpose

To introduce and test a direct reconstruction concept for intracavitary tandem ring applicators in MR image-based brachytherapy treatment planning.

Materials and methods

Optical measurements of transparent ring-phantoms provided the geometric relation between source path and the Vienna ring applicator as visible on MRI. For the manual direct reconstruction method (PLATO), the geometry plotted on a transparency was placed on the screen and rotated to fit with visible ring holes. With the software-integrated reconstruction method (OncentraGYN), the applicator geometry was directly used when placing the visible parts of the applicator in the 3D dataset. Clinical feasibility was tested in 10 clinical insertions. Reconstruction and dose calculation were performed independently on two treatment planning systems (PLATO and OncentraGYN) using MRI alone. DVH parameters for targets and organs at risk were analysed and compared to the clinically used radiograph/MRI registration-based method.

Results

The direct reconstruction concept for both methods was feasible and reduced treatment planning time. Evaluated DVH parameters for plans using direct reconstruction methods differed from clinically used plans (traditional reconstruction) in mean differences ?0.2 Gy for plans with 7 Gy prescribed dose.

Conclusion

If the relation between applicator shape visible on MRI and the source path is defined once, the reconstruction process can be performed by directly placing the applicator in the MRI dataset.     

The delineation of target volumes for radiotherapy of lung cancer patients

Purpose

Differences in the delineation of the gross target volume (GTV) and planning target volume (PTV) in patients with non-small-cell lung cancer are considerable. The focus of this work is on the analysis of observer-related reasons while controlling for other variables.

Methods

In three consecutive patients, eighteen physicians from fourteen different departments delineated the GTV and PTV in CT-slices using a detailed instruction for target delineation. Differences in the volumes, the delineated anatomic lymph node compartments and differences in every delineated pixel of the contoured volumes in the CT-slices (pixel-by-pixel-analysis) were evaluated for different groups: ten radiation oncologists from ten departments (ROs), four haematologic oncologists and chest physicians from four departments (HOs) and five radiation oncologists from one department (RO1D).

Results

Agreement (overlap ? 70% of the contoured pixels) for the GTV and PTV delineation was found in 16.3% and 23.7% (ROs), 30.4% and 38.6% (HOs) and 32.8% and 35.9% (RO1D), respectively.

Conclusion

A large interobserver variability in the PTV and much more in the GTV delineation were observed in spite of a detailed instruction for delineation. The variability was smallest for group ROID where due to repeated discussions and uniform teaching a better agreement was achieved.     

Mammary fat necrosis following radiotherapy in the conservative management of localized breast cancer: Does it matter?

Purpose

Fat necrosis is a well-described and relatively common complication arising from post-lumpectomy irradiation of the breast, most commonly breast brachytherapy. We wish to assess the clinical significance of fat necrosis resulting from post-lumpectomy breast irradiation.

Methods

We reviewed the literature to determine the overall incidence and significance of fat necrosis to determine whether or not fat necrosis poses a significant clinical problem.

Results

Fat necrosis occurs in up to one-quarter of patients following post-lumpectomy breast irradiation. Only rarely is invasive intervention required however, it does significantly degrade the quality of all modalities of breast imaging.

Conclusions

Fat necrosis is a common complication of radiotherapy which rarely requires therapeutic intervention. However, post-therapeutic clinical imaging such as mammography, ultrasound and magnetic resonance imaging are affected which may result in additional diagnostic procedures up to and including biopsy.