Prospective, randomized, multicenter study of intraosseous basivertebral nerve ablation for the treatment of chronic low back pain: 24-Month treatment arm results

BACKGROUND

Vertebral endplates, innervated by the basivertebral nerve, can be a source of vertebrogenic low back pain when damaged with inflammation, visible as types 1 or 2 Modic changes. A randomized controlled trial (RCT) compared basivertebral nerve ablation (BVNA) to standard care (SC) showed significant differences between arms at 3 and 6-months. At 12-months, significant improvements were sustained for BVNA. We report results of the BVNA arm at 24-months.

METHODS

Prospective, open label, single-arm follow-up of the BVNA treatment arm of a RCT in 20 US sites with visits at 6-weeks, and 3, 6, 9, 12 and 24-months. Paired comparisons to baseline were made for the BVNA arm at each timepoint for Oswestry Disability Index (ODI), Visual Analog Scale (VAS), Short Form Health Survey (SF-36), EQ-5D-5L, and responder rates.

RESULTS

140 patients were randomized, 66 to BVNA. In the 58 BVNA patients completing a 24-month visit, 67% had back pain for >5 years, 36% were actively taking opioids at baseline, 50% had prior epidural steroid injections, and 12% had prior low back surgery. Improvements in ODI, VAS, SF-36 PCS, and EQ-5D-5L were statistically significant at all timepoints through 2 years. At 24 months, ODI and VAS improved 28.5±16.2 points (from baseline 44.5; p < 0.001) and 4.1±2.7 cm (from baseline 6.6; p < 0.001), respectively. A combined responder rate of ODI≥15 and VAS≥2 was 73.7%. A ≥50% reduction in pain was reported in 72.4% of patients and 31.0% were pain-free at 2 years. At 24 months, only 3(5%) of patients had BVNA-level steroid injections, and 62% fewer patients were actively taking opioids. There were no serious device or device-procedure related adverse events reported through 24 months.

CONCLUSION

Intraosseous BVNA demonstrates an excellent safety profile and significant improvements in pain, function, and quality of life that are sustained through 24 months in patients with chronic vertebrogenic low back pain.

OP0090 EFFICACY OF SUBCUTANEOUS TANEZUMAB FOR THE TREATMENT OF CHRONIC LOW BACK PAIN: AN ANALYSIS OF BRIEF PAIN INVENTORY-SHORT FORM SCORES FROM A 56-WEEK, RANDOMIZED, PLACEBO- AND TRAMADOL-CONTROLLED, PHASE 3 TRIAL

Background:

Tanezumab, a monoclonal antibody against nerve growth factor, was recently evaluated in an 80 week placebo and tramadol-controlled trial in patients with chronic low back pain (CLBP) and a history of inadequate response to standard-of-care analgesics (NSAIDs, opioids, etc). Primary endpoint was change in Low Back Pain Intensity (LBPI) at week 16 vs placebo. Key secondary endpoints were the proportion of patients with ≥50% improvement in LBPI at week 16, change in Roland Morris Disability Questionnaire score at week 16, and change in LBPI at week 2 (all vs placebo). Tanezumab 10mg met the primary and all key secondary endpoints. Tanezumab 5mg did not meet the primary endpoint, but improved 2 of 3 key secondary endpoints. Due to the primary endpoint result and the statistical gate-keeping approach to control for multiple comparisons, a conclusion of superiority over placebo could not be made for the 5mg dose.

Objectives:

To further characterize tanezumab’s effects on pain and function in this trial through analysis of Brief Pain Inventory-short form (BPI-sf) scores.

Methods:

Patients received placebo (n=406), subcutaneous (SC) tanezumab 5mg (every 8 weeks; n=407), SC tanezumab 10mg (every 8 weeks; n=407) or oral tramadol prolonged-release (100-300mg/day; n=605). Pre-specified secondary endpoints included BPI-sf worst pain, average pain, the overall pain interference index, and selected individual domains of the index (general activity, walking ability, sleep, and normal work). Least squares (LS) mean (standard error [SE]) changes from baseline in BPI-sf scores were compared between groups (unadjusted for multiplicity) at week 16 using an analysis of covariance model. Scores range from 0-10 with higher scores indicating greater pain severity or functional impairment.

Results:

LS mean (SE) differences from placebo for worst pain were -0.52 (0.19) for tanezumab 5mg (p≤0.01), -0.54 (0.19) for tanezumab 10mg (≤0.01), and -0.24 (0.17) for tramadol (p=0.17). LS mean (SE) differences from placebo for average pain were -0.37 (0.18) for tanezumab 5mg (p=0.04), -0.46 (0.18) for tanezumab 10mg (≤0.01), and -0.17 (0.16) for tramadol (p=0.29). LS mean (SE) differences from placebo for the pain interference index were -0.41 (0.18) for tanezumab 5mg (p=0.03), -0.58 (0.18) for tanezumab 10mg (≤0.01), and -0.15 (0.17) for tramadol (p=0.39). Effects of tanezumab were not statistically different (p>0.05) from tramadol for worst pain, average pain, and the pain interference index, with exception of the pain interference index for tanezumab 10mg (p=0.01). Mean dose of tramadol was 203mg/day at week 16.

Tanezumab 10mg significantly (p<0.05) improved individual domains of the pain interference index (general activity, walking ability, sleep, and normal work) vs placebo and vs tramadol. Tanezumab 5mg significantly (p<0.05) improved pain interference with general activity and normal work vs placebo, and sleep vs placebo and vs tramadol. No statistical differences in any domain was observed for tramadol vs placebo.

Conclusion:

Tanezumab 5mg and 10mg significantly improved worst pain, average pain, and overall pain interference index scores vs placebo in patients with CLBP. Tanezumab 10mg also significantly improved the overall pain interference index vs tramadol. Tanezumab 5mg significantly improved most individual domains of the pain interference index vs placebo, while tanezumab 10mg significantly improved all domains assessed vs placebo and vs tramadol.

Disclosure of Interests:

John Markman Consultant of: Consultant: Trigemina, Editas Medicine, and Plasma Surgical; Advisory board: Clexio Biosciences, Flexion Therapeutics, Quark Pharmaceuticals, Quartet Medicine, Collegium Pharmaceutical, Purdue Pharma, Biogen, Novartis, Aptinyx, Nektar, Allergan, Grünenthal, Eli Lilly and Company, Depomed, Janssen Pharmaceuticals, Teva Pharmaceutical Industries, KemPharm, Abbott Laboratories, Plasma Surgical, Chromocell, Convergence Pharmaceuticals, Inspirion, Pfizer, Sanofi, Daiichi Sankyo, and Trevena; Data safety monitoring boards for Novartis and Allergan, Serge Perrot Consultant of: Grunenthal, Pfizer, Lilly, MSD, Sanofi, Menarini, Seiji Ohtori: None declared, Thomas Schnitzer Consultant of: Pfizer, Lilly, AstraZeneca, GSK, Said Beydoun Grant/research support from: Argenx, Catalyst Pharma, Mallinckrodt, Pfizer, UCB, Consultant of: Alexion, Akcea, Alnylam, CSL, Takeda, Mitsubishi Tanabe, Speakers bureau: Alexion, Akcea, Alnylam, CSL, Takeda, Mitsubishi Tanabe, Lars Viktrup Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Ruoyong Yang Shareholder of: Pfizer Inc, Employee of: Pfizer Inc, Candace Bramson Shareholder of: Pfizer Inc, Employee of: Pfizer Inc, Christine West Shareholder of: Pfizer Inc, Employee of: Pfizer Inc, Ken Verburg Shareholder of: Pfizer Inc, Employee of: Pfizer Inc

Abstract A50: Nanobiocojugates of differential imaging and treatment of brain metastatic tumors

Introduction: A significant clinical problem with brain metastatic (BM) tumors is drug delivery and diagnostic imaging to verify MRI enhancement(s) for planning treatment. MRI enhancement in cancer patient's brain might result from infection after chemotherapy that impairs immune system; metastasis from primary lung/breast cancer; or a new primary brain tumor. Unlike lung/breast, brain biopsies are often technically impossible. Therefore, there is urgent need for the development of effective theranostic (dual therapy and diagnostic) systems against brain metastatic cancer.

Most chemotherapeutic drugs or therapeutic monoclonal antibodies (mAb), Trastuzumab, Cetuximab, and Rituximab, are effective for primary tumor treatment but cannot penetrate blood brain barrier (BBB) failing to treat brain metastasis.

We used a natural nanobiopolymer, polymalic acid (PMLA), as a nanoplatform for the family of tumor-targeted PolycefinTM drugs to provide differential brain tumor imaging and treatment.

Methods: Three xenogeneic orthotropic human brain metastatic tumors, MDA-MB-474, HER2+ breast cancer; A549 lung cancer, and MDA-MB-468, triple negative breast cancer (TNBC), both EGFR+, were inoculated stereotactically into the brain of mice.

For diagnostic imaging, PolycefinTM was used with covalently attached MRI tracer Gadolinium (Gd-DOTA). Morpholino antisense oligonucleotides (AON) were conjugated to PolycefinTM to specifically inhibit gene/protein expression to block tumor growth. The combination of cell surface targeting mAbs, including anti-transferrin receptor (TfR) mAb for drug BBB transcytosis, and AONs to multiple tumor markers on the same delivery polymer was used for anti-tumor treatment.

MRI 1H imaging was performed on a 9.4-Tesla small animal MRI system. Treatment groups of animals included (1) HER2+ MDA-MB-474 breast cancer metastases targeted with PMLA-Gd-DOTA/HER2 mAb/TfR mAb; (2) EGFR+ MDA-MB-468 TNBC metastases targeted with PMLA-Gd-DOTA/EGFR mAb/TfR mAb; and (3) Controls for all treatments inoculated with PMLA-IgG mAb and clinical Gd.

Unpublished Results. Imaging: Dynamic T1 analysis. Similar data for specific tumor imaging were obtained for brain-implanted lung and breast tumors: the inverse of T1-1 relaxation time (proportional to Gd concentration) was measured in healthy brain part and in the tumor. T1-1 time dependence for Gd-DOTA-Polycefin (T1-1 ratio tumor/normal brain) was compared with clinically used Gd MRI agent, MultiHance®. After reaching a maximum, high T1-1 relative values prevailed for several hours for Gd-DOTA-mAb-Polycefin, but declined rapidly for Gd. High contrast for Gd was seen in 20 min, whereas that for Gd-DOTA-Polycefin peaked in 45-60 min, and remained for up to 3 hrs. By differential MRI with anti-HER2 (Trastuzumab) or anti-EFGR (Cetuximab) mAb attached covalently to the nanoplatform, we were able to differentiate HER2+ from EGFR+ metastatic brain tumors with corresponding imaging controls.

Treatment: Animal survival after Polycefin treatment of various brain metastases was significantly higher than in untreated (PBS) or therapeutic mAb (Herceptin or Cetuximab) treated animals. These survival increases were as follows: 66% for lung cancer metastasis, 47% for HER2+ breast cancer metastasis, and 81% for TNBC metastasis.

Conclusions. We have developed a system for differential imaging and treatment of various metastatic brain tumors based on specific metastasis targeting, and inhibition of expression of tumor-specific genes/proteins. Systemic treatment with this system resulted in significantly increased survival of brain metastatic tumor-bearing animals.

Citation Format: Julia Y. Ljubimova, R. Patil, P. Gangalum, S. Wagner, S. Inoue, H. Ding, J. Portilla, K. Rekechenetskiy, K. Bindu, J. Markman, A. Chesnokova, K. L. Black, E. Holler. Nanobiocojugates of differential imaging and treatment of brain metastatic tumors. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A50.

Preliminary development of a responder index for chronic low back pain

OBJECTIVE

One of the greatest obstacles to identifying the most effective therapy for chronic low back pain (CLBP) is the lack of standardized outcome measures for assessing treatment effect in clinical trials. The aim of the OMERACT Special Interest Group was to discuss the development and validation of a preliminary responder index in CLBP.

METHODS

Patient data from 5 clinical trials of celecoxib and valdecoxib use in CLBP were used to assess the reliability and validity of multiple items in the outcome domains of pain, functioning, and overall impression of health. Candidate preliminary responder indices were selected on the basis of effect size, high chi-square test values, and a placebo response rate < or = 25%.

RESULTS

Candidate indices comprised improvements in single outcome measures and combinations of improvements and/or avoidance of worsening in multiple measures. The preliminary choice for the responder index was at least 30% improvement in pain, with an improvement of at least 30% in patient global assessment and no worsening in function.

CONCLUSION

Further studies are needed to refine a responder index for CLBP trials that is clinically relevant, reliable, and easy to administer for standardizing assessments across clinical trials.

Uncertainties in model-based outcome predictions for treatment planning

PURPOSE

Model-based treatment-plan-specific outcome predictions (such as normal tissue complication probability [NTCP] or the relative reduction in salivary function) are typically presented without reference to underlying uncertainties. We provide a method to assess the reliability of treatment-plan-specific dose-volume outcome model predictions.

METHODS AND MATERIALS

A practical method is proposed for evaluating model prediction based on the original input data together with bootstrap-based estimates of parameter uncertainties. The general framework is applicable to continuous variable predictions (e.g., prediction of long-term salivary function) and dichotomous variable predictions (e.g., tumor control probability [TCP] or NTCP). Using bootstrap resampling, a histogram of the likelihood of alternative parameter values is generated. For a given patient and treatment plan we generate a histogram of alternative model results by computing the model predicted outcome for each parameter set in the bootstrap list. Residual uncertainty ("noise") is accounted for by adding a random component to the computed outcome values. The residual noise distribution is estimated from the original fit between model predictions and patient data.

RESULTS

The method is demonstrated using a continuous-endpoint model to predict long-term salivary function for head-and-neck cancer patients. Histograms represent the probabilities for the level of posttreatment salivary function based on the input clinical data, the salivary function model, and the three-dimensional dose distribution. For some patients there is significant uncertainty in the prediction of xerostomia, whereas for other patients the predictions are expected to be more reliable. In contrast, TCP and NTCP endpoints are dichotomous, and parameter uncertainties should be folded directly into the estimated probabilities, thereby improving the accuracy of the estimates. Using bootstrap parameter estimates, competing treatment plans can be ranked based on the probability that one plan is superior to another. Thus, reliability of plan ranking could also be assessed.

CONCLUSIONS

A comprehensive framework for incorporating uncertainties into treatment-plan-specific outcome predictions is described. Uncertainty histograms for continuous variable endpoint models provide a straightforward method for visual review of the reliability of outcome predictions for each treatment plan.

Abutment dosimetry for serial tomotherapy

The dose distributions at the abutment region for serial tomotherapy are reviewed. While tomotherapy provides unparalleled dose distributions, precise couch motion and good patient immobilization are required because the dose in the abutment region changes by 25% for each millimeter of misalignment. The process of delivering intensity-modulated radiation therapy using sequentially delivered modulated arcs yields hot spots below and cold spots above the machine isocenter when arc angles of less than 360 degrees are used. The magnitude of the hot and cold spots increases significantly as the arc angle is reduced 180 degrees such as when limited by couch clearance restrictions. Placement of isocenter also significantly affects the dose heterogeneity in the abutment region, with the hot and cold spots increasing nearly linearly with off-axis distance in the vertical direction. Reduction of the magnitude of the abutment region dose heterogeneities is possible if helical delivery is provided by moving the couch during arc delivery. The dose heterogeneity can also be reduced by creating 2 treatment plans, each with slightly different abutment region positions, or by using multiple couch angles.

Characterization of a commercial multileaf collimator used for intensity modulated radiation therapy

The characteristics of a commercial multileaf collimator (MLC) to deliver static and dynamic multileaf collimation (SMLC and DMLC, respectively) were investigated to determine their influence on intensity modulated radiation therapy (IMRT) treatment planning and quality assurance. The influence of MLC leaf positioning accuracy on sequentially abutted SMLC fields was measured by creating abutting fields with selected gaps and overlaps. These data were also used to measure static leaf positioning precision. The characteristics of high leaf-velocity DMLC delivery were measured with constant velocity leaf sequences starting with an open field and closing a single leaf bank. A range of 1-72 monitor units (MU) was used providing a range of leaf velocities. The field abutment measurements yielded dose errors (as a percentage of the open field max dose) of 16.7+/-0.7% mm(-1) and 12.8+/-0.7% mm(-1) for 6 MV and 18 MV photon beams, respectively. The MLC leaf positioning precision was 0.080+/-0.018 mm (single standard deviation) highlighting the excellent delivery hardware tolerances for the tested beam delivery geometry. The high leaf-velocity DMLC measurements showed delivery artifacts when the leaf sequence and selected monitor units caused the linear accelerator to move the leaves at their maximum velocity while modulating the accelerator dose rate to deliver the desired leaf and MU sequence (termed leaf-velocity limited delivery). According to the vendor, a unique feature to their linear accelerator and MLC is that the dose rate is reduced to provide the correct cm MU(-1) leaf velocity when the delivery is leaf-velocity limited. However, it was found that the system delivered roughly 1 MU per pulse when the delivery was leaf-velocity limited causing dose profiles to exhibit discrete steps rather than a smooth dose gradient. The root mean square difference between the steps and desired linear gradient was less than 3% when more than 4 MU were used. The average dose per MU was greater and less than desired for closing and opening leaf patterns, respectively, when the delivery was leaf-velocity limited. The results indicated that the dose delivery artifacts should be minor for most clinical cases, but limit the assumption of dose linearity when significantly reducing the delivered dose for dosimeter characterization studies or QA measurements.

A prospective study of salivary function sparing in patients with head-and-neck cancers receiving intensity-modulated or three-dimensional radiation therapy: initial results

OBJECTIVES

In a prospective clinical study, we tested the hypothesis that sparing the parotid glands may result in significant objective and subjective improvement of xerostomia in patients with head-and-neck cancers. The functional outcome 6 months after the completion of radiation therapy is presented.

METHODS AND MATERIALS

From February 1997 to February 1999, 41 patients with head-and-neck cancers were enrolled in a prospective salivary function study. Inverse-planning intensity-modulated radiation therapy (IMRT) was used to treat 27 patients, and forward-planning three-dimensional radiation therapy in 14. To avoid potential bias in data interpretation, only patients whose submandibular glands received greater than 50 Gy were eligible. Attempts were made to spare the superficial lobe of the parotid glands to avoid underdosing tumor targets in the parapharyngeal space; however, the entire parotid volume was used to compute dose-volume histograms (DVHs) for this analysis. DVHs were computed for each gland separately. Parotid function was assessed objectively by measuring stimulated and unstimulated saliva flow before and 6 months after the completion of radiation therapy. Measurements were converted to flow rate (mL/min) and normalized relative to that before treatment. The corresponding quality-of-life (QOL) outcome was assessed by five questions regarding the patient's oral discomfort and eating/speaking problems.

RESULTS

We observed a correlation between parotid mean dose and the fractional reduction of stimulated saliva output at 6 months after the completion of radiation therapy. We further examined whether the functional outcome could be modeled as a function of dose. Two models were found to describe the dose-response data well. The first model assumed that each parotid gland is comprised of multiple independent parallel functional subunits (corresponding to computed tomography voxels) and that each gland contributes equally to overall flow, and that saliva output decreases exponentially as a quadratic function of irradiation dose to each voxel. The second approach uses the equivalent uniform dose (EUD) metrics, which assumes loss of salivary function with increase in EUD for each parotid gland independently. The analysis suggested that the mean dose to each parotid gland is a reasonable indicator for the functional outcome of each gland. The corresponding exponential coefficient was 0.0428/Gy (95% confidence interval: 0.01, 0.09). The QOL questions on eating/speaking function were significantly correlated with stimulated and unstimulated saliva flow at 6 months. In a multivariate analysis, a toxicity score derived from the model based on radiation dose to the parotid gland was found to be the sole significant predictive factor for xerostomia. Neither radiation technique (IMRT vs. non-IMRT) nor chemotherapy (yes or no) independently influenced the functional outcome of the salivary glands.

CONCLUSION

Sparing of the parotid glands translates into objective and subjective improvement of both xerostomia and QOL scores in patients with head-and-neck cancers receiving radiation therapy. Modeling results suggest an exponential relationship between saliva flow reduction and mean parotid dose for each gland. We found that the stimulated saliva flow at 6 months after treatment is reduced exponentially, for each gland independently, at a rate of approximately 4% per Gy of mean parotid dose.

On the validity of the superposition principle in dose calculations for intracavitary implants with shielded vaginal colpostats

Intracavitary vaginal applicators typically incorporate internal shielding to reduce dose to the bladder and rectum. While dose distributions about a single colpostat have been extensively measured and calculated, these studies neglect dosimetric perturbations arising from the contralateral colpostat or the intrauterine tandem. Dosimetric effects of inhomogeneities in brachytherapy is essential for both dose-based implant optimization as well as for a comparison with alternate modalities, such as intensity modulated radiation therapy. We have used Monte Carlo calculations to model dose distributions about both a Fletcher-Suit-Delclos (FSD) low dose-rate system and the microSelectron high dose-rate remote afterloading system. We have evaluated errors, relative to a Monte Carlo simulation based upon a complete applicator system, in superposition calculations based upon both precalculated single shielded applicator dose distributions as well as single unshielded source dose distributions. Errors were largely dominated by the primary photon attenuation, and were largest behind the shields and tandem. For the FSD applicators, applicator superposition showed differences ranging from a mean of 2.6% at high doses (>Manchester Point A dose) to 4.3% at low doses (<Manchester Point A dose) compared to the full geometry simulation. Source-only superposition yielded errors higher than 10% throughout the dose range. For the HDR applicator system, applicator superposition-induced errors ranging from 3.6%-6.3% at high and low doses, respectively. Source superposition caused errors of 5%-11%. These results indicate that precalculated applicator-based dose distributions can provide an excellent approximation of a full geometry Monte Carlo dose calculation for gynecological implants.

Experimental validation of dose calculation algorithms for the GliaSite RTS, a novel 125I liquid-filled balloon brachytherapy applicator

This paper compares experimentally measured and calculated dose-rate distributions for a novel 125I liquid-filled brachytherapy balloon applicator (the GliaSite RTS), designed for the treatment of malignant brain-tumor resection-cavity margins. This work is intended to comply with the American Association of Physicists in Medicine (AAPM) Radiation Therapy Committee's recommendations [Med. Phys. 25, 2269-2270 (1998)] for dosimetric characterization of low-energy photon interstitial brachytherapy sources. Absolute low dose-rate radiochromic film (RCF) dosimetry measurements were performed in coronal planes about the applicator. The applicator was placed in a solid water phantom, machined to conform to the inflated applicator's surface. The results were used to validate the accuracy of Monte Carlo photon transport (MCPT) simulations and a point-source dose-kernel algorithm in predicting dose to water. The absolute activity of the 125I solution was determined by intercomparing a National Institute of Standards and Technology (NIST) 125I standard with a known mass of radiotherapy solution (Iotrex) in an identical vial and geometry. For the two films not in contact with applicator, the average agreement between RCF and MCPT (specified as the mean absolute deviation in successive 4 mm rings) was found to be within +/-5% at distances 0.2-25 mm from the film centers. For the two films touching the catheter, the mean agreement was +/-14.5% and 7.5% near the balloon surface but improving to 7.5% and 6% by 3.5 mm from the surface. These errors, as large as 20% in isolated pixels, are likely due to trim damage, 125I contamination, and poor conformance with the balloon. At larger distances where the radiation doses were very low, the observed discrepancies were significantly larger than expected. We hypothesize that they are due to a dose-rate dependence of the RCF response. A 1%-10% average difference between a simple one-dimensional path-length semiempirical dose-kernel model and the MCPT calculations was observed over clinically relevant distances.

Validation of a precision radiochromic film dosimetry system for quantitative two-dimensional imaging of acute exposure dose distributions

We present an evaluation of the precision and accuracy of image-based radiochromic film (RCF) dosimetry performed using a commercial RCF product (Gafchromic MD-55-2, Nuclear Associates, Inc.) and a commercial high-spatial resolution (100 microm pixel size) He-Ne scanning-laser film-digitizer (Personal Densitometer, Molecular Dynamics, Inc.) as an optical density (OD) imaging system. The precision and accuracy of this dosimetry system are evaluated by performing RCF imaging dosimetry in well characterized conformal external beam and brachytherapy high dose-rate (HDR) radiation fields. Benchmarking of image-based RCF dosimetry is necessary due to many potential errors inherent to RCF dosimetry including: a temperature-dependent time evolution of RCF dose response; nonuniform response of RCF; and optical-polarization artifacts. In addition, laser-densitometer imaging artifacts can produce systematic OD measurement errors as large as 35% in the presence of high OD gradients. We present a RCF exposure and readout protocol that was developed for the accurate dosimetry of high dose rate (HDR) radiation sources. This protocol follows and expands upon the guidelines set forth by the American Association of Physicists in Medicine (AAPM) Task Group 55 report. Particular attention is focused on the OD imaging system, a scanning-laser film digitizer, modified to eliminate OD artifacts that were not addressed in the AAPM Task Group 55 report. RCF precision using this technique was evaluated with films given uniform 6 MV x-ray doses between 1 and 200 Gy. RCF absolute dose accuracy using this technique was evaluated by comparing RCF measurements to small volume ionization chamber measurements for conformal external-beam sources and an experimentally validated Monte Carlo photon-transport simulation code for a 192Ir brachytherapy source. Pixel-to-pixel standard deviations of uniformly irradiated films were less than 1% for doses between 10 and 150 Gy; between 1% and 5% for lower doses down to 1 Gy and 1% and 1.5% for higher doses up to 200 Gy. Pixel averaging to form 200-800 microm pixels reduces these standard deviations by a factor of 2 to 5. Comparisons of absolute dose show agreement within 1.5%-4% of dose benchmarks, consistent with a highly accurate dosimeter limited by its observed precision and the precision of the dose standards to which it is compared. These results provide a comprehensive benchmarking of RCF, enabling its use in the commissioning of novel HDR therapy sources.

Noise in polymer gel measurements using MRI

With the development of conformal radiotherapy, particularly intensity modulated radiation therapy (IMRT), there is a clear need for multidimensional dosimeters. A commercial polymerizing gel, BANG-2 gel (MGS Research, Inc., Guilford, CT), has recently been developed that shows potential as a multi-dimensional dosimeter. This study investigates and characterizes the noise and magnetic resonance (MR) artifacts from imaging BANG-2 gels. Seven cylindrical vials (4 cm diam, 20 cm length) were irradiated end on in a water bath and read using MRI (B0=1.5 T, TE=20 ms/100 ms, TR=3000 ms). The gel calibration compared the measured depth-dose distributions in water against the change in solvent-proton R2 relaxivity of the gel. A larger vial (13 cm diam, 14 cm length) was also irradiated to test the calibration accuracy in a vial of sufficient volume for dose distribution measurements. The calibration curve proved accurate to within 1.3% in determining the depth dose measured by the larger vial. An investigation of the voxel-to-voxel (IXIX 3 mm3) noise and sensitivity response curve showed that the voxel-to-voxel variation dominated the dose measurement uncertainty. The voxel-to-voxel standard deviation ranged from 0.2 Gy for the unirradiated gel to 0.7 Gy at 20 Gy. Slice-to-slice R2 magnitude deviations were also observed corresponding to 0.2 Gy. These variations limited the overall accuracy of the gel dose measurements and warrant an investigation of more accurate MR readout sequences.

An outbreak of Yersinia enterocolitica O:8 infections associated with pasteurized milk

In October 1995, an outbreak of Yersinia enterocolitica O:8 infections occurred in the Upper Valley of Vermont and New Hampshire. Ten patients were identified, median age 9 years (range, 6 months-44 years). Three patients were hospitalized; 1 underwent an appendectomy. Consumption of bottled pasteurized milk from a local dairy was associated with illness (matched odds ratio undefined; lower 95% confidence interval, 1.9). No deficiencies in pasteurization procedures or equipment were detected. Y. enterocolitica O:8 was isolated from 1 raw-milk sample and from a fecal sample from 1 dairy pig. The route of contamination was not determined; this outbreak likely resulted from postpasteurization contamination of milk. Dairy pigs were the most likely source of contamination. Milk bottles were likely contaminated by rinsing with untreated well water prior to filling or by other environmental routes. Educating dairy owners about Y. enterocolitica and postpasteurization contamination is necessary to prevent further outbreaks.

Abutment region dosimetry for serial tomotherapy

PURPOSE

A commercial intensity modulated radiation therapy system (Corvus, NOMOS Corp.) is presently used in our clinic to generate optimized dose distributions delivered using a proprietary dynamic multileaf collimator (DMLC) (MIMiC) composed of 20 opposed leaf pairs. On our accelerator (Clinac 600C/D, Varian Associates, Inc.) each MIMiC leaf projects to either 1.00 x 0.84 or 1.00 x 1.70 cm2 (depending on the treatment plan and termed 1 cm or 2 cm mode, respectively). The MIMiC is used to deliver serial (axial) tomotherapy treatment plans, in which the beam is delivered to a nearly cylindrical volume as the DMLC is rotated about the patient. For longer targets, the patient is moved (indexed) between treatments a distance corresponding to the projected leaf width. The treatment relies on precise indexing and a method was developed to measure the precision of indexing devices. A treatment planning study of the dosimetric effects of incorrect patient indexing and concluded that a dose heterogeneity of 10% mm(-1) resulted. Because the results may be sensitive to the dose model accuracy, we conducted a measurement-based investigation of the consequences of incorrect indexing using our accelerator. Although the indexing provides an accurate field abutment along the isocenter, due to beam divergence, hot and cold spots will be produced below and above isocenter, respectively, when less than 300 degree arcs were used. A preliminary study recently determined that for a 290 degree rotation in 1 cm mode, 15% cold and 7% hot spots were delivered to 7 cm above and below isocenter, respectively. This study completes the earlier work by investigating the dose heterogeneity as a function of position relative to the axis of rotation, arc length, and leaf width. The influence of random daily patient positioning errors is also investigated.

METHODS AND MATERIALS

Treatment plans were generated using 8.0 cm diameter cylindrical target volumes within a homogeneous rectilinear film phantom. The plans included both 1 and 2 cm mode, optimized for 300 degrees, 240 degrees, and 180 degrees gantry rotations. Coronal-oriented films were irradiated throughout the target volumes and scanned using a laser film digitizer. The central target irradiated in 1 cm mode was also used to investigate the effects of incorrect couch indexing.

RESULTS

The dose error as a function of couch index error was 25% mm(-1), significantly greater than previously reported. The clinically provided indexing system yielded 0.10 mm indexing precision. The intrinsic dose distributions indicated that more heterogeneous dose distributions resulted from the use of smaller gantry angle ranges and larger leaf projections. Using 300 degrees gantry angle and 1 cm mode yielded 7% hot and 15% cold spots 7 cm below and above isocenter, respectively. When a 180 degree gantry angle was used, the values changed to 22% hot and 27% cold spots for the same locations. The heterogeneities for the 2 cm mode were 70% greater than the corresponding 1 cm values.

CONCLUSIONS

While serial tomotherapy is used to deliver highly conformal dose distributions, significant dosimetric factors must be considered before treatment. The patient must be immobilized during treatment to avoid dose heterogeneities caused by incorrect indexing due to patient movement. Even under ideal conditions, beam divergence can cause significant abutment-region dose heterogeneities. The use of larger gantry angle ranges, smaller leaf widths, and appropriate locations of the gantry rotation axis can minimize these effects.

Evaluation of polymer gels and MRI as a 3-D dosimeter for intensity-modulated radiation therapy

BANG gel (MGS Research, Inc., Guilford, CT) has been evaluated for measuring intensity-modulated radiation therapy (IMRT) dose distributions. Treatment plans with target doses of 1500 cGy were generated by the Peacock IMRT system (NOMOS Corp., Sewickley, PA) using test target volumes. The gels were enclosed in 13 cm outer diameter cylindrical glass vessels. Dose calibration was conducted using seven smaller (4 cm diameter) cylindrical glass vessels irradiated to 0-1800 cGy in 300 cGy increments. Three-dimensional maps of the proton relaxation rate R2 were obtained using a 1.5 T magnetic resonance imaging (MRI) system (Siemens Medical Systems, Erlangen, Germany) and correlated with dose. A Hahn spin echo sequence was used with TR = 3 s, TE = 20 and 100 ms, NEX = 1, using 1 x 1 x 3 mm3 voxels. The MRI measurements were repeated weekly to identify the gel-aging characteristics. Ionization chamber, thermoluminescent dosimetry (TLD), and film dosimetry measurements of the IMRT dose distributions were obtained to compare against the gel results. The other dosimeters were used in a phantom with the same external cross-section as the gel phantom. The irradiated R2 values of the large vessels did not precisely track the smaller vessels, so the ionization chamber measurements were used to normalize the gel dose distributions. The point-to-point standard deviation of the gel dose measurements was 7.0 cGy. When compared with the ionization chamber measurements averaged over the chamber volume, 1% agreement was obtained. Comparisons against radiographic film dose distribution measurements and the treatment planning dose distribution calculation were used to determine the spatial localization accuracy of the gel and MRI. Spatial localization was better than 2 mm, and the dose was accurately determined by the gel both within and outside the target. The TLD chips were placed throughout the phantom to determine gel measurement precision in high- and low-dose regions. A multidimensional dose comparison tool that simultaneously examines the dose-difference and distance-to-agreement was used to evaluate the gel in both low-and high-dose gradient regions. When 3% and 3 mm criteria were used for the comparisons, more than 90% of the TLD measurements agreed with the gel, with the worst of 309 TLD chip measurements disagreeing by 40% of the criteria. All four MRI measurement session gel-measured dose distributions were compared to evaluate the time behavior of the gel. The low-dose regions were evaluated by comparison with TLD measurements at selected points, while high-dose regions were evaluated by directly comparing measured dose distributions. Tests using the multidimensional comparison tool showed detectable degradation beyond one week postirradiation, but all low-dose measurements passed relative to the test criteria and the dose distributions showed few regions that failed.