Peacock System Research Articles

Peacock

Latent Dirichlet allocation (LDA) is a popular topic modeling technique in academia but less so in industry, especially in large-scale applications involving search engine and online advertising systems. A main underlying reason is that the topic models used have been too small in scale to be useful; for example, some of the largest LDA models reported in literature have up to 10 3 topics, which difficultly cover the long-tail semantic word sets. In this article, we show that the number of topics is a key factor that can significantly boost the utility of topic-modeling systems. In particular, we show that a “big” LDA model with at least 10 5 topics inferred from 10 9 search queries can achieve a significant improvement on industrial search engine and online advertising systems, both of which serve hundreds of millions of users. We develop a novel distributed system called Peacock to learn big LDA models from big data. The main features of Peacock include hierarchical distributed architecture, real-time prediction, and topic de-duplication. We empirically demonstrate that the Peacock system is capable of providing significant benefits via highly scalable LDA topic models for several industrial applications.

A Monte Carlo Model for Independent Dose Verification in Serial Tomotherapy

Due to the very high complexity of IMRT treatment plans, it is imperative to perform dose verification, preferably before patient delivery. The aim of this project is to develop a Monte-Carlo-based model to verify the final dose distributions of plans developed using the Peacock system (CORVUS Treatment Planning System and MIMiC collimator). The system delivers radiation through arc therapy and uses sinogram files to determine the state of each of the multileaf collimator leaves. In-house software was developed using Matlab to decode the sinograms and create blocklets that are used as input in an MCSIM model of the MIMiC collimator attached to a Varian Clinac 600C. After validating the model, a prostate and head and neck case were simulated. The CORVUS-predicted dose distributions were compared with the Monte Carlo dose distributions. As expected, the results agreed very closely for the homogeneous case of the prostate but there were large discrepancies observed for the more heterogeneous head and neck case.

SU-FF-T-299: Monte Carlo Based Dose Verification for Serial Tomotherapy

Purpose: To develop a Monte Carlo model to verify the final dose distributions and monitor units for serial tomotherapy plans developed and delivered using the Peacock system (Corvus Treatment Planning System and MIMiC collimator, Nomos Corp., Sewickley, PA). Materials and methods: The Peacock system delivers the dose to the patient using arc therapy. The treatment plan is created in Corvus were sinograms are created for each arc in order to dictate the state of each of the MIMiC leaves at different locations along the arc. In‐house functions were written in Matlab (Mathworks Inc., Natick, MA) to decode these sinograms. A simple three‐field plan (three gantry positions), as well as full patient treatment plans were simulated using our Monte Carlo model and the same plans were delivered using the Peacock system in solid water. Films were placed in the solid water phantom in order to measure the dose distribution for comparison against the Monte Carlo calculations. Matlab functions were written to convert the Monte Carlo output into a format RIT113 (RIT Inc., Colorado Springs, CO) could read. This allowed us to co‐register the calculated dose maps and the measured ones in order to compare the two. Results: The Monte Carlo calculated dose distribution from the complete arc therapy in solid water phantom was compared against film measurements. The agreement was within 2%. The comparison between Monte Carlo results and Corvus calculated dose distribution revealed that Corvus would fail to accurately compute the dose in the region where inhomogeneities were present. Conclusions: Based on the agreement between Monte Carlo and measurements we can use the Monte Carlo system as an independent quality assurance tool in order to verify dose distributions and MUs per arc computed by the Corvus.

Intensity-Modulated Radiation Therapy (IMRT) for Newly Diagnosed and Recurrent Intracranial Meningiomas: Preliminary Results

The purpose of this study was to evaluate tumor control, complications, and outcome from intensity-modulated radiation therapy (IMRT) for intracranial meningiomas. Between July 1997 and November 2003, patients with intracranial meningiomas were treated at our institution with the NOMOS Peacock system utilizing the Multileaf Intensity Modulating Collimator (MIMiC). Thirty-five patients with 37 lesions (35 benign and two atypical histology) were identified with a minimum of six months of radiologic follow-up for this retrospective review. The median age of the patients was 65 years with a median KPS of 90 prior to treatment with IMRT. The median MRI/CT follow-up for the 37 treated lesions was 19.1 months (range 6.4-62.4 months). Twenty meningiomas (54%) were previously treated with surgery/radiosurgery prior to IMRT, and 17 meningiomas (46%) were treated with IMRT primarily after diagnosis was established by MRI/CT. The median time from previous surgery to treatment with IMRT was 18.1 months. The median tumor dose was 50.4 Gy prescribed to the 87% isodose line providing a median target coverage of 95%. Local control was at 97% three years after treatment with IMRT. Only three patients exhibited local failure after treatment. Although local control was slightly better in the upfront-IMRT lesions as compared to the lesions treated with prior surgery/radiosurgery (100% vs 95%), this difference was not statistically significant. On univariate analysis, the IMRT prescription dose and maximum dose were found to be predictors for local control (p=0.05). On multivariate analysis, these factors did not remain significant for influencing local control. No long-term complications from IMRT were documented among the 35 patients. In conclusion, intensity-modulated radiation therapy is a safe and effective treatment for some intracranial meningiomas. A greater number of patients with longer follow-up after treatment may be needed to determine treatment variables predicting for long-term tumor control.

A preliminary analysis of patterns of failure in patients treated with intensity modulated radiotherapy (IMRT) for head and neck cancer: The University of Nebraska Medical Center experience

To analyze the patterns of failure in patients with head-and-neck cancer treated with IMRT. Between May 2000 and December 2003, 188 patients received IMRT for head-and-neck cancer at the University Nebraska Medical Center. Most patients (97%) were treated with the Peacock system using a dynamic multivane intensity-modulating multileaf collimator (MIMiC), and the remainder patients were treated with MLC-based step-and-shoot IMRT. Thirty patients who either received IMRT for palliation (23 patients) or did not complete the planned treatments (7 patients) were excluded from analysis. One hundred and fifty-eight patients received IMRT with curative intent. Of the 158 patients, 46 were women and 112 were men (median age 60 years, range 11–87). One hundred and twenty-five patients (79%) had squamous cell carcinoma. Twenty-six patients (16%) were treated for recurrent disease. In patients who had primary disease, 112 (85%) were stage III or IV. Seventy-seven patients (49%) received definitive IMRT, and 81 (51%) received adjuvant IMRT. Eighty-eight patients (56%) also received chemotherapy; 56/77 (73%) of definitive cases and 32/81 (40%) of postoperative cases. Twenty-five (16%) patients had previously received conventional radiation therapy. The IMRT was used only in the upper neck for most patients (96%). A conventional AP low-neck field was added when comprehensive neck treatment was indicated. A two-step treatment planning approach was used; namely an initial comprehensive field for all targets followed by a boost field for high-risk areas to ensure adequate fraction size for all intended targets. The dose was prescribed to the isodose that provided adequate coverage for each defined target (GTV, CTV1 and CTV2) depending upon the probability of tumor burden. In definitive IMRT cases, the median dose to the GTV/CTV1 was 70Gy (range 50-74Gy), and 50Gy (range 45-54Gy) to CTV2, whereas in the postoperative cases the median dose was 64Gy (range 50.4–72.4Gy) for CTV1 and 50Gy (range 45Gy-54Gy) for CTV2. The patterns of failure were analyzed. The probability of loco-regional control, distant metastasis, disease-free survival, and overall survival were calculated using the Kaplan-Meier method. The median follow-up was 17 months. A total of 137 patients (87%) had minimum follow-up of 6 months. Ten patients (6%) developed local or regional recurrences. Three of the loco-regional failures had persistent disease. Eight (5%) had loco-regional and distant failures, and 19 (12%) patients developed distant metastases as the only site of failure. All but one loco-regional failure occurred within the GTV or CTV1. One recurred in CTV2 area in the contra-lateral neck. The 3-year actuarial loco-regional control rate was 88%, and distant metastasis-free rate was 82%. The 3-year overall survival and disease-free survival rates were 80% and 77% respectively. We report one of the largest single institutional IMRT experiences in patients with head-and-neck cancer. IMRT is highly effective and offers excellent loco-regional control. Distant failure remains the predominant site for treatment failure. More effective systemic treatment is critical to improve overall disease-free survival

Hypofractionated intensity-modulated radiotherapy for primary glioblastoma multiforme

PurposeA pilot study was designed to evaluate the safety and efficacy of a novel regimen of hypofractionated intensity-modulated radiotherapy (RT) in the adjuvant treatment of primary glioblastoma multiforme (GBM). The rationale of the study was to combine the potential radiobiologic advantage of hypofractionation to GBM with a highly conformal radiotherapeutic technique. The study was designed to measure the acute and chronic morbidity of patients treated with this regimen, response of GBM to the treatment, overall survival, and time to disease progression after therapy completion. Methods and materialsTwenty eligible patients were accrued between February 1999 and May 2000 for the study. All patients had Karnofsky performance scores of ≥70. All patients were treated with intensity-modulated RT using the NOMOS Peacock system. A dose of 50 Gy was delivered in 5-Gy daily fractions within 2 weeks to enhancing primary disease, residual tumor, or surgical cavity. Simultaneously, 30 Gy was prescribed in 3-Gy daily fractions to surrounding edema. The time to progression was measured with serial neurologic examinations and MRI or CT scans after RT completion. Acute and late toxicity was graded using Radiation Therapy Oncology Group neurotoxicity scores. ResultsOf the 20 patients, 18 were evaluated for outcome. The median time to disease progression was 6 months after RT completion. The median overall survival was 7 months after treatment completion. All recurrences were within 2 cm of the operative bed. Neurotoxicity during therapy was minimal, with all patients experiencing Grade 0 or 1 toxicity. Late toxicity included 10 patients with Grade 0, 2 patients with Grade 2, and 3 patients with Grade 4 toxicity, manifesting as brain necrosis requiring surgical reexcision. The survival of the 3 patients with brain necrosis was 23, 20, and 9 months. Mortality in all cases was the result of tumor recurrence, with no mortality resulting from brain necrosis. ConclusionThis regimen of hypofractionated intensity-modulated RT did not improve the time to disease progression or overall survival compared with historical experience using conventional fractionation. However, the treatment duration was reduced from 6 weeks to 2 weeks, which may be of palliative benefit in certain subsets of patients. This treatment regimen demonstrated a greater incidence of brain necrosis requiring surgical intervention; however, the 3 patients experiencing this toxicity had longer survival times. Future investigation may be useful to determine which fraction size may be optimal for GBM when highly conformal RT is used in the adjuvant setting.

The use of rectal balloon during the delivery of intensity modulated radiotherapy (IMRT) for prostate cancer: more than just a prostate gland immobilization device?

The purpose of this study was to investigate the role of a rectal balloon for prostate immobilization and rectal toxicity reduction in patients receiving dose-escalated intensity-modulated radiotherapy for prostate cancer. Patients with localized prostate cancer who were undergoing intensity-modulated radiotherapy were treated in a prone position, immobilized with a customized Vac-Lok bag (MED-TEC, Orange City, IA). A rectal balloon with 100 cc of air was used to immobilize the prostate. The prostate displacements were measured using computed tomography (CT)-CT fusion on 10 patients who received radioactive seed implant before intensity-modulated radiotherapy. They were scanned twice weekly during 5 weeks of intensity-modulated radiotherapy, and breathing studies were also performed. Rectal toxicity was evaluated by use of Radiation Therapy Oncology Group scoring in 100 patients. They were treated to a mean dose of 76 Gy over 35 fractions (2.17-Gy fraction size). Dose-volume histogram of the rectum was assessed. A film phantom was constructed to simulate the 4-cm diameter air cavity that was created by the rectal balloon. Kodak XV2 films (Rochester NY) were used to measure and compare dose distribution with and without the air cavity. A fraction of 1.25 Gy was delivered to the phantom at isocenter with 15-MV photons by use of the NOMOS Peacock system and the MIMiC treatment delivery system (Sewickley, PA). The anterior-posterior and lateral prostate displacements were minimal, on the order of measurement uncertainty (approximately 1 mm). The standard deviation of superior-inferior displacement was 1.78 mm. Breathing studies showed no organ displacement during normal breathing when the rectal balloon was in place. The rectal toxicity profile was very favorable: 83% (83/100) patients had no rectal complaint, and 11% and 6% had grade 1 and 2 toxicity, respectively. Dose-volume histogram analysis revealed that in all of the patients, no more than 25% of the rectum received 70 Gy or greater. As visualized by film dosimetry, the dose at air-tissue interface was approximately 15% lower than that without an air cavity. The dose built up rapidly so that at 1 and 2 mm, the differential was approximately 8% and 5%, respectively. The dosimetric coverage at the depth of the posterior prostate wall was essentially equal, with or without the air cavity. The use of a rectal balloon during intensity-modulated radiotherapy significantly reduces prostate motion. Prostate immobilization thus allows a safer and smaller planning target volume margin. It has also helped spare the anterior rectal wall (by its dosimetric effects) and reduced the rectal volume that received high-dose radiation (by rectal wall distension). All these factors may have further contributed to the decreased rectal toxicity achieved by intensity-modulated radiotherapy, despite dose escalation and higher-than-conventional fraction size.

Intensity-modulated radiation therapy (IMRT) for meningioma

Purpose: To assess the safety and efficacy of intensity-modulated radiation therapy (IMRT) in the treatment of intracranial meningioma. Methods and Materials: Forty patients with intracranial meningioma (excluding optic nerve sheath meningiomas) were treated using IMRT with the NOMOS Peacock system between 1994 and 1999. Twenty-five patients received IMRT after surgery either as adjuvant therapy for incomplete resection or for recurrence, and 15 patients received definitive IMRT after presumptive diagnosis based on imaging. Thirty-two patients had skull base lesions, and 8 had nonskull base lesions. The prescribed dose ranged from 40 to 56 Gy (median 50.4 Gy) at 1.71 to 2 Gy per fraction, and the volume of the primary target ranged from 1.55 to 324.57 cc (median 20.22 cc). The mean dose to the target ranged from 44 to 60 Gy (median 53 Gy). Follow-up ranged from 6 to 71 months (median 30 months). Acute and chronic toxicity were assessed using Radiation Therapy Oncology Group (RTOG) morbidity criteria and tumor response was assessed by patient report, examination, and imaging. Overall survival, progression-free survival, and local control were calculated using the Kaplan-Meier method. Results: Cumulative 5-year local control, progression-free survival, and overall survival were 93%, 88%, and 89%, respectively. Two patients progressed after IMRT, one locally and one distantly. Each was treated with IMRT after multiple recurrences of benign meningioma over many years. Both were found to have malignant meningioma at the time of relapse after IMRT, and it is likely their tumors had already undergone malignant change by the time IMRT was given. Defined normal structures generally received a significantly lower dose than the target. The most common acute central nervous system (CNS) toxicity was mild headache, usually relieved with steroids. One patient experienced RTOG Grade 3 acute CNS toxicity, and 2 experienced Grade 3 or higher late CNS toxicity, with one possible treatment-related death. No toxicity was observed with mean doses to the optic nerve/chiasm up to 47 Gy and maximum doses up to 55 Gy. Conclusion: IMRT is a promising new technology that is safe and efficacious in the primary and adjuvant treatment of intracranial meningiomas. A history of local aggression may indicate malignant degeneration and predict a poorer outcome. Toxicity data are encouraging, but the potential for serious side effects exists, as demonstrated by one possible treatment-related death. Larger cohort and longer follow-up are needed to better define efficacy and late toxicity of IMRT.

The University of California, Irvine experience with tomotherapy using the Peacock system

Our institutional experience using the Peacock system for intensity-modulated radiation therapy (IMRT) is summarized. Over 100 patients were treated using this system, which is fitted to a Clinac 600C linac. Both cranial and extracranial lesions have been treated using this modality. Immobilization is achieved either with the Talon ™ system for cranial sites or an Aquaplast cast. Target volumes up to 500 cm 3 have been treated. Multiple lesions (up to 3) were treated in one setup. The range of dose/fractionation schemes used was 15 Gy/1 fx (radiosurgical treatment) — 80 Gy/40 fx. Dose validation studies were carried out using film and ion chamber dosimetry in a specially designed phantom. Optimal dose distributions were attainable using inverse treatment planning for IMRT delivery. These were found to encompass the target volumes accurately using dose validation phantom studies. Immobilization methods used were accurate to within 1 mm, as evidenced by daily portal films. IMRT using the Peacock system offers the advantage of delivery of conformal therapy to high doses safely and accurately. This provides the opportunity for dose escalation studies, retreatment of previously treated tumors, as well as treating multiple targets in one setup. The system may be fitted to a conventional linac without major modifications.

Quality assurance procedures for the peacock system

The Peacock system is the product of technological innovations that are changing the practice of radiotherapy. It uses dynamic beam modulation technique and inverse planning algorithm, both of which are new methodologies, to perform intensity-modulation radiation therapy (IMRT). The quality assurance (QA) procedure established by Task Group No. 40 did not adequately consider these emerging modalities. A review of literature indicates that published articles on QA procedures concentrate primarily on the verification of dose delivered to phantom during commissioning of the system and dose delivered to phantom before treating patients. Absolute dose measurements using ion chambers and relative dose measurements using film dosimetry have been used to verify delivered doses. QA on equipment performance and equipment safety is limited. This paper will discuss QA on equipment performance, equipment safety, and patient setup reproducibility.

Where goest the Peacock?

Since the treatment of the first patient in 1994, the Peacock® system has maintained its presence as the dominant method of intensity-modulated radiation therapy (IMRT) delivery. Currently in use at nearly 80 institutions, over 8000 patients have been treated using the system. Peacock treatments have been delivered to sites throughout the body, including CNS, head & neck, prostate, liver, kidney, lung, mediastinum, and extremities. IMRT, however, is a young and rapidly evolving treatment methodology. As institutions have explored new ways of improving radiation therapy with intensity-modulated techniques, the requirements for the Peacock system have also expanded. More sophisticated planning algorithms have been implemented to satisfy these new requirements, as well as better tools for treatment verification and quality assurance. In addition, new delivery techniques are being examined to improve the ability of IMRT to increase target volume doses while limiting organ-at-risk doses. One such technique, using helical tomotherapy (Peacock is an example of sequential tomotherapy), is currently being evaluated at one institution. Both techniques use narrow, modulated delivery beams. However, helical tomotherapy requires continuous movement of the couch during radiation, similar to helical CT. This work reviews the development of tomotherapy with the Peacock system. It then looks at current IMRT treatment techniques using tomotherapy, and how the field has broadened since the first treatments were delivered. Finally, it looks at the future of tomotherapy techniques, and how these techniques will adapt to the changing requirements for radiation therapy.

Independent dose calculations for the Peacock system

An independent dose calculation method has been developed to validate intensity-modulated radiation therapy (IMRT) plans from the NOMOS® PEACOCK System. After the plan is generated on the CORVUS planning system, the beam parameters are imported into an independent workstation. The beam parameters consist of intensity maps at each gantry angle and each arc position. In addition, CT scans of the patient are imported into the independent workstation to obtain the external contour of the patient. The coordinate system is defined relative to the alignment point chosen in the CORVUS plan. The independent calculation uses the pencil beam data viz tissue maximum ratio (TMR) and beam profiles for a single 1 × 0.8-cm beamlet formed by the NOMOS® multileaf intensity-modulating collimator (MIMiC) leaf. The pencil beam data were measured for the 6-MV photon beam from Siemens PRIMUS linear accelerator using film dosimetry. The dose at a point is calculated using the depth and off-axis distance from a given pencil beam, corrected for its beam intensity. Isodose distributions are generated using the independent dose calculations and compared to the CORVUS plans. Isodose distributions show good agreement with the CORVUS plans for a number of clinical cases. The independent dose calculation algorithm is described in this paper.

Comparative study between IMRT with NOMOS® BEAK® and linac-based radiosurgery in the treatment of intracranial lesions

A comparative study was undertaken to examine intracranial irradiation using intensity-modulation radiation therapy (IMRT) and linear accelerator-based radiosurgery. The IMRT was examined using the Peacock system with a BEAK® attachment. A clinical case involving a metastatic brain lesion, treated with 3 radiosurgery isocenters, was planned for IMRT. The radiosurgery was planned using the Leibinger planning system. The IMRT was planned using the CORVUS planning system. The CORVUS planning system uses an inverse planning algorithm, a recent development in radiotherapy. Isodose distributions and dose volume histograms were generated and compared. Analysis of the dosimetry shows that the dose conformity and homogeneity within the target using the RTOG guidelines are superior for IMRT. The advantages of IMRT using inverse planning system include the ease of planning and execution of treatment, especially for cases that involve concave targets that require multiple isocenters using radiosurgery.

Commissioning of Peacock system for intensity-modulated radiation therapy

The Peacock System was introduced to perform tomographic intensity-modulated radiation therapy (IMRT). Commissioning of the Peacock System included the alignment of the multileaf intensity-modulating collimator (MIMiC) to the beam axis, the alignment of the RTA device for immobilization, and checking the integrity of the CRANE for indexing the treatment couch. In addition, the secondary jaw settings, couch step size, and transmission through the leaves were determined. The dosimetric data required for the CORVUS planning system were divided into linear accelerator-specific and MIMiC-specific. The linear accelerator-specific dosimetric data were relative output in air, relative output in phantom, percent depth dose for a range of field sizes, and diagonal dose profiles for a large field size. The MIMiC-specific dosimetric data were the in-plane and cross-plane dose profiles of a small and a large field size to derive the penumbra fit. For each treatment unit, the Beam Utility software requires the data be entered into the CORVUS planning system in modular forms. These modules were treatment unit information, angle definition, configuration, gantry and couch angles range, dosimetry, results, and verification plans. After the appropriate machine data were entered, CORVUS created a dose model. The dose model was used to create known simple dose distribution for evaluation using the verification tools of the CORVUS. The planned doses for phantoms were confirmed using an ion chamber for point dose measurement and film for relative dose measurement. The planning system calibration factor was initially set at 1.0 and will be changed after data on clinical cases are acquired. The treatment unit was released for clinical use after the approval icon was checked in the verification plans module.

Stereotactic Radiotherapy of Central Nervous System and Head and Neck Lesions, Using a Conformal Intensity-Modulated Radiotherapy System (PeacockTM System)

The objective of this article is to evaluate single-fraction or fractionated stereotactic radiotherapy of central nervous system (CNS) and head and neck lesions using intensity-modulated radiotherapy (IMRT) with a commercially available system (Peacocktrade mark, Nomos Corporation, Sewickley, PA). This system allows tomotherapeutic delivery of intensity-modulated radiation, that is, the slice-by-slice treatment of the volume of interest with an intensity-modulated beam, making the delivery of highly conformal radiation to the target possible in both single or multiple fractions mode. During an 18-month period, 43 (21 males and 22 females) patients were treated, using a removable cranial screw-fixation device. Ages ranged from 10 to 77 years (mean, 52.2; median, 53.5). Intra- and extra-axial lesions, including head and neck malignancies and spine metastases, were treated. Clinical target volume ranged from 0.77 to 195 cm(3) (mean, 47.8; median, 29.90). The dose distribution was normalized to the maximum and was prescribed, in most cases, at the 80% or 90% isodose line (range, 65 to 96%; median, 85%; mean, 83.4%) and ranged from 14 to 80 Gy (mean, 48; median, 50). The number of fractions ranged from 1 to 40 (mean, 23; median, 25). In all but one patient, 90% of the prescription isodose line covered 100% of the clinical target volume. The heterogeneity index (the ratio between the maximum radiation dose and the prescribed dose) ranged between 1.0 and 1.50, whereas the conformity index (the ratio between the volume encompassed by the prescription isodose line and the clinical target volume) ranged between 1.0 and 4.5. There were no complications related to the radiation treatment. With a median follow-up of 6 months, more than 70% of our patients showed decreased lesion size. Stereotactic IMRT of CNS and head and neck lesions can be delivered safely and accurately. The Peacock system delivers stereotactic radiation in single or multiple fractions and has no volume limitations. It has been used to treat intracranial, head and neck, and spinal lesions. The option of fractionation, the lack of volume constraint, and the capability of treating intracranial, head and neck, and spinal pathology make stereotactic IMRT a valuable adjunct to established stereotactic radiotherapy systems delivering convergent-beam irradiation using the Linac or Gamma Knife. In a clinical setting that offers Linac, Gamma Knife radiosurgery, and conformal stereotactic radiotherapy, the latter may have advantages for treating large (> 25-cm(3)) and irregular lesions, especially when fractionation is considered useful.

Three-dimensional intensity-modulated radiotherapy in the treatment of nasopharyngeal carcinoma: the University of California–San Francisco experience

Purpose: To review our experience with three-dimensional intensity-modulated radiotherapy (IMRT) in the treatment of nasopharyngeal carcinoma. Methods and Materials: We reviewed the records of 35 patients who underwent 3D IMRT for nasopharyngeal carcinoma at the University of California–San Francisco between April 1995 and March 1998. According to the 1997 American Joint Committee on Cancer staging classification, 4 (12%) patients had Stage I disease, 6 (17%) had Stage II, 11 (32%) had Stage III, and 14 (40%) had Stage IV disease. IMRT of the primary tumor was delivered using one of the following three techniques: ( 1) manually cut partial transmission blocks, ( 2) computer-controlled autosequencing static multileaf collimator (MLC), and ( 3) Peacock system using a dynamic multivane intensity-modulating collimator (MIMiC). A forward 3D treatment-planning system was used for the first two methods, and an inverse treatment planning system was used for the third method. The neck was irradiated with a conventional technique using lateral opposed fields to the upper neck and an anterior field to the lower neck and supraclavicular fossae. The prescribed dose was 65–70 Gy to the gross tumor volume (GTV) and positive neck nodes, 60 Gy to the clinical target volume (CTV), and 50–60 Gy to the clinically negative neck. Eleven (32%) patients had fractionated high-dose-rate intracavitary brachytherapy boost to the primary tumor 1–2 weeks following external beam radiotherapy. Thirty-two (91%) patients also received cisplatin during, and cisplatin and 5-fluorouracil after, radiotherapy. Acute and late normal tissue effects were graded according to the Radiation Therapy Oncology Group (RTOG) radiation morbidity scoring criteria. Local-regional progression-free, distant metastasis-free survival and overall survival were estimated using the Kaplan–Meier method. Results: With a median follow-up of 21.8 months (range, 5–49 months), the local-regional progression-free rate was 100%. The 4-year overall survival was 94%, and the distant metastasis-free rate was 57%. The worst acute toxicity was Grade 2 in 16 (46%) patients, Grade 3 in 18 (51%) patients and Grade 4 in 1 (3%) patient. The worst late toxicity was Grade 1 in 15 (43%), Grade 2 in 13 (37%), and Grade 3 in 5 (14%) patients. Only 1 patient had a transient Grade 4 soft-tissue necrosis. At 24 months after treatment, 50% of the evaluated patients had Grade 0, 50% had Grade 1, and none had Grade 2 xerostomia. Analysis of the dose–volume histograms (DVHs) showed that the average maximum, mean, and minimum dose delivered were 79.5 Gy, 75.8 Gy, and 56.5 Gy to the GTV, and 78.9 Gy, 71.2 Gy, and 45.4 Gy to the CTV, respectively. An average of only 3% of the GTV and 2% of the CTV received less than 95% of the prescribed dose. The average dose to 5% of the brain stem, optic chiasm, and right and left optic nerves was 48.3 Gy, 23.9 Gy, 15.0 Gy, and 14.9 Gy, respectively. The average dose to 1 cc of the cervical spinal cord was 41.7 Gy. The doses delivered were within the tolerance of these critical normal structures. The average dose to 50% of the right and left parotids, pituitary, right and left T-M joints, and ears was 43.2 Gy, 41.0 Gy, 46.3 Gy, 60.5 Gy, 58.3 Gy, 52.0 Gy, and 52.2 Gy, respectively. Conclusion: 3D intensity-modulated radiotherapy provided improved target volume coverage and increased dose to the gross tumor with significant sparing of the salivary glands and other critical normal structures. Local-regional control rate with combined IMRT and chemotherapy was excellent, although distant metastasis remained unabated.

Comparison of intensity-modulated tomotherapy with stereotactically guided conformal radiotherapy for brain tumors

Purpose: Intensity-modulated radiotherapy (IMRT) offers the potential to more closely conform dose distributions to the target, and spare organs at risk (OAR). Its clinical value is still being defined. The present study aims to compare IMRT with stereotactically guided conformal radiotherapy (SCRT) for patients with medium size convex-shaped brain tumors.Methods and Materials: Five patients planned with SCRT were replanned with the IMRT-tomotherapy method using the Peacock system (Nomos Corporation). The planning target volume (PTV) and relevant OAR were assessed, and compared relative to SCRT plans using dose statistics, dose–volume histograms (DVH), and the Radiation Therapy Oncology Group (RTOG) stereotactic radiosurgery criteria.Results: The median and mean PTV were 78 cm3 and 85 cm3 respectively (range 62–119 cm3). The differences in PTV doses for the whole group (Peacock–SCRT ±1 SD) were 2% ± 1.8 (minimum PTV), and 0.1% ± 1.9 (maximum PTV). The PTV homogeneity achieved by Peacock was 12.1% ± 1.7 compared to 13.9% ± 1.3 with SCRT. Using RTOG guidelines, Peacock plans provided acceptable PTV coverage for all 5/5 plans compared to minor coverage deviations in 4/5 SCRT plans; acceptable homogeneity index for both plans (Peacock = 1.1 vs. SCRT = 1.2); and comparable conformity index (1.4 each). As a consequence of the transaxial method of arc delivery, the optic nerves received mean and maximum doses that were 11.1 to 11.6%, and 10.3 to 15.2% higher respectively with Peacock plan. The maximum optic lens, and brainstem dose were 3.1 to 4.8% higher, and 0.6% lower respectively with Peacock plan. However, all doses remained below the tolerance threshold (5 Gy for lens, and 50 Gy for optic nerves) and were clinically acceptable.Conclusions: The Peacock method provided improved PTV coverage, albeit small, in this group of convex tumors. Although the OAR doses were higher using the Peacock plans, all doses remained within the clinically defined threshold and were clinically acceptable. Further improvements may be expected using other methods of IMRT planning that do not limit the treatment delivery to transaxial arcs. Each IMRT system needs to be individually assessed as the paradigm utilized may provide different outcomes.

Clinical and financial issues for intensity-modulated radiation therapy delivery

Intensity-modulated radiation therapy (IMRT) is a term applied to a new technology that uses nonuniform radiation beams to achieve conformal dose distributions. This article reviews the use of a commercial system, the Peacock system, which uses a special multileaf collimator (MIMiC) to deliver the dose distribution using arc therapy and segmented fields, similar to a moving strip. Although initially designed for stereotactic radiosurgery, this system has been employed to treat various body sites. More than 300 patients have been treated at our institution in the past 4 years, mainly for cranial, head-and-neck, and prostate tumors. Presently, we treat 40 to 45 patients per day with this technology using two linear accelerators operating with 10 MV and 15 MV x-rays, as Peacock has become a standard therapy procedure. Cases are presented that show the unique ability of IMRT to deliver conformal dose distributions. Why this type of technology can become a standard procedure and why it is cost-effective therapy for both the institution and the patient are discussed.

A non-invasive immobilization system and related quality assurance for dynamic intensity modulated radiation therapy of intracranial and head and neck disease

Purpose: To develop and implement a non-invasive immobilization system guided by a dedicated quality assurance (QA) program for dynamic intensity-modulated radiotherapy (IMRT) of intracranial and head and neck disease, with IMRT delivered using the NOMOS Corporation’s Peacock System and MIMiC collimator. Methods and Materials: Thermoplastic face masks are combined with cradle-shaped polyurethane foaming agents and a dedicated quality assurance program to create a customized headholder system (CHS). Plastic shrinkage was studied to understand its effect on immobilization. Fiducial points for computerized tomography (CT) are obtained by placing multiple dabs of barium paste on mask surfaces at intersections of laser projections used for patient positioning. Fiducial lines are drawn on the cradle along laser projections aligned with nasal surfaces. Lateral CT topograms are annotated with a crosshair indicating the origin of the treatment planning and delivery coordinate system, and with lines delineating the projections of superior-inferior field borders of the linear accelerator’s secondary collimators, or with those of the fully open MIMiC. Port films exposed with and without the MIMiC are compared to annotated topograms to measure positional variance (PV) in superior-inferior (SI), right-left (RL), and anterior posterior (AP) directions. MIMiC vane patterns superposed on port films are applied to verify planned patterns. A 12-patient study of PV was performed by analyzing positions of 10 anatomic points on repeat CT topograms, plotting histograms of PV, and determining average PV. Results and Discussion: A 1.5 ± 0.3 mm SD shrinkage per 70 cm of thermoplastic was observed over 24 h. Average PV of 1.0 ± 0.8, 1.2 ± 1.1, and 1.3 ± 0.8 mm were measured in SI, AP, and RL directions, respectively. Lateral port films exposed with and without the MIMiC showed PV of 0.2 ± 1.3 and 0.8 ± 2.2 mm in AP and SI directions. Vane patterns superimposed on port films consistently verified the planned patterns. Conclusion: The CHS provided adequately reproducible immobilization for dynamic IMRT, and may be applicable to decrease PV for other cranial and head and neck external beam radiation therapy.

Tomotherapy

Tomotherapy is delivery of intensity-modulated, rotational radiation therapy using a fan-beam delivery. The NOMOS (Sewickley, PA) Peacock system is an example of sequential (or serial) tomotherapy that uses a fast-moving, actuator-driven multileaf collimator attached to a conventional C-arm gantry to modulate the beam intensity. In helical tomotherapy, the patient is continuously translated through a ring gantry as the fan beam rotates. The beam delivery geometry is similar to that of helical computed tomography (CT) and requires the use of slip rings to transmit power and data. A ring gantry provides a stable and accurate platform to perform tomographic verification using an unmodulated megavoltage beam. Moreover, megavoltage tomograms have adequate tissue contrast and resolution to provide setup verification. Assuming only translational and rotational offset errors, it is also possible to determine the offsets directly from tomographic projections, avoiding the time-consuming image reconstruction operation. The offsets can be used to modify the leaf delivery pattern to match the beam to the patient's anatomy on each day of a course of treatment. If tomographic representations of the patient are generated, this information can also be used to perform dose reconstruction. In this way, the actual dose distribution delivered can be superimposed onto the tomographic representation of the patient obtained at the time of treatment. The results can be compared with the planned isodose on the planning CT. This comparison may be used as an accurate basis for adaptive radiotherapy whereby the optimized delivery is modified before subsequent fractions. The verification afforded tomotherapy allows more precise conformal therapy. It also enables conformal avoidance radiotherapy, the complement to conformal therapy, for cases in which the tumor volume is ill-defined, but the locations of sensitive structures are adequately determined. A clinical tomotherapy unit is under construction at the University of Wisconsin.