SU-E-T-279: A Novel Electron-Beam Combined with Magnetic Field Application for Radiotherapy.

PURPOSE: The new beam and delivery system consists of an electron accelerator and a system of magnets (one or more). Introducing a transverse magnetic field in and near the tumor, causes the electrons to spiral in this region, thereby producing an effective peak in the depth dose distribution, within the tumor volume. Although the basic idea is not new, we suggest here for the first time, a viable as well as a workable, magnetic field configuration, which in addition to focusing the beam does not interfere with its propagation to the target. METHODS: The electron accelerator: can be a linear accelerator or any other type electron accelerator, capable of producing different electron energies for different depths and dose absorption accumulation. The Field size can be as small as a pencil beam and as big as any of the other standard field sizes that are used in radiotherapy. The scatter filter can be used or removed. The dose rate accumulation can be as higher as possible.The magnets are able to produce magnetic fields. The order, direction, width, place, shape and number of the magnetic fields define the shape and the Percentage Depth Dose (PDD) curve of the electron beam. Prototypes were successfully tested by means of computer simulation, using:COMSOL-Multiphsics for magnetic fields calculations. FLUKA package, for electron beam MC simulation. RESULTS: Our results suggest that by using an electron beam at different energies, combined with magnetic fields, we could modify the delivered dose. This is caused by manipulating the electron motion via the Lorentz force. The applied magnetic field, will focus the electron beam at a given depth and deposit the energy in a given volume and depth, where otherwise the electron energy will have spread deeper. The direction and magnitude of the magnetic fields will prevent the scattering of the electron beam and its absorption in remote volumes. In practice, we get a pseudo Bragg peak depth dose distribution, applying a relatively low cost system. The therapeutic efficiency induced by the system is of similar efficiency as the ion beam therapy techniques. CONCLUSIONS: Our novel concept demonstrates treatment that is almost similar to proton therapy and in some parameters even better performance.Unlike the current high-energy electron therapy, our system's beam deposit almost all of its energy on its target, with a low amount of radiation deposited in tissues from the surface of the skin to the front of tumor, and almost no "exit dose" beyond the tumor. This property will enables to hit tumors with higher, potentially more effective radiation doses, while being considerably less expensive.

Assessing the quality of conformal treatment planning: a new tool for quantitative comparison.

We develop a novel radiotherapy plan comparison index, critical organ scoring index (COSI), which is a measure of both target coverage and critical organ overdose. COSI is defined as COSI=1-(V(OAR)>tol/TC), where V(OAR)>tol is the fraction of volume of organ at risk receiving more than tolerance dose, and TC is the target coverage, VT,PI/VT, where VT,PI is the target volume receiving at a least prescription dose and VT is the total target volume. COSI approaches unity when the critical structure is completely spared and the target coverage is unity. We propose a two-dimensional, graphical representation of COSI versus conformity index (CI), where CI is a measure of a normal tissue overdose. We show that this 2D representation is a reliable, visual quantitative tool for evaluating competing plans. We generate COSI-CI plots for three sites: head and neck, cavernous sinus, and pancreas, and evaluate competing non-coplanar 3D and IMRT treatment plans. For all three sites this novel 2D representation assisted the physician in choosing the optimal plan, both in terms of target coverage and in terms of critical organ sparing. We verified each choice by analysing individual DVHs and isodose lines. Comparing our results to the widely used conformation number, we found that in all cases where there were discrepancies in the choice of the best treatment plan, the COSI-CI choice was considered the correct one, in several cases indicating that a non-coplanar 3D plan was superior to the IMRT plans. The choice of plan was quick, simple and accurate using the new graphical representation.

Feasibility and low toxicity of early radiotherapy after high-dose chemotherapy and autologous stem cell transplantation for patients with high-risk stage II-III and locally advanced breast carcinoma.

BACKGROUND: This prospective trial examined the feasibility, toxicity, and effectiveness of early locoregional radiotherapy after high-dose chemotherapy and autologous stem cell transplantation in patients with high-risk American Joint Committee on Cancer (AJCC) Stage II-III and locally advanced breast carcinoma. METHODS: One hundred forty-seven consecutive patients with high-risk and locally advanced breast carcinoma were included in the current study. All patients received induction chemotherapy with a doxorubicin-based therapy, which was consolidated with high-dose cyclophosphamide, carboplatin, and thiotepa followed by autologous stem cell support. Within 50 days of the transplant, the patients were treated with locoregional radiotherapy that included the chest wall or breast, the axilla and supraclavicular area, and the internal mammary chain. The volume of lung included in the treatment volume was kept to a minimum. The central lung distance of the tangential fields ranged from 0.6-2.0 cm (mean, 1.1 cm). Tamoxifen was given based on receptor status. RESULTS: One hundred forty-six of 147 patients received the planned treatment. Only six patients had a delay in the initiation of radiotherapy, and another 16 patients had delays during radiotherapy. Leukocyte and platelet toxicities during radiotherapy were not life-threatening and blood counts thereafter returned to normal. Grade 2 (according to National Cancer Institute Common Toxicity Criteria) skin toxicity occurred in 22% of patients and Grade 3 skin toxicity occurred in 6% of patients. Radiation pneumonitis was reported to occur in 5 patients (< 4%). After a median follow-up of 36 months from diagnosis (range, 6-64 months), there were no long-term organ toxicity and no secondary malignancy reported. No treatment-related deaths were reported. Three patients (< 3%) developed locoregional recurrence. CONCLUSIONS: Locoregional radiotherapy after high-dose chemotherapy and autologous stem cell transplantation appears to be feasible and can be delivered safely within 10 weeks of transplantation. The short-term and long-term toxicity are reported to be low, with good local control.

Linear accelerator radiosurgery for vestibular schwannoma.

OBJECT: The use of radiosurgery in the treatment of acoustic neuromas has increased substantially during the last decade. Most published experience relates to the use of the gamma knife. In this report, the authors review the methods and results of linear accelerator (LINAC) radiosurgery in 44 patients with acoustic neuromas who were treated between 1993 and 1997. METHODS: Computerized tomography scanning was selected as the stereotactic imaging modality for target definition. A single, conformally shaped isocenter was used in the treatment of 40 patients; two or three isocenters were used in four patients who harbored very irregular tumors. The radiation dose directed to the tumor border was the only parameter that changed during the study period: in the first 24 patients who were treated the dose was 15 to 20 Gy, whereas in the last 20 patients the dose was reduced to 11 to 14 Gy. After a mean follow-up period of 32 months (range 12-60 months), 98% of the tumors were controlled. The actuarial hearing preservation rate was 71%. New transient facial neuropathy developed in 24% of the patients and persisted to a mild degree in 8%. Radiation dose correlated significantly with the incidence of cranial neuropathy, particularly in large tumors (> or = 4 cm3). CONCLUSIONS: Single-isocenter LINAC radiosurgery proved to be an effective treatment for acoustic neuromas in this series, with results that were comparable with those reported for gamma knife radiosurgery and multiple isocenters.

Radiosurgery for acoustic neurinomas (vestibular schwannomas).

BACKGROUND: Radiosurgery is a therapeutic technique characterized by the delivery of a single high dose of ionizing radiation from an external source to a precisely defined intracranial target. The application of radiosurgery to the treatment of acoustic neurinomas has increased substantially in the last decade. Most of the published experience pertains to the use of the gamma knife. OBJECTIVES: To report the experience at the first Israeli Linear Accelerator Radiosurgery Unit in the management of 44 patients with acoustic neurinomas. METHODS: We analyzed the clinical records and imaging studies of all patients undergoing radiosurgery for acoustic neurinomas between 1993 and 1997, and quantified the changes in tumor volume, hearing status, and facial and trigeminal nerve function. The contribution of radiation dose and original tumor volume upon those variables was also studied. RESULTS: At a mean follow-up of 32 months (range 12-60), 98% of the tumors were controlled (75% had shrunk; 23% had stable volume). The actuarial hearing preservation rate was 71%. New transient facial neuropathy developed in 24% of the patients, persisting in mild degrees in 8%. Neuropathy correlated primarily with tumor volume. Tumors with volumes > 4 ml were at high risk when marginal radiation doses were > 1,400 cGy. Dose reduction to a maximum of 1,400 cGy produced no neuropathies in the last 20 patients, still preserving tumor control rates. CONCLUSIONS: Radiosurgery is an effective and cost-efficient therapeutic modality for newly diagnosed acoustic neurinomas in the elderly or medically infirm population, and for all residual or recurrent tumors after conventional surgery.