Peter Wootton

Impact of a multileaf collimator on treatment morbidity in localized carcinoma of the prostate

PURPOSE To evaluate the effectiveness of variable multileaf collimation, three-dimensional treatment planning, and computer-controlled conformal radiation therapy of prostate cancer. METHODS AND MATERIALS Two hundred and forty-five patients with locally advanced prostate cancer have completed treatment over a 9-year time span using a multileaf collimator and conformal treatment techniques on the University of Washington cyclotron. All patients had three-dimensional treatment planning with computed tomography scans in the treatment position, and had treatment fields individually shaped to the target volume with a continuously variable multileaf collimator. Treatment was delivered under computer control with network transfer of the multileaf collimator settings from the treatment planning computer to the cyclotron control system. RESULTS The multileaf collimator combined with three-dimensional treatment planning results in elegant dose distributions. These neuron dose distributions resulted in a reduced local/regional tumor failure rate with no increase in complications when compared to control treatment with photons in a randomized trial. Neutron treatment delivered at other institutions without conformal beam shaping resulted in the same improvement in local-regional tumor control rates, but was associated with a significantly higher normal tissue complication rate than seen with conformal neutron beam delivery techniques (grade 3 and 4 cumulative late normal tissue toxicity rates of 39% vs. 10%, p = 0.0007). CONCLUSIONS Conformal treatment of prostate cancer using a multileaf collimated neutron beam results in increased local/regional tumor control rates with low normal tissue toxicities. This experience is directly applicable to the conformal treatment of prostate cancer with photons.

Uniformity in dosimetry protocols for therapeutic applications of fast neutron beams.

In this supplement to both the American and the European protocols for clinical neutron dosimetry, new recommendations are given with respect to the basic physical parameters and experimental techniques employed. For neutron dosimetry, the air kerma or exposure calibration in a photon beam is the most suitable method for the calibration of tissue-equivalent ionization chambers until calibration in a standard neutron field becomes available. More recent data are recommended for the physical parameters required for the photon calibration as well as for the measurements in the neutron beam. Water is recommended as the reference phantom material due to its similarity in absorption and scattering properties to muscle. The resulting overall change in absorbed dose calculated according to this supplement, compared with the original protocols, will be smaller than about +/- 2% due to differences in the basic physical parameters. An additional change of several percent occurs at depth in a phantom as a result of the difference between water and the muscle-equivalent liquid formerly recommended as the reference phantom material.

Dosimetry intercomparisons between fast-neutron radiotherapy facilities.

Neutron dosimetry intercomparison visits have been made by physicists from the M. D. Anderson Hospital-Texas A&M University Project to the Naval Research Laboratory, the University of Washington, and the MRC Cyclotron at Hammersmith Hospital. The Naval Research Laboratory and University of Washington physicists have made dosimetry intercomparisons at the Texas A&M Variable-Energy Cyclotron (TAMVEC). The parameters that are usually measured during these visits are tissue kerma in air, tissue dose at depth of dose maximum, relative central-axis depth dose, neutron/gamma ratios in air and in phantom, and photon calibrations of ionization chambers. In addition, beam profiles and dose buildup curves are sometimes measured. Other parameters that are compared are values of W, stopping power ratios, kerma corrections, and calculations that lead to the statement of tumor doses for patients. This paper presents some of the results of the intercomparisons and discusses the implications of the findings.

Boron neutron capture enhanced fast neutron radiotherapy for malignant gliomas and other tumors

Both fast neutron radiotherapy and boron neutron capturetherapy have been investigated as new radiation treatmenttechniques for patients with malignant gliomas. While eachof these techniques individually has shown the potentialfor pathological eradication of malignant glioma, to dateneither has evolved into an accepted, improved methodof treatment. We have recently begun a researchprogram investigating the feasibility of combining the benefitsof both types of therapy. As a fastneutron beam penetrates tissue some of the particlesare degraded to thermal energies. These can becaptured by 10B or other suitable isotopes resultingin a highly-localized release of additional energy duringa course of fast neutron radiotherapy. In thisarticle we will review the rationale for suchan approach, and review the underlying physics aswell as in vitro, in vivo, and earlyhuman studies testing its feasibility. If appropriate carrieragents can be found that preferentially-localize in tumorcells, this approach cna be applied to manydifferent tumor systems.

Measurement of photon dose fraction in a neutron radiotherapy beam.

Photon dose fractions (PDFs) have been measured in and around a neutron radiotherapy beam with a tissue-equivalent proportional counter (TEPC) and with paired ion chambers. The PDFs were found to increase linearly with increasing field size and width depth in phantom. PDFs were shown to decrease with decreasing phantom size and to be larger in the shielded region of the phantom than in the direct beam. Uncertainties in the PDF values were estimated to be 10%-15% for the TEPC measurements but about 50% for the measurement made with ion chambers.

ENHANCEMENT OF FAST NEUTRON BEAMS WITH BORON NEUTRON CAPTURE THERAPY : A MECHANISM FOR ACHIEVING A SELECTIVE, CONCOMITANT TUMOR BOOST

Both fast neutron radiotherapy and boron neutron capture therapy (BNCT) have been utilized to treat malignant disease. Herein we discuss the potential of combining these treatments to enhance the effectiveness of fast neutron therapy through a concomitant BNCT boost. Using a fast neutron beam generated from a 50 MeV proton on beryllium reaction, we have determined that 0.1% of the beam per microgram of boron-10 per gram of tissue (microgram/g) can be deposited via BNCT. Our mathematical modeling predicts that BNCT enhancement of our beam will lead to an additional 1-2 logs of tumor cell kill for boron-10 concentrations of 30-50 micrograms/g. We have validated this via V-79 cell line in vitro measurements. A Poisson model estimation of how this additional cell kill will influence local tumor control, predicts that BNCT enhancement of fast neutron radiation will lead to a clinically significant improvement in outcome.

Integration of radiotherapy planning systems and radiotherapy treatment equipment: 11 years experience

PURPOSE We have investigated the requirements, design, implementation, and operation of a computer-controlled medical accelerator with multileaf collimator (MLC), integrated with a radiation treatment-planning system (RTPS), and we report on the performance, benefits, and lessons learned from this experience. METHODS AND MATERIALS In 1984 the University of Washington installed a computer-controlled radiation therapy machine (the Clinical Neutron Therapy System, or CNTS) with a multileaf collimator. Since the beginning of operation the control system computer has been connected by commercially available network hardware and software to three generations of radiation treatment-planning systems. Semiautomated setup and completely computerized check and confirm were incorporated into the system from the beginning of clinical operation in 1984. The system cannot deliver a patient treatment without a computer-prepared treatment plan. RESULTS The CNTS has been in use for routine patient treatments for over 11 years. The cost of the network connection and software was an insignificant fraction of the facility cost. Operation has been efficient and reliable. Of the 441 machine-related session reschedulings (out of 18,432 sessions total) during the past 9 years, only 20 were due to problems with data transfer between the RTPS and CNTS, associated primarily with two incidents. Close integration with the treatment-planning system allows complex treatments to be delivered. Dramatic evolution of the departmental treatment-planning system has not required any changes or redesign of either the accelerator control system or the network connection. CONCLUSIONS Our experience shows that a large degree of automation is possible with reasonable effort, by using well-known software and hardware design strategies. The lessons we have learned from this can be carried over into photon therapy now that photon accelerators with MLC facilities are commercially available.

Control system specification for a cyclotron and neutron therapy facility

A comprehensive specification for the computer control system of a cyclotron and treatment facility that provides particle beams for cancer treatments for fast neutrons, production of medical isotopes, and physics experiments is discussed. The control system is described as thoroughly as is practical using standard technical English, supplemented by tables, diagrams, and algebraic equations. This specification comprises over 300 single-spaced pages. A more precise and compact specification might be achieved by making greater use of formal mathematical notations instead of English. Work has begun on a formal specification of the system, using the Z and Petri net notations.<<ETX>>

The radiation therapy dosimetry network in the United States

The United States government and the governments of sixteen other countries have established radiation standards laboratories which house the primary standards dosimeters of the respective countries. In the United States, three regional calibration laboratories were established to disseminate the national radiation standards through the use of secondary standards dosimeters. These, in turn, are used for calibration of radiation field instruments used to measure radiation applied in therapy. These laboratories are periodically accredited by the American Assocation of Physicists in Medicine (AAPM). In 1976, AAPM established a Committee on Radiation Calibration Needs in Therapy to conduct a study of the adequacy of the therapy dosimetry network in the United States. According to this study, 1322 centers were performing radiotherapy in 1978, and 1057 radiation instruments were used to calibrate the therapy machines in these facilities. In more than 99% of the institutions, medical physicists are responsible for carrying out the necessary calibrations. The study showed that there is a need, though not an urgent one, for an additional regional calibration laboratory in the Far Western United States. Establishment of such a laboratory would not be excessively disruptive to the existing laboratories.

Dosimetric properties of neutrons from 21-MeV deuteron bombardment of a deuterium gas target.

Spectra, yields, average energies, and kerma rates in tissue of neutrons from 21-MeV deuteron bombardment of deuterium gas targets have been calculated for target thicknesses of 1, 3.5, and 5 MeV. A high pressure gas cell was constructed and was filled with 33 atm of D2 gas (equivalent to an energy loss of 3.5 MeV for 21-MeV deuterons); dose rate, dose buildup, and depth-dose properties of neutrons produced by the D(d,n) reaction were measured. Dosimetric properties of these neutrons are superior to those of neutrons from a thick Be target bombarded by a deuteron beam of the same energy.