Pedro Andreo, Dosimetry and Medical Radiation Physics Section, IAEA David T Burns, Bureau International des Poids et Measures (BIPM) Klaus Hohlfeld, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany M Saiful Huq, Thomas Jefferson University, Philadelphia, USA Tatsuaki Kanai, National Institute of Radiological Sciences (NIRS), Chiba, Japan Fedele Laitano, Ente per le Nuove Tecnologie L’Energia e L’Ambiente (ENEA), Rome, Italy Vere Smyth, National Radiation Laboratory (NRL), Christchurch, New Zealand Stefaan Vynckier, Catholic University of Louvain (UCL), Brussels, Belgium

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Absorbed Dose Determination in External Beam Radiotherapy: An International Code of Practice for Dosimetry based on Standards of Absorbed Dose to Water

Purpose: The irradiation system and biophysical characteristics of carbon beams are examined regarding radiation therapy. Methods and Materials: An irradiation system was developed for heavy-ion radiotherapy. Wobbler magnets and a scatterer were used for flattening the radiation field. A patient-positioning system using X ray and image intensifiers was also installed in the irradiation system. The depth-dose distributions of the carbon beams were modified to make a spread-out Bragg peak, which was designed based on the biophysical characteristics of monoenergetic beams. A dosimetry system for heavy-ion radiotherapy was established to deliver heavy-ion doses safely to the patients according to the treatment planning. A carbon beam of 80 keV/mm in the spread-out Bragg peak was found to be equivalent in biological responses to the neutron beam that is produced at cyclotron facility in National Institute Radiological Sciences (NIRS) by bombarding 30-MeV deuteron beam on beryllium target. The fractionation schedule of the NIRS neutron therapy was adapted for the first clinical trials using carbon beams. Results: Carbon beams, 290, 350, and 400 MeV/u, were used for a clinical trial from June of 1994. Over 300 patients have already been treated by this irradiation system by the end of 1997. © 1999 Elsevier Science Inc. Heavy ion radiotherapy, Irradiation system.

Biophysical characteristics of HIMAC clinical irradiation system for heavy-ion radiation therapy.

High-energy beams of charged nuclear particles (protons and heavier ions) offer significant advantages for the treatment of deep-seated local tumors in comparison to conventional megavolt photon therapy. Their physical depth-dose distribution in tissue is characterized by a small entrance dose and a distinct maximum (Bragg peak) near the end of range with a sharp fall-off at the distal edge. Taking full advantage of the well-defined range and the small lateral beam spread, modern scanning beam systems allow delivery of the dose with millimeter precision. In addition, projectiles heavier than protons such as carbon ions exhibit an enhanced biological effectiveness in the Bragg peak region caused by the dense ionization of individual particle tracks resulting in reduced cellular repair. This makes them particularly attractive for the treatment of radio-resistant tumors localized near organs at risk. While tumor therapy with protons is a well-established treatment modality with more than 60 000 patients treated worldwide, the application of heavy ions is so far restricted to a few facilities only. Nevertheless, results of clinical phase I-II trials provide evidence that carbon-ion radiotherapy might be beneficial in several tumor entities. This article reviews the progress in heavy-ion therapy, including physical and technical developments, radiobiological studiesmore » and models, as well as radiooncological studies. As a result of the promising clinical results obtained with carbon-ion beams in the past ten years at the Heavy Ion Medical Accelerator facility (Japan) and in a pilot project at GSI Darmstadt (Germany), the plans for new clinical centers for heavy-ion or combined proton and heavy-ion therapy have recently received a substantial boost.« less

Heavy-ion tumor therapy: Physical and radiobiological benefits

The characteristic Bragg peak of protons or heavy ions provides a good localization of dose in three dimensions. Through their ability to deliver laterally and distally shaped homogenous fields, protons have been shown to be a precise and practical method for delivering highly conformal radiotherapy. However, in an analogous manner to intensity modulation for photons, protons can be used to construct dose distributions through the application of many individually inhomogeneous fields, but with the localization of dose in the Bragg peak providing the possibility of modulating intensity within each field in two or three dimensions. We describe four different methods of intensity modulation for protons and describe how these have been implemented in an existing proton planning system. As a preliminary evaluation of the efficacy of these methods, each has been applied to an example case using a variety of field combinations. Dose-volume histogram analysis of the resulting dose distributions shows that when large numbers of fields are used, all techniques exhibit both good target homogeneity and sparing of neighbouring critical structures, with little difference between the four techniques being discerned. As the number of fields is decreased, however, only a full 3D modulation of individual Bragg peaks can preserve both target coverage and sparing of normal tissues. We conclude that the 3D method provides the greatest flexibility for constructing conformal doses in challenging situations, but that when large numbers of beam ports are available, little advantage may be gained from the additional modulation of intensity in depth.

https://iopscience.iop.org/article/10.1088/0031-9155/44/1/014/pdf

Intensity modulation methods for proton radiotherapy.

Purpose: In order to reduce the treatment margin of the moving target due to breathing, we developed a gated irradiation system for heavy-ion radiotherapy. Methods and Materials: The motion of a patient due to respiration is detected by the motion of the body surface around the chest wall. A respiratory sensor was developed using an infrared light spot and a position-sensitive detector. A timing signal to request a beam is generated in response to the respiration waveform, and a carbon beam is extracted from the synchrotron using a RF-knockout method. CT images for treatment planning are taken in synchronization with the respiratory motion. For patient positioning, digitized fluoroscopic images superimposed with the respiration waveform were used. The relation between the respiratory sensor signal and the organ motion was examined using digitized video images from fluoroscopy. The performance of our gated system was demonstrated by using the moving phantom, and dose profiles were measured in the direction of phantom motion. Results: The timing of gate-on is set at the end of the expiratory phase, because the motion of the diaphragm is slower and more reproducible than during the inspiratory phase. The signal of the respiratory sensor shows a phase difference of 120 milliseconds between lower and upper locations on the chest wall. The motion of diaphragm is delayed by 200 milliseconds from the respiration waveform at the lower location. The beam extraction system worked according to the beam on/off logic for gating, and the gated CT scanner performed well. The lateral penumbra size of the dose profile along the moving axis was distinguishably decreased by the gated irradiation. The ratio of the nongated to gated lateral fall-off was 4.3, 3.5, and 2.0 under the stroke of 40.0, 29.0, and 13.0 mm respectively. Conclusion: We developed a total treatment system of gated irradiation for heavy-ion radiotherapy. We found that with this system the target margin along the body axis could be decreased to 5–10 mm although the target moved twice or three times. Over 150 patients with lung or liver cancer had already been treated by this gated irradiation system by the end of July 1999.

Respiratory gated irradiation system for heavy-ion radiotherapy

Heavy ion synchrotron for medical use —HIMAC project at NIRS-Japan—

In order to provide a uniform and desirable dose distribution over a large radiation field, spot beam scanning is one of the most useful methods. A new spot beam scanning system was constructed for a 70 MeV proton beam. The lateral dose distribution was uniform with +/- 2.5% for an 18 cm square field. It was possible to control the dose at each point in the radiation field by this spot scanning method. This system has been confirmed to be satisfactory for delivering a proton beam in the desired field shape and dose level.

Spot scanning system for proton radiotherapy

A new beam course, a projectile fragment separator to provide radioactive beams, is under construction at HIMAC. A primary purpose of the new beam course is to study medical applications of radioactive beams. The specifications and status of the beam course and a preliminary result using carbon beams are summarized.

New secondary beam course for medical use in HIMAC

HIMAC at NIRS is a heavy-ion synchrotron complex dedicated to the medical use. It consists of an injector system, a two-synchrotron ring system, a high-energy beam delivery system, and an irradiation sys­ tem. Heavy ions such as He, C, Ne, Si, and Ar are accelerated in an energy range of 100-800 MeV/u and are delivered to six irradiation rooms as vertical and/or horizontal beams.

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Heavy ion medical accelerator in Chiba (HIMAC)

The HIMAC (Heavy-Ion Medical Accelerator in Chiba) project is in progress. Necessary characteristics for the HIMAC ion source are high current ( 130–630 μA with a q/A of 1 7 ) from He to Ar, good stability, long life and easy maintenance. To attain these characteristics, an indirectly heated PIG ion source test bench has been designed and constructed since 1985. A low-energy beam transport line has also been installed in order to test the beam quality and the matching condition with an RFQ linac (8–800 keV/u). For N, Ne and Ar, preliminary experiments have been carried out on the arc characteristics, ion extraction and charge spectra since 1987. The radial emittance has also been measured and is 150 π mm mrad for a 40 μA Ar3+ beam (0.64 keV/u).

H. Ogawa

Papers

Heavy ion synchrotron for medical use —HIMAC project at NIRS-Japan—

Spot scanning system for proton radiotherapy

New secondary beam course for medical use in HIMAC

Heavy ion medical accelerator in Chiba (HIMAC)

HIMAC PIG ion source development