Radiological physics characteristics of the extracted heavy ion beams of the bevatron.

Studies of the depth-ionization properties and the biological effects of heavy ion beams produced at the bevatron have extended work previously done with less energetic beams from other sources. Results indicate that heavy ion beams are suitable for tumor therapy, studies relating to space biology, and fundamental radiobiology.

Normal tissue complication probabilities: variable dose per fraction.

Because of the large amount of data generated by 3D treatment planning, new tools are being developed for the evaluation and optimization of the plans. Estimates of the probability of local control of the tumor and for the probability of specific normal tissue complications are among the new tools. The normal tissue complication probability (NTCP) is based on clinical estimates of the tolerance doses for specific tissues/organs. These tolerance doses are assumed to apply for uniform partial and full volume irradiations delivered at 2 Gy per fraction and 5 fractions per week. A different tolerance dose may apply when the dose is delivered at a different dose per fraction and over a different period of time. This study evaluates the maximum change expected in the NTCP when the normal structure receives the dose at a different dose per fraction than the target volume due to different choices in the delivery of the daily fraction.

Optimization of radiation therapy, III: A method of assessing complication probabilities from dose-volume histograms.

To predict the likelihood of success of a therapeutic strategy, one must be able to assess the effects of the treatment upon both diseased and healthy tissues. This paper proposes a method for determining the probability that a healthy organ that receives a non-uniform distribution of X-irradiation, heat, chemotherapy, or other agent will escape complications. Starting with any given dose distribution, a dose-cumulative-volume histogram for the organ is generated. This is then reduced by an interpolation scheme (involving the volume-weighting of complication probabilities) to a slightly different histogram that corresponds to the same overall likelihood of complications, but which contains one less step. The procedure is repeated, one step at a time, until there remains a final, single-step histogram, for which the complication probability can be determined. The formalism makes use of a complication response function C(D, V) which, for the given treatment schedule, represents the probability of complications arising when the fraction V of the organ receives dose D and the rest of the organ gets none. Although the data required to generate this function are sparse at present, it should be possible to obtain the necessary information from in vivo and clinical studies. Volume effects are taken explicitly into account in two ways: the precise shape of the patient's histogram is employed in the calculation, and the complication response function is a function of the volume.

Optimization of radiation therapy, IV: A dose-volume histogram reduction algorithm.

A general formalism for estimating the complication probability for non-uniform irradiation of a normal tissue structure has been developed and used by the NCI-sponsored committee on "Evaluation of Treatment Planning for Particle Beam Radiotherapy." The approach involves reducing an N-step dose-volume histogram for the tissue (obtained from the 3D treatment plan) to an equivalent (N-1)-step histogram; this procedure is repeated until there remains a single-step histogram, the complication probability of which can readily be determined. This note provides technical details concerning the histogram-reduction algorithm. Results obtained using it are compared with those for two alternative histogram-reduction algorithms.

Heavy charged-particle induced lesions in rabbit cerebral cortex.

Fourteen male rabbits received single doses of 20, 40, and 80 Gy of neon irradiation with an extended Bragg peak. They were sacrificed at 1 day, 1 week, and 6 months post-irradiation. The tissue changes which showed a significant time-dose relationship were leakage of carbon particles from blood vessels, focal arachnoiditis, hemorrhage, cystic necrosis, and a total histopathologic score using a point system of grading. The focal nature of the lesions was clearly demonstrated with 2 mm thick macrotome sections. The transition zone between damaged brain and microscopically normal appearing brain was less than 1 mm and the tissue damage induced was morphologically similar to that of other radiation modalities. These findings may have important therapeutic implications for patients. The sharply demarcated boundaries of heavy charged-particle induced lesions suggest these beams will be useful for obliterating tissue in areas where it is critical that a transition from undamaged to severely damaged tissue must occur over a short distance, such as in the central nervous system.

Heavy charged-particle stereotactic radiosurgery: cerebral angiography and CT in the treatment of intracranial vascular malformations.

A method is described for stereotactic localization of intracranial arteriovenous malformations (AVM) and for calculating treatment plans for heavy charged-particle Bragg peak radiosurgery. A stereotactic frame and head immobilization system is used to correlate the images of multivessel cerebral angiography and computed tomography. The AVM is imaged by angiography, and the frame provides the stereotactic coordinates for transfer of this target to CT images for the calculation of treatment plans. The CT data are used to calculate the residual ranges and compensation for the charged-particle beam required for each treatment port. Three-dimensional coordinates for the patient positioner are calculated, and stereotactic radiosurgery is performed. Verification of the accuracy of the stereotactic positioning is obtained with computer-generated overlays of the vascular malformation, stereotactic fiducial markers, and bony landmarks on orthogonal radiographs immediately prior to treatment. Using these procedures, the accuracy of the repositioning of the patient at each of a series of imaging and treatment procedures is typically within 1 mm in each of three orthogonal planes.

Comparison of different radiation types and irradiation geometries in stereotactic radiosurgery.

Recent interest in stereotactic radiosurgery of intracranial lesions, and the development of stereotactic irradiation techniques has led to the need for a systematic and complete comparison of these methods. A method for conducting these comparisons is proposed and is applied to a set of currently-used stereotactic radiosurgical techniques. Three-dimensional treatment planning calculations are used to compare dose distributions for several different radiation types and irradiation geometries. Calculations were performed using charged particles (H, He, C, and Ne ions) and the irradiation geometry currently used at Lawrence Berkeley Laboratory. Photons in the Gamma Knife configuration and the Heidelberg Linac arc method are used. The 3-dimensional dose distributions were evaluated by means of dose-volume histograms and integral doses to the target volume and to normal brain. The effects of target volume, shape and location are studied. The charged particle dose distributions are more favorable than those of the photon methods. The differences between charged particles and photons increase with increasing target volume. The differences between different charged particle species are small, as are the effects of target shape and location.

Biological response across a ridge filter carbon ion Bragg peak.

The dose distribution of carbon ion beams was modified to cover 14 cm peak width using a ridge filter suitable for clinical application. The results of cell survival as a function of depth of penetration of carbon ions and the mouse skin (foot) response at the proximal-, mid-, and distal-peak positions using four daily fractions are reported. The objective of these studies is to verify whether the dose distribution in the peak region is properly compensated to produce uniform biological effect. The implications of the shape of the dose distribution in the peak region to radiotherapy application are discussed.

Stereotactic frame for neuroradiology and charged particle Bragg peak radiosurgery of intracranial disorders.

The application of heavy charged particle Bragg peak radiosurgery for the treatment of intracranial vascular and other disorders requires a system of precise patient immobilization and stereotactic localization of defined intracranial targets. The process of using stereotactic neuroradiological procedures (including cerebral angiography, CT scanning and magnetic resonance imaging) for target definition and localization, and complex treatment planning constrain such a system to be adaptable and reusable. This paper describes a removable stereotactic frame-mask system that is used to immobilize and reposition the patient during stereotactic neuroradiological procedures and charged particle radiosurgery. It consists of four parts--(a) a plastic mask for immobilizing the patient's head; (b) a lucite-graphite mounting frame; (c) a set of fiducial markers; and (d) interfaces between the frame for immobilization and fixation to various diagnostic and therapeutic patient couches. The relationship between each component and the radiosurgical procedure is discussed. This system has proven to be safe, reliable, and noninvasive and it does not require fixation to the bones of the face or skull. When integrated into the radiosurgical treatment planning and localization procedures developed at Lawrence Berkeley Laboratory, it is capable of reliably repositioning the patient to 1 mm in each of three planes and contouring the intracranial target reliably to this accuracy. The application of this stereotactic system in heavy charged particle radiosurgery of intracranial arteriovenous malformations is described in other reports.

Treatment planning study for carcinoma of the esophagus: helium ions versus photons.

Helium ion radiotherapy significantly reduces dose to adjoining critical structures in the treatment of carcinoma of the esophagus when the same treatment plan is compared with megavoltage photon therapy. A five-field 18 MV photon treatment plan, selected to minimize lung dose, is compared with helium ions using the same field configuration. Dose volume histograms show target coverage, as well as dose delivered to critical structures lung, heart, mediastinum, and spinal cord. Although both helium ions and photons deliver approximately the same lung dose for this treatment plan, radiation to the heart and spinal cord from this field arrangement is significantly reduced with the helium ion beam. The concentration of dose at the tumor site, while sparing surrounding normal tissue, is characteristic of charged particle therapy, particularly with light ions, which includes particles with Z from that of protons (Z = 1) through that of neon (Z = 10).