Douglas Jones

Radiation therapy dosimetry reviews by the centers for radiological physics

Abstract Six Centers for Radiological Physics (CRP) have performed over 250 dosimetric site reviews at institutions participating in the Division of Cancer Control and Rehabilitation therapy networks and/or as affiliates in Oncology Group Clinical trials. For the initial site visits, institution stated output calibration was within ±3% of that measured by the CRPs for 87 % of the therapy machines reviewed. The accuracy of methods utilized in calculating tumor dose were assessed by using a set of reference cases of varying complexity. At the time of the first visit, 90% of the calculated doses for these reference cases were within ±5% of that prescribed by the CRPs. Other parameters, important for the accurate delivery of prescribed dose, were also checked as part of the review protocol. Many institutions have received multiple reviews and a significant reduction in the variance of machine calibration and calculated tumor dose for the reference cases is evident.

A non-contacting intraoperative electron cone apparatus.

Aluminum tubes, 20 cm long, of various diameter and face angle have been used to collimate electron beams for intraoperative radiotherapy. The tubes placed in a body cavity are clamped to the treatment couch. A thin rod is fixed coaxially to a disc which is placed on the entrance face of the tube. A stepwise procedure involving couch translation, rotation, and gantry rotation is used to align the central axis of the beam with the axis of the cone. Further collimation is provided by an aperture mounted in an assembly which slides into the standard accessory holder of the machine and is separated by a 10 cm air gap from the tube in the patient. Careful adjustment of this aperture diameter results in a relatively uniform dose across the treated area. The use of 3 mm wall thickness aluminum tube provides for minimal leakage outside of the cone. A camera has been mounted to a plate that also mounts in the standard accessory holder and is used to document the area treated.

Implanted Right Atrial Catheters for Continuous Infusion of Solutions into Dogs

Silastic catheters were fabricated and aseptically implanted through the skin into the jugular vein of 64 dogs with the intravascular tip located in the right atrium. Solutions were infused through the catheter at 2 to 2.5 mL/h by a portable pump worn by the dog. Following 9.2 Gy total body irradiation (TBI) and allogeneic bone marrow transplantation (BMT), succinyl acetone, an experimental chemotherapeutic agent, was infused into 34 dogs. Hematopoietic growth factors were infused into an additional 30 dogs, two of which had 9.2 Gy TBI and an autologous BMT, and four of which had 4.0 Gy TBI and no BMT. All dogs received continuous oral and parenteral antibiotics while the catheters were in place. All catheters functioned well until electively removed (n = 28) or until the dogs died or were euthanized (n = 36) at 12 to 68 days after implantation. Mean length of catheter function was 30.3 +/- 1.5 (SEM) days. No catheters were dislodged and there was no evidence of catheter-related blood loss or sepsis. Semiquantitative cultures of 5 catheters were negative, but Staphylococcus epidermidis was isolated from 3 of 7 catheters cultured in broth. Six dogs had thrombosis adjacent to the intravascular catheter tip. The catheters were well tolerated and facilitated successful long-term infusion of solutions into dogs.

Radiotherapy treatment planning using lymphoscintigraphy

A method for the three dimensional location of lymph nodes with respect to the skin surface is described. The technique is based on the reconstruction of surface shape using isocentric radiographs taken with metal chains draped on the patient. Registration of the radiographic study to the lymphoscintigraphic study is accomplished automatically by matching the location of four radiopaque and radioisotope markers. This method allows nodes to be located in a beams eye view with any set up of an isocentric radiotherapy machine. An accurate determination of the depth of lymph nodes is obtained, which is of value in electron beam therapy.

A radiolucent bite-block apparatus

A bite-block, patient immobilization apparatus has been constructed using all plastic parts. The apparatus may be used in C-T scanning without detriment to the images produced. The construction details are given and the procedure used to produce a bite block is described. A method to reduce electron backscattering onto the buccal mucosa from metal fillings is given.

The Quantitative Description of a Radiation Therapy Plan

A computer program has been designed to describe radiation therapy plans in numerical as opposed to graphical terms. Treatment is specified by using the average dose in the target area. The rationale for its development and an illustration of its use are given.

A basis for blocking the spinal cord in opposed field irradiation

The concept of partial tolerance is applied to the equivalent dose formula for spinal cord tolerance to allow for the change in dose when open and blocked fields are used in a course of radiotherapy. The field arrangement considered is parallel opposed irradiation. Certain assumptions are made regarding the contribution of dose to the spinal cord from open and blocked fields, which allows for the development of an equation to calculate the number of fractions that require spinal cord shielding in the posterior field. The use of a form to facilitate these calculations is described.

Measurements of the dose distribution in mantle fields

A polystyrene phantom has been constructed which is a model for a reference case employed by the Centers for Radiological Physics in their assessment of irregular field calculation methods. Considerations in the phantom design are given. Measurements of the dose distribution determined in the irradiation of this phantom by 13 machines in the energy range from Co-60 to 15 MV X rays are reported. The clinical significance of the variations observed is discussed. The results clearly demonstrate the need for off-axis calculations in the mantle irradiations and suggest that the off-axis energy change in linear accelerator beams is an important parameter in the dose calculations.

A port film marker

A device is described consisting of brass strips embedded in a plastic plate. When inserted in a radiation beam, it produces an image of a cross centered in the field. Cuts in the brass at defined intervals project a scale on the film used to determine a magnification factor. A marker in the lower right-hand quadrant provides rapid, unequivocal orientation of the film. This capability of orientation to a beams-eye-view makes anatomical markers redundant.

The simulation of electron beam therapy employing cone collimation.

A simple device is described which is used to determine treatment distance and beam direction in electron therapy employing cone collimation. A technique for the production of irregular field templates and localization films is given.