Robert Stanton

Treatment planning for prostate implant with loose seeds.

A new method of treatment planning for the I-125 and Pd-103 permanent interstitial prostate implant is developed, which does not use the traditional nomograms but automatically generates optimized source configurations. An iterative algorithm is used that places one seed at a step. The volume dose of target is calculated at each step to determine the coldest spot where the next source is to be placed, so that the dose uniformity of target is best improved as source placement proceeds. At each step, the total activity required for the seed configuration as so established is calculated by normalizing the minimal dose to the prescribed dose. An optimized configuration is the one that takes the minimized total activity. Around its minimum the total activity has a very small variation with the number of seeds. Consequently multiple clinically acceptable seed configurations with similar total activity but different individual activities are generated simultaneously. In our computer generated treatment plans most of the seeds are distributed in the periphery of the target, similar to the Paterson-Parker pattern of a volume implant.

Electrical constancy check for remote‐reading op–amp radiation dosimeters

A constancy check is described for dosimeters using fast op-amp electrometers with remote ionization chambers. The checks usefulness is reported, as are capacitance values for some commercial ion chambers.

Dosimetric Considerations in the Choice of Photon Energy for External Beam Radiation Therapy: Clinical Examples

Laughlin, Mohan, and Kutcher have evaluated photon beams for Co-60 through 24 MV for eight clinical disease sites plus pediatrics and concluded that two energy ranges are required for the best patient care: a 4 to 6 MV beam and a 10 to 18 MV beam. The present study investigates the question which two energies in a dual energy machine are optimum for the average patient mix. The method used is to calculate two dimensional sample cases including breast, head and neck, and pelvic tumors on the same treatment planning system using machine data including Co-60, 4 MV, 6 MV, 10 MV, and 18 MV x-ray beams. The resulting plans were evaluated considering tumor doses, spinal cord doses, doses to subcutaneous tissues and doses to other radiosensitive structures. The conclusion is that the optimum two beams are 6 and 10 MV.