Extended collimator model for pencil-beam dose calculation in proton radiotherapy.

We have developed a simple collimator model to improve the accuracy of penumbra behaviour in pencil-beam dose calculation for proton radiotherapy. In this model, transmission of particles through a three-dimensionally extended opening of a collimator is calculated in conjunction with phase-space distribution of the particles. Comparison of the dose distributions calculated using the new three-dimensional collimator model and the conventional two-dimensional model to lateral dose profiles experimentally measured with collimated proton beams showed the superiority of the new model over the conventional one.

Ridge filter design for proton therapy at Hyogo Ion Beam Medical Center.

At the Hyogo Ion Beam Medical Center (HIBMC) we have developed a new design method for the bar ridge filter used in proton therapy, taking into consideration the scattering and nuclear interaction effects within the filter itself, which are introduced in the design. In our beam delivery system, the bar ridge filter is employed as the range modulator. It is combined with the wobbler system, and produces a three-dimensionally uniform spread-out Bragg peak (SOBP). The design program predicts the three-dimensional dose distribution. Ridge filters of 3-12 cm SOBP in 1 cm increments were designed in the maximum radiation field for 150 MeV and 190 MeV proton beams so that a uniform physical dose area is obtained in the SOBP region three-dimensionally. Measurements were performed with the constructed ridge filters to verify the uniformity and these were compared with the predictions of the design program. The predictions and measurements were found to be in agreement except for the 12 cm SOBP. The uniformities were better than +/- 3.0% for all SOBPs produced. The ridge filters are now clinically in use.

Physiologic reactions after proton beam therapy in patients with prostate cancer: significance of urinary autoactivation.

PURPOSE: Proton therapy is a sophisticated treatment modality for prostate cancer. We investigated how physiologic factors affected the distribution of autoactivation as detected by positron emission tomography (PET) after proton beam therapy. METHODS AND MATERIALS: Autoactivation was evaluated in 59 patients treated with a 210-MeV proton beam. Data acquisition for autoactivation by PET started 5 minutes after proton irradiation to assess activation. In the first 29 patients, five regions of interest were evaluated: planning target volume (PTV) center, urinary bladder inside the PTV, urinary bladder outside the PTV, rectum (outside the PTV), and contralateral femoral bone head (outside the PTV). In the remaining 30 patients, urine activity was measured directly. In a phantom study autoactivation and its diffusion after proton beam irradiation were evaluated with water or an ice block. RESULTS: Mean activities calculated by use of PET were 629.3 Bq in the PTV center, 555.6 Bq in the urinary bladder inside the PTV, 332.5 Bq in the urinary bladder outside the PTV, 88.4 Bq in the rectum, and 23.7 Bq in the femoral bone head (p < 0.001). Mean urine activity was 679.4 Bq, recorded 10 minutes after therapy completion, and the half-life for urine autoactivation was 4.5 minutes. CONCLUSIONS: Urine is a major diffusion mediator of autoactivation after proton beam therapy. Our results indicate that physiologic factors can influence PET images of autoactivation in the context of proton beam therapy verification.