At our hospital, radiation therapy including particle therapy is primarily focused on two aspects of cancer treatment: (1) clinical confirmation of the safety and efficacy of radiation therapy and (2) the development of more precise and easy to apply treatment techniques.
Many in-house, multi-institutional, and JCOG clinical trials have so far been conducted. Two prospective studies of combined chemotherapy and radiotherapy for treating head and neck cancers were performed. Both studies showed that a combined modality regimen was feasible.
In chemoradiotherapy for carcinoma of the thoracic esophagus, the chemotherapy regimen and the radiotherapy (RT) technique have been modified. Radiation-induced pneumonitis has been analyzed among 43 patients who completed the treatment according to the new technique. Among them, Grades 2 and 3 pneumonitis were observed in 2 and 1 patient, respectively. Our new RT technique is thus considered to be safe.
Quality assurance is one of the most important issues in multi-institutional clinical studies. In this regard, several investigations were performed on this issue.
The preliminary results of a multi-institutional phase II trial of 151 patients who had been treated with proton beam therapy (PBT) were analyzed. The primary endpoint of the study was the incidence of late rectal toxicity > grade 2 at 2 years. Preliminary results were 3.9%. A retrospective multi-institutional study for localized or locally advanced prostate cancer treated by photon therapy was also analyzed (161).
Respiratory-gated radiotherapy is useful for minimizing the volume of normal tissues that is irradiated as a result of the shifting of internal structures during respiratory movements. Although dose distributions can be expected to improve using this technique, the actual absorbed dose distributions have not yet been clearly elucidated. Therefore, absorbed dose distributions have been experimentally determined using a phantom system that simulates patient respiration.
Through the use of a positron emission tomography (PET) apparatus, proton-irradiated volume can be confirmed by the detection of pair annihilation gamma rays from the positron emitter nuclei. These nuclei are generated by the reaction between irradiated proton nuclei and the nuclei in the irradiation target. In our proton treatment room, a beam ON-LINE PET system has been installed, and clinical data collection has already been initiated (162).
Dosimetric characteristics of a metal oxide-silicon semiconductor field effect transistor detector are also investigated with megavoltage photon beams for patient dose verification (163).
In proton beam therapy, the dose monitoring system was upgraded. Monte Carlo simulation was used for evaluating accurate dose distributions (164), and a novel design method of ridge filters has also been developed (165).
● T. Ogino ●
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