Dosimetry characteristics of four fast neutron generators involved in rtog interinstitutional clinical trials

Abstract

Purpose : To demonstrate the consistency of dosimetry data used for four fast neutron generators involved in interinstitutional clinical trials. Methods and Materials : Central-axis dosimetry characteristics (field size dependence, percentage depth dose, beam modifier factors) at four institutions were measured by independent physicists from the Radiological Physics Center. These measurements were made in water with a single set of dosimetry equipment using tissue equivalent ionization chambers. Measurements were made with the chamber cavities filled with stationary air and flowing tissue-equivalent gas. All measurements were performed using techniques developed by the Radiological Physics Center for conventional radiotherapy equipment. The results of our measurements were compared to the data used by the institution to determine the consistency of patient doses reported to the Radiation Therapy Oncology Group. Results : The agreement of the Radiological Physics Center and institution data is similar to what is typically found with conventional radiotherapy equipment. Conclusions : The doses reported by these institutions to the Fast Neutron Working Group of the Radiation Therapy Oncology Group are consistent, within accepted clinical criteria.