Prostate cancer. Standardization and improvement in efficiency of heavy ion radiotherapy

Efficacy is excellent and adverse effect is scarce of heavy ion radiotherapy (HIR) in National Institute of Radiological Sciences (NIRS) of prostate cancer which exhibits little inter-individual variations. This conceivably makes it easy to standardize and improve HIR procedure, and this paper describes the effort for it hitherto and future view. For Standardization: Fixation of the body is made by individually prepared foot-rest and lower abdominal shell which have clinically resulted in reduced rectal injury and high local control rate. In addition, 256-raw 4D CT findings reveal that the target prostate hardly moves to give enough small intra-fractional change: validity of fixation. Adverse events related with rectum can be reduced by pre-evaluation of the irradiation field by dose-volume histogram (DVH) method using a reference DVH (derived from patients whose rectal injury has been ≤grade 1). Well-designed clinical phase II trial of HIR by carbon and proton beams in 6 facilities including NIRS is to be conducted with the primary end point of recurrence and crude survivals. For Improvement: Rehearsal before therapy can be omitted with use of digitally reconstructed radiography of 2.5 mm slice CT images for planning. Efforts have been paid to make the therapy period shorter from the beginning of HIR in 1995, and the present schedule of 16 irradiations/4 weeks has attained 25% increment of the patient number treated. Future: Both local recurrence and adverse effect should be 0%. For this, to reduce the therapy period, further efforts to make the irradiation field more exact for irradiating the target alone are considered. (K.T.)