In vivo alanine/electron spin resonance (ESR) dosimetry in radiotherapy of prostate cancer: A feasibility study

PurposeWe have developed a device to evaluate the potential of alanine/electron spin resonance (ESR) dosimetry for quality assurance in 3D conformal radiotherapy for prostate cancer. It consists of a rectal balloon carrying eight alanine dosimeter probes and two metal markers to document the exact position of the balloon. We measured the effects of an air-filled rectal balloon on the dose at the rectal wall and compared these results with the applied dose distribution of the treatment planning system.Materials and methodsDuring 10 fractions with 2.0 Gy per fraction, the accumulated doses were measured in 3 patients. The results of the ESR measurements were compared to the applied doses.ResultsIt was possible to insert the device without clinical complications and without additional rectal discomfort for the patients. The measurements of the dose accumulated at the anterior and the posterior rectal wall agreed with the applied dose within a mean deviation of 1.5% (overestimation of the dose) and 3.5% (underestimation of the dose), respectively. However, clinically significant differences between applied and measured rectal doses were seen in a patient with a hip prosthesis. In this case, the dose at the anterior rectal wall was overestimated by the TPS by about 11% and the dose at the posterior rectal wall was underestimated by approximately 7%.ConclusionThe method presented in this study is useful for quality control of irradiations in vivo.