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A comparison of prone three-dimensional conformal radiotherapy with supine intensity-modulated radiotherapy for prostate cancer: which technique is more effective for rectal sparing?

¹ Department of Radiological and Medical Sciences, Nagoya University Graduate School of Medicine, Nagoya, ² Department of Medical Physics, Southern Tohoku Research Institute for Neuroscience, Koriyama, ³ School of Health Sciences, Nagoya University, Nagoya, ⁴ Department of Radiation Oncology, Southern Tohoku Research Institute for Neuroscience, Koriyama, Japan

Correspondence: Takahiro Kato, Department of Radiological and Medical Sciences, Nagoya University Graduate School of Medicine, 1-1-20 Daikominami, Higashiku, Nagoya 461-8673, Japan. E-mail: takahiro.kato{at}mt.strins.or.jp

The purpose of this study was to assess the potential dose reductions to the rectum with three-dimensional conformal radiotherapy in the prone position (prone 3D-CRT) compared with intensity-modulated radiotherapy in the supine position (supine IMRT) for prostate cancer. 17 prostate cancer patients underwent treatment planning CT scans in the supine and prone positions. Prone 3D-CRT and supine IMRT plans were constructed for each patient and compared in terms of the volume of rectum exposed to the V90 (volume of rectum receiving at least 90% of the prescription dose) as the high dose region. It was confirmed that supine IMRT was significantly superior to prone 3D-CRT (p = 0.023). Although, in some cases, the distance between the seminal vesicles and the rectum could change by more than 20 mm in the transition from supine to prone, the change in distance was 5 mm in many other cases. While prone 3D-CRT resulted in significant improvements in some patients in terms of rectal sparing, the degree of the effect may be dependent on a patient's anatomy and physical condition in prone 3D-CRT compared with supine IMRT. If the cases in which prone 3D-CRT was more effective in rectal dose reduction could be extracted using some anatomical predictor before treatment planning, prone 3D-CRT may be appropriate in such a case. We consider that prone 3D-CRT still warrants further investigation because of its advantages in terms of simplicity, cost-effectiveness and labour saving; continued research to find an appropriate anatomical predictor is required.