Aim: To compare DVHs for OARs in two different positions - prone and supine - for prostate cancer patients irradiated with a Tomotherapy unit.
Background: In the era of dose escalation, the choice of optimal patient immobilization plays an essential role in radiotherapy of prostate cancer.
Materials and methods: The study included 24 patients who were allocated to 3 risk groups based on D'Amico criteria; 12 patients represented a low or intermediate and 12 a high risk group. FOR EACH PATIENT TWO TREATMENT PLANS WERE PERFORMED: one in the supine and one in the prone position. PTV included the prostate, seminal vesicles and lymph nodes for the high risk group and the prostate and seminal vesicles for the intermediate or low risk groups. DVHs for the two positions were compared according to parameters: Dmean, D70, D50 and D20 for the bladder and rectum and Dmean, D10 for the intestine. The position accuracy was verified using daily MVCT.
Results: Prone position was associated with lower doses in OARs, especially in the rectum. Despite the fact that in the entire group the differences between tested parameters were not large, the Dmean and D10 for the intestine were statistically significant. In the case of irradiation only to the prostate and seminal vesicles, the prone position allowed for substantial reduction of all tested DVH parameters in the bladder and rectum, except D20 for bladder. Moreover, the Dmean and D50 parameter differences for the bladder were statistically significant. No significant differences between positions reproducibility were demonstrated.
Conclusion: In patients irradiated to prostate and seminal vesicles, the prone position may support sparing of the rectum and bladder. The reproducibility of position arrangement in both positions is comparable.
Keywords: Positioning; Prostate cancer; Radiotherapy; Tomotherapy.