gms | German Medical Science

Purpose: Since 2001 a stereotactic ultrasound based system is used for optimisation of daily patient positioning in radiotherapy of prostate cancer. In ca. 2000 alignments shifts of more than 1 cm (max 2cm) were observed in about 10% of cases. This means, that in these cases either there is a loss of dose to the prostate or the irradiated rectal volume increases. Thepurpose of this study was, to evaluate the effect of image guided radiotherapy with stereotactic ultrasound on effectivity and late rectal toxicity in radiotherapy of prostate cancer.

Materials/Methods: 42 pat with prostate cancer without hormonal treatment were included. A planning target volume (PTV) including the prostate and seminal vesicles with a safety margin of 1.5cm in anterior and lateral and 1cm in posterior direction was treated with a total dose of 66 Gy and a boost -PTV excluding the seminal vesicles was treated with additional 4 Gy in single dose fractions of 2 Gy. Planning CT scans were performed with empty rectum and moderate filled bladder. 22 pat (group1) were treated with daily stereotactic ultrasound positioning, the other 20 pat (group 2) a verification film was performed once a week. PSA-values were evaluated after 1.5, 3, 6, 9 and12 month. In addition late rectal toxicity according to LENT-SOMA scale was evaluated with a follow up of 2-3 years in group 1 and 3-4 years in group 2.

Results: Mean percentage of PSA reduction after 1.5, 3 ,6 ,9 and 12 month form group 1 and group 2 was 36% vs 31%, 25% vs 21%, 25% vs 13%, 19% vs 13% and 17% vs 14%. There was no significant difference. In group 2 two pats showed late rectal toxicity grade 3 (persistent rectal bleeding), no toxicity greater grade 3 occurred in group 1.

Conclusion: There is no difference in post treatment PSA-values between the two groups. We think, that because of treatment planning with empty rectum, the prostate can only move in anterior direction in relation to the PTV and therefore there is no loss of dose. But according to rectal filling the irradiated rectal volume increases with consequently more toxicity. Even with this small number of pat a trend towards lesser rectal toxicity is shown with stereotactic ultrasound. This should be evaluated with a larger number of patients.