ESTIMATION OF THE INCIDENCE OF LATE BLADDER AND RECTUM COMPLICATIONS AFTER HIGH-DOSE (70-78 GY) CONFORMAL RADIOTHERAPY FOR PROSTATE-CANCER,USING DOSE-VOLUME HISTOGRAMS

Purpose: To investigate whether Dose-Volume Histogram (DVH) parameters can be used to identify risk groups for developing late gastrointesti nal (GI) and genitourinary (GU) complications after conformal radiothe rapy for prostate cancer. Methods and Materials: DVH parameters were a nalyzed for 130 patients with localized prostate cancer, treated with conformal radiotherapy in a dose-escalating protocol (70-78 Gy, 2 Gy p er fraction). The incidence of late (>6 months) GI and GU complication s was classified using the RTOG/EORTC and the SOMA/LENT scoring system . In addition, GI complications were divided in nonsevere and severe ( requiring one or more laser treatments or blood transfusions) rectal b leeding. The median follow-up time was 24 months. We investigated whet her rectal and bladder wall volumes, irradiated to various dose levels , correlated with the observed actuarial incidences of GI and GU compl ications, using volume as a continuous variable. Subsequently, for eac h dose level in the DVH, the rectal wall volumes were dichotomized usi ng different volumes as cutoff levels. The impact of the total radiati on dose, and the maximum radiation dose in the rectal and bladder wall was analyzed as well. Results: The actuarial incidence at 2 years for GI complications greater than or equal to Grade II was 14% (RTOG/EORT C) or 20% (SOMA/LENT); for GU complications greater than or equal to G rade III 8% (RTOG/EORTC) or 20% (SOMA/LENT). Neither for GI complicati ons greater than or equal to Grade II (RTOG/EORTC or SOMA/LENT), nor f or GU complications greater than or equal to GradeIII (RTOG/EORTC or S OMA/LENT), was a significant correlation found between any of the DVH parameters and the actuarial incidence of complications. For severe re ctal bleeding (actuarial incidence at 2 years 3%), four consecutive vo lume cutoff levels were found, which significantly discriminated betwe en high and low risk. A trend was observed that a total radiation dose greater than or equal to 74 Gy (or a maximum radiation dose in the re ctal wall >75 Gy) resulted in a higher incidence of severe rectal blee ding (p = 0.07). Conclusions: These data show that dose escalation up to 78 Gy, using a conformal technique, is feasible. However, these dat a have also demonstrated that the incidence of severe late rectal blee ding is increased above certain dose-volume thresholds. (C) 1998 Elsev ier Science Inc.