Introduction of VMAT, IGRT, and IMRT-Reduced Acute GI Toxicity in Prostate Cancer Patients

Abstract

During the last decade new techniques with significant dose reductions to organs at risk in prostate cancer patients have been introduced. The purpose of this study is to determine to what extent rectal dose reduction has led to a reduction in gastrointestinal (GI) toxicity. Therefore we compared acute proctitis of Volumetric Modulated Arc Therapy (VMAT) treated patients in our institution with previous data from IMRT and Image Guided IMRT (IG-IMRT), conventional 3D-conformal (3DCRT) and whole pelvic RT + 3DCRT (P+3DCRT).Acute proctitis is known to be a predictor for late GI toxicity (consequential effect). Patients with localized prostate cancer filled out identical questionnaires on bowel symptoms at baseline and during RT. We evaluated the items of blood loss, mucus loss, and diarrhea at week 6. Currently data of 33 VMAT patients(ongoing study) were compared to data of 109 IMRT/IG-IMRT patients,274 3DCRT patients and 227 P+3DCRT patients (Table). All patients received 10 Gy per week to the target volume in 2 Gy daily fractions (up to 60 Gy in week 6), except for the VMAT group who received 11 Gy / week in 2.2 Gy daily fractions (up to 66 Gy in week 6). We scored % with ≥1 and ≥2 complaints,and % for each symptom. At baseline, 4% reported mucus loss, 1% blood loss and 1% watery diarrhea (comparable between groups). At week 6 (median 39 days after start for VMAT and (P+)3DCRT and 42 days for IMRT), VMAT patients reported significantly less watery diarrhea (0%) compared to IMRT (12%, p = 0.04) and (P+)3DCRT(13%, p = 0.03).Reported blood loss was 3% versus 8% for IMRT (p = 0.3), 17% for 3DCRT (p = 0.04) and 21% for P+3DCRT (p = 0.01).Reported mucus loss was 36% versus 26% (p = 0.3), 54% (p = 0.06) and 58% (p = 0.02), respectively. Differences between IMRT and IG-IMRT were small and non-significant (+/-3%).Less VMAT patients reported ≥1 and ≥2 complaints (Table): these differences were statistically significant compared to 3DCRT techniques, but not compared to IMRT groups. In general, the reduction in rectal dose caused by the introduction of IMRT, IG-IMRT and VMAT has led to a reduction in acute GI toxicity. Ata slightly higher dose rate per week, VMAT patients reported lower blood loss and significant lower diarrhea rates but non-significant higher mucus loss rates compared to IMRT. We aim at including another 60 VMAT patients to establish current toxicity levels more accurately.