Pelvic bone anatomy vs implanted gold seed marker registration for image-guided intensity modulated radiotherapy for prostate carcinoma: Comparative analysis of inter-fraction motion and toxicities.

Objectives: We compared the prostate motion variability and toxicities between patients treated with gold marker registration based IG-IMRT (IG-IMRT-M) and bony landmark registration based IG-IMRT (IG-IMRT-B).

Methods: T1c-T3b (node negative), intermediate and high risk (non-metastatic) adenocarcinoma of prostate, age ≥18years, Karnofsky Performance Status of ≥70 were included in this retrospective study. The prostate motion variability, acute and late radiation toxicities between the two treatment arms (IG-IMRT-M versus IG-IMRT-B) were compared.

Results: Total of 35 patients (17 for IG-IMRT-M and 18 for IG-IMRT-B) were treated with a median radiotherapy dose of 76 Gray. The prostate variability observed with and without markers in millimeter was 4.1±2.3 vs 3.7±2.1 [Antero-Posterior (A-P); p=0.001], 2.3±1.5 vs 2.1±1.2 [Superior-Inferior (S-I); p=0.095] and 1.1±1.7 vs 0.4±1.4 [Left-Right (L-R); p=0.003]. There was higher acute toxicity in IG-IMRT-B arm compared to IG-IMRT-M arm in terms of grade ≥2 diarrhea [50% vs 11% OR=7.5 (1.3-42.7); p=0.02] and grade ≥2 proctitis [38% vs 5.8%, OR=10.1 (1.09-94.1); p=0.04]. At a median follow up of 36months, the late genitourinary toxicities grade ≥2 [27% vs 0%; p=0.04] were higher in the IG-IMRT-B arm compared to IG-IMRT-M arm.

Conclusions: IG-IMRT-M detects higher prostate motion variability as compared to IG-IMRT-B, inferring a significant prostate motion inside fixed pelvic bony cavity. The addition of marker based image guidance results in higher precision of prostate localization and lesser acute and late toxicities.