A dose escalated fiducial marker-based image guided radical radiotherapy in locally advanced prostate cancers: A single institute experience from India

Abstract

Image guided radiotherapy (IGRT) is one of the most commonly used treatment in LAPC. Dose escalation >74 Gy has shown to improve the biochemical control and freedom from failure rate in LAPC.We started treating LAPC patients with dose escalated IGRT in our institute since 2008. We did a retrospective analysis to see the biochemical relapse-free survival, cancer-specific survival, and bladder and rectal toxicity. A total of 50 consecutive prostate cancer patients were treated with dose escalated IGRT between January 2008 to Dec 2013. Out of these, 37 patients of LAPC were analyzed and their medical records were retrieved. All were biopsy proven adenocarcinoma of prostate with D'Amico high risk category (PSA >20 ng/mL or Gleason score (GS) >7 or T2c-T4). Three gold fiducial markers were placed in the prostate. Patients were immobilized in supine position with either ankle or knee rest. Partial bladder filling and rectum emptying protocol was followed. Clinical target volume (CTV) segmentation was done according to EORTC recommendation. Population based PTV expansion from CTV of 10 mm (cranio-caudal), 10 mm (medio-lateral), 10 mm (anterior) and 5 mm (posterior) was given. In patients with radiologically enlarged pelvic lymph node, whole pelvis intensity modulated radiation therapy (IMRT) to a dose of 50.4 Gy/28# followed by prostatic boost 26Gy/13# by IMRT using image guidance. Rest of the patients received prostate only RT to a dose of 76Gy/38# by IGRT. Daily On board KV images were taken and 2D-2D fiducial marker matching was done and shifts were applied on machine before treatment. Biochemical relapse was defined as per Phoenix definition (nadir + 2 ng/mL). Radiation Therapy Oncology Group (RTOG) toxicity grading system was used to document acute and late toxicity. Median age of patients was 66 years. Median pre-treatment PSA was 22 ng/mL. Thirty patients (81%) had T3/T4 lesions and nodal metastasis was seen in 11 (30%). Median GS was 8. Median radiotherapy dose was 76 Gy. Imaging before radiation delivery was done in 19(51%) patients and 100% in 14 (38%) patients. With a median follow up of 6.5 years, 5-year biochemical relapse-free survival (bRFS) and cancer-specific survival (CSS) was 66% and 79% respectively. Mean bRFS and CSS were 71 months and 83 months however Median bRFS and CSS were not reached. Distant metastasis was seen in 8 (22%). RTOG grade III bladder and rectal toxicity was seen in 2 (6%) and 2 (6%) patients respectively. Dose escalated IGRT with fiducial marker positional verification for LAPC is doable in Indian setup provided more emphasis given on daily on-board imaging with rigorous bladder filling and rectal emptying protocol. Long term follow up is needed to assess the effect on distant disease-free survival and CSS.