ESTRO 2024 - Abstract Book

S2377

Clinical - Urology

ESTRO 2024

targets during ultrahypofractionated MRIgRT is yet unknown. Therefore, a subsequent study will investigate the positional stability of prostate and SV without RB and compare results with the here presented data.

Keywords: MRIgRT, ultrahypofractionated, endorectal balloon

977

Poster Discussion

Prostate SBRT with an empty bladder: challenging the dogma

Shivani Pradeep Sable 1 , Simran Gulati 1 , Maneesh Singh 1 , Suman Ghosh 1 , Reena Phurailatpam 2 , Ritesh Mhatre 2 , Akash Pawar 3 , Priyamvada Maitre 1 , Vedang Murthy 1 1 Tata Memorial Centre, Homi Bhabha National Institute, Radiation Oncology, Mumbai, India. 2 Tata Memorial Centre, Homi Bhabha National Institute, Medical Physics, Mumbai, India. 3 Tata Memorial Centre, Homi Bhabha National Institute, Statistics, Mumbai, India

Purpose/Objective:

Traditionally, radiotherapy planning and delivery in prostate cancer is done with a full bladder. This has logistical challenges and is associated with patient discomfort. Opting for a treatment with an empty bladder is an appealing approach. This analysis was done as a preliminary assessment for feasibility of treatment with empty bladder and SBRT for the ongoing EMPTY RT phase 2 trial (CTRI/2023/08/056231).

Material/Methods:

The objective was to assess the acute genitourinary toxicity and know the empty bladder volume variability. Patients diagnosed with histologically proven prostate cancer who were planned for SBRT to prostate with or without pelvic nodes with an empty bladder were included. Patients who received re-radiation, post-op radiation or moderate hypofractionation were excluded. All patients were simulated and treated at every fraction with an empty bladder immediately after voiding. The CTV included prostate, seminal vesicles ± pelvic nodes. A 0.3-0.5cm CTV to PTV margin was grown in anterior or antero-superior direction to reduce PTV overlap with bladder. The radiation dose for prostate was 35-36.25Gy in 5 fractions, and 25Gy in 5 fractions for pelvis. The bladder constraints from PRIME trial (NCT03561961) were used for planning [1]. Image guided radiotherapy was used for every fraction. The Common Terminology Criteria for Adverse Events version 5 (CTCAE) scoring scale was used to record toxicity. The bladder was delineated in all five CBCT images and variation of bladder filling between simulation and treatment has been reported with median and interquartile range (IQR).

Results:

The median age was 68 years. Half of the patients were low volume metastatic, and rest intermediate or high risk. 75% (30/40) patients received prostate only RT and 25% (10/40) patients received prostate and pelvic RT. Over half