ESTRO 2024 - Abstract Book

S5905

RTT - Service evaluation, quality assurance and risk management

ESTRO 2024

Purpose/Objective:

Daily variations in rectal and bladder filling result in anatomy changes and may lead to a difference in delivered dose with respect to the treatment planning. Using daily cone-beam CT (CBCT) dose accumulation for bladder and rectum we investigated differences in actual delivery and planning.

Material/Methods:

Patient Selection and Characteristics: The study included 32 patients with intermediate-risk prostate cancer with a good performance score (ECOG 0-1), a prostate volume of less than 60 cm 3 , an IPSS score of less than 15 and no hip prostheses. Patients received a ultra hypofractionated (UHF) treatment with a total dose of 36.25 Gy in five fractions. Preparation: To ensure adequate bladder filling, patients were instructed to drink 400 cm 3 of water one hour prior to treatment. Instructions were given for managing rectal filling, including voiding if rectal filling exceeded a diameter of 5 cm.

Treatment Planning: The planning process was carried out by two specialized radiation therapists based on the planning goals outlined in Table 1.

Treatment and Position Verification: During each treatment fraction, the treating radiation oncologist, clinical physicist and radiation therapists were present. Pre- and post-treatment CBCT scans were taken for position verification and correction. Dose Calculation and Analysis: On each daily CBCT, the bladder and rectum were delineated by three radiation therapists and validated by one radiation oncologist. A deformable registration between the planning CT and CBCT was performed. For each treatment fraction, the dose in the bladder and rectum was calculated on the CBCT and deformed, using the CBCT-CT registration. Finally, a cumulative dose for all five fractions was calculated and compared with the planned dose and planning goals.