Dosimetric comparison of inverse optimization with geometric optimization in combination with graphical optimization...

Area of Science:

• Radiation Oncology
• Medical Physics
• Brachytherapy

Background:

• High-dose-rate (HDR) interstitial brachytherapy is a key treatment for prostate cancer.
• Treatment planning aims to maximize dose to the target while minimizing dose to organs at risk.
• Geometric Optimization (GO) and Anatomy-Based Inverse Optimization (ABIO) are planning techniques with distinct approaches.

Purpose of the Study:

• To compare the efficacy of Geometric Optimization (GO) against Anatomy-Based Inverse Optimization (ABIO) in HDR interstitial brachytherapy for prostate cancer.
• To evaluate target coverage, organ-at-risk sparing, dose homogeneity, and conformity between the two planning techniques.

Main Methods:

• Five prostate cancer patients treated with HDR brachytherapy were retrospectively studied.
• CT scans were used to delineate the target volume and critical structures (rectum, bladder, urethra).
• Treatment plans were generated using GO and ABIO, with and without graphical optimization (GrO). Dose-volume histograms (DVHs) and planning indices were analyzed.

Main Results:

• ABIO alone resulted in clinically unacceptable target coverage (82±13%).
• ABIO combined with graphical optimization (ABIO_gr) demonstrated superior sparing of the urethra (D(2%,U) 122.7±4%) and better conformity (0.82) compared to GO (0.71).
• GO provided superior dose homogeneity (DHI 0.81) compared to ABIO_gr (0.75), though ABIO_gr plans were clinically acceptable.

Conclusions:

• Anatomy-Based Inverse Optimization (ABIO) alone is not clinically acceptable for target coverage in prostate HDR brachytherapy.
• ABIO combined with graphical optimization (ABIO_gr) offers significant advantages in critical structure sparing and plan conformity over Geometric Optimization (GO).
• ABIO_gr allows for potential dose escalation to the target while respecting urethral tolerance, warranting further clinical toxicity studies.