Abstract
Publications have reported the benefits of using high‐dose‐rate brachytherapy (HDRB) for the treatment of prostate cancer, since it provides similar biochemical control as other treatments while showing lowest long‐term complications to the organs at risk (OAR). With the inclusion of anatomy‐based inverse planning optimizers, HDRB has the advantage of potentially allowing dose escalation. Among the algorithms used, the Inverse Planning Simulated Annealing (IPSA) optimizer is widely employed since it provides adequate dose coverage, minimizing dose to the OAR, but it is known to generate large dwell times in particular positions of the catheter. As an alternative, the Hybrid Inverse treatment Planning Optimization (HIPO) algorithm was recently implemented in Oncentra Brachytherapy V. 4.3. The aim of this work was to compare, with the aid of radiobiological models, plans obtained with IPSA and HIPO to assess their use in our clinical practice. Thirty patients were calculated with IPSA and HIPO to achieve our department's clinical constraints. To evaluate their performance, dosimetric data were collected: Prostate PTV D90(%),V100(%),V150(%), and V200(%), Urethra D10(%), Rectum D2cc(%), and conformity indices. Additionally tumor control probability (TCP) and normal tissue complication probability (NTCP) were calculated with the BioSuite software. The HIPO optimization was performed firstly with Prostate PTV (HIPOPTV) and then with Urethra as priority 1 (HIPOurethra). Initial optimization constraints were then modified to see the effects on dosimetric parameters, TCPs, and NTCPs. HIPO optimizations could reduce TCPs up to 10%–20% for all PTVs lower than 74 cm3. For the urethra, IPSA and HIPOurethra provided similar NTCPs for the majority of volume sizes, whereas HIPOPTV resulted in large NTCP values. These findings were in agreement with dosimetric values. By increasing the PTV maximum dose constraints for HIPOurethra plans, TCPs were found to be in agreement with IPSA without affecting the urethral NTCPs.PACS numbers: 87.55.‐x, 87.55.de, 87.55.dh, 87.53.Jw
Highlights
The quality of HDR brachytherapy planning has advanced with the introduction of inverse planning optimizers similar to those used in external beam planning.[11,12,13] These algorithms, which are implemented in commercial treatment planning systems (TPS), generate reproducible treatment plans in a faster way by using clinical constraints set by the users
The last two columns represent the statistical significance of the differences between doses calculated with Inverse Planning Simulated Annealing optimization algorithm (IPSA) and, respectively, HIPOPTV and HIPOurethra
The results show that IPSA and HIPOurethra provided similar normal tissue complication probability (NTCP) for the majority of cases and volume sizes, with HIPOurethra generally being lower than IPSA
Summary
HDR is widely used, due to the recent ability to integrate 3D images into the treatment planning process These images, which can be obtained either by computed tomography (CT) scans or ultrasound, provide the possibility to perform an accurate treatment plan based on the anatomy of the patient and the position of the implant at the time of treatment. IPSA is an anatomy-based algorithm which optimizes the source dwell times using a simulated annealing algorithm, based on the work by Kirpatrick et al [14] and developed for brachytherapy applications by Lessard and Pouliot.[11] The model is governed entirely by the anatomy of the patient contoured from a CT scan and by a series of surface or volumetric prescribed dose constraints set by the user at the time of planning. It was not initially designed to include a smoothness function to take into account the distribution of a single dwell time with respect to the adjacent ones
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