An automated planning strategy for near real-time adaptive proton therapy in prostate cancer

Abstract

Proton therapy plans are very sensitive to anatomical changes such as density changes along the pencil-beam paths and changes in organ shape and location. Previously, we developed a restoration method which compensates for density changes along the pencil-beam paths but which is unable to adapt for anatomical changes. This study's purpose is to develop and evaluate an automated method for adaptation of IMPT plans in near real-time to the anatomy of the day. We developed an automated treatment plan adaptation method using (1) a restoration of spot positions (Bragg peaks) by adapting the energies to the new water equivalent path lengths; and (2) a spot addition to fully cover the target of the day, followed by a fast reference point method optimization of the spot weights resulting in a Pareto optimal plan for the daily anatomy. The method was developed and evaluated using 8-10 repeat CT scans of 11 prostate cancer patients, prescribing 55 Gy(RBE) (seminal vesicles and lymph nodes) with a boost to 74 Gy(RBE) (prostate). Applying the automated adaptation method resulted in a clinically acceptable target coverage (V [Formula: see text] 98% and V [Formula: see text] 2%) for 96% of the scans after a single iteration of adding 2500 spots. The other scans obtained target coverages with V [Formula: see text] 98% and 2< V [Formula: see text] 5%. When using two spot-addition iterations, all scans obtained clinically acceptable results. Compared to the restoration method the adaptation lowered the mean dose to rectum and bladder with median values of 6.2 Gy(RBE) and 4.7 Gy(RBE) respectively. The largest improvements were obtained for V for both rectum and bladder, with median differences of 10.3%-point and 10.8%-point respectively, and maximum differences up to 22%-point. The two adaptation steps took on average 7.3 s and 1.7 min respectively. No user interaction was needed, making this fast and fully automated method a first step towards online adaptive proton therapy.

Stability of daily rectal movement and effectiveness of replanning protocols for sparing rectal doses based on the daily CT images during proton treatment for prostate cancer

“…One of the best approaches to this issue is the use of online adaptive planning in combination with CT image guidance, and simulation studies using daily CT images acquired during the treatment have thus been conducted. [6][7][8] However, further research is needed to examine the contouring and quality assurance of online planning, and this must be done for clinical practice. A replanning protocol based on the statistical knowledge of daily anatomical movements over treatment periods may provide much simpler and more realistic clinical applications compared to the online adaptation of radiation formation to daily random changes.…”

Automatic configuration of the reference point method for fully automated multi‐objective treatment planning applied to oropharyngeal cancer

“…5 The procedure was successfully applied to prostate IMRT, 9 and adaptive prostate and cervix IMPT. 13,14 This paper further develops and investigates the proposed automatic RPM configuration for a heterogeneous group of oropharyngeal cancer patients, with 22 objectives used in automatic plan generation. In previous work, 9 creation and evaluation of RPM configurations was based on convex plan criteria.…”

“…Recently, we proposed a new automatic procedure to configure the reference point method (RPM), a special case of the LRPM . The procedure was successfully applied to prostate IMRT, and adaptive prostate and cervix IMPT …”

Plan Selection in Proton Therapy of Locally Advanced Prostate Cancer with Simultaneous Treatment of Multiple Targets

“…In adaptive PT of prostate cancer, simulation studies have mainly concerned online replanning. 4,9,10 Online replanning has also been studied for photon radiation therapy, but the additional workload required, for example, for contouring and plan quality assurance, has obstructed the vast majority of the simulation studies from reaching clinical practice. 11 Plan selection has, however, been implemented successfully across several pelvic sites and enabled normal tissue sparing in photon radiation therapy.…”