The effectiveness of combined gating and re-scanning for treating mobile targets with proton spot scanning. An experimental and simulation-based investigation

Abstract

Organ motion is one of the major obstacles in radiotherapy and charged particle therapy. Even more so, the theoretical advantages of dose distributions in scanned ion beam therapy may be lost due to the interplay between organ motion and beam scanning. Several techniques for dealing with this problem have been devised. In re-scanning, the target volume is scanned several times to average out the motion effects. In gating and breath-hold, dose is only delivered if the tumour is in a narrow window of position. Experiments have been performed to verify if gating and re-scanning are effective means of motion mitigation. Dose distributions were acquired in a lateral plane of a homogeneous phantom. For a spherical target volume and regular motion gating was sufficient. However, for realistic, irregular motion or a patient target volume, gating did not reduce the interplay effect to an acceptable level. Combining gating with re-scanning recovered the dose distributions. The simplest re-scanning approach, where a treatment plan is duplicated several times and applied in sequence, was not efficient. Simulations of different combinations of gating window sizes and re-scanning schemes revealed that reducing the gating window is the most efficient approach. However, very small gating windows are not robust for irregular motion.

Pencil beam scanning proton therapy of Hodgkin’s lymphoma in deep inspiration breath-hold: A case series report

“…DIBH technique is a motion mitigation technique that, if successfully applied, creates an almost static geometrical situation [6,7]. However, the reproducibility of the breath-hold may degrade the planned dose distribution caused by small anatomical changes and interplay effects.…”

“…The combination of pencil beam scanning (PBS) proton therapy and deep inspiration breath-hold (DIBH) technique improves the sparing effect even further [4,5] due to favourable anatomical changes compared to free breathing (FB). Furthermore, a successfully applied DIBH technique minimizes the effect of respiratory motion on range uncertainties and interplay effects [6,7].…”

Empowering Intensity Modulated Proton Therapy Through Physics and Technology: An Overview

“…Such a strategy would require a large number of rescans to be effective and lead to increased blurring at the margins. The potential of repainting/rescanning has been reported by PSI investigators in several publications [86, 102, 103] and by Rietzel and Bert [104]. Alternatively, a “phase-controlled” rescanning may be employed, which combines respiratory gating with rescanning.…”

Optimization of motion management parameters in a synchrotron‐based spot scanning system

“…While gating has a history of successfully reducing the size of treatment volumes required to cover moving targets, suboptimal results are possible when it is applied to spot‐scanned proton treatments. Residual motion inside the gate can still disrupt dosimetric homogeneity, and complex target shapes and deliveries can render erratic results . Moreover, long treatment times are possible from the combined dynamics of beam‐off and accelerator recharge (for synchrotron systems) periods .…”