Proton energy optimization and reduction for intensity-modulated proton therapy

Abstract

Intensity-modulated proton therapy (IMPT) is commonly delivered via the spot-scanning technique. To “scan” the target volume, the proton beam is controlled by varying its energy to penetrate the patient’s body at different depths. Although scanning the proton beamlets or spots with the same energy can be as fast as 10–20 m/s, changing from one proton energy to another requires approximately two additional seconds. The total IMPT delivery time thus depends mainly on the number of proton energies used in a treatment. Current treatment planning systems typically use all proton energies that are required for the proton beam to penetrate in a range from the distal edge to the proximal edge of the target. The optimal selection of proton energies has not been well studied. In this study, we sought to determine the feasibility of optimizing and reducing the number of proton energies in IMPT planning. We proposed an iterative mixed-integer programming optimization method to select a subset of all available proton energies while satisfying dosimetric criteria. We applied our proposed method to six patient datasets: four cases of prostate cancer, one case of lung cancer, and one case of mesothelioma. The numbers of energies were reduced by 14.3%–18.9% for the prostate cancer cases, 11.0% for the lung cancer cases, and 26.5% for the mesothelioma case. The results indicate that the number of proton energies used in conventionally designed IMPT plans can be reduced without degrading dosimetric performance. The IMPT delivery efficiency could be improved by energy layer optimization leading to increased throughput for a busy proton center in which a delivery system with slow energy switch is employed.

Shortening Delivery Times of Intensity Modulated Proton Therapy by Reducing Proton Energy Layers During Treatment Plan Optimization

“…Very recently, Cao et al (24) published an alternative method to reduce energy layers in IMPT treatment plans. They proposed a mixed-integer programming approach, iteratively reducing the number of energy layers until the plan quality degraded beyond a user-defined level.…”

Early experience with intensity modulated proton therapy for lung-intact mesothelioma: A case series

“…Because of the memory and speed limitations of our 32-bit commercial TPS, the data set was exported from the TPS to an in-housedeveloped IMPT system for optimization and dose calculations that incorporated machine delivery constraints. [6][7][8] The optimized spot weights determined by the in-house system were saved as a DICOM file and imported into the commercial TPS, where the dose was then recalculated. In-house worst-case robust evaluation tools were used to analyze the IMPT plan against 3-mm setup and 3.5% range uncertainties.…”

Redefine the role of range shifter in treating bilateral head and neck cancer in the era of Intensity Modulated Proton Therapy

“…In current routine clinical practice, the maximum number of proton beam angles used for treating bilateral HNC patients is four fields. As the ELST is still the most important concept for the PBS delivery efficiency, there has been multiple publications 14, 15 on the energy layer reduction methods to shorten the beam delivery time for IMPT and results has been promising. Thus, the most important question is to evaluate the feasibility of using more beam angles while reducing the delivery time while maintaining similar plan quality.…”

“…Beam angles in 8F IMPT_noRS were evenly distributed (45 o apart) and energy layer reduction method 14, 15 was used to reduce the total number of energy layers while maintaining a similar robust plan quality. Dosimetric quality and beam delivery time of each plan was evaluated by comparing 8F IMPT_noRS and 4F IMPT_noRS plan groups (Table 2).…”