Towards effective and efficient patient-specific quality assurance for spot scanning proton therapy.

X Zhu,Andrew Lee,Xiaodong Zhang,Narayan Sahoo,Steven Frank,Anita Mahajan,Falk Poenisch,Yupeng Li,Dennis Mackin,Michael Gillin,Heng Li

doi:10.3390/cancers7020631

Abstract

An intensity-modulated proton therapy (IMPT) patient-specific quality assurance (PSQA) program based on measurement alone can be very time consuming due to the highly modulated dose distributions of IMPT fields. Incorporating independent dose calculation and treatment log file analysis could reduce the time required for measurements. In this article, we summarize our effort to develop an efficient and effective PSQA program that consists of three components: measurements, independent dose calculation, and analysis of patient-specific treatment delivery log files. Measurements included two-dimensional (2D) measurements using an ionization chamber array detector for each field delivered at the planned gantry angles with the electronic medical record (EMR) system in the QA mode and the accelerator control system (ACS) in the treatment mode, and additional measurements at depths for each field with the ACS in physics mode and without the EMR system. Dose distributions for each field in a water phantom were calculated independently using a recently developed in-house pencil beam algorithm and compared with those obtained using the treatment planning system (TPS). The treatment log file for each field was analyzed in terms of deviations in delivered spot positions from their planned positions using various statistical methods. Using this improved PSQA program, we were able to verify the integrity of the data transfer from the TPS to the EMR to the ACS, the dose calculation of the TPS, and the treatment delivery, including the dose delivered and spot positions. On the basis of this experience, we estimate that the in-room measurement time required for each complex IMPT case (e.g., a patient receiving bilateral IMPT for head and neck cancer) is less than 1 h using the improved PSQA program. Our experience demonstrates that it is possible to develop an efficient and effective PSQA program for IMPT with the equipment and resources available in the clinic.

Highlights

Proton therapy can be delivered using either scattering or scanning beam methods [1,2]
We previously reported our patient-specific quality assurance (PSQA) experience for single-field uniform dose (SFUD) patients that was based on measurement only and derived from a PSQA program for intensity-modulated radiation therapy (IMRT) with photons [8]
We extended our PSQA program for prostate cancer patients to other disease sites of patients with the following modifications: First, for treatment fields delivered through the electronic medical record (EMR) system, the point dose measurements obtained in the phantom used for prostate patients (Figure 3A) were replaced with 2D measurements using a

Summary

Introduction

Proton therapy can be delivered using either scattering or scanning beam methods [1,2]. The first approach is single-field optimization (SFO), in which the spot weights are optimized on a field-by-field basis; that is, each field is optimized individually to deliver a fraction of the prescribed doses to the entire target volume(s). SFO is most commonly used to produce a uniform dose over the entire target volume by each field, known as single-field uniform dose (SFUD); it is used to create a simultaneously integrated boost by each field, called single-field integrated boost (SFIB) [7]. The second approach to optimize an SSPT plan is multiple-field optimization (MFO), in which the weights of all spots in all fields are optimized simultaneously to produce the desired dose distribution. This approach is commonly known as IMPT

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