Reducing re-setups and treatment time in head and neck proton therapy: The role of quantitative imaging protocol

Image guidance is fundamental for mitigating uncertainties in head and neck (HN) intensity-modulated proton therapy (IMPT). This study discussed the development of a quantitative imaging protocol for HN IMPT and analysed its impact in reducing re-setups.

An updated quantitative imaging protocol was developed to serve as a guideline for the radiation therapists (RTTs) to address various scenarios commonly encountered in HN IMPT. The primary objective was to reduce unnecessary re-setups and streamline treatment workflow. One main quantifiable element introduced in the updated protocol is the range of soft-tissue contour variations acceptable for treatment delivery. This was achieved using in-house simulation of various soft-tissue contour thicknesses and evaluation of the resulting clinical target volume (CTV) dose coverage. To analyse the effectiveness of this quantitative imaging protocol, re-setup occurrences before and after its implementation were collated and evaluated.

A soft-tissue contour variation of ≤0.7 cm was defined as acceptable, preserving CTV D95 % coverage within the allowable ±3 % deviation from the nominal plan. This was introduced into the updated imaging protocol as one of the various quantifiable elements incorporated. Upon introduction of the updated quantitative imaging protocol, the percentage of treatment fractions that require re-setups reduced significantly from 32.3 % to 27.8 % (p<0.01). Similarly, the frequency of ≥3 re-setups and the number of patients sent for re-planning due to setup issues also decreased substantially (p=0.002 and p<0.01, respectively).

Quantitative imaging protocol for HN IMPT is effective in addressing various scenarios that contribute to re-setups. Implementation reduced re-setup rates from 32.3 % to 27.8 % (p<0.01) and re-planning frequency from 26.7 % to 12.5 %. It contributed to improved workflow efficiency and resource use, along with overall reduced treatment time.

Integrating factors specific to HN IMPT in the imaging protocol can streamline the image guidance processes.