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Periodic Report Summary 1 - PROTONSPOTSCANMET (Improving physical dosimetry and developing biologically-relevant metrology for spot-scanned proton therapy beams)

Proton therapy is an advanced form of radiotherapy which has the potential to deliver a dose map that closely matches the tumour volume.
This project sought to resolve some of the unanswered questions surrounding quality assurance in spot-scanned proton therapy. The research performed can be divided into two main categories: physical and biological dosimetry.

Physical dosimetry
This part of the project focused on the metrology of individual proton tracks. We irradiated a series of Fluorescent Nuclear Track Detectors (FNTDs) at Massachusetts General Hospital, using a mono-energetic proton beam (Fig 1). In parallel, we simulated the proton energy depositions down to the nanometre scale, using the TOPAS-nBio Monte Carlo platform (Fig 2). Together with collaborators from MD Anderson we set up a protocol to image the FNTDs using a confocal laser scanning microscope (Fig 3). We developed an analysis pipeline to extract imaged parameters for proton tracks at different positions along the proton beam’s path.

Outcomes: using FNTDs we were able to experimentally replicate the trends that we observed in our TOPAS-nBio simulations. Our results represent an important first step
towards the experimental validation of Monte Carlo simulations on the sub-cellular scale and demonstrate that FNTDs enable experimental study of the microdosimetric properties of individual protons.

Underwood TSA, W Sung, CH McFadden, SJ McMahon, DC Hall, A McNamara et al. (2017) Comparing stochastic proton interactions simulated using TOPAS-nBio to experimental data from fluorescent nuclear track detectors. Accepted: Physics in Medicine and Biology, Feb 2017.

Biological dosimetry
Here our focus was to better understand the uncertainties associated with the biological effectiveness of proton beams. Initially, we performed radiobiological modeling for patients with prostate cancer. We are currently working to perform clinical validation of such modeling via post-treatment image analyses.

There exists strong clinical motivation to use anterior proton beams to treat patients with prostate cancer as such beams avoid the femoral heads and hip prostheses. However, published models predict that proton beams have an elevated relative biological effectiveness (RBE) at their distal edge: for anterior prostate beams this elevated RBE coincides with sensitive rectal tissue. In this work we combined TOPAS Monte Carlo simulations with radiobiological modelling for prostate patients. We considered patient cohorts treated with and without rectum spacer gel insertion (a novel protocol designed to better spare the rectum during radiotherapy).

Outcomes: for the cohort without rectum spacer gels, our research indicated that use of anterior proton beams was not appropriate. However, for the second cohort, we found that the rectum spacer gels suitably mitigated the biological uncertainties associated with such beams.

Underwood TSA, Voog JC, Moteabbed M, Tang S, Cahlon O, Soffen E, et al. (2016) Hydrogel rectum-prostate spacers mitigate the uncertainties in proton relative biological effectiveness associated with anterior-oblique beams. Accepted: Acta Oncologica, Dec 2016
Underwood TSA, Giantsoudi D, Moteabbed M, Zietman A, Efstathiou J, et al. (2016) Can we advance proton therapy for prostate? Considering alternative beam angles and RBE variations when comparing against IMRT? Int J Radiation Oncol Biol Phys, 95:1:454
Underwood TSA, Paganetti H (2016) Variable Proton RBE: how do we move forward? Int J Radiation Oncol Biol Phys, 95:1:56

Related information

Reported by

UNIVERSITY COLLEGE LONDON
United Kingdom

Subjects

Life Sciences
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