Peter Watson

Name: Peter Watson, MSc

Level at MPU: PhD

Email: peter.watson [at]

Supervisor(s): Dr. Jan Seuntjens

Research interests: Kilovoltage dosimetry, Intraoperative radiotherapy, Electronic brachytherapy


Research summary

The INTRABEAM system (Carl Zeiss, Germany) is a miniature x-ray source for use in intraoperative radiotherapy and brachytherapy. Currently, this source is calibrated in a relative way using an indirect measurement of absorbed dose (energy per unit mass). The absolute primary standard for measuring absorbed dose from ionizing radiation is calorimetry, whereby dose is measured directly via temperature change of a medium. Thus, the ideal calibration technique for miniature x-ray sources would be calorimetry-based. The purpose of this project is to evaluate the current dosimetry formalism of the INTRABEAM system, and to develop a calorimetry-based absorbed dose protocol for these sources. 

A monte carlo model of the INTRABEAM source has been developed and validated in-air using the EGSnrc particle transport code. Using this model, ionization chamber correction and conversion factors can be accurately calculated for the INTRABEAM source, and compared with accepted values. Next, the feasibility of performing a calorimetric dose measurement with the INTRABEAM source will be investigated. A protoype calorimeter will then be constructed, and characterised in terms of stability and noise. Once characterised, dose measurements with the calorimeter will be performed and compared with ionization chamber and radiochromic film measurements. The establishment of a calorimetry-based dose protocol for miniature x-ray sources, such as the INTRABEAM system, would help reduce dosimetric uncertainties. This increased confidence in delivered dose would allow for direct comparison between INTRABEAM and other existing commercial miniature x-ray devices. It would also assist with investigating the use of INTRABEAM at different cancer sites in the body, and for combining INTRABEAM treatments with external beam radiotherapy. Most importantly, reducing the uncertainty of delivered dose will ultimately lead to improving patient outcome.


Key publications

  1. Watson, P., Mainegra-Hing, E., Tomic, N., & Seuntjens, J. (2015). Implementation of an efficient Monte Carlo calculation for CBCT scatter correction: phantom study. Journal Of Applied Clinical Medical Physics, 16(4). doi:10.1120/jacmp.v16i4.5393



McGill Physics Graduate Fellowship (2013)

Research Institute of the MUHC Studentship (2011)

NSERC Undergraduate Research Award (declined) (2006)

Back to top