Physics-aspects of dose accuracy in high dose rate (HDR) brachytherapy: source dosimetry, treatment planning, equipment performance and in vivo verification techniques

Abstract

This study provides a review of recent publications on the physics-aspects of dosimetric accuracy in high dose rate (HDR) brachytherapy. The discussion of accuracy is primarily concerned with uncertainties, but methods to improve dose conformation to the prescribed intended dose distribution are also noted. The main aim of the paper is to review current practical techniques and methods employed for HDR brachytherapy dosimetry. This includes work on the determination of dose rate fields around brachytherapy sources, the capability of treatment planning systems, the performance of treatment units and methods to verify dose delivery. This work highlights the determinants of accuracy in HDR dosimetry and treatment delivery and presents a selection of papers, focusing on articles from the last five years, to reflect active areas of research and development. Apart from Monte Carlo modelling of source dosimetry, there is no clear consensus on the optimum techniques to be used to assure dosimetric accuracy through all the processes involved in HDR brachytherapy treatment. With the exception of the ESTRO mailed dosimetry service, there is little dosimetric audit activity reported in the literature, when compared with external beam radiotherapy verification.

TRUS-probe integrated MOSkin detectors for rectal wall in vivo dosimetry in HDR brachytherapy: In phantom feasibility study

“…Therefore, to ensure the delivered dose agrees within acceptable limits to that planned, rigorous quality assurance (QA) procedures should be implemented for independent treatment verification. In particular, effective and accurate QA methods need to be developed, as the complexity of BT delivery has rapidly increased (Palmer et al, 2012;Tanderup et al, 2013) and new highly fractionation schemes (i.e., 26-27Gy in two fraction or 19-21Gy in one single fraction) have recently been introduced (Morton and Hoskin, 2013).…”

An investigation of a PRESAGE®in vivodosimeter for brachytherapy

“…Although TLDs are most commonly used, they have depth dependent sensitivity (Palmer et al 2012) and measure the dose only at a single point (McJury et al 2000). Diamond detectors were found to have dose rate dependence as well as a large rigid structure that prevent them from being inserted in-vivo (Lambert et al 2007).…”

“…Diamond detectors were found to have dose rate dependence as well as a large rigid structure that prevent them from being inserted in-vivo (Lambert et al 2007). MOSFETs contain uncertainties in angular dependence and are prone to calibration drift (Palmer et al 2012). The ideal in-vivo dose verification method would have the ability to be inserted into cavities without disruption to treatment, ability to provide high resolution dose profiles along steep dose gradients and provide fast acquisition read out time for a high patient load (Guo et al 2006a).…”

Dosimetric audit in brachytherapy

“…Many dosimetry systems have been investigated in the past decade for brachytherapy measurement, including gel dosimetry, TLDs, semiconductor diodes, ionization chambers, metal oxide semiconductor field effect transiter (MOSFET) detectors, alanine, radiochromic film, radiochromic plastic, calorimetry and optically stimulated or radioluminescent detectors. 21 The need for dosimetric audit in brachytherapy exactly mirrors the need in external beam radiotherapy: to detect any errors, to provide reassurance, to enable improvements and to demonstrate compliance. There are of course numerous sources of uncertainty in brachytherapy, 22 and there have been previous errors in brachytherapy delivery, [23][24][25][26] including well-type chamber calibration error, 27 confusion over units 28 and media reports of at least two incidents involving incorrect dwell positions.…”