Radiotherapy Physics and Engineering

The radiotherapy physics and engineering unit operates at Karolinska University Hospital Solna and Stockholm South General Hospital. The physicist and engineering staff are involved in providing virtually all forms of radiotherapy, including brachytherapy and Gamma Knife treatments, in addition to external beam therapy with linacs. The unit is also closely involved with the new national proton therapy facility, Skandionkliniken. Research interests reflect the broad spectrum of treatment modalities and techniques provided to patients.

A selection of ongoing projects

Gastro-intestinal toxicity in prostate cancer radiotherapy: spatial patterns of the dose distribution and patient-related predictors

Investigators:

Eva Onjukka (1), Giovanna Gagliardi (1), Tiziana Rancati (2) and Claudio Fiorino (3)

Affiliations:

Karolinska University Hospital (1),1 Istituto Nazionale dei Tumori (IT) (2) and 1 St Raffaele Hospital (Italy) (3)

A fraction of prostate cancer patients suffer from gastro-intestinal complications following radiotherapy. This project investigates how the spatial distribution of dose given to the rectum in patients affects the incidence and severity of complications. To conduct such a study an investigator has to move beyond the gross data reduction of the dose volume histogram (DVH) and develop new tools for dosimetric comparisons. 

Monte Carlo calculated phase space files using PRIMO for small field dosimetry calculations

Investigators:

Hamza Benmakhlouf and Pedro Andreo

Affiliations:

Karolinska University Hospital

Monte Carlo calculation for small-field dosimetry has been an active research area since the publication of a new small-field dosimetry formalism in 2008. Output correction factors have been published for several detectors, beam qualities and field sizes. Correct determination for each linac model and collimation technique has the potential to improve dosimetric accuracy. This project undertakes an extensive series of simulations and output factor determinations for a variety of linacs using the PRIMO software (based on the PENELOPE Monte Carlo system).

A practical utilization of Dual Energy CT (DECT) for proton therapy dose planning

Investigators:

Jens Zimmerman, Patrik Nowik and Gavin Poludniowski

Affiliations:

Karolinska University Hospital

The aim of this project is to find a practical solution to the problem of how to use Dual Energy CT scans for proton dose planning in a commercial Treatment Planning System. Comparisons will be made with the current clinical method used at the Skandion clinic (Uppsala, Sweden) – the stoichiometric method using standard single-energy CT scans. Experimental validations of the approaches will be performed. 

Development of a microMOSFET system for "end-to-end"- quality controls and in-vivo dosimetry of brachytherapy

Investigators:

Maria Persson (1), Josef Nilsson (2), Enrique Castellanos (2) and Åsa Carlsson Tedgren (1, 2)

Affiliations:

Karolinska University Hospital (1) and Karolinska Institutet (2)

Can a microMOSFET system available at the brachytherapy department at Karolinska University Hospital, be optimized to provide reliable verification of delivered absorbed doses? Typically in brachytherapy, no measurements of delivered doses are routinely possible. An "end-to-end" test using detectors such as the microMOSFET provide an opportunity to verify multiple stages of the treatment chain, and has the potential to further increase patient safety.

Challenging a radiotherapy paradigm: employing daily alternating volumetric modulated arc therapy plans to increase plan quality or decrease treatment time

Investigators:

Tobias Pommer

Affiliations:

Karolinska University Hospital

The paradigm that has long dominated in conventional fractionated radiotherapy is that the patient receives repeat treatments of a single radiotherapy treatment plan. To the extent that it is possible, identical dose distributions are delivered in each fraction. In a theoretical planning study for patients treated with VMAT, this project seeks to demonstrate that more efficient or superior treatments are possible by challenging this perceived wisdom. 

Development of external beam combination radiotherapy for head and neck cancer, in order to reduce dose loads and related morbidity for larynx and swallowing muscles in patients who undergo radiotherapy with curative intent

Investigators:

Elias Lindbäck, Ingmar Lax and Claes Mercke

Affiliations:

Karolinska University Hospital

Swallowing-morbidity as a result of radiotherapy for head and neck cancer can have a profound impact on the quality of life and health of a small number of patients. This theoretical planning study seeks to demonstrate that through an innovative use of established external beam radiotherapy techniques (IMRT, VMAT), the likelihood of serious morbidity (Grade 3-4) can be substantially reduced in particularly at-risk patients. 

Modelling delivered doses to lung tumours in Stereotactic Body Radiotherapy

Investigators:

Kristin Karlsson, Ingmar Lax, Elias Lindbäck, Peter Wersäll, Karin Lindberg and Gavin Poludniowski

Affiliations:

Karolinska University Hospital and Karolinska Institutet

Local control at 3 years for non-small-cell-lung-cancer (NSCLC) treated with stereotactic body radiotherapy (SBRT) was about 90% prior to the introduction of online soft-tissue image-guidance. This project asks: given geometrical uncertainties (breathing, setup errors) what doses were likely to have been actually delivered and how did this improve after on-line image-guidance was introduced? 

Proton Radiotherapy Verification and Dosimetry Applications (PRaVDA)

Investigators:

Gavin Poludniowski (as a member of the PRaVDA Consortium)

Affiliation:

Karolinska University Hospital

The quality of treatment possible with proton therapy is to a great extent limited by uncertainties on where the protons will stop in the patient. The PRaVDA Consortium is a UK-lead collaboration to address this issue, funded by a 3-year Wellcome Trust translation grant (Grant 098285). The project aims to demonstrate with innovative detector technology that imaging proton beams can reduce treatment uncertainties and be a practical tool for planning and verification.

Recent publications

On the Monte Carlo simulation of small-field micro-diamond detectors for megavoltage photon dosimetry

Investigators:

Pedro Andreo (1), Hugo Palmans (2, 3), Maria Marteinsdóttir (1), Hamza Benmakhlouf (1) and Åsa Carlsson-Tedgren (1)

Affiliations:

Karolinska University Hospital (1), National Physical Laboratory (UK) (2) and EBG MedAustron (AT) (3)

Detector-specific output correction factors for small photon beam dosimetry are commonly based on Monte Carlo simulations, with geometry descriptions derived from manufacturer blueprints. Using a PTW-60019 micro-diamond detector and the EGSnrc and PENELOPE Monte Carlo systems, discrepancies with published experimental data were identified and found to be due to differences between the design blueprints of a detector and its manufacturer production. Therefore, although Monte Carlo offers some advantages over experimentally determined values, experimental data should be used to validate calculations.

Long-term results of a prospective phase II trial of medically inoperable stage I NSCLC treated with SBRT – the Nordic experience

Investigators:

Karin Lindberg (1, 2), Jan Nyman (3), Vendela Riesenfeld Källskog (4), Morten Hoyer (5),  Jo Å Lund (6, 7), Ingmar Lax (1, 2),  Peter Wersäll (1, 2),  Kristin Karlsson (1, 2), Signe Friesland (1, 2) and Rolf Lewensohn (1, 2)

Affiliations:

Karolinska Institutet (1), Karolinska University Hospital (2), Sahlgrenska University Hospital (3), Uppsala University Hospital (4), Aarhus University Hospital (DK) (5), St. Olavs Hospital (NO) (6) and Norwegian University of Science and Technology (NO) (7)

In recent years, hypofractionated stereotactic body radiation therapy (SBRT) has emerged as an option for patients with non-small cell lung cancer (NSCLC), who are not suitable for surgery. In this Nordic long-term follow-up study, 67% of patients were found to be relapse free and the local control rate at four and five years was 79% (CI 95% 64 – 95%), further supporting SBRT as an effective treatment modality even in a medically impaired patient cohort.

Proton radiography and tomography with application to proton therapy

Investigators:

Gavin Poludniowski (1), Nigel Allinson (2) and Phil Evans (3)

Affiliations:

Karolinska University Hospital (1), University of Lincoln (UK) (2) and University of Surrey (UK) (3)

Proton radiography and tomography have promised benefit for proton therapy, since their first proposal in the 1960s. More than just providing anatomical images, proton transmission imaging provides the potential for improved treatment planning and verification. This article introduces the principles of proton radiography and tomography and the historical developments, discusses the modern prototype systems and primary design issues.

Assessment of testicular dose during preoperative radiotherapy for rectal cancer

Investigators:

Christian Buchli (1), Massoud Al Abani (2), Madelene Ahlberg (1), Torbjörn Holm (1), Tone Fokstuen (2), Matteo Bottai (1), Jan-Erik Frödin (1), Ingmar Lax (2) and Anna Martling (1)

Affiliations:

Karolinska Ínstitutet1 and Karolinska University Hospital2

Radiotherapy for rectal cancer can have adverse effects on testicular function. Estimates of delivered testicular dose, however, are potentially complicated by variability in the position of testes. This study investigated planned and delivered testicular using both plan CT (acquired before treatment) and cone-beam CT scans (acquired during treatment course) for a large set of patients. Testicular doses calculated based on plan-CT proved to be accurate estimation of delivered doses with no statistically significant difference to calculations based on treatment-room cone-beam CT.

Implication of using MRI co-registered with CT in Leksell Gamma Knife® dose planning for patients with vestibular schwannoma

Investigators:

Theresa Wangerid (1, 2), Hamza Benmakhlouf (1), Per Grane (1), Jiri Bartek Jr. (1, 3), Mikael Svensson (1) and Petter Förander (1)

Affiliations:

Karolinska University Hospital (1), S:t Göran Hospital (2) and Copenhagen University Hospital Rigshospitalet (DK) (3)

Shifts in stereotactic coordinates and resulting differences in dose distributions were investigated for Gamma knife radiosurgery of vestibular schwannoma (acoustic neuroma), when planning was based on a stereotactic MRI (current protocol) or a non-stereotactic MRI was fused with a stereotactic CT. Coordinate shifts were observed between the approaches, resulting in non-negligible changes in dose distributions. Assessment of the potential risk of clinical consequences requires further study.

The performance of normal-tissue complication probability models in the presence of confounding factors

Investigators:

Eva Onjukka (1), Colin Baker (2) and Alan Nahum (2)

Affiliations:

Karolinska University Hospital (1) and Clatterbridge Cancer Centre (UK) (2)

Modelling Normal Tissue Complication Probability (NTCP) in radiotherapy is one of the most import and most difficult challenges, with several empirical NTCP models appearing in the literature. In this study, the investigators demonstrate, using the examples of "lung" and "rectum" complications, that identifying confounding factors such as patient radiosensitivity and health status are more important than the precise NTCP model chosen.