School of Physics and Astrophysics

Dynamic Conformal Arc Therapy in Stereotactic Ablative Radiotherapy

Dynamic Conformal Arc Therapy in Stereotactic Ablative Radiotherapy

This study aims to commission a radiation treatment technique (DCAT) for use at Perth Radiation Oncology (Genesis Cancer Care WA) and evaluate it dosimetrically in comparison to other pre-existing treatment modalities when used in stereotactic ablative radiotherapy (SABR). 

The use of Stereotactic treatments on medical linear accelerators has evolved in recent years from a technique exclusive to brain tumours and using invasive immobilisation devices attached directly to the skull, into the treatment of many tumour sites around the body and with minimal or no immobilisation needed. The major advantages of Stereotactic Ablative Radiotherapy (SABR) over traditional therapy are the superior tumour control and quicker overall treatment times for patients. Where once patients were required to come in for treatment five times a week for six weeks, with SABR a treatment can be delivered in only one to five sessions – a great benefit to both the patient and the resources of a radiotherapy clinic.

Recently, with the development of more advanced techniques such as Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Radiotherapy (VMAT), there has been a lot of interest in the application of these to SABR treatments. These techniques modulate the beam intensity and so achieve much better conformity around the target tumour whilst sparing healthy tissue as much as possible. VMAT in particular has all the advantages of IMRT but applies it continuously as the gantry rotates around the patient in real time, thus reducing treatment times markedly. However, these techniques both involve the regular use of extremely small fields in creating these modulated beams and in doing so introduce a large uncertainty into the treatment planning process as the dosimetry of small fields is not well understood. 

A medical linear accelerator with the beam being shaped by the multi-leaf collimator (MLC)

A medical linear accelerator with the beam being shaped by the multi-leaf collimator (MLC) [Credit: VarianTM]

Example of DCAT beam shapes as gantry rotates around the patient

Example of DCAT beam shapes as gantry rotates around the patient [Credit: Heidelberg University]

Dynamic Conformal Arc Therapy (DCAT) is similar to VMAT in that the treatment is delivered continuously as the gantry rotates around the patient. However, rather than the beam being continuously modulated as it rotates, the leaves simply conform to the shape of the target as seen from the point of view of the beam source. Whilst this may at first glance seem like a 'watered down' version of VMAT, it may confer advantages both dosimetrically and in planning. Firstly, it has been shown in VMAT and IMRT treatments that the modulation involved can lead to higher overall dose to healthy tissue than older treatments such as 3D CRT. This is not such a huge problem in traditional fractionation schemes, but in SABR this could potentially lead to serious complications. Secondly, the extremely small fields employed in the modulated techniques have large uncertainties associated with them and so the dose as calculated by a treatment planning system (TPS) may not be what is actually delivered. Again, this may be a problem with potentially large consequences in SABR treatments. DCAT avoids both of these issues as its fields encompass the whole tumour at all times and has been shown to use less monitor units (i.e. less dose) than IMRT treatments. An additional benefit is that DCAT is also very easy to plan on the TPS whereas VMAT and IMRT use considerable resources and time to create.

This research will first commission the DCAT technique at Perth Radiation Oncology and then examine the proposed advantages it may possess over other techniques in the realm of SABR. If successful, the goal is to use DCAT clinically to help improve patient outcomes and reduce load on the clinic.

 

This Page

Last updated:
Monday, 3 February, 2014 5:49 PM

http://www.physics.uwa.edu.au/2482911