Image Guided Radiation Therapy for Prostate Cancer

South Eastern Sydney Illawarra Area Health Service

Abstract

Prostate Cancer Radiation Therapy relies on daily delivery of a precise dose of radiation to a volume of tissue that contains the prostate gland. Treatment accuracy is limited by random day to day variations in prostate position. This treatment is hindered by dose limiting toxicity of surrounding healthy tissues. The Illawarra Cancer Care Centre (ICCC) has investigated and implemented the use of gold markers implanted into the prostate to allow accurate daily image guidance of treatment to the prostate. Treatment accuracy is improved significantly (9mm to 4mm, p=0.0001). The average volume of healthy tissue irradiated could be reduced from 132.91cm3 to 84.38cm3 (p<0.0001). This approach will be adopted as standard care once new equipment is installed early in 2009.

Aim

To increase the accuracy of prostate radiotherapy delivery, thereby reducing the volume of healthy tissue irradiated.

Nature of the Problem

Prostate radiotherapy requires accurate targeting of the prostate in order to avoid adverse side effects to surrounding structures. Prostate position can vary significantly within the bony pelvis; therefore a margin for error in treatment design is required. A margin for error is a compromise between rectum and bladder irradiation, and ensuring curative dose delivery to the entire prostate each and every treatment. Attempts to reduce the margin for error are limited by prostate position variability, figure (1).

Extent of the Problem

Figure (2) shows the spread of treatment accuracy for 35 recent cases (256 images) indicating the need for a broad margin to not only account for the variation in alignment with the bony structures, but also the unpredictable position of the prostate which is known to vary by up to 1cm.

ICCC treats 130 prostate cancer patients per year equating to over 4800 prostate treatments based on an approximation of the prostate’s position. Ideally we would guide the treatment to the prostate each and every treatment to ensure the dose is delivered to the prostate alone. This would allow a reduction in the margin for error resulting in less healthy tissue irradiated.

Strategic Importance

This project aligns with category seven of the NSW Health State Plan Towards 2010, by making smart choices about the purchase and utilisation of new technologies. ICCC is in the process of purchasing state of the art imaging technologies, so we are positioning to take advantage of this new technology and implement image guided prostate radiotherapy as standard care.

This project also aligns with State Plan Priority S2 - “Improving survival rates and quality of life”. Improving accuracy and reducing healthy tissue irradiated will improve long term survival rates and improve quality of life by reducing toxicity (Pollack, 2002).

Planning and Implementing Solutions

A multidisciplinary group investigation concluded that implanted prostate markers are the most effective solution to overcome prostate position variability. The University of Wollongong Human Ethics Committee confirmed this would be a quality improvement exercise, and local funding was sourced to purchase the 1.5 x 3mm gold markers pre-loaded in 17 gauge needles.

Specific procedures were developed for all aspects of planning and treatment, and were tested on an anthropomorphic phantom with implanted markers.  Staff training was conducted ensuring consistency of practice and complete understanding, given the significant change in practice. A dedicated database was established to record all treatment accuracy data as the standard commercially available system was inadequate.

After insertion of the markers under ultrasound, these patients undergo standard radiotherapy planning.

At each daily treatment the prostate position is ascertained prior to treatment delivery. Acquired images showing the prostate markers are aligned with planning reference images to calculate variations in the intended treatment location. Variations exceeding a predefined tolerance (5mm) require re-alignment of the treatment with the prostate markers. This involves fine adjustments to the position of the treatment couch resulting in accurate alignment of the treatment area to the prostate gland. A second set of verification images are then acquired to confirm the corrections. Figure (5) shows this comparison process.

Figure 5a	Figure 5b
Figure 5c Figure (5) Planned treatment position relative to markers (left), position relative to markers pre-treatment (centre), confirmation image (right). Markers circled in red.

Equipment availability is currently restricting implementation of this technique to a small number of cases but installation of the newest imaging technologies in 2009 will remedy this. Once installed this equipment provides the opportunity and capacity to implement this as standard care for all prostate cancer patients we treat.

Outcomes and Evaluation

Treatment accuracy is now possible to within 5mm, therefore allowing a reduction in our margin for error and potentially an increase in prescribed dose. Figure (6) shows the substantial improvement in treatment accuracy when implanted markers are used for daily treatment guidance. Based on bony landmarks alone, accuracy is 9mm, but with the use of daily corrections to implanted markers the treatment accuracy is 4mm (p=0.0001).

This improvement in treatment accuracy allows a significant reduction in error margins resulting in an appreciable reduction in treatment side effects. Figure (7) shows the impact reduced margins have on the volume of healthy tissue irradiated. Based on current accuracy a 7mm margin is more than achievable, and a 5mm margin is possible with further refinement. By reducing the volume of healthy tissue treated the space between the two curves in figure (6) increases, resulting in lower side effects for the same impact on tumour.

Sustaining Change

The installation of new imaging equipment early in 2009 will give capacity to implement this approach as standard care for all prostate cancer treated at the ICCC. The demonstrated improvements in treatment delivery are the motivation for our patient focused service to continue to refine and develop this and other improvements.

High levels of staff involvement have resulted in strong ownership which supports the change whilst procedural documentation underpins staff training and orientation. The multidisciplinary implementation group will continue to play a key role in monitoring and further refining the technique. Patient acceptance has been 100%.

Future Scope

This technique will be adopted as standard care for prostate cancer at the ICCC.  As a result all 130+ cases of prostate cancer will receive image guided radiation therapy based on gold markers with a treatment accuracy of at least 5 if not 3mm.

This technique is transferable to any radiation therapy department with the required imaging technology.  While numerous centres have the capability, ICCC have once again shown to be NSW leaders in the implementation of significant quality improvements.

References

Pollack A, Zagars GK, Starkschall G, et al. Prostate Cancer radiation dose response: Results of the MD Anderson Phase III randomized trial. Int J Riat Oncol Biol Phys 2002;53:1097-1105

Project Team

Justin Dixon, Elias Nasser, Sheree Barlin, Anthony Arnold

Contact

This project was entered in the 2008 NSW Health Awards, Make Smart Choices about the Costs and Benefits of Health Services category.

More about the 2008 NSW Health Awards