The application of positron emission tomography/computed tomography in radiation treatment planning: effect on gross target volume definition and treatment management

AIMS

To analyse the effect of the use of molecular imaging on gross target volume (GTV) definition and treatment management.

MATERIALS AND METHODS

Fifty patients with various solid tumours who underwent positron emission tomography (PET)/computed tomography (CT) simulation for radiotherapy planning from 2006 to 2008 were enrolled in this study. First, F-18 fluorodeoxyglucose (FDG)-PET and CT scans of the treatment site in the treatment position and then a whole body scan were carried out with a dedicated PET/CT scanner and fused thereafter. FDG-avid primary tumour and lymph nodes were included into the GTV. A multidisciplinary team defined the target volume, and contouring was carried out by a radiation oncologist using visual methods. To compare the PET/CT-based volumes with CT-based volumes, contours were drawn on CT-only data with the help of site-specific radiologists who were blind to the PET/CT results after a median time of 7 months.

RESULTS

In general, our PET/CT volumes were larger than our CT-based volumes. This difference was significant in patients with head and neck cancers. Major changes (> or =25%) in GTV delineation were observed in 44% of patients. In 16% of cases, PET/CT detected incidental second primaries and metastatic disease, changing the treatment strategy from curative to palliative.

CONCLUSIONS

Integrating functional imaging with FDG-PET/CT into the radiotherapy planning process resulted in major changes in a significant proportion of our patients. An interdisciplinary approach between imaging and radiation oncology departments is essential in defining the target volumes.

Dosimetric comparison of intensity modulated pelvic radiotherapy with 3D conformal radiotherapy in patients with gynecologic malignancies

PURPOSE

Before initiating an intensity modulated radiotherapy (IMRT) program for gynecologic malignancies we prospectively evaluated the potential benefits of IMRT by dose volume histogram comparison of IMRT and 3D conformal radiotherapy plans.

METHODS

Plans of ten consecutive patients with cervical and endometrial cancer were evaluated. For each patient a 4-field box technique was compared to an IMRT plan. Both plans were normalized to deliver 50.4 Gy to the PTV in six patients and 45 Gy in the remaining four. Isodose distributions and dose volume histograms were compared in seven dose levels.

RESULTS

IMRT reduced the volume of small bowel receiving more than 45 Gy in all patients. The average absolute volume of small bowel receiving 45 Gy was significantly reduced from 318 cc to 33 cc. No significant increase in the volume of small bowel receiving less than 20 Gy was observed. Rectum, bladder and bone marrow volumes receiving high doses were also significantly reduced with IMRT.

CONCLUSIONS

IMRT significantly reduces the volume of normal tissues irradiated to high doses without compromising the target coverage. This may potentially lead to a reduction in treatment related toxicities.