核医学と放射線治療

3D Image based Customized versus Standard Treatment Planning for Cervical Cancer High Dose Rate Brachytherapy with Tandem and Ovoids

Abstract

Paul Mobit, Michael C. Baird, Madhava R. Kanakamedala, Waleed F. Mourad, Satyaseelan Packianathan, Srinivasan Vijayakumar and Claus Chunli Yang

Purpose and Objective(s): To investigate the advantages of volumetric treatment planning in HDR brachytherapy for cervical carcinoma compared to standardized loading based on 2-D planning techniques.
Materials and Methods: Our institution uses volume-based 3-D planning for each tandem and ovoid (T&O) insertion for HDR brachytherapy in the treatment of advanced cervical carcinoma. Here, we attempt to define the benefits of this approach. We re-planned 48 CT-based treatment plans on 12 patients (treated in our facility between February, 2009 and February, 2010) using a commonly used 2-D standard HDR loading of the T&O. All patients had received 4 fractions of 6.5 Gy or 5 fractions of 5.5 Gy to point H or A. The following organs at risk (OARs) were contoured: rectum, bladder, sigmoid, and small bowel. Our customized planning approach required the adjustment of source dwell times and positions to keep doses to the OARs below 80% of the prescription dose. The standardized HDR planning, however, bases the loading time on the length of the tandem. The dwell time for each tandem source position is the same. The dwell time multipliers for the ovoids were 0.33, 0.665 and 1.0, proportionate to the 2 cm, 4 cm, and 6 cm tandem length, respectively. The dose to the highest 2 cc (D2cc) of the OARs were also determined and analyzed.
Results: There was a marked change in the value and location of the D2cc for all OARs from one HDR session to the next in both the standard and customized plans. When the data for the 48 plans were analyzed together, there were no significant differences between the customized plans and the standardized plans. However, when data for the individual plans were analyzed, 35% of the 2-D based plans did not meet our treatment planning objectives.
Conclusion: Using customized plans for HDR T&O brachytherapy did not always reduce the doses to the rectum, bladder, sigmoid, and small bowels compared to the standardized plans. The dose to the small bowel could be up to 15% higher than the dose to point H or A in the standard plans indicating that customized plans may be superior to the standardized ones for the treatment of patients where this dose is critical.