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Three dimensional conformal radiation therapy in pediatric parameningeal rhabdomyosarcomas
J M Michalski1, R K Sur, W B Harms
1Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University Medical Center, St. Louis, MO 63110, USA.
Insights
Three dimensional (3D) treatment planning improves radiation therapy for pediatric head and neck rhabdomyosarcomas. This method offers better tumor coverage and may reduce complications compared to traditional 2D planning.
Area of Science:
- Radiation Oncology
- Pediatric Oncology
- Medical Imaging
Background:
- Parameningeal head and neck rhabdomyosarcomas are rare pediatric cancers.
- Effective treatment planning is crucial for optimizing outcomes and minimizing toxicity.
Purpose of the Study:
- To evaluate the effectiveness of three dimensional (3D) treatment planning compared to two dimensional (2D) planning for pediatric head and neck rhabdomyosarcomas.
Main Methods:
- Five pediatric patients with parameningeal rhabdomyosarcoma underwent treatment planning using both 3D and 2D methods.
- Computed tomography (CT) scans were used to define tumor and normal tissue volumes.
- Dosimetric coverage of the tumor, margins, and organs at risk was compared between the two planning techniques.
Main Results:
- The 3D planning method provided a more accurate assessment of gross tumor volume compared to the 2D method.
- The 2D method often underestimated tumor size and resulted in inadequate dosimetric coverage, especially when margins for subclinical disease were included.
- The 3D approach demonstrated superior coverage of the tumor and its margins while potentially sparing adjacent normal tissues.
Conclusions:
- Three dimensional conformal radiation therapy offers significant advantages in treating pediatric head and neck sarcomas.
- Improved target volume coverage with 3D planning may enhance local tumor control.
- Reduced radiation dose to critical structures with 3D planning can potentially decrease the incidence of long-term adverse effects in children.
Purpose:
We evaluated the utility of three dimensional (3D) treatment planning in the management of children with parameningeal head and neck rhabdomyosarcomas.
Methods And Materials:
Five children with parameningeal rhabdomyosarcoma were referred for treatment at our radiation oncology center from May 1990 through January 1993. Each patient was evaluated, staged, and treated according to the Intergroup Rhabdomyosarcoma Study. Patients were immobilized and underwent a computed tomography scan with contrast in the treatment position. Tumor and normal tissues were identified with assistance from a diagnostic radiologist and defined in each slice. The patients were then planned and treated with the assistance of a 3D treatment planning system. A second plan was then devised by another physician without the benefit of the 3D volumetric display. The target volumes designed with the 3D system and the two-dimensional (2D) method were then compared. The dosimetric coverage to tumor, tumor plus margin, and normal tissues was also compared with the two methods of treatment planning.
Results:
The apparent size of the gross tumor volume was underestimated with the conventional 2D planning method relative to the 3D method. When margin was added around the gross tumor to account for microscopic extension of disease in the 2D method, the expected area of coverage improved relative to the 3D method. In each circumstance, the minimum dose that covered the gross tumor was substantially less with the 2D method than with the 3D method. The inadequate dosimetric coverage was especially pronounced when the necessary margin to account for subclinical disease was added. In each case, the 2D plans would have delivered substantial dose to adjacent normal tissues and organs, resulting in a higher incidence of significant complications.
Conclusions:
3D conformal radiation therapy has a demonstrated advantage in the treatment of sarcomas of the head and neck. The improved dosimetric coverage of the tumor and its margin for subclinical extensions may result in improvement in local control of these tumors. In addition, lowering of radiation dose to adjacent critical structures may help lower the incidence of adverse late effects in children.