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Published on: April 17, 2012
Fractionated stereotactic radiotherapy for pediatric patients with retinoblastoma
Patrick D Higgins1, Bruce J Gerbi, Mark Macedon
1Department of Therapeutic Radiology-Radiation Oncology, University of Minnesota, Minneapolis, Minnesota 55455, USA. higgi010@umn.edu
Insights
Fractionated stereotactic radiotherapy (SRT) using a modified head frame offers precise orbital tumor treatment for infants. This technique significantly reduces normal tissue complication probabilities (NTCP) in pediatric retinoblastoma patients.
Area of Science:
- Radiation Oncology
- Pediatric Oncology
- Medical Physics
Background:
- Fractionated stereotactic radiotherapy (SRT) is a precise radiation technique.
- Infants with bilateral retinoblastoma require specialized treatment approaches.
- Anesthesia is often necessary for pediatric radiation treatments.
Purpose of the Study:
- To evaluate the application of a modified Gill-Thomas-Cosman (GTC) relocatable head frame for fractionated stereotactic radiotherapy (SRT) in infants.
- To assess the treatment reproducibility and efficacy for bilateral retinoblastoma in young children.
- To compare the normal tissue complication probabilities (NTCP) of SRT with standard treatment techniques for orbital bone growth inhibition.
Main Methods:
- A modified Gill-Thomas-Cosman (GTC) relocatable head frame was adapted for infant treatment under anesthesia.
- Two infants with bilateral retinoblastoma were treated using SRT on a Varian linear accelerator.
- Setup reproducibility was measured, and dose-volume histograms were used to calculate NTCP for orbital bone areas.
Main Results:
- The modified GTC head frame provided excellent setup reproducibility with an average deviation of 0.35 +/- 0.79 mm.
- Fractionated SRT delivered doses between 2520 and 3960 cGy in 180 cGy fractions.
- Normal tissue complication probabilities (NTCP) for pediatric bone growth inhibition were reduced from 95-100% with standard methods to 16% or less with SRT.
Conclusions:
- The modified GTC head frame enables precise and reproducible fractionated stereotactic radiotherapy in infants.
- SRT significantly reduces the risk of normal tissue complications, particularly bone growth inhibition, in pediatric retinoblastoma patients.
- This technique improves treatment accuracy, facilitates patient management under anesthesia, and minimizes cosmetic defects in growing children.
Abstract:
In this report we discuss the application of a modified Gill-Thomas-Cosman (GTC) relocatable head frame to enable fractionated stereotactic radiotherapy (SRT) of infants under anesthesia. This system has been used to treat two infants, ages 12 and 18 months for bilateral retinoblastoma on a Varian 6/100 linear accelerator. The GTC head frame was used to reproduceably position and treat the orbits of these children to between 2520 and 3960 cGy in 180 cGy fractions. A standard head and neck tray, with accompanying thermoplastic mask, was adapted to mount to the head frame to enable these treatments. We found the maximum average deviation in the repeat fixations, as compared with the initial fitting data, to be +/- 2 mm. The overall average difference and standard deviation in measurement was 0.47 +/- 0.63 mm for the first case, and 0.19 +/- 0.94 mm for the second case with a combined average of 0.35 +/- 0.79 mm overall from a total of 381 point measurements. The stereotactic treatment plan (Radionics) incorporated a single isocenter for each orbit and 3-4 arcs per isocenter. Inter-comparisons have been made between this technique and a standard lateral field technique, designed using the SRS planning system. Dose-volume histograms and corresponding normal tissue complication probabilities (NTCP) based on pediatric bone growth inhibition have been calculated for each method for the orbital bone areas. We have found that the NTCP is reduced from 95-100% in the standard treatment method to 16% or less with SRT. Use of the modified head frame provides excellent setup reproducibility, facilitates access to patients for anesthesia and reduces the chances of a poor cosmetic result in these growing children.
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