Inter- and Intrafractional Positional Uncertainties in Pediatric Radiotherapy Patients With Brain and Head and Neck Tumors

Abstract

Purpose To estimate radiation therapy planning margins based on inter- and intrafractional uncertainty for pediatric brain and head and neck tumor patients at different imaging frequencies. Methods Pediatric patients with brain (n = 83) and head and neck (n = 17) tumors (median age = 7.2 years) were enrolled on an internal review board–approved localization protocol and stratified according to treatment position and use of anesthesia. Megavoltage cone-beam CT (CBCT) was performed before each treatment and after every other treatment. The pretreatment offsets were used to calculate the interfractional setup uncertainty (SU), and posttreatment offsets were used to calculate the intrafractional residual uncertainty (RU). The SU and RU are the patient-related components of the setup margin (SM), which is part of the planning target volume (PTV). SU data was used to simulate four intervention strategies using different imaging frequencies and thresholds. Results The SM based on all patients treated on this study was 2.1 mm (SU = 0.9 mm, RU = 1.9 mm) and varied according to treatment position (supine = 1.8 mm, prone = 2.6 mm) and use of anesthesia (with = 1.7 mm, without = 2.5 mm) because of differences in the RU. The average SU for a 2-mm threshold based on no imaging, once per week imaging, initial five images, and daily imaging was 3.6, 2.1, 2.2, and 0.9 mm, respectively. Conclusion On the basis of this study, the SM component of the PTV may be reduced to 2 mm for daily CBCT compared with 3.5 mm for weekly CBCT. Considering patients who undergo daily pretreatment CBCT, the SM is larger for those treated in the prone position or smaller for those treated under anesthesia because of differences in the RU.

Dependence of intrafraction motion on fraction duration for pediatric patients with brain tumors

“…This is similar to our previous findings, ( 1 ) and the findings in the adult population for intracranial tumors. ( 2 , 5 , 6 ) However, unlike Hoogeman et al ( 2 ) who found that the amount of intrafraction motion increased with fraction duration, we found no correlation between fraction duration and intrafraction motion.…”

“…One hundred pediatric patients enrolled on a prospective daily localization protocol ( 1 ) were included in this study. Criteria for inclusion included age $<\hspace{0.17em}18$ years, intracranial target, $>20$ treatment fraction with daily localization, and treated in the supine position.…”

“…( 1 ) Based on the data from 100 children, we found that the setup uncertainty could be limited to 2 mm. We noted that there was some dependence on patient positioning (supine vs. prone) and the use of general anesthesia (yes vs. no).…”

Geometrical uncertainty margins in 3D conformal radiotherapy in the pediatric age group

“…We classified patients into head and neck and non-head and neck tumors without further site specification [12]. Another two recent publications from St. Jude Children's Hospital, Memphis, studied the uncertainty margin restricted to head and neck pediatric patients (including brain tumor) [13,14]. These four studies represent the whole published pediatric experience on setup uncertainty till now.…”

Improvement of Therapeutic Index for Brain Tumors with Daily Image Guidance

“…Planning target volume (PTV) is defined as "a geometrical concept, and it is defined to select appropriate beam sizes and beam arrangements, taking into consideration the net effect of all the possible geometrical variations and inaccuracies in order to ensure that the prescribed dose is actually absorbed in the CTV" [1]. The PTV is composed of two factors: (1) the internal margin (IM) which relies on temporal changes in position, volume, and shape of the CTV and the (2) setup margin (SM) which accounts for uncertainties in patient position and beam delivery that is inherent with fractionated irradiation [2][3][4]. If the margin between the CTV and PTV is too large, there is a higher likelihood of excessive radiation to normal tissue [5].…”