Dosimetric comparison of integral dose for different techniques of craniospinal irradiation

Abstract

Aim: Comparison of the integral dose (ID) delivered to organs at risk (OAR), non-target body and target body by using different techniques of craniospinal irradiation (CSI). Materials and methods: Ten CSI patients (medulloblastoma) already planned and treated either with linear accelerator three-dimensional conformal radiation therapy (Linac-3DCRT) technique or with linear accelerator RapidArc (Linac-RapidArc) technique by Novalis-Tx Linac machine have been analysed. Retrospectively, these patients are again planned on Radixact-X9 Linac with Helical, Direct-3DCRT and Direct-intensity-modulated radiation therapy (Direct-IMRT) techniques. The dose prescription to planning target volume brain (PTV-Brain) and PTV-Spine is 36 Gy in 20 fractions and is kept the same for all techniques. The target body, non-target body, OARs and total body dose are compared. Results: ID is lowest in the RapidArc plan for every patient in comparison to Helical and Direct-IMRT. The ID for Body-PTV was found slightly higher in the RapidArc plan in comparison to 3DCRT plans. But there is better normal tissue sparing for most of the OARs in RapidArc plans if it compares with 3DCRT plans. Findings: RapidArc is a better alternative for the treatment of CSI. It provides better target coverage and better OARs sparing from any other treatment techniques.

Validation of the geometric equivalent field concept in total scatter factor calculations, for half‐, quarter‐ and off‐isocenter asymmetric square fields

“…The S cp , S cp , D f %, and 𝚫 S cp were calculated from Equations ( 3), ( 5), (6), and (7) F I G U R E 5 S cp difference D f % between the beam energies of 18 MV (L 1 ) and 23 MV (L 2 ), for all studied fields. S cp, scatter factor.…”

“…The S cp , S cp , D f %, and 𝚫 S cp were calculated from Equations (3), ( 5), (6), and (7) Also, computerized investigations proved that these differences are small at the IC and large away from it under the same conditions. 3,24,37 In addition, Ian et al 25,26 proved, after correcting the missing tissue in breast, that these differences increase with the decreasing energy of the photon beam.…”

“…The S cp , S cp , D f %, and 𝚫 S cp were calculated from Equations (3), ( 5), (6), and (7) 10 × 10 cm 2 and also (r) does not exceed 7 cm in most clinical cases, 25,26,38 so the difference is within 1% (Table 5). This also applies to cases of the brain and head & neck radiotherapy.…”

“…The uncertainty of the S cp measurements was calculated as the standard deviation (STDEV.P) of the three measurements for the SSF s and SOF s including the respective OAR measurements, and the SD of the four averages of the measurements of the four alternative quadrants for the SHF s and SQF s using Equation (7).…”

“…TFs are usually described using the notation (y 1 ,y 2 ,x 1 ,x 2 ), where y 1 , y 2 , x 1 and x 2 are the respective collimator jaw positions (in cm) determined at the level of the IC. Asymmetric fields are commonly used in radiotherapy, and regarding treatment planning, there are three special categories of interest (for singleisocenter techniques), according to the location of the IC with respect to the TF: (a) The IC is centered at an edge of the TF, as in the case of the half -beams used in the treatment of breast, 4 as shown in Figure 1a, head and neck, 5 and craniospinal tumors, 6,7 (b) The IC is located at a corner of the TF as in the case of a quarterbeams used for the treatment of the chest wall in breast cancer cases, 4,8 as shown in Figure 1b, c) The IC is outside TF, in special cases like the off -isocenter-beams are used for the treatment of the supraclavicular area and the boost field used for breast tumors, 9 as shown in Figure 1c and d, respectively.…”