Cranio Spinal Irradiation of Medulloblastoma Using High Precision Techniques – A Dosimetric Comparison

• Published in: Technology in cancer research & treatment Vol. 14; no. 4; pp. 491 - 496
• Main Authors: Pichandi, A., Ganesh, K.M., Jerrin, A., Balaji, K., Sridhar, P.S., Surega, A.
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA SAGE Publications 01-08-2015
• Subjects: Flattening filter free photons; Medulloblastoma; Cranio spinal irradiation
• ISSN: 1533-0346; 1533-0338
• DOI: 10.7785/tcrt.2012.500421

Radiotherapy planning, delivery and junction dose verification remain exigent for Cranio
Spinal Irradiation (CSI) in medulloblastoma patients. This study aims to evaluate high
precision techniques such as Intensity Modulated Radiation Therapy (IMRT), Rapid Arc
Therapy (RA) with and without flattening filter (FF) on the basis of dosimetric analysis.
Five patients treated with jagged junction Intensity Modulated RadioTherapy (IMRT) using
dynamic Multi Leaf Collimators (MLC) were randomly selected for this retrospective study.
IMRT, Rapid Arc (RA) plans were simulated in the same CT data set with and without
flattening filter. Total dose prescribed was 28.80 Gy in 16 fractions. An evaluation
criterion of 98% of PTV receiving 100% of the prescription dose was followed in all plans.
Twenty treatment plans with 260 Dose Volume Histograms (DVHs) was created. Dosimetric
parameters such as Dmax, Dmin, Dmean, V95%,
V107%, CI for PTV and Dmax, Dmean, V80%,
V50%, V30%, V10% for Organs At Risk (OAR) were
extracted from DVHs. Treatment delivery efficiency was also evaluated for total Beam On
Time (BOT). FFF Rapid Arc therapy (6F_RA) resulted in conformal doses
throughout the cranio spinal axis. FF and FFF dynamic IMRT had minimal V107%,
1.23% and 2.88% compared to 49.15 and 66.36 of rapid arc therapy (with and without FF).
6F_IMRT resulted in lesser mean doses to eyes, liver, lungs and kidneys. Heart mean dose
was less (3.08 Gy) with 6X_IMRT. Thyroid and esophagus doses could be reduced to about
41.2% and 10% respectively with 6F_RA. The BOT for the treatment techniques were 3.43 min
(6X_IMRT), 1.59 min (6F_IMRT), 5min (6X_RA), 4.5 min (6F_RA). Removal of flattening filter
in IMRT could improve dose coverage along the caniospinal axis and normal tissue sparing.
A reduction of 46.3% BOT could increase treatment efficiency of 6F_IMRT compared to
6X_IMRT. CSI could be simpler since junction doses can be evaded in IMRT and RA
techniques.