Use of Flattening Filter-Free Photon Beams in Treating Medulloblastoma: A Dosimetric Evaluation

Aim. To evaluate the dosimetric benefits of flattening filter-free (FFF) photon beams in intensity modulated radiation therapy (IMRT) and Rapid Arc (RA) over conventional CSI methods. Methods and Materials. Five patients treated with IMRT using static multileaf collimators (MLC) were randomly selected for this retrospective study. Dynamic MLC IMRT, RA, and conformal therapy (3DCRT) were iterated with the same CT data sets with and without flattening filter photons. Total dose prescribed was 28.80？Gy in 16 fractions. Dosimetric parameters such as , , , , , DHI, and CI for PTV and , , , , , and for OARs were extracted from DVHs. Beam on time (BOT) for various plans was also compared. Results. FFF RA therapy (6F_RA) resulted in highly homogeneous and conformal doses throughout the craniospinal axis. 3DCRT resulted in the highest (SD) , whereas flattening filter (FF) and FFF dynamic IMRT had a minimum . 6F_RA and 6F_DMLC resulted in lesser doses to thyroid, eyes, esophagus, liver, lungs, and kidneys. Conclusion. FFF IMRT and FFF RA for CSI have definite dosimetric advantages over 3DCRT technique in terms of target coverage and OAR sparing. Use of FFF in IMRT resulted in 50% reduction in BOT, thereby increasing the treatment efficiency. 1. Introduction Medulloblastoma is a fast growing tumor of the cerebellum (posterior fossa) that controls stability, posture, and complex motor functions such as verbal communication and swallowing. About 400 new patients, primarily children, were diagnosed in the US every year, slightly more often in males than in females [1]. It is the most common brain tumor in children aged four and younger and the second most common brain tumor in children aged 5–14 years [2]. Subsequent to surgery, medulloblastoma is usually treated with CSI. Although radiation therapy had proven successful, investigators are still looking for new ways to mitigate the potential side effects of this treatment [2]. Treatment related late complications are usually hearing disability, declined cognition, cardiomyopathy, cataract formation, retarded growth, endocrine dysfunction, and second malignancies. Clinicians consider using techniques such as IMRT and RA that aim to converge beams of radiation directly at the tumor eventually improving the long term complications free survival. However, radiotherapy (RT) planning, delivery, and junction dose verification remain exigent for craniospinal irradiation (CSI) in medulloblastoma patients. Hence investigating the emerging new RT techniques such as FFF in IMRT and RA on the basis of dose volume parameters was