Comparison of Static Conformal Beam and Intensity Modulated Radiation Therapy for Intracranial Stereotactic Radiosurgery XC13-XC15
Pramod Kumar Gupta,
Department of Radiation Oncology, Super Speciality Cancer Institute and Hospital, Lucknow, Uttar Pradesh, India.
Introduction: Stereotactic Radiosurgery (SRS) by high end Linear Accelerator is very common. There are different treatment planning and delivery options for doing Linear accelerator based SRS namely by Conformal beam or dynamic conformal arc or Intensity Modulated Radiotherapy (IMRT).
Aim: To perform a dosimetric comparison between the static conformal beam and fixed field IMRT for intracranial SRS planning.
Materials and Methods: A retrospective study was conducted in which four patients treated for single lesion brain metastasis by frame-based SRS (18 Gy) on a 6 MV linear accelerator equipped with microMLC (3 mm) were included. All these patients were planned using BrianLAB iPlan system (PBC algorithm with heterogeneity correction) using 9-14 non-coplanar static conformal fields. For each case, fixed-field IMRT plans were also generated using the same field arrangement. Target coverage V95% (target volume receiving 95% dose) and D95 (dose to 95% target volume), normal tissue sparing 80% dose volume (V80%), 50% dose volume (V50%) and 25% dose volume (V25%) and treatment efficiency (total Monitor Units (MU)) were compared between conformal fields and IMRT.
Results: The median target volume for all the lesions was 10.67cc, range 2.90-28.85 cc. Target coverage of conformal beam and IMRT was almost similar (p=0.78). V95% and D95 of conformal beam plan were 96.9±1.7 % and 17.4±0.3 Gy; whereas the readings for IMRT were 98.9±1.6 and 17.7±0.3 Gy, respectively (p=0.18). V80%, V50% and V25% of conformal beam plan were 21.9±18.5cc, 41.1±33.4cc, and 121.5±89.3cc, respectively; on contrary the same for IMRT were 23.9±18.5cc, 45.8±33.8cc, and 122.5±94.5cc. (p= 0.11) When comparing the treatment efficiency, the conformal beam plan resulted in a significantly smaller total MU. The total MU of conformal beam plan was 3080.5±306.8 MU (median: 3172.5 MU); whereas the same for IMRT was 4905.3±360.1 MU (median: 5034 MU) (p=0.04).
Conclusion: Conformal beam SRS planning is no different from fixed field IMRT plan in terms of target coverage and normal tissue sparing; however conformal beam plan resulted in a significantly smaller total MU which may have a clinical impact.