AUTHOR=Sethi Anil , Emami Bahman , Small William , Thomas Tarita O. 

TITLE=Intraoperative Radiotherapy With INTRABEAM: Technical and Dosimetric Considerations

JOURNAL=Frontiers in Oncology

VOLUME=Volume 8 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2018.00074

DOI=10.3389/fonc.2018.00074

ISSN=2234-943X

ABSTRACT=Purpose:  
We evaluate dose characteristics and clinical applications of treatment accessories used in intra-operative radiotherapy (IORT) and make site specific recommendations for their optimal use.
Methods and Materials:  
Dose measurements were performed for a low energy (50 kV) X-ray INTRABEAM source.  For spherical, flat, surface and needle applicators, the following dosimetric parameters were measured: depth-dose (DD) profiles, surface dose (Ds), output factors (OF), and target dose homogeneity (DH).  Optical density versus exposure calibration films were employed to obtain 2-dimensional dose distributions in planes parallel and perpendicular to beam direction.  Film results were verified via repeat dose measurements with a parallel-plate ionization chamber in a custom water tank.   The impact of applicator design on dose distributions was evaluated.  
Results:
Spherical applicators are commonly used for treating the inner-surface of breast lumpectomy cavity.  Flat and surface applicators provide uniform planar dose for head & neck, abdomen and pelvis targets.   Needle applicators are designed for kypho-IORT of spinal metastasis.  Typically, larger applicators produce a more homogeneous target dose region with lower surface dose, but require longer treatment times.  For 4-cm diameter spherical, flat and surface applicators, dose rates were found to be: 0.8Gy/min, 0.3Gy/min and 2.2Gy/min respectively.  The dose rate for a needle applicator was 7.04Gy/min at 5mm distance from the applicator surface.  Overall, film results were in excellent agreement with ion-chamber data.  
Conclusions:
Intra-operative radiotherapy may be delivered with a variety of site-specific applicators.  Appropriate applicator selection is paramount for safe, effective and efficient IORT delivery.   Results of this study should help enable clinicians assure optimized target dose coverage and reduced normal tissue exposure.