for some , brachytherapy ( bt ) is something on the brink of extinction and their arguments are not scarce .
brachytherapy might not sound too appealing for the average radiation oncologist because it implies transition from behind the screen to the or .
blood appears as a real scenario and most of them chose from the beginning to avoid it willingly .
it is not only about the lack of surgical skills , but also that most junior radiation oncologists do not actually have the chance to see or practice the technique in their centers .
moreover , bt is by itself a niche domain , as there are rather few indications for it , as compared to external beam radiotherapy ( ebrt ) .
therefore , for most of them , bt is something more like  see not touch  .
last but not least , in a domain driven by ebrt , investing in bt might not seem too appealing for developers . fortunately , some of these issues can be corrected . with proper indications and good technique
thus , in their effort to keep the domain alive , doctors that advocate for it tried to replace the human hand for the  bloody  part while keeping the radiation therapy spirit friendly to radiation oncologists . as a result of this struggle for accessibility , safety , precision , and accuracy , bt robotic systems appeared .
the aim of this paper is to evaluate the current situation in the field of robotic brachytherapy , briefly outline the existing systems , their technical aspects , and limitations , and to present a custom - made solution to the problem , a universal brachytherapy robotic system , para - brachyrob .
the purpose of bt is to achieve , by interstitial radioactive seed implantation ( low - dose - rate 
hdr , or pulse - dose - rate  pdr brachytherapy ) , a high conformal dose distribution to cover the target volume . at the same time
it is thus an efficient treatment for virtual any small to medium sized well defined tumor , which can be reached by visual / palpable guidance , provided that correct indications and accurate technique are met .
while the indication is based only on knowledge , usually set by multi - disciplinary team ( mdt ) decision , the technique requires a high degree of skill and the use of real - time image guidance , which can be improved by automation .
the report of the joint task group 192 of the american association of physicists in medicine ( aapm ) and the groupe europen de curiethrapie ( gec)-european society for radiotherapy & oncology ( estro ) reviews the robotics institute of america 's ( ria ) definition and classification of robots , and makes a clear distinction between  automation  and  autonomy  .
it raises two fundamental questions on  autonomy by an automatic system  : autonomy from whom ? and autonomy to do what ?
the first addresses the matter of permission for the robot to conduct its operations without human supervision .
 described by sheridan ( plan , teach , monitor , intervene , learn )   and refers to treatment execution , supervision of treatment planning , monitoring , and intervention .
it also proposes the modification of system performance based on previous learning or teaching experiences .
based on these degrees , the report proposes a new classification of automatic systems , more appropriate for bt robots and different from that elaborated by the ria . instead of subdividing robots into classes ( 1 - 4 ) , it puts them on four levels of autonomy ( i - iv ) .
the denomination  class ( 1 - 4 ) robot operating at level of autonomy ( i - iv )  might not be uncommon .
there are currently no available level iv medical robots , i.e. machines capable to create and complete all the tasks without human interaction .
as they yet do not possess full autonomy and work in a human environment , bt robotic systems are required to meet the saur ( safety , accuracy , user - friendliness , and reliability ) criteria
. indeed , apart from widening the indications of the technique , increasing its availability by automation and by reducing the learning curve , these robots aim at improving accuracy .
when applied for permanent bt , this relates to precise seed placement , finding optimal seed locations , decreasing surgical trauma , and finally protecting medical staff from radiation exposure .
an extensive list of the additional functional recommendations on robotic bt systems can be consulted in the joint task group 192 's report
. however , the ultimate purpose is not to bring a machine to the existing level of human expertise but to better implants and enhance the quality of care in a consistent , reproducible way .
this means extending the indications of bt while keeping it at the same level of minimal invasiveness or even increasing the efficacy / toxicity ratio .
a checklist that should be satisfied by every bt robotic system in this respect is provided by the same report . in terms of accuracy ,
manual seeds placement have an accuracy of 3 - 6 mm when placed in vivo with a rigid template .
conversely , robotic systems are required to acquire a spatial accuracy of less than 1 mm in phantom models .
they are also demanded to solve issues such as tissue deformation ( by rotational needle insertion ) , needle deviation ( fixed needle trajectory , sensors for pressure and pulsations ) , and to avoid edema , which would prevent the correct distribution of the delivered dose as planned pre - implant and intra - operatively ( dynamic planning by update of dosimetry ) .
patient position and existing imaging technology can be limiting the robotic system 's degree of freedom ( dof ) , and construction materials ( for example , the dorsal - lithotomic position for prostate brachytherapy might impair the transperineal insertion with direct visualization on ct and/or mri because of the limited space in the ct / mri / bore ; all the cables for mri guided robot must be with no magnetizable material such iron or copper , rising significantly the costs ) .
system adaptability is advised so that the future advances in 3d imaging technology could offer a real advantage to these systems .
prostate deformation / rotation during implant and bevel - tip needle steering effect lead also to problems such as significant target displacements and spinning , respectively . at the same time , reaching a higher level of autonomy is hindered by the operator 's need of manual control and the consequent preference for a master - slave interface . from this perspective
, the catheter placement in the abdomen , pelvis , or thorax can be guided by the da vinci surgery robot , after resection , biopsy , or if the cancer is judged inoperable .
image - guided brachytherapy ( igbt ) comprises bt robotic systems that currently use mri ( magnetic resonance imaging ) , ct ( computed tomography ) , or trus ( trans - rectal ultrasound ) . while the first provides the best soft tissue contrast ,
there are a dozen of robotic systems developed worldwide , few to have been used on patients ( first , euclidean , and jhu1 ) .
only one has received the fda and ce approvals and become commercially available for prostate bt applications : fully integrated real - time seed treatment ( first system , oncentra integrated prostate solution device , elekta - nucletron , veenendaal , the netherlands , a level ii robotic system ) .
the aapm and gec - estro guideline for image - guided robotic bt report of task group 192 issued in october 2014   provides an exhaustive table with all the existing brachytherapy robotic systems .
they are analyzed by : ( 1 ) ria class , ( 2 ) level of autonomy , ( 3 ) application , ( 4 ) imaging modality , ( 5 ) dof , ( 6 ) number of channel / needle , ( 7 ) needle insertion , ( 8) needle rotation , ( 9 ) angled insertion , ( 10 ) seed delivery , ( 11 ) needle withdraw , ( 12 ) physical template , ( 13 ) template / perineum area coverage , ( 14 ) depth movement , ( 15 ) tps , ( 16 ) needle - tip positioning accuracy in the air , ( 17 ) needle - tip positioning accuracy in phantom , ( 18 ) accuracy in seed deposition , ( 19 ) emergency stop , ( 20 ) provision for reverting to conventional mode , ( 21 ) force - torque sensor , ( 22 ) fda approval .
a brief summary of the current brachytherapy robotic systems , their developers , applications , and imaging modality is given in figure 1 .
the mean calibration error for the prostate bt robots is in the range of 0.5 mm . in tissue
mimicking phantoms , the mean needle angulations error at 10 cm depth is around 0.5 , translating into a seed placement overall mean error of around 3 mm . in practice ,
the main contributor for error is the needle deflection through the real prostate ( due to different tissue densities including cancer stiffness , adenoma elasticity , prostate calcifications , or previously inserted seeds , etc . ) . picturing the centers currently involved in developing brachytherapy robotic systems .
key : name , institution / company , targeted organ , imaging modality ; # the only systems used on patients for clinical brachytherapy ; * the only commercially available system ( approved by fda and ce ) the majority of systems have thus been tailored for prostate and lung source implantation ( the latter to a lesser extent ) . therefore , implementing a universal bt robotic system is one of the field 's main directions of development [ 7 , 8 ] .
a solution to the above mentioned limitations was proposed by the research center for industrial robots simulation and testing ( cester ) cluj - napoca , romania , which developed a family of modular parallel robots for brachytherapy ( br1 , br2 , br3 ) ( figure 2 ) for hdr brachytherapy .
the aim was to obtain ct - based dosimetry for inoperable cancers with robotic assisted needle placement ( thoracic , abdominal , and pelvic cancers ) ( figure 3 ) . based on simulation results and on the expertise of radiation oncology specialists , the last system , br3 ,
the constructive solution is a ct - compatible , remote control , and portable system with 5 degrees of freedom ( dof ) : x , y , z , angulation and rotation .
it is small enough to fit the 80 cm gantry when mounted on the ct - table but it can be also fixed to the ground .
para - brachyrob brachytherapy system components and use : a ) cylindrical modules and arms ; b ) control unit ; c ) system fixed on the ct - table ; d ) system fixed on the ground 3d simulation of para - brachyrob robotic assisted brachytherapy with the cylindrical modules mounted on the ct - table ( from top left ) : applications in lung , liver , prostate , and kidney cancers the kinematic scheme of pbr consists of two cylindrical modules of 3 dof each . besides the similar first two active joints , which perform a translational movement ,
they both associate two distal passive joints , while an additional active joint is characteristic of the needle insertion module .
thanks to this structure , the br3 model of pbr eliminates the fixed frame of the previous two models , br1 and br2 . in brief , the system 's technical requirements include : ( 1 ) 5-dof ( x , y , z ,  ,  ) , ( 2 ) double rigid grip for needles of various lengths ( 5 - 25 cm ) , ( 3 ) sterile cap for needle contact , ( 4 ) sensor for resistance and for vibration , with dual signalization ( audio and visual ) , ( 5 ) precision of in vivo contact < 3 mm in any direction , ( 6 ) automatic charger for up to 20 needles , and ( 7 ) double safety blocking mechanism .
a contiguous 2 mm slice thickness ct acquisition of the zone of interest is done . as principle , the coordinates of the target are linked with the external tattoos ( as in ebrt ) , the attaching points of the robot to the couch , and with the fiducials placed in the tumor or in its close proximity .
the contouring of the target and organs at risk is done like for a classical ebrt planning .
the software proposes solutions for needle placement , avoiding the organs at risk ( pre - plan ) .
optimization is performed by different angles insertions if needed , until all the dosimetry predefined constraints are fulfilled .
the next day , the patient , under local , spinal or general anesthesia ( as required by the tumor localization ) is repositioned the same way on the ct - couch ( laser alignment on the tattoos , as for ebrt ) , and the robot is rigidly attached to the couch in the specially designed articulation points ( visible on the ct images ) .
then the robot automatically moves to the insertion start position , according to the shifts generated by the planning system and starts the implantation , with the most  safe  needle , under ct guidance in any particular moment asked by the operating team .
the procedure is checked periodically from outside the room by couples of ct slices ( or alternatively from inside the operating room by trans - abdominal ultrasound ) and pursuit catheter by catheter , if only minor deviations are encountered .
final ct acquisition is done for the real dosimetry , and hdr ( or pdr ) bt plan can be delivered .
at present , automate ( partial or full procedure ) seems to be the best solution for bringing bt back to stage . by
increasing its availability and consequently reducing the technique 's learning curve , more junior radiation oncologists are expected to turn their attention to bt , and , consequently , more patients could benefit . for the time - being , the oncentra integrated prostate solution device is the only robotic system commercially available for ldr seeds bt . among a dozen of
custom - made and under development systems , our parallel robot para - brachyrob , thanks to its versatility and technical capabilities , might be a pioneer of the next generation precision tools in bt .
 in a field dominated by external beam radiation therapy ( ebrt ) , both the therapeutic and technical possibilities of brachytherapy ( bt ) are underrated , shadowed by protons and intensity modulated radiotherapy . decreasing expertise and indications , as well as increasing lack of specific bt training for radiation therapy ( rt ) residents led to the real need of shortening its learning curve and making it more popular . developing robotic bt devices can be a way to mitigate the above issues . 
 there are many teams working at custom - made robotic bt platforms to perfect and overcome the limitations of the existing systems . 
 this paper provides a picture of the current state - of - the - art in robotic assisted bt , as it also conveys the author 's solution to the problem , a parallel robot that uses ct - guidance . 
Purpose
Technical considerations
Existing systems
Our experience: the Para-BrachyRob (PBR)
Conclusions
Disclosure