the success of radiotherapy ( rt ) depends not upon the expense and complexity involved , but upon the correctness of techniques .
correct portal - design calls for correct knowledge regarding the location of the target volumes to be treated .
traditional bony - landmarks may have been used as a surrogate , but they do not always correlate with the actual location of the soft - tissue target - volumes .
the four - field - box ( 4fb ) technique for cervical carcinoma is often utilized to improve dose homogeneity .
the exact placement of the posterior border on the lateral portals of this technique is unfortunately not supported by stone - hard consensus ; placing it at the s2-s3 junction may increase the chance of sparing rectum but at the risk of target - miss .
we intend to demonstrate the potential benefits with the use of sectional imaging in safely delineating target - volumes .
a lady on evaluation and referral from her gynecologist , presented to us with the diagnosis of stage - ib2 cervical - carcinoma staged as per the figo ( federation of international gynaecologists and obstetricians ) system . as we were preparing to initiate this patient on a course of concurrent chemo - rt , we had the opportunity to review her magnetic - resonance imaging ( mri ) films obtained earlier by her gynecologist .
we noticed a stark retroversion of the uterus , which almost abutted the sacrum [ figure 1 ] .
this finding made us ponder over the potential perils associated with the conventional 4fb technique , which is widely utilized worldwide for portal design for cervical - carcinomas .
given that the uterine and cervical lymphatics are interconnected , and that disease extension from the cervix to the uterus is highly probable , the current consensus state that the entire uterine - corpus should be a part of the clinical - target - volume ( ctv ) for every patient of cervical - carcinoma .
the uterus , being a mobile organ may manifest various positions , which can not be taken into account during bony - landmark based planning .
unless the true position of the uterus can be determined with imaging , it would be risky to place the posterior - margin of lateral fields at the s2-s3 junction .
magnetic resonance imaging showing a retroverted uterine corpus extending well beyond the posterior border of the s2-s3 junction
concurrent chemo - rt is a standard of care in the curative approach for stage - ib2 cervical - carcinoma .
though there has been a recent emergence of the use of 3d - imaging based techniques , however , a considerable majority of patients across the world are treated with traditional rt techniques even to this day , mainly owing to the fact that cervical - cancer is mainly a disease of the developing world which suffers shortages with regards to advanced planning and treatment systems .
conventional techniques may involve either the opposed anteroposterior - posteroanterior ( ap / pa ) two - field technique , or the 4fb technique - planned using radiologically determined bony - landmarks . in the 4fb technique ,
lateral portals are added with an intention to reduce the dose to the bowel anteriorly and to the rectum posteriorly .
conventional techniques have been found to provide equivalent results in comparison to 3d - rt , which is more expensive and complex
. however , inadequate coverage with improper portal - design can preclude chances of cure .
the ap and pa field definitions are similar with the two - field and the 4fb technique .
the caveat with the implementation of the 4fb technique has always been ( and still continues to be ) the fact that are no unanimous guidelines regarding the margin definitions for the lateral portals .
the controversy lies in the definition of the posterior - margin of the lateral - portal .
some authorities recommend its placement at or 0.5 cm posterior to the anterior - border of the s2-s3 interspace . with particular reference to the treatment of stage - ib carcinomas
, one definition suggests that the posterior border be placed in such a way as to cover atleast 50% of the rectum .
however , our point of contention would be that such a definition would be oblivious to the status of the uterine - position [ figure 1 ] and rectal - distension . placing the posterior - margin of the lateral - portals at s2-s3 junction using bony references from radiographs
was found to be inadequate to cover the ctv in patients with bulky - disease .
an evaluation of the ctv coverage by using the s2-s3 junction for the posterior border of the lateral fields revealed an inability to cover the optimal target - volumes in about half of the stage - ib patients.[57 ] the consequent effects on local - control were also quantified . among stage - ib patients , the local - control at 3-years was 100% for patients who had adequate margins , compared to a drastically reduced value of 71% for patients of the same stage with inadequate margins .
since cervical carcinoma is staged clinically with the figo - system ( which gives no regard to the utility of imaging to describe uterine - corpus involvement ) , it would be potentially dangerous to apply a  one definition fits all  philosophy in designing portals for patients with staged ib2 with the figo system .
the current consensus recommends the inclusion of the entire uterine - corpus into the ctv mainly since the uterine and cervical lymphatics are interconnected .
retroverted uterus ( after all , a normal variation of the uterine - position ) may extend well beyond the line falling from the s2-s3 junction [ figure 1 ] .
the presence of uterine - retroversion is unlikely to be detected unless use is made of ct or mri . given that the ctv would be incomplete without the inclusion of the entire uterus , the design of lateral portals of the 4fb technique should never be based on bony references
. it should be individualized to the patient 's soft - tissue imaging ( with ct / mri ) obtained in the treatment position .
usage of bony - landmarks for portal definition is insensitive to uterine flexion / version , which would be influenced by bladder and rectal filling .
mri , if used in treatment planning provides a very accurate definition of the individual morbid anatomy .
lateral portals designed using sagittal mri would help in a safe and confident placement of posterior margins .
ct would be a reasonable alternative if mri based planning is unavailable , given that vivid soft - tissue detail and accurate reconstructions can be had with helical ct - scanners . in concluding , we remind the reader that as per current consensus , the ctv for cervical - carcinoma would be incomplete without the inclusion of the entire uterus .
the uterus is not a fixed organ , and has many possible variations in its position , which can not be encompassed by bony - landmark based planning .
ct / mri based target delineation provides an opportunity to take the uterine position and bulk into account .
 radiation therapy ( rt ) plays a pivotal role in the curative approach for carcinoma of the cervix . 
 inspite of the emergence of various new conformal techniques in rt , conventional techniques still hold vital importance . 
 majority of the patients worldwide are treated with 2d - rt techniques . 
 2d - rt techniques have been proven to be non - inferior and simpler in comparison to 3d - rt in the context of carcinoma of the cervix . 
 however , inadequate target volume coverage with improper portal design can preclude the chances of cure . 
 we demonstrate the need for abolishing guesswork in terms of target volume determination through the example of a patient 's sagittal magnetic resonance image showing a case of the retroverted uterus which would have been likely to be missed from the treatment portals if they were designed using definitions based on bony landmarks . 