in patients with clinically localized prostate cancer , prostate permanent seed brachytherapy ( pb ) is associated with excellent biochemical control rates [ 15 ] . the american brachytherapy society consensus guidelines recommend that ct - based postoperative dosimetry is to be performed at any time between 0 - 60 days after pb . many centers , including ours , perform the post - implant ct scan on day 0 or day 1 , as this is more convenient for the patient , allows for early identification of dosimetric problems and closes the learning loop , while the memory of the procedure is still recent . however , it is recognized that that undertaking the procedure at this time would under estimate the dosimetric parameters , because of the presence of edema [ 5 , 6 ] . while there are several reports of prostate multisector dosimetry data obtained from ct or mri scans performed at intervals ranging from 14 - 70 days after pb , there are no reports on multisector dosimetry performed in the immediate post - implant period [ 712 ] . this study was undertaken to determine the results of prostate multisector dosimetry performed in the immediate post - implant period on day 1 post - implant dosimetry after i pb . the data in this study was obtained from 75 consecutive patients treated by a single radiation oncologist ( jak ) . these patients underwent i prostate brachytherapy as sole therapy to a dose of 144 gy ( aapm tg-43 ) prescribed to the prostate gland planning target volume . all patients had low - risk prostate cancer ( stage t1c / t2a [ 1992 ajcc criteria ] with a gleason score  6 , and serum psa  10 ng / ml ) . the trus volume study was performed jointly by the radiation oncologist and urologist using b&k ultrasound ( b&k medical , herlev , denmark ) unit and a barzell - whitmore stepper ( barzell - whitmore maroon bells , inc . , images were obtained at 5 mm intervals from base to apex of the prostate gland . ultrasound pre - planning was performed using a urethral - sparing modified uniform loading technique , described by the seattle prostate institute using the prowess version 3.1 treatment planning system ( prowess , chico , ca ) [ 1 , 3 ] . the prostate clinical target volume was the outline of the prostate gland at the time of the volume study ( fig . this volume was expanded by 2 mm anteriorly and laterally , and 5 mm inferiorly and no margin was applied posteriorly and superiorly to define the planning target volume ( ptv ) . the prostate gland is outlined in cyan , 144 gy ( 100% ) isodose line in yellow and 216 gy ( 150% ) isodose line in red . the multisector dosimetric parameters are : base ( top row ) : d90 = = 168.3 gy , v100 = 99.8% ; mid gland ( middle row ) : d90 = 177.1 gy , v100 = 100.0% ; apex ( bottom row ) : d90 = 162.2 gy , v100 = 98.9% all patients underwent brachytherapy under spinal or general anesthesia . prostate brachytherapy was then performed using a standard template - guided transperineal technique using preloaded needles and free seeds from the anterior to the posterior regions of the prostate gland as described earlier . all patients had a post - implant ct scan performed on day 1 after brachytherapy . the ct scans were performed at 3 mm intervals , using 3 mm slice thickness and post - implant dosimetry was performed using the prowess version 3.1 treatment planning system ( prowess , chico , ca , usa ) . a good quality prostate implant was defined by v100  80% on day 1 post - implant dosimetry [ 3 , 5 , 12 ] . one of the major impediments to the uniform conduct of prostate multisector dosimetry is the lack of consensus in the definition of the various prostate sectors . a number of reports have described brachytherapy doses to the prostate base , mid gland , and apex using varying definitions [ 712 ] . in one report , the base was represented by the two superior most ct slices and the apex was designated as the two inferior most ct slices . in other reports the prostate gland was divided supero - inferiorly into two or three equal quadrants [ 810 ] . in two recent reports , the prostate was divided into three equal quadrants ( base , mid gland , apex ) along its length , and then each quadrant was divided into four sectors by using perpendicular or oblique dividers for a total of 12 sectors [ 11 , 12 ] . in another report by d'amico et al . that reviewed 104 radical prostatectomy specimens for anterior basal cancer involvement to define implant volume in low - risk prostate cancer , the superior - most 1 cm of the gland was defined as the prostate base . given the lack of consensus , we have utilized this superior - most 1 cm definition for defining the prostate base on pre - implant ultrasound ( us ) and post - implant ct scans . while the d'amico report defined the prostate apex as the distal 5 mm of the gland , we used the distal 1 cm to define the apex similar to the base definition , because of the volumetric and dosimetric limitations imposed by using just 1 or 2 axial images on the ultrasound or ct scans . the mid gland was defined as the region in between the base and apex on pre- and post - implant ultrasound and ct images . as can be observed in figures 1 and 2 , the definition of the prostate base , mid gland , and apex used in this report is quite similar to the definition used by merrick et al . , the pre - implant v100 and d90 , and post - implant v100 and d90 , and v150 were determined for the entire gland , prostate base , mid gland , and apex in 75 consecutive patients . day 1 post - implant ct scan dosimetry of the patient in figure 1 after i brachytherapy . the prostate gland is outlined in yellow and the rectum in blue , 144 gy ( 100% ) isodose line in green , and 216 gy ( 150% ) isodose line in red . the multisector dosimetric parameters are : base ( top row ) : d90 = 95.9 gy , v100 = 71.0% ; mid gland ( middle row ) : d90 = 147.6 gy , v100 = 90.7% ; apex ( bottom row ) : d90 = 168.5 gy , v100 = 95.7% the pre - implant v100 and d90 , and post - implant v100 and d90 , and v150 were determined for the entire gland , prostate base , mid gland , and apex . these dose values for the entire gland and prostate sub - regions were compared using a two - tailed student 's t - test to determine potential areas of under dosage on pre - implant or post - implant dosimetry . the data in this study was obtained from 75 consecutive patients treated by a single radiation oncologist ( jak ) . these patients underwent i prostate brachytherapy as sole therapy to a dose of 144 gy ( aapm tg-43 ) prescribed to the prostate gland planning target volume . all patients had low - risk prostate cancer ( stage t1c / t2a [ 1992 ajcc criteria ] with a gleason score  6 , and serum psa  10 ng / ml ) . the trus volume study was performed jointly by the radiation oncologist and urologist using b&k ultrasound ( b&k medical , herlev , denmark ) unit and a barzell - whitmore stepper ( barzell - whitmore maroon bells , inc . , images were obtained at 5 mm intervals from base to apex of the prostate gland . ultrasound pre - planning was performed using a urethral - sparing modified uniform loading technique , described by the seattle prostate institute using the prowess version 3.1 treatment planning system ( prowess , chico , ca ) [ 1 , 3 ] . the prostate clinical target volume was the outline of the prostate gland at the time of the volume study ( fig . this volume was expanded by 2 mm anteriorly and laterally , and 5 mm inferiorly and no margin was applied posteriorly and superiorly to define the planning target volume ( ptv ) . the prostate gland is outlined in cyan , 144 gy ( 100% ) isodose line in yellow and 216 gy ( 150% ) isodose line in red . the multisector dosimetric parameters are : base ( top row ) : d90 = = 168.3 gy , v100 = 99.8% ; mid gland ( middle row ) : d90 = 177.1 gy , v100 = 100.0% ; apex ( bottom row ) : d90 = 162.2 gy , v100 = 98.9% prostate brachytherapy was then performed using a standard template - guided transperineal technique using preloaded needles and free seeds from the anterior to the posterior regions of the prostate gland as described earlier . all patients had a post - implant ct scan performed on day 1 after brachytherapy . the ct scans were performed at 3 mm intervals , using 3 mm slice thickness and post - implant dosimetry was performed using the prowess version 3.1 treatment planning system ( prowess , chico , ca , usa ) . a good quality prostate implant was defined by v100  80% on day 1 post - implant dosimetry [ 3 , 5 , 12 ] . one of the major impediments to the uniform conduct of prostate multisector dosimetry is the lack of consensus in the definition of the various prostate sectors . a number of reports have described brachytherapy doses to the prostate base , mid gland , and apex using varying definitions [ 712 ] . in one report , the base was represented by the two superior most ct slices and the apex was designated as the two inferior most ct slices . in other reports the prostate gland was divided supero - inferiorly into two or three equal quadrants [ 810 ] . in two recent reports , the prostate was divided into three equal quadrants ( base , mid gland , apex ) along its length , and then each quadrant was divided into four sectors by using perpendicular or oblique dividers for a total of 12 sectors [ 11 , 12 ] . in another report by d'amico et al . that reviewed 104 radical prostatectomy specimens for anterior basal cancer involvement to define implant volume in low - risk prostate cancer , the superior - most 1 cm of the gland was defined as the prostate base . given the lack of consensus , we have utilized this superior - most 1 cm definition for defining the prostate base on pre - implant ultrasound ( us ) and post - implant ct scans . while the d'amico report defined the prostate apex as the distal 5 mm of the gland , we used the distal 1 cm to define the apex similar to the base definition , because of the volumetric and dosimetric limitations imposed by using just 1 or 2 axial images on the ultrasound or ct scans . the mid gland was defined as the region in between the base and apex on pre- and post - implant ultrasound and ct images . as can be observed in figures 1 and 2 , the definition of the prostate base , mid gland , and apex used in this report is quite similar to the definition used by merrick et al . the pre - implant v100 and d90 , and post - implant v100 and d90 , and v150 were determined for the entire gland , prostate base , mid gland , and apex in 75 consecutive patients . day 1 post - implant ct scan dosimetry of the patient in figure 1 after i brachytherapy . the prostate gland is outlined in yellow and the rectum in blue , 144 gy ( 100% ) isodose line in green , and 216 gy ( 150% ) isodose line in red . the multisector dosimetric parameters are : base ( top row ) : d90 = 95.9 gy , v100 = 71.0% ; mid gland ( middle row ) : d90 = 147.6 gy , v100 = 90.7% ; apex ( bottom row ) : d90 = 168.5 gy , v100 = 95.7% the pre - implant v100 and d90 , and post - implant v100 and d90 , and v150 were determined for the entire gland , prostate base , mid gland , and apex . these dose values for the entire gland and prostate sub - regions were compared using a two - tailed student 's t - test to determine potential areas of under dosage on pre - implant or post - implant dosimetry . a p value of < 0.05 indicated statistical significance . the mean v100 (  sd ) for the entire prostate gland ( pg ) , prostate base ( pgb ) , prostate mid - gland ( pmg ) , and prostate apex ( pa ) was 99.2% (  1% ) , 98.9% (  1% ) , 99.5% (  1% ) , and 98.5% (  4% ) , respectively . the mean d90 (  sd ) for the pg , pgb , pmg , and pa was 174.1 gy (  8.14 ) , 166.1 gy (  6.63 ) , 178.7 gy (  8.25 ) , and 170.3 (  1.42 ) , respectively . there was no statistically significant under dosage of the prostate base with respect to v100 compared to the entire gland ( p value 0.20 ) and apex ( p value 0.36 ) . the magnitude of under dosage of the base v100 compared to mid gland was 0.6% ( p value < 0.01 ) . the base d90 was statistically significantly lower compared to the mid gland and apex , however , the average magnitude of under dosage was small at 12.6 gy and 4.2 gy , respectively ( table 1 ) . multisector dosimetry for v100 and d90 of the prostate mid gland and apex revealed no significant under dosage in these regions . comparison of v100 and d90 of the prostate base relative to the entire prostate gland , mid - gland , and apex on pre - implant ultrasound multisector dosimetry v100  percentage volume of the prostate gland that receives 100% of prescription dose , d90  dose ( gy ) that treats 90% of the prostate gland volume , sd  standard deviation the mean volume (  sd ) of the pg , pgb , pmg , and pa was 50.9 cc (  14.0 ) , 14 cc (  3.8 ) , 30.2 cc (  11.2 ) , and 6.8 cc (  2.3 ) , respectively . all patients had good quality implants based on v100  80% to the entire prostate gland per the seattle prostate institute guidelines . the mean v100 (  sd ) for the pg , pgb , pmg , and pa was 90.2% (  6 ) , 77.9% (  14 ) , 95.1% (  5 ) , and 90.6% (  12 ) , respectively . the mean d90 for pg , pgb , pmg , and pa was 148.7 gy (  22.1 ) , 125.7 gy (  23.3 ) , 170.3 gy (  26 ) , and 157.4 gy (  29.5 ) , respectively . the mean v150 for the pg , pgb , pmg , and pa was 52.8% (  15.5 ) , 34.8% (  16.6 ) , 61.1% (  17.7 ) , and 53.5% (  22.0 ) , respectively . there was significant under dosage of the prostate base relative to the entire prostate gland , mid - gland , and apex for mean v100 ( p value < 0.01 ) and d90 ( p value < 0.01 ) . the average magnitude of under dosage for the prostate base compared to the midgland and apex was 17.2% and 22.7% for v100 , and 44.6 gy and 31.7 gy for d90 , respectively ( table 2 ) . multisector dosimetry for v100 and d90 of the prostate mid gland and apex revealed no under dosage in these regions . to the contrary , there actually was a significant increase in v150 in these regions by 26.3% and 18.7% , respectively , compared to the prostate base ( p value < 0.01 ) . comparison of v100 and d90 of the prostate base relative to the entire prostate gland , mid - gland , and apex on day 1 post - implant ct scan multisector dosimetry v100  percentage volume of the prostate gland that receives 100% of prescription dose , d90  dose ( gy ) that treats 90% of the prostate gland volume , sd  standard deviation the mean v100 (  sd ) for the entire prostate gland ( pg ) , prostate base ( pgb ) , prostate mid - gland ( pmg ) , and prostate apex ( pa ) was 99.2% (  1% ) , 98.9% (  1% ) , 99.5% (  1% ) , and 98.5% (  4% ) , respectively . the mean d90 (  sd ) for the pg , pgb , pmg , and pa was 174.1 gy (  8.14 ) , 166.1 gy (  6.63 ) , 178.7 gy (  8.25 ) , and 170.3 (  1.42 ) , respectively . there was no statistically significant under dosage of the prostate base with respect to v100 compared to the entire gland ( p value 0.20 ) and apex ( p value 0.36 ) . the magnitude of under dosage of the base v100 compared to mid gland was 0.6% ( p value < 0.01 ) . the base d90 was statistically significantly lower compared to the mid gland and apex , however , the average magnitude of under dosage was small at 12.6 gy and 4.2 gy , respectively ( table 1 ) . multisector dosimetry for v100 and d90 of the prostate mid gland and apex revealed no significant under dosage in these regions . comparison of v100 and d90 of the prostate base relative to the entire prostate gland , mid - gland , and apex on pre - implant ultrasound multisector dosimetry v100  percentage volume of the prostate gland that receives 100% of prescription dose , d90  dose ( gy ) that treats 90% of the prostate gland volume , sd  standard deviation the mean volume (  sd ) of the pg , pgb , pmg , and pa was 50.9 cc (  14.0 ) , 14 cc (  3.8 ) , 30.2 cc (  11.2 ) , and 6.8 cc (  2.3 ) , respectively . all patients had good quality implants based on v100  80% to the entire prostate gland per the seattle prostate institute guidelines . the mean v100 (  sd ) for the pg , pgb , pmg , and pa was 90.2% (  6 ) , 77.9% (  14 ) , 95.1% (  5 ) , and 90.6% (  12 ) , respectively . the mean d90 for pg , pgb , pmg , and pa was 148.7 gy (  22.1 ) , 125.7 gy (  23.3 ) , 170.3 gy (  26 ) , and 157.4 gy (  29.5 ) , respectively . the mean v150 for the pg , pgb , pmg , and pa was 52.8% (  15.5 ) , 34.8% (  16.6 ) , 61.1% (  17.7 ) , and 53.5% (  22.0 ) , respectively . there was significant under dosage of the prostate base relative to the entire prostate gland , mid - gland , and apex for mean v100 ( p value < 0.01 ) and d90 ( p value < 0.01 ) . the average magnitude of under dosage for the prostate base compared to the midgland and apex was 17.2% and 22.7% for v100 , and 44.6 gy and 31.7 gy for d90 , respectively ( table 2 ) . multisector dosimetry for v100 and d90 of the prostate mid gland and apex revealed no under dosage in these regions . to the contrary , there actually was a significant increase in v150 in these regions by 26.3% and 18.7% , respectively , compared to the prostate base ( p value < 0.01 ) . comparison of v100 and d90 of the prostate base relative to the entire prostate gland , mid - gland , and apex on day 1 post - implant ct scan multisector dosimetry v100  percentage volume of the prostate gland that receives 100% of prescription dose , d90  dose ( gy ) that treats 90% of the prostate gland volume , sd  standard deviation there is considerable variation in the practice of pre- and post - implant dosimetry [ 5 , 1517 ] . the pre - implant dose coverage of the prostate gland ( v100 ) is generally > 95% . however , similar to the vancouver series , our analysis of pre - implant dosimetry also demonstrated some degree of under dosage of the prostate base relative to mid gland and apex . however , in both of these reports , the magnitude of post - implant under dosage of the prostate base was significantly greater than any under dosage that was observed on pre - implant ultrasound dosimetry . the current indicators of good quality implants such as v100 and d90 considers the dose coverage of 90 - 100% of the prostate volume by a specific dose [ 15 ] . while several reports have suggested a significant correlation between d90 and biochemical control [ 4 , 17 ] , others have not found such a correlation . this discrepancy may in part be due to the fact that these dose - volume descriptors do not give an accurate assessment of whether the tumor bearing sectors within the prostate gland were adequately dosed or not . although the prescribed minimum dose to the prostate gland is approximately 145 gy , the dose to quadrants within the prostate gland can vary from 60 gy to > 500 gy . the clinical impact of such a variable dose distribution in the different prostate sub - regions on tumor control rates is not known . to our knowledge , there have been no reports on post - implant multisector dosimetry in the immediate post - implant ( day 0 - 1 ) period . at least six reports using differing definitions for the various prostate sectors has described above and have performed dosimetric analysis at intervals of 14 - 70 days after brachytherapy . performed a segmental analysis of prostate dose from ct scans on 32 patients at 6 - 8 weeks after i brachytherapy . they observed that the average d90 to the basal segments was approximately 80% compared to 90 - 95% to the mid - section and apex of the gland . analyzed the dose to four quadrants of the prostate gland in 30 patients from ct scans performed 12 - 70 days after i brachytherapy . the mean v100 for the anterior superior quadrant was 78.5% compared to 90 - 99% for the other quadrants of the gland . similarly , the mean d90 to the anterior superior quadrant was 130.6 gy compared to 162 - 198.6 gy in the other quadrants . in another report by maletz et al . there was significant under dosage of the anterior base v100 and d90 from mri and ct post - implant dosimetry performed at 2 - 4 weeks after pd brachytherapy in 45 patients . similarly , butzbach et al . reported that under dosage of the prostate base led to significantly smaller extraprostatic margin with dose coverage in the base ( 2.5 - 3.5 mm ) , compared to the mid gland and apex (  4.5 mm ) on post implant dosimetry in 22 patients 20 - 53 days after pd brachytherapy . recently reported on dosimetry data on twelve prostate sectors from the pro - qura database performed at a median of 30 days after brachytherapy . they reported that 33% , 4.6% , and 10.5% of all base , mid gland , and apical sectors of the prostate were considered of minimal quality with a v100 < 80% . specifically , 59.2% of the anterior base and 30.3% of the posterior base had minimal quality dose coverage . similarly , yoosuf et al . has shown significant under dosage of the base and anterior mid gland on ct - based 12 sector dosimetry performed 28 days after i brachytherapy in 50 patients . our data demonstrates a similar under dosage of the prostate base in the immediate post - implant period on day 1 multisector dosimetry revealing a prostate base under dosage compared to the mid gland and apex by an average magnitude of 17.2% and 22.7% for v100 , and 44.6 gy and 31.7 gy for d90 , respectively . our report did not find any under dosage in the prostate mid gland and apex sectors . this report adds to the existing literature on under dosage of the prostate base on post - implant dosimetry performed 2 weeks to 70 days after implantation by demonstrating that day 1 post - implant multisector dosimetry also shows significant basal under dosage . an argument could be made that there would be more swelling in the immediate post - implant period , and that more errors would be associated with ct - based contouring as in this report , thus accentuating potential areas of underdosage on day 1 dosimetry . however , our results are no different from the other published reports on post - implant dosimetry using ct and mri scans done 14 - 70 days after brachytherapy [ 712 ] . thus , despite the lack of consistency in the definition of prostate sectors , isotopes , timing , and inter and intra - observer variability associated with post - implant dosimetry , this report and others demonstrates a broad consensus that significant under dosage of the prostate base is commonly observed on ct / mri scans performed at intervals of 1 - 70 days after prostate brachytherapy [ 5 , 712 ] . there are several reasons for the under dosage of the base including loss of seeds into the bladder or periprostatic venous plexus , inferior migration of seeds during implantation , incorrect location of the needle tip relative to the base , needle drag on the prostate gland , needle splay , and errors in accurate definition of the prostate base on ct scans [ 1012 , 20 ] . another important reason could be due to the fact that unlike other quadrants of the prostate gland , a ptv margin can not be applied superiorly to the base as seeds intended for tissues 5 mm superior to the base would either be lost in the urinary bladder or get implanted in the bladder wall that could result in increased urinary complications . this may also explain the slight under dosage of the base seen on pre - implant dosimetry in this report . the clinical significance of under dosage of the prostate base or anterior regions of the prostate gland is unknown . however , such under dosage has the potential to decrease tumor control rates considering that > 75% of prostate tumors are multifocal , and 5 - 30% of low - risk tumors may actually have higher grade and higher stages of cancer [ 22 , 23 ] . further , recent reports have shown an increased incidence ( 20 - 25% ) of anterior - predominant prostate cancers in patients undergoing prostatectomy after aggressive screening , and involvement of all regions of the prostate gland including the base in low - risk patients undergoing template - guided saturation biopsies . for all of these reasons , similar to the practice of radical prostatectomy and external beam radiotherapy , every attempt should be made to treat the entire prostate gland including the base with prostate brachytherapy . the use of mri scans for post - implant dosimetry may provide a more accurate definition of prostate volumes , however , this is not currently the standard of care [ 5 , 26 ] . in this report we have used a simple definition to divide the prostate into three sectors : base , mid gland , and apex that can easily be utilized for routine sector specific dosimetric analysis on pre- and post - implant us and ct scans . the clinical utility to dividing the gland into more number of sectors as done by others is uncertain , especially because of the difficulty in accurately depositing seeds , and thus delivering the dose specifically in smaller sectors of the prostate gland . in the future , prostate multisector dosimetry may have more clinical importance with the increasing use of multiparametic mri scans for intra - prostatic tumor localization and staging . the combined use of multiparametric mri , pre and post - implant assessment of v100 and d90 for the entire prostate gland , prostate base , mid gland , and apex has the potential to improve tumor control rates by ascertaining that tumor bearing regions within the prostate gland , especially at the base are adequately treated and not under dosed after good quality brachytherapy . the measures that could be utilized to reduce under dosage intra - operatively or compensate for under dosage post - operatively , especially in patients with a high risk of tumor involvement of the base may include : the addition of a 5 mm planning margin superiorly into the seminal vesicles ; use of unconventional seed loading to increase the number of seeds or the use of higher strength seeds at the base ; use of high dose rate brachytherapy ; or the addition of external beam irradiation ( 45 gy ) to brachytherapy in intermediate and high risk patients . studies are underway at our institution to determine the prognostic significance of prostate quadrant dosimetry on biochemical outcomes . this report demonstrates that there is significant under dosage of the prostate base compared to the mid - gland and apex in the immediate post - implant period based on day 1 post - implant dosimetry . despite the wide variability in the practice of post - implant dosimetry with regard to timing after brachytherapy , type of scans ( ct vs. mri ) and the criteria used to define prostate sectors , the areas of under dosage in the prostate gland are not randomly distributed , but are consistently observed in the basal segments of the prostate gland . further research is warranted to investigate measures to avoid under dosage of the prostate base and to study its potential clinical significance .
purposewhile there are several reports of prostate multisector dosimetry data obtained from ct or mri scans performed at intervals ranging from 14 - 70 days after prostate brachytherapy ( pb ) , there are no reports on multisector dosimetry performed in the immediate post - implant period . 
 this study was undertaken to determine the results of prostate multisector dosimetry performed in the immediate post - implant period on day 1 post - implant dosimetry after 125i pb.material and methodsthe day 1 post - implant ct - based v100 and d90 were determined for the prostate base ( pgb ) and compared to doses to the entire gland ( pg ) , mid - gland ( pmg ) , and apex ( pa ) in 75 patients who underwent 125i pb to a dose of 144 gy . 
 similar multisector dosimetry was also performed on the pre - implant ultrasound volume study scans of these patients.resultsall patients had good quality implants . on day 1 post - implant multisector dosimetry 
 there was significant under dosage of the pgb for both v100 and d90 . 
 the average magnitude of under dosage of pgb compared to pmg and pa was 17.2% and 22.7% for v100 and 44.6 gy and 31.7 gy for d90 , respectively . 
 on pre - implant multisector dosimetry there was no statistically significant under dosage of the pgb for v100 , but the pgb d90 was significantly lower compared to pmg and pa , however , the average magnitude of under dosage was small at 12.6 gy and 4.2 gy , respectively.conclusionsthis report demonstrates that similar to other reports on more delayed post - implant multisector dosimetry data , there is significant under dosage of the prostate base in the immediate post - implant period based on day 1 post - implant dosimetry . 
 the clinical significance of this under dosage remains to be defined and further studies are warranted .