A novel curvilinear approach for prostate seed implantation

A novel curvilinear approach for prostate seed implantation

Tarun K. Poddera)

Department of Radiation Oncology, Leo Jenkins Cancer Center, Brody School of Medicine, East Carolina
University, Greenville, North Carolina 27834

Adam P. Dicker

Department of Radiation Oncology, Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson
University, Philadelphia, Pennsylvania 19107

Parsaoran Hutapea and Kurosh Darvish

Department of Mechanical Engineering, Temple University, Philadelphia, Pennsylvania 19122

Yan Yu

Department of Radiation Oncology, Kimmel Cancer Center, Jefferson Medical College, Thomas Jefferson
University, Philadelphia, Pennsylvania 19107

(Received 3 January 2012; revised 17 February 2012; accepted for publication 27 February 2012;
published 15 March 2012)

Purpose: A new technique called “curvilinear approach” for prostate seed implantation has been
proposed. The purpose of this study is to evaluate the dosimetric benefit of curvilinear distribution
of seeds for low-dose-rate (LDR) prostate brachytherapy.
Methods: Twenty LDR prostate brachytherapy cases planned intraoperatively with VariSeed plan-
ning system and I-125 seeds were randomly selected as reference rectilinear cases. All the cases
were replanned by using curved-needle approach keeping the same individual source strength and
the volume receiving 100% of prescribed dose 145 Gy (V100). Parameters such as number of nee-
dles, seeds, and the dose coverage of the prostate (D90, V150, V200), urethra (D30, D10) and rectum
(D5, V100) were compared for the rectilinear and the curvilinear methods. Statistical significance
was assessed using two-tailed student’s t-test.
Results: Reduction of the required number of needles and seeds in curvilinear method were 30.5%
(p < 0.001) and 11.8% (p < 0.49), respectively. Dose to the urethra was reduced significantly; D30
reduced by 10.1% (p < 0.01) and D10 reduced by 9.9% (p < 0.02). Reduction in rectum dose D5
was 18.5% (p < 0.03) and V100 was also reduced from 0.93 cc in rectilinear to 0.21 cc in curvilinear
(p < 0.001). Also the V150 and V200 coverage of prostate reduced by 18.8% (p < 0.01) and 33.9%
(p < 0.001), respectively.
Conclusions: Significant improvement in the relevant dosimetric parameters was observed in cur-
vilinear needle approach. Prostate dose homogeneity (V150, V200) improved while urethral dose
was reduced, which might potentially result in better treatment outcome. Reduction in rectal dose
could potentially reduce rectal toxicity and complications. Reduction in number of needles would
minimize edema and thereby could improve postimplant urinary incontinence. This study indicates
that the curvilinear implantation approach is dosimetrically superior to conventional rectilinear im-
plantation technique. VC 2012 American Association of Physicists in Medicine.
[http://dx.doi.org/10.1118/1.3694110]

Key words: prostate cancer, radioactive seed implantation, curvilinear method, prostate brachyther-
apy, dose distribution

I. INTRODUCTION tum should be minimal without compromising required dose

Low-dose-rate (LDR) brachytherapy is one of the most effec- coverage to the prostate.
tive treatment modalities for early stage prostate cancer.1–9
Treatment outcome greatly depends on the quality of the radi- More than 70% of the tumor foci are located in the periph-
oactive seed implantation including technique used, needle eral zone of the prostate.10,11 However, insertion of a needle
placement accuracy, seed delivery accuracy, and dose distri-
bution. However, anatomy of the prostate having centrally in the peripheral zone is challenging due to the difficulty in
located urethra demands that the radioactive seeds be distrib-
uted peripherally for prescribed dose coverage to the prostate puncturing prostate capsule away from central axis (Fig. 1),
and minimal dose to the urethra. Additionally, dose to the rec-
increased needle obliquity angle, inadequacy/non rigidity in

supporting of the prostate, and single point proximal-end
actuation of a long slender needle.3 Additionally, the anterior

midgland and base of the prostate can be inadequately
treated12 and analyzed because of the difficulty in placing

1887 Med. Phys. 39 (4), April 2012 0094-2405/2012/39(4)/1887/6/$30.00 VC 2012 Am. Assoc. Phys. Med. 1887

1888 Podder et al.: Curvilinear seed implantation 1888

FIG. 1. Ultrasound (U/S) images showing prostate deformation in capsule puncturing and insertion taken during prostate brachytherapy procedure in the opera-
tion room. White vertical line (marked I) is the reference line for initial position of the prostate apex, vertical dotted line (marked as III) is position of the cap-
sule at needle insertion location; with respect to this line one can observe the prostate deformation during (b) is about 22 mm, and after (c) needle puncturing
the capsule the deformation is about 12 mm. Moreover, the needle has deflected laterally about 4 mm (horizontal dotted and solid lines, marked as IV–V).

conventional needles at the desired location for collecting strated a significant effect on the risk of urinary obstructive
symptoms.19 The range of edema has been nicely summarized
required biopsy samples. Some of the issues can be eliminated in the report of the AAPM TG-137.20 Keyes et al. have
reported that over the course of their program, they deliber-
by developing a new type of needle which could be placed ately reduced the number of needles and operating room (OR)
time per patient, which potentially minimized intraoperative
more conformably according to the shape of the prostate trauma and might contribute to less toxicity.21 Eapen et al.
reported that needle-induced prostate trauma during brachy-
gland (Fig. 2). therapy contributed to acute urinary toxicity and suggested
the need to minimize the manipulation of needles with peri-
Moreover, Kao et al. reported that patients with a mini- urethral trajectories.22 Shah and Ennis investigated the effect
of number of needles used and associated rectal toxicities,
mum D90 of 180 Gy had outstanding local control and toxic- i.e., acute diarrhea toxicity.23 They observed that higher rate
ity profiles, particularly for long-term urinary and sexual of acute diarrhea with use of more needles might have been
function.13 Pin˜a et al. has reported that a D90 of 180 Gy is due to more trauma sustained near the anterior rectal wall
associated with excellent biochemical disease-free survival from those needles used for implanting the posterior prostate,
and acceptable toxicity.14 Stock et al. pointed out that factors causing potentially more postimplant edema in this region
with resultant diarrhea. Therefore, it appears that reductions
associated with more precise implantation, decreased post- in number of needles used or needle manipulation are impor-
tant for prostate brachytherapy. Investigators have suggested
implant edema, new technology/technique, and increased that urethral D10 dose is predictive for patients at higher risk
number of seeds would lead to higher D90 values.15 How- of urinary incontinence. To decrease the risk of this complica-
ever, higher D90 may be associated with higher doses to criti- tion, an effort should be made to keep the urethral D10 dose as
cal structures such as urethra, rectum, and neurovascular close to the prescribed dose as possible.16,24

bundle. Therefore, dose distribution should be evaluated cau- We are developing flexible needle that will be capable of
being curved to conform the prostate geometry [Fig. 2(b)].
tiously while increasing D90 value. In the proposed approach using new type of needles the
Another important factor is prostate edema16–20 which is insertion would be close to the central axis of the prostate

proportional to the number of needle insertion/manipulation

and number of needle used. Waterman et al. investigated

extensively the effects of edema on dose distribution using
125I and 103Pd seeds, and suggested to incorporate these
effects in dosimetric plans.16,17 Kehwar et al. have suggested

that the effect of edema must be accounted for when defining

the seed positions, to avoid the possibility of poor dosimetric
and radiobiologic results for 131Cs seed implants.18 Bucci

et al. reported that the amount of postimplant edema demon-

FIG. 2. Accessing various parts of the prostate—(a) conventional rectilinear approach of prostate brachytherapy needle insertion pattern with straight needles
requiring 7 needles (note that the patient must be set up in the OR in the lithotomy position) and (b) proposed curvilinear conformal smart needle insertion
requiring 4 needles (in any convenient needle entry orientation).

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1889 Podder et al.: Curvilinear seed implantation 1889

FIG. 3. The LoBS (left) and LaBS (right) smart needle design.

and thus the peripheral insertion of manipulation needle needle body segment-1 can be actuated so that force which
would be reduced [Fig. 2(b)]. In this current study, the dosi- will produce moment about the opposite point. Therefore, by
metric potentials of curvilinear distribution of seeds are com- manipulating the force the amount of needle curvature can
pared with conventional rectilinear distribution of seeds. be controlled. By rotating the needle at desired angle, any
needle trajectory can be achieved for reaching the target
II. MATERIALS AND METHODS while avoiding obstacles (or critical organ) and conforming
organ geometry. The self-actuating smart needling system is
In conventional LDR brachytherapy approach, seeds are under development and is not the focus of this study. In this
delivered in prostate through needles inserted rectilinearly study, the dosimetric benefits for a rectilinear distribution of
with limited flexibility and maneuverability [Fig. 2(a)]. We radioactive sources for prostate brachytherapy have been
are developing a new type of flexible self actuated “smart” investigated.
needle which will be able to be inserted close to central loca-
tion and then bent to conform the prostate geometry as A total of twenty LDR prostate brachytherapy cases used
shown in Fig. 2(b). This will potentially reduce the required clinically were randomly selected as reference rectilinear
number of needle as well as eliminate the difficulties in pe- cases. These cases were planned intra-operatively with Vari-
ripheral needle placement as done conventionally [Figs. 1 Seed version7.2 using I-125 seeds (STM-1251 model). All the
and 2(a)]. cases were replanned by using curved-needles approach keep-
ing the same individual seed’s activity and volume receiving
The objective of our ongoing work is to design a new dis- 100% of prescribed dose 145Gy (V100). The air-kerma
tributed actuation system along the needle’s body (active/ strength of the used seeds ranged from 0.61 to 0.85 U and av-
smart needling), exploiting the steering advantage of the erage was 0.67 U (per seed; 1 U ¼ 1 lGy m2/h). The dosimet-
bevel-tip geometry (bevel angle), developing a flexible nee- ric plans were planned by the same physicist to minimize the
dle body having sensors at the needle tip and along the body interperson variability. Parameters such as number of total
for real-time tracking/detection of the needle using a feed- needle, number of total seeds (or total strength), and dose cov-
back closed-loop control for real-time steering of the needle erage of prostate (D90, V100, V150, V200), urethra (D10, D30)
toward the target. We are currently developing two types of and rectum (D5, V100 in cm3) were evaluated.19 Statistical sig-
needle design and actuation techniques: Longitudinal body nificances were assessed using two-tailed student’s t-test and
segment (LoBS) design and lateral body segment (LaBS) p-values less than 5% were considered significant.
design (see Fig. 3).25
III. RESULTS
For LoBS design, the needle is separated into multiple
segments along its length to improve maneuverability of the Remarkable benefits of curvilinear approach as compared
needle tip. This device incorporates four Nitinol wires per with rectilinear approach were observed (Table I). Signifi-
segment along its tubular substructure. The ends of each cant improvement was observed in almost all studied param-
wire are secured to anchors, which are attached to non con- eters for curvilinear approach. For the same dosimetric
ducting collets. The displacement and the speed of actuation coverage of the prostate (V100 ¼ 99.9%), average reductions
is a function of the power supplied to each Nitinol wire. in required number of needles and seeds (or activity) were
Bending in arbitrary directions can be accomplished by 30.5% (p < 0.001) and 11.8% (p ¼ 0.49), respectively for the
adjusting the electrical duty cycles of the Nitinol wires. For curvilinear approach. The p-value for reduction of seeds was
LaBS design, the needle body is made of Nitinol having lat- not statistically significant. It is not very critical to reduce
eral segments (two or multiple of paired segments along the number of seeds or total activity, provided all other relevant
needle length). Each segment is an actuator made of Nitinol, dosimetric criteria are satisfied. More conformal placement
which will be capable of manipulating the needle tip, accord- of needles and seeds translated in a reduction in urethral
ing to the sensory feedback information. The distal end of doses, D10 by 20.7Gy (9.9%, p < 0.02) and D30 by 20.8 Gy
the actuator segments of the needle body are hinged at dif- (10.1%, p < 0.01). Prostate dose homogeneities were
ferent points when the needle needs to be curved down the

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1890 Podder et al.: Curvilinear seed implantation 1890

TABLE I. Comparison of proposed curvilinear approach and conventional rectilinear approach. p-value
(two-tailed)
Parameter Rectilinear method Curvilinear method Difference
(n ¼ 20) Average 6 SD (range) Average 6 SD (range) < 0.001
À6.0 (À30.5%) < 0.49
Total needle 19.2 6 2.6 (14–23) 13.2 6 1.4 (10–15) À7.4 (À11.8%) < 0.37
Total seed 62.5 6 11.2 (43–85) 55.1 6 10.4 (38–74) À4.5 (À11.8%)
Total activity (mCi) 38.3 6 6.3 (28.3–47.3) 33.8 6 4.9 (25.3–40.3) < 0.04
À15.4 (À7.8%) < 0.85
Prostate (average ¼ 41.3 cm3, range ¼ 26.6–53.2 cm3): 183.3 6 6.8 (176.3–194.5) À0.01 (À0.01%) < 0.01
99.97 6 0.06 (99.83–100) À15.2 (À18.8%) < 0.001
D90 (Gy) 198.7 6 9.9 (182.9–215.2) À14.8 (À33.9%)
V100 (cm3) 99.98 6 0.06 (99.8–100) 65.7 6 5.3 (57.8–75.9) < 0.02
V150 (cm3) 80.9 6 6.8 (68.5–89.8) 28.9 6 3.3 (26.0–35.5) À20.7 (À9.9%) < 0.01
V200 (cm3) 43.7 6 6.0 (32.7–53.4) À20.8 (À10.1%)
189.2 6 8.1 (178.3–208.8) < 0.03
Urethra: 209.9 6 12.2 (186.2–228.7) 184.3 6 7.4 (172.5–200.2) À29.7 (À18.5%) < 0.001
D10 (Gy) 205.1 6 10.4 (184.3–219.9) À0.72 (À77.8%)
D30 (Gy) 130.5 6 12.3 (111.0–151.1)
0.21 6 0.17 (0.03–0.61)
Rectum: 160.2 6 15.9 (137.9–196.8)
0.93 6 0.51 (0.19–2.0)
D5 (Gy)
V100 (cm3)

improved; V150, reduced by 18.8% (p < 0.01) and V200 tional rectilinear approach. Large reduction of number of
reduced by 33.9% (p < 0.001). The average rectal dose needles (about 30%) would potentially reduce the edema as
(V100) reduced from 0.93 cm3 in rectilinear to 0.21 cm3 in well as the associated urinary incontinence. Prostate dose ho-
curvilinear (77.8%, p < 0.001) and D5 reduced from 160.2 mogeneity (V150, V200) improved while urethral doses (D10
Gy in rectilinear to 130.5 Gy in curvilinear (18.5%, and D30) reduced by about 10%. Although the doses to
p < 0.03). The cumulative dose-volume-histogram (DVH) rectum were within acceptable limits (V100 ¼ 0.93 cm3,
and three views (sagittal, transversal, and coronal) of the D5 ¼ 160 Gy), further reduction in rectal doses (V100
dose distribution of a representative case have been pre- ¼ 0.21 cm3, D5 ¼ 130.5 Gy) may potentially reduce rectal
sented in Figs. 4 and 5. toxicity and complications.

IV. DISCUSSION Overall, this study indicated that clinical implementation
of the proposed smart needle may potentially improve radia-
A significant reduction was observed in almost all studied tion dose distribution and reduce dose to critical organs and
parameters for curvilinear approach as compared to conven- thereby would potentially improve quality of life and sur-
vival of the prostate cancer patients.

FIG. 4. Dose-volume-histogram (DVH) of prostate, urethra and rectum in (a) conventional rectilinear implantation (dotted lines) and (b) proposed curvilinear
implantation (solid lines).

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1891 Podder et al.: Curvilinear seed implantation 1891

FIG. 5. Sagittal, axial/ transversal and coronal views of the isodose lines (outer continuous thin line indicates the prescribed isodose line; cc implies cm3).

V. CONCLUSIONS cant improvement in almost all the dosimetric parameters
for curvilinear approach was noticed. Prostate dose homoge-
The new curvilinear needle approach can enhance dose neity improved while urethral dose is reduced, which would
conformality to the prostate. Consequently, reduction in the potentially result in better treatment. Considerable reduction
number of needles can minimize edema and thereby may in rectal dose would potentially reduce rectal toxicity and
improve urethra toxicities, and treatment outcome. Signifi- complications. This study indicates that the curvilinear

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1892 Podder et al.: Curvilinear seed implantation 1892

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