• The traditional implant systems (Manchester, Quimby, and Paris) were developed
before the advent of computer-aided dosimetry for implant therapy.
• For target volumes identified intraoperatively by palpation and direct visualization, classic systems continue to guide the radiation oncologist in arranging and positioning sources relative to the target volume. They also serve as the basis of dose prescription, whether or not computer-assisted treatment planning is used.
• For all types of implants, classic systems are useful for advance planning of interstitial implants and for manually verifying postinsertion computer plans.
• An interstitial implant system consists of the following elements:
1. Distribution rules: Given a target volume, these rules determine how to distribute the radioactive sources and applicators in and around the target volume.
2. Dose-specification and implant-optimization criteria: At the heart of each system is a dose-specification criterion (definition of prescribed dose). In the Manchester or Paterson-Parker system, for example, the prescribed dose is the modal dose in the volume bounded by the peripheral sources. The distribution rules and dose-
specification criterion together constitute a compromise among implant quality indices, such as dose homogeneity within the target volume, normal tissue sparing, number of catheters implanted (amount of trauma inflicted), dosimetric margin around the target, and presence of high-dose regions outside the target.
3. Dose calculation aids: These are used to estimate the source strengths required to achieve the prescribed dose rate (as specified by the system) for source
arrangements satisfying its distribution rules. Older systems (Manchester and
Quimby) use tables that give dose delivered per mgRaEq-h as a function of treatment volume or area. The more recent Paris system makes extensive use of computerized treatment planning to relate absorbed dose to source strength and treatment time.
Manchester System
• The Manchester system, developed by Ralston Paterson and Herbert Parker (4–6), is
called the Paterson-Parker (P-P) system.
• The P-P system is the most relevant of the classic systems to the practice patterns of
North American radiation oncologists.
• Table 9-2 lists the rules of the Manchester system. Table 9-3 lists the stated dose per mgRaEq-h and integrated reference air kerma as a function of treated area or
volume.
• Figure 9-1 illustrates a classic Manchester implant with crossed ends, using iridium 192 (192Ir) line sources and 1-cm spacing to treat a cylindric target volume 5 cm in diameter and 5 cm high. The required source strength is calculated as follows: Target volume height = active needle length = 5 cm
Assume: minimum peripheral dose rate = 45 cGy/h and belt:core:end:end = 4:2:1:1
mgRaEq of each 3 cm wire = 3 · 0.317 = 1.42 mgRaEq mgRaEq of each 4.5 cm wire = 3.4 · 0.317 = 0.95 mgRaEq
• Figure 9-2 demonstrates that by increasing the interneedle spacing to 1.3 cm, the need for differential loading can be eliminated.
Because ends are uncrossed, required active length = target length/0.85 = 5.9 cm
Assuming a minimum peripheral dose rate of 45 cGy/h and belt:core = 4:2,
• Figure 9-3 illustrates application of the Manchester system to the same 5-cm × 5-cm cylindric target volume, using 192Ir ribbons with seed-to-seed spacing of 1 cm and an intercatheter spacing of 1.3 cm. Note that the distribution rules are satisfied almost exactly by using uniform seed strengths.
Equivalently, the first and last seeds can be treated as "end" seeds, bisecting the target boundaries.
• Either way, treated volume = π · (2.5)2 · 5.0 = 98.2 cm3.
By choice of spacing, distribution rules are met by using seeds of equal strength.
= 0.33 mgRaEq/seed
• Figure 9-4 illustrates application of the P-P system to a modern planar implant. As both ends are uncrossed, active length is to target length/0.92 = 5/0.81 = 6.2 cm. The shortest ribbon of active length to 6.2 cm contains 7 seeds (AL = 7 cm).
Lookup area = area treated = 4 × 7 × 0.92 = 22.7 cm2.
Note that there are 10 central seeds and 18 peripheral seeds, a ratio of 0.64:0.36, which closely approximates the recommended 2/3:1/3 ratio. For this spacing, uniform- strength seeds can be used.
Assuming a minimum peripheral dose rate of 45 cGy/h:
Fig. 9-1: A: A 5-cm high by 5-cm diameter cylindric target volume implanted with 35 differentially
loaded wires spaced at 1-cm intervals. B: Resultant central transverse and coronal isodose curves plotted as percentages of the computer-calculated mean control dose (MCD) value of 56.3 cGy per hour (100%): 110% (62 cGy per hour), 100% (56 cGy per hour), 90% (51 cGy per hour), 80% (45 cGy per hour), 60% (34 cGy per hour), 40% (23 cGy per hour), and 11% (12 cGy per hour). Note that 80% of MCD, 45 cGy per hour, agrees exactly with the minimum peripheral dose rate of 45 cGy per hour predicted by the Paterson-Parker tables. (From Williamson JF. Physics of brachytherapy. In: Perez CA, Brady LW, eds. Principles and practice of radiation oncology, 3rd ed. Philadelphia: Lippincott– Raven, 1998:405–468, with permission.)
Fig. 9-2: A 5-cm × 5-cm cylindric volume implanted by uniform strength 137Cs needles spaced at 1.3-cm intervals. (From Williamson JF. Physics of brachytherapy. In: Perez CA, Brady LW, eds. Principles and practice of radiation oncology, 3rd ed. Philadelphia: Lippincott–Raven, 1998:405–468, with permission.)
Fig. 9-3: A: A 5-cm × 5-cm cylindric target volume implanted with uniform-strength 192Ir ribbons spaced at 1.3-cm intervals. B: Resultant central transverse and coronal isodose curves normalized to the mean control dose (MCD) value of 58.9 cGy per hour (100%): 115% (68 cGy per hour), 100% (59 cGy per hour), 90% (53 cGy per hour), 80% (47 cGy per hour), 60% (35 cGy per hour), 40% (24 cGy per hour), and 20% (12 cGy per hour). Note that 80% of MCD, 47 cGy per hour, agrees closely with the minimum peripheral dose rate of 45 cGy per hour predicted by the Paterson-Parker tables. (From Williamson JF. Physics of brachytherapy. In: Perez CA, Brady LW, eds. Principles and practice of
radiation oncology, 3rd ed. Philadelphia: Lippincott–Raven, 1998:405–468, with
Fig. 9-4: A 1-cm-thick target with an area of 4 cm2 × 5 cm2 is to be treated with a single-
plane Manchester implant using 192Ir ribbons. A minimum dose rate of 45 cGy per hour is
desired, and interneedle spacing is 1.3 cm. (From Williamson JF. Physics of
brachytherapy. In: Perez CA, Brady LW, eds. Principles and practice of radiation oncology, 3rd ed. Philadelphia: Lippincott–Raven, 1998:405–468, with permission.)
Quimby System
• The Quimby system was developed by Quimby and Castro (10) at New York
Memorial Hospital between 1920 and 1940 (Table 9-4).
• This system is much less complex than the P-P system and was intended to be used
with the limited radium 226 (226Ra)–needle inventories (usually 1 mgRaEq per cm)
used in clinics in the United States during that period.
Paris System
• The Paris system was developed in the early 1960s by Pierquin, Chassange, and
Marinello (8,9) and was motivated by the 192Ir afterloading techniques developed by Henschke (8,9).
• Outside the United States, the Paris system is the most widely used approach for
definitive brachytherapy of localized lesions in the head and neck, breast, and many other sites.
Table 9-2: Manchester system characteristics
Feature Paterson and Parker (Manchester system) rules
Dose specification criterion
Effective minimum dose is 10% above the absolute minimum dose in treatment plane or volume
Dose gradient Dose in treatment volume or plane varies by no more than ±10% from
stated dose, except for localized hot spots
Linear activity Variable: 0.66 and 0.33 mgRaEq/cm
Source strength distribution
Area <25 cm2: 2/3 periphery,
1
/3 center
Planar 25 < area <100 cm2: 1/2 periphery,
1 /2 center Area >100 cm2: 1/3 periphery, 2 /3 center Source strength distribution Cylinder: belt:core:end:end = 4:2:1:1
Volume Sphere: belt:core = 6:2
Cube: 1/8 of the activity in each face
2
/8 of the activity in the core
Spacing Constant uniform spacing
Crossing needles Planar implant: Target area effectively treated is reduced in length by
10% per uncrossed end
Volume implant: Target volume effectively treated is reduced by 7.5% per uncrossed end
Elongation corrections Long:short dimension: 1.5:1.0 2:1 2.5:1.0 3:1 4:1 Correction factors for mgRaEq-h Planar: 1.025 1.05 1.07 1.09 1.12 Volume: 1.03 1.06 1.10 1.15 1.23
From Williamson JF. Physics of brachytherapy. In: Perez CA, Brady LW, eds. Principles and
practice of radiation oncology, 3rd ed. Philadelphia: Lippincott–Raven, 1998:405–468, with
permission.
Table 9-3: Manchester implant tables
Volume implants Planar implants
Volume (cm3) mgRaEq-ha 1,000 P-PR Minimum dose/IRAKb cGy/(µGy·m2) Area (cm2) mgRaEq-ha 1,000 P-PR Minimum dose/IRAKb cGy/(µGy·m2) 1 34 3.49 0 30 4.48 2 54 2.20 2 97 1.38 3 70 1.68 4 141 0.953 4 85 1.38 6 177 0.759 5 99 1.194 8 206 0.652 10 158 0.752 10 235 0.572 15 207 0.574 12 261 0.515 20 251 0.474 14 288 0.466 25 291 0.408 16 315 0.426 30 329 0.361 18 342 0.393 40 398 0.298 20 368 0.365 50 462 0.257 24 417 0.322 60 522 0.228 28 466 0.288
70 579 0.206 32 513 0.262 80 633 0.188 36 558 0.241 90 684 0.174 40 603 0.223 100 734 0.162 44 644 0.209 110 782 0.152 48 685 0.196 120 829 0.143 52 725 0.185 140 919 0.129 56 762 0.176 160 1,005 0.118 60 800 0.168 180 1,087 0.110 64 837 0.160 200 1,166 0.102 68 873 0.154 220 1,242 0.0958 72 908 0.148 240 1,316 0.0904 76 945 0.142 260 1,389 0.0857 80 981 0.137 280 1,459 0.0815 84 1,016 0.132 300 1,528 0.0779 88 1,052 0.128 320 1,595 0.0746 92 1,087 0.124 340 1,661 0.0716 96 1,122 0.120 360 1,725 0.0690 100 1,155 0.116 380 1,788 0.0665 120 1,307 0.103 400 1,851 0.0643 140 1,463 0.0918 — — — 160 1,608 0.0835 — — — 180 1,746 0.0769 — — — 200 1,880 0.0715 — — — 220 2,008 0.0669 — — — 240 2,132 0.0630 — — — 260 2,256 0.0595 — — — 280 2,372 0.0566 — — — 300 2,495 0.0538
1,000 P-PR, 1,000 Manchester system roentgens; IRAK, integrated reference air-kerma.
a
Original Manchester values from Paterson R, Parker HM. A dosage system for interstitial
radium therapy. Br J Radiol 1938;11:313–339, with permission.
b
Modified from original values for 192Ir, assuming 8.6 Gy minimum peripheral dose per 1,000
P-PR and 7.227 µGy·m2/mgRaEq-h.
From Williamson JF. Physics of brachytherapy. In: Perez CA, Brady LW, eds. Principles and
practice of radiation oncology, 3rd ed. Philadelphia: Lippincott–Raven, 1998:405–468, with
permission.
Table 9-4: Quimby system characteristics
Feature Quimby system rules
Dose and dose rate 5,000–6,000 R in 3–4 days (60–70 R/h).
Dose specification criterion
Planar implants/molds: The point 5 mm from the needle plane along the perpendicular line passing through the center of the source array.
Volume implant: Dose appears to be delivered to a point located 3–5 mm outside implanted volume near the peripheral needle tips.
Dose gradient Large central high-dose regions are characteristic of volume
implants, whereas planar implants underdose the edges of the target area relative to the stated dose.
Linear activity Constant (1.0 mgRaEq/cm used historically; 0.5 mgRaEq/cm
commonly used). Activity distribution:
planar and volume
Identical strength needles spaced uniformly throughout target area or volume.
Spacing Preferably 1.5 cm and for seeds not less than 1 cm.
Crossing needles Planar: not clear.
Volume: If not used, active ends should extend beyond target volume margin by 7.5%.
Elongation corrections
Planar: not used.
Volume: Use Manchester system corrections.
From Williamson JF. Physics of brachytherapy. In: Perez CA, Brady LW, eds. Principles and
practice of radiation oncology, 3rd ed. Philadelphia: Lippincott–Raven, 1998:405–468, with
permission.