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Dosimetric impact of source-positioning uncertainty in high-dose-rate balloon brachytherapy of breast cancer.

Kim Y - J Contemp Brachytherapy (2015)

Bottom Line: PTV_EVAL dosimetry deteriorated with larger average/maximum reduction (from ± 1 mm to ± 4 mm) for larger source position uncertainty (p value < 0.0001): from 1.0%/2.5%, 3.3%/5.9%, 6.3%/10.0% to 9.8%/14.5% for D95; from 1.0%/2.6%, 3.1%/5.7%, 5.8%/8.9% to 8.7%/12.3% for V100; from 0.2%/1.5%, 1.0%/4.0%, 2.7%/6.8% to 5.1%/10.3% for V90. ≥ ± 3 mm shift reduced average D95 to < 95% and average V100 to < 90%.While skin and rib Dmax change was case-specific, its absolute change (∣Δ(Value)∣) showed that larger shift and high dose group had larger variation compared to smaller and lower dose group (p value < 0.0001), respectively.In this case, sufficient dosimetric planning margins are required.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, The University of Arizona, Tucson, AZ, USA.

ABSTRACT

Purpose: To evaluate the dosimetric impact of source-positioning uncertainty in high-dose-rate (HDR) balloon brachytherapy of breast cancer.

Material and methods: For 49 HDR balloon patients, each dwell position of catheter(s) was manually shifted distally (+) and proximally (-) with a magnitude from 1 to 4 mm. Total 392 plans were retrospectively generated and compared to corresponding clinical plans using 7 dosimetric parameters: dose (D95) to 95% of planning target volume for evaluation (PTV_EVAL), and volume covered by 100% and 90% of the prescribed dose (PD) (V100 and V90); skin and rib maximum point dose (Dmax); normal breast tissue volume receiving 150% and 200% of PD (V150 and V200).

Results: PTV_EVAL dosimetry deteriorated with larger average/maximum reduction (from ± 1 mm to ± 4 mm) for larger source position uncertainty (p value < 0.0001): from 1.0%/2.5%, 3.3%/5.9%, 6.3%/10.0% to 9.8%/14.5% for D95; from 1.0%/2.6%, 3.1%/5.7%, 5.8%/8.9% to 8.7%/12.3% for V100; from 0.2%/1.5%, 1.0%/4.0%, 2.7%/6.8% to 5.1%/10.3% for V90. ≥ ± 3 mm shift reduced average D95 to < 95% and average V100 to < 90%. While skin and rib Dmax change was case-specific, its absolute change (∣Δ(Value)∣) showed that larger shift and high dose group had larger variation compared to smaller and lower dose group (p value < 0.0001), respectively. Normal breast tissue V150 variation was case-specific and small. Average ∣Δ(V150)∣ was 0.2 cc for the largest shift (± 4 mm) with maximum < 1.7 cc. V200 was increased with higher elevation for larger shift: from 6.4 cc/9.8 cc, 7.0 cc/10.1 cc, 8.0 cc/11.3 cc to 9.2 cc/ 13.0 cc.

Conclusions: The tolerance of ± 2 mm recommended by AAPM TG 56 is clinically acceptable in most clinical cases. However, special attention should be paid to a case where both skin and rib are located proximally to balloon, and the orientation of balloon catheter(s) is vertical to these critical structures. In this case, sufficient dosimetric planning margins are required.

No MeSH data available.


Related in: MedlinePlus

Schematic diagrams for three possible geometries of skin and rib relative to the single lumen MammoSite® balloon. Eight rectangles inside the balloon represent eight possible dwell positions for an 192Ir source along the catheter. A) Balloon is located more than 1 cm away from the volume of (skin –5 mm) and pectoralis muscles. The shape of PTV_EVAL is a spherical shell with 1 cm thickness denoted with gray color. B) Skin spacing is less than 0.7 cm and the volume of (skin –5 mm) is excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding the cap in skin side. C) The (rib + pectoralis muscle) spacing is also less than 0.7 cm and the volume is also excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding both caps in skin and rib sides. In all diagrams, two extreme balloon insertion orientations are displayed: one is vertical “Orient (V)” and the other is parallel “Orient (P)” to the skin and rib
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Figure 0004: Schematic diagrams for three possible geometries of skin and rib relative to the single lumen MammoSite® balloon. Eight rectangles inside the balloon represent eight possible dwell positions for an 192Ir source along the catheter. A) Balloon is located more than 1 cm away from the volume of (skin –5 mm) and pectoralis muscles. The shape of PTV_EVAL is a spherical shell with 1 cm thickness denoted with gray color. B) Skin spacing is less than 0.7 cm and the volume of (skin –5 mm) is excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding the cap in skin side. C) The (rib + pectoralis muscle) spacing is also less than 0.7 cm and the volume is also excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding both caps in skin and rib sides. In all diagrams, two extreme balloon insertion orientations are displayed: one is vertical “Orient (V)” and the other is parallel “Orient (P)” to the skin and rib

Mentions: Schematic diagrams in Figure 4 depict three representative clinical cases for single lumen MammoSite® balloon applicator depending upon the minimal distances from the balloon to the skin/rib structures (skin spacing and rib spacing): (A) both spacings ≥ 0.7 cm; (B) either spacing (particularly, skin spacing in this example) < 0.7 cm; (C) both spacings < 0.7 cm. In Case (A), an optimal dose distribution can be obtained with eight available dwell positions, comforming to the outer surface of spherical shell. Skin and rib Dmax values are less than the prescribed dose because both spacings are > 1 cm. In Case (B), skin Dmax is more than the prescribed dose due to skin spacing of < 0.7 cm. It can be reduced to less than the prescribed dose if MLB applicator is used. In Case (C), both skin and rib Dmax would be higher than the prescribed dose due to < 0.7 cm of skin and rib spacings. Both Dmax values can be reduced using MLB applicator and dose distribution may be ellipsoidal shape, conforming to the outer surface of PTV_EVAL (grey color in Figure 4C). However, even though MLB is able to reduce OARs dose with multi-lumen, the dose shaping capability is highly limited if the orientation of balloon insertion is vertical to the OARs: Orient (V) in Figure 4B and 4C. All outer lumens are perpendicular to skin and rib and the minimal distances from each outer lumen to OARs is the same. Therefore, the best orientation of balloon insertion is parallel to the skin and rib: Orient (P) in Figure 4 in order to maximize the dose shaping capability of MLB applicator.


Dosimetric impact of source-positioning uncertainty in high-dose-rate balloon brachytherapy of breast cancer.

Kim Y - J Contemp Brachytherapy (2015)

Schematic diagrams for three possible geometries of skin and rib relative to the single lumen MammoSite® balloon. Eight rectangles inside the balloon represent eight possible dwell positions for an 192Ir source along the catheter. A) Balloon is located more than 1 cm away from the volume of (skin –5 mm) and pectoralis muscles. The shape of PTV_EVAL is a spherical shell with 1 cm thickness denoted with gray color. B) Skin spacing is less than 0.7 cm and the volume of (skin –5 mm) is excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding the cap in skin side. C) The (rib + pectoralis muscle) spacing is also less than 0.7 cm and the volume is also excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding both caps in skin and rib sides. In all diagrams, two extreme balloon insertion orientations are displayed: one is vertical “Orient (V)” and the other is parallel “Orient (P)” to the skin and rib
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663215&req=5

Figure 0004: Schematic diagrams for three possible geometries of skin and rib relative to the single lumen MammoSite® balloon. Eight rectangles inside the balloon represent eight possible dwell positions for an 192Ir source along the catheter. A) Balloon is located more than 1 cm away from the volume of (skin –5 mm) and pectoralis muscles. The shape of PTV_EVAL is a spherical shell with 1 cm thickness denoted with gray color. B) Skin spacing is less than 0.7 cm and the volume of (skin –5 mm) is excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding the cap in skin side. C) The (rib + pectoralis muscle) spacing is also less than 0.7 cm and the volume is also excluded from the spherical shell. Hence, the shape of PTV_EVAL is a spherical shell excluding both caps in skin and rib sides. In all diagrams, two extreme balloon insertion orientations are displayed: one is vertical “Orient (V)” and the other is parallel “Orient (P)” to the skin and rib
Mentions: Schematic diagrams in Figure 4 depict three representative clinical cases for single lumen MammoSite® balloon applicator depending upon the minimal distances from the balloon to the skin/rib structures (skin spacing and rib spacing): (A) both spacings ≥ 0.7 cm; (B) either spacing (particularly, skin spacing in this example) < 0.7 cm; (C) both spacings < 0.7 cm. In Case (A), an optimal dose distribution can be obtained with eight available dwell positions, comforming to the outer surface of spherical shell. Skin and rib Dmax values are less than the prescribed dose because both spacings are > 1 cm. In Case (B), skin Dmax is more than the prescribed dose due to skin spacing of < 0.7 cm. It can be reduced to less than the prescribed dose if MLB applicator is used. In Case (C), both skin and rib Dmax would be higher than the prescribed dose due to < 0.7 cm of skin and rib spacings. Both Dmax values can be reduced using MLB applicator and dose distribution may be ellipsoidal shape, conforming to the outer surface of PTV_EVAL (grey color in Figure 4C). However, even though MLB is able to reduce OARs dose with multi-lumen, the dose shaping capability is highly limited if the orientation of balloon insertion is vertical to the OARs: Orient (V) in Figure 4B and 4C. All outer lumens are perpendicular to skin and rib and the minimal distances from each outer lumen to OARs is the same. Therefore, the best orientation of balloon insertion is parallel to the skin and rib: Orient (P) in Figure 4 in order to maximize the dose shaping capability of MLB applicator.

Bottom Line: PTV_EVAL dosimetry deteriorated with larger average/maximum reduction (from ± 1 mm to ± 4 mm) for larger source position uncertainty (p value < 0.0001): from 1.0%/2.5%, 3.3%/5.9%, 6.3%/10.0% to 9.8%/14.5% for D95; from 1.0%/2.6%, 3.1%/5.7%, 5.8%/8.9% to 8.7%/12.3% for V100; from 0.2%/1.5%, 1.0%/4.0%, 2.7%/6.8% to 5.1%/10.3% for V90. ≥ ± 3 mm shift reduced average D95 to < 95% and average V100 to < 90%.While skin and rib Dmax change was case-specific, its absolute change (∣Δ(Value)∣) showed that larger shift and high dose group had larger variation compared to smaller and lower dose group (p value < 0.0001), respectively.In this case, sufficient dosimetric planning margins are required.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, The University of Arizona, Tucson, AZ, USA.

ABSTRACT

Purpose: To evaluate the dosimetric impact of source-positioning uncertainty in high-dose-rate (HDR) balloon brachytherapy of breast cancer.

Material and methods: For 49 HDR balloon patients, each dwell position of catheter(s) was manually shifted distally (+) and proximally (-) with a magnitude from 1 to 4 mm. Total 392 plans were retrospectively generated and compared to corresponding clinical plans using 7 dosimetric parameters: dose (D95) to 95% of planning target volume for evaluation (PTV_EVAL), and volume covered by 100% and 90% of the prescribed dose (PD) (V100 and V90); skin and rib maximum point dose (Dmax); normal breast tissue volume receiving 150% and 200% of PD (V150 and V200).

Results: PTV_EVAL dosimetry deteriorated with larger average/maximum reduction (from ± 1 mm to ± 4 mm) for larger source position uncertainty (p value < 0.0001): from 1.0%/2.5%, 3.3%/5.9%, 6.3%/10.0% to 9.8%/14.5% for D95; from 1.0%/2.6%, 3.1%/5.7%, 5.8%/8.9% to 8.7%/12.3% for V100; from 0.2%/1.5%, 1.0%/4.0%, 2.7%/6.8% to 5.1%/10.3% for V90. ≥ ± 3 mm shift reduced average D95 to < 95% and average V100 to < 90%. While skin and rib Dmax change was case-specific, its absolute change (∣Δ(Value)∣) showed that larger shift and high dose group had larger variation compared to smaller and lower dose group (p value < 0.0001), respectively. Normal breast tissue V150 variation was case-specific and small. Average ∣Δ(V150)∣ was 0.2 cc for the largest shift (± 4 mm) with maximum < 1.7 cc. V200 was increased with higher elevation for larger shift: from 6.4 cc/9.8 cc, 7.0 cc/10.1 cc, 8.0 cc/11.3 cc to 9.2 cc/ 13.0 cc.

Conclusions: The tolerance of ± 2 mm recommended by AAPM TG 56 is clinically acceptable in most clinical cases. However, special attention should be paid to a case where both skin and rib are located proximally to balloon, and the orientation of balloon catheter(s) is vertical to these critical structures. In this case, sufficient dosimetric planning margins are required.

No MeSH data available.


Related in: MedlinePlus