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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

Skin Dmax(A) and rib Dmax(B) variation due to positioning uncertainty ranging from –4 mm to +4 mm. The 49 data in the reference plans were ranked and categorized into low dose (25 data) and high dose (24 data) groups. The individual line graph shows each patient data points for low dose group (left panel) and high dose group (right panel), respectively. For each patient, solid line is used if the average modulus of change (∣ΔValue∣) is > 3% while dash line is used in case of ∣ΔValue∣ ≤ 3%
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Figure 0003: Skin Dmax(A) and rib Dmax(B) variation due to positioning uncertainty ranging from –4 mm to +4 mm. The 49 data in the reference plans were ranked and categorized into low dose (25 data) and high dose (24 data) groups. The individual line graph shows each patient data points for low dose group (left panel) and high dose group (right panel), respectively. For each patient, solid line is used if the average modulus of change (∣ΔValue∣) is > 3% while dash line is used in case of ∣ΔValue∣ ≤ 3%

Mentions: When it comes to presenting group data, if most data in a group show a trend for change (i.e., decrease), descriptive statistics of the group is useful to show the trend. Hence, statistical box graphs were used to show a trend of deviation of PTV_EVAL D95, V100, and V90 (Figure 1), and normal breast tissue V200 values (Figure 2). On contrast, if each individual datum is case-specific within the group, the variation of individual datum cannot be shown with group statistics. Positive and negative deviations can be cancelled each other when grouping the individual data. Therefore, individual line graphs were employed to show individual variations of skin and rib Dmax (Figure 3). To avoid the cancellation between positive and negative changes within a simulation group, particularly for skin and rib Dmax values and normal breast tissue V150 values, absolute variation (modulus of change: ∣(ΔValue)∣ = ∣(ValueSimulation – ValueReference)∣) was also investigated between 8 simulation groups.


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

Kim Y - J Contemp Brachytherapy (2015)

Skin Dmax(A) and rib Dmax(B) variation due to positioning uncertainty ranging from –4 mm to +4 mm. The 49 data in the reference plans were ranked and categorized into low dose (25 data) and high dose (24 data) groups. The individual line graph shows each patient data points for low dose group (left panel) and high dose group (right panel), respectively. For each patient, solid line is used if the average modulus of change (∣ΔValue∣) is > 3% while dash line is used in case of ∣ΔValue∣ ≤ 3%
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 0003: Skin Dmax(A) and rib Dmax(B) variation due to positioning uncertainty ranging from –4 mm to +4 mm. The 49 data in the reference plans were ranked and categorized into low dose (25 data) and high dose (24 data) groups. The individual line graph shows each patient data points for low dose group (left panel) and high dose group (right panel), respectively. For each patient, solid line is used if the average modulus of change (∣ΔValue∣) is > 3% while dash line is used in case of ∣ΔValue∣ ≤ 3%
Mentions: When it comes to presenting group data, if most data in a group show a trend for change (i.e., decrease), descriptive statistics of the group is useful to show the trend. Hence, statistical box graphs were used to show a trend of deviation of PTV_EVAL D95, V100, and V90 (Figure 1), and normal breast tissue V200 values (Figure 2). On contrast, if each individual datum is case-specific within the group, the variation of individual datum cannot be shown with group statistics. Positive and negative deviations can be cancelled each other when grouping the individual data. Therefore, individual line graphs were employed to show individual variations of skin and rib Dmax (Figure 3). To avoid the cancellation between positive and negative changes within a simulation group, particularly for skin and rib Dmax values and normal breast tissue V150 values, absolute variation (modulus of change: ∣(ΔValue)∣ = ∣(ValueSimulation – ValueReference)∣) was also investigated between 8 simulation groups.

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