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Role of step size and max dwell time in anatomy based inverse optimization for prostate implants.

Manikandan A, Sarkar B, Rajendran VT, King PR, Sresty NV, Holla R, Kotur S, Nadendla S - J Med Phys (2013)

Bottom Line: No appreciable difference in plan quality was observed with variation in maximum source dwell time.The step size plays a significant role in plan optimization for prostate implants.Our study supports use of a 0.5 cm step size for prostate implants.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, Indo American Cancer Hospital and Research Centre, Hyderabad, Andhra Pradesh, India.

ABSTRACT
In high dose rate (HDR) brachytherapy, the source dwell times and dwell positions are vital parameters in achieving a desirable implant dose distribution. Inverse treatment planning requires an optimal choice of these parameters to achieve the desired target coverage with the lowest achievable dose to the organs at risk (OAR). This study was designed to evaluate the optimum source step size and maximum source dwell time for prostate brachytherapy implants using an Ir-192 source. In total, one hundred inverse treatment plans were generated for the four patients included in this study. Twenty-five treatment plans were created for each patient by varying the step size and maximum source dwell time during anatomy-based, inverse-planned optimization. Other relevant treatment planning parameters were kept constant, including the dose constraints and source dwell positions. Each plan was evaluated for target coverage, urethral and rectal dose sparing, treatment time, relative target dose homogeneity, and nonuniformity ratio. The plans with 0.5 cm step size were seen to have clinically acceptable tumor coverage, minimal normal structure doses, and minimum treatment time as compared with the other step sizes. The target coverage for this step size is 87% of the prescription dose, while the urethral and maximum rectal doses were 107.3 and 68.7%, respectively. No appreciable difference in plan quality was observed with variation in maximum source dwell time. The step size plays a significant role in plan optimization for prostate implants. Our study supports use of a 0.5 cm step size for prostate implants.

No MeSH data available.


Related in: MedlinePlus

(a) Variation of planning target volume receiving 200% of prescription dose with maximum dwell time. (b) Variation of percentage PTV receiving 200% of prescription dose with maximum dwell time
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Figure 1: (a) Variation of planning target volume receiving 200% of prescription dose with maximum dwell time. (b) Variation of percentage PTV receiving 200% of prescription dose with maximum dwell time

Mentions: Mean SD of V200 for different step sizes varied from 0.16 to 1.26. Variation of V200 with step size for a given dwell time is presented in Figure 1a. The variation in V200 with the variation in maximum dwell time constraint was insignificant, as compared to the variation with step size. V200 shows a variation of 3.5-5% with the maximum dwell time variation. The treatment plan using a 40 s dwell time had a lower V200 value of 3.5%. In addition, the minimum value of mean SD of V200 was 2.3% for 40 s plans, while other plans had more than 2.6% SD. It reached the value 3.1% when the maximum dwell time was set to be 100 s. The variation of V200 and its with respect to maximum dwell time is represented in Figure 1b.


Role of step size and max dwell time in anatomy based inverse optimization for prostate implants.

Manikandan A, Sarkar B, Rajendran VT, King PR, Sresty NV, Holla R, Kotur S, Nadendla S - J Med Phys (2013)

(a) Variation of planning target volume receiving 200% of prescription dose with maximum dwell time. (b) Variation of percentage PTV receiving 200% of prescription dose with maximum dwell time
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3775040&req=5

Figure 1: (a) Variation of planning target volume receiving 200% of prescription dose with maximum dwell time. (b) Variation of percentage PTV receiving 200% of prescription dose with maximum dwell time
Mentions: Mean SD of V200 for different step sizes varied from 0.16 to 1.26. Variation of V200 with step size for a given dwell time is presented in Figure 1a. The variation in V200 with the variation in maximum dwell time constraint was insignificant, as compared to the variation with step size. V200 shows a variation of 3.5-5% with the maximum dwell time variation. The treatment plan using a 40 s dwell time had a lower V200 value of 3.5%. In addition, the minimum value of mean SD of V200 was 2.3% for 40 s plans, while other plans had more than 2.6% SD. It reached the value 3.1% when the maximum dwell time was set to be 100 s. The variation of V200 and its with respect to maximum dwell time is represented in Figure 1b.

Bottom Line: No appreciable difference in plan quality was observed with variation in maximum source dwell time.The step size plays a significant role in plan optimization for prostate implants.Our study supports use of a 0.5 cm step size for prostate implants.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiotherapy, Indo American Cancer Hospital and Research Centre, Hyderabad, Andhra Pradesh, India.

ABSTRACT
In high dose rate (HDR) brachytherapy, the source dwell times and dwell positions are vital parameters in achieving a desirable implant dose distribution. Inverse treatment planning requires an optimal choice of these parameters to achieve the desired target coverage with the lowest achievable dose to the organs at risk (OAR). This study was designed to evaluate the optimum source step size and maximum source dwell time for prostate brachytherapy implants using an Ir-192 source. In total, one hundred inverse treatment plans were generated for the four patients included in this study. Twenty-five treatment plans were created for each patient by varying the step size and maximum source dwell time during anatomy-based, inverse-planned optimization. Other relevant treatment planning parameters were kept constant, including the dose constraints and source dwell positions. Each plan was evaluated for target coverage, urethral and rectal dose sparing, treatment time, relative target dose homogeneity, and nonuniformity ratio. The plans with 0.5 cm step size were seen to have clinically acceptable tumor coverage, minimal normal structure doses, and minimum treatment time as compared with the other step sizes. The target coverage for this step size is 87% of the prescription dose, while the urethral and maximum rectal doses were 107.3 and 68.7%, respectively. No appreciable difference in plan quality was observed with variation in maximum source dwell time. The step size plays a significant role in plan optimization for prostate implants. Our study supports use of a 0.5 cm step size for prostate implants.

No MeSH data available.


Related in: MedlinePlus