Journal of Medical Physics
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Year : 2013  |  Volume : 38  |  Issue : 3  |  Page : 148-154

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

1 Department of Radiotherapy, Indo American Cancer Hospital and Research Centre, Hyderabad, Andhra Pradesh, India
2 Department of Radiotherapy, AMRI Hospitals, Kolkata, West Bengal, India
3 Department of Radiotherapy, Jupiter Hospital, Mumbai, Maharashtra, India
4 Department of Medical Physics, Anderson Regional Medical Center, Meridian, Mississippi, USA
5 Department of Medical Physics and Radiation Safety, Amrita Institute of Medical Sciences, Cochin, Kerela, India
6 Department of Radiotherapy, Inlaks and Budhrani Hospital, Pune, Maharashtra, India
7 Department of Radiotherapy, Government General Hospital, Guntur, Andhra Pradesh, India

Correspondence Address:
Arjunan Manikandan
Department of Radiotherapy, Basavatharakam Indoamerican Cancer Hospital and Research Centre, Banjara Hills, Hyderabad, Andhra Pradesh
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Source of Support: None, Conflict of Interest: None

PMID: 24049323

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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.

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