Abstract
Treatment planning is a trial and error process that determines optimal dwell times, dose distribution, and loading pattern for high dose rate brachytherapy. Planning systems offer a number of dose calculation methods to either normalize or optimize the radiation dose. Each method has its own characteristics for achieving therapeutic dose to mitigate cancer growth without harming contiguous normal tissues. Our aim is to propose the best suited method for planning interstitial brachytherapy. 40 cervical cancer patients were randomly selected and 5 planning methods were iterated. Graphical optimization was compared with implant geometry and dose point normalization/optimization techniques using dosimetrical and radiobiological plan quality indices retrospectively. Mean tumor control probability was similar in all the methods with no statistical significance. Mean normal tissue complication probability for bladder and rectum is 0.3252 and 0.3126 (P = 0.0001), respectively, in graphical optimized plans compared to other methods. There was no significant correlation found between Conformity Index and tumor control probability when the plans were ranked according to Pearson product moment method (r = −0.120). Graphical optimization can result in maximum sparing of normal tissues.
Highlights
Cervical cancer is a major cancer burden which constitutes number one among Indian women with relative survival rate of 48.7% [1]
Homogeneity of dose distribution is higher for graphical optimization technique (Gr O) and Dose point normalization (DP N) plans which is obvious from the mean Dose Homogeneity Index (DHI) values 0.6629 and 0.6282, respectively, whereas other methods resulted in a lesser homogeneous dose inside the target (Table 1)
Overdose Volume Index (ODI) and Dose Nonuniformity Index (DNR) were less for Gr O and DP N methods
Summary
Cervical cancer is a major cancer burden which constitutes number one among Indian women with relative survival rate of 48.7% [1]. EBRT followed with brachytherapy (BT) is the standard of care and an integral part of local control of the disease. Cervix carcinoma has been treated with HDR BT for more than 30 years. It has advantages in terms of local recurrence, mortality, and late complications for the clinical stages I, II and III, similar to those of Low Dose Rate therapy [2]. The present standard of care using concomitant chemotherapy and radiotherapy has resulted in 80–90% local control rates for early stages [3,4,5]. A decline of about 67– 75% is noted for advanced stages because of the local failure due to inadequate dose coverage [6,7,8]
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