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SU‐GG‐T‐56: On the Impact of Dose Sculpting Optimization in High Resolution (3.0 Tesla) MRI‐Guided HDR Brachytherapy for GYN Cancer: For Different High Risk CTV Sizes
Author(s) -
Kim Y,
Xia J
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3468442
Subject(s) - rectum , brachytherapy , nuclear medicine , medicine , dosimetry , radiation therapy , radiology , surgery
Purpose: To quantify the impact of volume optimization (OPT), when utilizing tandem and ovoid applicators in high resolution (3.0 Tesla) MRI for different high risk (HR)‐CTV sizes. Materials and Methods: The IR (intermediate)‐ and, HR‐CTV and organs‐at‐risk (OAR; rectum, bladder, and sigmoid) were delineated for 25 HDR plans of six patients with FIGO stage Ib1‐IV cervical cancer. A conventional plan was re‐optimized using Dose‐Sculpting OPT where the D90 (HR‐CTV) was optimized to receive the prescription dose (Rx). Three subgroups were categorized according to HR‐CTV volumes; Non‐Bulky (< 20 cc), Low‐Bulky, and Bulky (≥ 40 cc). The differences in D90 (HR‐CTV), normalized to Rx, were quantified, while D2cc of the OAR, normalized to the dose limits. The values of D100 (HR‐CTV), and D90 (IR‐CTV), normalized to Rx, were quantified while the values of ICRU rectum and bladder point doses, normalized to their D2cc values. Results: For the Non‐Bulky group, Dose‐Sculpting OPT maximized the sparing without compromising the D90 (HR‐CTV). The D2cc were reduced on average −21 ± 20%, −17 ± 8%, and −20 ± 11% for rectum, the bladder, and the sigmoid while the difference in D90 (HR‐CTV) was on average −0.3 ± 1%. The differences of D90 were improved on average +13 ± 11% in the Bulky group, but only from 64% to 77%, showing that even Dose‐Sculpting OPT is limited in improving tumor coverage in the Bulky group. In the Low‐Bulky group, on average +6 ± 4% were found in D90, from 89% to 95%. However, the sigmoid sparing was improved on average −18 ± 14% for all. The doses at Point A were 78% (Non‐Bulky), 105% (Low‐Bulky), and 120% (Bulky) of Rx. Conclusion: Utilizing Dose‐Sculpting OPT, OAR sparing was significantly improved for small HR‐CTV without compromising HR‐CTV coverage. The sigmoid sparing was significantly improved for all HR‐CTV sizes.