ESTRO 36 Abstract Book

S507 ESTRO 36 2017 _______________________________________________________________________________________________

same score, 36% had a better final score, and 4.4% had a worse final score. Patient age, tumor location, tumor size, number of catheters, V100 (volume receiving 100% of the prescription dose), V150 (volume receiving 150% of the prescription dose), DNR (dose non-uniformity ratio), and skin D max (maximum skin dose) were correlated with the final cosmetic scores and with the change in cosmetic scores between both photographs. Only lower DNR values (0.3 vs 0.26; p=0.009) were significantly associated with improved cosmetic outcome vs same/worse cosmetic outcome.

Results The median plane Dmax dose was 1.33 Gy (40% of 3.4Gy, range 0.24-3.74 Gy) and showed moderate correlation with grade of skin marks (0.505, p value 0.000). Similarly, the closest distance of the CTV, prescription isodose (Figure 2) and first-last dwell position was 1.74 (range 0.32-6.58), 1.09 (range 0.02-5.71) and 1.55 (range 0.25- 4.58) cm respectively all of which also showed moderate correlation (-0.444, -0.471 and -0.495 respectively, p value 0.000 for each). 70.1% (61/85) planes with Dmax <40% of prescribed dose showed invisible or faint marks and 72.1% (62/88) planes with Dmax >40% of prescribed dose showed clear or prominent marks (p = 0.001). 86.4% (19/22) planes with closest distance from CTV <0.7 cm and 91.4% (32/35) planes with closest distance from 85% Isodose < 0.5 cm showed clear or prominent marks (p = 0.001). There was very high correlation between closest distance from CTV 0.7 cm and closest distance from isodose 0.5 cm (0.715). Taking 1.33 Gy (40% of prescription dose per fraction) as a cut –off value for plane Dmax resulting in clear-prominent implant marks on ROC curve resulted in sensitivity 65% and specificity 60%.

Conclusion APBI using interstitial multicatheter HDR-IMBT adjuvant to BCS results in acceptable rates of late toxicity and cosmetic outcome. Deterioration in the breast cosmetic scores occurs in less than 5% of the patients. The final breast cosmetic outcome seems to be mainly influenced by the cosmetic result of the surgery. Lower DNR value is significantly associated with better cosmetic outcome. PO-0923 Does catheter entry-exit dosimetry correlate with grade of skin marks after breast brachytherapy? T. Wadasadawala 1 , R. Krishnamurthy 1 , U. Gayake 1 , R. Phurailatpam 1 , S. Paul 1 , R. Sarin 1 1 Actrec-Tata Memorial Centre, Radiation Oncology, Navi Mumbai, India Purpose or Objective Grade of post-implant skin marks after multi-cathetar interstitial brachytherapy (MIB) is an important factor in determining cosmesis. This study intends to establish the correlation if any between catheter entry-exit (E-E) dosimetry and grade of skin marks at the E-E sites. Material and Methods Visibility of the post implant E-E catheter marks was noted plane-wise for 25 patients (173 planes) with minimum 18 months follow-up post implant. All patients were treated with 34 Gy in 10 fractions, twice a day at minimum 6 hours apart. These were graded as 'not visible', 'faint', 'clear' and 'prominent'. Dose received by the skin at the E-E sites was calculated from the treated plans which were retrieved from the Oncentra treatment planning system (Figure 1). Dose maximum (Dmax) for each plane was determined meticulously. Closest distance of each E-E point in each plane from the respective first or last dwell position, clinical target volume (CTV) and the reference isodose (85%) was measured. Statistical analysis was done in IBM SPSS version 21. Correlation between quality of implant marks and dosimetric parameters was analyzed using Spearman’s co-efficient (single tailed). Chi square test was done between the quality of marks and plane Dmax as well as closest distances each from CTV, prescription isodose and first or last dwell position. ROC curve was used to determine dose constraints.

Conclusion This study highlights the need for minimization of dose to the skin E-E site for reducing the risk of clear or prominent skin marks which affect cosmesis. Wherever possible it is advisable to edit the CTV to maintain a safe distance between the prescription isodose from the skin E-E points. However, larger sample size needs to be studied to increase sensitivity and specificity of the E-E dose constraint. PO-0924 HDR boost in CT3 breast carcinoma with neoadjuvant chemotherapy and conserving therapy F. Romero 1 , J. Guinot 1 , M. Santos 1 , M. Tortajada 1 , P. Santamaría 1 , L. Oliver 1 , V. Campo 1 , L. Arribas 1 1 Fundación Instituto Valenciano de Oncología, Radiation Oncology, Valencia, Spain