ESTRO 2021 Abstract Book

S934

ESTRO 2021

(range 36-465), mean PTV to whole breast volume ratio was 21% (range 7-53%). Mean age was 65 years (range 45-88). Mean follow-up was 21 months (range 0 – 46). Acute skin toxicity after 2 weeks was low with 70/26/4% grade 0/1/2. 6-months, 1, 2, 3 and 4-year follow-up data was available from 128, 88, 63, 23 and 3 patients. 77/23%, 78/22%, 85/15%, 78/22%, 100/0% of patients reported no/minimal to tolerable pain and 91/90/89/95/100% of patients developed no change in skin sensitivity in 6-months, 1-, 2-, 3- and 4-years, respectively. Patient-reported cosmetic outcomes were assessed excellent/good/fair in 72/25/3%, 80/19/1%, 82/18/0%, 91/9/0% and 100/0/0% in 6-month, 1, 2, 3, 4 years, respectively. One to three years side effects were mild (grade 0/1/2 fibrosis in 85/14/1%, 84/16/0%, 90/10/0%; grade 0/1/2 atrophy in 83/15/2%, 86/10/3%, 87/13/0%; grade 1 skin telangiectasia/edema in 5/6%, 6/5%, 6/6% of patients in 1, 2 and 3 years respectively). 2 ipsilateral breast recurrence were recorded by now

(03/2021). Conclusion

We herewith confirmed the high early and intermediate term treatment tolerance of APBI in carefully selected early breast cancer patients. APBI is most appreciated by patients and economically efficient as an additional advantage for busy centers.

PO-1123 Post mastectomy RT planning on institutional, RTOG & ESTRO contouring guidelines comparison B. Sarkar 1 , T. Shahid 2 , G. Indira 3 , S.S. Biswal 4 , S. Sengupta 5 , L.N. Biswas 5 , S. Goswami 6 , C.R. Pusarla 4 , A. de 3 , T. Ghosh 7 , M. Mukherjee 7 , A. Samanta 7 , R. Raj 7 , J. Bhattacharya 7 1 Apollo Hospitals , Radiation Oncology , KOLKATA, India; 2 Apollo Hospitals , Radiatkon Oncology, KOLKATA, India; 3 Apollo Hospitals, Radiation Oncology, KOLKATA, India; 4 Apollo Hospitals, Radiation Oncology, Kolkata, India; 5 Apollo Hospitals , Radiation Oncology, KOLKATA, India; 6 Apollo Hsopitals, Radiation Oncology, KOLKATA, India; 7 Apollo Hospitals , Radiation Oncology , KOLKATA, India Purpose or Objective Several consensus guidelines are published for delineation of clinical target volume (CTV) for post mastectomy chest wall irradiation (PMRT), but there is no agreement on which is the most appropriate method. A conservative low volume CTV can have recurrence outside the coverage area while a big volume CTV will significantly increase heart and lung dose. In the current study we prospectively compared the dosimetric impact of the two most commonly used contouring guidelines (RTOG and ESTRO) and our institutional protocol (IP). Materials and Methods Fifty (50) patients, for whom PMRT was indicated were included. For each patient, three sets of contouring following RTOG, ESTRO guidelines and Institutional protocol were carried out and verified by two senior clinicians. The posterior border of the institutional protocol was kept at the posterior border of the pectoralis major muscle excluding the ribs. 3DCRT planning with Field in Field (FiF) was created for each set of contours to deliver a dose of 40Gy in 15 Fractions. No patient received axilla or internal mammary irradiation. Apart from heart, lung and opposite breast left anterior descending (LAD) artery was also contoured as Organ at risk (OARs). Dosimetric comparison of dose distribution and dose to OARs was done among the three groups by one-way repeated measures ANOVA and post-hoc analysis. Results RTOG plans had significantly less 90% dose coverage (87.2%) than the rest (ESTRO 95.7%, IP 95.0%, p <0.001). For 29(58%) left-sided breast cancers mean heart dose (MHD) were significantly different across RTOG (4.2 Gy ±1.8 Gy), ESTRO (3.0±1.6 Gy), IP (3.7±1.6 Gy) plans, p<0.0001. Heart V13 Gy were 9.0%, 6.2%, and 7.9% for RTOG, ESTRO, and IP respectively, and was significantly more with RTOG plan compared to the rest, p<0.0001). Significantly higher V25Gy was observed with RTOG plan over ESTRO (6.5% vs 4.4%, p=0.001) while no difference was observed with IP. Mean LAD doses were significantly different across three groups and highest with RTOG, 22.8 Gy followed by IP,20.3 Gy, and ESTRO 15.7 Gy. V20Gy of the ipsilateral lung was maximum with RTOG, 22±5.3% followed by IP and ESTRO plans, 21.5±5.8%, and 16.6±6.2% respectively. ESTRO plans significantly reduced lung dose compared to the other plans, p<0.0001. Similar findings were noted for ipsilateral & contralateral Mean Lung dose, V5 and V18Gy also. Conclusion A deep dorsal or posterior border significantly increased dose to critical OARs and was found to be associated with worse target volume coverage. A compromised dorsal border can significantly reduce OAR dose parameters and prevent long-term pulmonary and cardiac toxicities. The clinical difference of these practices in terms of local recurrence and long-term complications needs further research to establish the optimal contouring practice. PO-1124 Is there a role for bolus in the modern era of breast cancer treatments? A retrospective analysis. C. Félix Penido Mendes de Sousa 1 , M. Jenwei Chen 1 , P.J. Joffily Pinto 1 , S.L. Favareto 1 , F. Ko Chen 1 , C. Humeres Abrahão 1 , D. Guedes de Castro 1 , E. Santos Neto 1 , H. Ramos 1 , M.L. Gobo Silva 1 , R.C. Fogaroli 1 , A.C. Assis Pellizzon 2 , G. Rocha Melo Gondim 1 1 AC Camargo Cancer Center, Radiation Oncology, São Paulo, Brazil; 2 AC Camargo Cancer Center, Radiation Oncology, São Paulo , Brazil Purpose or Objective The use of bolus increases dose on the skin surface, and thus it is hypothesized that it could improve locorregional control in breast cancer patients with skin involvement. This benefit has never been proved in randomized trials, and since it can also increase side effects, its use is controversial. We aimed to evaluate if a significant benefit could be found, and also to elucidate the associated complications. Materials and Methods We retrospectively analysed data from 288 women, ages 25 to 71 (median = 46), who underwent mastectomy