ESTRO 2020 Abstract Book

S99 ESTRO 2020

cohort (n=200) ranged from 3.11% to 3.58%, depending on the risk estimation tool (3.11% ±5.14% Procam score; 3.39% ±3.67% Framingham score; 3.58% ±4.70% Reynolds score). A large number of the non-diabetic patients had a very low 10-year CVD baseline risk of ≤1%. Nevertheless, 8-9% of patients reached ≥10% baseline 10-year CVD risk. In contrast, diabetic patients (n=10) had significantly higher baseline CVD risks (11.76% ±12.43% Procam score; 24.23% ±14.59% Framingham score; 10.66% ±9.46% Reynolds score). Regarding radiation-induced CVD risks, the mean 10-year cumulative risk (Framingham score) following RT was 3.73% using the heart-sparing DIBH-technique (MHD: 1.42Gy) and 3.94% in free breathing (MHD: 2.33Gy), after adding a 10-year EAR of +0.34% (DIBH) and +0.55% (FB) to the baseline risks, respectively. Smoking status was one of the most important and modifiable baseline risk factors for CVD. After DIBH-RT, the 182 non-smoking patients had a mean 10-year cumulative risk of 3.55% (3.20% baseline risk, 0.35% EAR) as compared to 6.07% (5.60% baseline risk, 0.47% EAR) for the 28 smokers.

Patients were treated from 2015 to 2017 and selected based on consistent delineation. For each patient two Auto-Plans were created, one with minimal cardiac sparing (mean heart dose (MHD) <20 Gy EQD2) – mimicking the manual plan - and the second with more stringent objectives on the heart (MHD <8 - 12 Gy EQD2 and V 5Gy <35%). Differences in dose parameters between plans were tested using paired t-tests. Using NTCP models for overall survival based on MHD at 2 years, and pneumonitis based on mean lung dose (MLD) [Kwa et al. 1998], we assessed the effect of the decreased cardiac dose on overall survival, and increased MLD on pneumonitis risk using paired t-tests. Results Compared to the original plans, the Auto-Plans’ PTV coverage was slightly improved, V 90% was 0.4% higher, OAR doses were comparable. The added heart constraints did not significantly impair OAR doses (including lung), target coverage, target dose inhomogeneity or conformity. All DVH parameters remained within clinically acceptable ranges between different Auto-Plans. The average decrease in MHD was 0.41 Gy (range -2.34 – 7.44 Gy), in heart V 5Gy was 0.67% (range -14.8 - 20.2%). Cardiac sparing of ≥1 Gy was achieved in 14.3 % of patients. The average increase in MLD was 0.01 Gy (range -0.99 – 0.94 Gy) in the entire group and 0.34 Gy (range -0.29 – 0.94 Gy) in the responding 14.3% of patients. (Fig. 1) This translates to a significant expected increase in overall survival at 2 years of 0.5% (range -3 – 9%), p-value: 0.003, and a non-significant increased grade ≥2 pneumonitis risk of 0.02% (range -1 – 2%).

Conclusion In the present study, three different clinically applicable CVD prediction tools were used, which all showed comparable results and can be easily integrated into daily clinical routine in radiation oncology. A systematic evaluation and screening could identify patients with high baseline CVD risk factors who may benefit from primary prevention through counselling or pharmacotherapy interventions. As shown in the present study, this could result in a much higher benefit than from heart-sparing irradiation techniques alone. OC-0199 Cardiac sparing in advanced stage NSCLC patients: at what cost? R. Van Der Bel 1 , B. Stam 1 , D. Eekhout 1 , A. Tijhuis 1 , K. Kiers 1 , G. Wortel 1 , J. Belderbos 1 , S. Jan-Jakob 1 , T. Janssen 1 , E. Damen 1 1 Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective Cardiac toxicity is of increasing concern in lung radiotherapy. However, given current clinical practice regarding organ at risk constraints, it remains to be seen how much room there is for cardiac sparing. Therefore, we investigate the effects of more stringent heart constraints on heart dose in relation to other OAR and PTV dose parameters. How much room is there for heart sparing and what is the expected effect of it on lung toxicity and survival from possible cardiac toxicity? Material and Methods We retrospectively replanned 98 locally advanced stage NSCLC patients, receiving concurrent chemo-radiotherapy 66/58.08 Gy (tumour/involved lymph nodes) in 24 fractions using IMRT and Philips Auto-Planning in Pinnacle 3 .

Conclusion This automated planning study revealed that with a MHD constraint below 8 - 12 Gy (EQD2) for locally advanced NSCLC treated with radical intent a substantial expected increase in overall survival can be achieved without a relevant increase in pneumonitis risk. Cardiac sparing