Comparison of dose volume and dose mass histograms in lung and heart of patients with left sided breast cancer who underwent deep inspiration breath hold radiotherapy treatment technique

Aim: Comparison of dose volüme (DVH) and dose mass histograms (DMH) in terms of lung and heart in free breathing (FB) and Deep Inspiration Breath Hold (DIBH) radiotherapy plans in patients who underwent left breast radiotherapy after breast conserving surgery due to early stage breast cancer. Materials and Methods: Target and normal tissue volumes were contoured using computed tomography data from 35 patients with left breast cancer in FB and DIBH. IMRT was planned with a total dose of 50 Gy/25 fx for PTV in FB and DIBH. The DVHs belonging to a total of 70 plans and DMH based on DVH and electron density were taken in Matlab. DVHs and DMHs were compared for left lung, heart. Statistical analysis was performed by t-test, Wilcoxon test, Spearman correlation in SPSS-23.0. Results:In FB, Heart-Dmean (cGy) was 365.98±211.88 in DVH and 352.81±203.05 in DMH (p=0.791); in DIBH, it was 125.46±39.36 in DVH and 121.61±47.78 in DMH (p = 0.991). The mean volume of the left lung (cc) was 1114.25±286.92 in FB and 2115.48 ± 380.56 in DIBH. The mean total mass of the left lung(g) was 307.96±44.64 in FB and 335.44±65.02 in DIBH. In FB, left lung-Dmean (cGy) was 791.43±463.50 in DVH and 550.5±164.19 in DMH (p<0.005); in DIBH it was 689.31±208.35 in DVH and 505.35±198.84 in DMH (p<0.005). In FB, V20-M20 (%) of left lung were 13.35±5.65 in DVH and 9.85±4.87 in DMH (p<0.005); in DIBH, it was 11.80±4.72 in DVH and 8.81±4.28 in DMH (p<0.005).Left lung-Dmean (cGy) and V20(%) values were decreased -12.9 and -11.58 in DVH; they decreased -8.2 and -10.56 in DMH, respectively. The strong correlation were found in V20-M20 of left lung (R2 = 0.7864), V20-M20 of heart (R2 = 0.9982) and Dmean of heart (R2=0.9577) while Dmean of left lung had low correlation (R2=0.5316) between DVH–DMH. Conclusion: Depending on the breathing technique, the changes were observed for the heart; DVH and DMH are similar in FB and DIBH. However, with no significant difference of total left lung mass in DIBH, the mean dose decreased in "%" in DMH compared DVH. Therefore, DMH may be more sensitive and more meaningful than DVH in dosimetric evaluation for lung tissue with different electron densities. Further studies are needed to evaluate the advantages and disadvantages of DMH. Keywords: Free Breathing, Deep Inspiration Breath Hold, Dose Mass Histogram, Dose Volume Histogram, Matlab Page number: 149 Advisor: Doç. Dr. L. Zümre ARICAN ALICIKUŞ