Dosimetric impact of bone marrow sparing for robustly optimized IMPT for locally advanced cervical cancer

Abstract

Background and purpose: To investigate the trade-off between bone marrow sparing (BMS) and dose to organs at risk (OARs) for intensity modulated proton therapy (IMPT) for women with locally advanced cervical cancer (LACC). Materials and methods: Twenty LACC patients were retrospectively included. IMPT plans were created for each patient using automated treatment planning. These plans progressively reduced bone marrow mean doses by steps of 1 GyRBE, while constraining target coverage and conformality. The relation between bone marrow dose and bladder, small bowel, rectum, and sigmoid doses was evaluated. Results: A total of 140 IMPT plans were created. Plans without BMS had an average [range] bone marrow mean dose of 17.3 [14.7-21.6] Gy RBE , which reduced to 12.0 [10.0-14.0] Gy RBE with maximum BMS. The mean OAR dose [range] increased modestly for 1 Gy RBE BMS: 0.2 [0.0 - 0.6] Gy RBE for bladder, 0.3 [-0.2 - 0.7] Gy RBE for rectum, 0.4 [0.1 - 0.8] Gy RBE for small bowel, and 0.2 [-0.2 - 0.4] Gy RBE for sigmoid. Moreover, for maximum BMS, mean OAR doses [range] escalated by 3.3 [0.1 - 6.7] Gy RBE for bladder, 5.8 [1.8 - 12.4] Gy RBE for rectum, 3.9 [1.6 - 5.9] Gy RBE for small bowel, and 2.7 [0.6 - 5.9] Gy RBE for sigmoid. Conclusion: Achieving 1 Gy RBE BMS for IMPT is feasible for LACC patients with limited dosimetric impact on other OARs. While further bone marrow dose reduction is possible for some patients, it may increase OAR doses substantially for others. Hence, we recommend a personalized approach when introducing BMS into clinical IMPT treatment planning to carefully assess individual patient benefits and risks.