NTCP-Driven Comparison of Proton Versus VMAT Approaches for Reducing Hematologic and Gastrointestinal Toxicities in Anal Cancer Patients Receiving Definitive Chemoradiation
Article
Sabouri, P, Yam, M, Yu, J et al. (2021). NTCP-Driven Comparison of Proton Versus VMAT Approaches for Reducing Hematologic and Gastrointestinal Toxicities in Anal Cancer Patients Receiving Definitive Chemoradiation
. 111(3), e527-e528. 10.1016/j.ijrobp.2021.07.1439
Sabouri, P, Yam, M, Yu, J et al. (2021). NTCP-Driven Comparison of Proton Versus VMAT Approaches for Reducing Hematologic and Gastrointestinal Toxicities in Anal Cancer Patients Receiving Definitive Chemoradiation
. 111(3), e527-e528. 10.1016/j.ijrobp.2021.07.1439
PURPOSE/OBJECTIVE(S): Significant hematologic (heme) and/or gastrointestinal (GI) toxicities are routinely experienced by anal cancer (AC) patients undergoing definitive chemoradiation (CRT). Such toxicities affect not only quality of life, but can also lead to treatment interruptions that may compromise long-term treatment efficacy. Grade 3+ heme (HT3+) and GI toxicities (GIT3+) that are associated with both high and low doses to bone marrow (BM) and small bowel (SB) may be reduced using proton beam therapy. We applied normal tissue complication probability (NTCP) modeling to determine the optimal proton beam configuration that reduces the probability of HT3+ and GIT3+ in AC patients treated with intensity modulated proton therapy (IMPT) compared to volumetric-modulated arc therapy (VMAT). MATERIALS/METHODS: A total of 40 treatment plans were created for 10 AC patients using VMAT (2-3 arcs) and three proton configurations consisting of: 1) AP/PA fields; 2) AP+2 posterior-oblique proton fields (AP+POs) and 3) 2-lateral proton fields. Plans were optimized for a 30-fraction simultaneous integrated boost regimen that prescribed 54 Gy to gross disease and 45 Gy to elective regions. Robustness of each configuration was examined using routine quality assurance CT scans (QACTs) performed 1-4 times over the course of patient treatment. Total pelvic bone marrow (TPBM) was subdivided into lumbosacral spine (LSS), ilium (IL), and lower pelvic (LP). Acute HT3+ and GIT3+ risks were modeled using the LKB approach and studied for each configuration. RESULTS: Target coverage was robust for all three IMPT configurations and with less than 4% variation in CTV D95% calculated on QACTs. In comparison to VMAT and lateral proton configurations, AP/PA and AP+POs IMPT achieved 22% and 15% reductions in TPBM V5 Gy (P < 0.001), respectively, through better avoidance of pelvic and iliac bones. On average, VMAT plans produced pelvic bone marrow (PBM) mean doses of 27 Gy which translated to an average HT3+ risk of 12-25%; a reduction in PBM mean dose achieved with lateral proton beams reduced this risk to 8%-20% while AP/PA and AP+POs configurations were associated with the lowest risk of HT3+. Patient-averaged SB V5 Gy was significantly lower with IMPT (V5 Gy < 100CC) when compared with VMAT (V5 Gy < 300CC). CONCLUSION: PBT achieves considerably smaller volumes of pelvic OARs receiving low and moderate dose compared to VMAT, with AP/PA plans achieving the best overall sparing and lowest probability of HT3+. Clinical outcomes of PBT for AC remain poorly understand with little published data, and prospective evaluation of this novel treatment approach is needed.
