S1887
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
V5400, V5000, V4000, and V1400cGy were reduced by 12.9±7.2, 16.4±5.0, 18.6±11.3, and 20.9±9.6% on average, respectively. Reduction in V1400cGy was statistically significant (p<0.05). Rectal wall V5400, V5100 and V3300cGy decreased by 11.8±7.5, 12.8±5.0, and 14.1±13.1% on average, respectively. However, while these reductions were consistent, they were not statistically significant (p>0.1). Bladder (V5680, V5100, V4800, and V4000cGy) and bladder wall (V5300 and V2000cGy) metrics showed <3% mean change. Maximum doses for the left femoral heads showed a minor increase of 5.2±4.6% on average, while the right showed <1% change. Penile bulb Dmean and V2200cGy showed decreases of 4.2±1.7 and 6.2±2.6%, respectively. Small and large bowel Dmax demonstrated <2% change. PTV60 D0.1cc increased by <0.5%. All final MCO plans were generated within
acceptable target coverage and OAR sparing was still achieved in the majority of study subjects. As the VMAT plans take an average of 11 minutes longer to produce compared to the IMRT techniques, its utility may be hampered in the context of online adaptive planning for H&N radiotherapy subjects. Therefore, IMRT9 or IMRT12 may represent the best options for H&N adaptive radiotherapy using Ethos. References: [1] Martin PR et al., ASTRO 2025. Int J Radiat Oncol Biol Phys 2025;123(1S):e78-79[2] Cherpak A et al., COMP 2024. Med Phys 2024;51(8):5785-5835 Keywords: CBCT, adaptive radiotherapy, treatment technique Improvement of Rectal Dose in the Setting of Moderately Hypofractionated Prostate Radiation Therapy Daniel McDonald, William Godwin, Sean Roles, Stephanie Tan, Wen-Chih Tseng, Alyssa Gadsby, Ryan Mansfield, Jean Peng Radiation Medicine, Medical University of South Carolina, Charleston, USA Purpose/Objective: To evaluate single-structure targeted multi-criteria optimization (MCO) for reducing rectal dose in moderately hypofractionated prostate radiotherapy Digital Poster 2470 Targeted Multi-Criteria Optimization for Ten anonymized prostate cancer datasets were utilized. A skilled dosimetrist created moderately hypofractionated prostate treatment plans (6000 cGy in 20 fractions) for each dataset using standard optimization techniques (SO). Each plan utilized 10 MV photons and two VMAT arcs. The Eclipse v16.1 (Varian Medical Systems, Palo Alto, USA) planning system was used. Targeted MCO pareto plans, focusing on the rectum only, were then generated for each case utilizing a combined rectum objective. The midpoint on the MCO slider was selected to achieve rectal dose improvement without significantly affecting the remaining structures, and a final plan was generated. Total time for MCO plan generation was recorded. All MCO and SO plans were normalized to deliver the prescription dose to 95% of the PTV. MCO and SO plans were compared, and PTV and OAR doses were evaluated. OARs evaluated included: Bladder, bladder wall, rectum, rectal wall, right and left femoral heads, small bowel, large bowel, and penile bulb. Student’s t- test was used to assess significance. Results: treatment planning. Material/Methods: The rectum and rectal wall showed decreases in dose in all cases, and for all metrics evaluated. Rectum
15 minutes. Conclusion:
Single-structure targeted MCO allows for the rapid reduction in rectum and rectal wall dose, especially lower isodose levels, for moderately hypofractionated prostate treatment, without significantly affecting doses to the PTV or other OARs. This targeted workflow offers quick and consistent results. Keywords: Multi-Criteria Optimization, Prostate, Rectum Digital Poster 2512 Dosimetric feasibility of hypofractionated radiation therapy with simultaneously integrated central boost for retroperitoneal sarcoma Zoe L Cosner 1 , Katie Lee 2 , Yaguang Pei 3 , Kevin Liu 3 , Elizabeth H Baldini 3 , Miranda B Lam 3 1 Radiation Oncology, Harvard Radiation Oncology Program, Boston, USA. 2 Radiation Oncology, Mayo Clinic, Rochester, USA. 3 Radiation Oncology, Brigham and Women's Hospital and Dana-Farber Cancer Institute, Boston, USA Purpose/Objective: Retroperitoneal sarcomas (RPS) are rare malignancies that pose significant challenges due to size, anatomical location, and high risk of local recurrence.1 For patients with unresectable or medically inoperable RPS, radiation therapy (RT) is a treatment option, but conventional fractionation regimens are lengthy.3–5 Hypofractionated-RT (HFRT) offers a shorter alternative, with emerging evidence supporting its safety and comparable oncologic outcomes to standard fractionation.8 Simultaneous integrated boost (SIB) techniques allow selective dose escalation to tumor subregions while sparing normal tissues. For unresectable tumors, a central tumor SIB has been used in standard fractionation to maximize local
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