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The aim of this study was to investigate the effect of patient positioning based on either bone or soft-tissue matching for PT in oesophageal cancer and its impact on plan adaptation. Two retrospective patient cohorts treated with radiotherapy were included in the study. Cohort A consisted of 26 consecutive patients with a planning 4DCT scan (CT1) and a surveillance 4DCT scan (CT2) at fraction ten. Cohort B consisted of 17 patients selected based on large anatomical changes identified during treatment resulting in a rescan (CT2). Mean dose to the iCTV (sum of the CTVs in all respiratory phases) was 50.4 Gy (RBE) in 28 fractions or 41.4 Gy (RBE) in 23 fractions. A nominal pencil beam scanning plan was created using two posterior beams and robust optimization (5 mm setup, 3.5% range). For each patient, two rigid registrations were made between average (avg) CT1 and CT2: a match on the vertebral column (bone match) and a match on the iCTV (soft-tissue match). Robustness towards setup (5 mm) and range (3.5%) errors was evaluated at CT2. Robustness towards respiration was evaluated by recalculation of the plan on all phases of the CT2 scan. Dose coverage <96% would trigger adaptation. The statistical significance (p-value <0.05) between dose coverage for the two registration methods was assessed using the Wilcoxon signed rank test. All plans fulfilled V95%iCTV>99% for the nominal plan and V95%iCTV>97% for all respiratory phases and robustness scenarios at CT1. In two (8%) and three (18%) patients, V95%iCTV<96% on CT2 for Cohort A and B, respectively when bone match was used. For soft-tissue match, V95%iCTV >96% for all patients. V95%iCTV was significantly higher (p-value = 0.0001) for soft-tissue match than bone match. Anatomical changes during the treatment course led to target dose deterioration and a need for plan adaptation when using a bone match. [ABSTRACT FROM AUTHOR]

The Danish Breast Cancer Group (DBCG) Proton Trial randomizes breast cancer patients selected on high mean heart dose (MHD) or high lung dose (V20Gy/V17Gy) in the photon plan between photon and proton therapy. This study presents the proton plans and adaptation strategy for the first 43 breast cancer patients treated with protons in Denmark. Forty-four proton plans (one patient with bilateral cancer) were included; 2 local and 42 loco-regional including internal mammary nodes (IMN). Nineteen patients had a mastectomy and 25 a lumpectomy. The prescribed dose was either 50 Gy in 25 fractions (n = 30) or 40 Gy in 15 fractions (n = 14) wherefrom five received simultaneous integrated boost to the tumor bed. Using 2-3 en face proton fields, single-field optimization, robust optimization and a 5 cm range shifter ensured robustness towards breathing motion, setup- and range uncertainties. An anatomical evaluation was performed by evaluating the dose after adding/removing 3 mm and 5 mm tissue to/from the body-outline and used to define treatment tolerances for anatomical changes. The nominal and robust criteria were met for all patients except two. The median MHD was 1.5 Gy (0.5–3.4 Gy, 50 Gy) and 1.1 Gy (0.0–1.5 Gy, 40 Gy). The anatomical evaluations showed how 5 mm shrinkage approximately doubled the MHD while 5 mm swelling reduced target coverage of the IMN below constraints. Ensuring 3–5 mm robustness toward swelling was prioritized but not always achieved by robust optimization alone emphasizing the need for a distal margin. Twenty-eight patients received plan adaptation, eight patients received two, and one received five. This proton planning strategy ensured robust treatment plans within a pre-defined level of acceptable anatomical changes that fulfilled the planning criteria for most of the patients and ensured low MHD. [ABSTRACT FROM AUTHOR]