ESTRO 2023 - Abstract Book

S1740

Digital Posters

ESTRO 2023

Using HS proton therapy, it is possible to reduce the hippocampal dose from 23 to 9 Gy(RBE) with plans including very steep dose gradients. Yet, these plans showed great agreement between the planned and measured dose in the hippocampal area. This shows that HS proton therapy is dosimetrically feasible.

PO-1972 Dosimetric consequences of SCLC: comparisons among IMRT, proton and carbon-ion radiotherapy

X. Ming 1 , J. Mao 2 , N. Ma 2 , J. Chen 3 , W. Wang 4 , Y. Sheng 4

1 Shanghai Proton and Heavy Ion Center, Medical Physics, Shanghai, China; 2 Shanghai Proton and Heavy Ion Center, Radiation Oncology, Shanghai, China; 3 Shanghai Proton and Heavy Ion Center, Radiation Oncology, Shanghai , China; 4 Shanghai Proton and Heavy Ion Center, Medical Physics , Shanghai , China Purpose or Objective To compare the dosimetric difference and evaluate the normal tissue complication probability (NTCP) difference on the organs at risks (OARs) among intensity-modulated photon (IMRT), proton (IMPT) and carbon-ion (IMCT) radiotherapy for limited-staged small-cell lung cancer (LS-SCLC). Materials and Methods Ten patients with LS-SCLC were enrolled onto this study. Three radiation techniques of IMRT (step-and-shoot), IMPT and IMCT were applied for planning. For a single patient, the plans were all designed under the same total prescription dose, in which the planning target volume (PTV) of the internal gross target volume (IGTV) and of the clinical target volume (CTV) was irradiated with 69.3 Gy[relative biological effectiveness (RBE)] and 63 Gy(RBE) using simultaneously integrated boosting technique. The dosimetric parameters of the targets and OARs were compared among the three radiation techniques. NTCPs were estimated for heart, lung, esophagus and spinal cord by Lyman-Kutcher-Burman (LKB) and logistic models. The dose escalation was simulated under the aimed NTCP values (0.05, 0.10 and 0.50) of the three radiation techniques. Results The values of V95% (the percentage volume receiving ≥ 95% of the prescription doses) of the targets were all higher than 99.0% and reached the requirements of target coverage in the three radiation techniques. Almost all OARs were significantly spared (p = <0.001-0.027) by using particle radiotherapy except that D1cc (the dose to 1 cc of the volume) of main bronchial tree. The mean doses were significantly reduced by 8.8/8.0 Gy(RBE) (63.3%/57.6%) of heart, 5.1/6.0 Gy(RBE) (19.2%/22.6%) of ipsilateral lung, 4.2/4.0 Gy(RBE) (62.7%/59.7%) of contralateral lung and 4.7/4.9 Gy (RBE) (28.8%/30.1%) of both lungs in IMPT/IMCT plans. V5-V50 of heart, ipsilateral lung and both lungs were also significantly (p < 0.05) compressed by proton or carbon-ion radiation. D1cc of spinal cord was significantly reduced by 18.9/21.7 Gy(RBE) (50.0%/57.4%) in IMPT/IMCT plans. The mean NTCP of radiation-induced pneumonitis (RP) in ipsilateral lung was 0.39±0.33 (0.39±0.31) in IMPT plans and 0.36±0.32 (0.35±0.30) in IMCT plans rather than 0.66±0.30 (0.64±0.28) in IMRT plans by LKB (logistic) models. The target dose could be escalated into 78.3/76.9 Gy(RBE) with proton/carbon-ion radiation compared to 61.7 Gy with IMRT technique when 0.50 as NTCP in terms of RP in ipsilateral lung was applied.

Conclusion By proton or carbon-ion radiotherapy, OARs of LS-SCLC could be better spared than IMRT, with reducing more than 57.6% mean heart dose, 28.8% mean lung dose and 50.0% D1cc of spinal cord. The dosimetric advantage of IMPT and IMCT for LS SCLC resulted in lower NTCP and higher deliver dose to the targets compared to IMRT. Therefore, there would be a potential of better control on the side-effect and improvement of local control with the application of proton and carbon-ion radiotherapy in thoracic radiation.

PO-1973 3D Rescanning with motion synchronization for lung targets using a proton linac system.

N. Pienimaki 1,2 , W. Koz ł owska 1,2 , J. Bossé 2 , K. O'Shea 1,2 , J.B. Farr 1,2