Dosimetric Comparisons between Proton Beam Therapy and Modern Photon Radiation Techniques for Stage I Non-Small Cell Lung Cancer According to Tumor Location

Toward real-time, volumetric dosimetry for FLASH-capable clinical synchrocyclotrons using protoacoustic imaging

BACKGROUND

Radiation delivery with ultra-high dose rate (FLASH) radiotherapy (RT) holds promise for improving treatment outcomes and reducing side effects but poses challenges in radiation delivery accuracy due to its ultra-high dose rates. This necessitates the development of novel imaging and verification technologies tailored to these conditions.

PURPOSE

Our study explores the effectiveness of proton-induced acoustic imaging (PAI) in tracking the Bragg peak in three dimensions and in real time during FLASH proton irradiations, offering a method for volumetric beam imaging at both conventional and FLASH dose rates.

METHODS

We developed a three-dimensional (3D) PAI technique using a 256-element ultrasound detector array for FLASH dose rate proton beams. In the study, we tested protoacoustic signal with a beamline of a FLASH-capable synchrocyclotron, setting the distal 90% of the Bragg peak around 35 mm away from the ultrasound array. This configuration allowed us to assess various total proton radiation doses, maintaining a consistent beam output of 21 pC/pulse. We also explored a spectrum of dose rates, from 15 Gy/s up to a FLASH rate of 48 Gy/s, by administering a set number of pulses. Furthermore, we implemented a three-dot scanning beam approach to observe the distinct movements of individual Bragg peaks using PAI. All these procedures utilized a proton beam energy of 180 MeV to achieve the maximum possible dose rate.

RESULTS

Our findings indicate a strong linear relationship between protoacoustic signal amplitudes and delivered doses (R2 = 0.9997), with a consistent fit across different dose rates. The technique successfully provided 3D renderings of Bragg peaks at FLASH rates, validated through absolute Gamma index values.

CONCLUSIONS

The protoacoustic system demonstrates effectiveness in 3D visualization and tracking of the Bragg peak during FLASH proton therapy, representing a notable advancement in proton therapy quality assurance. This method promises enhancements in protoacoustic image guidance and real-time dosimetry, paving the way for more accurate and effective treatments in ultra-high dose rate therapy environments.

Comparison of proton therapy and photon therapy for early-stage non-small cell lung cancer: a meta-analysis

The use of proton therapy (PT) in early-stage non-small cell lung cancer (ES-NSCLC) remains controversial, with insufficient evidence to determine its superiority over photon therapy (XRT). We conducted a systematic review of PT trials in ES-NSCLC, analyzing dosimetry, efficacy, and safety across to inform clinical decision-making. Our study showed that PT reduced lung and heart dosimetric parameters compared to XRT, with significant differences in lung V5, lung V10 and mean heart dose (MHD). In terms of efficacy, there were no significant differences in 1-year OS, 3-year OS and 3-year PFS between PT and XRT. For toxicity, no significant difference was observed in treatment-related adverse events (TRAEs) and radiation pneumonitis (RP). Single-arm analysis of PT found that V5, V10, V20 of lung and heart V5 were 13.4%, 11.3%, 7.9% and 0.7%, respectively. The mean lung dose and MHD were 4.15 Gy and 0.17 Gy, respectively. The single-arm pooled 1-, 2-, 3- and 5-year OS rates for PT were 95.3%, 82.5%, 81.3% and 69.3%, respectively. PFS rate and local control rate at 3 years were 68.1% and 91.2%, respectively. The rates of TRAEs of grade ≥ 3 and grade ≥ 2 were 2.8% and 19.8%, respectively. The grade ≥ 2 RP occurred at a rate of 8.7%. In conclusion, PT had acceptable efficacy and safety, and was better at protecting organs at risk than XRT in ES-NSCLC. However, the survival and safety benefit of PT was not significant compared to XRT.

Dosimetric comparison of IMPT vs VMAT for multiple lung lesions: an NTCP model-based decision-making strategy

To compare the dosimetric differences in volumetric modulated arc therapy (VMAT) and intensity modulated proton therapy (IMPT) in stereotactic body radiation therapy (SBRT) of multiple lung lesions and determine a normal tissue complication probability (NTCP) model-based decision strategy that determines which treatment modality the patient will use. A total of 41 patients were retrospectively selected for this study. The number of patients with 1-6 lesions was 5, 16, 7, 6, 3, and 4, respectively. A prescription dose of 70 GyRBE in 10 fractions was given to each lesion. SBRT plans were generated using VMAT and IMPT. All the IMPT plans used robustness optimization with ± 3.5% range uncertainties and 5 mm setup uncertainties. Dosimetric metrics and the predicted NTCP value of radiation pneumonitis (RP), esophagitis, and pericarditis were analyzed to evaluate the potential clinical benefits between different planning groups. In addition, a threshold for the ratio of PTV to lungs (%) to determine whether a patient would benefit highly from IMPT was determined using receiver operating characteristic curves. All plans reached target coverage (V70GyRBE ≥ 95%). Compared with VMAT, IMPT resulted in a significantly lower dose of most thoracic normal tissues. For the 1-2, 3-4 and 5-6 lesion groups, the lung V5 was 29.90 ± 9.44%, 58.33 ± 13.35%, and 81.02 ± 5.91% for VMAT and 11.34 ± 3.11% (p < 0.001), 21.45 ± 3.80% (p < 0.001), and 32.48 ± 4.90% (p < 0.001) for IMPT, respectively. The lung V20 was 12.07 ± 4.94%, 25.57 ± 6.54%, and 43.99 ± 11.83% for VMAT and 6.76 ± 1.80% (p < 0.001), 13.14 ± 2.27% (p < 0.01), and 19.62 ± 3.48% (p < 0.01) for IMPT. The Dmean of the total lung was 7.65 ± 2.47 GyRBE, 14.78 ± 2.75 GyRBE, and 21.64 ± 4.07 GyRBE for VMAT and 3.69 ± 1.04 GyRBE (p < 0.001), 7.13 ± 1.41 GyRBE (p < 0.001), and 10.69 ± 1.81 GyRBE (p < 0.001) for IMPT. Additionally, in the VMAT group, the maximum NTCP value of radiation pneumonitis was 73.91%, whereas it was significantly lower in the IMPT group at 10.73%. The accuracy of our NTCP model-based decision model, which combines the number of lesions and PTV/Lungs (%), was 97.6%. The study demonstrated that the IMPT SBRT for multiple lung lesions had satisfactory dosimetry results, even when the number of lesions reached 6. The NTCP model-based decision strategy presented in our study could serve as an effective tool in clinical practice, aiding in the selection of the optimal treatment modality between VMAT and IMPT.

Cardiac Substructures Dosimetric Predictors for Cardiac Toxicity After Definitive Radiotherapy in Esophageal Cancer

PURPOSE

To investigate the predictive value of the cardiac substructures (CSs) dosimetric parameters for cardiac toxicity after definitive radiation therapy in locally advanced esophageal cancer.

METHODS AND MATERIALS

Between August 2010 and January 2016, 716 patients with stage 2-3 esophageal cancer receiving definitive radiation therapy at 2 institutions were divided into training (n = 432) and external validation (n = 284) cohorts. Dose-volume histogram parameters for the whole heart (WH) and CSs were extracted. Competing risks and Cox regressions analyses were performed. The predictive performance of the models was evaluated using the area under the receiver operating characteristic curve (AUC) and the Brier score.

RESULTS

With a median follow-up of 93 months, 68 patients (15.7%) developed grade ≥3 cardiac events (G3+ CEs), with a median of 13.5 months to the first event. Multivariable analysis showed left ventricle, left anterior descending (LAD), and mean left circumflex (LCX) variables were significantly associated with G3+ CEs. The AUCs and Brier scores demonstrated favorable predictive accuracies of the models integrating these CS variables when predicting G3+ CEs in the training and validation cohorts. However, compared with the WH variables, the CS variables did not significantly improve the prediction of G3+ CEs. Nevertheless, when G3+ acute coronary syndrome and/or congestive heart failure (ACS/CHF) CE was the outcome of interest, models based on the LAD or LCX variables were superior to the WH variable models in training and validation cohorts.

CONCLUSIONS

Models based on CS variables showed favorable predictive accuracy for G3+ CEs. The LAD and LCX variables significantly improved the prediction of G3+ ACS/CHF events compared with the WH variables. Radiation doses to CSs, such as LCX and LAD, should be monitored to help reduce the occurrence of significant CEs in patients with esophageal cancer undergoing definitive radiation therapy.

Clinical Outcomes Following Proton and Photon Stereotactic Body Radiation Therapy for Early-Stage Lung Cancer

Simple Summary

The current study reports the clinical outcomes of proton and photon stereotactic body radiation therapy (SBRT) for early-stage lung cancer. Out of 202 patients who met the inclusion criteria, 34 received proton SBRT and 168 received photon SBRT. Patients at high risk of developing post-SBRT radiation pneumonitis tended to receive proton SBRT. Oncologic outcomes and toxicity profiles were comparable between treatment modalities. Proton SBRT could be considered for patients with high risk of radiation pneumonitis.

Abstract

We aimed to report the clinical outcomes following stereotactic body radiation therapy (SBRT) using photon or proton equipment in early-stage lung cancer. We retrospectively reviewed 202 cT1-2N0M0 lung cancer patients who underwent SBRT with 60 Gy in four consecutive fractions between 2010 and 2019 at our institution: 168 photon SBRT and 34 proton SBRT. Patients who underwent proton SBRT had relatively poor baseline lung condition compared to those who underwent photon SBRT. Clinical outcomes were comparable between treatment modalities: 5-year local control (90.8% vs. 83.6%, p = 0.602); progression-free survival (61.6% vs. 57.8%, p = 0.370); overall survival (51.7% vs. 51.9%, p = 0.475); and cause-specific survival (70.3% vs. 62.6%, p = 0.618). There was no statistically significant difference in grade ≥ 2 toxicities: radiation pneumonitis (19.6% vs. 26.4%, p = 0.371); musculoskeletal (13.7% vs. 5.9%, p = 0.264); and skin (3.6% vs. 0.0%, p = 0.604). In the binary logistic regression analysis of grade ≥3 radiation pneumonitis, poor performance status and poor baseline diffusion capacity of lung for carbon monoxide were significant. To summarize, though patients with high risk of developing lung toxicity underwent proton SBRT more frequently, the SBRT techniques resulted in comparable oncologic outcomes with similar toxicity profiles. Proton SBRT could be considered for patients at high risk of radiation pneumonitis.

Proton Beam Therapy versus Photon Radiotherapy for Stage I Non-Small Cell Lung Cancer

Simple Summary

Stereotactic body radiotherapy (SABR) is accepted as a standard of care for patients who are not candidates for surgery in stage I non-small cell lung cancer (NSCLC). SABR has shown encouraging disease control and acceptable toxicity in peripherally located stage I NSCLC. However, for centrally located tumors around the proximal bronchial tree or for tumors located close to the chest wall, toxicities by SABR are not negligible. Therefore, proton beam therapy (PBT), which provides better organ at risk (OAR) sparing than photon radiotherapy by the Bragg peak, was tested and investigated to reduce radiation-induced toxicities in stage I NSCLC. Here, we compared 112 and 117 stage I NSCLC patients who underwent PBT and photon radiotherapy, respectively. PBT showed significantly lower lung and heart radiation exposure than photon radiotherapy without worsening disease control. PBT could be an effective treatment to reduce long-term toxicities of the lung and heart.

Abstract

Proton beam therapy (PBT) and photon radiotherapy for stage I non-small cell lung cancer (NSCLC) were compared in terms of clinical outcomes and dosimetry. Data were obtained from patients who underwent PBT or photon radiotherapy at two institutions—the only two facilities where PBT is available in the Republic of Korea. Multivariate Cox proportional hazards models and propensity score-matched analyses were used to compare local progression-free survival (PFS) and overall survival (OS). Survival and radiation exposure to the lungs were compared in the matched population. Of 289 patients included in the analyses, 112 and 177 underwent PBT and photon radiotherapy, respectively. With a median follow-up duration of 27 months, the 2-year local PFS and OS rates were 94.0% and 83.0%, respectively. In the multivariate analysis, a biologically effective dose (BED₁₀, using α/β = 10 Gy) of ≥125 cobalt gray equivalents was significantly associated with improved local PFS and OS. In the matched analyses, the local PFS and OS did not differ between groups. However, PBT showed significantly lower lung and heart radiation exposure in the mean dose, V5, and V10 than photon radiotherapy. PBT significantly reduced radiation exposure to the heart and lungs without worsening disease control in stage I NSCLC patients.