Nominal plan robustness may predict plan degradation in proton therapy for oropharyngeal head-and-neck cancer.

Institutional Audit of Adaptive Re-Planning With Pencil Beam Scanning Proton Beam Therapy

Clinical Implementation of Intensity Modulated Proton Therapy in Thoracic Malignancies

Patterns of Adaptive Replanning in Proton Therapy for Thoracic Malignancies

Assessment of Dosimetric Changes and Adaptive Replanning for Intraoperatively Placed Brachytherapy Applicators during Accelerated Partial Breast Irradiation

Anatomic changes may occur during chemoradiation treatment for lung cancers, requiring adaptive replanning. Here we characterize these cases. We retrospectively studied lung cancer cases that underwent resimulation and adaptive replanning during 1/2016-3/2019. We compared first and second CT-simulation regarding tumor location, timing of change, tumor volume, anatomical alteration and change in simulation technique. We also compared dosimetric parameters between the plans, recorded local control, and overall survival outcomes. Out of 281 patients, 58 underwent replanning (20.6%). Histology included small cell (22.4%) and non-small cell (77.6%). Stage III was in 91.4%. Mean radiation dose of 59.4 Gray (Gy) (range 50-66Gy).Tumor location was peribronchial in 53.5%. Timing of replanning was in the first, second and final third of the treatment course in 26%, 43% and 31% respectively. Changes in gross tumor volume were observed in 74%; mean gross tumor volume was 276.7cc vs 192.7 cc (first vs second simulation, p = 0.001). Anatomical changes were identified in 35.4% including pleural fluid accumulation, atelectasis or pneumothorax alteration. Change in simulation technique was performed in 25.9%, including breath-hold or continuous positive airway pressure.Changes in dosimetric parameters when the same technique was used: lung V20Gy 26% (standard deviation, SD 7.6) vs 25.3% (SD 6.6) (p = 0.36), mean lung dose 15.1 Gy (SD 3.7) vs 14.7Gy (SD 3.3) (p = 0.23), heart V40Gy 10.2% (SD13) vs 7.2% (SD 9.8) (p = 0.037). When simulation technique changed: lung V20Gy 30.8% (SD 8.2) vs 27.3% (SD 8) (p = 0.012), mean lung dose 17.3 Gy (SD 4.4) vs 15.3 Gy (SD 3.8) (p = 0.007), heart V40Gy 11.1% (SD 14.7) vs 6.5% (SD 6.7) (p = 0.014).2 year local control was 60.7% (95% confidence interval, 34.5-79.2%), and median overall survival was 19.7 months. Adaptive replanning of radiation was performed in a fifth of locally advanced lung cancer patients. In most cases tumor volume decreased, or atelectasis resolved, causing mediastinal shifts, which, if unidentified and left uncorrected, may have led to local failure and increased toxicity. The heart V40Gy was reduced significantly in all cases, but significant reduction in lung doses was evident only if simulation technique was altered. In locally advanced lung cancer image-guidance with cone beam CT can detect significant mediastinal shifts and gross tumor volume changes that raise the need for adaptive replanning. Image guidance-triggered adaptive replanning should be added to the armament of advanced radiation treatment planning in locally advanced lung cancer.

BackgroundProton beam therapy is promising for the treatment of head and neck cancer (HNC), but it is sensitive to uncertainties in patient positioning and particle range. Studies have shown that the planning target volume (PTV) concept may not be sufficient to ensure robustness of the target coverage. A few planning studies have considered irradiation of unilateral HNC targets with protons, but they have only taken into account the dose on the nominal plan, without considering anatomy changes occurring during the treatment course.MethodsFour pencil beam scanning (PBS) proton therapy plans were calculated for 8 HNC patients with unilateral target volumes: single-field (SFO) and multi-field optimized (MFO) plans, either using the PTV concept or clinical target volume (CTV)-based robust optimization. The dose was recalculated on computed tomography (CT) scans acquired during the treatment course. Doses to target volumes and organs at risk (OARs) were compared for the nominal plans, cumulative doses considering anatomical changes, and additional setup and range errors in each fraction. If required, the treatment plan was adapted, and the dose was compared with the non-adapted plan.ResultsAll nominal plans fulfilled the clinical specifications for target coverage, but significantly higher doses on the ipsilateral parotid gland were found for both SFO approaches. MFO PTV-based plans had the lowest robustness against range and setup errors. During the treatment course, the influence of the anatomical variation on the dose has shown to be patient specific, mostly independent of the chosen planning approach. Nine plans in four patients required adaptation, which led to a significant improvement of the target coverage and a slight reduction in the OAR dose in comparison to the cumulative dose without adaptation.ConclusionsThe use of robust MFO optimization is recommended for ensuring plan robustness and reduced doses in the ipsilateral parotid gland. Anatomical changes occurring during the treatment course might degrade the target coverage and increase the dose in the OARs, independent of the chosen planning approach. For some patients, a plan adaptation may be required.

Advancing (Proton) Radiation Therapy

PurposeTo compare dose distributions and robustness in treatment plans from eight European centres in preparation for the European randomized phase-III PROTECT-trial investigating the effect of proton therapy (PT) versus photon therapy (XT) for oesophageal cancer. Materials and methodsAll centres optimized one PT and one XT nominal plan using delineated 4DCT scans for four patients receiving 50.4 Gy (RBE) in 28 fractions. Target volume receiving 95% of prescribed dose (V95%iCTVtotal) should be >99%. Robustness towards setup, range, and respiration was evaluated. The plans were recalculated on a surveillance 4DCT (sCT) acquired at fraction ten and robustness evaluation was performed to evaluate the effect of respiration and inter-fractional anatomical changes. ResultsAll PT and XT plans complied with V95%iCTVtotal >99% for the nominal plan and V95%iCTVtotal >97% for all respiratory and robustness scenarios. Lung and heart dose varied considerably between centres for both modalities. The difference in mean lung dose and mean heart dose between each pair of XT and PT plans was in median [range] 4.8 Gy [1.1;7.6] and 8.4 Gy [1.9;24.5], respectively. Patients B and C showed large inter-fractional anatomical changes on sCT. For patient B, the minimum V95%iCTVtotal in the worst-case robustness scenario was 45% and 94% for XT and PT, respectively. For patient C, the minimum V95%iCTVtotal was 57% and 72% for XT and PT, respectively. Patient A and D showed minor inter-fractional changes and the minimum V95%iCTVtotal was >85%. ConclusionLarge variability in dose to the lungs and heart was observed for both modalities. Inter-fractional anatomical changes led to larger target dose deterioration for XT than PT plans.

Purpose: Our previous study showed that weekly dose monitoring using cone-beam CT (CBCT) images can guide the timing and need for adaptive re-planning during the treatment of head and neck (HN) cancer. Here we aim to confirm the dosimetric improvement of adaptive radiotherapy (ART) using weekly CBCTs. Methods: We randomly selected seven HN patients treated with ART due to noticeable anatomic changes. Twenty weekly images acquired during the second treatment course were included. These CBCTs were aligned with both the initial and re-planning simulation CTs according to the clinical shifts. Daily doses were re-calculated for both the initial and adaptive plans. Contours of the tumor and organs-at-risk (OARs) were manually delineated by a physician on the re-planning CT and then were transferred to the CBCTs for plan evaluation. Contour modifications were made based on the daily anatomic changes observed on CBCTs. All patients were treated with 70Gy to the primary tumor and 56Gy to the elective lymph nodes. Results: Volumetric changes of the tumor (range — 43.9%∼+15.9%) were observed. The average D99 to the primary tumor was (70.1±2.0)Gy (range 62.2∼72.5Gy) for the adaptive plan and (66.0±5.5)Gy (range 50.9∼70.7Gy) for the initial plan(p<<0.01). The average D99 to the elective neck was (56.3±1.3)Gy (range 52.8∼59.2Gy) for the adaptive plan and (52.4±7.0)Gy (range 37.7∼58.6Gy) for the initial plan(p=0.01). The parotid decreased in volume during the treatment course (range 7.3%∼42.2%). The average D_mean to the spared parotid decreased by 15.3% (p=0.002) for the adaptive plan when compared to the original. With ART, 4 out of 7 patients experienced better sparing of the spinal cord (D_max reduced by 2.5%∼10.2%) and the oral cavity (D_mean reduced by 3.5%∼20.1%). Conclusion: Weekly CBCT dosimetry confirms that ART is an effective method to accommodate on-treatment anatomic changes. In select patients, tumor coverage and OAR sparing may be improved with ART. Research is funded by Siemens.

Proton beam therapy (PBT) offers a unique potential for dose conformity to tumors while sparing surrounding healthy tissues. Current PBT accuracy, however, is fundamentally limited by range uncertainties from tissue density variations and anatomical changes, yet no clinically viable methods exist for localizing the dose delivery pulse-by-pulse inside patients during pencil beam scanning (PBS). We developed and clinically demonstrated a first-of-its-kind radiation acoustic beam localization (iRABL) system for real-time tracking PBS trajectory and mapping dose deposition deep in patient's body during PBT. A clinical-grade compact iRABL system featuring high speed, super-resolution, and high sensitivity was specifically designed for PBT applications. Its clinical feasibility was validated through the first-in-human study on prostate cancer patients, demonstrating the capability for in vivo proton dose mapping without interfering with treatment delivery. System performance, including spatial resolution, imaging speed for tracking beam trajectory and temporal dose accumulation, and dosimetric accuracy, was quantitatively characterized using tissue-equivalent phantoms and clinical treatment plans. This iRABL system achieved displacement resolution of 0.1 mm laterally and 0.2 mm axially, exceeding the acoustic diffraction limit by an order of magnitude and surpassing typical proton beam spot sizes. This super-resolution capability, combined with GPU-accelerated image reconstruction and processing, enabled single-pulse detection at a frame rate of 1 kHz, matching the proton system's pulse repetition rate. Dosimetric validation using clinical M-shaped treatment plans met clinical criteria with gamma index passing rates exceeding 90% at 3 mm/3% tolerance, confirming high accuracy for mapping delivered dose distributions. For the first time, by leveraging the high sensitivity and the high speed of our newly developed iRABL system, we are able to localize proton beam and map the proton dose deposition during PBS with sub-diffraction-limit spatial resolution, pulse-by-pulse imaging speed, and clinical grade accuracy. This capability, which addresses fundamental limitations in current treatment monitoring, holds promise for advancing PBT toward image-guided "proton surgery".

Proton Beam Therapy for Pancreas Cancer: PTCOG Consensus Recommendations for Simulation, Treatment Planning and Treatment Delivery

PurposeThis work evaluates an online adaptive (OA) workflow for head-and-neck (H&N) intensity-modulated proton therapy (IMPT) and compares it with full offline replanning (FOR) in patients with large anatomical changes. MethodsIMPT treatment plans are created retrospectively for a cohort of eight H&N cancer patients that previously required replanning during the course of treatment due to large anatomical changes. Daily cone-beam CTs (CBCT) are acquired and corrected for scatter, resulting in 253 analyzed fractions. To simulate the FOR workflow, nominal plans are created on the planning-CT and delivered until a repeated-CT is acquired; at this point, a new plan is created on the repeated-CT. To simulate the OA workflow, nominal plans are created on the planning-CT and adapted at each fraction using a simple beamlet weight-tuning technique. Dose distributions are calculated on the CBCTs with Monte Carlo for both delivery methods. The total treatment dose is accumulated on the planning-CT. ResultsDaily OA improved target coverage compared to FOR despite using smaller target margins. In the high-risk CTV, the median D98 degradation was 1.1 % and 2.1 % for OA and FOR, respectively. In the low-risk CTV, the same metrics yield 1.3 % and 5.2 % for OA and FOR, respectively. Smaller setup margins of OA reduced the dose to all OARs, which was most relevant for the parotid glands. ConclusionDaily OA can maintain prescription doses and constraints over the course of fractionated treatment, even in cases of large anatomical changes, reducing the necessity for manual replanning in H&N IMPT.

Deformable Image Registration and Dose Accumulation for Locally Advanced Non-Small Cell Lung Cancer, Comparing Delivered and Planned Radiotherapy Doses

Radiation Therapy for Locally Advanced Lung Cancer: Which Cases Require Adaptive Planning?

Surveying the clinical practice of treatment adaptation and motion management in particle therapy.