[18]F-fluoroethyl-l-tyrosine positron emission tomography for radiotherapy target delineation: Results from a Radiation Oncology credentialing program

Background and purpose

The [18]F-fluoroethyl-l-tyrosine (FET) PET in Glioblastoma (FIG) study is an Australian prospective, multi-centre trial evaluating FET PET for newly diagnosed glioblastoma management. The Radiation Oncology credentialing program aimed to assess the feasibility in Radiation Oncologist (RO) derivation of standard-of-care target volumes (TVMR) and hybrid target volumes (TVMR+FET) incorporating pre-defined FET PET biological tumour volumes (BTVs).

Materials and methods

Central review and analysis of TVMR and TVMR+FET was undertaken across three benchmarking cases. BTVs were pre-defined by a sole nuclear medicine expert. Intraclass correlation coefficient (ICC) confidence intervals (CIs) evaluated volume agreement. RO contour spatial and boundary agreement were evaluated (Dice similarity coefficient [DSC], Jaccard index [JAC], overlap volume [OV], Hausdorff distance [HD] and mean absolute surface distance [MASD]). Dose plan generation (one case per site) was assessed.

Results

Data from 19 ROs across 10 trial sites (54 initial submissions, 8 resubmissions requested, 4 conditional passes) was assessed with an initial pass rate of 77.8 %; all resubmissions passed. TVMR+FET were significantly larger than TVMR (p < 0.001) for all cases. RO gross tumour volume (GTV) agreement was moderate-to-excellent for GTVMR (ICC = 0.910; 95 % CI, 0.708-0.997) and good-to-excellent for GTVMR+FET (ICC = 0.965; 95 % CI, 0.871-0.999). GTVMR+FET showed greater spatial overlap and boundary agreement compared to GTVMR. For the clinical target volume (CTV), CTVMR+FET showed lower average boundary agreement versus CTVMR (MASD: 1.73 mm vs. 1.61 mm, p = 0.042). All sites passed the planning exercise.

Conclusions

The credentialing program demonstrated feasibility in successful credentialing of 19 ROs across 10 sites, increasing national expertise in TVMR+FET delineation.

Survey of brachytherapy training experience among radiation oncology trainees and fellows in the Royal Australian and New Zealand College of Radiologists (RANZCR)

INTRODUCTION

To evaluate brachytherapy training experience among trainees and fellows trained through the Royal Australian and New Zealand College of Radiologists (RANZCR).

METHODS

All current trainees and fellows (who obtained fellowship from 2015 onwards) were sent an online anonymous questionnaire on various aspects of brachytherapy training, including number of cases observed/ performed, opinions on brachytherapy assessment during training, barriers to brachytherapy training and future role of brachytherapy.

RESULTS

The overall survey response rate was 24% (40/161 trainees, 30/126 fellows). Of the 70 respondents, 50 (71%), 38 (54%) and 43 (61%) reported to have received formal brachytherapy teaching from radiation oncologists, radiation therapists and medical physicists respectively. Most respondents had exposure to gynaecology brachytherapy - two-thirds of trainees and all fellows have performed at least one gynaecology brachytherapy procedure. Prostate brachytherapy exposure was more limited - by the end of training, 27% and 13% of fellows did not have exposure to LDR and HDR prostate brachytherapy. More than two-thirds indicated there should be a minimum number of brachytherapy case requirements during training, and half indicated that trainees should be involved in ≥6 gynaecology brachytherapy procedures. Barriers affecting training include lack of caseload (70%) and perceived decreasing role of brachytherapy (66%). Forty-three percent of respondents were concerned about the decline in brachytherapy utilisation.

CONCLUSION

This is the first survey on brachytherapy training experience among RANZCR trainees and fellows. It highlighted limited brachytherapy exposure during RANZCR training, and the need to revisit brachytherapy training requirement in the current training programme, along with long-term brachytherapy workforce planning.

The use of collimator angle optimization and jaw tracking for VMAT-based single-isocenter multiple-target stereotactic radiosurgery for up to six targets in the Varian Eclipse treatment planning system

PURPOSE

Island blocking occurs in single-isocenter multiple-target (SIMT) stereotactic radiotherapy (SRS) whenever targets share multi-leaf collimator (MLC) leaf pairs. This study investigated the effect on plan quality and delivery, of reducing island blocking through collimator angle optimization (CAO). In addition, the effect of jaw tracking in this context was also investigated.

METHODS

For CAO, an algorithm was created that selects the collimator angle resulting in the lowest level of island blocking, for each beam in any given plan. Then, four volume-modulated arc therapy (VMAT) SIMT SRS plans each were generated for 10 retrospective patients: two CAO plans, with and without jaw tracking, and two plans with manually selected collimator angles, with and without jaw tracking. Plans were then assessed and compared using typical quality assurance procedures.

RESULTS

There were no substantial differences between plans with and without CAO. Jaw tracking produced statistically significant reduction in low-dose level parameters; healthy brain V10% and mean dose were reduced by 9.66% and 15.58%, respectively. However, quantitative values (108 cc for V10% and 0.35 Gy for mean dose) were relatively small in relation to clinical relevance. Though there were no statistically significant changes in plan deliverability, there was a notable trend of plans with jaw tracking having lower gamma analysis pass rates.

CONCLUSION

These findings suggest that CAO has limited benefit in VMAT SIMT SRS of 2-6 targets when using a low-dose penalty to the healthy brain during plan optimization in Eclipse. As clinical benefits of jaw tracking were found to be minimal and plan deliverability was potentially reduced, a cautious approach would be to exclude jaw tracking in SIMT SRS plans.

Australasian Gastro-Intestinal Trials Group (AGITG) MASTERPLAN: Randomized phase II study of modified neoadjuvant FOLFIRINOX alone or in combination with stereotactic radiotherapy (SBRT) for patients with high-risk and locally advanced pancreatic cancer

TPS4172

Background: Eighty per cent of patients with non-metastatic pancreatic cancer have high-risk, borderline resectable (BRPC) or locally advanced pancreas cancer (LAPC), conferring a 5-year overall survival of only 12%. MASTERPLAN evaluates the safety and activity of stereotactic body radiotherapy (SBRT) added to neoadjuvant chemotherapy in these patient cohorts. Methods: MASTERPLAN is an investigator-initiated prospective multi-centre randomized phase II trial. Inclusion criteria include histologically confirmed high-risk, BRPC or LAPC. High risk is defined as tumour > 4cm, extrapancreatic extension or node positive. Randomisation is 2:1 to chemotherapy + SBRT (investigational arm) or chemotherapy (control arm) by minimisation with stratification by operability (potentially operable - high risk; BRPC versus inoperable – LAPC; medically inoperable), planned chemotherapy and institution. Both treatment arms receive 6 x 2 weekly cycles of modified FOLFIRINOX (mFOLFIRINOX). Gemcitabine and nab-paclitaxel is permitted if mFOLFIRINOX is unsuitable. The investigational arm receives SBRT (40Gy in 5 fractions) with real time quality assurance. Resectability will be evaluated following initial chemotherapy +/- SBRT. Adjuvant chemotherapy is 6 cycles (12 weeks) of mFOLFIRINOX, or the same duration of gemcitabine and capecitabine (GEMCAP) if neoadjuvant gemcitabine/ nab-paclitaxel given. SBRT adverse events (AEs) will be recorded until study cessation. The primary endpoint is 12-month locoregional control. Secondary endpoints: safety, surgical morbidity and mortality, radiological response rate, progression free survival, pathological response rate, surgical resection rate, R0 resection rate, quality of life, deterioration free survival and overall survival. Biospecimens are collected for translational research for potential prognostic/predictive biomarkers of clinical endpoints and include serial tumour tissue collection from patients undergoing fiducial marker insertion and/or surgery, biopsy at disease progression, serial blood collection and serial buccal and faecal sample collection. An interim analysis will review locoregional failure, distant metastasis and rate of death on the first 40 patients after completion of 12 months follow up. The sample size is 120 patients (80 intervention:40 control), balanced for BRPC/LAPC (60 in each cohort). The minimum follow up is 12 months. The first site opened in October 2019 and 10 patients have been recruited from five sites at 17 Feb 2021. Overall 15 sites in Australia and New Zealand are planned to open to recruitment. Australian Clinical Trials Registry Number: ACTRN12619000409178. Clinical trial information: ACTRN12619000409178.

Comparison of TG43 and Hounsfield Unit-based TG186 brachytherapy dose metrics in Oncentra Brachy for 100 patients receiving interstitial partial breast irradiation

PURPOSE

The aim of the study was to conduct a retrospective analysis of 100 patients who received interstitial accelerated partial breast irradiation at a single institution, comparing the standard American Association of Physicists in Medicine Task Group (TG) 43 dose calculation algorithm to the model-based dose calculation algorithms (MBDCAs) available in the Oncentra Brachy treatment planning system.

METHODS AND MATERIALS

Dose-volume histogram parameters were compared between the different dose calculation algorithms for the planning target volume and organs at risk. and a statistical analysis was performed. The resulting changes in isodose distribution were assessed, with the worst-case data presented.

RESULTS

The TG43 algorithm calculated higher doses to all structures compared with the MBDCAs. The largest discrepancy was observed for the skin, with maximum doses on average 2.0% lower with the MBDCA. The newly released Hounsfield Unit-based algorithm further decreased the skin dose compared with TG43 by <0.5%.

CONCLUSIONS

This study demonstrates that the differences between TG43 and MBDCA as implemented in Oncentra Brachy for accelerated partial breast irradiation are clinically insignificant in the treatment area and nearby organs at risk. Justification for investing in MBDCAs for this treatment site is limited when considering the additional calculation time, introduced uncertainties, and cost.

BrachyView: development of an algorithm for real-time automatic LDR brachytherapy seed detection

BrachyView is a novel in-body imaging system developed to provide real-time intraoperative dosimetry for low dose rate prostate brachytherapy treatments. Seed positions can be reconstructed after in-vivo implantation using a high-resolution pinhole gamma camera inserted into the patient rectum. The obtained data is a set of 2D projections of the seeds on the image plane. The 3D reconstruction algorithm requires the identification of the seed's centre of mass. This work presents the development and techniques adopted to build an algorithm that provides the means for fully automatic seed centre of mass identification and 3D position reconstruction for real-time applications. The algorithm presented uses a local feature detector, speeded up robust features, to perform detection of brachytherapy seed 2D projections from images, allowing for robust seed identification. Initial results have been obtained with datasets of 30, 96 and 98 I-125 brachytherapy seeds implanted into a prostate gel phantom. It can detect 97% of seeds and correctly match 97% of seeds. The average overall computation time of 2.75 s per image and improved reconstruction accuracy of 22.87% for the 98 seed dataset was noted. Elimination processes for initial false positive detection removal have shown to be extremely effective, resulting in a 99.9% reduction of false positives, and when paired with automatic frame alignment and subtraction procedures allows for the effective removal of excess counts generated by previously implanted needles. The proposed algorithm will allow the BrachyView system to be used as a real-time intraoperative dosimetry tool for low dose rate prostate brachytherapy treatments.

A Clinician's Guide to Cancer-Derived Exosomes: Immune Interactions and Therapeutic Implications

Understanding of the role of immunity in the regulation of cancer growth continues to rapidly increase. This is fuelled by the impressive results yielded in recent years by immune checkpoint inhibitors, which block regulatory pathways to increase immune-mediated cancer destruction. Exosomes are cell-secreted membranous nanoscale vesicles that play important roles in regulating physiological and pathophysiological processes. Cancer-derived exosomes (CDEXs) and their biologically-active cargos have been proven to have varied effects in malignant progression, including the promotion of angiogenesis, metastasis, and favorable microenvironment modification. More recently, there is an increasing appreciation of their role in immune evasion. In addition to CDEXs, there are immune-derived exosomes that facilitate communication between immune cells in the non-malignant setting. Investigation of cancer-mediated mechanisms behind interruption or modification of these normal exosomal pathways may provide further understanding of how malignant immune evasion is accomplished. Accumulating evidence indicates that immune-active CDEXs also have the potential to impact clinical oncological management. Whilst immune checkpoint inhibitors have well-established pharmacologically-targeted pathways involving the immune system, other widely used treatments such as radiation and cytotoxic chemotherapies do not. Thus, investigating exosomes in immunotherapy is important for the development of next-generation combination therapies. In this article, we review the ways in which CDEXs impact individual immune cell types and how this contributes to the development of immune evasion. We discuss the relevance of lymphocytes and myeloid-lineage cells in the control of malignancy. In addition, we highlight the ways that CDEXs and their immune effects can impact current cancer therapies and the resulting clinical implications.

Endobronchial brachytherapy in the management of lung malignancies: 20 years of experience in an Australian center

OBJECTIVES

Management of end-stage lung cancers focuses on symptom control, requiring multimodality management. Endobronchial brachytherapy (EBB) is an evidence-based approach allowing safe delivery of clinically meaningful radiation doses. We provide a summary of treatment characteristics and clinical outcomes of EBB in a single center.

METHODS AND MATERIALS

Our retrospective study examined all EBB procedures performed at St George Hospital, NSW, Australia, between 1997 and 2016. Patients received single-fraction brachytherapy treatment under procedural sedation, using either the pulsed-dose-rate or high dose-rate modality. Symptomatic response was noted at the 4- to 6-week followup consultation.

RESULTS

Ninety-two EBB procedures were identified in 83 patients, with 75 patients treated with pulsed-dose-rate and 17 with high-dose-rate. Clinical and/or radiological airway obstruction in a prior high-dose irradiated volume was the most common indication for treatment (85%). Sixty (72%) patients had a partial or complete response of symptoms. Patients with hemoptysis were more likely to respond than those with airway obstruction (92% vs. 70%; p = 0.036). There was no difference in clinical response between pulsed-dose-rate and high-dose-rate patients (p = 0.24). Median overall survival was 8 months, with a statistically significant difference in those with clinical response (4 vs. 9 months; p = 0.0101). No Grade >2 toxicities were recorded.

CONCLUSIONS

We present the largest Australian series of EBB to date. We continue to demonstrate that despite a variety of symptomatic presentations and histologies, EBB is an effective approach to the palliation of malignant lung lesions. Given its low risk of toxicity, EBB is recommended as an option in the palliative treatment of endobronchial malignancies.

Hemithoracic radiation therapy after extrapleural pneumonectomy for malignant pleural mesothelioma: Toxicity and outcomes at an Australian institution

INTRODUCTION

We aim to report the outcome of patients with malignant pleural mesothelioma who underwent extrapleural pneumonectomy (EPP) and adjuvant hemithoracic radiotherapy with or without chemotherapy at a single Australian institution.

METHOD

Between July 2004 and March 2013, 53 patients were referred for radiation treatment following EPP, of whom 49 were suitable for adjuvant treatment. Radiation treatment initially involved a 3D conformal, mixed electron/photon technique, delivering 45-50.4 Gy in 25-28 fractions (31 patients) and subsequently a nine-field intensity-modulated radiotherapy technique, delivering 50.4-54 Gy in 28-30 fractions (18 patients). Fifty-five per cent of patients also received pre-operative chemotherapy. We assessed toxicity, disease-specific and overall survival in patients who commenced radiation treatment.

RESULTS

Forty-one patients (84%) completed treatment as prescribed. Six patients stopped prematurely due to toxicity, and two with disease progression. Most patients discontinuing due to toxicity received over 90% of the prescribed dose. Common acute toxicities included nausea, fatigue, anorexia and dermatitis. Severe early toxicities were rare. Late toxicities were uncommon, with the exception of a persistent elevation in liver enzymes in those with right-sided disease. Neither clinical hepatitis nor radiation pneumonitis was documented. With a median follow up of 18.7 months, median disease-free and overall survival were 21.6 and 30.5 months, respectively, and 2-year overall survival was 57.3%.

CONCLUSION

Hemithoracic radiotherapy following EPP, although associated with significant early toxicity, is well tolerated. Most patients complete the prescribed treatment, and clinically significant late toxicities are rare.

Corneal Optics after Reading, Microscopy and Computer Work

PURPOSE

To compare lid-induced changes in corneal optics following reading, microscopy and computer work.

METHODS

Nine subjects with normal ocular health were recruited for the study. Five subjects were myopic, two were emmetropic, one was astigmatic and one was hyperopic. Corneal topography was measured before and after 60 mins of reading a novel, performing a blood cell counting task on a microscope and Internet searching. Corneal topography data were used to derive the corneal wavefront Zernike coefficients up to the fourth order. A meridian analysis of instantaneous corneal power along the upper 90-degree semi-meridian was performed to examine local changes caused by eyelid pressure. Digital photography was used to capture body posture and eyelid position during the tasks.

RESULTS

Each of the three tasks showed systematically different effects on both the characteristics and location of corneal topography changes. Reading and microscopy generally exhibited larger and more centrally located changes compared with the computer task. Differences in wavefront aberration characteristics between the three tasks were apparent in both lower and higher order aberrations. The location of corneal distortions differed significantly between microscopy and computer work, with microscopy causing distortions to occur closer to the videokeratoscope measurement axis compared with computer work (p = 0.015).

CONCLUSIONS

Reading, microscopy and computer work have different effects on corneal aberrations. The results are in agreement with the hypothesis that lid-induced corneal aberrations may play a role in myopia development.