Definitive hyperfractionated, accelerated proton reirradiation for patients with pelvic malignancies

PTCOG Gastrointestinal Subcommittee Lower Gastrointestinal Tract Malignancies Consensus Statement

Purpose

Radiotherapy delivery in the definitive management of lower gastrointestinal (LGI) tract malignancies is associated with substantial risk of acute and late gastrointestinal (GI), genitourinary, dermatologic, and hematologic toxicities. Advanced radiation therapy techniques such as proton beam therapy (PBT) offer optimal dosimetric sparing of critical organs at risk, achieving a more favorable therapeutic ratio compared with photon therapy.

Materials and Methods

The international Particle Therapy Cooperative Group GI Subcommittee conducted a systematic literature review, from which consensus recommendations were developed on the application of PBT for LGI malignancies.

Results

Eleven recommendations on clinical indications for which PBT should be considered are presented with supporting literature, and each recommendation was assessed for level of evidence and strength of recommendation. Detailed technical guidelines pertaining to simulation, treatment planning and delivery, and image guidance are also provided.

Conclusion

PBT may be of significant value in select patients with LGI malignancies. Additional clinical data are needed to further elucidate the potential benefits of PBT for patients with anal cancer and rectal cancer.

Factors Associated With and Characteristics of Patients Receiving Proton Therapy at the End of Life

Purpose

To identify the characteristics, indications, and toxicities among patients receiving proton beam therapy (PBT) in the final year of life at an academic medical center.

Materials and Methods

A retrospective review of patients who received PBT within the final 12 months of life was performed. Electronic medical records were reviewed for patient and treatment details from 2010 to 2019. Patients were followed from the start of PBT until death or last follow-up. Acute (3 months) toxicities were graded using the Common Terminology Criteria for Adverse Events v5.0. Imaging response was assessed using the Response Evaluation Criteria in Solid Tumors v1.1. The χ2 test was used to evaluate factors associated with palliative treatment. Simple logistic regression was used to evaluate factors associated with toxicity.

Results

Bet299 patients were treated at the end of life (EOL) out of 5802 total patients treated with PBT (5.2%). Median age was 68 years (19-94 years), 58% male. The most common cancer was nonsmall cell lung cancer (27%). Patients were treated for symptom palliation alone (11%), durable control (57%), curative intent (16%), local recurrence (14%), or oligometastatic disease (2%). Forty-five percent received reirradiation. Median treatment time was 32 days (1-189 days). Acute toxicity was noted in 85% of the patients (31% G1, 53% G2, 15% G3). Thirteen patients (4%) experienced chronic toxicity. Breast and hematologic malignancy were associated with palliative intent χ2 (1, N = 14) = 17, P = .013; (χ2 (1, N = 14) = 18, P = .009).

Conclusion

The number of patients treated with PBT at the EOL was low compared to all comers. Many of these patients received treatment with definitive doses and concurrent systemic therapy. Some patients spent a large portion of their remaining days on treatment. A prognostic indicator may better optimize patient selection for PBT at the EOL.

Preoperative short-course radiation therapy with PROtons compared to photons in high-risk RECTal cancer (PRORECT): Initial dosimetric experience

Background and purpose

Neoadjuvant short-course radiotherapy (SCRT) followed by full-dose systemic chemotherapy is an established treatment modality in locally advanced rectal cancer (LARC). Until recently, SCRT has been exclusively delivered with photons. Proton beam therapy (PBT) may minimize acute toxicity, which in turn likely impacts favorably on the tolerability to subsequent chemotherapy. The aim of this study is a dosimetric comparison between SCRT with photons and protons in the randomized phase II trial PRORECT (NCT04525989).

Materials and methods

From June 2021 to June 2022, twenty consecutive patients with LARC have been treated according to study protocol. For each patient, both a VMAT and a PBT treatment plans have been generated and compared pairwise.

Results

Dose-volume histogram (DVH) analysis revealed that SCRT with protons significantly reduced radiation dose to pelvic organs at risk including bladder, bones, and bowel in comparison to SCRT with photons. Photon and proton treatment plans had equivalent conformity and homogeneity indexes.

Conclusion

Preoperative SCRT with protons offers a significant reduction of radiation dose to normal tissues compared with current photon-based radiotherapy technique. Demonstrated dosimetric advantages may translate into measurable clinical benefits in patients with LARC. Clinical implications of the dosimetric superiority of SCRT with protons will be presented in the coming reports from the PRORECT trial.

Proton Therapy in the Management of Luminal Gastrointestinal Cancers: Esophagus, Stomach, and Anorectum

While the role of proton therapy in gastric cancer is marginal, its role in esophageal and anorectal cancers is expanding. In esophageal cancer, protons are superior in sparing the organs at risk, as shown by multiple dosimetric studies. Literature is conflicting regarding clinical significance, but the preponderance of evidence suggests that protons yield similar or improved oncologic outcomes to photons at a decreased toxicity cost. Similarly, protons have improved sparing of the organs at risk in anorectal cancers, but clinical data is much more limited to date, and toxicity benefits have not yet been shown clinically. Large, randomized trials are currently underway for both disease sites.

Clinical and technical challenges of cancer reirradiation: Words of wisdom

Since the development of new radiotherapy techniques that have improved healthy tissue sparing, reirradiation (reRT) has become possible. The selection of patients eligible for reRT is complex given that it can induce severe or even fatal side effects. The first step should therefore be to assess, in the context of multidisciplinary staff meeting, the patient's physical status, the presence of sequelae resulting from the first irradiation and the best treatment option available. ReRT can be performed either curatively or palliatively to treat a cancer-related symptom that is detrimental to the patient's quality of life. The selected techniques for reRT should provide the best protection of healthy tissue. The construction of target volumes and the evaluation of constraints regarding the doses that can be used in this context have not yet been fully codified. These points raised in the literature suggest that randomized studies should be undertaken to answer pending questions.

The role of proton therapy in gynecological radiation oncology

Proton beam therapy is an external beam radiotherapy modality that offers potentially similar efficacy and reduced toxicity compared with photon radiotherapy due to little to no exit dose of radiation beyond the intended target. Improvements in radiotherapy from two-dimensional, to three-dimensional, to intensity-modulated radiation therapy have offered comparable to improved efficacy of radiation therapy with progressive reductions in toxicity. Proton beam therapy may offer further improvements, with multiple dosimetric studies demonstrating potential reductions in exposure of normal tissue to radiation, particularly bowel and bone marrow. Proton beam therapy offers avenues for dose escalation or re-irradiation, which were previously not feasible with photon radiotherapy. Although early clinical data generally demonstrate safety, feasibility, and efficacy in a few series, prospective clinical trials are limited and needed to better define who might benefit from proton therapy. In this review, we discuss the history, dosimetry, available clinical data, and technical needs to deliver high-quality proton therapy.

Dose-Escalated Magnetic Resonance Image–Guided Abdominopelvic Reirradiation With Continuous Intrafraction Visualization, Soft Tissue Tracking, and Automatic Beam Gating

Purpose

Methods and Materials

Results

Conclusions

A treatment planning comparison of photon stereotactic ablative radiotherapy and proton beam therapy for the re-irradiation of pelvic cancer recurrence

BACKGROUND

Patients who experience a pelvic cancer recurrence in or near a region that received initial radiotherapy, typically have few options for treatment. Organs at risk (OAR) have often reached their dose constraint limits leaving minimal dose remaining for standard re-irradiation (reRT). However, photon based stereotactic ablative radiotherapy (SABR) has been utilised for reRT with promising initial results although meeting OAR constraints can be challenging. Proton beam therapy (PBT) could offer an advantage.

MATERIALS AND METHODS

SABR plans used for treatment for ten pelvic reRT patients were dosimetrically compared to PBT plans retrospectively planned using the same CT and contour data. PBT plans were created to match the CTV dose coverage of SABR treatment plans with V100% ≥95%. An 'as low as reasonably achievable' approach was taken to OAR tolerances with consideration of OAR dose from the initial radiation (using equivalent dose in 2 Gy fractions).

RESULTS

Dosimetric comparison of relevant OAR statistics showed a decrease in OAR dose using PBT over SABR in all patients, with equivalent target coverage. The largest statistically significant reduction was seen for the colon D0.5 cm3 with a median reduction from 13.1 Gy to 5.9 Gy. There were statistically significant dose reductions in the median dose to small bowel, sacral plexus and cauda equina.

CONCLUSION

PBT has the potential for significant dose reductions for OARs in the pelvic reRT setting compared to SABR. However, it remains unclear if the magnitude of these OAR dose reductions will translate into clinical benefit.

Proton beam therapy in rectal cancer: A systematic review and meta-analysis

INTRODUCTION

Locally advanced rectal cancer is often treated with neoadjuvant chemoradiotherapy and surgery. Radiotherapy carries significant risk of toxicity to organs at risk (OAR). Proton beam therapy (PBT) has demonstrated to be effective in other cancers, delivering equivalent dosimetric radiation but with the benefit of improved sparing of OAR. This review compares dosimetric irradiation of OAR and oncological outcomes for PBT versus conventional photon-based radiotherapy in locally advanced rectal cancer.

METHODS

An electronic literature search was performed for studies with comparative cohorts receiving proton beam therapy and photon-based radiotherapy for rectal cancer.

RESULTS

Eight articles with a total of 127 patients met the inclusion criteria. There was significantly less irradiated small bowel with PBT compared to three-dimensional conformal radiation therapy (3DCRT) and intensity-modulated radiation therapy (IMRT) (MD -17.01, CI [-24.06, -9.96], p < 0.00001 and MD -6.96, CI [-12.99, -0.94], p = 0.02, respectively). Similar dosimetric results were observed for bladder and pelvic bone marrow. Three studies reported clinical and oncological results for PBT in recurrent rectal cancer with overall survival reported as 43 %, 68 % and 77.2 %, and one study in primary rectal cancer with 100 % disease free survival.

CONCLUSION

PBT treatment plans revealed significantly less irradiation of OAR for rectal cancer compared to conventional photon-based radiotherapy. Trials for recurrent rectal cancer and PBT have shown promising results. There are currently no ongoing clinical trials for primary rectal cancer and PBT. More research is required to validate its potential role in dose escalation, higher complete response rate and organ preservation without increasing toxicity.

Role of proton therapy in reirradiation and in the treatment of sarcomas

Reirradiation and irradiation of sarcoma is often difficult due to the frequent need for a high dose of radiation in order to increase tumor control. This can result in a greater risk of toxicity which can be mitigated with the use of proton therapy. The present review aims to summarize the role of proton therapy in these 2 clinical contexts.

A phase III randomized trial evaluating chemotherapy followed by pelvic reirradiation versus chemotherapy alone as preoperative treatment for locally recurrent rectal cancer - GRECCAR 15 trial protocol

AIM

Treatment strategies in locally recurrent rectal cancer (LRRC) are complex and need to be balanced against previous treatments received for the primary rectal cancer. Radiotherapy is an important component of treatment in LRRC. However, there is little high-quality evidence on the role of reirradiation in this cohort. Therefore, the aim of this trial is to assess the efficacy of neoadjuvant chemotherapy followed by pelvic reirradiation versus neoadjuvant chemotherapy alone on the rate of curative surgery (R0) in previously irradiated patients with LRRC.

METHOD

GRECCAR 15 is a prospective, multicentre, open-label, outcome assessor-blinded, superiority randomized controlled phase III clinical trial comparing neoadjuvant chemotherapy followed by pelvic reirradiation versus neoadjuvant chemotherapy alone in patients with LRRC previously irradiated for the primary cancer. Adult patients (>18 years old) with a histologically proven resectable LRRC, who have previously received pelvic radiotherapy for their primary rectal cancer at a dose of 25-50.4 Gy, and an Eastern Cooperative Oncology Group performance status of <2 will be eligible to participate. The pelvic reirradiation will consist of conformational intensity-modulated external irradiation, delivering a dose of 30.6 Gy with concomitant chemotherapy using capecitabine. The primary outcome of this trial is the R0 resection rate. Overall, GRECCAR 15 aims to recruit 186 patients to detect an absolute difference of 20% in the R0 resection rate with 80% power and 5% two-sided significance level.

CONCLUSION

The GRECCAR 15 trial is the first, definitive, phase III trial to investigate reirradiation in LRRC. The results of this trial will inform definitively the neoadjuvant treatment strategy in previously irradiated patients and assess whether there is any associated benefit of reirradiation in combination with induction chemotherapy in improving R0 resection rates.

Reirradiation for Rectal Cancer Using Pencil Beam Scanning Proton Therapy: A Single Institutional Experience

Purpose

Reirradiation for rectal cancer (RC) after prior pelvic radiation therapy (RT) has been shown to be safe and effective. However, limited data exist for proton therapy (PT), including pencil beam scanning proton therapy (PBS-PT). We hypothesize that PT is safe and feasible for re-treatment and may allow for decreased toxicity and treatment escalation.

Methods and materials

A single-institution, retrospective, institutional review board–approved analysis of all patients with RC and prior pelvic RT receiving PBS-PT reirradiation was performed. Data on patient and treatment characteristics and outcomes were collected. Local progression, progression-free survival, overall survival, and late grade >3 toxicity were estimated using the Kaplan-Meier method.

Results

Twenty-eight patients (median follow-up: 28.6 months) received PBS-PT reirradiation between 2016 and 2019, including 18 patients with recurrent RC (median prior dose: 54.0 Gy) and 10 patients with de novo RC and variable prior RT. The median reirradiation dose was 44.4 Gy (range, 16.0-60.0 Gy; 21 of 28 twice daily), and 24 of 28 patients received concurrent chemotherapy. Six underwent surgical resection. Three (10.7%) experienced grade 3 acute toxicities, and 1 did not complete RT owing to toxicity. Four (14.2%) had late grade <3 toxicity, including 1 grade 5 toxicity in a patient with a prior RT-related injury. The 1-year local progression, progression-free survival, and overall survival rates were 33.7% (95% confidence interval [CI], 14.5%-52.9%), 45.0% (95% CI, 26.2%-63.8%), and 81.8% (95% CI, 67.3%-96.3%), respectively.

Conclusions

This is the largest series using PT for reirradiation for RC and the first study using PBS-PT. Low acute toxicity rates and acceptable late toxicity support PBS-PT as an option for this high-risk patient population, with a need for continued follow-up.

Stereotactic Body Radiation Therapy Reirradiation for Locally Recurrent Rectal Cancer: Outcomes and Toxicity

Purpose

Stereotactic body radiation therapy (SBRT) has emerged as a potential therapeutic option for locally recurrent rectal cancer (LRRC) but contemporaneous clinical data are limited. We aimed to evaluate the local control, toxicity, and survival outcomes in a cohort of patients previously treated with neoadjuvant pelvic radiation therapy for nonmetastatic locally recurrent rectal cancer, now treated with SBRT.

Methods and Materials

Inoperable rectal cancer patients with ≤3 sites of pelvic recurrence and >6 months since prior pelvic radiation therapy were identified from a prospective registry over 4 years. SBRT dose was 30 Gy in 5 fractions, daily or alternate days, using cumulative organ at risk dose constraints. Primary outcome was local control (LC). Secondary outcomes were progression free survival, overall survival, toxicity, and patient reported quality of life scores using the EQ visual analog scale (EQ-VAS) tool.

Results

Thirty patients (35 targets) were included. Median gross tumor volume size was 14.3 cm³. In addition, 27 of 30 (90%) previously received 45 to 50.4 Gy in 25 of 28 fractions, with 10% receiving an alternative prescription. All patients received the planned reirradiation SBRT dose. The median follow-up was 24.5 months (interquartile range, 17.8-28.8). The 1-year LC was 84.9% (95% confidence interval [CI], 70.6-99) and a 2-year LC was 69% (95% CI, 51.8-91.9). The median progression free survival was 12.1 months (95% CI, 8.6-17.66), and median overall survival was 28.3 months (95% CI, 17.88-39.5 months). No patient experienced >G2 acute toxicity and only 1 patient experienced late G3 toxicity. Patient-reported QoL outcomes were improved at 3 months after SBRT (Δ EQ-VAS, +10 points, Wilcoxon signed-rank, P = .009).

Conclusions

Our study demonstrates that, for small volume pelvic disease relapses from rectal cancer, reirradiation with 30 Gy in 5 fractions is well tolerated and achieves an excellent balance between high local control rates with limited toxicity.

Proton Reirradiation: Expert Recommendations for Reducing Toxicities and Offering New Chances of Cure in Patients With Challenging Recurrence Malignancies

Local and regional recurrences are common following an initial course of radiotherapy, yet management of these recurrences remains a challenge. Reirradiation may be an optimal treatment approach for providing durable tumor control and even offering select patients with locoregional recurrences or new primary tumors a chance of cure, but photon reirradiation can be associated with considerable risks of high grade acute and late toxicities. The high conformality and lack of exit dose with proton therapy offer significant advantages for reirradiation. By decreasing dose to adjacent normal tissues, proton therapy can more safely deliver definitive instead of palliative doses of reirradiation, more safely dose escalate reirradiation treatment, and more safely allow for concurrent systemic therapy in the reirradiation setting. In this case-based analysis, renowned experts in the fields of proton therapy and of reirradiation present cases for which they recently employed proton reirradiation. This manuscript focuses on case studies in patients with lung cancer, head and neck malignancies, and pelvic malignancies. Considerations for when to deliver proton therapy in the reirradiation setting and the pros and cons of proton therapy are discussed, and the existing literature supporting the use of proton reirradiation for these disease sites is assessed.

Role of Proton Beam Therapy in Current Day Radiation Oncology Practice

Proton beam therapy (PBT), because of its unique physics of no–exit dose deposition in the tissue, is an exciting prospect. The phenomenon of Bragg peak allows protons to deposit their almost entire energy towards the end of the path of the proton and stops any further dose delivery. Braggs peak equips PBT with superior dosimetric advantage over photons or electrons because PBT doesn’t traverse the target/body but is stopped sharply at an energy dependent depth in the target/body. It also has no exit dose. Because of no exit dose and normal tissue sparing, PBT is hailed for its potential to bring superior outcomes. Pediatric malignancies is the most common malignancy where PBT have found utmost application. Nowadays, PBT is also being used in the treatment of other malignancies such as carcinoma prostate, carcinoma breast, head and neck malignancies, and gastrointestinal (GI) malignancies. Despite advantages of PBT, there is not only a high cost of setting up of PBT centers but also a lack of definitive phase-III data. Therefore, we review the role of PBT in current day practice of oncology to bring out the nuances that must guide the practice to choose suitable patients for PBT.