The normal tissue sparing potential of an adaptive plan selection strategy for re-irradiation of recurrent rectal cancer

Stereotactic MR-guided online adaptive radiotherapy reirradiation (SMART reRT) for locally recurrent pancreatic adenocarcinoma: A case report

INTRODUCTION

Stereotactic MR-guided online adaptive radiation therapy (SMART) has demonstrated a superior radiotherapeutic ratio for pancreatic patients, by enabling dose escalation while minimizing the dose to the proximal gastrointestinal organs at risk through online adaptive radiotherapy. The safe delivery of stereotactic body radiation therapy (SBRT) is of particular importance in the reirradiation setting and has been historically limited to CT-based nonadaptive modalities. Herein, we report the first use of online adaptive radiotherapy in the reirradiation setting, specifically for treatment of locally recurrent pancreatic adenocarcinoma through SMART reirradiation (SMART reRT).

CASE DESCRIPTION

We describe the treatment of a 68-year-old male who was diagnosed with, unresectable locally advanced pancreatic adenocarcinoma. Initial treatment included FOLFIRINOX followed by 45 Gy in 25 fractions on a helical intensity-modulated radiotherapy (IMRT) device with concurrent capecitabine, followed by a boost of 14.4 Gy in 8 fractions to a on an MR-guided radiotherapy (MRgRT) linac. At approximately 12 months from initial radiotherapy, the patient experienced local progression of the pancreas body/tail and therefore SMART reRT of 50 Gy in 5 fractions was initiated. The technical considerations of cumulative dose for gastrointestinal organs across multiple courses, treatment planning principles, and adaptive radiotherapy details are outlined in this case study. The patient tolerated treatment well with minimal fatigue.

CONCLUSIONS

The therapeutic ratio of reirradiation may be improved using daily MR guidance with online adaptive replanning, especially for lesions in proximity to critical structures. Future studies are warranted to assess long-term outcomes of dose escalated MR-guided reRT, define OAR dose constraints for reRT, and assess cumulative dose across the adapted SMART reRT fractions and the original RT plan.

Impact of interfractional target motion in locally advanced cervical cancer patients treated with spot scanning proton therapy using an internal target volume strategy

Background and purpose

The more localized dose deposition of proton therapy (PT) compared to photon therapy might allow a reduction in treatment-related side effects but induces additional challenges to address. The aim of this study was to evaluate the impact of interfractional motion on the target and organs at risk (OARs) in cervical cancer patients treated with spot scanning PT using an internal target volume (ITV) strategy.

Methods and materials

For ten locally advanced cervical cancer patients, empty and full bladder planning computed tomography (pCT) as well as 25 daily cone beam CTs (CBCTs) were available. The Clinical Target Volume (CTV), the High Risk CTV (CTV_HR) (gross tumor volume and whole cervix), the non-involved uterus as well as the OARs (bowel, bladder and rectum) were contoured on the daily CBCTs and transferred to the pCT through rigid bony match. Using synthetic CTs derived from pCTs, four-beam spot scanning PT plans were generated to target the patient-specific ITV with 45 Gy(RBE) in 25 fractions. This structure was defined based on pre-treatment MRI and CT to anticipate potential target motion throughout the treatment. D98% of the targets and V40Gy(RBE) of the OARs were extracted from the daily anatomies, accumulated and analyzed. In addition, the impact of bladder volume deviations from planning values on target and bowel dose was investigated.

Results

The ITV strategy ensured a total accumulated dose >42.75 Gy(RBE) to the CTV_HR for all ten patients. Two patients with large bladder-related uterus motion had accumulated dose to the non-involved uterus of 35.7 Gy(RBE) and 41.1 Gy(RBE). Variations in bowel V40Gy(RBE) were found to be correlated (Pearson r = −0.55; p-value <0.0001) with changes in bladder volume during treatment.

Conclusion

The ITV concept ensured adequate dose to the CTV_HR, but was insufficient for the non-involved uterus of patients subject to large target interfractional motion. CBCT monitoring and occasional replanning is recommended along the same lines as with photon radiotherapy in cervical cancer.

Patterns of practice for adaptive and real-time radiation therapy (POP-ART RT) part II: Offline and online plan adaption for interfractional changes

PURPOSE

The POP-ART RT study aims to determine to what extent and how intrafractional real-time respiratory motion management (RRMM), and plan adaptation for interfractional anatomical changes (ART) are used in clinical practice and to understand barriers to implementation. Here we report on part II: ART using more than one plan per target per treatment course.

MATERIALS AND METHODS

A questionnaire on the current practice of ART, wishes for expansion or implementation, and barriers to implementation was distributed worldwide. Four types of ART were discriminated: daily online replanning, online plan library, protocolled offline replanning (all three based on a protocol), and ad-hoc offline replanning.

RESULTS

The questionnaire was completed by 177 centres from 40 countries. ART was used by 61% of respondents (31% with protocol) for a median (range) of 3 (1-8) tumour sites. CBCT/MVCT was the main imaging modality except for online daily replanning (11 users) where 10 users used MR. Two thirds of respondents wished to implement ART for a new tumour site; 40% of these had plans to do it in the next 2 years. Human/material resources and technical limitations were the main barriers to further use and implementation.

CONCLUSIONS

ART was used for a broad range of tumour sites, mainly with ad-hoc offline replanning and for a median of 3 tumour sites. There was a large interest in implementing ART for more tumour sites, mainly limited by human/material resources and technical limitations. Daily online replanning was primarily performed on MR-linacs.

Re-irradiation for recurrent rectal cancer - a single-center experience

Background: There is no clear consensus on the use of re-irradiation (reRT) in the management of locally recurrent rectal cancer (LRRC). The aim of the present study was to investigate all reRT administered for rectal cancer at a large referral institution and to evaluate patient outcomes and toxicity.Material and methods: All patients with rectal cancer were identified who had received previous pelvic radiotherapy (RT) and underwent reRT during 2006-2016. Medical records and RT details of the primary tumor treatments and rectal cancer recurrence treatments were registered, including details on reRT, chemotherapy, surgery, adverse events, and long-term outcomes.Results: Of 77 patients who received ReRT, 67 had previously received pelvic RT for rectal cancer and were administered reRT for LRRC. Re-irradiation doses were 30.0-45.0 Gy, most often given as hyperfractionated RT in 1.2-1.5 Gy fractions twice daily with concomitant capecitabine. The median time since initial RT was 29 months (range, 13-174 months). Of 36 patients considered as potentially resectable, 20 underwent surgery for LRRC within 3 months after reRT. Operated patients had better 3-year overall survival (OS) (62%) compared to those who were not operated (16%; HR 0.32, p = .001). The median gross tumor volume (GTV) was 107 cm³, and 3-year OS was significantly better in patients with GTV <107 cm³ (44%) compared to patients with GTV ≥107 cm³ (21%; HR 0.52, p = .03).Conclusion: Three-year survival was significantly better for patients who underwent surgery after reRT or who had small tumor volume. Prospective clinical trials are recommended for further improvements in patient selection, outcomes, and toxicity assessment.

Dosimetric benefit of an adaptive treatment by means of plan selection for rectal cancer patients in both short and long course radiation therapy

BACKGROUND

To compare target coverage and dose to the organs at risk in two approaches to rectal cancer: a clinically implemented adaptive radiotherapy (ART) strategy using plan selection, and a non-adaptive (non-ART) strategy.

METHODS

The inclusion of the first 20 patients receiving adaptive radiotherapy produced 10 patients with a long treatment schedule (25x2Gy) and 10 patients with a short schedule (5X5Gy). We prepared a library of three plans with different anterior PTV margins to the upper mesorectum, and selected the most appropriate plan on daily Conebeam CT scans (CBCT). We also created a non-adaptive treatment plan with a 20 mm margin. Bowel bag, bladder and target volume were delineated on CBCT. Daily DHVs were calculated based on the dose distribution of the selected and non-adaptive plans. Coverage of the target volume was compared per fraction between the ART and non-ART plans, as was the dose to the bladder and small bowel, assessing the following dose levels: V15Gy, V30Gy, V40Gy, V15Gy and V95% for long treatment schedules, and V15Gy and V95% for short ones.

RESULTS

Target volume coverage was maintained from 98.3% (non-ART) to 99.0% (ART)(p = 0.878). In the small bowel, ART appeared to have produced significant reductions in the long treatment schedule at V15Gy, V40Gy, V45Gy and V95% (p <  0.05), but with small absolute differences. The DVH parameters tested for the short treatment schedule did not differ significantly. In the bladder, all DVH parameters in both schedules showed significant reductions (p <  0.05), also with small absolute differences.

CONCLUSIONS

The adaptive treatment maintained target coverage and reduced dose to the organs at risk.

TRIAL REGISTRATION

Medical Research Involving Human Subjects Act (WMO) does not apply to this study and was retrospectively approved by the Medical Ethics review Committee of the Academic Medical Center, W19_194 # 19.233.