An IGRT margin concept for pelvic lymph nodes in high-risk prostate cancer

Evaluation of the utility of rescans in the treatment of prostate and pelvic nodes with pencil beam scanning protons

To determine the necessity of the first week CT simulation rescan of pencil beam scanning (PBS) prostate patients requiring treatment to the pelvic lymph nodes. Patients were treated on a prospective registry trial sponsored by the Proton Collaborative Group (PCG-NCT01255748). A total of 42 patients with high-risk prostate cancer requiring treatment to the pelvic lymph nodes were evaluated in a single calendar year. The cohort consisted of a mix of intact prostate and postprostatectomy patients. Most of the patients were treated with a simultaneous integrated boost (SIB) approach for the majority of the plan. The radiation prescriptions varied depending on whether the patient had an intact prostate or prostate bed. The plan geometry consisted of two lateral beams and a single field optimization (SFO) dosimetric matching technique using pencil beam scanning proton therapy. An in-house protocol was established wherein all high-risk prostate patients had at least 1 rescan evaluation performed during the first 5 ± 2 fractions, which was used to determine whether the nominal approved plan was robust to daily setup uncertainties and anatomical variations. If the evaluation failed clinical analysis, an adaptive replan was created. If 5% or more of the evaluated rescans resulted in a qualified adaptive plan, the planning technique would be considered insufficient. Of the 42 patients investigated, five (11.9%) required an adaptive plan. As it turned out, all five of these patients would have been rescanned within the first 5 fractions of treatment, independent of the established rescan protocol, due to a physician, dosimetrist, or therapist requesting a rescan to investigate specific areas of concern regarding setup or anatomic changes. Of the 5 adaptive plans, only one (2.4%) meets the criteria of a qualified adaptive plan. Our findings substantiated that this policy of a planned rescan with the 5th fraction was no longer necessary, the dosimetric technique had proven to be robust, and moving forward we will only perform these rescans if there is a significant issue with daily setups or observed changes in anatomy.

Retrospective audit of inter-fraction motion for pelvic node radiotherapy in prostate cancer patients

INTRODUCTION

Pelvic lymph nodes move independently to the prostate. When delivering radiotherapy to prostate and pelvic lymph nodes, daily inter- and intra-fraction anatomical changes need to be accounted for. Planning target volume (PTV) margins, grown from the pelvic lymph node clinical target volume need to be determined, to account for this variation in position.

METHODS

Twenty patients who had daily online image guided radiotherapy to prostate and pelvic lymph nodes between April and December 2018 were selected. Ten pre-treatment verification images using cone beam CT from each patient were registered to pelvic bone anatomy, prostate soft tissue or fiducial markers and pelvic lymph node soft tissue to assess the accuracy of treatment delivery. Population systematic and random errors and PTV margins were calculated.

RESULTS

PTV margins of 0.4 cm, 0.4 cm and 0.7 cm left-right (LR), superior-inferior (SI) and anterior-posterior (AP) respectively were derived for the pelvic lymph nodes when registering to prostate. PTV margins of 0.3 cm, 0.2 cm and 0.4 cm LR, SI and AP respectively were derived for the pelvic lymph nodes when registering to bone. There was a posterior systematic shift of the prostate during the treatment course.

CONCLUSION

There is differential motion of pelvic lymph nodes to prostate and in the era of prostate and pelvic radiotherapy for patients with node positive prostate cancer; there is increasing importance in the accuracy of dose delivery to the involved lymph node. Hence, this group of patients may benefit from personalised radiotherapy PTV margins, especially if the involved pelvic lymph node is within the anterior part of the clinical target volume.

IMPLICATIONS FOR PRACTICE

Optimisation of dose delivery to the pelvic lymph nodes when prioritising the prostate in prostate and pelvic lymph node image guided radiotherapy.

Prehabilitation for patient positioning: pelvic exercises assist in minimizing inter-fraction sacral slope variability during radiation therapy

Reproducible patient positioning is essential for precision in radiation therapy (RT) delivery. We tested the hypothesis that a structured daily pre-treatment stretching regimen is both feasible and effective for minimizing variability in positioning, as measured by sacral slope angles (SSA). Eight female subjects undergoing pelvic radiotherapy performed a structured daily hip exercise regimen (extension and external rotation) immediately prior to both simulation imaging and daily treatment, throughout their RT course. This exercising cohort was compared to a retrospective review of 20 subjects (17 women and 3 men) undergoing RT, who had usual care. SSA measurements from daily pre-treatment imaging were compared to SSA measurements from the simulation CT. The average variation in SSA among the intervention subjects was 0.91° (± 0.58°), with a range among subjects of 0.57°-1.27°. The average variation for the control subjects was 2.27° (± 1.43°), ranging 1.22°-5.09°. The difference between the two groups was statistically significant (p = 0.0001). There was a statistically significant SSA variation between groups at each week of treatment. There was no significant variation among the intervention subjects between week 1 and later weeks, whereas subjects in the control group demonstrated significant SSA variation between week 1 and later weeks. We demonstrated a significant decrease in the variability of SSA by implementing a simple pre-treatment exercise program, while control subjects exhibited increasing variation in SSA over the course of treatment. We conclude that there is a potential benefit of prehabilitation during pelvic RT; however, a larger randomized control trial is required to confirm the findings.Clinical Trial: This research project was approved by the University of Massachusetts Medical School IRB (IRB ID H00012353) on January 21, 2017. The study is listed on ClinicalTrials.gov, provided by the U.S. National Library of Medicine, found with identifier NCT03242538.

Liquid Biopsy in Oligometastatic Prostate Cancer-A Biologist's Point of View

Prostate cancer (PCa) is the main cause of cancer-related mortality in males and the diagnosis, treatment, and care of these patients places a great burden on healthcare systems globally. Clinically, PCa is highly heterogeneous, ranging from indolent tumors to highly aggressive disease. In many cases treatment-generally either radiotherapy (RT) or surgery-can be curative. Several key genetic and demographic factors such as age, family history, genetic susceptibility, and race are associated with a high incidence of PCa. While our understanding of PCa, which is mainly based on the tools of molecular biology-has improved dramatically in recent years, efforts to better understand this complex disease have led to the identification of a new type of PCa-oligometastatic PCa. Oligometastatic disease should be considered an individual, heterogeneous entity with distinct metastatic phenotypes and, consequently, wide prognostic variability. In general, patients with oligometastatic disease typically present less biologically aggressive tumors whose metastatic potential is more limited and which are slow-growing. These patients are good candidates for more aggressive treatment approaches. The main aim of the presented review was to evaluate the utility of liquid biopsy for diagnostic purposes in PCa and for use in monitoring disease progression and treatment response, particularly in patients with oligometastatic PCa. Liquid biopsies offer a rapid, non-invasive approach whose use t is expected to play an important role in routine clinical practice to benefit patients. However, more research is needed to resolve the many existing discrepancies with regard to the definition and isolation method for specific biomarkers, as well as the need to determine the most appropriate markers. Consequently, the current priority in this field is to standardize liquid biopsy-based techniques. This review will help to improve understanding of the biology of PCa, particularly the recently defined condition known as "oligometastatic PCa". The presented review of the body of evidence suggests that additional research in molecular biology may help to establish novel treatments for oligometastatic PCa. In the near future, the treatment of PCa will require an interdisciplinary approach involving active cooperation among clinicians, physicians, and biologists.

Retrospective study comparing MR-guided radiation therapy (MRgRT) setup strategies for prostate treatment: repositioning vs. replanning

BACKGROUND

This study compared adaptive replanning and repositioning corrections based on soft-tissue matching for prostate cancer by using the magnetic resonance-guided radiation therapy (MRgRT) system.

METHODS

A total of 19 patients with prostate cancer were selected retrospectively. Weekly magnetic resonance image (MRI) scans were acquired for 5 weeks for each patient to observe the anatomic changes during the treatment course. Initial intensity-modulated radiation therapy (IMRT) plans (iIMRT) were generated for each patient with 13 coplanar ⁶⁰Co beams on a ViewRay™ system. Two techniques were applied: patient repositioning and replanning. For patient repositioning, one plan was created: soft-tissue (prostate) matching (Soft). The dose distribution was calculated for each MRI with the beam delivery parameters from the initial IMRT plan. The replanning technique was used to generate the Adaptive plan, which was the reoptimized plan for the weekly MRI. The dose-volumetric parameters of the planning target volume (PTV), bladder, and rectum were calculated for all plans. During the treatment course, the PTV, bladder, and rectum were evaluated for changes in volume and the effect on dosimetric parameters. The differences between the dose-volumetric parameters of the plans were examined through the Wilcoxon test. The initial plan was used as a baseline to compare the differences.

RESULTS

The Adaptive plan showed better target coverage during the treatment period, but the change was not significant in the Soft plan. There were significant differences in D_98%, D_95%, and D_2% in PTV between the Soft and Adaptive plans (p < 0.05) except for D_mean. There was no significant change in D_max and D_mean as the treatment progressed with all plans. All indices for the Adaptive plan stayed the same compared to those of iIMRT during the treatment course. There were significant differences in D_15%, D_25%, D_35%, and D_50% in the bladder between the Soft and Adaptive plans. The Adaptive plan showed the worse dose sparing than the Soft plan for the bladder according to each dosimetric index. In contrast to the bladder, the Adaptive plan achieved better sparing than the Soft plan during the treatment course. The significant differences were only observed in D_15% and D_35% between the Soft and Adaptive plans (p < 0.05).

CONCLUSIONS

Patient repositioning based on the target volume (Soft plan) can relatively retain the target coverage for patients and the OARs remain at a clinically tolerance level during the treatment course. The Adaptive plan did not clinically improve for the dose delivered to OARs, it kept the dose delivered to the target volume constant. However, the Adaptive plan is beneficial when the organ positions and volumes change considerable during treatment.

Risk-adapted moderate hypofractionation of prostate cancer : A prospective analysis of acute toxicity, QOL and outcome in 221 patients

Purpose

Prostate cancer (PCA) is highly heterogeneous in terms of its oncologic outcome. We therefore aimed to tailor radiation treatment to the risk status by using three different hypofractionated radiation regimen differing in applied dose, use of rectum spacer, inclusion of pelvic lymph nodes (pLN) and use of androgen deprivation therapy (ADT). Here we report on acute toxicity, quality of life (QOL) and oncologic outcome at a median follow-up of 12 months.

Methods

A total of 221 consecutive PCA patients received hypofractionated intensity-modulated radiotherapy (IMRT). Low-risk (LR) patients were planned to receive 60 Gy in 20 fractions (EQD2^α/β1.5 = 77.1 Gy), intermediate-risk (IR) patients 63 Gy in 21 fractions (EQD2^α/β1.5 = 81 Gy), and high-risk (HR) patients 67.5 Gy in 25 fractions (EQD2^α/β1.5 = 81 Gy) to the prostate and 50 Gy in 25 fractions to the pLN. Acute rectal toxicity was assessed by endoscopy. In addition, toxicity was scored using CTC-AE 4.0 and IPSS score, while QOL was assessed using QLQ-PR25 questionnaires.

Results

Acute CTC reactions were slightly higher in the HR regimen but reverted to baseline at 3 months. GI G2 toxicity was 4%, 0% and 12% for the LR, IR and HR regimen. Compared to IR patients, the increase in toxicity in HR patients was statistically significant (p = 0.002) and mainly caused by a higher incidence of diarrhea presumably due to pelvic EBRT. QOL scores of all domains were worse for the HR regimen (not significant).

Conclusion

Risk-adapted moderate hypofractionation is associated with low GI/GU toxicity. Given the higher rate of pelvic metastases in HR patients, slightly higher transient acute reactions should be outweighed by possible oncological benefits.

Plan quality for high-risk prostate cancer treated with high field magnetic resonance imaging guided radiotherapy

Background and purpose

Daily radiotherapy plan adaptation facilitated by a high field magnetic resonance linac (MRL) may potentially reduce the treated volume due to a reduction of the setup uncertainty. However, the technology also imposes limitations to the treatment technique compared to a standard linac. This study investigated the clinical quality of MRL treatment plans against current standard plans using identical planning target volume margins for high-risk prostate cancer patients.

Materials and methods

Twenty consecutive patients planned with our current clinical standard TPS and treated with single arc VMAT on standard linacs with 78 Gy in the prostate and 56 Gy for pelvic lymph nodes over 39 fractions were included. In addition, IMRT treatment plans for delivery by a 1.5 T MRL, using standard margins and dose objectives, were made in a dedicated TPS. Mean population dose volume histograms (DVH) and dose metrics were analyzed and clinical plan quality was evaluated by an oncologist.

Results

All MRL plans were considered clinically acceptable, and DVH analysis showed an overall high similarity to dose distributions of the clinically delivered plans. Mean target coverage was similar (78.0 Gy vs 77.8 Gy). Small but statistically significant differences were seen in doses to organs at risk; on average MRL plans reduced dose to the bladder (46.2 vs 48.3 Gy) compared to standard plans, while dose was higher to the bowel (29.2 vs 26.6 Gy) and penile bulb (16.5 vs 10.8 Gy).

Conclusion

MRL treatment plans were clinically acceptable and similar in quality to the current standard.