Results of intensity modulated radiotherapy (IMRT) in laryngeal and hypopharyngeal cancer: a dose escalation study

How rapid advances in imaging are defining the future of precision radiation oncology

Imaging has an essential role in the planning and delivery of radiotherapy. Recent advances in imaging have led to the development of advanced radiotherapy techniques—including image-guided radiotherapy, intensity-modulated radiotherapy, stereotactic body radiotherapy and proton beam therapy. The optimal use of imaging might enable higher doses of radiation to be delivered to the tumour, while sparing normal surrounding tissues. In this article, we review how the integration of existing and novel forms of computed tomography, magnetic resonance imaging and positron emission tomography have transformed tumour delineation in the radiotherapy planning process, and how these advances have the potential to allow a more individualised approach to the cancer therapy. Recent data suggest that imaging biomarkers that assess underlying tumour heterogeneity can identify areas within a tumour that are at higher risk of radio-resistance, and therefore potentially allow for biologically focussed dose escalation. The rapidly evolving concept of adaptive radiotherapy, including artificial intelligence, requires imaging during treatment to be used to modify radiotherapy on a daily basis. These advances have the potential to improve clinical outcomes and reduce radiation-related long-term toxicities. We outline how recent technological advances in both imaging and radiotherapy delivery can be combined to shape the future of precision radiation oncology.

Dose-volume response in acute dysphagia toxicity: Validating QUANTEC recommendations into clinical practice for head and neck radiotherapy

PURPOSE

To determine the validity of QUANTEC recommendations in predicting acute dysphagia using intensity-modulated head and neck radiotherapy.

MATERIAL AND METHODS

Seventy-six consecutive patients with locally advanced squamous cell carcinoma (SCC) of the head and neck +/- systemic therapy were analyzed. Multiple dose parameters for the larynx (V50Gy, Dmean and Dmax) were recorded. Acute dysphagia toxicity was prospectively scored in all treatment weeks (week 1-6 or 1-7) using CTCAEv3 by three blinded investigators. QUANTEC larynx recommendations (V50Gy < 27%, Dmean < 44 Gy, Dmean < 40 Gy, Dmax < 66 Gy) were used to group the cohort (i.e. V50Gy < 27% vs. V50Gy > 27%). The proportion of patients with Grade 3 dysphagia was compared within each group.

RESULTS

There was a significant reduction in the incidence of grade 3 toxicity in the V50Gy < or > 27% group at week 5 (14.3% vs. 45.2%, p = 0.01) and 6 (25.9% vs. 65.9%, p < 0.01). A significant reduction at week 5 (14.7% vs. 50.0, p = 0.02) and 6 (32.4% vs. 67.6%, p = 0.01) was seen in Dmean < 44 Gy when compared to Dmean > 44 Gy. Dmean < 40 Gy also delivered a significant reduction at week 5 (5.6% vs. 42.3%, p < 0.01) and week 6 (23.5% vs. 59.3%, p = 0.01). A significant toxicity reduction at treatment week 6 (28.0% vs. 63.0%, p = 0 < 01) was seen from Dmax < 66 Gy to Dmax > 66 Gy. V50Gy > 27% (p < 0.01), Dmean > 40 Gy (p = 0.01) and Dmax > 66 Gy (p < 0.01) were also predictors of Grade 3 dysphagia when analyzed with multiple clinical risk factors.

CONCLUSIONS

QUANTEC late toxicity recommendations for dose to larynx during IMRT are a useful predictor for acute dysphagia toxicity in this patient cohort. Furthermore, this included chemoradiotherapy regimes and post-operative radiotherapy patients, allowing for prophylactic implementation of supportive care measures.

Preventive sparing of spinal cord and brain stem in the initial irradiation of locally advanced head and neck cancers

Since reirradiation in recurrent head and neck patients is limited by previous treatment, a marked reduction of maximum doses to spinal cord and brain stem was investigated in the initial irradiation of stage III/IV head and neck cancers. Eighteen patients were planned by simultaneous integrated boost, prescribing 69.3 Gy to PTV1 and 56.1 Gy to PTV2. Nine 6 MV coplanar photon beams at equispaced gantry angles were chosen for each patient. Step‐and‐shoot IMRT was calculated by direct machine parameter optimization, with the maximum number of segments limited to 80. In the standard plan, optimization considered organs at risk (OAR), dose conformity, maximum dose <45 Gy to spinal cord and <50 Gy to brain stem. In the sparing plans, a marked reduction to spinal cord and brain stem were investigated, with/without changes in dose conformity. In the sparing plans, the maximum doses to spinal cord and brain stem were reduced from the initial values (43.5±2.2 Gy and 36.7±14.0 Gy), without significant changes on the other OARs. A marked difference (−15.9±1.9 Gy and −10.1±5.7 Gy) was obtained at the expense of a small difference (−1.3%±0.9%) from initial PTV195% coverage (96.6%±0.9%). Similar difference (−15.7±2.2 Gy and −10.2±6.1 Gy) was obtained compromising dose conformity, but unaffecting PTV195% and with negligible decrease in PTV295% (−0.3%±0.3% from the initial 98.3%±0.8%). A marked spinal cord and brain stem preventive sparing was feasible at the expense of a decrease in dose conformity or slightly compromising target coverage. A sparing should be recommended in highly recurrent tumors, to make potential reirradiation safer.

PACS number: 87.55.D

Clinical evaluation of intensity-modulated radiotherapy for head and neck cancers

Radiotherapy and surgery are the principal curative modalities in treatment of head and neck cancer. Conventional two-dimensional and three-dimensional conformal radiotherapy result in significant side effects and altered quality of life. Intensity-modulated radiotherapy (IMRT) can spare the normal tissues, while delivering a curative dose to the tumour-bearing tissues. This article reviews the current role of IMRT in head and neck cancer from the point of view of normal tissue sparing, and also reviews the current published literature by individual head and neck cancer subsites. In addition, we briefly discuss the role of image guidance in head and neck IMRT, and future directions in this area.

Recent advances in radiotherapy

Radiation therapy has come a long way from treatment planning based on orthogonal radiographs with large margins around tumours. Advances in imaging and radiation planning software have led to three-dimensional conformal radiotherapy and, further, to intensity modulated radiotherapy (IMRT). IMRT permits sparing of normal tissues and hence dose-escalation to tumours. IMRT is the current standard in treatment of head and prostate cancer and is being investigated in other tumour sites. Exquisitely sculpted dose distributions (increased geographical miss) with IMRT, plus tumour motion and anatomical changes during radiotherapy make image guided radiotherapy an essential part of modern radiation delivery. Various hardware and software tools are under investigation for optimal IGRT.

Advances in radiotherapy for head and neck cancer

Radiotherapy and surgery are the principal curative modalities in treatment of head and neck cancer. Conventional (two dimensional, 2D and three-dimensional conformal radiotherapy, 3DCRT) result in significant side-effects and altered quality of life. Intensity modulated radiotherapy (IMRT) can spare the normal tissues, while delivering a curative dose to the tumour bearing tissues. Technical advances like volumetric intensity modulated arc therapy (VMAT) have helped optimise IMRT further. Image guided radiotherapy (IGRT) can be used to aid target delineation and also help reduce the PTV margins to further enhance the therapeutic ratio. Particle therapy using protons provides significant advantage in terms of normal tissue sparing and is recommended for small cranial tumours and in radiotherapy for paediatric patients.

The value of magnetic resonance imaging in target volume delineation of base of tongue tumours--a study using flexible surface coils

INTRODUCTION

Magnetic resonance imaging (MRI) provides superior diagnostic accuracy over computed tomography (CT) in oropharyngeal tumours. Precise delineation of the gross tumour volume (GTV) is mandatory in radiotherapy planning when a GTV boost is required. CT volume definition in this regard is poor. We studied the feasibility of using flexible surface (flex-L) coils to obtain MR images for MR-CT fusion to assess the benefit of MRI over CT alone in planning base of tongue tumours.

METHODS

Eight patients underwent CT and MRI radiotherapy planning scans with an immobilisation device. Distortion-corrected T1-weighted post-contrast MR scans were fused to contrast-enhanced planning CT scans. GTV, clinical target and planning target volumes (CTV, PTV) and organs at risk (OAR) were delineated on CT, then on MRI with blinding to the CT images. The volumetric and spatial differences between MRI and CT volumes for GTV, CTV, PTV and OAR were compared. MR image distortions due to field inhomogeneity and non-linear gradients were corrected and the need for such correction was evaluated.

RESULTS

The mean primary GTV was larger on MRI (22.2 vs. 9.5 cm(3), p=0.05) than CT. The mean primary and nodal GTV (i.e. BOT and macroscopic nodes) was significantly larger on MRI (27.2 vs. 14.4 cm(3), p=0.05). The volume overlap index (VOI) between MRI and CT for the primary was 0.34 suggesting that MRI depicts parts of the primary tumour not detected by CT. There was no significant difference in volume delineation between MR and CT for CTV, PTV, nodal CTV and nodal PTV. MRI volumes for brainstem and spinal cord were significantly smaller due to improved organ definition (p=0.002). Susceptibility and gradient-related distortions were not found to be clinically significant.

CONCLUSION

MRI improves the definition of tongue base tumours and neurological structures. The use of MRI is recommended for GTV dose-escalation techniques to provide precise depiction of GTV and improved sparing of spinal cord and brainstem.