IMRT in the treatment of head and neck cancer: is the present already the future?

[Re-irradiation of head and neck cancers: Target volumes, technical evolutions and prospects]

Malignant tumors of the head and neck have a predominantly regional recurrence pattern, with most deaths resulting from this progression. Optimization of re-radiation in recurrence setting is a major objective for these patients. Extensive research has been carried out with the PubMed search engine to find publications dealing with this topic. The first attempts to reirradiate the ORL sphere date back to the 1980s and the first to be performed by intensity modulation conformational radiotherapy (IMRT) date back to the late 1990s. Compared to 3 dimensional conformal radiotherapy, IMRT improves clinical outcomes and reduces toxicity. In IMRT series, associated or not with concomitant chemotherapy, the locoregional control obtained at 2 years was of the order of 45 to 65% and the overall survival of 15 to 60%, depending on predictive factors. Grade 3 acute toxicity occurred on the order of 10 to 30% and late-grade 3 toxicity on the order of 15 to 50%. In a selected population with low volumes tumors, stereotactic re-irradiation at a minimum dose of 35Gy obtained outcome comparable to IMRT. Re-irradiation of head and neck tumors by proton therapy is rare. The toxicity rate appears to be lower than that usually seen after photon therapy. However, we do not have a long follow-up. This technique therefore remains reserved for search protocols and represents a future perspective in these situations.

The management of head and neck tumors with high technology radiation therapy

Squamous cell carcinoma is responsible for 90% of the head and neck cancers affecting over 600,000 people worldwide. Radiation therapy, surgery and chemotherapy are the most important treatment modalities in head and neck squamous cell carcinoma. The aim of this review is to summarize the recent innovations in head and neck radiation therapy, which intends to appreciate the cutting-edge intensity-modulated radiation therapy strategies to mitigate long-term toxicities and evaluate promising technologies in the field as adaptive treatment, dose painting and proton therapy.

The potential of proton beam radiation therapy in head and neck cancer

A group of Swedish oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy. The estimations have been based on current statistics of tumour incidence, number of patients potentially eligible for radiation treatment, scientific support from clinical trials and model dose planning studies and knowledge of the dose-response relations of different tumours and normal tissues. In head and neck cancer, including thyroid cancer, it is assessed that at least 300 patients annually will gain sufficiently from proton beam therapy, both to improve tumour control and to decrease toxicity to compensate for the increased treatment costs using protons.

Monte Carlo dose verification of prostate patients treated with simultaneous integrated boost intensity modulated radiation therapy

BACKGROUND

To evaluate the dosimetric differences between Superposition/Convolution (SC) and Monte Carlo (MC) calculated dose distributions for simultaneous integrated boost (SIB) prostate cancer intensity modulated radiotherapy (IMRT) compared to experimental (film) measurements and the implications for clinical treatments.

METHODS

Twenty-two prostate patients treated with an in-house SIB-IMRT protocol were selected. SC-based plans used for treatment were re-evaluated with EGS4-based MC calculations for treatment verification. Accuracy was evaluated with-respect-to film-based dosimetry. Comparisons used gamma (gamma)-index, distance-to-agreement (DTA), and superimposed dose distributions. The treatment plans were also compared based on dose-volume indices and 3-D gamma index for targets and critical structures.

RESULTS

Flat-phantom comparisons demonstrated that the MC algorithm predicted measurements better than the SC algorithm. The average PTVprostate D98 agreement between SC and MC was 1.2% +/- 1.1. For rectum, the average differences in SC and MC calculated D50 ranged from -3.6% to 3.4%. For small bowel, there were up to 30.2% +/- 40.7 (range: 0.2%, 115%) differences between SC and MC calculated average D50 index. For femurs, the differences in average D50 reached up to 8.6% +/- 3.6 (range: 1.2%, 14.5%). For PTVprostate and PTVnodes, the average gamma scores were >95.0%.

CONCLUSION

MC agrees better with film measurements than SC. Although, on average, SC-calculated doses agreed with MC calculations within the targets within 2%, there were deviations up to 5% for some patient's treatment plans. For some patients, the magnitude of such deviations might decrease the intended target dose levels that are required for the treatment protocol, placing the patients in different dose levels that do not satisfy the protocol dose requirements.

Psychosocial and economic impact of cancer

This article explores the psychosocial and economic implications of cancer and their relevance to the clinician. After a general overview of the topic, the authors focus on aspects of particular importance to the dental professional, including the psychosocial and economic implications of the oral complications of cancer and its therapy, head and neck cancers, and special issues among children with cancer and cancer survivors.

Potential for intensity-modulated radiation therapy to permit dose escalation for canine nasal cancer

We evaluated the impact of inverse planned intensity-modulated radiation therapy (IMRT) on the dose-volume histograms (DVHs) and on the normal tissue complication probabilities (NTCPs) of brain and eyes in dogs with nasal tumors. Nine dogs with large, caudally located nasal tumors were planned using conventional techniques and inverse planned IMRT for a total prescribed dose of 52.5 Gy in 3.5 Gy fractions. The equivalent uniform dose for brain and eyes was calculated to estimate the normal tissue complication probability (NTCP) of these organs. The NTCP values as well as the DVHs were used to compare the treatment plans. The dose distribution in IMRT plans was more conformal than in conventional plans. The average dose delivered to one-third of the brain was 10 Gy lower with the IMRT plan compared with conventional planning. The mean partial brain volume receiving 43.6 Gy or more was reduced by 25.6% with IMRT. As a consequence, the NTCPs were also significantly lower in the IMRT plans. The mean NTCP of brain was two times lower and at least one eye could be saved in all patients planed with IMRT. Another possibility with IMRT is dose escalation in the target to improve tumor control while keeping the NTCPs at the same level as for conventional planning. Veterinary

Recent Advances in Radiation Therapy for Head and Neck Cancer

The treatment of locally advanced or recurrent head and neck cancers has improved from single modality interventions of surgery and radiation therapy alone to include combined modality therapy with surgery, chemotherapy and radiation. Combined therapy has led to improved local control and disease-free survival. New developments in radiation oncology such as altered fractionation, three-dimensional conformal radiotherapy, intensity-modulated radiotherapy, stereotactic radiosurgery, fractionated stereotactic radiotherapy, charged-particle radiotherapy, neutron-beam radiotherapy, and brachytherapy have helped to improve this outlook even further. These recent advances allow for a higher dose to be delivered to the tumor while minimizing the dose delivered to the surrounding normal tissue. This article provides an update of the new developments in radiotherapy in the management of head and neck cancers.

Monte Carlo–based dosimetry of head-and-neck patients treated with SIB-IMRT

PURPOSE

To evaluate the accuracy of previously reported superposition/convolution (SC) dosimetric results by comparing with Monte Carlo (MC) dose calculations for head-and-neck intensity-modulated radiation therapy (IMRT) patients treated with the simultaneous integrated boost technique.

METHODS AND MATERIALS

Thirty-one plans from 24 patients previously treated on a phase I/II head-and-neck squamous cell carcinoma simultaneous integrated boost IMRT protocol were used. Clinical dose distributions, computed with an SC algorithm, were recomputed using an EGS4-based MC algorithm. Phantom-based dosimetry quantified the fluence prediction accuracy of each algorithm. Dose-volume indices were used to compare patient dose distributions.

RESULTS AND DISCUSSION

The MC algorithm predicts flat-phantom measurements better than the SC algorithm. Average patient dose indices agreed within 2.5% of the local dose for targets; 5.0% for parotids; and 1.9% for cord and brainstem. However, only 1 of 31 plans agreed within 3% for all indices; 4 of 31 agreed within 5%. In terms of the prescription dose, 4 of 31 plans agreed within 3% for all indices, whereas 28 of 31 agreed within 5%.

CONCLUSIONS

Average SC-computed doses agreed with MC results in the patient geometry; however deviations >5% were common. The fluence modulation prediction is likely the major source of the dose discrepancy. The observed dose deviations can impact dose escalation protocols, because they would result in shifting patients to higher dose levels.

The simultaneous integrated boost with proton beams in head and neck patients

The potential benefit of the simultaneous integrated boost (SIB) concept in proton therapy was investigated in a planning study. The proposed fractionation strategy consisted of a SIB treatment following a first phase of conventional fractionation to the elective volume (named SEQ/SIB). The novel method was compared to a conventional sequential fractionation and to a full SIB approach. Treatment plans were designed for five patients on the proton planning system developed for spot scanning at the Paul Scherrer Institute of Villigen (CH). Three to five beams were applied for all plans and fractionations. All effective dose distributions were corrected using biological models to take into account repopulation and time at repopulation onset. Corrected and uncorrected plans were compared on the basis of dosimetry criteria and dose-volume histograms. The results showed a dosimetric advantage for the SEQ/SIB approach in terms of target coverage, without significant disadvantages for risk structures and healthy tissue. Considering the high logistic impact and the limited availability of radiation facilities, the clinical exploitation of accelerated SIB treatment with protons appears promising.

Comparative dosimetric evaluation of the simultaneous integrated boost with photon intensity modulation in head and neck cancer patients

BACKGROUND AND PURPOSE

The objective of this study is to evaluate, at planning and dosimetric level, the potential benefits of the simultaneous integrated boost (SIB) concept with intensity-modulated radiation therapy (IMRT), using a comparative analysis on physical dose distributions corrected for radiobiological models. The concept of SIB at the end of the treatment has been analysed as an alternative acceleration scheme.

PATIENTS AND METHODS

Physical dose distributions were computed on a commercial planning system (Varian Cadplan-Helios) for five patients presenting with advanced head and neck carcinomas. Treatment plans were designed using five IMRT beams. Three fractionation strategies were compared in the study: the standard sequential irradiation SEQ of elective and boost volumes, the pure SIB, and a modified SIB (SEQ/SIB), where the actual SIB follows a first phase of conventional fractionation to the elective volume. All physical dose distributions were corrected using a linear quadratic biological model, taking into account also repopulation and time at repopulation onset. Objective quantities, derived from biological dose volume histograms, were used for the analysis.

RESULTS

Physical doses equivalent to 50 and 80 Gy (in fractions of 2 Gy) to elective volume and boost were calculated for the SIB and SEQ/SIB regimes. With SIB 54 and 72 Gy dose levels have to be delivered in 30 fractions, while in the SEQ/SIB scheme 36 Gy are delivered in 20 sessions to the elective volume, and further 18 and 35.5 Gy during the last 10 fractions are delivered to elective volume and boost, respectively (for a total physical dose of 71.5 Gy). The comparison showed: (1) the boost target homogeneity resulted in generally acceptable and comparable among sequential and modified SIB schemes, while it was statistically worse for the pure SIB approach; (2) the fraction of elective target volume not included in the boost volume was characterised by a higher level of dose heterogeneity; (3) the spinal cord never reached tolerance levels and maximum point dose was on average below 38 Gy (biologically corrected to 2 Gy/fraction); and (4) sparing of parotid glands strongly depends on their eventual inclusion in the target volumes: for glands not included or only partially included, it was possible on average to keep the dose to 2/3 of the volume below 29 Gy for all regimes (32 Gy as physical dose).

CONCLUSIONS

Feasibility of SIB techniques and in particular of the modified SIB appears to be dosimetrically proven and the results reported here justify the activation of a phase I protocol to verify clinically their impact using IMRT photon-based techniques.