Asymmetric arc technique for posterior pharyngeal wall and retropharyngeal space tumors

Treatment of squamous cell carcinoma of the posterior pharyngeal wall: Radiotherapy versus surgery

BACKGROUND

Treatment strategy in squamous cell carcinoma (SCC) of the posterior pharyngeal wall is still being debated.

METHODS

We performed a retrospective analysis according to delivered treatment.

RESULTS

One hundred eighty patients were treated between 1997 and 2011. Eighty-nine patients (49.4%) received surgery +/- radiotherapy (RT), whereas 91 (50.6%) received definitive RT +/- chemoradiotherapy (RT/CRT). Five-year overall survival (OS) was 33.4%. There was a significant 5-year OS benefit in surgical treatment versus RT/CRT (43% vs 24.1%; p = .002). Multivariate analysis showed that current smokers, T3 to T4 classification, well-differentiated SCC, and nonsurgical treatment were associated with reduced OS. Subgroup analysis showed significant survival benefit of surgical treatment compared with RT/CRT in patients with T1 to T2 but not in T3 to T4 disease.

CONCLUSION

Surgical management translated into a survival benefit, even in early T classification. These results should be interpreted with caution for selection bias. Surgery remains the standard of care in localized posterior pharyngeal wall SCC. Primary CRT should be considered for nonoperable disease. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1722-E1729.

'Boomerang' technique: an improved method for conformal treatment of locally advanced nasopharyngeal cancer

The primary aim of the present study was to assess radiation dosimetry and subsequent clinical outcomes in patients with locally advanced nasopharyngeal cancer using a novel radiation technique termed the 'Boomerang'. Dosimetric comparisons were made with both conventional and intensity modulated radiation therapy (IMRT) techniques. This is a study of 22 patients treated with this technique from June 1995 to October 1998. The technique used entailed delivery of 36 Gy in 18 fractions via parallel opposed fields, then 24 Gy in 12 fractions via asymmetric rotating arc fields for a total of 60 Gy in 30 fractions. Patients also received induction and concurrent chemotherapy. The radiation dosimetry was excellent. Dose-volume histograms showed that with the arc fields, 90% of the planning target volume received 94% of the prescribed dose. Relative to other conventional radiation therapy off-cord techniques, the Boomerang technique results in a 27% greater proportion of the prescribed dose being received by 90% of the planning target volume. This translates into an overall 10% greater dose received for the same prescribed dose. At 3 years, the actuarial loco-regional control rate, the failure-free survival rate and the overall survival rate were 91, 75 and 91%, respectively. At 5 years, the actuarial loco-regional control rate, the failure-free survival rate and the overall survival rate were 74, 62 and 71%, respectively. The Boomerang technique provided excellent radiation dosimetry with correspondingly good loco-regional control rates (in conjunction with chemotherapy) and very acceptable acute and late toxicity profiles. Because treatment can be delivered with conventional standard treatment planning and delivery systems, it is a validated treatment option for centres that do not have the capability or capacity for IMRT. A derivative of the Boomerang technique, excluding the parallel opposed component, is now our standard for patients with locally advanced nasopharyngeal cancer when IMRT is not available.

Intensity-modulated arc therapy simplified

PURPOSE

We present a treatment planning strategy for intensity-modulated radiation therapy using gantry arcs with dynamic multileaf collimator, previously termed intensity-modulated arc therapy (IMAT).

METHODS AND MATERIALS

The planning strategy is an extension of the photon bar arc and asymmetric arc techniques and is classified into three levels of complexity, with increasing number of gantry arcs. This principle allows us to generalize the analysis of the number of arcs required for intensity modulation for a given treatment site. Using a phantom, we illustrate how the current technique is more flexible than the photon bar arc technique. We then compare plans from our strategy with conventional three-dimensional conformal treatment plans for three sites: prostate (prostate plus seminal vesicles), posterior pharyngeal wall, and chest wall.

RESULTS

Our strategy generates superior IMAT treatment plans compared to conventional three-dimensional conformal plans. The IMAT plans spare critical organs well, and the trade-off for simplicity is that the dose uniformity in the target volume may not rival that of true inverse treatment plans.

CONCLUSIONS

The analyses presented in this paper give a better understanding of IMAT plans. Our strategy is easier to understand and more efficient in generating plans than inverse planning systems; our plans are also simpler to modify, and quality assurance is more intuitive.

Radiation techniques for head and neck tumors

PURPOSE

A technique that combines some advantages of conforming techniques for advanced oro- and hypopharyngeal carcinomas is proposed. The aim is to increase the dose homogeneity in the target volume relative to lateral opposed fields.

METHODS AND MATERIALS

This publication compares conforming radiation techniques based on standard equipment, standard linear accelerator setup and commercially available planning software with lateral opposed fields. More advanced conformal techniques reported in the literature are taken into account in a semi-quantitative manner. Our standard method uses an arc rotation, sparing the spinal cord. In contrast to earlier methods of this type, the resulting dose deficit in the vicinity of the spine is compensated by static lateral wedged fields. Dose distributions for 25 consecutive patients were planned.

RESULTS

The conforming techniques were found to produce more homogeneous dose distributions than lateral opposed fields. In the planning target volume (PTV) (mean: 940 cm(3)) a standard deviation of dose of 4.6% was achieved. Ninety-five percent of the PTV were enclosed by the 90% isodose. The maximal spinal cord dose was limited to 45 Gy. The dose distributions of these techniques could compete with literature data on advanced techniques (the published dose-volume histogram (DVHs) of PTVs were evaluated). At the linear accelerator time for realization took 14 min on average. The planning time is 1-4 h (mean: less than 2 h).

CONCLUSION

A rotational technique applicable with standard equipment is presented. Dose coverage of target volumes is improved, while the spinal cord is spared.

Clinical use of asymmetric collimators

PURPOSE

To illustrate some of the radiation treatment techniques with asymmetric collimators in one field dimension.

METHODS AND MATERIALS

Treatment planning for various sites is done with an in-house developed treatment planning system. Dose distributions in the central plane are illustrated.

RESULTS

The use of asymmetric collimation, in addition to being a replacement for cerrobend and lead blocks, can facilitate treatment setup with boost fields and with half-beam asymmetric fields as in matching two adjacent fields, in avoiding nearby critical organ or tissue, and in tangential breast treatment. The use of asymmetric collimators would alter the dose distribution across the radiation field and should be accounted for during treatment planning. In conjunction with arc rotation or multiple asymmetric fields, two-dimensional conformal radiotherapy is possible.

CONCLUSION

The full potential of asymmetric collimation requires the use of a proper treatment planning algorithm. Some of the treatment techniques with asymmetric collimation in one field dimension are shown here.