Intensity-modulated radiation therapy in head and neck cancer: Prescribed dose, clinical challenges and results

Assessment of anatomical and dosimetric changes by a deformable registration method during the course of intensity-modulated radiotherapy for nasopharyngeal carcinoma

The aim of this study was to quantify the anatomic variations and the dosimetric effects accessed by a deformable registration method throughout the entire course of radiotherapy, and to evaluate the necessity of replanning for patients with nasopharyngeal carcinoma (NPC). Plan1(CT1) was based on the original CT, and Plan2(CT2) was generated from the midtreatment CT scan acquired after 25 fractions of IMRT of Plan1. Both sets of CTs, RT structures and RT doses for the two group plans were transferred to a workstation, and then a hybrid IMRT plan, Plan1(CT2), was generated by deforming doses of Plan1 to CT2. Subsequently, the accumulated plan, Plan1 + 2(CT2), was generated to quantify the actual dosimetric effects during the course. The transverse diameter of the neck at the center of the odontoid process was (15.4 ± 1.0) cm and (14.4 ± 1.1) cm in CT1 and CT2, respectively (P < 0.05). Compared with CT1, the mean volumes of the right and left parotid glands were significantly decreased by (24.6 ± 11.9)% and (35.1 ± 20.1)%, respectively. Comparison of Plan1 (CT1) with Plan1 (CT2) indicated that the doses to targets decreased without replanning. With repeated CT and replanning after 25 fractions, the doses to targets would be improved. The doses to normal tissue were increased without replanning. For eight patients out of 12, the doses to the spinal cord and brainstem exceeded the constraints without replanning, while the corresponding values decreased with replanning. During the entire course of IMRT, the volumes of the targets and the parotid glands would be reduced significantly. Midtreatment CT scanning and replanning are recommended to ensure adaptive doses to the targets and critical normal tissues.

Clinical implications in the use of the PBC algorithm versus the AAA by comparison of different NTCP models/parameters

Purpose

Retrospective analysis of 3D clinical treatment plans to investigate qualitative, possible, clinical consequences of the use of PBC versus AAA.

Methods

The 3D dose distributions of 80 treatment plans at four different tumour sites, produced using PBC algorithm, were recalculated using AAA and the same number of monitor units provided by PBC and clinically delivered to each patient; the consequences of the difference on the dose-effect relations for normal tissue injury were studied by comparing different NTCP model/parameters extracted from a review of published studies. In this study the AAA dose calculation is considered as benchmark data. The paired Student t-test was used for statistical comparison of all results obtained from the use of the two algorithms.

Results

In the prostate plans, the AAA predicted lower NTCP value (NTCP_AAA) for the risk of late rectal bleeding for each of the seven combinations of NTCP parameters, the maximum mean decrease was 2.2%. In the head-and-neck treatments, each combination of parameters used for the risk of xerostemia from irradiation of the parotid glands involved lower NTCP_AAA, that varied from 12.8% (sd=3.0%) to 57.5% (sd=4.0%), while when the PBC algorithm was used the NTCP_PBC’s ranging was from 15.2% (sd=2.7%) to 63.8% (sd=3.8%), according the combination of parameters used; the differences were statistically significant. Also NTCP_AAA regarding the risk of radiation pneumonitis in the lung treatments was found to be lower than NTCP_PBC for each of the eight sets of NTCP parameters; the maximum mean decrease was 4.5%. A mean increase of 4.3% was found when the NTCP_AAA was calculated by the parameters evaluated from dose distribution calculated by a convolution-superposition (CS) algorithm. A markedly different pattern was observed for the risk relating to the development of pneumonitis following breast treatments: the AAA predicted higher NTCP value. The mean NTCP_AAA varied from 0.2% (sd = 0.1%) to 2.1% (sd = 0.3%), while the mean NTCP_PBC varied from 0.1% (sd = 0.0%) to 1.8% (sd = 0.2%) depending on the chosen parameters set.

Conclusions

When the original PBC treatment plans were recalculated using AAA with the same number of monitor units provided by PBC, the NTCP_AAA was lower than the NTCP_PBC, except for the breast treatments. The NTCP is strongly affected by the wide-ranging values of radiobiological parameters.

Simultaneous integrated boost-intensity-modulated radiotherapy in head and neck cancer

OBJECTIVES/HYPOTHESIS

To review toxicity and outcomes in patients with head and neck cancer treated with simultaneous integrated boost-intensity-modulated radiotherapy (SIB-IMRT).

STUDY DESIGN

Review of experience with the SIB-IMRT technique.

METHODS

Fifty patients were treated with the SIB-IMRT technique. Two possible schedules of radiation therapy (RT) were used: SIB 70 (70/60/54 in 33 fractions) and SIB 66 (66/60/54 in 33 fractions). Forty-one patients also received chemotherapy.

RESULTS

All but two patients completed treatment as prescribed. No G4 acute toxicity has been reported in our series. We did not observe any G3 to G4 chronic toxicity, apart from one case of cutaneous necrosis. After a median follow-up of 23.3 months (range, 1-60 months), 41 patients (82%) were alive and negative for disease, and one patient (2%) was alive with distant metastases. Eight patients (16%) died, seven because of progressive disease and one for other causes.

CONCLUSIONS

SIB-IMRT is a highly effective and safe technique of RT in the treatment of head and neck cancer.

Intensity-modulated radiotherapy in head and neck cancer: results of the prospective study GORTEC 2004-03

BACKGROUND AND PURPOSE

In 2003, the French Authority for Health (HAS) recommended the use of intensity modulated radiotherapy (IMRT) in prospective trial before its routine use. The Oncology and Radiotherapy Group for Head and Neck Cancer (GORTEC) proposed to evaluate prospectively acute and late toxicities, locoregional control and overall survival for patients treated for head and neck cancer (HNC) with IMRT and bilateral neck irradiation.

MATERIALS AND METHODS

Between 2002 and 2008, 208 patients with HNC were treated with IMRT in 8 centres. There were 38 nasopharynx, 117 oropharynx, 25 pharyngo-larynx, 24 oral cavity and 4 unknown primary (28.5% stage I-II and 71% Stage III-IV). Ninety-three patients (46%) had postoperative IMRT and 78 patients (37.5%) received concurrent chemotherapy. The doses were 70 Gy to the gross tumour, 66 Gy to the high-risk postoperative sites and 50 Gy to the subclinical disease. Toxicities were graded according to the RTOG-EORTC scales.

RESULTS

The median follow-up was 25.3 months (range: 0.4-72 months). There were 29 local-regional failures: 24 were in-field, three were marginal and one was out-field. The two-year loco-regional control and overall survival were 86% and 86.7%, respectively. At 18 months, grade ≥ 2 xerostomia was 16.1%. A mean dose to the spared parotid below 28 Gy led to significantly less grade ≥ 2 xerostomia (8.5% vs 24%) with a relative risk of 1.2 [95% CI: 1.02-1.41, p = 0.03]. Grade ≥ 2 xerostomia increased by approximately 3% per Gy of mean parotid dose up to 28, Gy then 7% per Gy above 33 Gy.

CONCLUSIONS

IMRT for HN cancer seems to reduce late toxicities without jeopardising local control and overall survival.

Radiation-induced salivary gland dysfunction results from p53-dependent apoptosis

PURPOSE

Radiotherapy for head-and-neck cancer causes adverse secondary side effects in the salivary glands and results in diminished quality of life for the patient. A previous in vivo study in parotid salivary glands demonstrated that targeted head-and-neck irradiation resulted in marked increases in phosphorylated p53 (serine(18)) and apoptosis, which was suppressed in transgenic mice expressing a constitutively active mutant of Akt1 (myr-Akt1).

METHODS AND MATERIALS

Transgenic and knockout mouse models were exposed to irradiation, and p53-mediated transcription, apoptosis, and salivary gland dysfunction were analyzed.

RESULTS

The proapoptotic p53 target genes PUMA and Bax were induced in parotid salivary glands of mice at early time points after therapeutic radiation. This dose-dependent induction requires expression of p53 because no radiation-induced expression of PUMA and Bax was observed in p53-/- mice. Radiation also induced apoptosis in the parotid gland in a dose-dependent manner, which was p53 dependent. Furthermore, expression of p53 was required for the acute and chronic loss of salivary function after irradiation. In contrast, apoptosis was not induced in p53-/- mice, and their salivary function was preserved after radiation exposure.

CONCLUSIONS

Apoptosis in the salivary glands after therapeutic head-and-neck irradiation is mediated by p53 and corresponds to salivary gland dysfunction in vivo.

Process control analysis of IMRT QA: implications for clinical trials

The purpose of this study is two-fold: first is to investigate the process of IMRT QA using control charts and second is to compare control chart limits to limits calculated using the standard deviation (sigma). Head and neck and prostate IMRT QA cases from seven institutions in both academic and community settings are considered. The percent difference between the point dose measurement in phantom and the corresponding result from the treatment planning system (TPS) is used for analysis. The average of the percent difference calculations defines the accuracy of the process and is called the process target. This represents the degree to which the process meets the clinical goal of 0% difference between the measurements and TPS. IMRT QA process ability defines the ability of the process to meet clinical specifications (e.g. 5% difference between the measurement and TPS). The process ability is defined in two ways: (1) the half-width of the control chart limits, and (2) the half-width of +/-3sigma limits. Process performance is characterized as being in one of four possible states that describes the stability of the process and its ability to meet clinical specifications. For the head and neck cases, the average process target across institutions was 0.3% (range: -1.5% to 2.9%). The average process ability using control chart limits was 7.2% (range: 5.3% to 9.8%) compared to 6.7% (range: 5.3% to 8.2%) using standard deviation limits. For the prostate cases, the average process target across the institutions was 0.2% (range: -1.8% to 1.4%). The average process ability using control chart limits was 4.4% (range: 1.3% to 9.4%) compared to 5.3% (range: 2.3% to 9.8%) using standard deviation limits. Using the standard deviation to characterize IMRT QA process performance resulted in processes being preferentially placed in one of the four states. This is in contrast to using control charts for process characterization where the IMRT QA processes were spread over three of the four states with none of the processes in the ideal state. Control charts may be used for IMRT QA in clinical trials to categorize process performance, minimize protocol variation and guide process improvements. For the duration of an institution's participation in a protocol, updated control charts can be periodically sent to the protocol QA center to document continued process performance to protocol specifications.