Presenter: Steven J. Frank Presenter Affiliation: University of Texas MD Anderson Cancer Center, Houston, TX.
There is currently an increasing incidence in oropharyngeal cancer (OPC), particularly in otherwise healthy patients age 40-60. In this group of patients, there is a very high likelihood of being cured, thus the side effects that develop from treatment can lead to significant burden for the remainder of the patient's life.
Compared to conventional 3D conformal techniques, intensity modulated radiation therapy (IMRT) allows for parotid sparing, thus decreasing rates of xerostomia. However, structures which previously received very little radiation are now receiving higher doses which can lead to an increase in other side effects.
Specifically, the authors note in their experience at their institution they see very high rates of nausea and vomiting as well as anterior oral mucositis in patients treated with concurrent chemotherapy.
There are many symptoms that can lead to a decrease in oral intake and subsequently weight loss and feed tube placement during treatment. These include fatigue, nausea, vomiting, dysgeusia, dysphagia, mucositis, pain and xerostomia.
A potential advantage of intensity modulated proton therapy (IMPT) over photon therapy (IMRT) in the treatment of OPC is a decrease in toxicity.
This study sought to quantify the incidence of gastrostomy tube use in their OPC patients treated with IMPT and compare this to gastrostomy use in patients treated with IMRT.
The study design was case-control.
26 patients with newly diagnosed with OPC were treated with IMPT between 2011 and 2012.
26 patients treated with IMRT were extracted from the author's database of patients with OPC treated between 2000 and 2009.
Cases were matched based on the following criteria, in order:
Unilateral vs. bilateral therapy
Tonsil vs. base of tongue primary
In the IMRT control group, 85% were treated using a mono-isocentric technique with a larynx block to 42 Gy and midline-block for the remainder of treatment.
The IMPT group was treated comprehensively from the base of skull to the clavicles.
All patients were treated with a simultaneous integrated boost (SIB) with 66-70 Gy in 30 – 33 fractions.
Comparisons of categorical variables were done with the chi-square test, and the t-test was used for comparison of means.
There was exact matching on the first 3 variables:
Laterality of therapy (21 bilateral; 5 unilateral)
Primary site (18 tonsil; 8 base of tongue)
Induction (IMPT-65%; IMRT-58%)
Concurrent (IMPT-50%; IMRT-58%)
There was a significant difference in age between the two groups, with the IMPT group being older than the IMRT group (mean 61 years vs. 56 years, p < .001).
Five patients treated with IMPT required placement of a gastrostomy tube (20%) compared with 12 treated with IMRT (48%); p = 0.037. The rate of feeding tube use in the matched IMRT cohort did match the rate of feeding tube use in the entire IMRT cohort of almost 1000 patients.
There was no difference in the median duration of feeding tube use, IMPT 4.2 months versus IMRT 4.7 months.
Dosimetric comparison between the two groups revealed lower mean doses to a sub-group of swallowing related structures with IMPT including anterior and posterior oral cavity and base of tongue. They saw no significant difference in dose to the constructions.
Additionally, they saw a decrease in dose to the emetic structures with IMPT.
All of the muscles of mastication received a lower dose using IMPT. The larynx received a lower dose in IMRT group as the majority of IMRT patients were treated with a midline larynx block.
Preliminary data suggest IMPT has a lower rate of grade 3 dysphagia compared to IMRT.
The authors found a 50% reduction in gastrostomy tubes with IMPT over IMRT.
A separate study done by the authors and also presented here at ASTRO evaluated just the IMPT patients. They found that post treatment, 65% of the patients treated with IMPT were evaluated with a modified barium swallow (MBS) and/or EGD. No patients had aspiration or stricture (Hutcheson and Frank, ASTRO 2013, Poster).
The authors are currently investigating the comparative benefits of IMPT and IMRT for OPC in a phase III randomized trial.
While not specifically dose de-escalation, the authors postulate that IMPT, principally due to less beam path toxicity, will have a lower toxicity profile compared to IMRT beyond rates of gastrostomy feeding tubes.
This study was among the first to show that IMPT for oropharyngeal cancer can decrease both dose to critical structures as well as allow adequate tumor dosing.
This was an encouraging initial retrospective case-control study showing an improvement in dose to critical structures as well as use of feeding tubes in patients treated with IMRT.
Given the retrospective nature of the study, there were understandable limitations. The IMPT patients were treated more recently than the IMRT patients. The authors did not report if they are currently treating all patients with IMPT, or if certain patients or tumor characteristics play a role in the decision of modality. Additionally, the authors reported a decrease in dose to the emetic structures with IMPT but did not present any data regarding if the rate of nausea/vomiting was lower. Lastly, there are no long term data regarding outcome or toxicity reported in this study.
The authors are in the process of opening a phase II/III randomized trial comparing IMRT to IMPT which should provide important information going forward.
Oct 4, 2011 - Treatment of localized prostate cancer using intensity modulated radiation therapy is associated with a considerable reduction in late bowel and rectal side effects and significantly decreased rectal and bladder toxicity compared to three-dimensional conformal radiation therapy, according to a study presented the annual meeting of the American Society for Radiation Oncology, held from Oct. 2 to 6 in Miami Beach.