Principal Component Analysis to Design Planning Target Volume in Oropharyngeal Cancers

PURPOSE/OBJECTIVE(S)

Standard translational shifts of the Clinical Target volume (CTV) to generate the Planning Target Volume (PTV) do not account for rotations. Head and neck positional misalignments derive in large part from rotations due to cervical spine arching and twisting in Cone Beam Computed Tomography (CBCT). Translational expansions do not track rotations, yielding coverage envelopes that unnecessarily overlap with adjacent structures. This work examines whether principal component analysis of the motion along all 6 degrees of freedom may be used to produce a more favorable PTV.

MATERIALS/METHODS

Seventy-five CBCTs of ten oropharyngeal cases were included. The records of couch shifts needed to align individual bony structures (C1-5, mandible and mastoid) between the planning image and CBCTs were recorded. A Principal Component Analysis of the shifts was used to generate an ellipsoid inflation of each CTV vertex along 6 degrees of freedom. The result was compared to a 3D ellipsoid based translational expansion, and to a described ellipsoid based vertex expansion along 6 degrees of freedom, with axes oriented in parallel to the treatment reference frame.

RESULTS

Themean (x, y) shifts in mm needed to align individually bodies C1 - C5 were respectively (-0.4, 0.5), (+.5, -0.2), (+-0.2, -0.2), (-0.2, +0.4), and (-0.5, +0.7), the monophasic pattern showing acquired curvature along both axes during treatment and demanding a PTV for coverage. A PTV was constructed using a described 6D ellipsoidal based boundary point expansion aligned along the reference frame axis or using a new theory to align against the principal components of the motion. A cyclical one-out method was used to validate the PTV models. Selected confidence intervals yielded complete coverage in >80% weeks in 80% cases. Validation testing disclosed similar complete coverage in 83-86% weekly CBCTs in the test cases with either method. The PCA 6D PTV could yield less normal structure overlap. A one out method was used to test overlap avoidance from PTVs constructed from a population of weekly CBCTs drawn from seven cases with one excluded. PTVs were drawn around target and constrictors on an extraneous case and imaged on a CT slice. Both a rolling 'ball' expansion of the vertices that applies a 3D translational ellipsoid and a PTV constructed using a 6D ellipsoid aligned against the standard reference frame overlapped with all or nearly all the constrictors in all but one trial (1/7). The 6D ellipsoid aligned against the principal motion components spared >70% of a constrictor in all trials (7/7).

CONCLUSION

PTVs remain needed to ensure target coverage in head and neck radiotherapy even with daily CT accuracy because of acquired spinal curvatures resulting in rotational displacements. A described 6D ellipsoid oriented to the reference frame can yield good coverage, but with unneeded constrictor coverage. A PCA analysis yields a PTV with equally good coverage but able to spare 70% of a constrictor.

A feasibility study of an intensive combined modality smoking cessation program in the radiation oncology clinic

19604

Background: Radiotherapy (RT) patients present for daily treatment over many weeks, often accompanied by friends and family. This represents a unique opportunity for intensive smoking intervention concurrently with RT in both cancer patients and their companions. Methods: Eligible participants included smoking cancer patients scheduled to receive = 3 weeks of RT and their smoking family/friends. All participants received bupropion and 9 individualized behavioral interventions (BI) in the RT clinic with an addiction professional, followed by 9–12 scheduled intensive relapse prevention encounters (in person or by telephone). The primary endpoint was feasibility determined by accrual and program completion. Other endpoints included carbon-monoxide (CO) confirmed and participant-reported tobacco abstinence. During 4 months of enrollment, smoking and basic eligibility data were prospectively collected on consultations seen in clinic. Results: Over 8 months 20 cancer patients and 3 family members were enrolled. Based on our sampling, this represented greater than 40% of eligible smokers seen in clinic. Six cancer patients withdrew, all on or before the third BI. 13 participants completed all 9 BIs while 4 patients completed 7–8 BIs. 11 participants reported compliance with bupropion therapy. One participant discontinued bupropion citing increased depression. No other possible adverse events to bupropion or BI were discovered. At the completion of BI, 16 participants had exhaled CO concentrations < 10ppm and 14 participants self-reported tobacco abstinence. Of the 17 participants completing 7–9 behavioral interventions, the median number of relapse prevention sessions was 4 (range 0–8). With a median follow-up of 5.85 months, the 3-month crude self-reported abstinence rate was 41% (7/17). Conclusions: Tobacco cessation with bupropion and intensive BI for cancer patients and their companions during RT was feasible. A significant number of eligible smokers enrolled and completed BI during RT. However, few participants completed scheduled prevention encounters following RT.

No significant financial relationships to disclose.

Gain in target dose from using Computer Controlled Radiation Therapy (CCRT) in the treatment of non-small cell lung cancer

PURPOSE

A study was undertaken to evaluate the gain from Computer Controlled Radiation Therapy in the treatment of non-small cell lung cancer. The purpose of this study is two-fold: (a) to measure the gain in the minimum target dose provided by Computer Controlled Radiation Therapy and (b) to determine the change in the minimum target dose as a function of the lung tolerance limits.

METHODS AND MATERIALS

Six cases of non-small cell lung cancer were studied by stimulating treatments with conventional and Computer Controlled Radiation Therapy techniques. For conventional treatments, a boost dose was delivered to the gross tumor volume via a pair of opposed oblique fields with a fixed gantry angle. For Computer Controlled Radiation Therapy, the gantry angle was allowed to change along the longitudinal axis of the patient. Prescriptions had to satisfy a bound on the maximum dose in the spinal cord and a limit on the amount of contralateral lung which could exceed 20 Gy. The boost dose was increased until either a tolerance limit was reached or minimum target dose of 80 Gy was delivered.

RESULTS

A minimum target dose of 80 Gy could be given to three of four patients who could not receive 80 Gy with conventional therapy. A minimum target dose of 80 Gy could be given to the remaining two patients with either technique.

CONCLUSION

The gain from computer controlled radiation therapy strongly depended on the chosen lung tolerance limit. A 10 to 20 Gy gain in minimum target dose could be found for some patients, but the gain was significantly reduced for a relatively small decrease in the amount of lung permitted a dose above 20 Gy.

Multimodality treatment of stage IIIA non-small-cell lung carcinoma: a critical review of the literature and strategies for future research

PURPOSE AND DESIGN

Stage IIIA non-small-cell lung carcinoma (NSCLC) is composed of regionally advanced yet potentially resectable disease. Many trials have evaluated a variety of therapeutic strategies. Most have been single-arm phase II trials, although a number of comparative phase III trials have also been performed. This review critically evaluates the existing literature on the treatment of stage IIIA NSCLC, particularly the various multimodality approaches that have been used.

RESULTS

A review of the existing literature does not establish the optimal treatment of stage IIIA NSCLC. Although radiation therapy alone remains the most commonly administered therapy for apparently unresectable disease, the status of radiation as a "standard" therapy can be seriously challenged based on existing data. Similarly, although a number of studies have established that surgical resection is clearly feasible in selected patients with stage IIIA disease, the efficacy of surgery also remains to be definitively established. Many studies have explored neoadjuvant chemotherapy, either in conjunction with radiation or surgery, with results that are best described as conflicting and controversial.

CONCLUSIONS

Without question, randomized phase III trials are required at this time to define what is to be considered optimal treatment. An attempt is made to define the most important questions that should be addressed in future phase III trials. Additionally, a number of study designs are suggested to best answer the therapeutic questions posed.