Is Sparing the Deep Lobes of Parotid Gland Necessary on Intensity Modulated Radion Therapy of Head and Neck Cancers? (original) (raw)
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International Journal of Medical Research and Review, 2019
Introduction: Radiotherapy in head and neck cancers is treated for several weeks and daily setup and reproducibility is a challenge. This daily variability causes setup errors which accounts planning target volume margins. Reduced PTV margins have to be taken to decrease the dose to the parotid glands, without compromising on loco regional control rates. The present study is done to identify setup errors and see the feasibility to decrease the PTV margins by creating dummy radiotherapy plans in order to decrease dose to parotid glands. Material and Methods: 420 portal images were evaluated for setup errors in three dimensions (Antero Posterior, Left to Right and Superior to Inferior) which were performed in ten patients of oropharyngeal squamous cell carcinoma. All patients were treated in supine position using immobilization cast. After target volume delineation a PTV margin of 7 mm was given. Dosimetric parameters of PTV and organs at risk were assessed. PTV margins were calculated according to three methods proposed by Stroom, Van Herk and ICRU 62. Dummy radiotherapy plans were generated using new PTV margins and compared with 7mm PTV margins. The data was analyzed using 3-way ANNOVA test for statistical significance. Results: The optimum PTV margins were 4mm in LR and SI direction and 7mm in AP direction. The PTV parameters (V95, D95, Dmax, Dmean, HI and CI) had no significant difference among different radiotherapy plans with different PTV margins. There was a significant decrease in the dose to right parotid (39.12 Gy to 32.88Gy; p-0.04), left parotid (37.90 to 31.21Gy; p-0.03) and parotid combined (38.65 to 31.45 Gy; p-0.01) when 7mm PTV margins were reduced to 4mm PTV margins. The results of dummy radiotherapy plans using asymmetric PTV margins (LR-4mm, SI-4mm and AP-7mm) and symmetrical PTV margins (4mm in all directions) are compared with PTV margins (7mm in all directions), in terms of PTV and OAR dosimetric parameters. Conclusion: The decreased PTV margins of 4mm decreases the dose to the parotid significantly. The implementation of radiotherapy plans needs to be supplemented by daily IGRT.
Parotid sparing irradiation for the head and neck cancers
Journal of Ayub Medical College, Abbottabad : JAMC
Several authors have shown that xerostomia restricts nutritional intake and limits the ability of patients to maintain normal weight. When both parotids are irradiated, patients never fully regain their normal weight, however if one parotid is irradiated the patients are able to fully recover their weight with in the year. There are certain sites in the head and neck where small and lateralized cancers with diminished risk of contralateral neck metastases can be treated with parotid sparing techniques, i.e., oral cavity, retromolar trigone, anterior tonsillar pillar, tonsillar fossa, and true vocal cord. In these sites it is appropriate to spare the opposite parotid and closely observe the un-irradiated neck. Based on Dr. O' Sullivans long term follow up of patients with cancers of the oral cavity and tonsil, we are encouraged that patients can be irradiated with homo-lateral parotid techniques with out jeopardizing loco-regional control. Hazuka et al and Maesa et al suggested t...
Head and neck intensity modulated radiotherapy parotid glands: time of re-planning
La radiologia medica, 2013
Purpose To investigate the correct time point for replanning by evaluating dosimetric changes in the parotid glands (PGs) during intensity-modulated radiotherapy (IMRT) in head and neck cancer patients. Materials and methods Patients with head and neck cancer treated with IMRT were enrolled. During treatment all patients underwent cone-beam computed tomography (CBCT) scans to verify the set-up. CBCT scans at treatment days 10, 15, 20 and 25 were used to transfer the original plan (CBCT plan I, II, III, IV, respectively) using rigid registration between the two. The PGs were retrospectively contoured and evaluated with the dose-volume histogram. The mean dose, the dose to 50 % of volume, and the percentage of volume receiving 30 and 50 Gy were evaluated for each PG. The Wilcoxon sign ranked test was used to evaluate the effects of dosimetric variations and values \0.05 were taken to be significant. Results From February to June 2011, ten patients were enrolled and five IMRT plans were evaluated for each patient. All the dosimetric parameters increased throughout the treatment course. However, this increase was statistically significant at treatment days 10 and 15 (CBCT plan I, II; p = 0.02, p = 0.03, respectively). Conclusion CBCT is a feasible method to assess the dosimetric changes in the PGs. Our data showed that checking the PG volume and dose could be indicated during the third week of treatment.
Strahlentherapie und Onkologie, 2005
Background and Purpose: Intensity-modulated radiotherapy (IMRT) is used in most reported techniques for bilateral neck irradiation that aim at parotid gland sparing. A relatively simple conformal parotid-sparing technique (ConPas) was developed that uses no beam-intensity modulation. The purpose of this paper is to demonstrate, in patients with larynx or hypopharynx carcinoma, that ConPas enables adequate coverage of the primary tumor and the bilateral neck nodes, while keeping the mean parotid dose (MPD) < 26 Gy. Patients and Methods: Treatment plans using ConPas and the conventional technique (using one anteroposterior supraclavicular and two lateral beams) were computed for ten consecutive patients with T1-4 N0-1 larynx or hypopharynx carcinoma (not T1 glottic). A dose of 46 Gy was prescribed to the primary tumor and the bilateral neck nodes, planned either with the conventional technique or ConPas, followed by a boost up to 70 Gy with a simple two-field technique. The target coverage of both techniques was compared using the V 95 , the percentage of the planning target volume (PTV) of the primary tumor and nodal regions receiving at least 95% of the prescribed elective dose. The MPDs and the normal-tissue complication probabilities (NTCPs) of the parotid glands were compared using either technique including the boost up to 70 Gy. Dosimetric verification of the technique has been carried out, using ionization chamber measurements and film dosimetry. Results: The mean V 95 was 85.2% and 91.2% (p = 0.08), the mean MPD 38.7 Gy and 25.4 Gy (p < 0.001), and the mean NTCP for the parotid glands 0.87 and 0.22 (p < 0.001) for the conventional technique and ConPas, respectively. The dosimetric verification shows a good agreement between dose calculation and measurement. Conclusion: ConPas enables adequate target coverage and clinically relevant parotid sparing in bilateral neck irradiation without beam-intensity modulation.
2000
To Irene have been disappointing with conventional therapy, within the range of 30-40%, and the majority of these patients will eventually die of cancer [38, 39]. There have been numerous attempts to make treatment of these tumours more effective by modifying fractionation in radiotherapy schedules and by combining radiotherapy with chemotherapeutic agents. In head and neck cancer patients, the ultimate cause of death is most often locoregional recurrence of cancer, and therefore, it is of utmost importance to develop treatment protocols that are able to produce maximal local control figures.
International Journal of Radiation Oncology*Biology*Physics, 2013
Purpose-Doses actually delivered to the parotid glands during radiotherapy often exceed planned doses. We hypothesized that the delivered doses correlate better with parotid salivary output than the planned doses, used in all previous studies, and that determining these correlations will help decisions regarding adaptive re-planning (ART) aimed at reducing the delivered doses. Methods and Materials-Prospective study: oropharyngeal cancer patients treated definitively with chemo-irradiation underwent daily cone beam CT (CBCT) with clinical setup alignment based on C2 posterior edge. Parotid glands in the CBCTs were aligned by deformable registration to calculate cumulative delivered doses. Stimulated salivary flow rates were measured separately from each parotid gland pretherapy and periodically posttherapy. Results-36 parotid glands of 18 patients were analyzed. Average mean planned doses was 32 Gy and differences from planned to delivered mean gland doses were −4.9 to +8.4 Gy, median difference +2.2 Gy in glands whose delivered doses increased relative to planned. Both planned and delivered mean doses were significantly correlated with post-treatment salivary outputs at almost all post-therapy time points, without statistically significant differences in the correlations. Large dispersions [on average, standard deviation (SD) 3.6 Gy] characterized the dose/effect relationships for both. The differences between the cumulative delivered doses and planned doses were evident already at first fraction (r=0.92, p<0.0001) due to complex setup deviations, e.g. rotations and neck articulations, uncorrected by the translational clinical alignments. Conclusions-After daily translational setup corrections, differences between planned and delivered doses in most glands were small relative to the SDs of the dose/saliva data, suggesting that ART is not likely to gain measurable salivary output improvement in most cases. These differences were observed already at first treatment, indicating potential benefit for more complex
Journal of applied clinical medical physics, 2017
The sparing of the parotid glands in the treatment of head and neck cancers is of clinical relevance as high doses to the salivary glands may result in xerostomia. Xerostomia is a major cause of decreased quality of life for head and neck patients. This paper explores the relationship between the overlap of the target volumes and their expansions with the parotid glands for helical delivery plans and their ability to be spared. Various overlapping volumes were examined, and an overlap with a high statistical relevance was found. A model that predicts exceeding tolerance parotid mean dose based on its fractional overlapping volume with PTVs was developed. A fractional overlapping volume of 0.083 between the parotid gland and the high dose PTV plus 5 mm expansion - was determined to be the threshold value to predict parotid D > 26 Gy for parotids that overlap with the high dose PTV plus 5 mm expansion. If the parotid gland only overlaps with the intermediate dose target (and/or low...
The British Journal of Radiology, 2012
Objectives: This study evaluates the interobserver variation in parotid gland delineation and its impact on intensity-modulated radiotherapy (IMRT) solutions. Methods: The CT volumetric data sets of 10 patients with oropharyngeal squamous cell carcinoma who had been treated with parotid-sparing IMRT were used. Four radiation oncologists and three radiologists delineated the parotid gland that had been spared using IMRT. The dose-volume histogram (DVH) for each study contour was calculated using the IMRT plan actually delivered for that patient. This was compared with the original DVH obtained when the plan was used clinically. Results: 70 study contours were analysed. The mean parotid dose achieved during the actual treatment was within 10% of 24 Gy for all cases. Using the study contours, the mean parotid dose obtained was within 10% of 24 Gy for only 53% of volumes by radiation oncologists and 55% of volumes by radiologists. The parotid DVHs of 46% of the study contours were sufficiently different from those used clinically, such that a different IMRT plan would have been produced. Conclusion: Interobserver variation in parotid gland delineation is significant. Further studies are required to determine ways of improving the interobserver consistency in parotid gland definition.
Anticancer Research
Background/Aim: Optimal planning of radiotherapy for head-and-neck cancers should consider the risk of xerostomia. This study investigated the prognostic value of dosevolume parameters of the parotid glands. Patients and Methods: Dose-volume parameters were evaluated for xerostomia in 145 patients including D40 (minimum dose to 40% of corresponding parotid volume), D60 (minimum dose to 60%), D80 (minimum dose to 80%), and mean dose of ipsilateral, contralateral, and bilateral parotid glands. Results: Grade ≥2 xerostomia was significantly associated with D40 of ipsilateral and all parameters of bilateral glands; trends were found for all other parameters. Grade ≥3 xerostomia was significantly associated with D80 of bilateral glands; trends were found for other parameters of ipsilateral and bilateral glands. Conclusion: Since grade ≥2 xerostomia was associated with all parameters, D40, D60, and D80 did not provide additional information to mean doses. D80 of bilateral glands is a new factor and more predictive than mean dose regarding grade ≥3 xerostomia.